| Abstract: | Since the utilization of hotspots as a frame of reference (Morgan, 1971), the suggestion that some or all hotspots move with respect to each other has been proposed (e.g. Molnar and Atwater, 1973). The stakes in this long-standing debate are high. In one case, hotspots can serve as a reference useful for a wide range of studies, including those of past climate, which require knowledge of the paleoposition of continental and ocean plates. In another, some hotspot tracks primarily record motion of the underlying mantle, invalidating not only some plate reconstructions, but also measures of true polar wander (TPW), the theoretical motion of the entire Earth with respect to the spin axis (Goldreich and Toomre, 1969). The Pacific Ocean, with its striking examples of hotspot-related topography, offers many opportunities for tests of hotspot fixity. Basalt colatitude data from Ocean Drilling Program sites (Resolution and MIT Guyots) show little latitudinal motion for the mid-Cretaceous (130-95 Ma) Pacific plate. When compared to data from North America and the Atlantic, these Pacific data suggest relatively rapid (34 +/- 8 mm yr-1) motion of the Atlantic hotspots relative to Pacific hotspots (Tarduno and Gee, 1995). The total offset amounts to a systematic reconstruction error of ~1300 km in the Atlantic realm. Late Cretaceous basalt colatitudes from the Hawaiian-Emperor chain (Detroit Seamount) suggest southward motion of the Hawaiian hotspots since 81 Ma (Tarduno and Cottrell, 1997), a result supported by recent investigations during Ocean Drilling Program Leg 197 (Tarduno et al., in press). Data from both time intervals indicate that cumulative offsets of the Earth relative to the spin axis during the past 130 million years have been less than 5o (Cottrell and Tarduno, 2000; Tarduno and Smirnov, 2001). Instead, these new analyses of Pacific and other global data indicate large scale, episodic motion between groups of hotspots. The mid-Cretaceous motion is of special interest because it correlates with major volcanism on the Indian and Pacific plates, including formation of the Kerguelen and Ontong Java Plateaus (Tarduno et al., 1991), consistent with rapid mantle convection.
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Tarduno, J.A., Duncan, R.A., and Scholl, D., and Shipboard Scientific Party, Initial Reports Ocean Drilling Program, Leg 197, in press. |