JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 89, NO. B13, PAGES 11,261-11,272,DECEMBER 10, 1984
Geology and Geochronologyof the Line Islands
S. O. SCHLANGER,
1 M. O. GARCIA,B. H. KEATING,J. J. NAUGHTON,
W. W. SAGER,
2 J. g. HAGGERTY,
3 ANDJ. g. PHILPOTTS
4
Hawaii Institute of Geophysics,
Universityof Hawaii, Honolulu
R. A. DUNCAN
Schoolof Oceano•Iraphy,
Ore,ionState University,Corvallis
Geologicaland geophysicalstudiesalong the entire length of the Line Islands were undertakenin
order to test the hot spot model for the origin of this major linear island chain. Volcanic rocks were
recoveredin 21 dredgehauls and fossiliferoussedimentaryrocks were recoveredin 19 dredgehauls.
Volcanic rocks from the Line Islands are alkalic basalts and hawaiites. In addition, a tholeiitic basalt and
a phonolite have been recoveredfrom the central part of the Line chain. Microprobe analysesof
groundmassaugitein the alkalic basaltsindicatethat they contain high TiO2 (1.0-4.0 wt %) and A1203
(3.4-9.1 wt %) and are of alkaline to peralkaline affinities.Major element compositionsof the Line
Islandsvolcanicrocks are very comparableto Hawaiian volcanicrocks.Trace elementand rare earth
elementanalysesalso indicatethat the rocksare typical of oceanicisland alkalic lavas' the Line Islands
lavas are very much unlike typical mid-oceanridge or fracturezone basalts.Dating of theserocks by
'•øAr-39Ar,
K-Ar, andpaleontological
methods,
combined
with DeepSeaDrillingProjectdatafromsites
165, 315, and 316 and previouslydated dredgedrocks, provide agesof volcaniceventsat 20 localities
along the chain from 18øN to 9øS,a distanceof almost4000 km. All of thesedatesdefinemid-Cretaceous
to late Eoceneedificeor ridge-buildingvolcanicevents.Eocenevolcaniceventstook place from 15øN to
9øS, and Late Cretaceousevents took place from 18øN to 9øS. In the southern Line Islands both
Cretaceousand Eoceneeventstook place on the sameedificeor ridge, indicatingrecurrentvolcanismat
a singlelocality. The irregular distribution of atolls in the chain, the fact that Late Cretaceousreefs
flourishedalong a distanceof approximately2500 km in the central and southernLine Islands,and the
observationthat spatiallycloselyrelated seamountsexhibit different subsidencehistoriesare interpreted
asindicatingthat largesegments
of the chainhavenot followeda t •/2 relatedsubsidence
path.Magnetic
surveysof 11 seamountsshow that four of the seamounts,from the central Line chain, give virtual
geomagneticpoles which fall well to the north of virtual geomagneticpoles of Cretaceousseamounts.
Thesefour polesagreewith other paleomagneticdata of middle-lateEocene-earlyOligoceneage from
the Pacific.One of thesefourseamounts
yieldeda '•øAr-39Ar
total fusionageof 39 Ma. Because
thepoles
of all four seamountsfall into a tight group we infer that they are probably of middle-lateEoceneage to
early Oligoceneage.The other three seamountsas well as one seamontfrom the Line Islandsanalyzed
previouslyall give virtual geomagneticpoleswhich agreewith Late Cretaceouspaleomagneticdata from
the Pacific.Of thesefour seamounts,
threegiveLate Cretaceous
'•øAr-39Aragesrangingfrom 71 to 85
Ma; another, in the southernLine Islands, is interpreted,on paleontologicalevidence,to be of Late
Cretaceousage.The origin of the Line Islandshas beenascribedby previousworkersto the effectsof a
singlehot spot and to the action of four hot spots.The singlehot spot model cannot accountfor all of
the volcanicedificesin the Line Islands, although it doesexplain a general age progressionof 9.6 _+0.4
cm/yr from north to south along the chain derivedfrom a number of dated edifices.The four hot spot
model accountsfor more of the dated volcanicedificesbut still doesnot explain all of the availabledata.
The petrologic data argue against a mid-ocean ridge or transform fault origin proposedby earlier
workers.The complexvolcanicprovincerepresentedby the Line Islandsremainsa challengeto existing
models for the origin of midplate volcanism in the Pacific. An atoll drilling program which could
determine edifice building histories,paleolatitudesof seamountformation, and subsidencerates and
patternsin the Line Islandsis needed.
INTRODUCTION
AND BACKGROUND
The Line Islands geologicalprovince,capped by the atolls
of Johnston, Palmyra, Washington, Fanning, Christmas, and
Caroline islands,is made up of dozens of simple and composite seamountsand linear ridgesthat extend from Horizon
Guyot and JohnstonIsland in the north to the northeastend
of the Tuamotu Islands in the south (Figure 1). The Line
Islands are a major bathymetric feature of the central Pacific
comparable in size to the Hawaiian-Emperor chain to the
north
and
the
Marshall-Gilbert-Ellice
chain
to
the
west.
Morgan [1972], arguingfrom the fact that the Line-Tuamotu
geometrictrends appear to parallel the Emperor-Hawaiian
• Now at Departmentof GeologicalSciences,
NorthwesternUnitrends,postulatedthat the Line and Tuamotu chainswere the
versity,Evanston,Illinois.
2 Now at Departmentof Oceanography,
TexasA & M University, temporal and genetic equivalentsof the Emperor and Hawaiian chains, all four of these major featureshaving develCollege Station.
3 Now at Departmentof Geosciences,
Universityof Tulsa,Tulsa, oped through the actions of two hot spots fixed relative to
Oklahoma.
each other for the past 70 Ma. Jarrard and Clague [1977]
'• Now at U.S. GeologicalSurvey,National Center,Reston,Virpointed out that geometric and paleomagnetic evidence
ginia.
argued against the proposition that the Line and Emperor
Copyright1984by theAmericanGeophysical
Union.
chainswere entirely coeval.
At the time the above argumentswere put forward, reliable
Paper number4B0781.
datesfor volcanicactivity over any significantportions of the
0148-0227/84/004B-0781$05.00
11,261
11,262
SCHLANGER
ET AL.' GEOLOGYAND GEOCHRONOLOGY
OFTHELINE ISLANDS
of midplate volcanismalong suchcrosstrends were influenced
by older Line Islands structures. He implied that several
chainsof volcanoson crosstrends were formed by individual
hot spots that crossedthe main Line chain. Both DSDP drilling in the central Line Islandsand the dating of rocksdredged
/
from
ß
O
/.,•
•0o
Eocene volcanism
'
Kingman
Palmyra
!
I
/
H•a*shington
Is.
o
o
•
Jarvis
Is.eRD_4
ZO
o
IS,
RD-35
o
seamounts
in the cross trend
showed
that
both
Late
Cretaceousand Eocene volcanism had occurred there [Lanphere and Dalryrnple, 1976; Saito and Ozirna, 1977]. Further,
paleontological studies of rocks dredged from seamountsin
the southern Line Islands [Haggetty et al., 1982] showedthat
both Late Cretaceousand Eocenevolcanismhad taken place
in the vicinity of Caroline Island (Figure 1, RD-44 and RD45). The wide geographicdistribution of both Cretaceousand
RD-39
PCOD-6
--
Christmas
over a distance
of several thousands
ted the Line Islands in Eocene time. Vivid
Is.
o
C'/•ø•e•ton
.. •o
e
of ki-
lometersalong the Line chain is regardedby us as establishing
the fact that the Line Islands were not formed by the action of
a singlehot spot. That the southern Line Islands as well as the
centralLine Islandswereformedby a complexoverprintingof
volcanic eventswas suggestedby Crough and darrard [1981].
They showed that a depth and geoid anomaly extends from
the Marquesas Islands into the southern Line Islands and
ascribedthis anomaly to the trace of a hot spot which transievidence that the
Line chain has a complexhistory of volcanismas comparedto
that of the Emperor chain is containedin W. Haxby's geotectonic imagery map of the Pacific Basin [see Francheteau,
1983], a sketch map of which is shown here as Figure 2. In
addition
to the marked
Line cross trend that cuts across the
central Line Islands at 10øN a number of other linear ridges
intersect the northern and central Line Islands; the southern-
most of theseextendstoward the Marquesas Islands and lies
along the depth and geoid anomaly of Crough and darrard
[1981]. The en echelon appearanceof much of the central
Line Islands could be due to the presence of these short
NW-SE trending features which intersect the main Line Islands trend. Bathymetrically then, the Line chain bears little
resemblanceto the relativelysimpleEmperor chain.
