ELSEVIER Earth and Planetary Science Letters 163 (1998) 53–68

The Magellan seamount trail: implications for Cretaceous hotspotvolcanism and absolute Pacific plate motion

Anthony A.P. Koppers a,Ł, Hubert Staudigel a,b, Jan R. Wijbrans a, Malcolm S. Pringle a,c

a Laboratory of Isotope Geology, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlandsb Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego,

La Jolla, CA 92093-0225, USAc Argon Isotope Facility, Scottish Universities Research and Reactor Centre, Rankine Avenue, East Kilbride G75 0QF, UK

Received 10 March 1998; revised version received 28 July 1998; accepted 11 August 1998

Abstract

The Magellan Seamount Trail (MST) delineates a northwest trending chain of four Cretaceous guyots in the WestPacific Seamount Province (WPSP). Seamount morphology, 40Ar=39Ar geochronology and Sr–Nd–Pb geochemistry of theMST provides evidence for a hotspot origin between the Samoa, Rarotonga and Society hotspots of the South PacificIsotopic and Thermal Anomaly (SOPITA). The MST yields an excellent linear age progression of 47:6 š 1:6 mm=yr.r 2 D 1:000; MSWD D 0.23; 1¦ SE) including Vlinder guyot (95:1š 0:5 Ma, n D 5; 2¦ SD), Pako guyot (91:3š 0:3 Ma,n D 3/ and Ioah guyot (87:1 š 0:3 Ma, n D 2/. The MST also exhibits a small range in Sr–Nd–Pb isotopic compositionsindicating enriched mantle sources with an affinity of EMI. Nevertheless, three volcanic events are found out of sequencewith linear MST hotspot volcanism: (1) an independent volcanic pedestal was formed 4–7 Myr before shield-volcanismstarted at Vlinder guyot, (2) a post-erosional volcanic cone was formed at least 20–30 Myr after drowning of Vlinderguyot, and (3) Ita Mai Tai guyot (118:1 š 0:5 Ma, n D 3/ was formed 34–36 Myr before the MST hotspot arrived at thepredicted location of this guyot. By identifying and ruling out discordant volcanic events, we can use the age progressionin MST to test the fixity of its hotspot. When presuming the fixed hotspot hypothesis, the local age progressions of theMST (47:6 š 1:6 mm=yr) and the copolar Musicians seamount trail (55:8 š 6:4 mm=yr) are not compatible with their100–80 Ma Euler pole. We investigate two options: (1) acceptance of a ‘forced’ Euler pole obeying the hotspot hypothesisby using both the age progressions and the azimuths of the studied seamount trails, or (2) acceptance of a ‘best-fit’ Eulerpole by using the azimuths of the studied seamount trail exclusively. In the first option, the angular speed of the Pacificplate during the 100–80 Ma stage pole is calculated at 0:502š 0:017º=Myr. In the second option, the ‘best-fit’ Euler poleis found approximately 35º different from the ‘forced’ Euler pole. We argue that the observed age progressions can only bereconciled with the ‘best-fit’ pole when allowing for the relative movement of the MST and Musicians mantle plumes withrespect to one another. The calculated maximum velocity component parallel to the line of age progression could then beas much as 23 mm=yr for the mantle plumes — when assuming one fixed hotspot in this alternate model. 1998 ElsevierScience B.V. All rights reserved.

Keywords: hot spots; plate tectonics; movement; seamounts; Ar-40=Ar-39; morphology

Ł Corresponding author. Tel.: C31 (20) 4447 403; Fax: C31 (20) 6462 457; E-mail: kopa@geo.vu.nl

0012-821X/98/$ – see front matter 1998 Elsevier Science B.V. All rights reserved.PII: S 0 0 1 2 - 8 2 1 X ( 9 8 ) 0 0 1 7 5 - 7

54 A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68

1. Introduction

The assumptions of the hotspot hypothesis arenow being subjected to critical re-evaluations. Theapparent fixity of mantle plumes [1] was largely un-questioned for the last 25 years, but recent studieshave explored possible movement between the Indo-Atlantic and Pacific hotspot systems [2–5] and indi-vidual mantle plumes with respect to ambient mantle[6]. In addition, mantle plumes have been questionedas the sole mechanism controlling hotspot volcanism[7,8]. Understanding the nature of hotspot volcan-ism is though important, because hotspots trails areused to obtain the absolute motion of the lithosphericplates through geological time and because hotspotsare an important means of heat transport between thedeep mantle and the Earth’s lithosphere.

In this study the Magellan Seamount Trail (MST)in the West Pacific Seamount Province (WPSP;Fig. 1) is investigated. This hotspot trail is de-fined as a complex, short and discontinuous chainof guyots (Fig. 2) which formed in what is now theSouth Pacific Isotopic and Thermal Anomaly (SO-PITA; Fig. 1). The ages of the studied guyots areestimated to range between 100–80 Ma based on theorientation of the MST and existing models of abso-lute Pacific plate motion [7,9–13]. This age range issimilar to that found for Late Cretaceous seamountvolcanism in the Marshall Islands [14,15], the Went-worth seamounts [16], the Musicians seamounts [17]and the Line Islands [18]. The MST, therefore, al-

Fig. 1. Location of the West Pacific Seamount Province (WPSP)and the Musicians seamount trail. The South Pacific Isotopic andThermal Mantle Anomaly (SOPITA), the DUPAL isotopic mantleanomaly, and the present day active hotspots of the Pacific Ocean(filled circles) are plotted for reference.

lows (1) to study short-lived Cretaceous hotspotvolcanism, (2) to assess the fixed hotspot hypothesis[1] in conjunction with copolar seamount trails, and(3) to determine the longevity of the SOPITA byestablishing links with currently-active hotspots inthe Pacific. We use 18 new 40Ar=39Ar ages in com-bination with a detailed morphological analysis ofVlinder and Sr–Nd–Pb isotope geochemistry to doc-ument the well-defined age-progression associatedwith the Magellan hotspot. In particular, we will uti-lize the difference in the observed age progressionsof the copolar Magellan and Musicians seamounttrails (Fig. 1) to test the ‘fixity’ of their hotspotsand the implication for absolute Pacific plate motionduring the 100–80 Ma stage pole.

2. Analytical methods and data presentation

Incremental heating 40Ar=39Ar age determinationswere performed on hornblende, plagioclase, ground-mass K-feldspar and bulk crystalline groundmassseparates using an argon laser probe combined witha MAP-215=50 mass spectrometer at the Labora-tory of Isotope Geology, Vrije Universiteit Ams-terdam [19]. Sample preparation, acid-leaching andmass-spectrometry are in described in [20]. Plateauages and argon-isotope isochron ages were calcu-lated as weighted means using 1=¦ 2 as weightingfactor [21] and as YORK2 least-squared fits withcorrelated errors [22] on the basis of the flux monitorTaylor Creek Rhyolite (TCR) sanidine (27.92 Ma).The age results are summarized in Table 1 and the40Ar=39Ar analytical data are available as Appendix1: EPSL Online Background Dataset 1. We alsoprovide Sr–Nd–Pb isotope composition and isotopedilution analyses for the MST basalts studied andtheir mineral phases as Appendix 2: EPSL OnlineBackground Dataset 1. Complementary major andtrace element analyses are provided as Appendix 3:EPSL Online Background Dataset 1.

