Planetary Science

Debating the Grandest Canyon

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Science  29 Jun 2012:
Vol. 336, Issue 6089, pp. 1620
DOI: 10.1126/science.336.6089.1620-a

Valles Marineris is a prominent trough on Mars that extends for several thousands of kilometers and is 5 to 10 km deep, the longest, deepest canyon in the solar system (the Grand Canyon is less than 2 km deep). Although it lies on the edge of Mars' giant volcano Tharsis, the formation of Valles Marineris has been debated. Two recent papers provide a thorough discussion of previous models and approach the canyon's formation in different ways. Andrews-Hanna, in a final of three papers analyzing the feature, proposes that the trough formed as a direct result of Tharsis—the mass of this giant volcanic center is not fully supported by the underlying crust, and it formed in part over a preexisting tectonic boundary on Mars. Volcanism focused along this boundary could have weakened the crust, allowing localized subsidence and flow of the crust at depth, forming the trough. Yin mapped the geology along Valles Marineris in detail in several areas and argues that left-lateral strike-slip faulting along the trough, yielding displacement of more than 100 km, was important. Such faulting can enhance subsidence, as seen on Earth in places such as the Dead Sea Basin and Death Valley. Neither model requires large amounts of extension across the trough.

J. Geophys. Res. 117, 10.1029/2012JE004059 (2012); Lithosphere 4, 10.1130/L192.1 (2012).

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