Hendersonand Gordon [1982] and Duncan [1983] have addressedthe complexity of the Line Islands and argue, based
on plate motion reconstructionsover the past 150 Ma, that
several hot spots are needed to model the evolution of the
Line
Islands.
If all linear
volcanic
features
or chains of vol-
Fig. 1. Chart of the Line Islands showingthe track of R/V Kana
Keoki (dashedline) through the area. Dredge stationsare indicated by
RD numbers; piston core stations by PCOD numbers; seamount
magnetizationsurveysby L numbers.
LineIslands •-•
Cross-Trend
...,•
/•"'
G•ppe•
tø•
Line Islands were not available. Driling along the Line Islands
on Deep Sea Drilling Project (DSDP) legs 17 and 33 (see
Winterer et al. [1973] and Schlangeret al. [1976] for details)
'
Main Line x
showedthat volcanicepisodesin the northern Line Islands at
"•, o•Island
Chain
•
site 171 on Horizon Guyot and at sites 165, 315, and 316 in
the central Line Islands were more temporally complex than
could be accountedfor by using the Emperor chain as a
model for the development of the Line Islands. Winterer
[1976] in an extensivereview of the data relevant to the forFig. 2. Sketchmap of major featuresin the Line Islandsprovince
mation of the Line Islands emphasizedthe importanceof the (unlabeledlinear trendsare after the geotectonicimagerymap of W.
Line crosstrend (Figure 2) and argued that repeatedepisodes Haxby from Francheteau[1983]).
SCHLANGER
ET AL.' GEOLOGYAND GEOCHRONOLOGY
OF THE LINE ISLANDS
11,263
canic edificesoriginate solely by hot spot activity of the
Hawaiian-Emperorstyle,then a number of hot spotsmust
crosstrend is the relic of a central Pacific rift systemthat
have contributed to the formation of the Line Islands. Other
Strontium isotopicratios have been determinedon some of
these rocks using both untreated and HCl-leached material.
Unfortunately, most of these samplesare at least somewhat
altered,and the valuesreportedhave very large uncertainties
(e.g.,0.7030 _+0.0009).Thereforeit is difficult to interpret the
valueswith any confidence.Nevertheless,
the reportedinitial
mechanismsfor the linear localizationof volcanicactivity
have been put forward.Farrat and Dixon [1981] postulated
the presenceof a long transformfracturezone that extended
from the Emperor Trough through the Gardner Seamounts
and the Line Islands.Orwig and Kroenke[1980] also proposed a fracture zone origin for the Line Islands. Natland
[1976] consideredthat the petrologyof rocksfrom the central
Line Islandsindicatedtheir similarity to rift associatedvolcanismof the Africantype. Winterer [1976] also invokedfis-
underwent limited crustal extension.
87Sr-SaSr
ratiosfor basaltsvaryfrom0.7028to 0.7039(all but
one between0.7035 and 0.7039),virtually overlappingthe reported range for Hawaiian volcanic rocks (0.7029-0.7041
[Lanphereet al., 1980]) and generallyhigherthan typical midsures and fractures in the Line Islands to account for some of
oceanridgebasalts(MORB) ratios(0.7026-0.7035[Schillinget
the volcanicactivity there.
at., 1983]).
It is the purposeof this paper to presentthe geological,
Previouspetrologicstudieshave all beenon samplesrecovgeochemical,and palcomagneticdata that will outline the eredfrom the northernhalf of the Line chain;no sampleshad
constraintson any modelsproposedfor the evolutionof the been recovered from the chain south of DSDP site 315 near
Line Islands.
Fanning Island at about 4øN. During the R/V Kana Keoki
1979 cruises,sampleswere dredged from along the entire
lengthof the chain (Figure 1).
CRUISE OPERATIONS
The rocks recoveredfrom dredge stationsand those preThe geologicand geophysicalstudiesof the Line Islands viouslyreportedfrom the Line Islands[Basset al., 1973;Jackdiscussedhere were undertakenduring three cruises(of R/V sonet al., 1976; Natland, 1976] are almostentirelymoderately
Kana Keoki) to the area in the fall of 1979 (Figure 1). The to severelyaltered alkalic basalts and hawaiites. In addition,
objectivesof these cruiseswere to dredge edifice volcanic tholeiitic basalts and a phonolite have been recoveredfrom
rocks and cappinglimestone,take piston coresin submarine the central part of the chain [Natland, 1976]. The alkalic bavalleysincisedinto the sedimentaryapron of the central Line saltscontain phenocrystsof plagioclase,olivine (replacedby
Islands province, conduct seamountmagnetizationstudies, iddingsite),and, rarely, augitc. The hawaiitesare generally
and to collect magnetic,gravity, and bathymetric data rele- aphyric, although some contain rare phenocrystsof plagiovant to the problem of the evolution of the Line Islands.Our claseand/or brown hornblende.The matrix of both rock types
bathymetricmapping showedthat someexistingbathymetry consistpredominantlyof plagioclase,titaniferousaugitc,titanwas incorrectand misleading.Among our discoverieswere an iferousmagnetite,and, locally, clays replacingglassand oliunmappedseamountat 1lø40'N, 160ø40'W,a ridgewhichrises vine. Mineralogically,these rocks are typical of Hawaiian
to 2700 m in depth connectinga seamountat 6ø20'N, 158øW lavas.
with a ridge at 6ø20'N, 159ø30'W;and a ridge nearly 300 km
Microprobe analysesof groundmassaugitc in the Line Islong consistingof eight peaks ranging from 3000 to 2150 m lands lavas indicate that they contain high TiO2 (1.0-4.0 wt
depth connectingCaroline Island at 10øS, 150ø20'W with a
%) and A1203(2.0-9.1 wt %) [Jacksonet al., 1976]. A plot of
seamountat 7ø35'S,151ø35'W.In addition, Carol Guyot (9øN,
SiO: versusAIeO3 showsthe Line Islandslavas to be of alka158øW)and Vostok Island (10øS,152øYW) were found to be
line to peralkaline affinitiesbased upon the classificationof
incorrectlycontoured.
LeBas [1962] (Figure 3), although two samples,RD-33-4 and
A total of 21 dredgesrecoveredvolcanicrocks.Sedimentary RD-43-1 from the central Line Islands are of the nonalkaline
rock sampleswere recoveredin 19 dredges.In addition, seditype.
ments(and in one casebasaltpebbles)were recoveredfrom six
The freshestsamplesfrom eachdredgehaul were chemically
piston cores.Underway gravity and magneticswere recorded
analyzed(Table 1). All of the samplesare moderatelyaltered.
over the entirelengthof the Line chainand over the marginof
Some sampleshave high Fe:O3/FeO ratios and P:O5 and
the Tuamotu Ridge. Eleven seamountmagnetizationsurveys
H20 contents.Nevertheless,the leastalteredsamplesare simiwere conducted.
lar chemically to Hawaiian alkalic lavas. They plot in the
Hawaiian alkalic lava field and span the range from alkalic
PETROLOGY
olivine basalt to mugeariteusing the classificationof Coombs
Previouspetrologicwork on volcanicrocks from the Line and Wilkinson[1969].
Islands is almost entirely reported on in the DSDP initial
Rare earth elements(REE) were determinedby isotopedilureports of legs 17 and 33 [Winterer et al., 1973; Schlangeret tion massspectrometryon selectedsamples.One of the samal., 1976]. At DSDP site 315, six flow units of transitional ples (RD-60-6) has the REE pattern of a typical Hawaiian
basalt (intermediate in composition between Hawaiian tho- tholeiite(Figure 4). The other samplesshown have REE conleiitic and alkalic lavas) were recovered[Jacksonet al., 1976]. centrations similar to those of Hawaiian alkalic lavas.
Hawaiites,somecontainingbrown amphibole,were recovered
Jacksonet al. [1976], in addressingthe suggestionthat the
at DSDP site 165 [Bass et al., 1973]. A wide variety of rocks Line Islands are an abandoned ridge crest, argue that the
dredgedfrom the northern and central portions of the Line chemistryof the basaltsdrilled at DSDP sites165 and 315 are
Islandsincludetholeiites,alkalic basalts,hawaiites,phonolites, inconsistentwith a ridgecrestorigin. In their reviewof analyand potassicnephelinites.Natland [1976] consideredthe po- sesin hand following leg 33 [Jacksonet al., 1976] they came
tassicnephelinitesdredged at four locations in the Line Is- to the conclusionthat the Line Islandsare made up of basaltic
lands area as similar in compositionand origin to potassic rocksthat are similar to basaltsof the Hawaiian chain. Analymafic lavas from African rift zones.He argued that the pres- ses reported here support the argument that the main Line
ence of such rocks in the Line cross trend indicated that the
Islandschain was built of effusionsof typical alkalic and tho-
11,264
SCHLANGERET AL.: GEOLOGYAND GEOCHRONOLOGY
OF THE LINE ISLANDS
x
52
51
NONAL
50-
ALKALINE
46-
:"•iiii!•',:,•-;ii•ii!!i-'.iii!i
"i::'7
.:;•:.':•i•'•iiiiii!i:i!iii!i!i•:..
