Tectonics of the southern escarpment of Ishtar Terra on venus from observations of morphology and gravity

Abstract

Maxima of calculated topographical line-of-sight (LOS) gravity attractions caused by Ishtar Terra are shifted to the north with respect to the measured LOS free air gravity maxima south of the highland. This implies a tendency to isostatic compensation of central Ishtar and mass surpluses at the continental border and the southern forelands. The following scenario is compatible with the interpretation of the gravity anomalies and morphological features. Relative motions of the lowland Sedna Planitia against continental Ishtar Terra have caused buckling and flat subduction of the lowland lithospheric material. (Deep subduction can be ruled out by thermal reasons). The free air gravity high is modelled by surplus masses of the buckling and of the high density subducting plate. Evidence for this is given by several compressional features like Ut and Vesta Rupes at the southern continental border and ridges at the SW-flanks of Maxwell Montes. It is further supported by several possible volcanic-tectonic depressions located in the southern part of Ishtar. This local interpretation does not necessarily imply the existence of global plate tectonics on Venus like on Earth, but at least limited horizontal movements of the Venusian lithosphere seem to be likely. This result shows that plate recycling must be considered for heat transfer through the lithosphere beside conduction and hot spot volcanism.