EPSL
ELSEVIER
Earth and Planetary Science Letters 153 (1997) 171-180
Paleomagnetic evidence for motion of the Hawaiian hotspot
during formation of the Emperor seamounts
John A. Tarduno
*, Rory
D. Cottrell
Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA
Received
13 June 1997; revised 23 September
1997; accepted 23 September
1997
Abstract
The bend in the Hawaiian-Emperor
chain is the best example of a change in plate motion recorded in a fixed-hotspot
frame of reference. Alternatively, the bend might record primarily differences in motion of the Hawaiian hotspot relative to
the Pacific lithosphere. New paleomagnetic data from the Emperor chain support the latter view. Although the rate of motion
is difficult to constrain because of uncertainties posed by true polar wander and limited sampling of the chain, the best
available paleomagnetic data suggest Pacific hotspots may have moved at rates comparable to those of lithospheric plates
( > 30 mm yr- ’ ) in late Cret aceous to early Tertiary times (81-43 Ma). If correct, this requires a major change in how we
view mantle dynamics and the history of plate motions. In the early to mid-Cretaceous (128-95 Ma), hotspots in the Atlantic
moved at similar rates. These episodes during which groups of hotspots appear to move rapidly are separated by times of
much slower motion, such as the past 5 m.y. 0 1997 Elsevier Science B.V.
Keyvords: Hawaii; Emperor Seamounts;
hotspots; plate tectonics;
1. Introduction
Many of our ideas on where mantle plumes originate, how they interact with the convecting mantle
and how plates have moved in the past rest on
interpretations
of the Hawaiian-Emperor
hotspot
track. One reason the track has attained this conceptual stature lies in its prominent bend at 43 Ma. The
bend, which separates the westward-trending
Hawaiian islands from the northward-trending
Emperor
seamounts (Fig. l), has no equal among the Earth’s
hotspot tracks; it is the clearest physical manifesta-
* Corresponding
author.
movement:
paleomagnetism
tion of a change in plate motion in a fixed hotspot
reference frame. Because the bend is so distinct it
can be used to estimate plume diameters and to place
bounds on the convecting mantle wind that may
deflect plumes [l].
However, shortly after hotspots were used as a
frame of reference [2], apparent discrepancies involving the Hawaiian-Emperor
track arose [3]. Attempts
to model past plate motions failed to predict the
bend; instead, a more westerly track was derived [4].
Tests of the fixed hotspot hypothesis suggested large
relative motions between Hawaii and other hotspots
[3,5], but uncertainties in the plate circuits employed
in these tests limited their resolving power [6].
Recently Norton [7] has suggested that the bend
0012-821X/97/$17.00
0 1997 Elsevier Science B.V. All rights reserved.
PII SOO12-821X(97)00169-6
J.A. Tarduno, R.D. Cottrell/ Earth and Planetav Science Letters 153 (1997) 171-180
172
records when the Hawaiian hotspot became fixed in
the mantle, rather than a change in plate motion.
Prior to 43 Ma, the Hawaiian hotspot would have
moved southward, creating the Emperor seamount
chain. This proposal is testable by paleomagnetism.
If the hotspot has remained fixed, the paleolatitudes
of extinct volcanic edifices comprising the Emperor
chain should equal that of present-day Hawaii. New
data obtained from Detroit Seamount, part of Emperor chain near the Aleutian-Kuril trench (Fig. 1)
allow us to conduct such a test.
2. Detroit Seamount
During Ocean Drilling Program Leg 145, 87m of
massive and pillowed lava flows were penetrated on
Detroit Seamount (Hole 884E: 51”27.034’N,
168”20.216’E). The basalt sequence can be separated
into 13 lithologic units based on chilled margins and
phenocryst content (Fig. 1) [8]. “‘Ar/ 39Arradiometric data yield a plateau age of 8 1.2 + 1.3 Ma for a
plagioclase free component and an isochron age date
of 80.0 k 0.9 Ma [9]. This age is older than the
160’
160’
200’
220’
@St/l&o
Nintoku
_
Flow
Units
B
B
_
_
i7
_
C
_
C
c
IT
D
D
E
5_
E
_
T
_
F
F
G
G
z
_
H
_
H
H
;
L
;
I
J
8
Inclination
Groups
80
-60
-40
-20
0
Inclination (O)
Fig. 1. Basalt stratigraphy [8] and characteristic remanent magnetization (ChRM) inclinations vs. depth in meters below seafloor (mbsf) from
Detroit Seamount. Open symbols represent positive inclinations (flow unit 4) that have been inverted. Inset is a Mercator projection of the
North Pacific Basin showing the Hawaiian-Emperor
Seamount chain with locations of Detroit (triangle) and Suiko seamounts (square).
