THE GEOMORPHOLOGY AND EVOLUTION OF HECATE-CHASMA, VENUS

Hecate Chasma is a discontinuous trough and fracture system extending from Atla Regio through Asteria Regio. A detailed examination of Hecat e Chasma using Magellan image and altimetry data reveals morphologic f eatures such as normal faults (including graben), compressional ridges , a variety of volcanic edifices, and coronae, There is no evidence fo r a systematic age progression among coronae in chains, thus a single, stationary thermal anomaly underlying a moving lithosphere is an unli kely origin for the chains, A comparison of the observed features with two possible models of evolution, subduction/delamination or lithosph eric extension with limited rifting, shows some similarities between t he predicted morphologies of each model and Hecate Chasma, The dominan ce of features related to upwelling and extensional tectonism strongly favor an extensional origin for this zone. The corona chain may have been formed by upwellings related to Rayleigh-Taylor instabilities, si milar to those observed at terrestrial mid-ocean ridges, but in an env ironment of limited spreading. (C) 1996 Academic Press, Inc.