Paleomagnetic During Evidence for Motion of the Hawaiian Hotspot

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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; movement: paleomagnetism

1. Introduction tion of a change in plate motion in a fixed hotspot reference frame. Because the bend is so distinct it Many of our ideas on where mantle plumes origi- can be used to estimate plume diameters and to place nate, how they interact with the convecting mantle bounds on the convecting mantle wind that may and how plates have moved in the past rest on deflect plumes [l]. interpretations of the Hawaiian-Emperor hotspot However, shortly after hotspots were used as a track. One reason the track has attained this concep- frame of reference [2], apparent discrepancies involv- tual stature lies in its prominent bend at 43 Ma. The ing the Hawaiian-Emperor track arose [3]. Attempts bend, which separates the westward-trending Hawai- to model past plate motions failed to predict the ian islands from the northward-trending Emperor bend; instead, a more westerly track was derived [4]. seamounts (Fig. l), has no equal among the Earth’s Tests of the fixed hotspot hypothesis suggested large hotspot tracks; it is the clearest physical manifesta- relative motions between Hawaii and other hotspots [3,5], but uncertainties in the plate circuits employed in these tests limited their resolving power [6]. * Corresponding author. 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)00169-6 172 J.A. Tarduno, R.D. Cottrell/ Earth and Planetav Science Letters 153 (1997) 171-180 records when the Hawaiian hotspot became fixed in 2. Detroit Seamount the mantle, rather than a change in plate motion. Prior to 43 Ma, the Hawaiian hotspot would have During Ocean Drilling Program Leg 145, 87m of moved southward, creating the Emperor seamount massive and pillowed lava flows were penetrated on chain. This proposal is testable by paleomagnetism. Detroit Seamount (Hole 884E: 51”27.034’N, If the hotspot has remained fixed, the paleolatitudes 168”20.216’E). The basalt sequence can be separated of extinct volcanic edifices comprising the Emperor into 13 lithologic units based on chilled margins and chain should equal that of present-day Hawaii. New phenocryst content (Fig. 1) [8]. “‘Ar/ 39Ar radiomet- data obtained from Detroit Seamount, part of Em- ric data yield a plateau age of 8 1.2 + 1.3 Ma for a peror chain near the Aleutian-Kuril trench (Fig. 1) plagioclase free component and an isochron age date allow us to conduct such a test. of 80.0 k 0.9 Ma [9]. This age is older than the

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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) 171-180 173

65-75 Ma age assumed in hotspot-based plate mo- ence of hematite (Fig. 2). If this hematite carries a tion models [lo]. coherent field direction, there should be a consistent Tarduno and Gee [I l] derived a paleolatitude of difference between its declination and the declination 32.6” from preliminary paleomagnetic data collected isolated at lower temperatures, for samples of the by the Shipboard Scientific Party [8]. This nominal same lithologic unit. Such consistency was not ob- value does not agree with the current position of the served. The inclination of the high unblocking tem- Hawaiian hotspot or any predictions based on other perature component is also inconsistent between paleomagnetic data [ 111. The dispersion character- lithologic units, leading us to conclude that hematite istics of the preliminary data suggest that a reliable carries no useful geomagnetic signal in these rocks. paleolatitude might be obtainable with a thorough Characteristic remanent magnetizations (ChRMs) land-based study [ 111. 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 = 3. Rock magnetism and paleomagnetism 10). But because hematite can bias alternating field Azimuthally unoriented samples (n = 94) were results, we consider only the thermal demagnetiza- collected from the recovered basalt cores and ana- tion data below. lyzed in the Paleomagnetic Laboratory at the Univer- Nearly all the ChRM’s have negative inclinations, sity of Rochester. Koenigsberger ratios for the sam- the only exception being samples from lithologic ples average 9.89, suggesting high stability of rema- unit 4 (n = 6). The coring record suggests that it is nence. Magnetic hysteresis curves show character- unlikely these positive inclinations are artifacts istics ranging from multi- to single- domain, but over caused by the accidental inversion of samples during half the data have parameters attributable to single core recovery or storage [S]. Assuming a northern domain behavior. Together the hysteresis parameter hemisphere origin, the negative inclinations denote data lie along a trend that mimics that displayed by reversed polarity. This polarity assignment is consis- magnetite and low-titanium titanomagnetites [12]. tent with the “Ar/ j9Ar radiometric age data that This similarity is also seen in unblocking tempera- suggests eruption of the basahs during chron 33R of ture characteristics. the Campanian [13]. Some prior work in the Pacific Each sample was subjected to detailed thermal has noted a possible geomagnetic excursion within demagnetization (25°C steps with a temperature range sediments recording chron 33R [14]; the positive of 50-675°C). A subsample from each unit was also inclinations observed from lithologic unit 4 might demagnetized using stepwise alternating field treat- record this excursion. Because excursions could have ment in increments of 5-10 mT (5-100 mT). Upon a cause different from that of normal secular varia- thermal and alternating field demagnetization, most tion, we have excluded data from unit 4 from our samples showed a univectorial decay after the re- subsequent inclination analysis. moval of a small viscous magnetization (Fig. 2), These positive inclinations, however, provide allowing calculation of a characteristic direction with valuable information on the fidelity of the magneti- principal component analysis (n = 79). zation isolated. A common source of bias in pateo- Some exceptions to this ideal behavior were noted. magnetic data derived from oceanic core material is In a few samples, a stronger and coherent low-tem- a nearly vertical drilling-induced remanence. The perature component was observed, attributable to the positive inclinations argue against the presence of modem field at the site. For ten samples, the demag- such an overprint because they are nearly opposite netization decay was less regular and a Fisher aver- the mean of the negative inclinations (see below). age was used to obtain the final direction and magnetic alteration caused by thermal treatment forced 4. Inclination group models and secular variation us to reject results from five samples. Approximately 10% of samples analyzed showed Another potential problem in obtaining paleomag- an additional component having unblocking tempera- netic data from a basalt drill hole is the uncertain tures greater than 580°C which indicates the pres- timescale between eruptions. If most flows reflect 74 J.A. Tarduno, R.D. Cottrell/ Earth and Planetary Science Letters 153 (19971 171-180

