Abstract

The Thaumasian lava plateau developed within an already deformed domain, consisting of composite orogenic belts. A crude scheme of the deformation history of the Thaumasian plateau summarizing the most significant events of its polycyclic development is presented here. It is suggested that the region evolved in four tectonism phases: (1) alpinotype regional compression, formation of basement nappes (early and middle Noachian orogen); (2) late Noachian regional, domal uplift, and denudation of the internal fold belt; (3) late Noachian-early Hesperian supracrustal deformation, as décollement nappes; and (4) Hesperian crustal foundering and great effusion of trap basalts flooding of the inner, alreadypeneplain mountain belts, balanced by uplifting of peripheral arcuate rim-highlands (swells and mountain belts). The two orogenic arcs of the Coprates and Thaumasia -Claritas belts exhibit thrusting vergence and orogenic migration, E- and SW-directed, indicating the presence of topographic doming associated with plume activity, which was probably positioned, in the late Noachian, upon the modern Solis planum lowland. There is a substantial possibility that the two arcs followed different tectonic evolutions. The lateral intrusion of hot, mafic fluids in interconnected fractures, near the crust-mantle boundary, is supposed to have been an important driving mechanism of tectonism beneath the plateau region. The thick bodies of diapir-like, moving aqueous fluid were probably related to ascending deepmantle plumes.