61-3
•
•
":'"'•••-:ii•i•!ii•!iiii
:•
-;:•il
:..
'"
:::?•i!i!iii::::.
59-13
....
,.::::..:
......
:.:.-?•!,;•,;:.:?-,
.o
]
A
.0_ 47
•
,-,,.
lO
E,
PERALKALINE
45'
44
'
0
]
I
[
I
]
2
'
I
]
3
I
4
'
I
5
•
K
I
6
'
I
'
7
I
8
'
La Ce
I
Nd
Sm Eu Gd
Dy
Er
Yb Lu
Fig. 4. Chondrite-normalized rare earth element patterns for
somerepresentativelavas from the Line Islands. Fields for Hawaiian
tholeiitesand alkalics and mid-ocean ridge basalt (MORB) from Basaltic VolcanismStudy Project [1981].
'
9
AI203 Wt.%
Fig. 3. SiO2 and AI203 wt % in groundmassclinopyroxene [Winterer et al., 1973; Schlangeret al., 1976]. At DSDP site
grains from lavas from the Line chain. Fields for nonalkaline,alka165 a complex and long history of Cretaceousvolcanismwas
line, and peralkaline rocks are from LeBas [1962]. A, RD-41-1; B,
revealed [Lanphere and Dalrymple, 1976; Winterer et al.,
1973]. Three basalt units interbedded with fossiliferoussediments were cored at the site. Between the two deepestbasalt
leiitic Hawaiian type lavas and that there is no compelling flows fossils of the Eiffelithus eximus zone were recovered.
evidencethat a ridge crest origin is warranted for the Line Taking the base of this zone to be at the SantonianCampanian boundary dated at 83 Ma by Harland et al.
Islands.
[1982], we can deduce that volcanism was active at least 83
GEOCHRONOLOGY
Ma. The age of the deepestbasalt, based on sedimentation
The basic data set constrainingdiscussionsof the origin of rate argumentscould be as old as 93-101 Ma [Lanphere and
linear island chains consistsof determinations of the ages of Dalrymple, 1976]. Higher in the sectionat site 165 are thick
volcanic breccia and sandstone beds which indicate that latevolcanicedifice formation along the chain. The data used in
stage
volcanismpersistedinto the Tetralithus trifiduszone of
this paper consistof datesderivedfrom interpretationof volcanicand sedimentarysequences
drilled on DSDP legs17 and late Campanian age dated at 74 Ma by Harland et al. [1982].
33, edifice ages determined by dating of fossil assemblages A rock dredgedfrom the large seamountjust to the east of site
RD-41-2; C, RD-44-2; D, RD-54-2; E, RD-59-1, H, RD-59-9; I, RD59-10; J, RD-59-15; K, RD-63-7; X, RD-52-7.
dredgedfrom seamounts,and radiometricagesdeterminedby
4øAr-39Arand K-Ar methodson dredgedrockscollectedby
the Hawaii Institute of Geophysics(RD and PC prefix) and
the ScrippsInstitution of Oceanography(D suffix)(Figures 5
and 6 and Tables 2 and 3). Becauseage determinationslie at
the heart of any discussionon the origin of a chain suchas the
Line Islands, the data used are discussedbelow in the geological context of the variouslocationsshown on Figures 1 and 5.
Three DSDP siteswere drilled along the central Line chain
in an attempt to reconstructthe history of edifice building
TABLE 1. Major ElementAnalysesof Volcanic Rocks From the
Line Islands Chain
165 was dated at 72 Ma usingthe 4øAr-39Armethod[Saito
and Ozima, 1977]. Thus major volcanism in the immediate
vicinity of site 165 occurredover a time span of at least l l
Ma, from 72 to 83 Ma and possibly longer. At site 315
[Schlangeret al., 1976] the east flank of the Fanning Island
edifice was drilled. The basalt cored at the bottom of the hole
180
øW
160
•id_-Pacific
fo
x
:L/-•
M
rl/••••
t
40Ar-39Ar
Ages
ß This
8(143D)
60-6
59-13
41-2
3.62
0.14
MgO
5.48
CaO
Na20
K20
P205
11.85
1.97
1.21
0.93
H 20 +
3.29
H20CO 2
2.48
1.05
Total
99.92
2.60
2.56
0.09
0.09
2.20
4.57
8.66 10.30
3.22
2.95
2.46
1.03
1.98
0.58
1.95
2.43
1.26
1.92
0.02
0.08
100.02 99.62
5.56
1.96
0.18
0.18
4.57
6.85
8.11 12.55
2.86
2.58
1.94
0.91
1.88
0.37
3.60
0.62
1.93
0.74
0.17
0.16
99.93 99.78
øN
,
(RDS9) 083 (133D)
43-1
44-3
45-1
••
52-2
x 79•128D)
_& •
SiO2 41.70 45.20 46.45 42.90 45.20 42.75 41.75 38.65 44.55
3.88
2.02
2.78
2.88
2.60
3.22
2.34
2.93
TiO 2
3.48
AI203 13.53 17.02 16.20 17.64 13.74 17.97 15.80 15.72 15.87
9.48
8.44
5.81 11.12 13.27 13.68 11.36
9.70
Fe20 3 9.19
FeO
MnO
20
2
56 0
61-1
paper
0$aito&Ozima(1977)
"••_•4 •)•6(RD63)
Fossil
Ages
• •81 83(RD61)
f(>78)
Sample
63-7
140
0.97
0.92
0.48
3.04
0.13
0.12
0.21
0.15
0.97
1.92
1.13
4.05
8.58 10.19 14.76 11.53
3.34
3.02
2.83
2.60
1.75
1.29
1.71
0.92
2.12
2.81
5.87
1.48
3.39
2.54
2.51
1.50
1.90
2.16
1.37
1.27
0.29
0.37
0.83
0.24
99.85 99.79 99.77 99.83
(pc2•
o • (RD4')
DS•P
31••9(RD43)
.
LINE ISLANDS
f(>78)
o
ø(RO44)
172 Marque
f(44-50)
0
1000
I
Analyst' K. Ramlal, Universityof Manitoba.
•39•B•33)
km
o /•._•_
1
(RD45)
-10
0 DSDP 318 f(~52)
I
Fig. 5. Stationlocationsand agedeterminations
in the Line chain.
$CHLANGER
ET AL.' GEOLOGYAND GEOCHRONOLOGY
OF THE LINE ISLANDS
11,265
Mid-Pacific
Mtns
40Ar-39Ar
ß This
85
Ages
paper
0 8aito&Ozima(
1976,1977)
45
motus
al
4500
K-Ar Ages
85
,TH
ß
45
o
o
ß
o
H•'...
o
'....
ß
ß
bl
4500
a•o
Distanc'e
27•o
from
ß
,•oo
b
9•)0
Line-Tuamotu
Bend
km
Fig. 6. Radiometricand paleontologic
agesin the Line chain.(a) '•øAr-39Aragesshownas solidcirclesweredetermined in this study; open circlesare datesfrom Saito and Ozima [1976, 1977]. The solid line showsa rate of migration of
volcanismof 9.6 + 0.4 cm/yr which would accountfor many of the agesdetermined.(b) K-Ar agesand biostratigraphic
age determinations(DSDP sites165, 315, and 316 and seamounts(H) from Haggetty et al. [1982]).
yielded a feldspar fraction K-Ar age of 91.2 + 2.7 Ma [Lanphere and Dalrymple, 1976]. Their age convertsto 93.3 Ma
upon usingnew constants[Harland et al., 1982], the age used
in this paper. Nannofossilsof the Marthasteritesfurcatuszone
were recovered 85 m above the basalt. These sediments are of
Coniacian age, the M. furcatus zone being dated at 88 Ma
[Hadand et al., 1982]. The correlationof the fossilage and the
K-Ar age at site 315 arguesfor a cessationof major edifice
building activity at ,,-93 Ma. Further, Premoli-Silvaand Brusa
[1981] record the presenceof a mid-Cretaceous Cuneolina
assemblage
in turbiditesat this site,implying the existenceof a
seamount in the photic zone in Cenomanian-Albian time,
>90
,,- 95 Ma.
3.
At
DSDP
site 316
the
cessation
of volcanic
edifice
building is estimatedat 81-83 Ma; initiation of volcanismis
undated.
In our study of rocks dredgedfrom the Line Islands,both
K-Ar and '•øAr-39Ardating techniqueswere employedto
Ma.