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a. , 1 -80 ? F-60 0 ‘E g -40 = 2 -20 - Predicted I from Pacific APWP

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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 could easily obtain a biased inclination-only averages derived from each flow paleolatitude estimate by giving equal weight to each unit [HI for serial correlation using established for- flow unit. To address this concern we check the mulations 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 Wander path (APWP) [20-231. Published poles for level, they are combined. These analyses lead us to 3 8 1 Ma [20,21] suggest much lower values than we inclination group models for n = 83 samples (see observe. The discrepancy is significant at the 99% Figs. 1 and 3). Of these the lo-inclination group confidence level using any of the inclination group model is preferred, where groups are distinct at models (Fig. 3). > 95% confidence level 1161. Given the large difference between our new re- The average inclination value for Detroit sults and predicted values, it is prudent to review the Seamount using the lo-inclination group model is factors that could result in gross errors. These in- - 55.7”_+,7$“.Importantly, the average inclination de- clude (1) the lack of adequate sampling of secular rived from the other models does not vary signifi- variation, (2) the presence of unremoved overprint cantly from this value (Fig. 3). The directional angu- magnetizations and (3) inclination bias caused by lar dispersion was estimated from the inclination- off-vertical drilling or unrecognized tectonic tilting model data and transformed into pole-space for com- of the basalt sequence. parison with global data sets 117,181. The dispersion Of these, the first is inconsistent with our angular of virtual geomagnetic poles from global igneous dispersion values. Although the basalts are remark- rocks is available for two relevant time windows, able fresh, we believe the hematite component ob- 45-80 and 80-l 10 Ma [19]. Although the 80- 110 served may have been acquired during weathering Ma interval nominally fits the age of Detroit episodes between eruptions, further supporting our Seamount, the global data groups have some age conclusion that a significant time elapsed between overlap. Nevertheless, the angular dispersion is indis- flow emplacement. Our detailed demagnetization data tinguishable from the predicted virtual geomagnetic argue against the second possibility. If the data were pole scatter regardless of the time used or the choice biased by an unremoved magnetization, a potential of inclination group model (Fig. 3). 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 5. Paleolatitude estimate and uncertainties be to shallow the resultant vector. Our result, however, is too steep compared with predicted values. The angular dispersion displayed by the new data Tilts of l-3” have been reported previously for strongly suggests that the Detroit Seamount basalt some of the northern Emperor seamounts 1241. Be- sequence averages secular variation. Our preferred cause these tilts are small and the angle between the inclination group model suggests a paleolatitude of remanent magnetization vector and likely down-dip 36.2”_+,~$‘, clearly discordant from the present-day azimuth of tilt is large (> 60”), the effect on our latitude of the Hawaiian hotspot ( u 19? (Fig. 3). We paleolatitude results is negligible. Logging was hin- can also compare our new paleolatitude estimate dered by sediment infilling and equipment failure with that predicted from the Pacific Apparent Polar 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 and Planeta? Science Letters 153 (19971171-180 177 basalt cores. However, some dip measurements were units. On this basis we have no reason to believe that made at unit contacts. The contact dips range from 0” drilling was significantly off-vertical or that the units (units 8 and 10) to 5” (unit 1) in the massive basalt were tectonically tilted since eruption.