1 URL: http:==www=elsevier.nl=locate=epsl, mirror site:http:==www=elsevier.com=locate=epsl

A.A

.P.Koppers

etal./E

arthand

Planetary

ScienceL

etters163

(1998)53–68

55

Table 1Sample information and 40Ar=39Ar data from the Magellan seamount trail

Lab code Field number Depth Location Rock type Sample type Age spectrum Tot fusion Inverse isochron analyses(m) Age š 2¦

(Ma)Lat. Lon. Age š 2¦ 39Ar MSWD n Age š 2¦ 40Ar=36Ar MSWD

(Ma) (%) (Ma) intercept

Vlinder guyot: main volcanismVL-1-1 TUNES 6 29-1 2200 17.12 154.33 hawaiite grndm 95.0 š 0.7 52 16.5 6 94.5 š 0.7VL-1-4 TUNES 6 29-29 2200 17.12 154.33 hawaiite plag [20] 95.4 š 1.5 49 5.2 4 92.8 š 1.6 95.2 š 1.9 305.0 š 59.2 5.0

plag [20] 96.6 š 0.7 41 6.6 5 96.2 š 0.6VL-1-8 TUNES 6 29-10 2200 17.12 154.33 alkali basalt plag 92.3 š 1.7 96 1.1 7 93.0 š 4.7 92.7 š 2.1 291.6 š 12.9 1.2OMA-1 TUNES 6 32-14 3400 16.40 154.35 hawaiite plag 95.6 š 0.7 49 0.9 4 93.8 š 1.3 95.5 š 0.8 309.4 š 16.4 0.7

plag 93.3 š 2.2 80 0.3 4 96.0 š 6.3 94.3 š 2.6 306.3 š 8.5 1.2

Vlinder guyot: NW pedestalVL-1-5 TUNES 6 28-1 2400 17.03 154.07 hbl basanite hbl 100.2 š 0.4 93 1.5 11 100.4 š 0.7 100.2 š 0.4 291.7 š 3.3 1.5VL-1-6 TUNES 6 27-1Oa 3100 16.98 154.02 hbl basanite grndm kfs 102.4 š 0.5 100 4.1 8 102.4 š 0.5 102.3 š 0.7 300.6 š 23.5 4.9VL-1-9 TUNES 6 27-9a 3100 16.98 154.02 hbl basanite grndm kfs 101.6 š 0.6 100 7.4 11 101.7 š 0.6 101.1 š 0.6 321.7 š 19.4 4.4

Pako guyotPAK-1 MW8805 RD-66-1 2025 15.88 155.15 hawaiite plag 90.9 š 0.5 65 1.3 9 89.4 š 1.3 90.8 š 0.5 299.7 š 6.5 1.1PAK-2 MW8805 RD-67-3 1600 15.50 155.02 hawaiite aph bas 92.3 š 0.7 19 2.9 3 94.3 š 0.9PAK-3 MW8805 RD-67-2 1600 15.50 155.02 hawaiite aph bas 91.2 š 0.4 25 2.1 3 92.3 š 0.5

Ioah guyotIOA-3 PUSH I-065-5 4000 14.13 155.88 hawaiite grndm 88.5 š 0.7 53 2.8 9 86.8 š 1.4IOA-4 PUSH I-056-6 1600 14.18 155.98 hawaiite grndm 86.7 š 0.4 61 0.7 9 86.2 š 0.7

Ita-Mai-Tai guyotITA- 1 PUSH I-053 4000 12.98 156.68 hawaiite plag [20] 120.0 š 0.8 64 1.7 6 120.4 š 1.4 120.0 š 0.8 295.8 š 2.5 1.5

grndm [20] 117.9 š 0.9 42 5.9 7 112.3 š 1.1ITA-2 PUSH I-038 2700 12.97 156.75 hawaiite plag [20] 118.5 š 0.8 100 13.0 8 118.5 š 0.7 118.5 š 0.8 293.0 š 25.5 13.5

grndm [20] 118.0 š 0.7 49 9.1 6 116.4 š 0.8

Geochemical data are expressed as wt%. K=Ca values are either calculated as weighted means for the age spectra or using recombined totals of 39ArK and 37ArCa for thetotal fusions. Reported errors on the 40Ar=38Ar ages are on the 95% confidence level including 0.2–0.3% standard deviation in the J-value. All samples where monitoredagainst Taylor Creek Rhyolite (TCR) sanidine (27.92 Ma). MSWD values for the age plateaus and inverse isochrons are calculated using N � 1 and N � 2 degrees offreedom, respectively.

56 A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68

A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68 57

3. Vlinder guyot morphology

The seabeam bathymetry of Vlinder guyot sug-gests multiple phases of magmatism followed byrejuvenated volcanism and flank collapse. Vlinderhas a flat top at ¾1500 m water depth and is ap-proximately 40 by 50 km wide and 3.5 km high(Fig. 2A). Four rift zones extend from the mainsummit platform (Fig. 2C) with azimuths (in º) andlength of rifts (in km) of 025=40, 176=50, 239=30

Fig. 3. Cross sections for Vlinder Guyot. (A) The smooth summit platform of Vlinder is extended to Oma-Vlinder, indicatingsimultaneous drowning and erosion of both edifices. (B) Note here the symmetric shape of the uneroded, post-erosional cone that israising for ¾500 m above the summit platform. Cross-section lines are shown in Fig. 2B.

Fig. 2. Sample locations, 40Ar=39Ar data and morphology of Vlinder guyot. (A) Bathymetric map of the Magellan Seamount Trail(MST). New 40Ar=39Ar ages are shown in conjunction with the Jurassic geomagnetic reversals (red lines) for the oceanic basement (M28D 158–159 Ma; M32 D 161–162 Ma; M35 D 164 Ma). Fracture zones (blue lines) are based on the geomagnetic reversal patterns[36], except for Osagawara FZ#1 and FZ#2 that are based on seismic profiling [37]. The Osagawara fracture zone represents ¾600 kmof horizontal motion as derived from the displacement of magnetic anomaly M35. Age results for two ODP Leg 129 drill sites intothe oceanic basement are plotted for reference [38]. This map has been drawn using the predicted bathymetry database produced by[43] on basis of altimetric gravity data. (B) Detailed bathymetric map of Vlinder guyot using seabeam swath data from the TUNES 6cruise. Contours represent 200 m depth intervals. Dredge locations and the cross section lines A–A0 and B–B0 of Fig. 3 are denoted. (C)Simplified map of Vlinder indicating the positions of rift zones, two independent intrusion centers and the post-erosional cone. (Inset)Enlarged map of the northern rim of Vlinder’s summit platform showing evidence for massive mass wasting due to oversteepening ofthis seamount flank. The shown upslope amphitheater is 4.8 km wide and 10.7 km long and is located near the emerging point of the NErift zone. Such emerging points mark the transition of intrusive magmatic activity from the central summit to the rift zone and may besusceptible to de-stabilization because of the superposition of two distinct intrusive mechanisms: radial tilt caused by central intrusions[25] and rift zone extension caused by horizontal expansion of the upper portion of the rift zone [26–28]. These processes togethermay result in over-steepened flanks and subsequently into the failure of this fraction of the main summit triggering major rock-slides. Asimilar preference for the development of landslides was found in other oceanic volcanoes, such as on the SW flank of Kilauea, Hawaii[26,28,29] and the E flank of Piton de la Fournaise, La Reunion [28]. Contours represent 100 m depth intervals. All maps have beenproduced using Generic Mapping Tools [44].