At site 316, basalt basement was not reached. The oldest
sedimentspenetratedyielded foraminiferaand nannofossilsof
early Campanian age (77-80 Ma) associatedwith basaltic
breccias and volcanic
[Schlangeret al., 1976]. In summary the DSDP resultsfrom
the main Line Islandssystemshowthe following'
1. Volcanism at site 165 and the nearby seamount from
which dredgehaul 130-D was taken occurredfrom 83 Ma (or
possiblyealier) to 72 Ma.
2. At site 315, major edifice constructionceasedby ,--93
Ma; initiation of volcanism is undated but could be prior to
sandstones. On the basis of the corre-
lation of stratigraphicsectionsbetweensites316, 315, and 165,
basalt basementat 316 probably lies ,,-75 m below the deepest sedimentsrecovered;the data of cessationof major edificebuilding volcanism at 316 can be estimatedat ,,-81-83 Ma
examinethe distributionof ageswithin this volcaniclineament
(Figures 5 and 6 and Tables 2 and 3). Previous attempts at
measuringreliable crystallization ages by the conventional
K-Ar method [Davis et al., 1980] have been frustratedby the
effects of seawater alteration.
Both K addition
and Ar loss
during low-temperature clay and zeolite formation, in the
presenceof seawater,will causethe measuredage to be systematicallylower than the rock crystallizationage.Reconnais-
SCHLANGER ET AL.' GEOLOGY AND GEOCHRONOLOGY OF THE LINE ISLANDS
11,266
TABLE 2. The 4øAr-a9Ar
Total FusionAgeData on DredgedVolcanicRocksFrom the Line Islands
Chain
Percent
Radiogenic
Sample
143D-102
142D-11
RD63-7
RD59-12
RD61-1
RD61-5
128D-11
RD33-1
123D-15
PCOD-6-2
RD41-1
RD43-1
RD44-3
RD45-26D
RD52-1
RD52-2
Location
19ø30'N, 169ø0YW
18ø00'N, 169ø05'W
16ø27'N, 168ø1YW
12ø31'N, 167ø0YW
14ø59'N, 166ø27'W
14ø59'N, 166ø27'W
9ø15'N, 160ø45'W
8ø11'N, 161ø55'W
5ø50'N, 160ø45'W
2ø35'N, 158ø30'W
2ø06'N, 157ø21'W
0ø42'S, 155ø17'W
7ø35'S, 151ø3YW
9ø04'S, 150ø42'W
15ø01'S, 149ø02'W
15ø01'S, 149ø02'W
'•øAr-a6Ar '•øAr-a9Ar 37Ar-'•øAr*
3011.
57028.
1456.
2463.
965.9
835.3
642.1
379.8
2251.
2524.
705.8
702.4
461.8
633.7
544.1
472.7
32.03
38.16
35.36
71.24
86.32
79.74
59.24
128.84
28.74
58.05
23.57
33.15
65.24
53.57
75.62
81.12
0.0538
0.0092
0.1525
0.0106
0.0149
0.0221
0.0089
0.0371
0.1058
0.0243
0.1929
0.0956
0.0445
0.1238
0.0869
0.0914
Age + 1•
½øAr
x 106years
90.0
99.4
79.4
88.0
69.4
65.1
53.8
22.2
76.4
88.2
57.7
57.6
35.9
53.1
45.6
37.4
88.1
93.4
86.0
85.0
81.4
+ 0.4
+ 1.3
+ 0.9
+ 1.1
+ 1.1
82.6 +_0.7
78.7 + 1.3
39.3 + 1.5
76.4 + 0.5
69.8 + 1.0
35.5 + 0.9
59.0 + 0.8
71.9 + 1.4
70.5 + 1.1
47.4 + 0.9
41.8 + 0.9
*Ar 37 correctedfor decaysinceirradiation.
sanceK-Ar agesdeterminedin this study(Table 3) weresimilarly scatteredand significantlylower than indirectage estimatesbasedon paleontologicdata [Haggerry et al., 1982] or
seamountmagnetizationstudies[Sager,1983a].
erally fresh,particularly in the more trachytic-texturedrocks
(143D-102, 142D-11, RD-59-12, and PROD6-2). Olivine
phenocrystsare commonly altered to iddingsite.The matrix
phasessuchas feldsparand clinopyroxeneare generallyfresh,
but where devitrified glass occurred, it has been altered to
clays.Zeolitesand calcite are common in vesiclesand along
microfractures.A further indication of the degreeof alteration
of these samplesis the high-H20 content in most samples
(between0.6 and 3.6 wt %) and in rare cases,high-CO2 content (up to 1 wt %).
Argon isotopic compositionswere measuredusing an AEI
Recently,the applicationof the '•øAr-39Artotal fusion
method to dating moderately altered submarine volcanic
rocks has proven successfulin determiningconsistentages
[Dalrympleand Clague,1976; Duncan,1978, 1982; Dalrymple
et al., 1981]. Accordingto these studiesit is probable that
39Ar,derivedfrom K-bearingalterationmineralsor from K
residingon grain boundaries,escapesfrom the sampleduring
equippedwith 3BArspikeand air
neutronirradiationor extractionline bake-out.Radiogenic MS-10Smassspectrometer
For 4øAr-39Ar
ages,splitaliquots
'•øArwas lost from preciselythesesitesduringalteration,so calibrationpipettesystems.
of crushed sampleswere irridiated at the U.S. Geological
the age signalfrom the low-temperaturealterationphasesis
essentially
erasedprior to samplefusion.Thusthe 4øAr-39Ar SurveyTRIGA Reactor in Denver, Colorado, for 4 hours at 1
MW power. Operating conditions and isotope interference
correctionshave beendescribedby Dalrympleet al. [1981].
That conventionalK-Ar analysesunderestimatethe agesof
Line Islands volcanic rocks is particularly apparent in the
scatteredagesof samplesfrom the same seamount(RD-45-1,
RD-45-26D) or neighboringseamounts(Table 3 and Figure 6).
Where indirect age estimatesare available,K-Ar age determi-
age commonlyapproachesthe crystallizationage becausethe
predominantsourceof nonatmospheric
argon is the primary
crystallinephases.
Sampleswere selectedfrom the Line Islandscollectionsfor
K-Ar and '•øAr-39Argeochronology
on the basisof thin section examination.Petrographically,all samplesshow slight to
moderatealteration. Augite and feldsparphenocrystsare gen-
TABLE 3. K-Ar Age determinationsFrom DredgedVolcanicRocksFrom the Line IslandsChain
Percent
Sample
143D-102
RD63-7
RD61-1
133D-9
128D-11
RD33-1
123D-15
PCOD-6-2
RD41-1
RD43-1
RD44-3
RD45-1
RD45-26D
RD52-2
Location
Percent
K
Radiogenic'•øAr
x 10-s cma/g
19ø30'N, 169ø0YW
16ø27'N, 168ø1YW
14ø59'N, 166ø27'W
12ø04'N, 165ø50'W
9ø15'N, 160ø45'W
8ø11'N, 161ø55'W
5ø50'N, 160ø45'W
2ø35'N, 158ø30'W
2ø06'N, 157ø21'W
0ø42'S, 155ø17'W
7ø35'S, 151ø3YW
9ø04'S, 150ø42'W
9ø04'S, 150ø42'W
2.097
1.194
2.098
1.666
0.725
0.695
1.996
1.601
1.016
1.411
1.120
1.301
0.915
0.6128
0.2589
0.4840
0.4808
0.1370
0.0625
0.3478
0.3783
0.1005
0.2047
0.1780
0.2259
0.2133
15ø01'S,149ø02'W
0.742
0.0712
,,
Radiogenic
Ar
88.8
78.6
67.3
65.8
56.6
44.8
86.6
90.2
75.6
53.8
32.8
34.4
58.4
35.9
Age* + 1•
x 106 years
73.7 +
55.0 +
59.8 +
72.8 +
48.0 +
23.5 +
44.3 +
61.2 +
25.3 +
37.8 +
41.4 +
45.2 +
59.0 +
0.8
0.6
0.6
1.3
0.6
0.3
0.5
0.6
0.3
0.4
0.5
0.6
0.7
25.1 + 0.4
*Agescalculated
fromthefollowing
decayandabundance
constants'
2•= 0.581x 10-•ø yr-" 2• =
4.962 x 10-'ø yr-" '•øK/K = 1.167x 10-'• mol/mol.