r .6 mm/y! ;40 50 mm/yr : .- 40 mm/yr % 1 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 heterogeneities in the mantle [29]. The Pacific hemisphere is thought to have rotated to the south 1301; The new paleomagnetic results from Detroit this motion is consistent with some predictions based Seamount directly question the validity of the late on global paleomagnetic data from the continents Cretaceous Pacific Apparent Polar Wander Path. But and the assumption of fixed Atlantic hotspots during how could these prior late Cretaceous results be so late Cretaceous-Tertiary times [31]. errant? The answer may lie in systematic errors in The sense of the discrepancy between the new some of the data used to define paleomagnetic poles Detroit paleolatitude estimate and the present-day for oceanic plates. Previous poles for the late Creta- Hawaiian hotspot latitude is the same (to the south), ceous Pacific plate are heavily or solely based on the as that between Suiko and Hawaii. Could an earlier inversion of magnetic surveys over seamounts phase of true polar wander explain the discrepancy [20,21]. Reviews of the methods used to fit these between paleo- and present-day latitude posed by the poles suggest they are far more uncertain than com- new Detroit Seamount data? We can use the same monly supposed [25]. In addition, viscous magnetiza- global continental data that support the Suiko-TPW tions can bias the resulting pole positions [26]. The model to test whether this is an acceptable explana- effect could be especially pronounced when these tion [ 111, with the caveat that the test relies on fixed secondary magnetizations are superimposed on a re- Atlantic hotspots. The true polar wander predictions versed polarity primary direction, as is the case here. do not agree with the new Detroit Seamount data. Our undemagnetized basalt NRM data support this Instead, the discrepancy between paleolatitudes and concept because the distribution is skewed (index = present-day hotspot latitude should be less for 81 1.3) toward low inclinations. The effect could be m.y. old rocks [3 I, 111. 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 8. Pacific hotspot motion and its implications marine magnetic anomaly skewness data of comparable age [27]. Having excluded late Cretaceous true polar wander, we must now seriously entertain motion of the Hawaiian hotspot during generation of the Emperor 7. True polar wander chain [5,7] as an explanation for the new data. This motion can be examined by using the new data, The Detroit Seamount result presented here is one previous results from Suiko Seamount and the physi- of only a few Cretaceous paleolatitude values from cal record of volcanic edifices comprising the Em- Pacific plate basalt sequences that adequately aver- peror chain. We can isolate the latitudinal history of ages secular variation. Others include Suiko the Emperor seamounts from that of the Hawaiian Seamount (65 Ma) [ 161, MIT Guyot (121 Ma) and chain by subtracting the difference between the pre- Resolution Guyot (128 Ma), [11,17]. Suiko Seamount sent-day latitudes of the 43 Ma bend and Hawaii is also part of the Emperor trend (Fig. 1). The null from the present-day latitudes of each of the Em- hypothesis that the paleolatitude result from Suiko peror seamounts. In effect, we slide the Emperor (27”, n = 40) [ 161 is drawn from the same population trend down the Hawaiian chain to the present-day as the Detroit data presented here (n = 10) is re- latitude of Hawaii (Fig. 4). In so doing, we produce jected at the 95% confidence level using non-para- a plot predicting the paleolatitude of Emperor metric tests (Kolmogorov-Smimov). seamounts if they were formed by a moving hotspot The 8” discrepancy between the Suiko Seamount beneath a stationary plate. The new Detroit result paleolatitude and the present-day latitude of the together with the Suiko Seamount data parallel this Hawaiian hotspot has been attributed previously to predicted trend and therefore support the hotspot early Cenozoic true polar wander [281, a rotation of motion hypothesis [5,7]. Differences between the the entire solid Earth in response to shifting mass data and predicted values, and the uncertainties in J.A. Tarduno, R.D. Cottrell/ Earth and Planetary Science Letters 153 f 19971 I71 -180 179 the paleomagnetic estimates, also allow for signiti- Together with the similarity of the Hawaiian-Em- cant northward plate motion (Fig. 4). peror track to