Structural and volcanic evolution of Martian and terrestrial shield volcanoes

摘要

A basaltic volcano is much more than merely an accumulation of lava flows and pyroclastic rocks, and its morphology is conditioned by many parameters additional to the rheology of its lava flows. This truism expresses the fact that a basaltic volcano is a complex system of intrusives as well as effusive rock bodies. The external morphology of a major basaltic volcano, either on Mars or on the Earth, thus depends at least as much on the internal plumbing system of the volcano as on the flow behavior of its lava flows. Not only does the shape (morphology) of the volcano depend on the balance between internal and external forces, but also for Mars the degree of interaction between intrusives and regolith volatiles will be influenced by the internal structure of the volcano. This three-year project was therefore designed to further understanding of terrestrial volcanoes and to translate that knowledge into the interpretation of similar landforms on Mars. Earlier studies had shown that melt water release from areas peripheral to major volcanic constructs may have been a common phenomenon, and mapping of channels within the Tharsis region appears to confirm this view. In addition, such volcano/ground ice interactions may also have influenced the distribution of explosive volcanism on Mars. Thus, this project attempted to investigate the relative roles of extrusive and intrusive activity on Mars using terrestrial analogs and photogeologic mapping of Viking Orbiter images and to identify the places where consequent release of melt water took place at the surface around martian volcanoes. The objectives of this project were to perform a structural analysis of basaltic shield volcanoes on the Earth, thereby enabling the mechanism(s) of volcano growth, intrusion, and subsidence of martian volcanoes to be predicted. Information on the mechanism(s) of dike intrusion and summit collapse for terrestrial volcanoes is to be used to help interpret the volcanic and tectonic evolution of martian shields volcanoes and the possible consequences of volcano/ground ice interactions, as derived from photogeologic mapping and numerical modeling.