JOURNAL OF PETROLOGY
VOLUME 44
NUMBER 9
PAGES 1525±1559
2003
DOI: 10.1093/petrology/egg048
Kilauea East Rift Zone Magmatism:
an Episode 54 Perspective
CARL R. THORNBER1*, CHRISTINA HELIKER2,
DAVID R. SHERROD2, JAMES P. KAUAHIKAUA2, ASTA MIKLIUS2,
PAUL G. OKUBO2, FRANK A. TRUSDELL2, JAMES R. BUDAHN3,
W. IAN RIDLEY3 AND GREGORY P. MEEKER3
1
US GEOLOGICAL SURVEY, CASCADES VOLCANO OBSERVATORY, VANCOUVER, WA 98683, USA
2
US GEOLOGICAL SURVEY, HAWAIIAN VOLCANO OBSERVATORY, HAWAII NATIONAL PARK, HI 96718, USA
3
US GEOLOGICAL SURVEY, DENVER FEDERAL CENTER, DENVER, CO 80225, USA
RECEIVED DECEMBER 12, 2001; ACCEPTED MARCH 11, 2003
On January 29±30, 1997, prolonged steady-state effusion of
lava from Pu'u'O'o was briefly disrupted by shallow extension
beneath Napau Crater, 1±4 km uprift of the active Kilauea vent.
A 23-h-long eruption (episode 54) ensued from fissures that
were overlapping or en echelon with eruptive fissures formed
during episode 1 in 1983 and those of earlier rift zone eruptions
in 1963 and 1968. Combined geophysical and petrologic data for
the 1994±1999 eruptive interval, including episode 54, reveal
a variety of shallow magmatic conditions that persist in association with prolonged rift zone eruption. Near-vent lava samples
document a significant range in composition, temperature and
crystallinity of pre-eruptive magma. As supported by phenocryst±liquid relations and Kilauea mineral thermometers established herein, the rift zone extension that led to episode 54
resulted in mixture of near-cotectic magma with discrete
magma bodies cooled to 1100 C. Mixing models indicate
that magmas isolated beneath Napau Crater since 1963 and
1968 constituted 32±65% of the hybrid mixtures erupted during
episode 54. Geophysical measurements support passive displacement of open-system magma along the active east rift conduit
into closed-system rift-reservoirs along a shallow zone of extension. Geophysical and petrologic data for early episode 55 document the gradual flushing of episode 54 related magma during
magmatic recharge of the edifice.
INTRODUCTION
KEY WORDS: Hawaii; Kilauea; glass thermometry; magma mixing;
mineral thermometry
The well-monitored episode 54 disruption in steadystate lava effusion of Kilauea volcano presents an
opportunity to evaluate the origins of mixed-magma
components that are inherently associated with prolonged rift zone eruption. Like a skylight above an
active lava tube, which provides an opportunity to
study the physical and chemical processes associated
with lava transport from the vent, the eruptive fissures
of episode 54 are windows into the magmatic plumbing
system between the summit reservoir and Pu'u'O'o.
For the past two decades, amidst nearly continuous
rift zone eruption and recharge of new magma into the
summit region, progressive outward movement of the
south flank of Kilauea has accommodated an increasingly efficient magma conduit through the shallow
upper±middle east rift zone. Details of magmatic conditions that may persist within and along this 16-kmlong rift conduit between the summit and the vent are
poorly understood, but may be broadly inferred from
what is known of systematic differences in lava chemistry between summit and rift zone eruptions of
Kilauea and Mauna Loa volcanoes. Kilauea summit
eruptions are primarily restricted to olivine-phyric
tholeiites with MgO contents of 468 wt %, as regulated by olivine fractionation and accumulation within
the summit reservoir (Wright & Fiske, 1971). Rhodes
and coworkers [see Rhodes (1995) and references
*Corresponding author. E-mail: [email protected]
Published by Oxford University Press
JOURNAL OF PETROLOGY
VOLUME 44
NUMBER 9
SEPTEMBER 2003
Fig. 1. 1983±1998 vent locations and lava flows of Kilauea east rift zone eruptive activity. Hawaii island inset map in the upper right corner
shows the location of this area along the east rift zone (erz) of Kilauea Volcano (swrz, SW rift zone). Episode 53 flow field (1992±1997) is shown
in a medium dark shade. Darkest shaded area shows extent of episode 55 flow field (1997±1998) with the main lava tube shown as a white line.
The area of episode 54, January 1997, lava flows in and near Napau Crater is shown in black. Locations of nearby seismic monitoring stations
are indicated as MPR and STC.
therein] emphasized the preponderance of lava compositions at the low-MgO end of an olivine control
trend ( 70 wt % MgO) for both summit and rift
eruptions of Kilauea and Mauna Loa. They proposed
that such compositions reflect the persistence of shallow
open-system reservoirs where magma is chemically
`buffered' at near-cotectic compositions as a result of
continuous replenishment of primitive melt. Both
Rhodes (1995) and Fodor et al. (1993) interpreted
Hawaiian phenocryst assemblages as indicators of
open-system fractionation within actively replenished,
shallow magma reservoirs.
In contrast to the limited range of olivine-saturated
magma that characterizes summit eruptions, a broader
array of lava chemistry is erupted along rift zones.
Historic Kilauea rift eruptions with relatively evolved
compositions are restricted to short-lived events following repose intervals of decades (Wright, 1971; Wright
& Fiske, 1971; Wright & Helz, 1996). Variations of
plagioclase and pyroxene phenocryst compositions and
textures in these small volumes of evolved lava indicate
pre-eruptive mixing between rift-stored, fractionated
magma and rift-transported, olivine-saturated magma
(Helz & Wright, 1992; Fodor & Moore 1994; Clague
et al., 1995; Wright & Helz, 1996; Yang et al., 1999).
Evidence that pockets of magma have persisted
along Kilauea's east rift zone during the present eruption is provided by petrologic and geophysical studies.
As demonstrated by Wolfe et al. (1988) and Garcia et al.
(1989), olivine±plagioclase±clinopyroxene-saturated
tholeiite erupted through fissures extending 75 km
from the west edge of Napau Crater during episodes
1±3 (Fig. 1) were hybrid mixtures resulting from magmatic dike propagation through pre-existing reservoirs
of cooler magma isolated within the rift. Pockets of
rift-resident magma may also persist as open-system
reservoirs maintained in connection with fresh magma
supplied from the summit region, as is suggested by the
persistence of shallow deformation sources beneath
Makaophui Crater and uprift of the Pu'u'O'o vent
(Okamura et al., 1988; Hoffman et al., 1990; Owen
et al., 2000).
Approximately 97% of the 2 km3 of lava produced
during this 20-year-old rift zone eruption is weakly
olivine-phryic, with minor chromian spinel, and has
MgO contents ranging from 68 to 96 wt %
(Thornber, 2003). The majority of this volume has
been issued during prolonged intervals of near steadystate eruption from July 1986 to January 1997 (episodes 48±53) and since mid-1997 (episode 55). During
these episodes, olivine±liquid relations of near-vent
samples indicate near-equilibrium crystallization from
melts equivalent to their bulk composition, without
significant loss or accumulation of olivine during transit along the length of the rift-conduit (Garcia et al.,
1996; Thornber, 2001). Cyclic variations of lava
1526
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
composition and temperature observed throughout
prolonged eruptive intervals portray the repetition of
a limited range of olivine-saturated magmatic conditions, the Mg end-members of which are maintained
by open-system recharge of the edifice beneath the
summit region (Thornber, 2003).
Steady-state magmatic and eruptive conditions at
Kilauea were briefly disrupted on January 29±30,
1997, when fissures opened in Napau Crater, uprift of
the active vent (episode 54). For the first time since the
onset of this eruption in 1983, lower-temperature and
fractionated lava compositions were erupted that are
consistent with derivation from a mixture of rift-stored
magma and magma in the active eruption conduit
(Thornber et al., 1997; Garcia et al., 2000; Thornber,
2001). In this paper, we present and assess the detailed
petrography and geochemistry of minerals, glasses and
bulk samples of lava erupted before, during and after
episode 54. Our petrologic interpretations of Kilauea
rift zone magmatism are constrained by extensive geological and geophysical data. A brief summary of eruptive behavior and geophysical evidence for magma
movement along the summit-to-vent conduit, before,
during, and after episode 54 is presented below. This
information provides important geologic context for
the petrologic modeling of rift zone magmatic processes
that follows.
ERUPTION NARRATIVEÐBEFORE,
DURING, AND AFTER EPISODE 54
The Pu'u'O'o eruption began on January 3, 1983,
when fissures opened in Napau Crater, 12 km downrift
from the summit. The onset of eruptive activity was
preceded by summit deflation as a dike propagated
down the east rift zone (Okamura et al., 1988). The
eruption soon localized at the eventual site of Pu'u'O'o,
which, once established, was the main vent from 1983
to 1986 and again from 1992 to the present, after
6 years of eruption from Kupaianaha. A more detailed
narrative account of post-1983 eruptive activity has
been presented by Heliker & Mattox (2003, and references therein). From mid-1994 until 1997, episode 53
of the eruption persisted in a steady-state mode with
crater pond activity at Pu'u'O'o accompanied by
a single continuously active vent on the uprift side of
the cone. The flank vent fed a lava tube system that
extended 11 km to the ocean (Fig. 1).
During the early evening hours of January 29, 1997,
episode 53 ended dramatically when the Pu'u'O'o lava
pond and west flank vent suddenly drained and the
crater floor and west wall of the cone collapsed into the
void. As confirmed by onsite observations and GOES
satellite imagery (Harris et al., 1997), episode 54 began
at 0240 h (HST) on January 30, when a new eruptive
fissure opened on the floor of Napau Crater. During the
next 22 h, 300 000 m3 of lava (dense rock equivalent)
were erupted from six fissures along a northeasterly line
in the Napau Crater area, 2±4 km uprift of Pu'u'O'o.
These eruptive fissures were overlapping and en echelon with fissures that marked the onset of this eruption
in 1983 (Fig. 2) and with earlier fissure eruptions in
1963 and 1968 (Moore & Koyanagi, 1969; Jackson
et al., 1975). Fissures A±D erupted along a line of
13 km length, striking N60 E from the center of
Napau Crater. Fissure E, 130 m in length, opened
en echelon and 150 m SE of fissure D, within a preexisting graben. An unexpected change in the northeastward progression of erupted fissures A±E occurred
when fissure F opened in the west wall of Napau
Crater, on-strike with earlier fissures but SW of the
initial fissure, A. Most of the lava from fissure F poured
out of the crater wall and ponded at its base. This last
gasp of episode 54 concluded at 0033 h on January 31.
On the morning of February 1, observers at Pu'u'O'o
saw that the west side of the cone had collapsed and the
crater floor had dropped 150 m to a depth of 210 m
below the low point on the crater rim, 65 m below the
pre-1983 surface. Seismic records indicate that drainback and floor collapse at Pu'u'O'o occurred between
1845 and 2015 h on January 29. At 2015 h, a low
rumbling roar was heard from the Pu'u'O'o vent
area, signaling the collapse of the west side of the
Pu'u'O'o cone, after magma had drained and the
crater floor had collapsed into the void.
The end of episode 54 was followed by a 24 day
eruptive pause, the longest hiatus in the eruption
since 1986. On February 24, 1997, the first lava of
episode 55 appeared deep within the Pu'u'O'o crater.
Initial episode 55 activity was limited to an active lava
pond fed from the uprift edge of the crater. The pond
rose steadily to the elevation of flank vents that began
erupting on March 28. After 3 months of shield building around sporadically active Pu'u'O'o flank vents,
a predominant vent on the SW flank of the cone began
to steadily feed a new easterly flow (Cashman et al.,
1999). This unstable interval of early episode 55 was
characterized by interplay of Pu'u'O'o pond and flank
vent activity. The crater overflowed several times in
1997, producing the first lava flows originating from
the Pu'u'O'o crater since 1986.
Through successive advancement of flows and tubes,
lava reached the coast in mid-July and, by August
1997, a relatively stable tube system of 11 km length
was serving as a lava pipeline from the vent to the
ocean [see Harris & Thornber (1999) for detailed
maps]. As was the case during episode 53, the mid1997 to 1999 interval of episode 55 was punctuated by
brief and intermittent eruptive pauses.
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VOLUME 44
NUMBER 9
SEPTEMBER 2003
Fig. 2. Napau Crater area showing 1983 (episode 1) lava flows (dark gray), 1997 (episode 54) lava flows (light gray) and early episode 55 lava
flows (stippled). Episode 54 fissures are indicated with dark lines. The temporal sequence of episode 54 fissure eruptions corresponds to the
alphabetic order of fissure names (A, B, C, D, E and F). Also shown are locations of lava samples taken during episode 54 (KE54-1848 to
-1869) and early episode 1 (KE1-49 to -52).
GEOPHYSICAL SIGNATURE OF
SHALLOW MAGMA MOVEMENTÐ
BEFORE, DURING AND AFTER
EPISODE 54
Throughout the Pu'u'O'o±Kupaianaha eruption,
magmatic continuity between a summit reservoir and
rift vents is demonstrated by correlations between
summit inflation and deflation and surges and lulls
in eruptive activity (Okamura et al., 1988; Wolfe et al.,
1988; Garcia et al., 1996; Thornber et al., 1996;
Denlinger, 1997; Heliker et al., 1998; Thornber, 2001;
Cervelli et al., 2002). During near-steady-state eruption
of episode 53, an efficient pressure balance between the
summit reservoir and the Pu'u'O'o vent is indicated by
correlation of precursory summit deformation and
short-term fluctuations in eruptive vigor at the vent
(e.g. Thornber et al., 1995, 1996). In contrast to this
summit-controlled eruptive behavior, the timing of
events associated with episode 54 indicates that sudden
shallow rift zone extension beneath Napau Crater preceded magma withdrawal from the summit reservoir.
An annotated chronology of eruptive activity, seismicity and deformation associated with episode 54 is
presented in Fig. 3.
Global positioning system (GPS) deformation data
presented by Owen et al. (2000) constrain the timing
and geometry of summit and upper east rift zone
deformation associated with magma displacement during episode 54. Their model suggests that 2 m of rift
extension occurred at depths 525 km in the Napau
Crater area during the January 1997 event. This value
corresponds to the 18 m of cumulative surface extension estimated from our field measurements of fresh
surface cracks paralleling episode 54 fissures in Napau
Crater. Continuous GPS data show that the rift opening began 8 h before fissure eruption, concurrent with
shallow earthquakes in this zone and before the onset
of summit deflation (Fig. 3). Owen et al. (2000) demonstrated that rift-extension rates of 4 cm/h at the onset
of the event decreased with time before and during
fissure eruptions at Napau Crater, and they recognized
a second point-source of deflation associated with this
event at shallow depths beneath Makaopuhi Crater.
Their geodetic model of magma withdrawal from
beneath Makaopuhi crater is consistent with seismic
records indicating shallow tremor and earthquake
swarms located near Makaopuhi before and during
the episode 54 fissure eruptions (see Fig. 3 caption).
