Extensional history of Mars' Tharsis Region

Graben structures in the outer part of Mars' Tharsis region follow calculated stress patterns that are based on Tharsis topographic and gravity anomalies and flexural response of the lithosphere. However, Tharsis extension is not evenly distributed - most extension is concentrated in the Alba, Tempe, Valles Marineris, and Syria-Thaumasia volcanotectonic provinces. Preliminary results suggest that the overall extension of Tharsis produced by loading is about 8 km (based on the assumption that the Sirenum province exemplifies the overall extension of Tharsis), whereas the total circumferential extension of the Tharsis region estimated thus far is about 33 km (an estimate was not made for the Syria-Thaumasia province, and evidence in some other areas may be buried). It is concluded that local tectonism, possibly caused by intrusion and passive and active rifting, produced most of the extension in the Tharsis region.