Mathematics – Logic
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt........22w&link_type=abstract
PHD thesis, Fachbereich Geowissenschaften Freie Universität Berlin, 160 pages
Mathematics
Logic
7
Mars, Crater Statistics, Geological History
Scientific paper
This thesis was conducted in the framework of the German Research Foundation's priority program "Mars and the Terrestrial Planets". The aim was to improve and/or verify the existing chronostratigraphic system of Mars and to understand globally the geologic evolutionary history of Mars focusing on the volcanic, fluvial, and possible glacial processes. This implies the photogeologic analysis of all available types of Martian imagery in order to cover the diversity of Martian landforms in time and space. Therefore, crater frequencies are determined for appropriate geologically mapped units and absolute ages derived. The lunar crater production function and the chronology model was confirmed for the Martian case, e.g. the theoretical crater production function was proven over the entire (50 meters to 500 kilometers). Any deviation from the confirmed Martian standard crater production function indicate resurfacing events. In such cases the method of age determination has been improved. The influence of secondary cratering on a measurement is at most 10 percent. Type areas of the Martian epochs (Noachian, Hesperian and Amazonian) such as Noachis Terra, Hesperia Planum, northern lowland regions, Amazonis and Elysium Planitia, have been examined, to understanding the role of water during the Martian geologic evolution. The younger fluvial erosion is closely related to volcanic activity and occurred in episodes over the last 2 billion years. Extensive measurements in volcanic units allowed for the interpretation of the evolution ary history of Martian volcanic activity. An interplay of volcanic processes with ancient and more recent fluvial and glacial activity is confirmed. Globally, the volcanic activity started very early in the Martian evolution. Most of the volcanoes achieved their present dimensions at least until 3.5 Ga ago. Later volcanic resurfacing indicates a weakening of the volcanic activity after the construct-forming period. Another major finding is that the volcanic activity on Mars continued until very recently (e.g. 2 Ma at the flanks of Olympus Mons), and is more wide--spread than believed earlier. The crystallization ages of basaltic Martian meteorites (about 180 Ma, 450 Ma and 1.3 Ga) confirm this finding. The enigmatic Medusae Fossae formation could be dated for the first time indicating that explosive volcanic eruption occurred even as recently as 1.6 Ga ago. By understanding the evolutionary history of Martian volcanic constructs, the formation time of large impact basins, as well as the evolution of the northern lowlands and the dichotomy boundary, essential time--markers have been gathered in this work, and a coherent view on the global geological evolution of Mars is derived from these ages. Providing that the time--frame outlined in this study is correct, the timing for the thermodynamical evolution of Mars can be assessed. This study revealed that the youngest epoch, the Amazonian, is reflected in a variety of landforms, and includes an absolute time span of three-quarters of the geological record of Mars. This implies that the Amazonian-Hesperian time-stratigraphic boundaries have to be revisited.
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