the Louisville track [32], these obser- As discussed above, the paleolatitude of Suiko vations suggest that rather than moving alone [7], Seamount has been attributed previously to Cenozoic Hawaii may have moved southward with a group of true polar wander. If correct, our plot (Fig. 4) would Pacific hotspots in late Cretaceous-early Tertiary suggest the hotspot source moved southward only times. During the mid-Cretaceous, hotspots in the between 81 and 65 Ma. This rate, calculated from Atlantic moved at rates of N 30 mm yr-‘, relative to the present-day latitudinal difference between the the latitudinally stable Pacific hotspots. These Detroit and Suiko seamounts is 49 mm yr- ’ If episodes of fast motion by groups of hotspots appear northward plate motion occurred at the same time as to be separated by intervals of much slower move- southward hotspot motion, this rate is an overesti- ment, such as the last 5 m.y. If correct, any hotspot mate. To avoid this problem we can estimate the rate reference frame is at most temporally and spatially of hotspot motion directly from the paleolatitude limited. Discontinuities in these regional frames could difference. The rate using the paleolatitude data is indicate major changes in mantle convection on scales higher at 64 mm yr- ’ , but has a substantial uncer- reminiscent of the long-wavelength velocity hetero- tainty ( f 43 mm yr- ‘, 1v error). geneities defined by global seismic tomography [33]. Acceptance of prior interpretations of Cenozoic true polar wander, however, leads to seemingly unlikely coincidences which must be invoked to ex- Acknowledgements plain the age progressive Emperor change. The rate of latitudinal motion defined by the Emperor chain We thank the members of the Paleomagnetic Re- prior to 65 Ma is within 12% of the rate afterward. search Group at the University of Rochester for their Prior to 65 Ma, the rate would reflect mainly hotspot assistance, Art Goldstein for use of his susceptibility motion with only a small component of plate motion. meter, John Miller for assistance in obtaining sam- After 65 Ma, the rate would record only plate mo- ples, P. Wessel and W.H.F. Smith for GMT soft- tion. To maintain a nearly constant latitudinal pro- ware, G. Acton, R. Duncan and R. Van der Voo for gression with age, a large instantaneous increase of review comments, and D. Wilson, R. Gordon and J. plate velocity (a factor of _ 5) is required at 65 Ma. Gee for discussions. This work was supported by the Although we cannot exclude this possibility, we National Science Foundation. [RV] 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 References directed to determine whether unrecognized late Cre- taceous-Cenozoic motion of Atlantic hotspots has ill R.A. Duncan, M.A. Richards, Hotspots, mantle plumes, flood led to overestimates of true polar wander, as has basalts and true polar wander. Rev. Geophys. 29 (1991) 3 I-50. been shown for older time intervals [ 111. If so, the [21 W.J. Morgan, Convection plumes in the lower mantle, Na- Hawaiian hotspot may have moved continuously ture (London) 230 (1971142-43. southward from 81 to 43 Ma [7], at a rate of 30-50 [31 P. Molnar, T. Atwater, Relative motion of hotspots in the mm yr-‘, while the Pacific plate moved slowly mantle, Nature (London) 246 (19731288-291. northward, with both motions recorded in a paleo- [41 S.C. Solomon, N.H. Sleep. D.M. Jurdy, Mechanical models for absolute plate motions in the Early Tertiary, .I. Geophys. magnetic (spin axis) frame of reference (Fig. 4). Res. 82 (1977) 203-213. Comparison of these new findings with prior re- [51 P. Molnar. J. Stock. Relative motions of hotspots in the sults from Resolution, MIT and Wodejebato guyots Pacific, Atlantic and Indian oceans since late Cretaceous [111 allows us to obtain a synoptic view of hotspot time, Nature (London) 327 (19871587-59 1. motion. Although there are larger uncertainties in the l61 G.D. Acton, R.G. Gordon, Paleomagnetic tests of Pacific plate reconstructions and implications for motions between data from Wodejebato Guyot, they are also derived hotspots. Science 263 (19941 1246- 1254. from rocks of chron 33R-age and are consistent with [71 1.0. Norton, Plate motions in the North Pacific: The 43 Ma the conclusions derived here from Detroit Seamount. Nonevent. Tectonics 14 ( 1995) 1080- 1094. 180 J.A. Tarduno, R.D. Cottrell/Earth and Planetary Science Letters 153 (1997) 171-180

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