SCHLANGER
ET AL.' GEOLOGYAND GEOCHRONOLOGY
OF THE LINE ISLANDS
11,267
nations are always younger,by 9-30 Ma, and are not reliable
indicatorsof samplecrystallizationage,despitegenerallyhigh
proportionsof radiogenicargon.
studied,but a usefulresultwas obtainedfrom only one, L3 in
Figure 1 [Harrison et al., 1975]. The magnetizationparameters and virtual geomagneticpoles (VGP's) derived from the
The '•øAr-39Ar
total fusionagesaremuchmoreconsistent, eight seamountmagneticmodelsthat yieldedapparentlyrelihowever(Table 2 and Figure 6). Where multiple samplesfrom ableresultsare givenalongwith '•øAr-S9Ar
agesdetermined
the sameseamountwereanalyzed(RD-61-1, RD-61-5, RD-52- for them in Table 4.
1, and RD-52-2), age agreementwas good. Samples from
The goodnessof fit ratio (GFR) [Richardset al., 1967],
neighboring seamounts(143D-102, 142D-11, and RD-63-7; measuring the match between the observed and calculated
RD-44-3 and RD45-26D) gave similar ages.Further, the con- anomalies,is high for all of the seamountsanalyzedin this
cordance of our radiometric dates with age determinations study,ranging from 3.1 to 5.2. The larger the GFR the better
based on paleontologicaland seamountmagnetizationdata the agreement between the observedand calculated anomaindicatethat the '•øAr-39Ar
agesare reliable.Haggettyet al. lies; usually a GFR of 1.8-2.0 is consideredto be the mini[1982] determineda minimum age of 70-75 Ma, basedon the mum acceptablevalue for a reliablemagneticinversion[Haroccurrence of Late Cretaceous shallow water fossils, for the
risonet al., 1975; Sager,1983a].Not only do the GFR's of the
seamountfrom which RD-45 was taken; as shown on Table 2,
Line seamountsindicate excellent results, but the paleoRD-45-26D yieldeda '•øAr-39Arage of 70.5+ 1.1 Ma. Sea- magnetic poles derived from these seamountsare consistent
mount L8 has a virtual geomagneticpole which lies closeto a among themselvesand with other Pacific seamount VGP's.
Maestrichtian pole of both Gordon [1982a] and Sager Moreover,the VGP's of the reliably dated seamountsfrom the
[1982a];RD-44-3fromthisseamount
yieldeda '•øAr-S9Ar
age chain that have been studiedpaleomagneticallyare in close
of 71.9 + 1.4 Ma, within the 65-73 Ma spanof the Maestrich- agreementwith other Pacific paleomagneticdata of the same
tian stageaccordingto Harland et al. [1982]. The majority of age,as is discussedbelow.
sampleagesfalls along a linear array, from older seamountsin
Four of the Line seamountsgaveVGP's closerto the geothe north (-,•93 Ma) to youngerseamountsin the south(-,•44 graphicpole than any VGP derivedfrom a CretaceousPacific
Ma at the Line-Tuamotu bend). The overall consistencyof seamount(Figure 7) implying that thesefour seamountsare
this data set encouragesconfidencein theseestimatesof vol- youngerthan Cretaceousage. These four VGP's are located
cano ages. It is difficult to imagine, for instance,a process closeto the VGP's of three Pacificseamountsthat probably
which would produce progressivelygreater alteration to the formed during the late Eocene or early Oligocene.Of the
south to yield the observedpattern. A rate of migration of three,one is inferredto be approximately41-42 Ma of ageby
volcanismof 9.6 + 0.4 cm/yr bestfits the linear array of sea- its positionin the Hawaiianseamount
chainand by its magmount ages.A number of ages,however, do not fall on the netic polarity [Sager, 1984]. The other tWO seamountsare
main linear trend, these are also considered reliable and are
located in the eastern Pacific on seafloor 45 and 37 Ma old as
discussed below.
indicated by magneticlineations[Sager, 1983b]. In addition
Earlierstudieshavereported'•øAr-39Aragedeterminations to this data, a DSDP sedimentpa!eolatitude(site 166) calcufrom a number of seamounts in the northern and central Line
Islands[Saitoand Ozirna,1976,1977].Whereboth '•øAr-39Ar
total fusion and incrementalheatingageswere reported,we
have plotted the total fusionagesconsideredto be reliableby
Saito and Ozima (shownas open circles)for comparisonwith
theagesdetermined
in the presentstudy(shownas solidcirdes) in Figure 6. Two seamounts,130D and 133D, yield Cretaceousageswhich fall along the main linear trend. Another is
Eocenein age. Saito and Ozirna [1977] reported an isochron
age of 127.5 + 5.0 Ma and a total fusion age of 114.8 + 1.3
Ma for 142D dredged from the northern end of the Line
Islands.We determinedan age of 93.4 + 1.3 Ma for this site.
The reasonfor this discrepancyis unknown. Other agesfrom
neighboring seamountssupport our younger age determinations, however.
SEAMOUNT PALEOMAGNETISM
Measurement and analysisof the magnetic field of a seamount can yield information on the paleoazimuthand latitudinal transport of a seamountsubsequentto its formation
and on the locationof its virtual geomagneticpole (VGP); the
location
of its VGP
allows inferences to be drawn
as to the
age of the seamount. In this paper the implications of the
paleomagnetic
resultsfor periodsof volcanismalong the Line
chain are stressed.The details of the surveysand data reduction methods are describedby Sager and Keating [this
issue]and Sager [1983a].
To these ends, 11 seamounts in and around the Line chain
latedfrom samplesspanningthe late Eoceneand early Oligocene records a paleopole locus in agreement.with the four
Line IslandsVGP's as doesa paleoequatortransitdetermined
from sediment facies examined at DSDP Site 163 [Sager,
1983b].
Of the four seamountsthat give high-latitude VGP's, only
one has been dredgedand dated. SeamountL4 (RD-33) has
an4øAr-39Ar
totalfusionageof 39.3-+_
1.5Ma. Seamount
L5
is directly adjacent(and possiblyconnected•to) to seamount
L4 [Sager and Keating, this issue]and is thus likely to be the
sameage,particularly consideringthe nearnessof their VGP's
(Figure 7). Neither L6 nor L7 have been dated, but the proximity of their VGP's to the other Eocene-Oligocenepaleomagneticpoles coupledwith the fact that a significantnumber
of Eocene ages have been determinedfor seamountsin the
Line Islands(Table 3) [Saito and Ozima, 1977; Haggerry et al.,
1982] suggeststhat these two seamountsare also likely to be
the sameage.
The other four Line Islands seamounts studied paleomagnetically produced VGP's that are located among the
VGP's of Pacific seamountsof Cretaceousage. Both L1 and
L8 haveVGP's locatednear the Maastrichtianpaleomagnetic
polescalculatedby Gordon[1982a] and Sager[1983a] (Figure
8). L1 is undated,but a rock from L8 yieldedan '•øAr-39Ar
total fusion age of 71.9 _+1.4 Ma (RD-44) which agreeswell
with the age inferredfor the volcanofrom fossils[Haggerry et
al., 1982] and from its reversedpolarity [Sager and Keating,
this issue].
Seamounts L2 and L3 are located close to one another in
were surveyedfor paleomagneticanalysis;of these,sevengave
apparently reliable results.Previous to our work, eight sea- theLine chain(Figure7) andhave4øAr-39Ar
total fusionages
mountsin and around the chain had been paleomagnetically that are virtually identical, 85.0 _+1.1 Ma (L2, RD-59) and
11,268
SCHLANGERlETAL.' GEOLOGYAND GEOCHRONOLOGY
OF THE LINE ISLANDS
TABLE 4.
Magnetization Parametersfor Line Islands Seamounts
Location
VGP
ID
Latitude
N
Watkins
L1
17.5
190.8
68.8
Nagata
L2
12.5
193.0
61.6
12.0
194.2
8.2
7.9
198.1
198.1
Name
Kapsitotwa L3
Stanley
Willoughby
L4
L5
Chapman L6
Longitude Latitude
E
N
3.4
Longitude Inclination
E
( + Down)
33.5
-4.3
Declination
( + East)
352.0
4.0
- 29.0
4.4
47.5
333.5
-36.6
28.0
75.6
78.2
356.5
14.6
- 10.5
- 7.8
5.3
0.7
355.6
199.9
75.7
37.8
- 19.7
Clarke
L7
- 3.3
206.0
80.0
20.4
- 25.3
Uyeda
L8
- 7.5
208.5
68.5
345.6*
40.1
1.0
195.7
Intensity,
A/m
GFR
Age,
m.y.
Reference
2
5.8
5.2
3.8
3.7
85.0 + 1.1
5.1
3.7
82.7+ 3.6
3
3.2
3.5
4.7
4.4
39.3 + 1.5
4
4
4.7/8.0
1
4.3
3.3
4.0
6.9
3.1
4
4
71.9 + 1.4
4
GFR, goodnessof fit ratio. References'1, Keating and Sager [1980]' 2, Sager et al. [1982]' 3, Harrison et al. [1975]' 4, Sager and Keating
[this issue].
