ELSEVIER Earth and Planetary Science Letters 170 (1999) 105±117 www.elsevier.com/locate/epsl Are the Paci®c and Indo±Atlantic hotspots ®xed? Testing the plate circuit through Antarctica Vic DiVenere a,c,Ł,DennisV.Kentb,c a Department of Earth and Environmental Science, C.W. Post Campus, Long Island University, Brookville, NY 11548, USA b Department of Geological Sciences, Rutgers University, Piscataway, NY 08854-8066, USA c Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA Received 10 December 1998; revised version received 14 April 1999; accepted 16 April 1999 Abstract It is often assumed that hotspots are ®xed relative to one another and thus constitute a global reference frame for measuring absolute plate motions and true polar wander. But it has long been known that the best documented hotspot track, the Hawaiian±Emperor chain, is inconsistent with the internally coherent tracks left by the Indo±Atlantic hotspots. This inconsistency is due either to unquanti®ed motions within the plate circuit linking the Paci®c with other plates, for example, between East and West Antarctica, or relative motion between the Hawaiian±Emperor and Indo±Atlantic hotspots. Analysis of recent paleomagnetic results from Marie Byrd Land in West Antarctica con®rms that there has been post-100 Ma motion between West Antarctica (Marie Byrd Land) and East Antarctica. However, incorporation of this motion into the plate circuit does not account for the Cenozoic hotspot discrepancy. Comparison of an updated inventory of Paci®c and non-Paci®c paleomagnetic data does not show a signi®cant systematic discrepancy, which, along with other observations, indicates that missing plate boundaries and other errors in the plate circuit play a relatively small role in the hotspot inconsistency. We conclude that most of the apparent motion between the Hawaiian±Emperor and Indo±Atlantic hotspots is real. The best-estimate average drift rate between these sets of hotspots is approximately 25 mm=yr since 65 Ma, ignoring errors in the plate circuit and a small contribution from Cenozoic motions between East and West Antarctica. 1999 Elsevier Science B.V. All rights reserved. Keywords: hot spots; plate tectonics; paleomagnetism; Hawaii; Antarctica 1. Introduction plumes are ®xed relative to one another and there- fore constitute a ®xed mantle reference frame. From During the 1960s and 1970s it became evident this ®xed reference frame the `absolute' motions of that the active ends of many volcanic island and lithospheric plates might be measured (e.g. [5,6]). seamount chains in the Paci®c and elsewhere lie However, tests of hotspot ®xity have shown a sig- above deep-seated sources of hot rising mantle mate- ni®cant discrepancy between the Hawaiian±Emperor rial [1,2]. Morgan [3,4] boldly proposed that mantle and Indo±Atlantic hotspots (e.g. [7,8]), although the discrepancy has often been ascribed to unquanti®ed Ł Corresponding author. Tel.: C1-516-299-2034; Fax: C1-516- plate motions especially within the Antarctic plate 299-3945; E-mail: [email protected] [9] or perhaps Paci®c plate [10]. In this paper we 0012-821X/99/$ ± see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S0012-821X(99)00096-5 106 V. DiVenere, D.V. Kent / Earth and Planetary Science Letters 170 (1999) 105±117 examine the relative ®xity of Indo±Atlantic versus of the hotspot beneath Kilauea, to about 43 Ma at Paci®c hotspots by testing the global plate circuit the bend between the Hawaiian and Emperor chains, through Antarctica. to about 81 Ma at the Detroit Plateau [14] in the north Paci®c near the Aleutian Trench (Fig. 1). This classic, well-de®ned hotspot track is the best choice 2. Testing hotspot ®xity for comparing Paci®c hotspots with Indo±Atlantic hotspots. Testing the ®xity of hotspots requires that the mo- Studies comparing Indo±Atlantic hotspot tracks tion of the hotspots relative to their overlying plates with the Hawaiian±Emperor hotspot track on the and the relative motions of the plates be known. Paci®c plate have found signi®cant discrepancies Hotspot to plate relative motions are determined between the predicted vs. actual hotspot track [7±10] by mapping the age progression of volcanic chains. (Fig. 1). The discrepancy is particularly large prior Plate to plate relative motions are determined from to the 43 Ma bend in the Hawaiian±Emperor chain, the rate and direction of sea¯oor spreading on inter- for example the offset between the predicted and vening midocean ridges as determined from marine actual position of the hotspot around 65 m.y. ago is magnetic anomalies and fracture zone trends. 