Other
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.v12b0577h&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #V12B-0577
Other
5420 Impact Phenomena (Includes Cratering), 8149 Planetary Tectonics (5475), 8414 Eruption Mechanisms, 8450 Planetary Volcanism (5480)
Scientific paper
The distribution of hotspots on the Earth has a distinct antipodal character, which has previously been shown to be statistically significant (p<0.05) for one long (117) and two short ( ˜40-50) hotspot lists [1]. One possible mechanism for the creation of antipodal hotspot pairs is the focusing of seismic energy from a major bolide impact at its antipode. Reflected tensile body waves would converge along the axis beneath the antipode possibly causing fracturing to depth [2], and the greatest focusing of seismic energy from fundamental-mode surface waves has been shown to occur in the antipodal asthenosphere where seismic attenuation is greatest [3]. A major impact, therefore, might produce hotspot volcanism at the impact site (particularly on oceanic crust [4]), and produce flood basalts and a second hotspot from the focused disruption at its antipode. In this study, three predictions of this model are tested. (1) All `primary' hotspots on Earth initially had near-antipodal hotspots or impact structures. (2) Volcanic activity at both antipodal hotspots of a given pair began at about the same time. And (3), antipodal hotspot pairs have only one flood basalt province and/or impact site between them. A list of 54 primary hotspots is constructed from five commonly cited short hotspot lists. Of these, 28 form near-antipodal pairs mostly within conservative limits for hotspot drift rates from initial antipodality ( ˜20 mm/yr). Of the remaining 26, 14 are nearly antipodal to `secondary' hotspots from the long (117) hotspot list [5] or other volcanic features. Another primary hotspot (Comores, ˜10 Ma) was antipodal to the proposed Ewing impact structure ( ˜7-11 Ma) in the Pacific Ocean. Many antipodal hotspots have similar ages (e.g. Galápagos, ˜85 Ma; Nikitin, ˜80 Ma), and no contradictions to this prediction have been found. Only two primary hotspots (Hawai`i, Louisville) have continental antipodal sites where no volcanic features exist. These two hotspots, however, are among the oldest (>100 Myr) and could have drifted quite far from antipodality with their opposite hotspots. The remaining 9 primary hotspots have antipodes in the Pacific Ocean where submerged hotspots or impact structures could yet be identified. All hotspots antipodal to those associated with flood basalt provinces or formed in continental crust are, or were, in oceanic crust suggesting links between major deep-ocean impacts, greater impact/seismic efficiency, and the creation of antipodal hotspot pairs. In general, `spotless' areas [5] occur opposite to continental masses, and no hotspot volcanism is found at or antipodal to known continental impact structures. [1] Rampino and Caldeira, GRL (1992) 2011; [2] Schultz and Gault, The Moon (1975) 159; [3] Boslough et al., GSA Spec. Pap. 307 (1996) 541; [4] Roddy et al., Int. J. Impact Eng. (1987) 525; [5] Vogt, JGR (1981) 950.
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