*Reverselypolarized,southpole given.
82.7 + 3.6 Ma (L3, 133D) [Saito and Ozirna, 1977], yet their
VGP's are separatedby over 22ø. This phenomenonwas puzzling until it was noted that apparent polar wanderjust prior
to 80 Ma was very rapid (Figure 8) [Gordon, 1983; Sager,
1983a], so that a differenceof only a few million yearsin the
+
age of two samplescould result in a larger separationof their
paleopoles.Consequently,we hypothesizethat L2 is slightly
youngerthan L3, whichis allowedwithin the analyticaluncer-
taintyof their 'tøAr-S9Ar
total fusionages.
VOLCANIC EVENTS
The above describedDSDP results,radiometric ages,biostratigraphic ages, and paleomagneticresults determined for
seamountsand linear ridges in the Line Islands reveal the
complexityof volcaniceventsin this province.Figures/5and 6
summarize the relevent radiometric and fossil age determinationsfrom the site of Horizon Guyot south to the Tuamotu
NP
+
•o
20
3
Islands. Table 2 lists the data referred to in this section. For
the purposesof this discussionthe well-definedLine chain is
taken to extend from Horizon Guyot and the northern end of
the linear ridge from which dredge 142-D was taken to the
southern end of the line of seamounts from which RD-45
+
NP
was
•'
L5
L4
Fig. 7. Comparison of high-latitude seamount paleopoles and
Pacific Eocenepaleomagneticdata. The VGP's of seamountsL4-L7
are shown by open stars. L4 has a total fusion age of 39 + 1.5 Ma.
SeamountsEl, E2, and HR1 have VGP's shown by the solid stars.
HR1 has been assignedan age of 41-42 Ma by its positionin the
Hawaiian chain [Sager, 1984] and E1 and E2 have maximum agesof
45 and 37 Ma, respectively,determinedby the age of the seafloor
upon whichthey rest[Sager,1984]. The heavyline is a segmentof the
small circle that is the locus of the paleomagneticpoles measured
from sedimentsamplesfrom DSDP site 166. These samplesrange in
age from Oligoceneto Eocene [Jarrard, 1973]. The thin line is a
similar segmentof the polar circleestimatedfrom the identificationof
equatorialsediments
in the coresfrom DSDP site 163.It wasdetermined that this site crossedthe equator 43 + 6 Ma [Suarez and
Molnar, 1980]. The large dot is the mean position of the Eocene
seamountVGP's and the ellipseis the 95% confidenceregion of the
mean paleomagneticpole [Sager, 1984]. The small dots connectedby
the dashedlinesare positionsof the paleopolepredictedby the Pacific plate/hot spot rotation model of Jarrard and Clague [1977] (with
rotation rate correctedby Dalryrnpleet al. [1977]) labeled at 10-Ma
intervals. The diamonds are the VGP's of Cretaceous seamounts from
Harrisonet al. [ 1975].Map projectionis polarequalarea.
Fig. 8. Comparison of Line Islands seamount paleomagnetic
poles with Pacific apparent polar wander paths. The Line Islands
VGP's are shownby solidstars.Solid circlesshowthe locationsof the
meanpaleomagnetic
polescalculatedby Sager[1983a,1984],whereas
the solid squaresrepresentthe mean pole positionsof Gordon[1982a,
1983]. The solid line is the apparent polar wander path of Sager
[1983a]' the dashedline, the path of Gordon[1983]. The 95% confidenceregionssurroundingthe mean paleomagneticpolesare shown
as ellipses,and the numberswithin the ellipsesare the mean agesof
the poles in millions of years. SeamountsL2, L3, L4, and L8 have
total fusion agesof 85.0 + 1.1, 82.7 + 3.6, 39.3 + 1.1, and 71.9 + 1.4
Ma, respectively.Map projectionis polar equal area.
SCHLANGER
ET AL.' GEOLOGYAND GEOCHRONOLOGY
OF THE LINE ISLANDS
11,269
taken that extendnorth from Caroline Island. The sequenceof
At the southern
volcanic events at both the northern
dates represented by PCOD-6 (69.8 _+1.0 Ma), RD-41
(35.5 _+0.9 Ma), RD-43 (59.0 _+0.8 Ma), and DSDP site 316
(minimum age of cessationof volcanismat 81-83 Ma) presents
further complicationsfor a singlehot spot linear progression
model. Sample PCOD-6 consistedof a relatively fresh cobble
of plagioclase-richbasalt in a piston core taken in a turbiditefilled basin which lies downslopefrom the site of RD-41. This
basalt cobblemust representdebrisfrom a seamount.Thus we
see in a very close geological conjunction edifice ages of
and southern boundaries
of the Line chain are also complex. Drilling on Horizon
Guyot [Winterer et al., 1973] showed this ridge to have a
history of two Cretaceous volcanic events separated by a
period of Cenomanian reef growth. Further, dates obtained in
our study from the northeast end of the Tuamotu Islands of
41.8 +_0.9 and 47.4 _+0.9 Ma (RD-52) complicate the generally accepted argument that the Line-Tuamotu elbow is
coevalwith the Emperor-Hawaiian elbow dated at 43 Ma. On
the basisof fossilevidencederived from drilling at DSDP site
318 in the Tuamotu chain [Schlan•teret al., 1976], where late
early Eocene shallow water fossilsin turbidites overlie the
presumedbasalt basement,it was argued that the volcanic
edificesof the Tuamotu ridge could have formed more than 51
Ma. Also, Ha•l•lerty et al. [1982] determined, paleontologically,that Eocenevolcanism,-,•44-50 Ma, took place in
the southern
Line
chain
at the site of RD-45.
Therefore
the
end of the central Line Islands the cluster of
69.8 + 1.0 and 35.5 + 0.9 Ma. The PCOD-6
and RD-43
dates
fit on the linear progressionline of Figure 6. The cessationof
volcanism at DSDP site 316 greatly predates both PCOD-6
and RD-43; three distinct periodsof volcanismare seenin this
region. SeamountL7 of this paper, of Eoceneage, could also
be ascribedto the main age-progressive
trend linear ridge.
The final
set of dates to be discussed are those from
the
the Line-Tuamotu elbow took place from more than 51 to 42
southernLine Islands,dredgehauls RD-44 and RD-45. Prior
to the determination of radiometric age dates from these
dredgehauls,Ha•t•tertyet al. [1982] had determinedon fossi.
Ma.
evidence that the seamount
Within the Line chain the following chronologicdata needs
to be taken into account. As shown on Figures 5 and 6, the
majority of dated volcanicedificesdefine an overall age progressionalong the Line chain from the location of dredge
142-D (93.4 _+1.3 Ma) to the Line-Tuamotu elbow. Watkins
Seamount(L1 of this paper; Figure 1) is also consideredto be
of Late Cretaceousage. A rate of migration of volcanism of
9.6 +_0.4 cm/yr best fits this trend. However, deviationsfrom
the progressivetrend exist. The cluster of agesrepresentedby
RD-63 (86.0_+ 0.9 Ma), RD-61 (81.4 _+1.1 Ma, 82.6 _+0.7
Ma), RD-59 (85.0 _+ 1.1 Ma), and 133-D (84.4 _+0.9 Ma) are
associatedwith 137D dated at -,•57 Ma by Saito and Ozima
[1977]. The elongate ridge from which 137-D was dredged
exactly parallels the ridges from which RD-63 and RD-61
were taken; RD-59 is from an isolated seamountlying off the
southernend of the ridge from which 137-D was taken. It is
difficult to reconcilethis parallelism of ridgeswith the path of
a single hot spot to account for both the Cretaceous and
Paleoceneages in this short sector of the Line Islands. Fur-
had a minimum age of 70-75 Ma. This seamountis cappedby
coarse-grainedbioclasticlimestoneof reefal origin which contains rudists, calcareousalgae, and volcanic rock fragments.
Further, volcanic peperite was dredged from the RD-45 seamount. Tests of planktonic foraminifera incorporated into this
volcanicrock have been dated as middle Eocenein age, 44-50
Ma [Ha•t•terty et al., 1982]. The ages of 71.9 q-1.4 and
70.5 q- 1.1 Ma reported here are consistent with the Maestrichtian age of shield-buildingvolcanismat theseseamounts
data available
at this time show that volcanism
in the area of
ther, 137-D lies to the north of the well-defined Line cross
trend (Figure 1). SeamountsL2 and L3 of this paper (Table 4
and Figure 1) yielded Cretaceous ages based on paleomagneticswhich are in accordwith the radiometricage determinations
of RD-59
and 133-D.
