Elysium Region, Mars: Tests of Lithospheric Loading Models for the Formation of Tectonic Features

The. ce.c.c•ncl largest volcanic province on Mar• lies in the E!?ium region I•ike the larger Tharsis province, Elysium is marked by a topographic rise and a broad free air gravity anomaly and also exhibits a complex assortment of tectonic and volcanic features. We test the hypothesis that the tectonic features in the Elysium region are the product of stresses produced by loading of the Martian lithosphere. We consider loading at three different scales: local loading by individual volcanoes, regional loading of the lithosphere from above or below, and quasi-global loading by Tharsis. A comparison of flexural stresses with lithospheric strength and with the inferred maximum depth of faulting confirms that concentric graben around Elysium Mons can be explained as resulting from local flexure of an elastic lithosphere about 50 km thick in response to the volcano load. Volcanic loading on a regional scale, however, leads to predicted stresses inconsistent with all observed tectonic features, suggesting that loading by widespread emplacement of thick plains deposits was not an important factor in the tectonic evolution of the Elysium region. A number of linear extensional features oriented generally NW-SE may have been the result of flexural uplift of the lithosphere on the scale of the Elysium rise. The global stress field associated with the support of the Tharsis rise appears to have influenced the development of many of the tectonic features in the Elysium region, including Cerberus Rupes and the systems of ridges,in eastern and western Elysium. The comparisons of stress models for Elysium with the preserved tectonic features support a succession of stress fields operating at different imes in the region. While the order in which those stress fields operated cannot be determined from present geological observations, thermal and mechanical arguments favor the hypothesis that any flexural uplift of the lithosphere by a mantle thermal anomaly preceded or occurred contemporaneously with emplacement of the largest volcanic loads.