This geophysical suggestion of magma displacement
from an open-system rift-reservoir sustained beneath
Makaopuhi is supported by leveling data obtained in
1983 at the onset of this eruption, which identified the
same point-source for inflation related to magma
intrusion (Okamura et al., 1988).
Steady summit inflation associated with magma
recharge began when episode 54 ended and continued
1528
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
Fig. 3. Kilauea east rift and summit geophysical record from 1200 h, January 29, 1997 to 0000 h, February 1, 1997. (a) Relative Seismic
Amplitude (RSAM) averaged over 10 min intervals at STC station located midway between Pu'u'O'o and Napau Crater. The timing of the
Pu'u'O'o vent drainback and collapse of the west crater wall and of tremor associated with eruptive fountaining of each of the five episode 54
eruptive fissures (A±E) is indicated. ~, formation time of individual samples used in this investigation, numbered here with letters
corresponding to each of the fissures sampled. (b) RSAM at MPR station located on the south rim of Makaopuhi Crater. Black bars indicate
number of discrete earthquakes per 10 min intervals located in the vicinity of Makaopuhi, Napau and Pu'u'O'o (right axis scale). Earthquakes
counted range from magnitude 09 to 30 at a depth range of 0±45 km. (c) RSAM at NPT station located within Kilauea's summit caldera.
Black bars indicate the number of discrete earthquakes located in the summit and upper-east-rift region; magnitude and depth range as in (b).
(d) Summit tilt (microradians) measured electronically near the west rim of the summit caldera. Deflation of summit is indicated by a decrease
in microradians. Distinct rift zone seismic activity commenced 8 h before the episode 54 fissure eruption, when a swarm of shallow earthquakes
(1±4 km depth) occurred near Makaopuhi Crater at 1841 h (HST) on January 29, 1997. At 1845 h, a dramatic increase in shallow tremor was
recorded at STC and MPR stations (a, b), located between Napau Crater and Pu'u'O'o and at Makaopuhi Crater, respectively (see Fig. 1).
Amidst continued shallow earthquake swarms, rift zone tremor escalated quickly and within 11 min (at 1852 h) was accompanied by slowly
increasing shallow tremor at Kilauea's summit [NPT station, (c)] and by gradual onset of rapid summit deflation, measured by tiltmeters (d).
Draining and collapse at Pu'u'O'o are reflected by the intense tremor at STC and MPK between 1845 and 2015 h and by a magnitude 23
earthquake beneath Pu'u'O'o at 1914 h. Shallow tremor and earthquakes continued to increase in intensity near Makaopuhi after the 1914 h
seismic burst recorded at STC, with the MPR signal peaking at 2040 h. After this time and until fissure A opened in Napau Crater at 0240 h,
overall rift zone tremor diminished but persisted at higher intensity at Makaopuhi than at Pu'u'O'o [compare (a) and (b)]. In this preeruptive interval, deflation rate and seismicity remained high at the summit. The onset of episode 54 eruptive activity was marked by an
increase in seismic tremor recorded at STC (a). The timing of vigorous lava fountaining from fissures A±E was mirrored by peaks in tremor
intensity during each of these eruptive intervals, with the highest prolonged fountaining of 10±30 m at fissure D corresponding to the most
intense shallow tremor during this event. Variations in level of activity at fissure F correspond to the timing of peaks in seismic tremor that were
more clearly recorded at MPR (b).
1529
JOURNAL OF PETROLOGY
VOLUME 44
until steady-state magmatic and eruptive conditions
were re-established in July 1997 (Owen et al., 2000;
Thornber, 2001). The timing of the onset of episode 55
Pu'u O'o activity was accurately forecast at the
Hawaiian Volcano Observatory by assuming continued magma recharge at a rate equivalent to an average
effusion rate of episode 53.
PETROLOGIC SAMPLING
The best possible assessment of pre-eruptive magmatic
conditions through time is achieved by frequent sampling and analysis of vent tephra and spatter, including
Pele's tears and hair, of tube-contained lava flows and
of surface lava flows at the vent. Details of collection
techniques used to obtain samples from 1994 to
1999 have been presented by Thornber et al. (2002)
along with detailed time, location and sampling information. During periods of steady-state eruption of
late episode 53 (September 1994±January 1997) and
episode 55 (July 1997±January 1999), 306 rapidly
quenched lava samples from near-vent locations were
obtained at near-weekly intervals. Twenty-two lava
samples were obtained during episode 54, the locations
of which are shown in Fig. 2. The majority of these
samples were quenched from a molten state at the time
of collection; others were collected while still warm.
The formation time of individual samples from each
of the eruptive fissures (A±F) is indicated in Fig. 3a.
During early episode 55 (April±July 1997), 22 samples
of fountain spatter and spatter cone overflows or flow
breaches from sporadic vents on the west and SW
flanks of the Pu'u'O'o cone were obtained.
NUMBER 9
SEPTEMBER 2003
been presented by Thornber (2001). As substantiated
by wet chemical analysis (see Thornber, 2001), ferrous
iron concentrations in whole rocks and glasses are
calculated from the total iron oxide concentration assuming an average FeO/(FeO ‡ Fe2O3)
value of 09.
Whole-rock major element analyses were performed
at the USGS analytical facility in Denver using X-ray
fluorescence (XRF) techniques as described by
Taggart et al. (1987). All major element data reported
are normalized to 100% after correction for 51 wt %
of volatile loss-on-ignition. Repeated XRF analyses of
four USGS Kilauea standards (wt % MgO from 54 to
143) provided analytical control in each of 13 sample
batches analyzed from 1994 to 1999, details of which
have been presented by Thornber et al. (2002). Standard reproducibilities are less than 1s ˆ 001 wt % for
K2O and MnO, 002 for TiO2 and P2O5, 003 for CaO
and Na2O, 005 for Al2O3, FeO (total-iron) and MgO,
and 013 for SiO2.
Whole-rock trace element analyses of samples were
obtained by instrumental neutron activation analysis
(INAA) at USGS Denver; the techniques and analytical precision have been described by Baedecker
& McKown (1987). Glass trace element analysis of
small (1 mm±1 cm) episode 53 Pele's tear samples
were conducted by laser ablation±inductively coupled
plasma mass spectrometry (LA±ICP-MS) at USGS,
Denver. Repeated analyses of a secondary standard
basaltic glass, ENDV, indicates precision for most
elements of 1±16% (Ridley & Lichte, 1998).
ANALYTICAL METHODS
WHOLE-ROCK MAJOR AND TRACE
ELEMENT GEOCHEMISTRY
Microbeam quantitative analyses and imagery used in
this study were performed at the US Geological Survey
(USGS) Denver Microbeam Facility using a JEOL
8900 electron microprobe and a JEOL 5900 scanning
electron microscope. Qualitative compositional information of electron backscatter imagery was used to
augment petrographic assessments of mineral proportions and zonation characteristics. Thornber et al.
(2002) has provided details of microprobe operating
conditions, analytical accuracy and precision. Major
element glass compositions used for all plots and calculations are the average of 10 analyses per sample. Estimated errors in MgO and total FeO (FeOt ˆ Fe2O3 ‡
FeO) concentrations used in glass thermometry calculations [T C ˆ 201 wt % MgO ‡ 1014 C (Helz
& Thornber, 1987)] and in calculations involving
olivine±liquid and pyroxene±liquid MgO/FeO distribution coefficients [KD ˆ (MgO/FeO)xl /(MgO/
FeO)Liq (Roeder, 1974; Grove & Bryan, 1983)] have
Bulk lava and glass major element chemistry for individual samples used in this study have been provided by
Thornber et al. (2002) and can be accessed on the internet at http://geopubs.wr.usgs.gov/open-file/of 02-017.
The average and variance of major and trace element
compositions of bulk lava and Pele's tear glasses
collected during steady-state eruption intervals of
episodes 53 and 55 are presented in Table 1. Major
and trace element data for episode 54 and early episode
55 samples are provided in Tables 2 and 3, respectively.
Whole-rock MgO variation of lava erupted throughout the 1994±1999 interval (including episode 54,
Fig. 4) defines an apparent trend of progressive lowpressure cooling and multiphase crystallization of
Kilauean magma (e.g. see discussion by Thompson
& Tilley, 1969; Helz & Thornber, 1987; Clague et al.,
1995; Yang et al., 1996). Bulk MgO values of
episode 54, fissure A±E lava cluster near an average
of 64 wt % (1s ˆ 09, for 13 samples) and the average
1530
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
Table 1: Averaged major and trace element compositions of samples from the steady-state eruption
intervals of episodes 53 and 55
Episode 53 steady-state
Episode 55 steady-state
Sample no.:
KE53-1536F to -1842F
KE53-1533T to -1846T
KE55-1912F to -2089F
Time interval:
9/22/94±1/23/97
9/06/94±1/29/97
8/22/97±1/7/99
KE55-1921T to -2083T
9/18/98±11/19/98
Sample type:
Tube
Tears
Tube
Tears
Anal. type:
XRF
EMPA
XRF
EMPA
No. analyzed:
102
90
68
38
Av.
SD
7%MgOn
Av.
SD
Av.
SD
Av.
SD
wt %
SiO2
Al2O3
FeOt
MgO
CaO
Na2O
50.61
13.19
0.04
0.12
51.06
13.68
51.38
13.46
0.48
0.21
50.52
13.17
0.13
0.16
51.31
13.41
0.27
0.10
11.50
8.47
0.07
0.28
11.42
7.00
10.99
6.90
0.11
0.16
11.42
8.92
0.09
0.23
10.91
7.40
0.12
0.13
10.83
2.15
0.09
0.02
0.01
11.24
2.23
10.95
2.35
0.11
10.63
2.14
10.77
2.36
0.44
2.49
0.27
0.43
2.42
0.24
0.07
0.04
0.01
0.21
0.07
0.02
0.06
0.01
0.17
100.00
0.16
0.01
99.27
0.42
2.40
0.26
0.03
0.01
MnO
0.17
0.00
Total
100.00
K2O
TiO2
P2O5
MgO T ( C)
1184
5
1153
0.09
0.02
0.41
2.34
0.29
0.03
0.02
0.17
0.00
100.00
3
1193
Anal. type:
INAA
ICPMS
INAA
No. analyzed:
23
37
6
Av.
SD
7%MgOn
Av.
SD
Av.
9.0
Sr
323
Ba
103
Th
U
La
Ce
Nd
Sm
Eu
Gd
Tb
Ho
Tm
Yb
Lu
Zr
Hf
0.69
0.28
11.04
27.66
19.33
5.35
1.77
5.49
0.84
1.02
0.35
2.05
0.28
147
3.49
1.4
13
9.4
7.8
0 .3
8.9
4
SD
0.9
337
329
14
321
6
8
0.05
107
0.72
112
4
102
3
0.03
0.27
0.29
11.52
0.58
0.64
28.86
20.18
0.13
0.03
5.58
1.85
0.12
0.02
5.72
0.88
0.03
0.01
1.06
0.37
0.04
0.01
2.13
0.29
9
0.08
154
3.65
0.80
0.27
0.10
0.05
0.64
0.24
0.06
0.02
11.72
26.02
0.40
0.81
10.72
26.45
0.11
0.25
20.29
5.52
0.65
0.20
18.18
5.12
0.30
0.05
1.93
5.74
0.08
0.19
1.75
5.42
0.02
0.05
0.86
1.05
0.03
0.04
0.82
0.98
0.02
0.02
0.47
2.52
0.02
0.11
0.34
1.98
0.01
0.02
0.29
148
8
3.76
1531
0.19
152
3.33
0.04
0.01
0.16
0.01
99.33
ppm
Rb
0.40
2.38
0.23
0.01
13
0.03
1163
3
JOURNAL OF PETROLOGY
VOLUME 44
NUMBER 9
SEPTEMBER 2003
Table 1: continued
Episode 53 steady-state
Episode 55 steady-state
Sample no.:
KE53-1536F to -1842F
KE53-1533T to -1846T
KE55-1912F to -2089F
KE55-1921T to -2083T
Time interval:
9/22/94±1/23/97
9/06/94±1/29/97
8/22/97±1/7/99
9/18/98±11/19/98
Tears
Sample type:
Tube
Tears
Tube
Anal. type:
INAA
ICPMS
INAA
No. analyzed:
23
37
6
Av.
Ta
Sc
0.85
30.3
SD
0.03
175.7
7%MgOn
0.88
31.6
Av.
SD
0.99
31.2
0.24
0.9
Av.
0.78
29.8
SD
0.01
0.2
Co
423.3
60.8
0.6
21.4
441.8
63.4
474.0
50.2
7.1
0.5
Ni
137.3
22.0
143.4
152.7
5.2
Cr
Major element data are reproduced from Thornber (2001). Data include XRF and INAA whole-rock analyses for tubecontained lava flow samples and electron microprobe analysis (EMPA) and inductively coupled plasma mass spectrometry
(ICPMS) results for glasses of Pele's tears collected at Pu'u'O'o. Episode 53: September 1994±January 1997, including the
7 wt % MgO normalized composition. Episode 55: August 1997±January 1999. MgO thermometry (MgO T C) calculated for
bulk lava and tear glass using the method of Helz & Thornber (1987). Av., average; SD, standard deviation.
MgO content of fissure F lava is 58 wt % (1s ˆ 006
for nine samples). In episode 54 lava, moderately
incompatible elements that are incorporated by plagioclase and clinopyroxene (e.g. Ca and Sc) below the
multiphase cotectic at 7 wt % MgO are depleted,
whereas highly incompatible elements (e.g. large ion
lithophiles, rare earths and Ti, Zr, Hf, etc.) are variably enriched relative to olivine-controlled compositions. Episode 53 and 55 bulk lava compositions are
within a range of 76±96 wt % MgO and the incompatible element variation in this range is consistent
with olivine-only fractionation. Pu'u'O'o tear glasses
from episodes 53 and 55 are limited to a small range of
near-cotectic compositions with an average wt % MgO
of 69 (1s ˆ 016 for 90 samples) and 74 (1s ˆ 013,
for 38 samples), respectively (Fig. 4). Major and trace
element variation of tear glasses samples are closely
matched by the 7% MgO normalized composition
(as determined by equilibrium olivine subtraction)
and define the low-Mg end of the olivine control trends
of episode 53 and 55 whole-rock data.
As pointed out by Garcia et al. (2000), differences
between incompatible element ratios of episode 54 and
steady-state episode 53 and 55 lava preclude a simple
petrogenetic relation of comagmatic fractionation.
A hybrid character of episode 54 lava is independently
suggested by the geochemical data of this investigation.
A comparison of relative incompatible-element variations (e.g. La/Yb vs Ce) for episode 54 lava with that of
prior and subsequent steady-state eruption products
(Fig. 5) demonstrates that the recent Napau Crater
lava has a magmatic component that is chemically
distinct from magma within the active rift conduit.
Determining the nature of the mix is an objective of
this investigation to assess magmatic conditions that
persist within the rift zone.
