Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....1402b&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #1402
Astronomy and Astrophysics
Astronomy
Scientific paper
The fundamentals of present-day Pacific tectonics are observed to be: its N/S mirror-symmetry about the Equator, displayed by the major transforms; its E/W asymmetry, represented by the western motion of the world's largest plate, originating in the eastern Equatorial Pacific; and correspondingly, development of the globally most voluminous subduction, at the western Pacific margin. The configuration seen at present is maintained at a fundamental level. The maximum in convective upwelling develops as coalescing plumes in the Galapagos region in the eastern Pacific. This has been found (Lonsdale 1988; McGuire and Hilde 2002; Chen and Lin 2002) to produce steady westward propagation of the Nazca/Cocos axis. Continually renewed, it determines the orientation and locus of a quasi-stationary EPR, centered on the Equator. Magnetic dating of boundaries in satellite gravity images records the Cenozoic history of the EPR, namely re-orientation in consequence of slow counter-clockwise re-orientation of the Equator. Relative to the present, during Maastrichtian times both Equator and plate motion were aligned WNW, recorded paleomagnetically and by features in the western, older part of the Pacific crust. Material subducted at that time accumulated principally beneath the SE Asia margin. Its slow heating is believed to play a role in the deep-seated activity and back-arc spreading associated with latter-day convergence in that region. The mechanism primarily responsible for the Pacific regime may be that mantle convection is not immune, as is generally tacitly supposed, to the minute westward tilt (c. 0.36°) under which it takes place. The latter, now astronomically quantifiable without tidal identification, represents the attraction component of water and solid-Earth masses which averaged over unit day lags the direction of purely geocentric g. Under gravity minutely E/W asymmetric, convection as always promoting the most efficient dissipative configuration, favors disproportionately large surface-west displacement, maximum at the contemporary Equator (=west limb of EPR upwelling). Some conclusions are a), that it is no longer adequate to model global convection assuming that angular momentum is conserved internally; in reality a considerable part is exported, here measured by expansion of the lunar orbit; and b), that the tectonics of an Earth simultaneously under vigorous convection and in asynchronous rotation relative to the mass center of Kuiper's Earth-Moon double planet, differs fundamentally from the regime developing within a fictitious isolated planet.
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