and 315=15. In addition, the NW-rift zone displaystwo minor rifts that branch out backwards to themain volcano (Fig. 2C) suggesting an independentand possibly earlier, volcanic system at this location(17º200N–154º020E), whereby the latter is suggestedby our radiometric dating. These minor rift zones arecharacterized by numerous uneroded volcanic cones(Fig. 2B) and most probably did not emerge abovesealevel as opposed to Vlinder’s main summit sincethey are located ¾1750 m deeper (Fig. 3A). Dredge

58 A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68

D-27 (3100 m depth) sampled one of the unerodedvolcanic cones, whereas dredge D-28 (2400 m depth)sampled the W-flank of the inferred NW volcanicpedestal (Fig. 2B). The SE-rift of Vlinder guyotdisplays a satellite volcano (Oma-Vlinder) that fallson the extension of the convex elevation profile ofthe main summit (Fig. 3A). This observation indi-cates that both Vlinder and Oma-Vlinder representthe main shield-building stage and that both weredrowned during the same subsidence event. DredgeD-32 (3400 m depth) sampled the SW flank ofOma-Vlinder, whereas dredge D-29 (2200 m depth)sampled an escarpment resulting from submarinelandslides (Fig. 2C). The otherwise very flat summitplatform also displays an uneroded, symmetrical vol-canic cone (Fig. 3B). Based on its 500 m height anda thermal lithospheric subsidence for oceanic crustyounger than 90 Ma of d(t[Ma]) D 2600C 340ðpt[Ma] [23] this suggests at least 20–30 Myr of base-ment subsidence between drowning and erosion ofVlinder’s shield and rejuvenation of volcanism.

Such complex magmatic histories — includingmultiple intrusion centers, rift zone volcanism andrejuvenation — are common to seamount volcanoesof the Vlinder size-category. For the voluminousPako, Ioah and Ita Mai Tai guyots we anticipatesimilarly complex magmatic histories. Meaningfulgeochronologic analyses of such seamounts, thus,have to include careful structural analysis of theseamount morphology and multiple 40Ar=39Ar agedeterminations on multiple sample sites.

4. 40Ar=39Ar geochronology

Incremental heating 40Ar=39Ar ages were de-termined on five well-crystallized groundmass andseven mineral separates from Vlinder, Pako and Ioahguyot (Fig. 4). Six 40Ar=39Ar ages from a previousstudy by Koppers et al. [20] for Ita Mai Tai (ITA-1;ITA-2) and Vlinder guyot (VLI-4) are included.

To determine whether an incremental heating ex-periment yields meaningful crystallization ages, weadopted quality criteria proposed by Fleck et al. [30]

Fig. 4. Incremental heating 40Ar=39Ar analyses for Vlinder guyot, Pako guyot and Ioah guyot presented as age plateau diagrams. Dataare listed in Table 1.

and Pringle [17]: (1) the high temperature plateausin the age spectra should include more than threeincremental heating steps and at least 50% of thetotal amount of 39ArK released, (2) the plateau andisochron ages should be concordant at the 95% con-fidence level, (3) the 40Ar=36Ar intercepts on theisochron diagrams should be equal to the atmo-spheric value of 295.5 at the 95% confidence level,and (4) the mean squared weighted deviations [22]for both the plateau ages (MSWD D SUMS=N � 1)and isochron ages (MSWD D SUMS=N � 2) shouldbe sufficiently small compared to F-statistic distri-butions. Although these criteria are well suited forthe evaluation of 40Ar=39Ar results from mineralseparates, they are not applicable for the evaluationof altered groundmass separates [20]. Based on theanalyses of 32 well-crystallized groundmass sam-ples, Koppers et al. [20] showed that groundmassesgenerally provide reliable crystallization ages — de-spite the inability to perform isochron analyses forsuch experiments and typical age plateau widthsranging between 30–70% of the total amount of39ArK released.

Vlinder guyot. Two age groups are observed atVlinder guyot: (1) an older group ranging in agebetween 100.2–102.4 Ma reflecting volcanism at theindependent NW pedestal, and (2) a younger groupwith a combined age of 95:1 š 0:5 Ma .n D 5/ re-flecting simultaneous volcanism for the main summitand the SE-rift ‘Oma-Vlinder’ volcano (Fig. 2A).The older age group includes hornblende sampleVLI-5 (100:2 š 0:4 Ma) and K-feldspar samplesVLI-6 (102:4 š 0:5 Ma) and VLI-9 (101:6 š 0:6Ma). These experiments display concordance in theirplateau, isochron and total fusion ages. However,the K-feldspars have high MSWD values indicat-ing an increased scatter of data points around theirplateaus and isochrons. VLI-9 has also an 40Ar=36Arintercept value of 321:7 š 19:4 that is high com-pared to the atmospheric value of 295.5. Both thehigh MSWD and 40Ar=36Ar intercept values maybe a consequence of the high potassium content ofthese K-feldspars increasing the radiogenic compo-nent (VLI-6 D 92:9%; VLI-9 D 94:0%). Such high

A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68 59

60 A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68

radiogenic components result in (1) smaller analyti-cal uncertainties for 36Ar=40Ar and 39Ar=40Ar ratios,in (2) a narrow clustering of data points close to the39Ar=40Ar axis, and, consequently, in (3) an increaseof the calculated SUMS of the mean deviationsfrom the isochron and a less accurate extrapolationto the 36Ar=40Ar axes to calculate the trapped ar-gon component. The combined age of 95:1 š 0:5Ma .n D 5/ for the younger age group includesplagioclase samples VLI-4 (95:4 š 1:5 Ma), VLI-8(92:3 š 1:7 Ma) and OMA-1 (95:6 š 0:7 Ma), andgroundmass samples VLI-1 (95:0 š 0:7 Ma) andVLI-4 (96:6 š 0:7 Ma). The younger age of VLI-8probably represents younger shield-building volcan-ism or rejuvenation. All plagioclase analyses meetthe adopted quality criteria and are accepted as goodcrystallization ages, except for the plagioclase anal-yses of VLI-4 which has MSWD values between5.0–5.2. The high MSWD values again may be ex-plained by the observed high radiogenic component(VLI-4 D 96:1%), but also by the fact that only fourdata points were used in the age calculations. Thegroundmass plateau ages of VLI-1 and VLI-4 arewithin error to their total fusion ages at the 95%confidence level. This internal age concordance to-gether with the agreement of the groundmass plateauages with comagmatic plagioclase ages indicates thatthe groundmass samples have largely retained theirradiogenic argon signatures and exhibit meaningful40Ar=39Ar ages.

