Geological and geodynamical studies of the origin and history of the Tharsis and Valles Marineris regions of Mars.

摘要

In this thesis I use data from the Mars Global Surveyor (MGS) spacecraft to examine the physical and geological properties of the lithosphere and crust of the Tharsis region of Mars, a vast volcanic and tectonic province. Two geodynamical studies utilize line-of-sight spacecraft accelerations from the Radio Science Experiment and topography from the Mars Laser Orbiter Altimeter (MOLA) for the primary purpose of estimating the effective elastic thickness (Te) for various regions of Tharsis. The value of Te provides temporal and spatial information regarding the formation of crustal features and the values derived in this study are used to infer the evolution of Tharsis over its ∼4.5 billion year history. Thaumasia, the oldest preserved region of Tharsis, is identified in this study as a large corona (a volcanic-tectonic feature identified on Venus). Using corona as an analog, a thin, elastic shell model is developed. Thaumasia is found to be in near-isostatic equilibrium consistent with an ancient formation age. Admittances for three regions of Tharsis are determined and fit with theoretical admittances. From this, Te across Tharsis is inferred to have varied over time and topographic loading appears to have become increasingly confined to the western margin. A photogeologic study of Valles Marineris, a vast canyon system that incises the crust of Tharsis to a depth exceeding 10 km, provides lithologic information regarding the composition of the crust. The rocks that comprise the upper crust of Thaumasia are interpreted to be primarily resulting from effusive flood basalt volcanism and near-surface magmatic intrusion. From these studies, it is concluded that: (1) Tharsis is largely the result of volcanic construction, (2) Thuamasia is the remnant of a large corona-like feature similar to Artemis Corona on Venus and formed within 500 Ma after planetary accretion, (3) volcanic effusion rates were very high during this time with the bulk of Tharsis being emplaced within the first billion years of the planet's history and quickly diminishing thereafter, and (4) volcanic activity has persisted throughout the last ∼3.5 billion years of Martian history in more localized regions confined to the western half of the province.