Inclination groupings are based on lithology and inclination-only averaging [ 15- 171. In the 1 l-inclination group model, adjacent inclination
averages are distinct at the 90% confidence level; in the lo-inclination group model (preferred), averages are distinct at > 95% confidence.
J.A. Tarduno, R.D. Conrell/Earth
and Planetar?; Science Letters 153 (1997) 171-180
65-75 Ma age assumed in hotspot-based plate motion models [lo].
Tarduno and Gee [I l] derived a paleolatitude of
32.6” from preliminary paleomagnetic data collected
by the Shipboard Scientific Party [8]. This nominal
value does not agree with the current position of the
Hawaiian hotspot or any predictions based on other
paleomagnetic
data [ 111. The dispersion characteristics of the preliminary data suggest that a reliable
paleolatitude
might be obtainable with a thorough
land-based study [ 111.
3. Rock magnetism
and paleomagnetism
Azimuthally
unoriented
samples (n = 94) were
collected from the recovered basalt cores and analyzed in the Paleomagnetic Laboratory at the University of Rochester. Koenigsberger ratios for the samples average 9.89, suggesting high stability of remanence. Magnetic hysteresis curves show characteristics ranging from multi- to single- domain, but over
half the data have parameters attributable to single
domain behavior. Together the hysteresis parameter
data lie along a trend that mimics that displayed by
magnetite and low-titanium
titanomagnetites
[12].
This similarity is also seen in unblocking temperature characteristics.
Each sample was subjected to detailed thermal
demagnetization (25°C steps with a temperature range
of 50-675°C). A subsample from each unit was also
demagnetized using stepwise alternating field treatment in increments of 5-10 mT (5-100 mT). Upon
thermal and alternating field demagnetization,
most
samples showed a univectorial decay after the removal of a small viscous magnetization
(Fig. 2),
allowing calculation of a characteristic direction with
principal component analysis (n = 79).
Some exceptions to this ideal behavior were noted.
In a few samples, a stronger and coherent low-temperature component was observed, attributable to the
modem field at the site. For ten samples, the demagnetization decay was less regular and a Fisher average was used to obtain the final direction and magnetic alteration caused by thermal treatment forced
us to reject results from five samples.
Approximately
10% of samples analyzed showed
an additional component having unblocking temperatures greater than 580°C which indicates the pres-
173
ence of hematite (Fig. 2). If this hematite carries a
coherent field direction, there should be a consistent
difference between its declination and the declination
isolated at lower temperatures, for samples of the
same lithologic unit. Such consistency was not observed. The inclination of the high unblocking temperature component
is also inconsistent
between
lithologic units, leading us to conclude that hematite
carries no useful geomagnetic signal in these rocks.
Characteristic
remanent
magnetizations
(ChRMs)
calculated from the thermal demagnetization
data
and those derived from the alternating field data are
very similar (AF values: I = 57.9Y:!:30, k = 20, n =
10). But because hematite can bias alternating field
results, we consider only the thermal demagnetization data below.
Nearly all the ChRM’s have negative inclinations,
the only exception being samples from lithologic
unit 4 (n = 6). The coring record suggests that it is
unlikely
these positive inclinations
are artifacts
caused by the accidental inversion of samples during
core recovery or storage [S]. Assuming a northern
hemisphere origin, the negative inclinations denote
reversed polarity. This polarity assignment is consistent with the “Ar/ j9Ar radiometric age data that
suggests eruption of the basahs during chron 33R of
the Campanian [13]. Some prior work in the Pacific
has noted a possible geomagnetic excursion within
sediments recording chron 33R [14]; the positive
inclinations
observed from lithologic unit 4 might
record this excursion. Because excursions could have
a cause different from that of normal secular variation, we have excluded data from unit 4 from our
subsequent inclination analysis.