Pako guyot. Three 40Ar=39Ar age determinationshave been performed from two different dredge siteson Pako guyot (Fig. 2A). The age range betweenPAK-1 (90:9 š 0:5 Ma: N-slope) and the combinedage of PAK-2 and PAK-3 (91:5 š 0:3 Ma: S-slope)reflects Pako’s shield-building phase, yielding anaverage age of 91:3 š 0:3 Ma .n D 3/. The anal-ysis of the PAK-1 plagioclase is of high quality:it has concordant plateau, isochron and total fusionages, its high temperature plateau represents 65% ofthe total of 39ArK released in 9 contiguous incre-ments, and its trapped argon signature of 299:7š 6:5is within 2¦ -error of the atmospheric value. The40Ar=39Ar analyses of the two aphyric hawaiitesPAK-2 (92:3 š 0:7 Ma) and PAK-3 (91:2 š 0:4Ma) are respectively characterized by: (1) short ageplateaus including 19% and 25% of the total amountof 39ArK released, (2) K=Ca ratios equal to (�1.0%)

or lower than (�8.5%) the bulk hawaiite K=Ca ra-tios as measured before irradiation, and (3) totalfusion ages slightly higher than the plateau ages.The latter two observations are explained by an in-creased recoil loss of 39ArK compared to the lossof 40Ar* and 37ArCa from the alteration phases inthe hawaiites. The diminishing effects of recoil inthese phases with increasing temperature results inan exponentially decreasing age spectra from agestoo high in the low temperature section to short ageplateaus in the higher temperature section [20]. Be-cause the plateau ages of PAK-1 (plag), PAK-2 andPAK-3 are concordant, we conclude that the analysesof both aphyric hawaiites give reliable estimates oftheir crystallization age.

Ioah guyot. The combined age of two ground-mass samples from two different dredge sites onthe east slope of Ioah (Fig. 2A) is 87:1 š 0:3 Maand most probably reflects the formation of its vol-canic shield. The groundmass plateau ages of IOA-3(88:5š 0:7 Ma) and IOA-4 (86:7š 0:4 Ma) are con-cordant with their total fusion ages. But these sam-ples display negative discordances in their measuredK=Ca ratios (IOA-3 D �13:1%; IOA-4 D �18:4%)and high atmospheric components (IOA-3 D 18%;IOA-4 D 20%). These observations indicate that thegroundmasses may have lost 39ArK and 40Ar* propor-tionally compared to 37ArCa due to the preferentialoutgassing of the alteration phases [20].

Ita Mai Tai guyot: Two samples from two differ-ent dredge sites on the northeast slope of Ita Mai Tai(Fig. 2A) have been dated for their groundmass andcomagmatic plagioclase [20]. Three out of four agesare concordant at the 95% confidence level, result-ing in a combined age of 118:1 š 0:5 Ma excludingthe age of the ITA-1 plagioclase (120:0 š 0:8 Ma).The older plagioclase age may be explained by in-corporation of plagioclase xenocrysts in the basalticmagma introducing an excess argon signature [20].The measured age range most probably representsthe shield-building phase on Ita Mai Tai guyot, sincesampling represents the entire stratigraphic heightbetween the 4000–2700 m dredge depths. The re-sulting age of 118–120 Ma is unexpected; it fallsdistinctively outside the expected age range of 100–80 Ma based on the morphological orientation ofthe MST and existing absolute plate motion models[7,9–13].

A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68 61

5. Discussion and interpretation

5.1. Life time of Vlinder guyot

Volcanism on volcanic islands is known to oc-cur over significant periods of time. The Hawaiianislands, for example, show complete volcanic histo-ries for 5–6 Myr with quiescent period up to 2.5Myr [31]. This observation is confirmed by 7 Myrof volcanism at Jasper seamount [32] in the Pacific,and by 5 Myr at St. Helena Island [33] and 16 Myrat Nashville seamount [34] in the Atlantic. How-ever, the build-up of their (tholeiitic) shields (95–98% of the volcanoes) generally is confined to thefirst 0.5–1.5 Myr of volcanism [31]. Rejuvenatedvolcanism is also observed for most hotspot chainsin the South Pacific Isotopic and Thermal Anomaly(SOPITA; Fig. 1) in the French Polynesian Islands.Post-erosional volcanism at e.g. Ua Pou in the Mar-quesas Islands occurred about 2.3–3.5 Myr later thanshield-building volcanism [35].

The volcanic history of Vlinder illustrates both thesuperposition of intra-plate volcanism upon an oldervolcanic pedestal and post-erosional volcanism. Weidentified three stages of volcanism: (1) formationof a volcanic pedestal to the NW of Vlinder, (2)formation of Vlinder’s main shield 4–7 Myr afterformation of this pedestal, and (3) formation of apost-erosional cone at least 20–30 Myr after drown-ing of Vlinder. The volcanic pedestal of Vlinder wasformed upon an 50–60 Ma old oceanic basement andcannot be related to hotspot volcanism sensu stricto,even not when modeling the age progressing includ-ing an independent intrusion center to the NW ofVlinder’s main summit (Fig. 5A). By identifying andruling out this discordant volcanic phase, the mainshield-building stage of volcanism is distinguishedwhich simultaneously formed Vlinder guyot and theOma-Vlinder volcano on the SE-rift (cf. Fig. 2).

The post-erosional volcanic cone on top of Vlin-der’s summit platform (Fig. 3) must have beenformed at least 20–30 Myr after drowning and ero-sion of Vlinder guyot. It is difficult to hold that thedelayed post-erosional volcanism was still associatedwith the MST hotspot. Backtracking exercises showthat Vlinder guyot passed close to the currently-active Samoa hotspot when it was 20–30 Myr old,between 75–65 Myr ago (Fig. 6). Although there

is no evidence that the Samoa hotspot was active75–65 Myr ago, it seems the only candidate hotspotto rejuvenate volcanism at Vlinder by superposition.

5.2. Age progression in the Magellan seamount trail

To model an age progression for the MST the in-trusion centers of the guyots studied and their oldestages were determined. Here we critically depend onthe morphological analyses of these guyots. Becausedredge locations on rift zones represent the distribu-tion of lavas due to superficial magmatic processes,these sample sites are linked to the formation ofthe seamounts and not to the position of the mantleplume. In Fig. 2C the rift zone structure on Vlin-der guyot is displayed including the locations ofits inferred intrusion centers. The major rifts extendfor 15–50 km from Vlinder’s main intrusion cen-ter, which is typical for guyots of the Vlinder andHawaiian size-category (cf. Kilauea [27–29]). Suchsecond order variations (<50 km) in the modeledMST age progression are, thus, largely eliminated byusing the locations of the intrusion centers instead ofthe dredge sites.