Twenty-two vent samples collected during early episode 55 show a time progression from lower to higher
Mg contents that span the range between those of
steady-state bulk-liquids and tear glasses (Table 3,
Fig. 4). There is petrologic evidence (presented below)
indicating that this apparent olivine-controlled fractionation trend also results from mixing of magma within
the shallow rift zone.
Petrographic overview
Episode 53 and episode 55 steady-state Pele's tears,
vent spatter and near-vent tube samples typically consist of vesicular glass and 1±4 vol. % of 06±07 mm,
subhedral to euhedral olivine phenocrysts. Microphenocrysts of chromian spinel are commonly included
within olivine crystals, which also frequently contain
glass inclusions. A detailed account of petrographic
and chemical variations of chromian spinel in episode
53±55 steady-state lava has been provided by Roeder
et al. (2003). Acicular microlites of plagioclase (usually
550 mm long) and associated clinopyroxene are occasionally observed in upper elevation tube flow and vent
spatter samples and are rarely observed in Pele's tears.
1532
Table 2: Major and trace element compositions of episode 54 and episode 1 Napau Crater lava samples
No.:
KE54-
KE54- KE54- KE54- KE54-
KE54- KE54- KE54-
KE54- KE54-
KE54-
KE54-
KE54- KE54- KE54-
KE54- KE54- KE54- KE54-
KE54-
1849S 1850S 1848S 1851S 1852S
1853S 1854S 1855S
1856S 1857S
1858F
1859S
1860S 1861F 1862F
1865S 1863F 1866S 1864F
1867S 1868S 1869S 49
KE54-
KE54-
1997
KE1-
KE1-
KE1-
50
51
52
02/01
02/01
02/01
1983
30/01
30/01 30/01 30/01 30/01
30/01 30/01 30/01
30/01 30/01
30/01
30/01
30/01 30/01 30/01
30/01 30/01 31/01 31/01
31/01
30/01
30/01
02:50
03:30
05:00
06:10
06:13
06:19
06:46
07:02
13:37
14:12
14:40
16:56
18:31
21:38
22:37
23:00
23:33
00:00
00:08
00:30
22:00
22:00
A
A
C
B
B
B
B
D
D
D
E
E
F
F
F
F
F
F
F
F
F
02/01
W. Nap E. Nap E. Nap E. Nap
51.0
50.8
50.9
51.0
51.0
50.9
50.9
50.9
50.8
50.9
51.0
50.9
50.9
51.1
51.2
51.2
51.3
51.2
51.2
51.2
51.1
51.2
50.98
50.9
50.9
51.0
Al2O3
13.8
13.8
13.8
13.9
13.9
14.0
14.0
14.0
14.0
13.9
13.9
13.9
13.8
13.8
13.7
13.7
13.7
13.8
13.7
13.7
13.7
13.7
14.0
14.0
14.0
13.9
FeOt
11.6
11.9
11.7
11.7
11.8
11.7
11.7
11.7
11.7
11.8
11.8
11.7
11.7
12.0
12.1
12.1
12.1
12.0
12.0
12.0
12.1
12.1
11.3
11.7
11.7
11.6
MgO
6. 5
6.4
6.5
6.3
6. 3
6. 3
6. 3
6. 3
6.4
6. 3
6. 3
6.5
6.5
5. 8
5. 8
5. 8
5.7
5.8
5.8
5. 9
5. 9
5.7
6.8
6.4
6. 4
6. 4
CaO
10.5
10.4
10.6
10.5
10.5
10.4
10.4
10.4
10.6
10.5
10.3
10.5
10.5
9. 7
9. 7
9. 7
9.7
9.8
9.7
9. 8
9. 8
9.7
10.9
10.4
10.5
10.5
Na2O
2. 5
2.5
2.5
2.5
2. 5
2. 5
2. 5
2. 5
2.5
2. 5
2. 5
2.5
2.5
2. 7
2. 7
2. 7
2.7
2.7
2.8
2. 7
2. 7
2.7
2.4
2.5
2. 5
2. 5
K 2O
0.58
0.60
0.57
0.61
0.60
0.60
0.60
0.60
0.59
0.60
0.61
0.59
0.60
0.71
0.73
0.73
0.73
0.71
0.72
0. 7
0. 7
0.7
0.5
0.59
0.59
0.59
TiO2
2. 9
3.0
2.9
3.1
3. 0
3. 0
3. 0
3. 0
3.0
3. 0
3. 0
3.0
3.0
3. 5
3. 5
3. 5
3.5
3.4
3.5
3. 4
3. 4
3.5
2.71
3.0
3. 0
3. 0
P 2O5
0.35
0.37
0.36
0.36
0.35
0.36
0.36
0.36
0.36
0.36
0.36
0.36
0.36
0.42
0.43
0.43
0.43
0.42
0.43
0. 4
0. 4
0.4
0.3
0.35
0.34
0.35
MnO
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0. 2
0. 2
0.2
0.17
0.17
0.17
0.17
Total
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
1144
1142
1145
1141
1140
1141
1141
1141
1142
1142
1140
1145
1144
1131
1130
1130
1129
1131
1130
100
100
100
100
100
100
100
1131.9 1132.5 1129.3 1151
1142
1142
1142
MgO
T (C)
Rb
11.4
11.5
11.1
12.0
11.5
10.8
15.7
16.2
12.7
11.9
11.4
12.0
Sr
384
384
381
378
393
371
356
366
369
431
410
393
Ba
141
152
140
139
156
141
172
164
136
146
150
145
Th
1.11
1.15
1.19
1.18
1.26
1.13
1.46
1.38
1
1.13
1.13
1.12
U
0.437
0.411
0.403
0.395
0.424
0.374
0.485
0.473
0.372
0.405
0.435
0.399
La
15.50
16.20
16.00
16.40
16.80
15.50
20.10
19.50
14.2
16.2
16.5
15.9
Ce
38.20
39.50
39.00
39.20
41.00
37.40
49.40
47.40
35.9
38.3
41.3
39.6
Nd
25.50
26.30
26.80
25.20
27.30
24.60
31.40
30.70
23.7
26.5
27.1
25.8
Sm
6.33
6.69
6.49
6.66
6.81
6.23
7.96
7.61
6.24
6.76
7.01
6.74
Eu
2.17
2.21
2.27
2.27
2.28
2.17
2.60
2.62
2.05
2.26
2.28
2.23
Gd
6.71
7.00
6.85
6.90
6.87
6.61
8.41
8.60
6.58
7.13
7.12
6. 9
Tb
0.99
1.01
0.98
1.00
1.04
0.97
1.23
1.20
0.978
1.05
1.06
1.02
Ho
1.10
1.18
1.12
1.15
1.16
1.10
1.44
1.35
1.19
1.3
1.29
1.22
Tm
0.41
0.41
0.39
0.40
0.41
0.41
0.50
0.48
0.369
0.389
0.417
0.383
KILAUEA EAST RIFT ZONE MAGMATISM
1533
SiO2
THORNBER et al.
Date:
Time:
Fissure: A
KE1-
No.:
KE54- KE54- KE54- KE54- KE54-
KE54-
KE54-
KE54-
1849S 1850S 1848S 1851S 1852S 1853S 1854S 1855S 1856S 1857S 1858F
KE54-
KE54-
KE54-
KE54-
KE54-
1859S
1860S 1861F 1862F
KE54- KE54-
KE54-
KE54- KE54-
KE54-
1865S 1863F 1866S 1864F
KE54-
KE54-
KE54-
1997
KE1-
KE1-
KE1-
50
51
52
02/01
02/01
02/01
1983
30/01
30/01
30/01
30/01
30/01
30/01
30/01
30/01
30/01
30/01
30/01
30/01
30/01
30/01 30/01
30/01
30/01 31/01
31/01
31/01
30/01
30/01
Time:
02:50
03:30
05:00
06:10
06:13
06:19
06:46
07:02
13:37
14:12
14:40
16:56
18:31
21:38
22:37
23:00
23:33
00:00
00:08
00:30
22:00
22:00
A
A
C
B
B
B
B
D
D
D
E
E
F
F
F
F
F
F
F
F
F
02/01
W. Nap E. Nap E. Nap E. Nap
1534
Yb
2.30
2.39
2.36
2.40
2.37
2.29
2.79
2.71
2.24
2.4
2. 4
2.34
Lu
0.32
0.32
0.32
0.32
0.32
0.31
0.39
0.37
0.311
0.323
0.33
0.32
Zr
200.0
201.0
198.0
172.0
211.0
191.0
251.0
243.0
192.0
195.0
210.0
201.0
4.60
4.69
4.68
4.68
4.87
4.43
5.66
5.60
4.26
4.56
4.69
4.51
Ta
1.25
1.28
1.28
1.32
1.35
1.24
1.61
1.55
1.12
1.26
1.31
1.26
29.50
28.70
145
30.30
126
29.80
123
30.30
117
29.70
119
30.00
131
88
80
158
30.7
29.5
Co
44
43
43
43
43
42
41
40
43
42.1
42.7
41.5
Ni
91
86
81
95
94
86
76
68
95.6
86.5
88.5
85.7
109
29.5
116
29.1
106
Episode 1 samples [as reported by Wolfe et al. (1988)] were reanalyzed for this study. Time and date of quenching, and fissure sources are indicated at the top of each
column.
SEPTEMBER 2003
29.10
Cr
Sc
NUMBER 9
Hf
VOLUME 44
Date:
Fissure: A
KE1-
1867S 1868S 1869S 49
JOURNAL OF PETROLOGY
Table 2: continued
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
Table 3: Major and trace element compositions of early episode 55 non-steady-state vent and
near-vent samples (March 31, 1997±July 29, 1997)
Number:
KE55-1878F
KE55-1884F
KE55-1892F
KE55-1894F
KE55-1906S
Date:
18/04/97
14/05/97
03/06/97
12/06/97
21/07/97
Time:
10:15
13:00
14:00
13:13
19:00
SiO2
Al2O3
FeOt
MgO
CaO
Na2O
K2O
TiO2
P2O5
MnO
Total
MgO T ( C)
Rb
50.8
13.5
50.8
13.4
50.9
13.4
50.8
13.3
50.8
13.4
11.4
7.7
11.5
7.8
11.4
7.8
11.4
7.9
11.4
8.2
11.1
2.2
11.0
2.2
11.0
2.2
11.0
2.2
10.9
2.1
0.41
2.4
0.41
2.4
0.42
2.4
0.41
2.4
0.39
2.4
0.26
0.17
0.31
0.17
0.28
0.17
0.31
0.17
0.28
0.17
100
100
100
100
100
1169
1171
1172
1173
1178
8.9
8.2
7.9
9.2
Sr
314
304
323
346
Ba
101
109
98
87
Th
0.71
0.274
0.79
0.284
0.82
0.246
0.78
0.223
9.1
320
95
0.77
11.20
29.00
11.00
28.20
11.00
28.30
11.00
27.80
0.275
11.10
27.50
20.00
5.59
18.90
5.44
19.50
5.38
18.80
5.34
18.20
5.36
1.83
5.53
1.78
5.59
1.78
5.74
1.78
5.61
1.78
5.66
0.86
1.06
0.87
1.04
0.85
1.08
0.84
1.04
0.85
1.07
0.36
2.19
0.36
2.08
0.37
2.07
0.37
2.11
0.36
2.11
0.31
154.0
0.30
164.0
0.29
131.0
0.30
157.0
0.30
136.0
Ta
3.60
0.89
3.46
0.85
3.47
0.85
3.45
0.82
3.43
0.81
Sc
31.40
30.90
31.00
30.80
30.90
U
La
Ce
Nd
Sm
Eu
Gd
Tb
Ho
Tm
Yb
Lu
Zr
Hf
Cr
352
367
371
371
Co
47
47
48
47
379
48
Ni
104
101
118
108
139
Data are presented for five of 22 early episode 55 samples which are representative of the increased wt % MgO progression
with time during this eruption restart interval (see Thornber, 2001, fig. 15).
Despite the chemical differences between lava from
fissures A±E and the more evolved fissure F lava, overall petrographic characteristics of episode 54 samples
are indistinguishable from one another and clearly
distinct from olivine-phyric episode 53 and 55 lava.
As determined by the bulk-rock density methods of
Houghton & Wilson (1989), episode 54 lava samples
are highly vesicular, ranging from 30 to 80 vol. %
vesicles with no clear correlation between vesicularity
and composition or fountain height. Matrices are
predominantly aphyric with proportions of glass ranging from 1 to 80 vol. %, varying significantly
1535
JOURNAL OF PETROLOGY
VOLUME 44
NUMBER 9
SEPTEMBER 2003
Fig. 4. MgO variation diagrams for selected major and trace elements in 1994±1998 eruptive products; symbols as indicated in the figure.
within and between samples owing to differences in
extent of microphyric to cryptocrystalline groundmass
crystallization during eruption and quenching. The
most striking petrographic features observed in electron backscatter images of these samples are the diverse
textural and zonation patterns among phenocrysts
(03±1 mm and rarely up to 3 mm) and microphenocrysts ( 01±03 mm) (Figs 6 and 7). Phenocrystic and
microphenocrystic plagioclase, clinopyroxene, and olivine ( chromian spinel) are present in all samples,
either as isolated grains or in glomerophyric aggregates
of phenocrysts or microphenocrysts. The phenocryst
population ranges up to 5 vol. % in these samples
and includes an assortment of rounded, euhedral and
angular fragments of clinopyroxene and plagioclase
that are occasionally intergrown as aggregates or clots
and may be unzoned, normally zoned, reversely zoned
or display more complex zonation patterns. This population also includes normally zoned and resorbed olivine
and a resorbed and a reversely zoned orthopyroxene
1536
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
complexly zoned olivine and a sector zoned clinopyroxene surrounded by a microphyric matrix that is itself
resorbed and overgrown by relatively Mg-rich clinopyroxene. Additional examples of variably reacted olivine phenocrysts in early episode 55 lava have been
presented by Thornber (2001, fig. 4c±g).
MINERAL AND GLASS CHEMISTRY
Fig. 5. La/Yb vs Ce for 1994±1999 bulk lava, including episode 54
(symbols are the same as in Fig. 4). The fractionation trend is
calculated using the partition coefficients of Pietruszka & Garcia
(1999) and assuming separation of trace amounts of olivine with
near-equal proportions of plagioclase and clinopyroxene from
a near-cotectic melt (episode 53, 7% MgO normalized value,
Table 1).
crystal, present in one fissure F sample. In addition,
glass inclusions are preserved in some olivine, plagioclase and clinopyroxene phenocrysts. Examples of
episode 54 phenocrysts, microphenocrysts and glomerophryic aggregates are shown in Fig. 6 and discussed in
more detail in the following sections pertaining to
individual mineral groups. Additional examples of
resorbed, normally zoned and overgrown crystals of
olivine in episode 54 lava have been presented by
Thornber (2001).
