Plate-scale potential-energy distributions and the fragmentation of ageing plates

Details Plate-scale potential-energy distributions and the fragmentation of ageing plates Plate-scale potential-energy distributions and the fragmentation of ageing plates

Aug 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.126..143s&link_type=abstract

Earth and Planetary Science Letters (ISSN 0012-821X), vol. 126, no. 1-3, p. 143-159

Physics

Geophysics

7

Earth (Planet), Fragmentation, Geoids, Lithosphere, Mid-Ocean Ridges, Ocean Bottom, Plates (Tectonics), Potential Energy, Tectonics, Continental Shelves, Geophysics, Mathematical Models, Ocean Models, Planetary Evolution, Stress Distribution

Scientific paper

Geoid anomalies associated with mid-ocean ridge systems and a number of continental margins imply that, on the scale of individual plates, the old ocean lithosphere represents a gravitational potential energy sink. Since lateral variations in potential energy contribute to deviatoric stresses in the lithosphere, the changing potential-energy distributions in individual plates associated with the growth and ageing of the oceanic lithosphere may be expected to result in changes in the intraplate stress field. Analytical models for simple plate geometries using lithospheric density models consistent with small positive (+6 m) geoid anomalies across continental margins show that the growth of oceanic lithospheric over a period of 200 Ma may contribute to a decline in the mean plate potential energy bar-U(sub p) of about -1 x 10(exp 12) N/m and thus contribute a mean extensional stress difference (bar-sigma(sub zz) - bar-sigma(sub xx)) in continental lithosphere of up to about 8 MPa (averaged over a 125 km thick lithosphere). These estimates are sensitive to the assumed mean continental potential energy bar-U(sub c), about which there is some uncertainty. For higher bar-U(sub c), approaching that of the mid-ocean ridges (U(sub MOR)), the net decline in bar-U(sub p) may be as much as -1.7 x 10(exp 12) N/m, whereas for significantly lower bar-U(sub c), approaching that of old ocean lithosphere, plate growth may increase bar-U(sub p) transiently by up to 2.7 x 10(exp 12) N/m, leading to compression in the continents. In the African and Antarctic plates the ageing of the ocean lithosphere since the late Jurassic is estimated to have contributed to a decline in bar-U(sub p) of about -0.6 x 10(exp 12) and -0.95 x 10(exp 12) N/m respectively, contributing a mean stress difference of about 5 MPa and 7.5 MPa in the respective continents. The predicted stress changes associated with ageing of the oceanic lithosphere may provide an important contribution to the stress fields that eventually lead to the fragmentation of ageing plates.

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