These positive inclinations,
however, provide
valuable information on the fidelity of the magnetization isolated. A common source of bias in pateomagnetic data derived from oceanic core material is
a nearly vertical drilling-induced
remanence.
The
positive inclinations
argue against the presence of
such an overprint because they are nearly opposite
the mean of the negative inclinations (see below).
4. Inclination group models and secular variation
Another potential problem in obtaining paleomagnetic data from a basalt drill hole is the uncertain
timescale between eruptions. If most flows reflect
74
J.A.
a.
Tarduno,
R.D. Cottrell/ Earth and Planetary Science Letters 153 (19971 171-180
b.
North,Up
No h,Up
1
25
East
West
West
East
South.Down
Sodh,Down
4
North,Up
C.
North,Up
I
325
t
1
West
West
ast
Sodth,Down
South.Down
J.A. Tarduno, RD. Cottrell/Earth
a.
,
175
and Planetap Science Letters 153 (1997) 171-180
1
-80
?
F-60
0
‘E
g -40
=
2
-20 -
-a0
e
Predicted
I from Pacific APWP
-
9 60 ‘ii
z 40 2
2 20 r
i
1
I
Present day latitude of Hawaii
10
11
12
inclination Groups
Fig. 3. (a) Average inclination values treating each flow unit independently (12 groups) and for 2 inclination-group
models. Errors are the
95% confidence interval. Also shown is the predicted inclination at 81 Ma based on prior Pacific Apparent Polar Wander path poles [20].
(b) Paleolatitude values for the inclination groups. Errors are 95% confidence interval. Also shown is the present-day latitude of the
Hawaiian hotspot (black line).
(c) Estimated angular dispersion (S) of the inclination groups (black line) shown vs. the predicted values for 45-80 Ma (dark gray field)
and 80-l 10 Ma ([ighr gray field) from [19].
(d) Orthographic
projection of the colatitude (labeled “Primary”) for Detroit seamount (srar). The colatitude is distinct at the 99%
confidence level (grqv) from previous 8 1 Ma poles comprising the Pacific Apparent Polar Wander Path (ellipses). Poles derived from the
following sources: 39 Ma, 1201: 57 Ma, [23]; 65 Ma, [22]; 72 Ma, [20]; 81 Ma, [21]; 82 Ma [20], 33n (79.1-73.6 Ma) [27].
rapid
eruptions,
one
paleolatitude
estimate
flow unit.
To address
could
easily
by giving
obtain
a biased
equal weight to each
this concern we check the
inclination-only
averages
derived
from
each
flow
unit [HI for serial correlation using established formulations 116-181. If adjacent inclination units do
Fig. 2. (a), (b). Thermal demagnetization
showing near univectorial decay to the origin after the removal of a small viscous overprint.
Temperature steps of 25°C were used in a temperature range of 50- 675°C. Inclination shown by boxes; declination by circles. Sample
identifications following conventions of the Ocean Drilling Program are as follows: (a) 145-884E-91-01,
30-32 cm; (b) 145-884E-3R-04,
15-17 cm.
(c) Thermal demagnetization
of sample (145-884E-lOR-05,
69-71 cm) showing a larger viscous component attributable to the present-day
field.
(d) Thermal demagnetization
of a sample (145-884E-2R-01, 50-52 cm) with a high-unblocking
(> 580°C) magnetization attributable to
hematite.
176
J.A. Tarduno, R.D. Cottrell/Earth
and Planeta? Science Letters 153 (1997) 171-180
not differ from each other at a given confidence
level, they are combined. These analyses lead us to 3
inclination group models for n = 83 samples (see
Figs. 1 and 3). Of these the lo-inclination
group
model is preferred, where groups are distinct at
> 95% confidence level 1161.