In the Line cross trend itself
(Figure 2), which has a geometrictrend distinct in the province, the only radiometric age obtained at 128D (78.7 +_1.3
Ma) plots in the main trend line shown in Figure 6 even
though the seamountfrom which the rock was taken lies far
from which
RD-45
was obtained
which must have been above sea level in Late Cretaceous
time
as determinedby the fossilevidenceof Haggerry et al. [1982].
These Cretaceousdates fall far above the postulated line of
progressionshown on Figure 6 and argue persuasivelyagainst
the formation of the Line Islands by a singlehot spot. In fact,
when consideredtogether with the DSDP results from 165,
315, and 316, one could argue that an older progressivetrend
existedwhich paralleled the trend line definedin Figure 6. The
phase of Eocene volcanic activity at RD-45 can be explained
by hot spot volcanism along the main trend. We wish to
emphasizethe followingpointsconcerningvolcanicevents'
1. The majority of dated volcanos can be interpreted as
defining an age-progressivevolcanic trend from 93 (142-D) to
44-50 Ma (RD-45 southward along the Line chain, which
supportsan origin by hot spot volcanismnow active in the
vicinity of Easter Island. During this period the Pacific plate
moved at 9.6 + 0.4 cm/yr acrossthis hot spot.
2.
Three
volcanos
exhibit
Eocene
and
Paleocene
vol-
canism (between 38 and 60 Ma) which does not fit this main
to the east of the main Line chain.
trend' 137-D at 15øN, RD-33 in the Line Islands cross trend,
Further, the long time span of volcanismat site 165 and the
age of 39.3 +_1.5 Ma obtained for RD-33 argue against a
straightforward age progressionalong the Line cross trend,
although both of theselocations,it could be argued,lie to the
south of the well-definedcrosstrend and may representvolcanic activity of Cretaceous age along the 9.6 _+0.4 cm/yr
progressionshown in Figure 6 complicated by Eocene volcanism along one of the SE trending ridges which intersects
the Line Islands chain. SeamountsL4 and L5 of this paper are
of Tertiary age based on paleomagneticdata. In the central
Line Islands the date of 76.4 _+0.5 Ma for dredge 123-D falls
on the line of age progressionsshown on Figure 6. However,
at site 315 major edifice building ceasedby 93.3 Ma and a
nearby seamount,L6 of this study,is probably of Eoceneage.
and RD-41 at 2øN. This small group of agespossiblyshowsan
age progression which could be related to volcanic overprinting by hot spot volcanism along the Line-Marquesas
Swell [Crou•th and Jarrard, 1981]. Alternatively, these volcanos representa period of rejuvenescence
not related to hot
spot volcanism but part of a Pacific-wide Eocene volcanic
event [Ha•t•terty et al., 1982]. In either case,the Eocene and
Paleoceneedificesand ridges sampled are in close proximity
to older Cretaceous edifices and ridges, as in the case of
RD-45 and the pair of ages shown by PCOD-6 and RD-41.
The same edificesmay be compositesof both Cretaceousand
Eocene volcanic episodesand clearly require a volcanic history requiring more than a singlehot spot.
3. The Cretaceous ages determined at DSDP sites 165,
11,270
SCHLANGERET AL.' GEOLOGYAND GEOCHRONOLOGY
OF THE LINE ISLANDS
315, and 316 and from RD-44 and RD-45 do not fit 9.6 + 0.4
cm/yr trend and could be interpreted as representinga progressiveage trend that is systematically10-20 Ma older than
the linear trend shown in Figure 6 which connectsthe Tuamotu elbow with the northernmostLine Islands.It is particularly difficult to fit the 93.3 Ma age of volcanismat DSDP site
315, which is concordantwith the age of the Cuneolinaassemblagethere,to the 9.6 + 0.4 cm/yr trend.
REEF GROWTH
AND SUBSIDENCE
One of the major implicationsof the hot spot model for the
developmentof a linear island chain is that the history of reef
growth along the chain should reflect the progressivechronology of volcanismalong the chain, provided that the volcanic
edificesbuilt from the seafloorinto the photic zone in latitudes
amenable to vigorous reef growth. The thicknessof the reef
cap on an edificewould depend on the subsidencepath of the
edifice. Along a hot spot path the edificesand the seafloor
would be expectedto sink along an age-depthcurve such as
one of those proposed by Parsons and Sclater [1977],
Heestandand Crou•th [1981], and Crou•th[1983] where depth
isequalto a functionof t •/2
The Emperor-Hawaiian chain is the best documented hot
spot trace in the Pacific Basin; along this chain the history of
reef growth and development follows a classical Darwinian
pattern [see Jackson et al., 1980]. Around the island of
Hawaii, now over the hot spot, only Recent reefs are known.
At Midway Island, drilling revealedthat reef growth has been
continuous since Miocene time [Ladd et al., 1970]. Drilling
along the Emperor chain showed that Paleocenereefal carbonates cap seamountsin that part of the chain. Failure of
atolls to maintain themselvesat sealevel in the Emperor chain
can be ascribedto the transport of the Emperor edificesinto
colder, northern waters as these edificesmoved NW atop the
Pacificplate. Moreover, an almostcontinuouschain of closely
spacedatolls extendsfrom Midway Island SE along the chain
to Gardner
Pinnacle
where
the volcanic
edifice breaks
sea
level.
Therefore,if the Line chain formed through the action of a
single hot spot, we would expect to see a history of reef
growth and subsidencealong the chain somewhatparallel but
older than that seen in the Emperor-Hawaiian chain. However, in the case of the Line chain, two kinds of data needed
for a detailed reconstructionof a subsidencehistory are largely lacking. First, the age of the seafloorin the vicinity of the
Line chain is poorly known, and second,the history of reef
growth can only be inferred from data from DSDP sites 165,
315, and 316 in the central part of the chain and dredge haul
sitesRD-44, 45, 46, and 47 in the southernpart of the chain.
The oldest known
reefs in the main Line chain were in the
vicinity of Fanning Island as shown by data from DSDP site
315. There Prernoli-Silva and Brusa [1981] report a midCretaceousCuneolinaassemblageof Cenomanian-Albian age
in turbidites of both late Campanian-middle Maestrichtian
and Oligocene age. The presenceof this mid-Cretaceousfauna
is in concordancewith the K-Ar age of 93.3 Ma reported for
the basal basalt
at DSDP
site 315. If we consider
Horizon
Guyot to be the northern extensionof the Line chain, then we
must consider the Cuneolina-bearingreef limestone drilled
there at DSDP site 171 [Winterer et al., 1973] to be coeval
with the mid-Cretaceous reef reported at DSDP site 315.
During late Campanian through early-middle Maestrichtian
time (70-75 Ma) reefsexistedin the vicinityof Kingman Reef
(DSDP site 165), Fanning Island (DSDP site 315), south of
ChristmasIsland (DSDP site 316), and on seamountsjust
north of Caroline Island (dredge hauls 44 and 45). The eXistenceof reefsof late Campanianto early-middleMaestrichtian
age along a 2500-km length of the Line chain from DSDP site
165 to RD-45 showsreef developmentover this distance between 70 and 75 Ma.
Evidencefor post-Cretaceousreef growth is only recorded
from DSDP site 165, where late Eocene reef-derived fossil
debris was cored in Oligocene turbidites [Premoli-Silva and
Brusa, 1981] and at Caroline Island (RD-46 and 47) where
dredge hauls recovered reef limestones of Eocene through
Plio-Pleistoceneage; Caroline Island is an atoll today [Ha•t•terty et al., 1982]. At the site of dredge haul RD-44, late
Cretaceousreefs were succeededby a late Paleoceneneriticshelfcarbonateunit, but by middle Eocenetime, pelagicsedimentation prevailed at this site. We can assumethat there are
sectionsof post-Cretaceousreefsbelow the atolls of the central Line chain. It is important to note that dredge hauls
RD-57 through 64 recovered no reefal limestone debris betweenJohnstonIsland and Kingman Reef.The morphologyof
the chain and the pattern of reef growth along it contrasts
with the Emperor-Hawaiian chain. Long sectionsof the Line
chain lack atolls, i.e., from JohnstonIsland to Kingman Reef
and from
Christmas
Island
to Caroline
Island.
