Other
Scientific paper
Oct 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989e%26psl..95...73a&link_type=abstract
Earth and Planetary Science Letters, Volume 95, Issue 1-2, p. 73-84.
Other
5
Scientific paper
Using depths to formation tops from 480 wells, changes in shape of the Michigan Basin during the Phanerozoic are determined. Flexural rigidity of the lithosphere is then estimated for several time intervals by assuming that changes in shape were caused by deflection of an elastic plate subjected to an axisymmetric load. It is found that the flexural rigidity generally increased over time, from less than 1022 N m early in the basin's history to more than 1023 N m late in the basin's development. This increase in rigidity is attributed to cooling and thickening of the elastic portion of the lithosphere as the basin was subsiding. Low flexural rigidity early in the basin's history indicates that the lithosphere was probably rejuvenated (heated, thinned, and possibly uplifted) prior to basin subsidence. The location of the load remained approximately fixed over time.
The rejuvenation process is investigated using a one-dimensional finite-difference thermal model in which a 142-km plate is temporarily heated from below. Taking the depth to the 450°C isotherm to be the effective elastic thickness of the lithosphere, rigidity predicted by the thermal model is consistent with the observed increase in rigidity over time. Furthermore, phase changes produced by heating during thermal rejuvenation, combined with the predicted thermal contraction following rejuvenation, explain the two episodes of subsidence observed in the Michigan Basin. We conclude that the lithosphere in this area was rejuvenated approximately 500 m.y. ago. As the lithosphere cooled, it thickened; it also contracted and subsided. Temperatures near the surface of the crust apparently were not raised sufficiently by lithospheric rejuvenation to alter the Keweenawan and older radiometric and paleomagnetic dates of basement rocks.
Current address: 1615 California, Suite 705, Denver, CO 80202, U.S.A.
Ahern Judson L.
Dikeou Panayes J.
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