The average
inclination
value
for Detroit
Seamount using the lo-inclination
group model is
- 55.7”_+,7$“.Importantly, the average inclination derived from the other models does not vary significantly from this value (Fig. 3). The directional angular dispersion was estimated from the inclinationmodel data and transformed into pole-space for comparison with global data sets 117,181. The dispersion
of virtual geomagnetic poles from global igneous
rocks is available for two relevant time windows,
45-80 and 80-l 10 Ma [19]. Although the 80- 110
Ma interval
nominally
fits the age of Detroit
Seamount, the global data groups have some age
overlap. Nevertheless, the angular dispersion is indistinguishable from the predicted virtual geomagnetic
pole scatter regardless of the time used or the choice
of inclination group model (Fig. 3).
5. Paleolatitude estimate and uncertainties
The angular dispersion displayed by the new data
strongly suggests that the Detroit Seamount basalt
sequence averages secular variation. Our preferred
inclination group model suggests a paleolatitude of
36.2”_+,~$‘, clearly discordant from the present-day
latitude of the Hawaiian hotspot ( u 19? (Fig. 3). We
can also compare our new paleolatitude
estimate
with that predicted from the Pacific Apparent Polar
Wander path (APWP) [20-231. Published poles for
8 1 Ma [20,21] suggest much lower values than we
observe. The discrepancy is significant at the 99%
confidence level using any of the inclination group
models (Fig. 3).
Given the large difference between our new results and predicted values, it is prudent to review the
factors that could result in gross errors. These include (1) the lack of adequate sampling of secular
variation, (2) the presence of unremoved overprint
magnetizations
and (3) inclination
bias caused by
off-vertical drilling or unrecognized tectonic tilting
of the basalt sequence.
Of these, the first is inconsistent with our angular
dispersion values. Although the basalts are remarkable fresh, we believe the hematite component observed may have been acquired during weathering
episodes between eruptions, further supporting our
conclusion that a significant time elapsed between
flow emplacement. Our detailed demagnetization data
argue against the second possibility. If the data were
biased by an unremoved magnetization,
a potential
culprit we have not yet addressed is the present-day
field at the site. Because the inclinations are negative, the net effect of this unremoved remanence will
be to shallow the resultant vector. Our result, however, is too steep compared with predicted values.
Tilts of l-3” have been reported previously for
some of the northern Emperor seamounts 1241. Because these tilts are small and the angle between the
remanent magnetization
vector and likely down-dip
azimuth of tilt is large (> 60”), the effect on our
paleolatitude results is negligible. Logging was hindered by sediment infilling and equipment failure
aboard ship, and data are therefore limited for the
Fig. 4. Plot of latitudinal distance from the 43 Ma bend in the Hawaiian-Emperor
hotspot track vs. age (light circles).Age data are not
available for Meiji, Tenchi and Jimmu: their positions based on a constant latitudinal progression are shown for reference. Dark gray circles
indicate positions after the difference between the present-day latitude of the 43 Ma bend and Hawaii is subtracted from each of the
present-day latitudes of the Emperor seamounts. In effect, we slide the Emperor trend down the Hawaii chain so that the bend coincides
with the position of Hawaii (inset). This reconstruction allows the following test. If the Emperor seamounts record mainly motion of the
Hawaiian hotspot, paleolatitudes should fall close to this corrected latitudinal trend; if the hotspot has been stationary, the paleolatitudes
should fall close to the present-day latitude of Hawaii. Triangles indicate the paleolatitudes of Suiko [16] and Detroit (this study) seamounts.
The light greyfield represents an interpretation that explains the difference between the paleolatitude of Suiko Seamount and that of Hawaii
by Cenozoic true polar wander (TPW) [28]. If this TPW interpretation is correct. the corrected latitudinal trend can be divided into two
segments. For the segment younger than 65 Ma (labeled I), the latitudinal trend must be the result of plate motion only. The older segment
(labeled 2) records both hotspot motion and plate motion. In the absence of TPW. the hotspot may have moved continuously southward at a
rate of 30-50 mm yr- ’ while the plate also drifted slowly northward (dark grey).
