S U M M A R YSatellite-measured regional gravity and terrain elevation data are becoming increasingly available for improving our understanding of the geological properties and history of the Earth, Moon, Mars, Venus and other planets. In assessing the geological significance of the existing and growing volumes of these regional data sets, there is great need for computing theoretical anomalous gravity fields from geological models in spherical coordinates. In the present study, we explicitly develop the elegant Gauss-Legendre quadrature formulation for numerically modelling the complete gravity effects (i.e. potential, vector and tensor gradient fields) of the spherical prism. As an application, we investigate the gradient components of the isostatic gravity anomalies that the upcoming Gravity Field and Steady State Ocean Circulation Explorer (GOCE) satellite mission is likely to map over a large tectonically active region of the Middle East centred on Iran.
New details on the east Antarctic gravity field from the Gravity Recovery and Climate Experiment (GRACE) mission reveal a prominent positive free‐air gravity anomaly over a roughly 500‐km diameter subglacial basin centered on (70°S, 120°E) in north central Wilkes Land. This regional inverse correlation between topography and gravity is quantitatively consistent with thinned crust from a giant meteorite impact underlain by an isostatically disturbed mantle plug. The inferred impact crater is nearly three times the size of the Chicxulub crater and presumably formed before the Cretaceous formation of the east Antarctic coast that cuts the projected ring faults. It extensively thinned and disrupted the Wilkes Land crust where the Kerguelen hot spot and Gondwana rifting developed but left the adjacent Australian block relatively undisturbed. The micrometeorite and fossil evidence suggests that the impact may have occurred at the beginning of the greatest extinction of life on Earth at ∼260 Ma when the Siberian Traps were effectively antipodal to it. Antipodal volcanism is common to large impact craters of the Moon and Mars and may also account for the antipodal relationships of essentially half of the Earth's large igneous provinces and hot spots. Thus, the impact may have triggered the “Great Dying” at the end of the Permian and contributed to the development of the hot spot that produced the Siberian Traps and now may underlie Iceland. The glacial ice up to a few kilometers thick that has covered the crater for the past 30–40 Ma poses formidable difficulties to sampling the subglacial geology. Thus, the most expedient and viable test of the prospective crater is to survey it for relevant airborne gravity and magnetic anomalies.
Many of the outlet glaciers in Greenland overlie deep and narrow trenches cut into the bedrock. It is well known that pronounced topography intensifies the geothermal heat flux in deep valleys and attenuates this flux on mountains. Here we investigate the magnitude of this effect for two subglacial trenches in Greenland. Heat flux variations are estimated for idealized geometries using solutions for plane slopes derived by Lachenbruch (1968). It is found that for channels such as the one under Jakobshavn Isbræ, topographic effects may increase the local geothermal heat flux by as much as 100%.
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