In Fig. 5A we have plotted all ages against dredgelocations to demonstrate the extent of the secondorder variation about the line that defines the MSTage progression. In addition, this diagram shows thehypothetical location of the independent NW in-trusion center of Vlinder guyot as opposed to itsdredge locations (cf. Fig. 2C). In both instances,the NW pedestal falls off the age progression lineand is 4–7 Myr older than expected from linearMST hotspot volcanism. To reconcile volcanism ofthe NW pedestal with a linear age progression ofMST hotspot volcanism, the NW pedestal would beexpected 225–270 km to the northwest of Vlinderguyot. This distance is clearly too large to accountfor rift zone volcanism (<50 km) related to themain shield-building phase at Vlinder. Moreover, theposition of Ita Mai Tai guyot cannot be reconciledwith a linear age progression line, because it exhibitsvolcanism 34–36 Myr older than expected from thismodel. Such a large age discrepancy points to an-other hotspot origin, although no other seamount trailis known to cross the MST at the location of Ita MaiTai prior to 100 Ma (Fig. 2A). The other measured40Ar=39Ar ages fall close to the age progression line

62A

.A.P.K

opperset

al./Earth

andP

lanetaryScience

Letters

163(1998)

53–68

Fig. 5. Volcanic age progression diagrams for the Magellan Seamount Trail (MST) and the Musicians Seamounts. We have plotted 40Ar=39Ar age data against angular (greatcircle) distances measured with respect to arbitrary points (MST D 12.6ºN–157.0ºE; Musicians D 25.0ºN–198.5ºW). Error bars on the ages represent errors on the 95%confidence level including a 0.2–0.3% standard deviation in the J-value. Estimated local plate velocities are as indicated in the data tables and errors are given as standarderrors. (A) In this diagram all measured ages of the Vlinder, Pako, Ioah and Ita Mai Tai guyots are plotted to allow the reader to judge the quality of these age data. Boththe NW pedestal of Vlinder guyot and Ita Mai Tai guyot yield ‘too old’ volcanism with respect to linear hotspot volcanism. (B) MST age progression compared to ageprogression in the Musicians seamounts [17]. Here the best ages and locations for Vlinder, Pako and Ioah are used instead of individual measurements and locations.

A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68 63

Fig. 6. Backtracked locations of guyots in the Magellan Seamount Trail (MST) with respect to currently active hotspots of the SouthPacific Isotopic and Thermal Anomaly (SOPITA) [42]. We used all models of absolute Pacific plate motion from the literature to comparethe robustness of this modeling [7,10–13]. In addition, we included the paleo-position of Vlinder guyot between 20–40 Myr afterformation from the MST hotspot (gray fields in rectangle) with respect to the SOPITA hotspots.

and have maximum differences of 1.8 Myr; exceptfor the VLI-8 plagioclase age that most probablyrepresents the younger limit of the shield-buildingstage at Vlinder.

In Fig. 5B we have plotted the best ages (i.e.combined ages) against the location of the inferredintrusion centers to compare age progressions forthe MST and Musicians seamount trail [17]. Weinfer that these combined ages yield reliable es-timates of the shield-building phase, because the40Ar=39Ar ages were derived from (1) different lo-cations along the rim of the main summits (Pako,Vlinder; Fig. 2A), (2) different stratigraphic heights(Ioah: 4000–1600 m, Vlinder: 3400–2200 m; Ta-ble 1), and (3) the landslide escarpment withinthe shield of Vlinder (Fig. 2C: inset). Good re-producibility and small analytical uncertainties inthe 40Ar=39Ar ages are achieved by using one datingtechnique, one laboratory, and since 15 out of 19samples were analyzed from one sample irradiation.Relative age differences between the MST guyots

(i.e. defining the age progression) are, therefore, de-termined accurately and without systematic error. Byusing YORK2 linear regressions with weighted er-rors .1=¦ 2/ on the ages [22] the local Pacific platevelocities are estimated at 47:6 š 1:6 (SE) mm=yrfor the MST and 55:8 š 6:4 (SE) mm=yr for theMusicians seamount trail. The MST age-progressionis perfectly linear (MSWD D 0.23; r 2 D 1:000/ indi-cating that the bulk of MST volcanism is compatiblewith a hotspot origin. Nonetheless, the observed lo-cal plate velocities for the MST and the Musiciansseamount trail are significantly different at the 65%confidence level.

5.3. Implications for absolute Pacific plate motionand the fixed hotspot hypothesis

The observed difference in local plate velocitiescan be utilized to constrain the location of the 100–80 Ma Pacific plate Euler pole by placing it fur-ther away from the Musicians seamount trail (high-

64 A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68

est velocity) than from the MST (lowest velocity).Moreover, when assuming Pacific plate rotation overfixed and copolar hotspots these different local platevelocities must translate to analogous angular veloc-ities for absolute plate motion. We, thus, have anextra constraint to check for the (relative) fixity ofcopolar mantle plumes. As will be shown below,none of the published Euler poles [7,9–13] proves tobe consistent with the measured local plate velocitiesduring the 100–80 Ma Pacific stage pole.

Constraints derived from local plate velocitieswere not used in previous models of the 100–80 MaPacific stage pole [7,9–13]. In these models the Eu-ler pole was exclusively derived from the azimuthsof a limited number of hotspot trails such as the Mu-sicians seamounts, Wentworth seamounts and LineIslands. For example, the Wessel and Kroenke pole[13] is perfectly fitted to the azimuth of the Musi-cians seamount trail as follows from the consistentangular distance of these seamounts to their Eulerpole (73:40 š 0:02, SD). But their model is lesswell fitted to the azimuth of the MST inducing anincreased spread in angular distance (37:82 š 0:98,SD). More importantly, their pole does not resultin comparable angular velocities for absolute Pa-cific plate motion as calculated from the observedlocal plate velocities at the 65–95% confidencelevel(MST D 0:693 š 0:023º=Myr, SE; MusiciansD 0:520 š 0:059º=Myr, SE; Fig. 5B).

For the 100–80 Ma stage pole an Euler pole(29ºN–297ºE; variance D 0.13) is derived utilizingan algorithm by Koppers [24] based on the fixedhotspot hypothesis [1]. With this algorithm the lo-cation of the 100–80 Ma Euler pole is estimatedusing (1) least-squared minimizations in the angulardistance between the Euler pole and all seamountsbetween 100–80 Myr old on the Pacific plate, and(2) consistency in the angular plate velocities as cal-culated from the observed local plate velocities. Infact, we inverted the location of 92 seamounts from8 different copolar seamount trails (i.e. the Magel-lan, Anewetak, Ralik, Ratak, Wentworth, Line, Lil-iuokalani and Musicians seamount trails) and thelocal plate velocities derived from the Magellan andMusicians seamount trails. This ‘forced’ Euler polegives angular velocities that are comparable at the65% confidence level (MST D 0:502š 0:017; Musi-cians D 0:501 š 0:057º=Myr) and yields an average

angular velocity of 0:502 š 0:016º=Myr (SE) for thePacific plate. The Musicians seamount trail is nowless well fitted (angular distance D 84:19 š 0:19,SD), but the fit on the MST is significantly improved(angular distance D 57:90 š 0:56, SD). In this cal-culation we ignored the less well-constrained localvelocity derived from the Line Islands (66:3 š 24:5mm=yr; [17]). We also employed an age-progres-sion for the MST in which the oldest measured agesfor Vlinder (i.e. NW pedestal) were omitted fromthe calculation on basis of morphological arguments.Significantly lower local plate velocities (26.1–26.4mm=yr) would be derived when using the oldestmeasured ages for the studied MST guyots. Recal-culation of the Euler pole model using these lowervelocities only adds to the discrepancy in the calcu-lated angular velocities of Pacific plate rotation andresults in a less well-defined ‘forced’ Euler pole withan increased variance.

