Other
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....10300h&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #10300
Other
Scientific paper
We describe the morphology of a large and complex graben structure in western Thaumasia which was often ascribed to rifting by previous authors (the Thaumasia "rift" or TR). We consider possible fault geometries, determine extension, and discuss shortly possible models for its origin. The TR is characterized by a strong (half)graben asymmetry. The master fault system changes from the western border in the northern part to the eastern border in the southern part (at ˜21^oS). Several profiles across the TR display features that might indicate a listric master fault, including an overall halfgraben geometry, tilted blocks, and a curvature of the hanging wall which is characteristic of a rollover. For a listric fault, the depth D to a detachment can be determined from the surficial fault dip (α), the tilt of the graben floor (θ), and the vertical offset (d). We measure a scarp height d of ˜2000 m and floor tilts θ between 0.9^o and 2.7^o. For α = 60^o, we obtain values of D between ˜33 km and ˜67 km (θ = 2.0^o and 1.0^o). Interestingly, these values correspond very well with recent estimations of the thickness of the elastic lithosphere T_e in S-Tharsis, as given by Zuber et al. (2000): Valles Marineris ˜60 km, Solis Planum ˜35 km. A listric W-dipping master fault in the middle and southern part of the TR might indicate gravitational gliding of an unstable part of the outward verging fold-and-thrust plateau margin towards W, i.e., toward the foreland of Thaumasia. However, slip along planar faults can also produce tilted graben floors and hanging wall flexure, so the observed morphology does not allow any firm statement about the fault geometry. Extension (assuming planar fault planes) was determined using the vertical displacement at faults. In the N, most of the extension occurred along a few major faults. In the S, it has been distributed among many smaller faults. Extension is 0.5 to 4.5 km (strain 1 to 3%). This is much less than 10 km, as previously calculated by other authors from scarp widths and shadows. While the structural geometry of the TR is more similar to classical rifts than that of Valles Marineris, there are better Martian analogues to terrestrial continental rifts, e.g., Tempe Fossae. Essential characteristics of continental rifts are: Regional domal uplift, crustal break-up, formation of through-going rift valleys, and rift-related volcanism. The structure and morpho-tectonics of the TR and the lack of extension-volcanism do not meet these criteria of terrestrial continental rifts. So far, the geodynamic processes that led to the formation of the TR are unclear (crustal break-down due to Thaumasia uplift? magma deficit near Syria Planum? a long-lived and late center of magmatectonic activity?).
Hauber Ernst
Kronberg Philipp P.
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