Typical glomerophyric aggregates of microphenocrysts are 05±1 mm in diameter, ranging up to
3 mm. These microphenocrystic clots usually consist
of plagioclase and clinopyroxene and, in some cases,
they include intercrystalline glass that is isolated and
compositionally distinct from matrix glasses. Microphenocrystic olivine±plagioclase clusters are present
in some samples and olivine microphenocrysts are
occasionally observed in association with plagioclase±
clinopyroxene intergrowths. In many samples, aggregated microphenocrysts are texturally distinct amidst
glassy or microphyric groundmass (Fig. 6h). Such
aggregates occasionally appear disrupted by flow
within the host lava as implied by alignment of surrounding matrix crystals. In other cases, such aggregates are obscured amid abundant isolated
microphenocrysts of similar size. Both isolated and
aggregated microphenocrysts may be normally zoned,
reversely zoned and unzoned.
Lava issued sporadically from Pu'u'O'o flank vents
during early stages of episode 55 contains variably
reacted phenocrysts of clinopyroxene and olivine with
complex zoning features, distinct reaction rims, and
plagioclase inclusions. Figure 7 shows an early episode
55 xenolithic aggregate composed of resorbed and
Olivine, plagioclase and pyroxene phenocrysts and
microphenocrysts in individual lava samples convey a
record of crystal growth and reaction in a range of
compositionally distinct magmas. Olivine±liquid relations of near-vent, steady-state lava demonstrate the
prevalence of Fo80±82 saturated magma at 1200 C,
within the active conduit (Thornber, 2001). Episode
54 and early episode 55 samples exhibit crystal±liquid
reactions indicative of pre-eruptive magma mixing
between conduit magma and cooler, phenocrystladen magma. The heterogeneity among glass compositions in episode 54 samples also provides strong
evidence for pre-eruptive mixing of discrete magmatic
components. Compositional and textural features
suggestive of magma mixing for each of the major
crystalline phases and discrete glasses within episode
54 samples are presented in turn.
Olivine
Deviations from equilibrium distribution of FeO and
MgO between eruption glasses and olivine in 1994±
1999 eruption products were used by Thornber (2001)
to define three types of olivine phenocrysts as: Type A
(near-equilibrium Fo/host-glass), Type B (high Fo/
host-glass) and Type C (low Fo/host-glass). In the
episode 54 sample suite, both the most differentiated
lava of fissure F and intermediate lava of fissures A±E
contain a range of Type B and Type A olivine crystals
(Table 4, Fig. 8a). The Type B olivine is compatible
with glasses or bulk liquids erupted during steady-state
eruptive intervals (Thornber, 2001) and episode 54
Type A compositions reflect crystallization from their
host-liquids. Close inspection of microcrystals within
the matrix of these samples reveals tiny remnants of
resorbed Type B olivine phenocrysts persisting among
euhedral and skeletal Type A microphenocrysts. Type B
olivine is more apparent and larger (up to 1 mm) in
fissure F samples (Fig. 6a) and less prominent and
smaller (up to 03 mm) in fissures A±E (Fig. 6b). The
Type B crystals exhibit variably resorbed outer margins,
normal core-to-rim zonation and exterior overgrowth
of either Type A skeletal olivine or clinopyroxene.
Two Type B olivine grains among a sparse population of resorbed olivine crystals observed in fissure A±E
samples were analyzed. At Fo841, a remnant Type B
1537
JOURNAL OF PETROLOGY
VOLUME 44
NUMBER 9
SEPTEMBER 2003
Fig. 6. Electron-backscatter images of episode 54 samples. In each image, plagioclase (plg) appears as darkest gray; glass (gls) as lighter gray;
olivine (OL) and augite (cpx) are intermediate gray and chromian spinel (sp) is white. Rounded black areas are vesicles and pits. White barscale in each image represents 100 mm. (a) Fissure F (KE54-1864); rounded Type B olivine (center) (Fo844 core and Fo777 rim) with cuspate
margins and glass inclusions (MgO T C ˆ 1130); small rounded Type A olivine grains (Fo78) occur on the margins of the phenocryst along
with hopper-like overgrowth of Type A olivine (Fo722) on the upper left side; the glass matrix (MgO T C ˆ 1116) also contains plagioclase
and augite microphenocrysts and microlites. (b) Fissure E (KE54-1860); triangular-shaped, resorbed Type B olivine (Fo806 core) is
continuously zoned toward a Type A olivine (Fo74) skeletal overgrowth; cr-spinel occurs as free-floating grains in the vicinity of Type B
olivine; glass matrix (MgO T C ˆ 1127) contains microphenocyrsts of Type A olivine, plagioclase and augite. (c) Fissure E (KE54-1860);
plagioclase phenocryst remnant (dark rounded and euhedral laths) with abundant glass inclusions (light gray) ranging from MgO T C of
1154 to 1125); inner to outer core of plagioclase remnants are reversely zoned (An76 to An805) and inner and outer rim is normally zoned
(An787 to An661). (d) Fissure F (KE54-1862); glomerocrystic aggregate of unzoned plagioclase phenocryst (An636) intergrown with resorbed
sector-zoned augite and surrounded by a uniform augite rim of Mg#773; core-to-rim dark and light sector zoning ranges from Mg#791 to
Mg#762 (points 1±3 in Table 5) and Mg#754 to Mg#775 (points 4±7 in Table 5), respectively; orthopyroxene (Mg#787) appears as a dark gray
lath in the upper left corner of the augite phenocryst. (e) Fissure F (KE54-1867); near-euhedral plagioclase±augite phenocryst intergrowth;
plagioclase is uniform in composition (An648) and augite phenocryst displays slight normal core-to-rim zonation (Mg#790 to Mg#794).
(f) Fissure E (KE54-1860); partially melted, resorbed and reversely zoned augite phenocryst. Rounded core of Mg#682 has an inner rim Mg#787
of a uniform overgrowth rim of Mg#780; and contains crystal irregular-shaped glass inclusions with cuspate boundaries (MgO T C ˆ 1088).
(g) Fissure F (KE54-1863); orthopyroxene phenocryst, slightly rounded, normally zoned (Mg#735 to Mg#780) and partially mantled by hostcompatible clinopyroxene microphenocrysts (Mg#774). (h) Fissure A (KE54-1849); glomerophyric aggregate of plagioclase (An673±639) and
augite (Mg#781) with compatible intracrystalline glass (MgO T C ˆ 1123) amidst matrix crystals and glass (MgO T C ˆ 1136).
1538
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
Fig. 7. Electron-backscatter image of lithic fragment in early
episode 55 sample KE55-1894. White bar-scale represents 100 mm.
Complexly zoned Type C olivine (center) with Fo776 core is
normally zoned to an inner rim of Fo739 and reversely zoned to a
uniform outer rim of Fo789. The inner to outer olivine rim contains
plagioclase ranging from An594 to An657, approaching highertemperature matrix microphenocryst compositions (An65±67). The
sector zoned augite (upper left) is normally zoned from the core
(Mg#818) to inner rim (Mg#831) with a lower-temperature augite
overgrowth (Mg#775), similar to matrix microphenocrysts (Mg#779).
Matrix glass has MgO T C of 1148.
olivine core in fissure B sample 1850 (Table 4) is a
compositional match for Type B olivine in steadystate lava (Thornber, 2001). This crystal displays continuous normal zoning into a skeletal overgrowth of
Fo798 and is locally associated with free-floating microlites of chromian spinel, a primary crystalline product
of a relatively primitive magma. An Fo806 Type B
olivine in fissure E, sample 1860 (Table 4, Fig. 6b) is
an angular phenocrystic fragment (025 mm) with
slightly rounded edges and a thin (520 mm), Fo74
rim. This olivine core composition overlaps the range
of near-equilibrium olivine in Pele's tears sampled during steady-state eruption at Pu'u'O'o (Thornber,
2001). Type A olivine microphenocrysts in fissure A±
E lava range in composition from Fo798 to Fo746 and
occur as normally zoned or unzoned crystals that are
either isolated in the matrix or intergrown with plagioclase at near-cotectic temperatures ( 1150 C).
Six Type B olivine grains analyzed in fissure F samples have core/rim compositional ranges from Fo792/
Fo751 to Fo844/Fo777 and coexist with Type A microphenocrysts ranging from Fo76 to Fo72 (Table 4).
Microphenocrysts of lower-Fo Type B olivine in fissure
F overlap the composition of Type A (nearequilibrium) microphenocrysts in fissures A±E.
Figure 6a shows a normally zoned and well-rounded
olivine phenocryst from fissure F (Fo844 core, Fo777
rim) with glass inclusions (see discussion of glasses
below). Small rounded Type A microphenocrysts
( 005 mm) of Fo78 composition surrounding this
crystal are intergrown with plagioclase and overgrown
by Fo73 skeletal olivine. The fine-scale cuspate texture
at the crystal±liquid interface of the larger olivine
phenocryst is evidence for partial resorption by the surrounding low-temperature liquid. Most other Type B
olivine crystals in episode 54 lava have similar skeletal
olivine overgrowth of angular or rounded cores with
cuspate margins (see Thornber, 2001, fig. 4b). Comparable examples of cuspate olivine texture, observed
in hybrid magmas erupted in the Kilauea 1959 summit
eruption and in the 1955 lower east rift eruption, are
interpreted as evidence for mixing of thermally and
chemically disparate magmas (Thornber & Huebner,
1985; Helz, 1987; Helz & Wright, 1992).
Early episode 55 olivine phenocrysts have been discussed in detail by Thornber (2001). These include an
array of normally zoned Type B compositions and
Type C phenocrysts with reversed to complex zoning
patterns that are unique to this post-episode 54 interval. Type C olivine within the lithic fragment in sample 1894 (Fig. 7) has an Fo776 core that is normally
zoned to a rim of Fo739. An overgrowth of Type A
Fo789 olivine surrounds the entire microphyric fragment. A second Type C olivine microphenocryst
(Fo733), which is intergrown with plagioclase, is
attached to this fragment (lower left, Fig. 7) and is
reversely zoned toward the Fo789 rim composition.
The low-Fo compositions of cores and inner rims of
these complexly zoned crystals are similar to nearequilibrium olivine in episode 54 lava. Higher-Fo
cores and outer rims record a history of post episode
54 magma mixing and subsequent incorporation in
early episode 55 conduit magma.
Plagioclase
Variations in core composition of plagioclase phenocrysts (An631±760) and microphenocrysts (An607±673)
reflect crystallization from a range of thermally and
compositionally distinct magmas (Tables 4 and 5;
Fig. 8b). Both phenocrysts (03±3 mm) and microphenocrysts (01±03 mm) occur as isolated crystals
and in aggregates with clinopyroxene. The variability
in the extent of crystal reaction features, including edge
resorption, internal melting and core-to-rim zonation,
imply differences in compatibility among different
crystals and different liquids and in post-mixing residence time before eruption.
The variety of plagioclase compositions and textural
relations in samples from fissures A±E record a diverse
1539
JOURNAL OF PETROLOGY
Table 4: Selected microprobe analyses of isolated phenocrysts (ph) and microphenocryts (mph) of olivine, pyroxene and plagioclase
Olivine
Fissure A Fissure B
KE54-no.:
Fissure F
1860
1861
1855
TYPE/morph: A mph
B mph
A mph A mph A mph
Core/rim:
core
SiO2
CaO
MnO
NiO
core
core
core
rim
core
1864
A mph B mph B mph
rim
core
core
core
1867
B ph
rim
core
rim
B mph/glm
B ph
core
core
rim
B ph
rim
core
A mph
rim
39.84
15.14
39.05
19.01
39.10
22.35
38.54
21.39
39.24
19.09
38.19
24.66
39.53
18.37
38.04
24.15
38.51
22.05
38.88
19.28
39.32
19.55
38.59
23.00
40.07
14.90
38.84
20.41
39.41
19.68
38.14
25.03
39.51
14.97
39.30
21.21
40.28
15.21
39.08
19.42
38.79
20.96
40.41
0.25
45.06
0.23
42.13
0.25
36.83
0.62
39.18
0.33
42.36
0.26
35.23
0.24
42.94
0.27
38.52
0.32
39.74
0.21
40.80
0.27
41.87
0.23
38.83
0.26
45.16
0.23
39.95
0.28
40.13
0.27
36.46
0.28
45.89
0.23
38.28
0.74
44.66
0.25
40.69
0.25
40.02
0.22
0.25
0.18
0.19
0.22
0.27
0.14
0.29
0.17
0.25
0.11
0.26
0.19
0.30
0.11
0.27
0.20
0.28
0.14
0.30
0.19
0.25
0.19
0.23
0.16
0.31
0.15
0.19
0.23
0.29
0.18
0.22
0.13
0.30
0.11
0.20
0.29
0.25
0.18
0.22
0.25
0.23
0.18
0.25
0.19
99.67 101.36 101.15 100.79
79.2
75.1
84.4
99.95
77.7
Total
99.51
78.7
1141
100.67 100.85