14.5ë or about 1600 km. This discrepancy may be Under the assumption that all hotspots are ®xed in explained by either unquanti®ed plate motion within the mantle with respect to one another, the motion of the plate circuit linking the north Paci®c to the Indian a plate over a given hotspot can be considered the ab- and Atlantic oceans (e.g. [10]) or it may indeed be solute motion of the plate. If the motion of a second caused by relative motion between the Indo±Atlantic plate relative to the ®rst is known, then the absolute and Paci®c hotspots. motion of the second plate may be simply calculated as the sum of the motion of the ®rst plate relative to the hotspots plus the motion of the second plate 3. Possible sources for apparent inter-hotspot relative to the ®rst. Conversely, if the hotspots are motion ®xed, one should be able to predict prior positions of any current hotspot with respect to the second Assuming hotspots are ®xed, there are a number plate. Comparison of predicted positions versus ac- of possible sources of error within the plate circuit tual mapped hotspot tracks should indicate whether linking the northern Paci®c plate (containing the the hotspots have moved relative to one another. Hawaiian±Emperor hotspot track) with the Atlantic Studies of hotspots in the Atlantic and Indian and Indian Ocean plates (with their hotspot tracks) oceans have found no signi®cant motion (less than 5 that could account for the discrepancy in compar- mm per year) between these plumes [11,12]. Thus, isons of the Hawaiian±Emperor hotspot track with hotspots responsible for such widely distributed fea- the Indo±Atlantic hotspot framework. Two general tures as the New England Seamounts in the north At- categories are errors in sea¯oor spreading models lantic, Tristan da Cunha, Walvis Ridge, and the Rio and undocumented plate boundaries or intraplate de- Grande Rise in the south Atlantic, ReÂunion Island formation. and the Mascarene Plateau, Ninety East Ridge, the Chagos±Laccadive Ridge, and the Kerguelen Plateau 3.1. Sea¯oor spreading parameters in the Indian Ocean, may constitute a coherent Indo± Atlantic hotspot reference frame, at least within the Sea¯oor spreading models linking the African and error bounds. Indian plates to Antarctica and the Antarctic plate to The Hawaiian±Emperor chain of islands and the Paci®c are constrained by magnetic anomalies seamounts on the Paci®c plate is an important record and fracture zone trends. Molnar and Stock [7] and of hotspot±plate relative motion. It is quite long Acton and Gordon [10] estimated errors associated (over 5000 km), therefore yielding good spatial res- with the sea¯oor spreading data and concluded that olution, and it is documented with many dates along they were not suf®cient to account for the hotspot track [13] extending from the present-day position discrepancy. The north±south component of the es- V. DiVenere, D.V. Kent / Earth and Planetary Science Letters 170 (1999) 105±117 107 Fig. 1. A view of the Paci®c, showing the Hawaiian±Emperor chain and predicted positions of the Hawaiian±Emperor hotspot track assuming that this hotspot has been ®xed with respect to the Indo±Atlantic hotspots. timated error is approximately 2ë to 2.5ë, at least a from North America, Africa, India, and Australia factor of 5 less than the pre-bend (e.g. ca. 65 Ma) were evenly distributed forming a generally smooth discrepancy in the predicted hotspot positions. Di- synthetic apparent polar wander (APW) path. Cande Venere et al. [15] also argued against large errors et al. [8] presented newly acquired sea¯oor spreading in published Cretaceous sea¯oor spreading data be- data linking Antarctica with the Paci®c plate. These cause paleomagnetic poles transferred to Antarctica new data did not remove the hotspot discrepancy. 108 V. DiVenere, D.V. Kent / Earth and Planetary Science Letters 170 (1999) 105±117 Using their reconstruction parameters for the south- and seamount-based (Pac 76s) poles and is therefore west Paci®c there is a 14.5ë discrepancy between not statistically distinct from these. the predicted and actual hotspot position at 64.7 Ma The general agreement between the north Paci®c, (Suiko Seamount, Fig. 1). New Zealand (south Paci®c) and non-Paci®c pale- omagnetic poles suggests that the Late Cretaceous 3.2. Coherence of the Paci®c plate plate circuit is reasonably well known and contains no signi®cant systematic bias. Another proposal to account for the apparent in- There is some disagreement between younger Pa- ter-hotspot discrepancy is an undocumented Ceno- ci®c and non-Paci®c results. The 65 Ma and 57 zoic plate boundary between the north and south Ma Paci®c poles are far-sided by statistically sig- Paci®c. Gordon and Cox [16] and Acton and Gor- ni®cant 6ë to 10ë with respect to the non-Paci®c don [10] proposed a possible plate boundary some- APW path. This might suggest post 57 Ma `exten- where to the north of the Eltanin Fracture Zone sion' between the Paci®c and Indo±Atlantic.