J.A. Tarduno, R.D. Cottrell/Eanh
177
and Planeta? Science Letters 153 (19971171-180
basalt cores. However, some dip measurements were
made at unit contacts. The contact dips range from 0”
(units 8 and 10) to 5” (unit 1) in the massive basalt
units. On this basis we have no reason to believe that
drilling was significantly off-vertical or that the units
were tectonically tilted since eruption.
60
50
r
;40
.6 mm/y!
50 mm/yr
:
.%
1
40 mm/yr
30 mm/yr
30
20 mm/yr
10 mm/yr
20
Hawaii
45
50
55
60
65
70
75
80
85
90
95
1
3
178
J.A. Tarduno, R.D. Cottrell/Earth
and Planetary Science Letters 153 (1997) 171-180
6. Pacific Apparent Polar Wander
The new paleomagnetic
results from Detroit
Seamount directly question the validity of the late
Cretaceous Pacific Apparent Polar Wander Path. But
how could these prior late Cretaceous results be so
errant? The answer may lie in systematic errors in
some of the data used to define paleomagnetic poles
for oceanic plates. Previous poles for the late Cretaceous Pacific plate are heavily or solely based on the
inversion
of magnetic
surveys over seamounts
[20,21]. Reviews of the methods used to fit these
poles suggest they are far more uncertain than commonly supposed [25]. In addition, viscous magnetizations can bias the resulting pole positions [26]. The
effect could be especially pronounced when these
secondary magnetizations
are superimposed on a reversed polarity primary direction, as is the case here.
Our undemagnetized
basalt NRM data support this
concept because the distribution is skewed (index =
1.3) toward low inclinations.
The effect could be
even greater if induced magnetizations
were also
considered
[26]. Interestingly,
high-latitude
poles
similar to our new colatitude result (Fig. 3) have
been reported recently from preliminary analyses of
marine magnetic anomaly skewness data of comparable age [27].
7. True polar wander
The Detroit Seamount result presented here is one
of only a few Cretaceous paleolatitude values from
Pacific plate basalt sequences that adequately averages secular
variation.
Others
include
Suiko
Seamount (65 Ma) [ 161, MIT Guyot (121 Ma) and
Resolution Guyot (128 Ma), [11,17]. Suiko Seamount
is also part of the Emperor trend (Fig. 1). The null
hypothesis that the paleolatitude result from Suiko
(27”, n = 40) [ 161 is drawn from the same population
as the Detroit data presented here (n = 10) is rejected at the 95% confidence level using non-parametric tests (Kolmogorov-Smimov).
The 8” discrepancy between the Suiko Seamount
paleolatitude
and the present-day
latitude of the
Hawaiian hotspot has been attributed previously to
early Cenozoic true polar wander [281, a rotation of
the entire solid Earth in response to shifting mass
heterogeneities in the mantle [29]. The Pacific hemisphere is thought to have rotated to the south 1301;
this motion is consistent with some predictions based
on global paleomagnetic
data from the continents
and the assumption of fixed Atlantic hotspots during
late Cretaceous-Tertiary
times [31].
The sense of the discrepancy between the new
Detroit paleolatitude
estimate and the present-day
Hawaiian hotspot latitude is the same (to the south),
as that between Suiko and Hawaii. Could an earlier
phase of true polar wander explain the discrepancy
between paleo- and present-day latitude posed by the
new Detroit Seamount data? We can use the same
global continental data that support the Suiko-TPW
model to test whether this is an acceptable explanation [ 111, with the caveat that the test relies on fixed
Atlantic hotspots. The true polar wander predictions
do not agree with the new Detroit Seamount data.
Instead, the discrepancy between paleolatitudes and
present-day hotspot latitude should be less for 81
m.y. old rocks [3 I, 111.