84.1
79.8
1199
1146
99.35
74.6
1124
99.81 101.40
76.6
79.8
1132
1146
98.74 101.57 101.45 101.00
80.6
74.0
76.3
71.8
1112
1159
1121
1131
79.0
1143
1143
1126
1202
1137
99.84 100.32 101.09
78.4
72.2
84.5
1140
1114
1204
99.96 100.86
76.3
84.0
1131
1197
99.84 100.43
78.9
77.3
1142
1135
SEPTEMBER 2003
38.92
19.50
%Fo
T ( C) Calc
rim
1863
NUMBER 9
MgO
core
B mph
1862
VOLUME 44
1540
1850
FeO*
1849
Fissure E
0.20
1.08
0.24
17.49
0.17
0.18
1.20
0.34
18.48
0.29
0.46
0.62
CaO
1541
13.5
78.7
19.7
68.2
Fs
T ( C) Calc 1079
Mg# cpx
1122
36.5
50.0
38.2
42.1
Total
Wo
En
98.58
100.06
K2O
Cr2O3
TiO2
MnO
Na2O
MgO
Al2O3
81.9
78.0
1135
49.8
11.0
49.8
14.1
1119
99.47
39.2
1.29
0.15
0.86
18.71
0.41
6.76
17.08
50.66
3.55
core
light
ph
1894
1138
11.9
82.6
31.9
56.3
99.83
0.67
0.18
0.44
15.67
0.20
7.49
19.91
53.65
1.62
1140
83.2
52.9
10.7
100.11
36.4
0.77
0.17
0.52
17.87
0.25
6.72
18.70
53.11
2.00
1137
10.9
82.5
38.0
51.1
99.81
0.68
0.12
0.62
18.57
0.24
6.81
17.93
52.72
2.12
1115
77.0
49.5
14.8
99.98
35.7
0.30
0.21
1.08
17.28
0.26
9.15
17.22
51.79
2.69
14.0
77.5
37.8
48.2
99.17
0.49
0.17
1.16
16.74
0.62
7.97
15.36
52.02
4.63
1117
Traverse from dark core to outermost rim
Early episode 55 clinopyroxene
99.52
36.2
17.03
0.28
8.49
16.84
8.31
17.24
12.18
14.64
FeO*
SiO2
52.18
3.19
outer
rim
inner
rim
50.61
3.03
core
Core/rim:
52.00
1.38
1860
ph
KE54-no.:
Type:
Fissure E clinopyroxene
1863
1138
20.4
78.7
4.1
75.5
100.31
0.15
0.24
0.59
2.12
13.38
27.71
54.61
1.52
1116
73.5
70.5
25.5
100.44
4.0
0.07
0.34
0.59
2.02
16.57
25.76
53.58
1.51
exsolved? core
mph incl. ph
1862
1117
25.3
73.6
4.1
70.6
100.40
0.07
0.34
0.60
2.07
16.41
25.68
53.57
1.66
core
outer
Fissure F orthopyroxene
inner
1129
22.5
76.5
4.4
73.1
100.60
0.09
0.29
0.64
2.26
14.72
26.82
54.26
1.52
rim
outer
1135
20.9
78.0
5 .0
74.2
101.14
0.13
0.30
0.63
2.57
13.77
27.47
54.65
1.63
rim
%Or
%ab
%an
1187
0.5
76.0
23.5
0.082
100.80
15.68
2.67
0.67
49.52
32.18
core
Ph
1860
1211
0.3
80.5
19.2
0.059
99.34
16.30
2.14
0.68
47.70
32.46
core
outer
1201
0.4
78.7
20.9
0.073
99.50
16.01
2.35
0.68
48.23
32.16
rim
core-
Fissure E plagioclase
1198
0.4
78.0
21.5
0.077
99.78
15.80
2.41
0.72
48.50
32.27
core-
1134
0.7
66.1
33.2
0.128
99.48
13.60
3.76
0.74
51.75
29.51
rim
outer
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
KE54-no.:
Type:
Core/rim:
Al2O3
FeOt
MgO
Na2O
MnO
TiO2
Cr2O3
Wo
En
Fs
Mg# cpx
T ( C) Calc
1850
1852
1854
Fissure E
1858
1859
1860
cpx
cpx
cpx
cpx
cpx
cpx
cpx
cpx
cpx
mph/glm
mph/glm
mtx
mph/glm
mph/glm
ph/glm
mph/glm
mph/glm
mtx
core
core
core
core
core
core
core
core
core
49.97
4.03
51.26
2.94
50.65
4.08
7.78
15.54
19.15
8.48
17.09
17.35
9.19
8.61
9.73
17.21
16.02
15.60
18.47
15.60
15.98
0.29
0.18
0.31
0.24
0.27
0.21
0.27
0.19
0.55
0.20
1.52
0.37
1.19
0.17
1.74
0.44
1.99
0.24
98.84
40.9
99.02
36.3
99.81
34.0
46.2
13.0
49.8
13.9
78.1
78.2
1119
1120
50.06
4.28
50.19
3.90
51.71
3.32
49.68
5.22
7.99
8.40
16.25
18.18
18.70
16.36
8.24
16.46
18.64
7.65
17.02
18.66
8.52
16.72
17.73
9.39
14.64
17.96
0.25
0.21
0.24
0.23
0.24
0.20
0.26
0.21
0.28
0.15
0.52
0.20
1.83
0.14
1.33
0.56
1.06
0.57
1.55
0.47
1.06
0.52
1.21
0.14
2.04
0.28
99.49
39.4
100.08
35.3
99.59
38.6
100.62
33.5
100.14
38.9
99.47
38.6
99.78
37.2
99.92
39.3
50.8
15.2
46.3
14.4
47.9
16.8
48.1
13.3
53.1
13.4
47.7
13.4
49.0
12.4
48.8
13.9
44.6
16.1
76.9
76.3
74.1
78.3
79.9
78.0
79.9
77.8
73.5
1112
51.38
4.67
1103
50.66
4.17
rim
51.58
3.48
1115
49.47
4.65
core
1121
1127
1119
1127
1118
1101
SEPTEMBER 2003
Total
1849
Fissure D
NUMBER 9
CaO
Fissure B
VOLUME 44
1542
SiO2
Fissure A
JOURNAL OF PETROLOGY
Table 5: Selected microprobe analyses of clinopyroxene (cpx) and plagioclase (plg) phenocrysts (ph), microphenocrysts (mph) and matrix crystals
(mtx), occurring either as free-floating crystals or in glomerophyric aggregates (glm); data for adjacent mineral pairs are vertically aligned
99.49
63.9
35.3
0.8
99.53
67.3
32.1
0.6
Total
1543
50.64
3.62
49.49
4.41
0.27
0.20
0.41
0.22
MgO
Na2O
MnO
CaO
9.10
16.76
17.09
9.02
15.46
18.95
FeOt
SiO2
Al2O3
Anal. no.:
core
Core/rim:
1116
36.5
0 .8
100.07
62.7
4.13
0.14
1.04
12.87
52.80
29.09
core
0.27
0.20
17.65
18.15
8.32
52.46
1.95
1
0.27
0.18
8.56
17.18
17.43
52.14
1.99
2
Dark cor/rim traverse
ph/glm
cpx
cpx
mph/glm
1862
1861
Fissure F
Type:
KE54-no.:
T ( C) Calc
%Or
%Ab
%An
K2O
1122
3.93
0.14
3.59
0.10
Na2O
CaO
1136
0.85
12.91
0.82
13.61
FeOt
Al2O3
SiO2
52.54
29.12
rim
outer
rim
mph/glm
mph/glm
core
plg
plg
51.45
29.96
Core/rim:
Type:
0.33
0.24
17.24
17.14
9.61
51.41
3.05
3
1132
33.7
0.6
99.56
65.6
3.77
0.11
0.91
13.31
51.78
29.68
core
mph
plg
0.27
0.26
9.72
16.68
16.72
50.93
2.96
4
0.31
0.18
16.75
18.56
8.70
51.33
3.10
5
0.28
0.21
15.96
18.72
8.54
50.88
3.06
6
1117
36.2
1.0
100.56
62.8
4.05
0.17
1.27
12.75
53.36
28.96
core
mtx
plg
Light cor/rim traverse
1130
34.0
0.7
100.44
65.3
3.83
0.13
0.75
13.34
52.59
29.80
core
mph/glm
plg
0.31
0.20
8.58
16.38
18.63
51.05
3.37
7
1115
36.6
0.9
99.68
62.6
4.08
0.14
0.98
12.64
52.91
28.92
core
mph/glm
plg
0.27
0.23
9.02
17.17
17.44
51.70
2.46
1&4
avgcor
1112
37.2
0.8
0.22
0.21
16.72
17.56
8.71
50.67
3.60
core
ph
opx
1863
99.86
61.9
4.20
0.15
0.95
12.66
53.02
28.88
core
0.23
0.20
18.26
17.20
8.01
52.66
2.25
core
ph
cpx
1124
35.0
0.7
100.94
64.2
4.00
0.13
0.89
13.25
52.89
29.78
core
mph/glm
plg
0.29
0.19
15.25
19.73
8.42
50.08
3.88
rim
1131
33.8
0.7
99.84
65.5
3.83
0.12
0.90
13.41
52.13
29.45
core
ph/glm
plg
0.15
0.21
18.45
15.63
9.36
52.58
2.03
core
mph/glm
cpx
1864
0.25
0.20
8.53
18.01
17.08
52.74
2.00
core
ph/glm
cpx
1867
0.33
0.16
8.00
17.28
18.47
52.53
2.14
rim
1124
35.1
0.7
98.88
64.2
3.90
0.12
0.99
12.91
52.19
28.77
core
mph/glm
plg
0.22
0.17
7.93
17.46
17.01
51.54
3.56
core
mtx
cpx
1883
0.26
0.20
16.56
18.49
8.36
50.35
3.06
core
mtx
cpx
1894
0.20
0.19
17.73
17.77
8.60
52.69
1.82
core
mtx
cpx
1894
1103
38.7
1.0
100.24
60.3
4.43
0.17
0.92
12.50
53.48
28.75
core
mtx
plg
Early episode 55
1118
36.2
0.7
100.69
63.1
4.10
0.13
0.99
12.94
53.20
29.33
core
mph/glm
plg
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
rim
99.32
36.0
49.1
14.9
76.7
100.14
39.9
45.3
14.8
75.3
En
Mg# cpx
1544
Type:
4.16
0.17
99.55
61.5
37.6
1.0
4.33
0.14
99.87
60.7
38.4
0.8
Na2O
Total
T ( C) Calc 1106
%Or
%Ab
%An
K2O
1109
0.89
12.36
core
0.92
12.41
CaO
77.5
47.9
13.9
100.45
38.2
1.25
0.27
1117
5
77.0
46.7
14.0
99.16
39.3
1.27
0.24
1115
6
77.2
47.4
13.9
100.18
38.7
1.43
0.24
1116
7
1116
77.2
49.4
14.6
99.45
36.0
1.00
0.19
1&4
1118
36.3
0.7
99.36
63.1
4.08
0.12
0.71
12.89
52.36
29.21
core
ph/glm
FeOt
Al2O3
75.4
48.9
15.9
98.93
35.2
1.20
0.21
1109
4
plg
53.07
28.91
SiO2
76.2
49.3
15.4
100.45
35.3
1.20
0.22
1112
3
avgcor
mph/glm
rim
78.1
49.8
13.9
98.71
36.3
0.77
0.18
1120
2
Light cor/rim traverse
1127
34.3
0.9
99.71
64.8
3.87
0.15
0.89
13.21
52.08
29.51
core
ph
plg
1117
77.4
48.9
14.3
99.36
36.9
1.32
0.34
core
1132
33.4
0.9
99.46
65.7
3.70
0.15
0.71
13.22
52.07
29.61
core
ph
plg
1128
80.2
52.0
12.8
100.07
35.2
0.84
0.43
core
ph
cpx
1.64
0.35
1112
76.3
44.7
13.9
99.84
41.5
rim
cpx
1867
plg
1123
79.0
51.3
13.7
99.76
35.0
0.76
0.20
core
1119
36.1
0.7
100.54
63.2
4.08
0.13
1.02
12.93
52.95
29.43
core
1127
34.4
0.8
98.90
64.8
3.87
0.13
0.69
13.15
51.85
29.21
core
mph/glm ph/glm
plg
1119
77.9
52.9
15.0
99.49
32.1
0.91
0.17
core
mph/glm ph/glm
cpx
1864
0.85
0.24
1125
79.4
49.3
12.8
99.99
37.9
rim
1133
33.6
0.6
100.24
65.8
3.73
0.10
0.88
13.26
52.32
29.96
core
mtx
plg
1126
79.7
51.2
13.0
99.88
35.8
1.20
0.80
core
mtx
cpx
1883
1121
35.5
0.8
98.81
63.7
3.91
0.13
0.68
12.74
52.26
29.10
core
mtx
plg
1119
78.0
48.0
13.6
98.81
38.5
1.23
0.30
core
mtx
cpx
1894
1129
34.0
0.8
99.29
65.2
3.82
0.14
0.72
13.23
51.93
29.44
core
mtx
plg
1122
78.6
50.2
13.6
100.01
36.2
0.74
0.28
core
mtx
cpx
1894
NUMBER 9
53.14
28.93
Core/rim:
79.1
49.9
13.2
99.97
36.9
0.80
0.17
1123
1
Dark cor/rim traverse
ph
opx
1863
Early episode 55
VOLUME 44
plg
T ( C) Calc 1108
Fs
Wo
Total
1114
1.44
0.20
Cr2O3
TiO2
1.96
0.23
Anal. no.:
core
Core/rim:
ph/glm
cpx
cpx
mph/glm
1862
1861
Type:
KE54-no.:
Fissure F
Table 5: continued
JOURNAL OF PETROLOGY
SEPTEMBER 2003
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
Fig. 8. Average core and rim compositions of phenocrysts, microphenocrysts and matrix microlites for each of the episode 54 fissures (isolated
and glomerophyric microphenocrysts are not distinguished); arrows indicate direction of core-to-rim zonations. Symbols are as indicated
below each diagram. (a) Olivine (Fo%) categorized as Type A, Type B, and Type C; range of Type A phenocrysts is also shown for steadystate episode 53 and 55 samples. (b) Plagioclase (An%) phenocrysts include a fissure D sample reported by Garcia et al. (2000). (c) Pyroxene
(Mg#) data are for augite, except for the orthopyroxene phenocryst in a fissure F sample.
1545
JOURNAL OF PETROLOGY
VOLUME 44
range of crystallization and reaction histories. Figure 6c
shows a melted and reacted plagioclase phenocryst in
fissure E sample 1860 (Table 4). This phenocryst remnant is optically continuous but exhibits complex
chemical zonation from inner to outer core of An76 to
An805 and from inner to outer rim of An787 to An661.
Glass inclusions are pervasive throughout this grain
and provide evidence of internal melting. Phenocrystic
and microphenocrystic plagioclase with similar complex zonation patterns have been reported by Garcia
et al. (2000) in fissure D samples and are also plotted in
Figure 8b. These are interpreted here as metastable
remnants of relatively low-An phenocrysts that were
sequentially heated and cooled during a short interval of
pre-eruptive mixing of hotter and cooler magmas. The
high-An, reversely zoned core compositions have persisted as the refractory residua of partial melting during
incorporation of an originally lower-temperature
plagioclase in a relatively high-temperature magma.
The normally zoned rim compositions of this crystal
reflect subsequent reaction and overgrowth in lowertemperature hybrid magma. In contrast to these
reacted phenocrysts, an isolated An656 phenocryst in
fissure B lava sample 1850 (Table 5) has only slightly
rounded outer margins and no significant core-to-rim
zonation. Another An655 phenocryst with unreacted
morphology and uniform composition is intergrown
with clinopyroxene in a fissure E phenocryst aggregate
in sample 1859 (Table 5).
Glomerophyric plagioclase microphenocrysts in
lava from fissures A±E have cores ranging from An619
to An673. In fissure A sample 1849, a glomerophyric
plagioclase has distinct normal core-to-rim zonation
from An673 to An619, amidst clinopyroxene overgrowth
in an aggregate that also includes intercrystalline glass.
The compositional range of analyzed plagioclase
phenocryst and microphenocryst core compositions in
fissure F lava is similar to that in fissures A±E (Fig. 8b),
with the exception of the high-An refractory compositions of resorbed phenocrysts discussed above. Plagioclase intergrown with large clinopyroxene in fissure F
samples 1862 and 1867 (Fig. 6d and e) have An636 and
An648 cores, respectively (Table 5), and do not show
appreciable evidence of reaction. Core composition
among analyzed plagioclase microphenocrysts in fissure F ranges from An648 to An657 for free-floating
crystals in sample 1863 (Table 5, Fig. 6h) and from
An607 to An669 in glomerophyric aggregates in samples 1861 and 1862 (Table 5).
No large plagioclase phenocrysts were found in early
episode 55 lava. However, the presence of plagioclase
microlites that are included in Type C olivine crystals
indicates a pre-eruptive history involving short-term
mechanical mixing of hotter (olivine-only) and cooler
(plagioclase-bearing) magmas. Although present in
NUMBER 9
SEPTEMBER 2003
early episode 55 lava, this phenomenon is not observed
in steady-state eruption samples. A case for inclusion of
episode 54 related plagioclase microphenocrysts in
early episode 55 lava is apparent in sample 1894
(Fig. 7). Plagioclase in the lithic aggregate in this
sample ranges in composition from An591 to An673
from the inner to outer portion of the aphyric fragment, with rim compositions overlapping those of
microphyric plagioclase included by olivine, and
those of free-floating plagioclase microphenocrysts
and microlites in other early 55 glasses (Fig. 8b).
