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Is Tharsis Rise, Mars, a spreading volcano?

Andrea Borgia
Andrea Borgia
EDRA via di Fioranello 31, 00134 Roma, Italia; Visiting Professor at Geological Sciences Department, Rutgers University, Taylor Road, Piscataway, New Jersey 08854-8066, USA
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John B. Murray
John B. Murray
Department of Earth & Environmental Sciences, The Open University, Milton Keynes MK7 6AA, UK
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August 2010

A theoretical similarity derived for spreading volcanoes remains valid for over three orders of magnitude in size, from small slumping volcanoes to large ocean plates. This similarity means that Mount Etna, Sicily, can be used as a terrestrial analogue of Tharsis Rise on Mars. A quantitative comparison of surface structures suggests that Tharsis has been spreading outward as a result of movement of plates at a planetary scale, producing rifting through the summit of the Rise, folding around its periphery, and with radial tear-fault systems connecting the summit rifts to the basal folds. The tear-fault systems form the fossae, of which Valles Marineris is the largest, and decouple the various plates of the Rise, so Tharsis appears to be analogous to a terrestrial mid-ocean ridge, but without any corresponding subduction zone. Instead, like volcanoes, the Tharsis plates are obducted over the Martian crust. The maximum viscosity at the bottom of the Martian lithosphere, derived from our spreading analysis, is in the order of 1021 Pa s, so if the mantle of Mars is hot and ductile, we suggest that the spreading of Tharsis could still be occurring.

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Figures & Tables


GSA Special Papers

What Is a Volcano?

Edited by
Edgardo Cañón-Tapia
Edgardo Cañón-Tapia
Centro de Investigación Científica y de Educacíon Superior de Ensenada, Department of Geology, Baja California, Mexico C.P. 22860
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Alexandru Szakács
Alexandru Szakács
Sapientia University, Department of Environmental Sciences, Cluj-Napoca, Romania, and Romanian Academy, Institute of Geodynamics, Bucharest, Romania
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Geological Society of America
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