STRUCTURAL MAPPING AND LITHOSPHERIC FLEXURE IN THE FORMATION OF THE THAUMASIA HIGHLANDS, MARS

Recent work suggests that the Thaumasia Highlands formed as a flexural response to a large volcanic load in southern Tharsis. According to this hypothesis, the load caused flexure and subsidence of the underlying lithosphere along with rotation and uplift of the margins of the Thaumasia Plateau towards its interior during the Early Noachian. The Thaumasia Highlands, from Claritas Fossae in the west to the Coprates Rise in the east, would represent the flexed margin of the load. A flexural moat has been observed as a negative free-air anomaly immediately to the exterior of the Thaumasia Highlands and Plateau, supporting the hypothesis. Detailed fault mapping of the southwest margin of the Thaumasia Plateau has provided evidence supporting the lithospheric flexure hypothesis. This mapping, along with analysis and modeling of topographic profiles derived from MOLA DEMs, has revealed previously unrecognized large-scale normal faults, horsts, and wide (~20 km) graben located in the western Thaumasia Highlands. These structures curve, following the arcuate shape of the margin, and are consistent with formation as a result of the flexure. Flatirons mapped near the Coprates Rise are also consistent with this mechanism for the formation of the Thaumasia Highlands. Margin tectonics vary systematically with position, changing from concentric extension in the southwest to concentric thrust faulting and folding to the east, implying spatial variations in lithospheric and/or load characteristics in southern Tharsis during the Noachian.