8. Pacific hotspot motion and its implications
Having excluded late Cretaceous true polar wander, we must now seriously entertain motion of the
Hawaiian hotspot during generation of the Emperor
chain [5,7] as an explanation for the new data. This
motion can be examined by using the new data,
previous results from Suiko Seamount and the physical record of volcanic edifices comprising the Emperor chain. We can isolate the latitudinal history of
the Emperor seamounts from that of the Hawaiian
chain by subtracting the difference between the present-day latitudes of the 43 Ma bend and Hawaii
from the present-day latitudes of each of the Emperor seamounts. In effect, we slide the Emperor
trend down the Hawaiian chain to the present-day
latitude of Hawaii (Fig. 4). In so doing, we produce
a plot predicting
the paleolatitude
of Emperor
seamounts if they were formed by a moving hotspot
beneath a stationary plate. The new Detroit result
together with the Suiko Seamount data parallel this
predicted trend and therefore support the hotspot
motion hypothesis [5,7]. Differences between the
data and predicted values, and the uncertainties
in
J.A. Tarduno, R.D. Cottrell/ Earth and Planetary Science Letters 153 f 19971 I71 -180
the paleomagnetic
estimates, also allow for signiticant northward plate motion (Fig. 4).
As discussed above, the paleolatitude
of Suiko
Seamount has been attributed previously to Cenozoic
true polar wander. If correct, our plot (Fig. 4) would
suggest the hotspot source moved southward only
between 81 and 65 Ma. This rate, calculated from
the present-day
latitudinal difference between the
Detroit and Suiko seamounts is 49 mm yr- ’ If
northward plate motion occurred at the same time as
southward hotspot motion, this rate is an overestimate. To avoid this problem we can estimate the rate
of hotspot motion directly from the paleolatitude
difference. The rate using the paleolatitude data is
higher at 64 mm yr- ’ , but has a substantial uncertainty ( f 43 mm yr- ‘, 1v error).
Acceptance of prior interpretations
of Cenozoic
true polar wander, however, leads to seemingly unlikely coincidences
which must be invoked to explain the age progressive Emperor change. The rate
of latitudinal motion defined by the Emperor chain
prior to 65 Ma is within 12% of the rate afterward.
Prior to 65 Ma, the rate would reflect mainly hotspot
motion with only a small component of plate motion.
After 65 Ma, the rate would record only plate motion. To maintain a nearly constant latitudinal progression with age, a large instantaneous increase of
plate velocity (a factor of _ 5) is required at 65 Ma.
Although we cannot exclude this possibility, we
find the coincidences
hard to accept. Instead the
answer may lie in the way the true polar wander
curve has been derived; a continued effort should be
directed to determine whether unrecognized late Cretaceous-Cenozoic
motion of Atlantic hotspots has
led to overestimates
of true polar wander, as has
been shown for older time intervals [ 111. If so, the
Hawaiian hotspot may have moved continuously
southward from 81 to 43 Ma [7], at a rate of 30-50
mm yr-‘,
while the Pacific plate moved slowly
northward, with both motions recorded in a paleomagnetic (spin axis) frame of reference (Fig. 4).
Comparison of these new findings with prior results from Resolution, MIT and Wodejebato guyots
[111 allows us to obtain a synoptic view of hotspot
motion. Although there are larger uncertainties in the
data from Wodejebato Guyot, they are also derived
from rocks of chron 33R-age and are consistent with
the conclusions derived here from Detroit Seamount.
179
Together with the similarity of the Hawaiian-Emperor track to the Louisville track [32], these observations suggest that rather than moving alone [7],
Hawaii may have moved southward with a group of
Pacific hotspots in late Cretaceous-early
Tertiary
times. During the mid-Cretaceous,
hotspots in the
Atlantic moved at rates of N 30 mm yr-‘, relative to
the latitudinally
stable Pacific hotspots.
These
episodes of fast motion by groups of hotspots appear
to be separated by intervals of much slower movement, such as the last 5 m.y. If correct, any hotspot
reference frame is at most temporally and spatially
limited. Discontinuities in these regional frames could
indicate major changes in mantle convection on scales
reminiscent of the long-wavelength
velocity heterogeneities defined by global seismic tomography [33].
Acknowledgements
We thank the members of the Paleomagnetic Research Group at the University of Rochester for their
assistance, Art Goldstein for use of his susceptibility
meter, John Miller for assistance in obtaining samples, P. Wessel and W.H.F. Smith for GMT software, G. Acton, R. Duncan and R. Van der Voo for
review comments, and D. Wilson, R. Gordon and J.
Gee for discussions. This work was supported by the
National Science Foundation. [RV]
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