The ‘forced’ Euler pole (29ºN–297ºE) is signifi-cantly different compared to the ‘best-fit’ Euler pole(40º340N–259º470E; variance D 0.10) based exclu-sively on the 92 seamount locations [24]. There maybe three different explanations for this discrepancy:(1) the azimuths of the seamount trails are re-ori-entated by geological processes other than hotspotvolcanism, (2) an intraplate boundary formed atthis time, or (3) the observed age progressions inthe Magellan and Musicians seamount trails do notonly represent the local plate velocities due to therelative movement of hotspots. These explanationshave major implications for the hotspot hypothesisand the derivation of absolute plate motion fromhotspot trails; either hotspot volcanism is non-lin-ear, the hotspots are non-copolar or the hotspotsare non-fixed with respect to one another. The firstexplanations appear unlikely, because these geologi-cal processes should have consistently disturbed theorientation of all modeled seamount trails causingthe observed ¾35º shift from the ‘best-fit’ to the‘forced’ Euler pole. Local disturbances induced by,for example, the presence of active fracture zonesystems in the oceanic basement [7,39] cannot causesuch global effects. Furthermore, intraplate bound-aries were not formed within the Pacific plate duringthe 100–80 Ma stage pole, as based on the magneticanomaly maps [36]. On the contrary, the relativemovement of mantle plumes themselves does not

A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68 65

Table 2Modeled velocity of the Magellan and Musicians hotspots with respect to ambient mantle

Stage poles MST hotspot Musicians hotspot

Reference Lat. Lon. Controlled by Plate velocity Hotspot velocity Plate velocity Hotspot velocity

Duncan and Clague, 1985 [10] 36.00 284.00 azimuth 55.6 š 6.4 8.0 š 6.6 47.7 š 1.6 �8.0 š 6.6Engebretson et al., 1985 [11] 48.00 299.00 azimuth 54.5 š 6.2 6.9 š 6.4 48.7 š 1.6 �7.1 š 6.6Wessel and Kroenke, 1997 [13] 18.90 319.50 azimuth 35.7 š 4.2 �11.9 š 4.4 74.4 š 2.5 18.6 š 6.8Koppers, 1998 [24] 40.60 259.80 azimuth 70.9 š 8.1 23.3 š 8.3 37.4 š 1.2 �18.3 š 6.5Koppers, 1998 [24] 29.00 297.00 azimuth and 47.5 š 5.4 �0.1 š 5.7 55.9 š 1.8 0.1 š 6.6

velocity

Hotspot velocity components (in mm=yr) represent maximum estimates of the modeled hotspot motion parallel to the direction of platemotion. These velocities are the calculated differences between the modeled local plate velocities (see Table) and the observed local platevelocities for the MST .47:6š 1:6 mm=yr) and the Musicians seamount trail .55:8š 1:6 mm=yr). All errors are standard errors.

require the 35º shift in the location of the Euler pole.Such movements induce higher or lower apparentlocal plate velocities provided that hotspot motion issubparallel to plate motion; the general linear char-acter of hotspot trails and their age progressions willbe maintained at time scales of individual stage poles(10–20 Myr). With this model and knowing the ageprogressions for two copolar seamount trails, we areable to calculate the relative motion between theirhotspots. For example, we may permit the Musicianshotspot to move in the mantle with respect to a fixedMST hotspot. When accepting the ‘best-fit’ Eulerpole (40º340N–259º470E), the Musicians hotspot re-quires a relative velocity component of 18:3 š 6:5mm=yr opposite in direction of the local plate veloc-ity (37:4š 1:2 mm=yr, SE) as based on the observedage progression of 55:8 š 6:4 mm=yr in the Musi-cians seamount trail. Vice versa, the MST hotspotwould require a velocity component of 23:3 š 8:3mm=yr in the direction of the local plate velocity(70:9 š 8:1 mm=yr, SE). In Table 2 we listed themaximum velocity components for relative hotspotmotion, based on published stage poles and twoscenarios: (1) fixed MST vs. non-fixed Musicianshotspot, and (2) non-fixed MST vs. fixed Musicianshotspot. The calculated velocity components are de-pendent on the chosen Euler poles and the quoteduncertainties are dominated by the large (analytical)uncertainty in the age progression of the Musiciansseamount trail (11.4%). However, we alternativelymay interpret the 40Ar=39Ar ages of the MST basaltsto represent the younger limit of shield-building (i.e.the alkalic post-shield phase) and that shield-build-ing actually started up to 2 Myr before these basalts

erupted. This time range appears conservative whenconsidering the 0.5–1.5 Myr duration of tholeiiticshield-building for the more voluminous guyots inthe Hawaiian trail [31]. Based on the Euler pole ofWessel and Kroenke [13] and assigning an arbitraryduration of 2 Myr (instead of <1 Myr in Fig. 5B)to the MST shield-building phase still yields a sig-nificantly different angular velocity for the Pacificplate (0:690 š 0:060º=Myr, SE) when compared tothat calculated from the Musicians seamount trail(0:520 š 0:059º=Myr, SE). This calculation, there-fore, adds to the robustness of our model calcula-tions and the inferences on the observed discrepancybetween the local plate velocities and the ‘best-fit’Euler pole.

5.4. Hotspot origin in the SOPITA mantle source?

Backtracking of seamounts to their original po-sition of formation can be performed if the agesof these seamounts and the stage pole models ofabsolute plate motion are known. The success ofsuch modeling may be limited when hotspots movewith respect to one another. If the potential move-ment of hotspots is ignored, the current stage polemodels [7,9–13] reflect the ‘time-integrated’ finiterotations of (sub)parallel plate and hotspot motioncf. [6]. In that case the reconstructions yield whatthe location of the Magellan hotspot would be today,taking into account both plate motion and hotspotdrift. These reconstructions, thus, do not yield the‘ancient’ location of the Magellan hotspot in theSOPITA mantle when the MST formed, 100–80Myr ago. For truly fixed hotspots these ‘ancient’

66 A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68

and ‘present-day’ hotspot locations coincide. How-ever, the overall impact of hotspot motion over thelast 140 Myr is neither clear nor in quantitativeagreement with absolute Pacific plate motion. Wewill, therefore, adopt the previously published stagepole models to illustrate the typical uncertainties inthe backtrack reconstructions of the ‘present-day’hotspot locations.

In Fig. 6 the backtracked positions of the MSThotspot (Vlinder, Pako and Ioah guyot) and Ita MaiTai guyot are plotted with respect to the currently-active SOPITA hotspots. Despite the large variationin the used Pacific plate stage pole models [7,9–13], the MST hotspot would presently be locatedbetween the Samoa, Rarotonga and Society hotspots.This is in agreement with the observed Sr–Nd–Pbisotopic signatures that suggest a close resemblancewith these hotspots and an affinity for EMI (seeEPSL Online Background Dataset 2). However, wecannot resolve which currently-active hotspot mostclosely resembles the MST hotspot: (1) the isotopicsignatures of the Samoa, Rarotonga and Societyhotspots are too similar, (2) we have no compellingevidence that these hotspots have been constantlyactive over the last 100 Myr, and (3) the differ-ent stage pole models yield considerably differenthotspot locations (¾1000 km) for the MST. In addi-tion, the SOPITA and WPSP regions typically dis-play the presence of short and discontinuous hotspottrails (<20 Myr) rather than of long and continu-ous hotspot trails (>65 Myr) such as the Hawaiian–Emperor seamount trails [40]. We may, therefore,infer that the MST is linked to the SOPITA super-plume province as a whole [24,41,42], but that itshotspot volcanism was associated with the presenceof short-lived plumelets in the south Pacific mantleduring the 100–80 Ma stage pole.