Pyroxene
Phenocrysts and microphenocrysts of augite occur as
isolated crystals and in aggregates with plagioclase,
and cores have a wide compositional range with reaction features that include normal, reverse and complex
zoning (Fig. 8c), along with textural evidence for
resorption and partial melting. Details of clinopyroxene petrology, along with those of a particularly significant orthopyroxene phenocryst, place further
constraints on the nature and origin of magmas that
were mixed to form hybrid lava of episode 54. Also, the
presence of reacted pyroxene phenocrysts in early episode 55 lava provides additional evidence for the persistence of hybrid magma during the post-episode 54
interval of non-steady-state eruption at Pu'u'O'o.
Clinopyroxene microphenocryst cores in fissure A±E
samples range in Mg# from 799 to 763, overlapping
the 777±735 Mg# range of matrix microlites in these
samples (Fig. 8c and Table 5). Two large clinopyroxene phenocrysts observed in fissure E samples 1859 and
1860 have distinctly different character. The isolated
phenocryst in 1860 (Fig. 6f ) has a core of Mg#682 and
is extensively resorbed and reversely zoned, with a
distinct rim of Mg#787 (Table 4). This phenocryst
also has irregular-shaped glass inclusions with cuspate
texture along host±inclusion boundaries. These inclusions are interpreted as the products of intracrystalline
melting under conditions analogous to that of the
melted plagioclase phenocryst observed in this same
thin section. In contrast, the 1859 phenocryst is subhedral and intergrown with plagioclase, has a core
composition of Mg#799, and is normally zoned to an
Mg#780 rim (Table 5).
Analyzed clinopyroxene microphenocrysts from fissure F samples have cores of Mg#802±753. A free-floating microphenocryst in sample 1863 is normally zoned
from Mg#802 to Mg#763 (Table 5). Two fissure F
clinopyroxene phenocrysts in samples 1862 and 1867
are intergrown with plagioclase (Fig. 6d and e, respectively). A slight reversed zonation of the 1867
phenocryst is indicated by core to rim variation of
Mg#790±794 (Table 5) and the euhedral outline of this
1546
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
crystal is only slightly rounded, indicating a nearequilibrium relation with the host melt. The 1862 phenocryst is sector zoned, rounded and surrounded by a
thin homogeneous rim of clinopyroxene. Microprobe
traverses from core to rim of hour-glass sectors that
appear dark and light in electron backscatter image
reveal opposite zonation patterns. The core-to-rim
dark and light sector zoning ranges from Mg#791 to
Mg#762 and from Mg#754 to Mg#775, respectively
(Table 5). Both sectors are rimmed by clinopyroxene
of Mg#77, an apparent product of reaction between the
phenocryst and the host melt, indicating that development of sector zoning occurred before inclusion and
reaction with fissure F hybrid magma. As discussed in
the following section, an average Mg#773 for light and
dark sector cores in this crystal provides a reconstructed
composition that is compatible with the associated
An63 plagioclase phenocryst. This clinopyroxene also
contains orthopyroxene (Mg#787, Table 4) at the
intersection of the light sector core and the included
plagioclase. The relatively Mg-rich orthopyroxene is
lamellar-like and may have formed because of exsolution associated with sector zoning in the clinopyroxene
host. It is conceivable that sector zoning occurred during heating and partial resorption and that Mg-rich
orthopyroxene was produced in the buffered melt reaction between a hotter olivine-melt and clinopyroxene
‡ plagioclase (Yang et al., 1999). Similar orthopyroxene lamella development in complexly zoned augite
was described in hybrid lava of the 1960 east rift zone
eruption by Wright & Helz (1996, fig. 4) and is suggestive of a complex thermal history before inclusion in
host lavas. In contrast, Mg-rich orthopyroxene in
Kilauea east rift lava reported by Clague et al. (1995)
is rounded and often encloses rounded olivine. These are
interpreted based upon experimental phase relations to
have crystallized from primitive magmas at elevated
pressures between 2 and 045 GPa (Eggins, 1992).
A single free-floating orthopyroxene phenocryst was
identified in fissure F lava (sample 1863, Fig. 6g). This
slightly rounded phenocryst is normally zoned from
Mg#735 to Mg#780 (Table 4) and is partially mantled
by host-compatible clinopyroxene microphenocrysts
with Mg#774 (Table 5). Orthopyroxene phenocrysts
of similar composition, although rare at Kilauea, were
reported by Anderson & Wright (1972) as compatible
phases within examples of the most chemically fractionated Kilauea lava, including that produced during
early stages of the 1955 east rift zone eruption [also
described by Wright & Helz (1996)]. Orthopyroxene
of similar composition and appearance to that in sample 1863 occurs in hybrid 1960 eruption products.
These were described as metastable remnants of a
more fractionated magma by Fodor & Moore (1994)
and Wright & Helz (1996). As shown in experiments
using Kilauean basalt by Thompson & Tilley (1969),
this relatively iron-rich orthopyroxene composition is
restricted to low-pressure (5045 GPa) crystallization
from differentiated melts and appears on the lowpressure liquidus at temperatures below 1140 C from
a liquid at 5 wt % MgO.
No large phenocrysts of pyroxene are observed in
early episode 55 lava. Consistent with complexities of
olivine and plagioclase variations in the KE55-1894
lithic fragment, the small clinopyroxene phenocryst
(03 mm) in this cluster (Fig. 7) displays moderate
sector zoning with slightly reversed zonation from
inner to outer core (Mg#819 to Mg#832) and is normally zoned to an outer rim of Mg#770. The part of the
grain in contact with the host melt is uniformly
mantled by an Mg#775 clinopyroxene overgrowth
that is intermediate in composition between the
phenocryst and the Mg#780±800 clinopyroxene microlites analyzed in the matrix of this sample (Fig. 8c).
As suggested by Lofgren (1980), sector zoning in
clinopyroxene may develop because of rapid growth
during undercooling. The Mg# within the sectorzoned core of this crystal is anomalously high compared with the range of episode 54 clinopyroxene
phenocrysts, and may be explained by such metastable
growth.
Glass
Glass heterogeneities in episode 54 samples attest to
thermal and chemical disparities associated with
magma mixing before eruption (Table 6). Among the
samples analyzed, most have abundant areas of `clean'
matrix glass (i.e. devoid of quench crystals). Exceptions are the 1858 (fissure D), 1852 (fissure B) and
1860 (fissure E) samples, which have relatively evolved
glass compositions owing to extensive development of
microlitic to spherulitic groundmass during inefficient
quenching and non-equilibrium crystal growth in these
particular globs of fountain spatter. Such poorly
quenched glasses are not useful for application of glass
thermometry to assessment of pre-eruptive magmatic
temperatures, but they provide analog fractionated
compositions for lower-temperature liquids used to
calibrate multiphase mineral thermometers.
Average MgO contents of `clean' matrix glasses in
fissure A, B and E samples range from 602 to 616 wt %,
corresponding to pre-eruption temperatures of
1135±1138 C, as inferred using the glass thermometer
of Helz & Thornber (1987). The average glass composition in fissure F samples ranges from 49 to 55 wt %
MgO and defines a lower magmatic temperature range
of 1112±1124 C (Table 6). Eruption temperatures
for these temporally and spatially discrete fissures
are distinctly lower than the 1146±1168 C range of
1547
JOURNAL OF PETROLOGY
VOLUME 44
NUMBER 9
SEPTEMBER 2003
Table 6: Averages, standard deviations and ranges of 112 episode 54 matrix glass compositions in seven fissure
A±E samples and five fissure F samples
Fissure A
Fissure B
Fissure D
Fissure E
KE54-no.: 1849
1850
1852*
1854
1858*
1859
1860*
No. anal.: 7
10
1
10
10
14
3
Av.
SiO2
Al2O3
FeOt
MgO
SD
Av.
SD
Av.
SD
Av.
SD
0.13
0.11
51.23
13.42
50.85
13.28
0.20
0.07
51.65
13.01
0.16
0.06
51.08
13.56
0.32
0.15
51.08
12.31
0.07
0.49
11.84
6.06
0.08
0.06
11.65
6.10
0.11
0.03
13.84
5.05
11.65
6.16
0.15
0.12
12.21
5.68
0.09
0.06
11.53
6.02
0.34
0.14
15.12
3.84
0.38
0.38
0.06
10.02
2.71
10.16
2.69
0.08
9.48
9.91
0.11
9.85
0.06
0.61
0.03
0.02
2.42
0.71
2.65
0.63
0.08
0.02
2.61
0.68
0.02
0.01
3.08
0.35
0.04
0.03
3.18
0.37
3.10
0.32
0.04
0.03
3.41
0.36
0.05
0.02
0.02
0.16
0.17
0.02
0.24
0.00
98.75
0.51
0.02
0.40
0.18
99.88
0.42
0.64
TiO2
3.04
0.33
0.04
0.02
MnO
0.17
0.02
0.18
Total
98.31
0.50
0.00
99.18
0.51
Mg#
SD
50.99
13.36
K2O
P2O5
Av.
0.23
0.14
0.07
0.02
Na2O
SD
50.60
12.98
10.07
2.53
CaO
Av.
MgO T ( C)1136
1
1137
1
1116
1138
99.68
0.48
0.00
2
1128
8.63
0.27
0.58
2.39
0.87
0.10
0.07
2.99
0.32
0.05
0.03
4.24
0.46
0.40
0.06
0.17
0.02
0.65
0.19
0.00
0.24
99.14
0.51
0.00
1
0.19
0.15
0.05
1135
0.01
3
99.12
0.33
1091
0.03
8
Fissure F
KE54-no.: 1860
1861
1862
1863
1864
1867
No. anal.: 1
10
11
10
13
13
Av.
SiO2
Al2O3
FeOt
MgO
SD
Av.
SD
Av.
SD
Av.
SD
Av.
SD
51.33
12.60
51.34
12.52
0.15
0.07
50.93
12.44
0.29
0.16
51.70
12.43
0.20
0.06
51.81
12.73
0.37
0.24
51.30
13.02
0.26
0.09
12.68
5.62
12.60
5.26
0.12
0.05
12.75
4.87
0.13
0.10
12.61
5.06
0.08
0.05
12.53
5.00
0.19
0.10
12.16
5.45
0.17
0.04
CaO
9.75
9.12
0.08
9.05
0.10
9.09
0.06
9.22
0.08
9.36
0.06
Na2O
2.66
0.68
2.85
0.79
0.07
0.01
2.88
0.82
0.12
0.02
2.78
0.82
0.04
0.02
2.70
0.80
0.13
0.02
2.80
0.77
0.06
0.02
3.66
0.42
3.89
0.41
0.03
0.04
3.89
0.45
0.08
0.03
4.04
0.44
0.04
0.03
3.96
0.43
0.08
0.04
3.51
0.41
0.05
0.04
0.02
0.22
0.19
0.02
0.54
0.18
0.02
0.22
0.18
0.02
0.32
0.17
0.02
0.43
K2O
TiO2
P2O5
MnO
0.18
0.18
Total
99.59
0.47
98.98
0.45
Mg#
MgO T ( C)1127
1120
0.00
1
98.32
0.43
1112
0.01
2
99.19
0.44
1116
0.00
1
99.50
0.44
1115
0.00
2
99.00
0.47
1124
0.00
1
*Poorly quenched glass in samples 1852, 1858 and 1860.
steady-state eruption products. An average 10 C difference in glass temperatures between episode 54 sample groups is 7 C less than the difference of magmatic
temperatures that might be inferred from their bulkrock wt % MgO averages (see Thornber, 2001, appen-
dix 1), thus implying a difference in mixing proportions
of hotter and cooler magmas erupted from fissures A±E
and fissure F.
The overall CaO vs MgO variation of matrix glasses
in episode 54 samples reflects liquid depletion in
1548
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
Fig. 9. Compositions of matrix glasses and glass inclusions compared
with bulk lava. (a) CaO vs MgO; (b) K2O/TiO2 vs K2O. Symbols are
as indicated in the figure for episode 54 matrix glasses and glass
inclusions and average steady-state tear glasses. The black fields
show the ranges of episode 53, 54 and 55 bulk lava. The range of
episode 53 and 55 tear glasses and olivine glass inclusions (from
Thornber, 2001) are shown with dark and light gray fields, respectively. Episode 53 and 55 olivine inclusions define an olivine-controlled trend that is collinear with tear data but extends to lower Ca
contents owing to post-entrapment olivine crystallization along inclusion walls. A similar trend is observed for the Type A olivine inclusion
in fissure sample 1849.
clinopyroxene and plagioclase from the near-cotectic
compositional range of steady-state Pele's tear glasses
(Fig. 9a). The ratio of K/Ti vs K in matrix glasses
overlaps that of bulk lava in fissure A±E, fissure F
and steady-state eruption samples (Fig. 9b). This
comparison affirms the conclusion that episode 54
bulk lava compositions are not derived from fractionation of recent rift conduit magma but rather represent
two chemically distinct hybrid melt groups.
The coexistence of relatively evolved, lower-temperature glomerophyric glasses (1107±1123 C, Table 7
and Fig. 9) with less fractionated matrix glasses,
representing the hybrid host-liquid in fissure A±E sam-
ples, provides direct evidence for late-stage mixing
between discrete magmas. The K/Ti concentrations
in these glomerophyric inclusions (Fig. 9b) reflect a
range of mixed source characteristics. As further elaborated in our discussion of phenocryst±liquid relations,
microphenocryst core compositions in these aggregates
are compatible with their included glasses.
Intracrystalline glass inclusions in episode 54 olivine
phenocrysts provide conclusive evidence for crystal
growth in magmas of chemically disparate affinities.
The included glass in Type B olivine (Fo844) of fissure
F sample 1864 (Fig. 6a, Table 7) has the distinct
signature of olivine-incompatible elements in olivine
inclusions, matrix glasses and bulk lava of steadystate eruption intervals (Fig. 9). This and other highFo olivine in hybrid episode 54 lava are thus
considered to have originated from relatively primitive
magma associated with the long-term eruption. In
contrast, the inclusions in the core and rim of lowerFo olivine microphenocrysts of fissure A (samples 1849
and 1850) indicate crystallization from magma with
higher relative concentrations of incompatible
elements.
Inclusions in the fissure E sample 1860 resorbed
plagioclase (Fig. 6c) have a K/Ti vs K signature that
is comparable with episode 54 glomerophyric aggregates, matrix glasses and bulk lavas. However, compositions up to 70 wt % MgO reveal anomalously high
temperatures, suggesting that this relict crystal was
partially melted while in contact with a hightemperature magma. The 70 wt % MgO corresponds
to the olivine±plagioclase cotectic composition that
would be stable during plagioclase resorption by an
olivine-saturated liquid. The CaO depletion of these
glasses relative to normally fractionated liquids (Fig. 9)
is affected by CaO retention in a refractory high-An
solid residua product (An80) of plagioclase melting.