This
lack
of
atolls, consideringthat the Line chain was in latitudes amenable to reef growth throughout its history from Late Cretaceousto the present day, argues against a hot spot model
that would produce a chain capped by a more regularly disposed chain of atolls. Further, the irregular distribution of
atolls arguesfor a subsidencehistory along the chain at variance with one predicted by a regular age-depthrelationship
relatedto t •/2. Where reefinghistoryis knownfrom closely
spacededificessuch as the sites of RD-44, RD-45, and Caroline Island (RD-46 and 47), the subsidencehistory appearsto
have beencomplex.At RD-44 the apparentsuccession
of Late
Cretaceousreefs followed by late Paleoceneneritic shelf carbonatesand then by middle Eocenepelagicsedimentssuggests
that the edifice subsidedtoo quickly for the maintenanceof
reef growth; subsidenceat this site amounted to 1500 m since
Late Cretaceoustime. At RD-45, reef growth ceasedby Maestrichtian time, and the edifice has subsided 1200 m since that
time. At Caroline Island, reef growth has persistedat least
from Eocenetime to the presentday. We note that Epp [this
issue] estimated subsidencerates at DSDP sites 165 and 316
and at the sites of the seamountsfrom which dredge hauls
RD-44 and RD-45 were taken (see also Haggetty [1982] for
original data) and came to the conclusionthat each of these
sites underwent
different
subsidence histories no one of which
fit the subsidencepaths predicted by the age-depthcurves of
Parsonsand Sclater [1977], Heestandand Crough [1981] and
Crough [1983].
DISCUSSION
The purpose of the researchcarried out by the present authors was the testing of the various models put forward to
accountfor the Line chain. Beginningwith Morgan's [1972]
propositionthat the Line chain was generatedby a singlehot
spot other models followed. Natland [1976] argued that the
petrologiccharacter of severalbasaltic rocks recoveredfrom
the Line chain and the crosstrend indicatedthat at least parts
of the chain were part of a central Pacific rift systemof limited
crustal extension. Winterer [1976] postulated a ridge crest
origin for the main Line chain at ~ 110 Ma followedby ridge
jumps; he recognizedthe importanceof the NW-SE trending
crossridgesand proposedthat they were youngerthan the
main Line trend and that the complexityof the chainwas due
SCHLANOER
ET AL.: GEOLOOYAND GEOCHRONOLOGY
OF THE Ll•u• ISLANDS
11,271
to the passageof severalhot spotsacrossthe chain. Crough transformfaults,or activity at ridge crestsand we do not, for
andJarrard [1981] proposedthat one suchcrosstrend contin- the Line chain,acceptridgeerestor transformfault associated
volcanismas a major factor, then we are drawn, inductably,
ued into the Line chain from the MarquesasIslands, Farrar
and Dixon [1981] proposedfracturezone volcanismas a to the hot spot mechanismto accountfor the chain. Our data
major factor in the formation of the Lines. Hendersonand can be interpretedto show that two hot spotstraversedthe
Gordon[1982] have attempted to explain the complex vol- presentchain. However, both of these would have had to
canic history of the Line chain through the action of four hot follow parallelpathswith a time interval of from 10 to 20 m.y.
them.Onewouldexpectthat a second
hot spotpassspotsthat traversedthe area of the presentchain at different between
times.Finally, Epp [this issue]proposedtwo models,eachof ing so closelyalong an earlier hot spot trace would have
whichemploysa singlehot spot,for the evolutionof the Line produceda more morphologicallycoherentchain with many
chain. He arguesthat perturbationsof the signal,i.e., the sur- more atolls than we now see in the Line chain. The geotec1983] cerface expressionof volcanism,of the hot spot accountfor the tonicimagerymap of W. Haxby [seeFrancheteau,
tainly indicatesthat many possiblehot spot tracespassinto
complexchronologyof the volcaniceventsalong the chain.
The purposeof this sectionthen is to presentarguments the Line chain, at least one of which coincides with the hot
againstcertain modelsthat tend to invalidate them and that
spottrackbetween
theLinechainandiheMarquesas
aspro-
posedby CroughandJarrard [1981]. Henderson
and Gordon
[1982] proposethat four hot spots formed the Line chain,
whileit maynotbelogically
possible
to validatean hypothesis althoughtheir modeldoesnot accountfor many of the dated
by discoveringnew confirmingdata, it is possibleto invalidate edifices in the chain.
Beforecompletelyacceptingthe efficacyof multiplehot spot
an hypothesisby discoveringeven a singlenew piece of evidencethat contradictsthat hypothesis.
modelsin explainingindividualislandchainswe wish to emThe ridge crest model set is difficult to justify on palco- phasizethat complexvolcanicthronelogicsare not restricted
place constraintson other models.This sectionmight be
viewed as constructedafter the Popperian argument that
magneticgroundsinasmuchas the magneticanomaly patterns
implicit in suchmodelsare not k,nownin and around the Line
chain. A strongerargumentagainstthe ridge crestmodel lies
in the petrologiccharacter of the basaltsfrom the chain as
discussedabove. Our data and that of Jacksonet al. [1976]
show that the basalts in the Line chain are similar to those
to the Line chair• but characterize the entire Pacific Basin
from the Line Islands to the western subduetion zone bound-
aries
ofthepresent
Padfieplate[Schlanoer
andPremoli-$ilv
a,
1981; Schlanoeret al., 1981; Haooerty, 1982; Hagoerty et al.,
1982]. Both Cretaceousand Eocenevolcanismblanketedthis
westernpart of the PacificBasin; Cretaceous.
volcanismtook
found in the Empe•ror-Hawaiian
chain,the classichot spot
placeovera vastareabetween
~ 110and~ 70Ma [Wattset
trace; the basaltsare largelynormal oceanicislandbasalts.
el., 1980; Menard, 1964; Larsonand Schlanoer,1981; Rea and
Vallier, 1983]. Indeed, mid-Cretaceousvolcanismis a global
phenomenon[Schlanoeret al., 1981]. We propose that a
mechanismexiststhat would allow the surfaceexpressionof
The fracture zone model is attractive in that it would ac-
count for the simultaneity of much of the Cretaceousvolcanismalong the Line chain. However, a fracturezone origin
would imply large amounts of strike-slipdisplacementalong
the axis of the chain.Farrat and Dixon [1981] proposed1700
,
coevalvolcanismover wider areasthan that allowedfor in
necessarily
laterally restrictedhot spotmodels.
km of strike-slipmotion alonga fracturezonethat extended
Acknowledgments.
This research
wasSUl•po•rted
by the Officeof
from the Emperor Trough through the Gardner Seamounts
and through the entire Line chain. Gordon[1982b], basedon Naval Research.We especiallythank the captainand crew of the R/V
KanaKeokifor theireffortsduringthreecruises
of the shipin atolla review of available pale0magneticdata has effectivelyrefu- Studdedwaters.The governmentof the Republicof Kiribati kindly
ted the Farrar-Dixon
model.
Models that ascribethe Line chain to the action of a single
hot spot run into difficultiesin the face of the distribution
along the entirechain of radiometricand bigstratigraphicdata
relevent to the timing of volcanic edifice formation and
periods of reef growth. If we take the Emperor-Hawaiian
chain [seeJacksonet al., 1980] as the exampleof a singlehot
spottrace,we seethat individualedificesin that chain built up
from the seafloorto sealevel in 1-2 m.y. and the reefsimmedi-
allowed us to conduct research in their territorial waters. Also we
appreciatethe help and hospitalityof the peopleof FanningIsland
while R/V Kana Keoki lay disabledoff the island.Discussionson the
geologyof linear island chainswith R. Gordon and L. Henderson
wereenlightening
andhelpful.R. Gordonkindlyreviewedthe manuscript.Over the past decade,as a shipmate'on cruisesto the Line
Islandsand in the Courseof many fruitful discussions,
E. L. Winterer
hascontributedgreatlyto our efforts.Analysesof reefalfaunasin the
LineIslandsprovince
by I. Premoli-Silva
showed
theextentof Cretaceousreefgrowth.We thank J. Morgan and R. Jarrardfor critical
reviewsand helpfulsuggestions
for the improvement
of the original
ately formedon and around theseedifices.This example manuscript.Hawaii Instituteof Geophysicscontribution1486.
cannot be appliedto the Line chain. A singlehot spot moving
throughthe Line chain cannotaccountfor (1) the formationof
Cenomanianor older reefsat both Horizon Guyot and in the
vicinity of Fanning Island (DSDP site 315), (2) the Late Cre-
taceousand Eocenevolcanismrecordedat siteRD-45, (3) the
simultaneousappearanceof reefsof late Campanian to earlymiddle Maestrichtianage from near DSDP site 165 to the site
of RD-45, and (4) the irregular subsidencehistory of at least
parts of the Line chain.
Further, as shownon Figure 6, the trace of a singlehot spot
which may have causedthe progressivevolcanismalong the
chain at a plate motion rate of 9.6 + 0,4 cm/yr does not account for the agesof volcanismseenat DSDP sites 165, 315,
and 316 and at sites RD-44 and RD-45.
If we adhere to the generallyacceptedidea that significant
volcanismin the oceanic basins is due to hot spots, leaky
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(ReceivedJ,anuary 5, 1984;
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