6. Summary and conclusions

The Magellan Seamount Trail (MST) exhibits ahighly linear 40Ar=39Ar age progression for Vlinder,Pako and Ioah. This translates into a local Pacificplate velocity of 47:6 š 1:6 mm=yr and suggests a

2 URL: http:==www=elsevier.nl=locate=epsl, mirror site:http:==www=elsevier.com=locate=epsl

Cretaceous hotspot origin for the MST. Plate tec-tonic reconstructions have located this ancient MSThotspot between the currently-active Samoa, Raro-tonga and Society hotspots of the SOPITA mantleanomaly. This result is compatible with the observedsimilarity in Sr–Nd–Pb isotopic signatures of basaltsfrom the currently-active SOPITA hotspots and theCretaceous MST guyots, indicating enriched mantlesources with an EMI affinity.

There are three clear deviations from age pro-gressive hotspot volcanism in the MST: (1) the NWextension of Vlinder is 4–7 Myr older than expecteddelineating an independent volcanic pedestal, (2) anuneroded, post-erosional volcanic cone on top of thesummit platform of Vlinder was formed at least 20–30 Myr after drowning, and (3) Ita Mai Tai guyot is34–36 Myr older than expected. Both the latter twovolcanoes should have been produced from a magmasource other than the MST hotspot. These deviationsindicate that an in-depth morphological analysis incombination with multiple 40Ar=39Ar age determi-nations from multiple dredge sites is required forreliable constraints on age progressions in seamounttrails.

A contradiction arises when comparing the ob-tained age progression of the MST (47:6 š 1:6mm=yr) with the copolar Musicians seamount trail(55:8 š 6:4 mm=yr) within the limits of analyticaluncertainty. The difference in local plate velocitywas found to be incompatible with any of the pub-lished Euler poles for the 100–80 Ma stage polewhen presuming the fixed hotspot hypothesis. Wepursued two options: (1) acceptance of a ‘forced’Euler pole (29ºN–297ºE) obeying the fixed hotspothypothesis using the age progressions and azimuthsof the studied hotspot trails, or (2) acceptance ofa ‘best-fit’ pole (40º340N–259º470E) using the az-imuths of the studied hotspot trail exclusively. Inthe first option, the angular velocity of the Pacificplate during the 100–80 Ma stage pole was calcu-lated at 0:502 š 0:017º=Myr. In the second option,the Euler pole was found ¾35º different in great cir-cle distance from the pole obeying the fixed hotspothypothesis. In this case the observed age progres-sions could be reconciled with the ‘best-fit’ Eulerpole when allowing for relative movement of themantle plumes forming the Magellan and Musiciansseamount trails. It was modeled that the maximum

A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68 67

velocity component parallel to the line of age pro-gression could be as much as 23 mm=yr for thesehotspots — when assuming one fixed hotspot.

Acknowledgements

We thank Jason Phipps Morgan and Jason Mor-gan for many discussions on absolute plate motions.Dave Sandwell’s help with GMT was greatly ap-preciated. Jim Hein and Alice Davis (USGS) andY. Pushcharovsky (USSR Academy of Sciences) arethanked for providing key samples to this study.Gareth Davies, Gary Acton and an anomynousreviewer are thanked for their review comments.Contribution 98.07.03 of the Netherlands ResearchSchool of Sedimentary Geology (NSG). Financialsupport by the Netherlands Foundation of Earth Sci-ences Research (GOA-NWO: 750.60.005) and theNational Science Foundation (NSF-OCE: 91-02183).This paper serves as a part of the Ph.D. thesis ofAAPK. [RV]

References

[1] W.J. Morgan, Deep mantle convection plumes and platemotions, Am. Assoc. Pet. Geol. Bull. 56 (1972) 42–43.

[2] R.G. Gordon, C.D. Cape, Cenozoic latitudinal shift of theHawaiian hotspot and its implications for true polar wander,Earth Planet. Sci. Lett. 55 (1981) 37–47.

[3] W.W. Sager, U. Bleil, Latitudinal shift of Pacific hotspotsduring the late Cretaceous and early Tertiary, Nature 326(1987) 488–490.

[4] S.C. Cande, C.A. Raymond, J. Stock, W.F. Haxby, Geo-physics of the Pitman fracture zone and Pacific–Antarcticplate motions during the Cenozoic, Science 270 (1995)947–953.

[5] J.A. Tarduno, J. Gee, Large-scale motion between Pacificand Atlantic hotspots, Nature 378 (1995) 477–480.

[6] B. Steinberger, R.J. O’Connell, Changes of the Earth’srotation axes owing to advection of mantle density hetero-geneities, Nature 387 (1997) 169–173.

[7] D. Epp, Possible perturbations to hotspot traces and impli-cations for the origin and structure of the Line Islands, J.Geophys. Res. 89 (1984) 11273–11286.

[8] J. Phipps Morgan, W.J. Morgan, E. Price, Hotspot meltinggenerates both hotspot volcanism and a hotspot swell?, J.Geophys. Res. 100 (1995) 8045–8062.

[9] P. Lonsdale, Geography and history of the Louisvillehotspot chain in the Southwest Pacific, J. Geophys. Res.93 (1988) 3078–3104.

[10] R.A. Duncan, D.A. Clague, Pacific plate motion recordedby linear volcanic chains, in: A.E.A. Nairn, F.L. Stehli, S.Uyeda (Eds.), The Ocean Basins and Margins, The PacificOcean 7A, Plenum Press, New York, 1985, pp. 89–121.

[11] D. Engebretson, A. Cox, R. Gordon, Relative motions be-tween oceanic and continental plates in the Pacific basin,Geol. Soc. Am. Spec. Pap. 206, 1985.

[12] L.J. Henderson, Motion of the Pacific plate relative to thehotspots since the Jurassic and model of oceanic plateausof the Farallon plate, Ph.D. thesis, Northwestern University,USA, 1985.

[13] P. Wessel, L. Kroenke, A geometric technique for relocatinghotspots and refining absolute plate motions, Nature 387(1997) 365–369.

[14] A.S. Davis, M.S. Pringle, L.-B.G. Pickthorn, D.A. Clague,W.C. Schwab, Petrology and age of alkalic lava from theRatak Chain of the Marshall Islands, J. Geophys. Res. 94(1989) 5757–5774.

[15] J.M. Lincoln, M.S. Pringle, I. Premoli Silva, Early andLate Cretaceous volcanism and reef-building in the Mar-shall Islands, in: M.S. Pringle, W.W. Sager, W.V. Sliter, S.Stein (Eds.), The Mesozoic Pacific: Geology, Tectonics, andVolcanism, Monograph 77 (1993) 279–305, Am. Geophys.Union, Washington, D.C.

[16] M.S. Pringle and G.B. Dalrymple, Geochronological con-straints on a possible hot spot origin for Hess Rise andthe Wentworth Seamount Chain, in: M.S. Pringle, W.W.Sager, W.V. Sliter and S. Stein (Eds.), The Mesozoic Pa-cific: Geology, Tectonics, and Volcanism, Monograph 77(1993) 279–305, Am. Geophys. Union, Washington, D.C.