The survival of this discrete high-temperature glass
(1154 C) in host melts of much lower temperature
attests to a short time interval between magma mixing
and eruption of hybrid magmas.
MINERAL THERMOMETRY
DEDUCED FROM PHENOCRYST±
LIQUID RELATIONS
Equilibrium crystal±liquid distribution coefficients of
ferrousiron andmagnesium forolivine±basalt (KDol/liq ˆ
0300, Roeder, 1974), clinopyroxene±basalt (KDcpx/liq ˆ
0230, Grove & Bryan, 1983) and orthopyroxene±
basalt (KDopx/liq ˆ 0284, Beatie, 1993) are used in
conjunction with Kilauea MgO glass thermometry
(Helz & Thornber, 1987) to deduce crystallization
temperatures of phenocrysts in episode 54 lava. The
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Table 7: Averaged microprobe analyses of isolated glomerophyric or intracystalline glass inclusions in
episode 54 lava
E54 fissure:
A
B
E
F
A
Ke54-no.:
1849
1854
1860
1861
Host mineral:
Host composition:
No. analyses:
3
2
1
2
E
F
1849
1850
1860
1860
1864
Type A
Type A
Plg
Cpx
Type B
Olv
Olv
Fo787
Fo798
An805
Mg#682
Fo844
1
1
5
1
4
Olv
50.10
12.68
50.36
12.84
51.33
12.60
51.32
12.51
50.35
13.09
51.32
14.24
50.47
12.19
50.08
15.12
52.44
14.61
12.74
5.42
13.72
4.63
12.68
5.62
12.63
5.20
11.75
5.11
10.87
5.49
13.21
6.99
13.74
3.66
9.44
5.65
CaO
9.76
2.66
0.68
8.99
2.93
0.78
10.55
2.62
10.01
2.84
10.17
2.57
8.32
2.61
0.67
8.95
2.88
0.83
9.75
Na2O
11.41
2.49
3.42
0.39
3.93
0.40
3.66
0.42
3.87
0.42
0.61
3.19
0.67
2.77
0.67
3.11
0.19
98.10
0.20
98.81
0.18
99.59
0.19
98.88
0.38
0.13
0.28
0.14
0.33
0.20
98.03
0.190
98.74
0.241
99.92
0.216
SiO2
Al2O3
FeOt
MgO
K2O
TiO2
P2O5
MnO
Total
K/Ti
Mg#
0.196
0.457
0.212
0.400
T ( C) Incl
1123
1107
T ( C) Cpx
1119
1103
T ( C) Plg
1118
1107
1136
1138
0.186
0.467
1127
0.203
0.449
0.463
1119
1117
0.840
1154
3.74
0.39
0.19
99.10
0.217
0.345
1088
0.44
2.42
0.16
0.24
99.28
0.182
0.544
1128
1079
1194
T ( C) Olv
T ( C) Mtx
0.500
1124
3.05
0.81
1141
1146
1136
1137
1202
(1091)*
(1091)*
1115
*Poorly quenched glass in sample 1860.
variation of liquid Mg number [Mg#liq ˆ 100 mol %
MgOliq/(MgOliq ‡ FeOliq)] with temperatures calculated for glasses and bulk liquids of the 1994±1999
eruptive interval is shown in Fig. 10. In accordance
with known low-pressure phase relations for Kilauean
basalt (Thompson & Tilley, 1969; Helz & Thornber,
1987), these variations of Mg#liq with cooling present a
fractionation path for Kilauea magma primarily
affected by olivine and clinopyroxene crystallization
throughout the major crystallization interval from
1200 to 1100 C. At temperatures above
1150 C, calculated temperatures of bulk liquids
erupted during episodes 53 and 55 (198 samples,
Thornber, 2001) correspond to a linear olivinecontrolled Mg#liq variation, which is defined as
T… C†liq41150 ˆ 702 Mg#liq ‡ 767 …r2 ˆ 0:972†: …1†
Below 1150 C, the Mg#liq descent with temperature is defined by glass compositions controlled by
clinopyroxene and minor olivine fractionation as
T… C†liq51150 ˆ 302 Mg#liq ‡ 983 …r2 ˆ 0976†: …2†
The lower-temperature glass data include 168 individual analyses of matrix glasses in episode 54 and
early episode 55 samples and are extrapolated through
the range of hybrid bulk-rock compositions for each of
these samples and the average of all episode 53 steadystate tear glasses (900 analyses of 90 samples). The tear
glass composition represents a steady-state liquid
maintained at 1153 C (1s ˆ 3) near the multiphase
cotectic at the low end of the olivine control trend and
in equilibrium with Fo806 olivine.
Mineral thermometers for Kilauea olivine,
clinopyroxene and orthopyroxene are based upon
equilib rium Mg#xl/liq KD values for each of these
phases and Mg#liq/T( C)liq relations for recent
Kilauea liquids [equations (1) and (2)]. These mineral
thermometers for use in determining low-pressure
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THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
constrained empirical thermometer for plagioclase in
Kilauea basalt (with low H2O content) as
plagioclase thermometer :
T… C†liq ˆ …%Anplg ‡146†=0187:
Fig. 10. MgO thermometry vs Mg# for bulk lava samples (darkfilled circles) for steady-state eruption of episodes 53 and 55
(Thornber, 2001) and episode 54 fissures A±E and F. Average episode 53 and 55 steady-state lava compositions are indicated as
unfilled squares. Early episode 55 samples are shown as light gray
filled circles. Average Pele's tear glass compositions are shown for
episode 53 (unfilled star) and episode 55 (dark-filled star). Episode 54
matrix glasses, including low-Mg poorly quenched samples, are
shown as unfilled circles. The variation of Mg#liq with cooling
presents a low-pressure fractionation trend for recent Kilauea
magma from 1200 to 1100 C and defines the linear equations
[equations (1) and (2)], used to correlate mineral compositions with
MgO thermometry.
crystallization temperatures in Kilauea magma are
defined as follows:
high-Fo olivine thermometer …4Fo80 † :
T… C†liq41150 ˆ 117 Foolv ‡ 215
…3†
high-Fo olivine thermometer …5Fo80 † :
T… C†liq51150 ˆ 422 Foolv ‡ 809
…4†
clinopyroxene thermometer:
T… C†liq ˆ 404 Mgcpx ‡ 804
…5†
orthopyroxene thermometer:
T… C†liq ˆ 413 Mgopx ‡ 813:
…6†
The correlation of percent anorthite component in
plagioclase (% Anplg) with MgO liquid thermometry
shown in Fig. 11 is extrapolated from mineral core
analyses for 25 pairs of coexisting plagioclase±
clinopyroxene crystals in this sample suite (Table 5)
and using temperature values determined with the
clinopyroxene thermometer [equation (5)]. The resulting linear correlation between plagioclase composition
and temperature (r2 ˆ 083) defines a loosely
…7†
Temperatures calculated using these mineral thermometers [equations (3)±(7)] are inferred to represent
that of a liquid that is close to equilibrium with phenocrysts and microphenocrysts. The calculated crystal±liquid equilibrium temperatures for phenocrysts,
using Kilauea mineral thermometers, are presented
with corresponding mineral analyses in Tables 4 and
5. Independent validation of temperatures estimated
using these Mg±Fe equilibration schemes is provided
by comparison of mineral- and glass-thermometry
values for adjacent crystal±glass phases in two glomerophyric aggregates (samples 1849 and 1854) and for
glass-inclusion/host values of the 1860 clinopyroxene
(Fig. 6 h and f ). In each of these cases, temperatures of
the included glass are closely approximated by temperatures calculated from adjacent minerals (Table 7)
and are distinctly lower than that of surrounding
matrix glass.
PHENOCRYST DEFINED MAGMATIC
COMPONENTS IN EPISODE 54
HYBRID LAVA
The mineral chemistry of episode 54 phenocryst assemblages and the nature of phenocryst±matrix reactions
provide clear indications of the hybrid origin of these
rocks. With the exception of orthopyroxene in fissure F,
the diversity of phenocryst chemistry is comparable for
both fissure F and fissure A±E sample groups. Using
Kilauea mineral thermometers to determine the range
of source magma temperatures for the episode 54
phenocryst assemblages, we can ascribe a range of
variably fractionated magma compositions as likely
end-members for mixing. The range of temperatures
calculated for episode 54 phenocrysts, microphenocrysts and glass inclusions is similar in both fissure
A±E and fissure F datasets (Fig. 12) and indicates
crystallization from a similar range of variably cooled
and fractionated magma. The assemblage of relatively
high-, intermediate- and low-temperature phenocrysts
and glass inclusions in hybrid episode 54 lava suggests
a magma mixing process involving at least three shallow
magmatic components.
The pyroxene±plagioclase-saturated
hybrid component
Phenocrysts that define the most fractionated endmember involved in episode 54 mixing are those with
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Fig. 11. Plagioclase composition (An%) plotted vs Mg# temperature calculated using equation (5) for adjacent clinopyroxene in E54 samples
(Table 5). Symbols indicated in the figure denote morphology of plagioclase±clinopyroxene pairs. The slope defines the linear plagioclase
thermometer presented as equation (7).
calculated core temperatures clustering near 1120 C
(Fig. 12). Among this group of crystals, orthopyroxene
(Mg#735), clinopyroxene (Mg#782±682) and plagioclase (An640±605) phenocrysts have reversely zoned
or unzoned rims (Fig. 8). A distinct population of
isolated and glomerophyric plagioclase and clinopyroxene, along with associated interstitial glass inclusions, also range in temperature from 1130 C down to
1105 C. This temperature range corresponds to an
initial magma with 575 wt % MgO and crystallizing fractions of cooler liquid, down to 45 wt %
MgO. The presence of these low-temperature
phenocrysts and microphenocrysts in lava from fissures
A±E and fissure F indicates mixture of similar
rift-stored magma components in both episode 54
hybrid magmas.
A temperature of 1116 C for the sector-zoned clinopyroxene phenocryst that is intergrown with plagioclase in fissure F sample 1862 (Fig. 6d) is obtained
using an average Mg#773 of light and dark core sectors.
This value corresponds well to the 1118 C temperature
calculated for the coexisting An633 plagioclase, indicating that reconstituting an average core composition
may be a viable procedure for obtaining initial crystallization temperature for sector-zoned clinopyroxene. A
higher temperature of 1138 C calculated for the small
orthopyoxene lath in this aggregate (Mg#82) corresponds to the 1140 C four-phase saturation temperature at which olivine reacts with melt to form
orthopyroxene (Kinzler & Grove, 1992). This is consistent with orthopyroxene formation as a by-product
of sector zoning of the clinopyroxene host during exposure to a higher-temperature, olivine-saturated melt.
The preponderance of hybrid melt compositions corresponding to this temperature, both during episode 54
and from the same locations during episode 1, is
suggestive of chemical buffering resulting from the
mixing of hotter, olivine-saturated melt and a lowtemperature crystal±liquid assemblage as hypothesized
by Yang et al. (1999).
The near-cotectic hybrid component
The group of isolated and aggregated microphenocrysts of plagioclase (An65±67) and clinopyroxene
(Mg#807±832) with crystal-core temperatures ranging
from 1130 C to 1140 C, along with lower-Mg olivine
crystals (Fo784±80) of 1140±1150 C melt affinity,
all display varying degrees of normal zonation
( resorption) (Figs 8 and 13). This assemblage is
derived from shallow magma, ranging in composition
from 68 to 58 wt % MgO near the onset of multiphase precipitation of olivine ‡ plagioclase ‡ clinopyroxene. The episode 54 olivine crystals in this group
overlap the range of equilibrium olivine in episode 53
tears, erupted at temperatures corresponding to the
low-MgO end of olivine-only fractionation. At an average of 69 (1s ˆ 02), episode 53 tear glasses define
steady-state magmatic conditions that persist at nearcotectic conditions during actively replenished shallow
storage. The presence of similar olivine and hightemperature clinopyroxene and plagioclase microphenocrysts attests to the possibility that this steadystate cotectic component is an ingredient of the hybrid
mixtures.
The olivine-saturated hybrid component
Olivine microphenocrysts with Fo84 core compositions display normal zonation and resorption textures
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KILAUEA EAST RIFT ZONE MAGMATISM
Fig. 12. Compilation of mineral and glass temperatures calculated for samples of episode 54 fissures A±E and fissure F. (a) Estimated
equilibration temperatures of each mineral phase, sorted for fissures A±E and fissure F, shown for phenocrysts (circles) and microphenocrysts
(diamonds), with cores and rims indicated as filled and unfilled symbols, respectively. MgO glass temperatures are shown for matrix glasses
(filled circles), glomerophyric glass inclusions (filled diamonds) and intracrystalline glass inclusions (symbols as in Fig. 9). The range of bulk
liquid thermometry values for shallow magmatic components is shown at the top of the figure (see text for discussion). (b) Frequency
distribution of temperatures estimated for mineral phases and glomerophyric glass inclusions (glm glass) in episode 54 samples.
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Fig. 13. CaO/TiO2 vs MgO variation of mixing end-members, episode 54 hybrid lava compositions. Binary mixing curves are calculated
using equation of Langmuir et al. (1978).
demonstrating that these crystals are incompatible in
cooler, episode 54 hybrid melts. These crystals are
analogous to Type B olivine that crystallizes at
1200 C in equilibrium with summit-derived steadystate lava, before rift transport (Thornber, 2001). As
substantiated by glass-inclusion chemistry (discussed
above), such episode 54 olivine crystals are interpreted
as cognate to this eruption and are testimony to the
mixture of a summit-derived magma component in the
hybrid mixes. In comparison with an average Type B
olivine phenocryst size of 06±07 cm observed in
steady-state eruption products (Thornber, 2001), the
largest of these episode 54 remnant crystals is 03 mm.
Assuming approximate dissolution rates of olivine in
undercooled basalt to be of the order of 5±10 mm/h
(Thornber & Huebner, 1985), the observed difference
of less than 50% original size among surviving olivine
crystals is consistent with mixing and resorption during
the 38 h interval between the onset of rift zone extension and the end of the Napau eruption.
The presence of high-temperature, refractory plagioclase remnants (up to An805) further attests to preeruptive mixing of an 1200 C summit-magma
component. At 70 wt % MgO and 1154 C, glass
associated with melted plagioclase phenocrysts preserves a record of near-cotectic liquid production
during plagioclase dissolution by higher-temperature,
olivine-only, melts.
GEOCHEMICAL MODELS FOR THE
ORIGINS OF EPISODE 54 MIXED
MAGMAS
Phenocrysts and glass inclusions in episode 54 lava
imply the pre-eruptive mixture of at least three shallow
magmatic components with high-, intermediate- and
low-temperature affinities. Both geophysical and
petrologic evidence presented herein indicates that the
hotter and intermediate olivine-saturated components
of mixing were derived from magma associated with
prolonged steady-state eruption before this event. The
most evolved mixing components in both fissure F and
fissure A±E lava are indicated by low Mg# ortho- or
clinopyroxene phenocrysts to be liquids of 50 wt %
MgO. These are compositionally analogous to the most
fractionated lava known to have erupted along the
lower Kilauea east rift zone during the early phases of
the 1955 eruption (Wright & Fiske, 1971) and which
contains unreacted orthopyroxene of similar composition (Anderson & Wright, 1972).
