Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53c1531e&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53C-1531
Mathematics
Logic
[5410] Planetary Sciences: Solid Surface Planets / Composition, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5460] Planetary Sciences: Solid Surface Planets / Physical Properties Of Materials, [5480] Planetary Sciences: Solid Surface Planets / Volcanism
Scientific paper
Understanding the history of impact crater modification and alteration can provide insights into planet scale processes that have occurred throughout Martian history. We have identified a unique class of Martian craters with flat, high thermal inertia floors, mafic mineralogies, and degraded morphologies. By using physical material properties in combination with morphologic and mineralogical data, it is possible to constrain the formation and modification history of these craters and better understand the crater modification processes, including post-impact volcanism, chemical weathering and hydrothermal alteration. This class of crater is prevalent throughout the southern highlands of Mars. The craters studied have degraded walls and rims, no central peak, no clearly visible ejecta deposits, an average diameter of ~52km (ranging in size from 18.5km to 179km), and occur almost exclusively in the southern highlands indicating an old formation age. The thermal inertia values derived from Thermal Emission Imaging System (THEMIS) measurements of crater floors are consistent with competent rocky material, while the walls and surrounding plains are composed of a less cohesive material. We have used THEMIS, Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), and Thermal Emission Spectrometer (TES) data to constrain the compositional variability of ~60 sites with the highest thermal inertia values. In general, the crater floors have higher abundances of mafic minerals (e.g. pyroxenes and olivine), while the surrounding plains have lower abundances of mafic minerals but show an increase in high-Si phase abundance. The composition, morphology, and distribution suggest that old, flat floored craters were resurfaced by a post-impact process that resulted in material significantly more mafic than the surrounding terrain. A possible formation mechanism may be related to inflationary volcanism associated with the impact [Schultz, 1976]. In this model, during the impact event, the crust is fractured providing a conduit for magma to erupt onto the surface and infill the original crater floor. The source of this magma is not well constrained and may be related to the unloading of the early Martian mantle and crust, resulting in partial melting of the underlying material. The mineralogy of these materials is consistent with a picritic basalt and indicates a primitive magma source, such as the Martian mantle. We have identified and characterized a unique class of Martian craters that has gone previously unstudied. If the distribution of this crater type is considered and the proposed model is correct, it is likely that inflationary volcanism is an important widespread process on Mars that has gone previously undocumented. This process could be responsible for extended periods of hydrothermal activity, a source of energy for altering materials, and may indicate high crustal heat flow early in Mars history. Schultz, P. H. (1976), Floor-fractured lunar craters, Earth, Moon, and Planets, 15(3).
Bandfield Joshua L.
Christensen Per Rex
Edwards Christopher S.
Rogers David
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