[17] M.S. Pringle, Age progressive volcanism in the MusiciansSeamounts: a test of the hot spot hypothesis for the lateCretaceous Pacific, in: M.S. Pringle, W.W. Sager, W.V.Sliter S. Stein (Eds.), The Mesozoic Pacific: Geology, Tec-tonics, and Volcanism, Monograph 77 (1993) 279–305,Am. Geophys. Union, Washington, D.C.

[18] S.O. Schlanger, M.O. Garcia, B.H. Keating, J.J. Naughton,W.W. Sager, J.A. Haggerty, J.A. Philpotts, R.A. Duncan,Geology and geochronology of the Line Islands, J. Geo-phys. Res. 89 (1984) 11261–11272.

[19] J.R. Wijbrans, M.S. Pringle, A.A.P. Koppers, R. Scheveers,Argon geochronology of small samples using the Vulkaanargon laserprobe, Proc. K. Ned. Akad. Wet. 98 (1995) 185–218.

[20] A.A.P. Koppers, H. Staudigel, J.R. Wijbrans, Datingcrystalline groundmass separates of altered Cretaceousseamount basalts by the 40Ar=39Ar incremental heatingtechnique, Chem. Geol., submitted.

[21] J.R. Taylor, An Introduction to Error Analysis, UniversityScience Books, Mill Valley, CA, 1982, 270 pp.

[22] D. York, Least squares fitting of a straight line with corre-lated errors, Earth Planet. Sci. Lett. 5 (1969) 320–324.

[23] H.P. Johnson, R.L. Carlson, Variation of sea floor depthwith age: a test of models based on drilling results, Geo-phys. Res. Lett. 19 (1992) 1971–1974.

[24] A.A.P. Koppers, 40Ar=39Ar geochronology and isotope geo-chemistry of the West Pacific seamount province: impli-

68 A.A.P. Koppers et al. / Earth and Planetary Science Letters 163 (1998) 53–68

cations for Pacific plate motion and chemical geodynam-ics, Ph.D., Vrije Universiteit Amsterdam, the Netherlands,1998, 263 pp.

[25] H. Staudigel, H.-U. Schmincke, The Pliocene SeamountSeries of La Palma=Canary Islands, J. Geophys. Res. 89(1984) 11195–11215.

[26] D.A. Swanson, W.A. Duffiled, R.S. Fiske, Displacement ofthe south flank of Kilauea volcano: the result of forcefulintrusion of magma into the rift zones, U.S. Geol. Surv.Prof. Pap. 963, 1976.

[27] M.P. Ryan, R.Y. Koyanagi, R.S. Fiske, Modeling the three-dimensional structure of magma transport systems: appli-cation to Kilauea volcano, Hawaii, J. Geophys. Res. 86(1981) 7111–7129.

[28] W.A. Duffield, L. Stieltjes, J. Varet, Huge landslide blocksin the growth of Piton de la Fournaise, La Reunion, andKilauea volcano, Hawaii, J. Volcanol. Geothermal Res. 12(1982) 147–160.

[29] D.J. Fornari, J.G. Morre, L. Calk, A large submarinesand–rubble flow on Kilauea volcano, Hawaii, J. Volcanol.Geothermal Res. 5 (1979) 239–256.

[30] R.J. Fleck, J.F. Sutter, D.H. Elliot, Interpretation of dis-cordant 40Ar=39Ar age-spectra of Mesozoic tholeiites fromAntarctica, Geochim. Cosmochim. Acta 41 (1977) 15–32.

[31] D.A. Clague, G.B. Dalrymple, T.L. Wright, F.W. Klein,R.Y. Koyanagi, R.W. Decker, D.M. Thomas, TheHawaiian–Emperor chain, in: E.L. Winterer, D.M. Hus-song, R.W. Decker (Eds.), The Eastern Pacific Ocean andHawaii, the Geology of North America, Geol. Soc. ofAmerica, Boulder, CO, 1989, pp. 187–287.

[32] M. Pringle, H. Staudigel, J. Gee, Jasper Seamount: sevenmillion years of volcanism, Geology 19 (1991) 363–368.

[33] Abdel-Monem and Gast, Age of volcanism of St. Helena,Earth Planet. Sci. Lett. 2 (1967) 415–418.

[34] R.A. Duncan, Age progressive volcanism in the New Eng-land seamounts and the opening of the Central AtlanticOcean, J. Geophys. Res. 89 (1984) 9980–9990.

[35] J.D. Woodhead, Temporal geochemical evolution in oceanicintra-plate volcanics: a case study from the Marquesas

(French Polynesia) and comparison with other hotspots,Contrib. Mineral. Petrol. 111 (1992) 458–467.

[36] M. Nakanishi, K. Tamaki, K. Kobayashi, Magnetic anomalylineations from late Jurassic to Early Cretaceous in thewest-central Pacific Ocean, Geophys. J. Int. 144 (1992)535–545.

[37] L.J. Abrams, R.L. Larson, T.H. Shipley, Y. Lancelot, Creta-ceous volcanic sequences and Jurassic oceanic crust in theEast Mariana and Pigafetta basins of the western Pacific,in: M.S. Pringle, W.W. Sager, W.V. Sliter, S. Stein (Eds.),The Mesozoic Pacific: Geology, Tectonics, and Volcan-ism, Monograph 77 (1993) 77–101, Am. Geophys. Union,Washington, D.C.

[38] M.S. Pringle, Radiometric ages of basaltic basement recov-ered at sites 800, 801, and 802, Leg 129, Western PacificOcean, in: R.L. Larson, Y. Lancelot (Eds.), Proc. ODP Leg129, 1992, pp. 389–404.

[39] R.A. Duncan, M.T. McCulloch, H. Barszus, D.R. Nelson,Plume versus lithosphere sources for melts at Ua Pou,Marquesas Islands, Nature 322 (1986) 534–538.

[40] M.S. Pringle, A.A.P. Koppers, H. Staudigel, J.R. Wijbrans,Cretaceous Pacific volcanism: distribution in space, time,and source composition, U.S. Geol. Surv. Circ. 1107 (1994)256.

[41] A.A.P. Koppers, H. Staudigel, D.M. Christie, J.J. Dieu,M.S. Pringle, Sr–Nd–Pb Isotope Geochemistry of Leg 144West Pacific guyots: implications for the geochemical evo-lution of the ‘SOPITA’ mantle anomaly, in: J.A. Haggerty,I. Premoli Silva, F. Rack, M.K. McNutt (Eds.), Proc. ODPLeg 144, 1995, pp. 535–545.

[42] H. Staudigel, K.-H. Park, M. Pringle, J.L. Rubenstone,W.H.F. Smith, A. Zindler, The longevity of the South Pa-cific Isotope and Thermal Anomaly, Earth Planet. Sci. Lett.102 (1991) 24–44.

[43] W.H.F. Smith, D. Sandwell, Predicted bathymetry. Newglobal seafloor topography from satellite altimetry, Eos 315(1996) 37–46.

[44] P. Wessel, W.H.F. Smith, New version of the Generic Map-ping Tools released, Eos 76 (1995) 329.