Likely candidates for the low-temperature, riftstored components in fissures A±E and F hybrids are
the fractionated equivalents of magma last erupted
from overlapping Napau Crater fissures in 1983, 1968
and 1963. New major and trace element data were
obtained for four such lava samples from episode 1 of
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THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
the current eruption in January 1983 (Table 2). These
were collected from fissures that overlap or are en
echelon with episode 54 fissures (samples KE1-49,
-50, -51, -52; Fig. 2). Sample KE1-49 is from the initial
extrusion of episode 1 lava from a fissure in the NW
corner of Napau Crater. At 68 wt % MgO, the major
element composition of this lava is similar to the tear
glasses and the 7 wt % MgO-normalized compositions
of episode 53. Samples KE1-50 to -52 are from the east
Napau Crater area of episode 54 fissures D and E.
These episode 1 samples have major element compositions that are indistinguishable from the episode 54
fissure A±E products, averaging 64 wt % MgO, and
were also interpreted as having mixed-magma affinities
by Garcia et al. (1989). Before 1983, the most recent
magma erupted at a west Napau Crater location was in
1963. This magma is represented by sample 63-3 of
Moore & Koyanagi (1969), and had an MgO content
of 74 wt %. In east Napau Crater, the last pre-1983
magma erupted is that represented by sample 68-4 of
Jackson et al. (1975) with an MgO concentration of 77
wt %. Both reports on the earlier eruptions provide
major element compositional data but trace element
analyses for these samples are not available.
An early 1955 eruption sample with 50 wt % MgO
(TLW67-34, Wright & Fiske, 1971) provides an analog end-member composition as targeted by major element fractionation calculations, performed using the
multiple linear regression routine (PETMIX) of
Wright & Doherty (1970). Major element composition
of the analog evolved component was well matched
(i.e. low squared-residual sums for 10 unweighted
major-oxide components) by fractionating appropriate
phenocryst compositions (Tables 4 and 5) from each
these prospective parent compositions. Results indicate
that the west Napua magma could be derived from
either a 1983 or 1963 parent (KE1-49 or 63-3) with
36±40% fractionation of plagioclase and clinopyroxene
(with minor olivine). Major element compositions of
magma trapped beneath east Napau Crater are well
matched by 28% of fractionation of a similar phenocryst assemblage from a KE1-50 to -52 parent and
37% fractionation of the 1968 parent (68-4).
Major element bulk-mixing models using analog
closed-system and known open-system reservoir components to produce episode 54 hybrid magmas yielded
good matches with low residuals (Table 8b). The massbalanced proportions reproducing the fissure A±E
average composition are: 32% rift-stored component
(TLW67-34 analog), 67% cotectic component (7%
MgO-normalized episode 53 steady-state average composition, E53ss7%NRM, Table 1) and 504% summit±
conduit component (episode 55 steady-state average
composition, E55ss, Table 1). The average fissure F
composition is well matched by a mixture of these
respective components in proportions of 65%, 35%
and 51%. Binary mixing curves utilizing Ca/Ti variation with Mg (Langmuir et al., 1978) demonstrate
the feasibility of mixing paths between the analog riftstored component and magma in the active conduit
(Fig. 13). Both hybrid episode 54 magmas are slightly
Mg rich relative to a binary mixing line between the
highly evolved, closed-system magma and a nearcotectic, open-system melt, as a result of the minor
contribution of a hotter summit±conduit component
to the mix.
As demonstrated in a plot of La/Yb vs K2O (Fig. 14),
the incompatible element signatures of west and east
Napau 1983 magmatic fractionates preclude their parental association with the low-temperature components of episode 54 fissure F or fissure A±E hybrids.
These fractionation products were calculated assuming
Rayleigh fractionation (e.g. equations of Allegre &
Minster, 1978), using partition coefficients of
Pietruszka & Garcia (1999) and assuming fractionated
mineral proportions as defined by PETMIX major
element calculations. Based upon a general comparison
of incompatible-element ratios of unfractionated lava
compositions in a spatially and temporally diverse sample suite, Garcia et al. (2000) came to a similar conclusion regarding the lack of genetic association
between earlier products of this eruption and those of
episode 54.
La/Yb values of 1961 and 1968 summit eruptions
(from Pietruszka & Garcia, 1999) were used in lieu of
such data on 1963 and 1968 Napau lava for assessing
fractionation mixing and relations. This is considered a
reasonable assumption based upon strong evidence for
the steady decline in La/Yb ratios throughout this time
span for summit and rift zone eruption products
(Pietruszka & Garcia, 1999; Garcia et al., 2000;
Thornber, 2003). As shown in Fig. 14, the episode 54
hybrid magmas lie along binary mixing lines between
near open-system near-cotectic magma and the fractionated residue of spatially correlated magmas
erupted in 1963 and 1968. The relative end-member
proportions of these hybrid mixtures are consistent
with those estimated from major element mixing
calculations.
Hybrid lava produced during early stages of episode
55 reflects a continuous progression from lower to
higher Mg compositions until steady-state eruptive
conditions were established. This trend is quantified
by major element mixing calculations for samples
spaced throughout this April±July 1997 interval,
which show progressive binary mixing of near-cotectic
rift zone magma with a gradually dominant influx of
hotter, summit-derived conduit magma (Fig. 13).
Trace element modeling of the sequence of early episode 55 hybrid melts was also accomplished using mass
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Fig. 14. La/Yb vs K2O showing fractionation trends of potential rift-stored components and binary mixing lines extended from steady-state
near-cotectic magma through average episode 54 hybrid compositions from east and west Napau Crater (E54F and E54A±E). The wt % K2O
values of 1963 and 1968 Napau lava are from analyses of samples 63-3 and 68-4 reported by Moore & Koyanagi (1969) and Jackson et al.
(1975), respectively. The La/Yb values for 1963 east Napau lava and 1968 west Napau lava are extrapolated from values of 1961 and 1968
Kilauea summit eruptions (Pietruszka & Garcia, 1999).
balances between proportions of end-members defined
by major element differences. Near-perfect matches for
the major element binary-mixing model were
obtained. This time-integrated trend of gradually
increasing proportions of summit±conduit magma to
near-cotectic, open-system reservoir magma reflects
the flushing of cooler magma residing uprift of
Pu'u'O'o as the fluid-pressure balance within the
shallow summit±rift zone plumbing system became
re-established.
INTEGRATION OF GEOPHYSICAL
CONSTRAINTS AND PETROLOGIC
MODELS
Our petrologic interpretation of magmatic components involved in the production of episode 54 hybrid
lava is further substantiated by geophysical evidence.
Owen et al. (2000) hypothesized that the sudden shallow rift opening beneath Napau Crater resulted from
extensional stress related to long-term movement of
Kilauea's south flank. We suggest that this zone was
prone to extensional release owing to inherent weakness associated with the presence of small and isolated
shallow pockets of crystallizing 1963 and 1968 magma
above the active rift zone conduit. Petrologic data
implying that such rift-stored magmatic components
were mixed with magma persisting within and around
the conduit are supported by geodetic data indicating
that disruption of the pressurized summit±rift zone
conduit diverted magma from both uprift and downrift
areas into an extensional gap beneath Napau Crater.
Shallow extension associated with the event encompassed a volume of 23 106 m3 (Owen et al., 2000).
This volume is matched by the cumulative volume of
magma displaced from within the shallow magmatic
plumbing system. Displacement of 15 106 and 12 106 m3 of magma are inferred from modeled sources
beneath the summit caldera and Makaopuhi Crater,
respectively (Owen et al., 2000). Our measurements of
pre- and post-collapse dimensions of the Pu'u'O'o cone
and crater indicate that 127 106 m3 of magma was
diverted from beneath the vent area. [By comparison,
the size of the Pu'u O'o reservoir from 1983 to 1986 was
estimated as (10±12) 106 m3 by Hoffman et al. (1990)
and 18 106 m3 by Garcia et al. (1992).] Including our
estimate of 300 000 m3 of lava erupted during episode
54, the sum of displaced magma volumes from the
summit reservoir, Makaopuhi and Pu'u'O'o still leaves
73 106 m3 of rift expansion volume unaccounted
for. We infer that the missing volume is the volume of
the east rift zone conduit, which can be estimated by
multiplying the time required to repressurize the conduit (the 24 day eruptive pause), by an average
1556
THORNBER et al.
KILAUEA EAST RIFT ZONE MAGMATISM
episode 53 flux rate of 300 000 m3 /day (Thornber
et al., 1997).
Of the total episode 54 extensional volume, 55% was
accommodated by transfer of magma in an uprift
direction from beneath Pu'u'O'o and 36% was filled
by pre-existing conduit magma. Magma displaced in a
downrift direction from beneath Makaopuhi Crater
made up only 6% of the extensional volume. The
Pu'u'O'o and Makaopuhi sources were probably persisting as open-system reservoirs within the active conduit at the time of the event. The consistent 7 wt %
MgO composition of Pele's tears at Pu'u'O'o during
episode 53 reflects the near-cotectic condition that is
maintained by continuous replenishment with olivinesaturated magma along the conduit.
Only 1 vol. % of magma displaced into the zone of
extension erupted as episode 54 hybrid lava. The
erupted volume of 300 000 m3 represents a minimum
for the total volume of magma involved in the preeruptive mixtures. Geochemical mixing models imply
that the 270 000 m3 from fissures A±E comprised a
mixture of 67% of an open-system reservoir (nearcotectic composition) and 32% closed-system
evolved component. The 530 000 m3 of fissure F lava
contained a mixture of 65% closed-system reservoir
component and 35% near-cotectic, open-system
reservoir component. These proportions translate to
minimum volume estimates for the isolated closedsystem magma pockets of 86 000 m3 beneath east
Napau and 19 500 m3 beneath west Napau areas. Of
the total volume of displaced magma, only a very small
amount of near-cotectic magma is needed to accommodate this mixing scenario. This magmatic component is likely to be present as a density-stratified
magma associated with open-system reservoirs or as a
marginal facies located both uprift (Makaopuhi) and
downrift (Pu'u'O'o) of Napau Crater.
Olivine phenocryst reaction characteristics are compatible with mixing that occurred within the 38 h
duration of this event. The relative timing and volumes
of magma displacement from downrift and uprift locations corresponds to the eruptive sequence and volumes
of the two distinct episode 54 lava compositions. The
initial west-to-east propagation of fissures A±E probably occurred in response to greater initial extension in
the magma-laden zone beneath east Napau Crater.
This suddenly created gap was rapidly filled by a
large volume of magma displaced from the downrift
conduit and the Pu'u'O'o open-system reservoir. The
last, low-volume gasp of episode 54 in the west wall of
Napau Crater (fissure F) may have resulted from a
delayed encounter between the relatively small volume
of magma displaced from a Makaopuhi reservoir and
that of an isolated pocket beneath the west side of the
crater.
The steady rate of summit inflation after episode 54 is
evidence that the influx of primitive magma into the
summit magma chamber continued without interruption, despite a 24 day eruptive pause. Re-establishment
of the fluid-pressure balance in the shallow summit±rift
zone conduit was marked by recovery of summit deformation along with the reappearance of lava in the
Pu'u'O'o crater. Petrology and geochemistry of lava
erupted over the next 5 months indicates that cooler
hybrid magma in the disrupted conduit, uprift of
Pu'u'O'o, was gradually flushed out of the vent as
steady-state eruptive conditions were re-established.
SUMMARY
Episode 54 has provided the first conclusive evidence
for pre-eruptive mixing of hotter and cooler rift zone
magmas since the onset of this eruption in early 1983.
Petrologic and geophysical evidence supports our conclusion that distinct magmatic components along the
summit±rift zone conduit were passively intruded
beneath Napau Crater and mixed immediately before
the fissure eruption uprift of the long-lived Pu'u'O'o
vent. These components include variably fractionated
magmas that we interpret as persisting in both closedsystem and open-system reservoirs associated with the
long-term eruptive plumbing system.
During periods of steady-state rift zone eruption, an
efficient pressure balance is maintained along the
magma conduit between the summit and the vent,
and erupted magmas are restricted to a small range of
olivine-saturated bulk compositions. This stable condition is the end product of continuous input and turbulent mixing of primitive magma into the shallow
summit reservoir (Thornber, 2003). As the summit is
continually replenished, so it continually replenishes
the magma moving through the shallow rift zone to
the vent. The interaction of hotter, summit-derived
magma with open-system reservoirs along the rift
zone may account for a historic preponderance of
rift zone lava compositions maintained at the low end
of a Kilauean olivine-control trend. Pele's tears at
Pu'u'O'o reflect persistence of this near-cotectic condition beneath the vent and support the likelihood that
similar magma exists in open-system reservoirs along
the active rift zone conduit, particularly beneath
Makaopuhi Crater, which has long been known as a
point source of deformation.
During episode 54, steady-state eruption conditions
were disrupted by extensional release of lithostatic
pressure along the active conduit between the summit
and the vent. Geodetic, seismic and observational data
indicate that the extensional gap beneath Napau
Crater was filled with magma from both uprift
(Makaopuhi) and downrift (Pu'u'O'o) segments of
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JOURNAL OF PETROLOGY
VOLUME 44
the active conduit. A 23 h eruption ensued from a
sequence of fissures overlapping those of 1963, 1968
and 1983 rift zone eruptions. Phenocryst±liquid relations in episode 54 lava samples indicate that hotter
and cooler magmas were mixed during the preeruptive interval of extension and magma displacement. Major and trace element mixing models for
episode 54 hybrid lava imply the coexistence and mixture of evolved, closed-system fractionates and opensystem reservoirs that are actively replenished by
olivine-saturated magma. The chemical lineage of the
rift-stored components indicates they are of discrete
origin, resulting from closed-system fractionation of
magma erupted from these same fissures in 1963 and
1968. Petrologic data imply that such rift-stored magmatic components were mixed with magma persisting
within and around the conduit.
Within the context of eruption characteristics from
1994 to 1999, episode 54 has presented an opportunity
to evaluate shallow magmatic processes that are likely
to typify those associated with prolonged rift zone
eruptions of Hawaiian shield-building volcanoes.
ACKNOWLEDGEMENTS
This research on Kilauea eruption products is accomplished as part of a comprehensive and long-term volcano monitoring effort by the Geological Survey's
Hawaiian Volcano Observatory and with the essential
support of observatory staff and numerous student
volunteers. We greatly appreciate the contribution of
David Okita (Volcano Helitours) to our field efforts.
Dave Seims (USGS, Denver) completed high-quality
major element XRF analyses with incredible efficiency. This paper has benefited from formal technical
reviews by Drs R. T. Helz, L. G. Mastin and
W. E. Scott. The senior author is especially grateful
to Drs Aaron Pietruszka, Michael Rhodes and Marc
Norman, all experts on the petrology and geochemistry
of Hawaiian volcanism, for providing very insightful
and constructive reviews that significantly contributed
to this paper.
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