Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.u62a..04s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #U62A-04
Physics
5430 Interiors (8147), 5440 Magnetic Fields And Magnetism, 5455 Origin And Evolution, 5475 Tectonics (8149), 5480 Volcanism (8450)
Scientific paper
Among the many interests of Don Turcotte have been the terrestrial planets, both as individual bodies and as test beds for generalizations on the processes that have affected the form, evolution, and interior dynamics of Earth-like planets. Over a span of more than 20 years, Turcotte and his collaborators have contributed many insights into the surface evolution and mantle dynamics of Mars on topics ranging from the nature of support of long-wavelength topography, the origin of the Tharsis rise, the internal thermal evolution and its effect on topography and lithospheric stress, and the history of outgassing. A summary of recent findings concerning early Martian evolution permits Turcotte's contributions to be placed within the context of current understanding. Core-mantle differentiation occurred within 10-15 My of the start of solar system evolution, on the basis of isotope systematics in Martian meteorites. A magnetic dynamo was active in the early Noachian but apparently ceased before the end of heavy bombardment. Crustal formation was largely complete by the earliest Noachian, on the basis of the density of both well-preserved and largely buried impact structures. Gravity-topography admittances for Noachian terrain suggests that the general south-to-north thinning of the crust may have been the result of lower crustal flow, but rapid cooling of the crust is indicated by the preservation of early Noachian relief and large crustal magnetization anomalies. The onset of the Tharsis province as a site of voluminous magmatism and concentrated deformation likely postdated the establishment of the crustal thickness dichotomy, but much of the magmatism occurred prior to the formation of late Noachian valley networks. Extensive resurfacing of the northern hemisphere occurred in the Noachian, on the basis of the detection of large impact structures superposed on older filled basins. Extensive evidence for water-surface interactions during this period supports the view that much of the Noachian resurfacing occurred by the transport and deposition of sediments. Impact stripping of the atmosphere was substantial during the Noachian, and solar wind sputtering would have contributed to further atmospheric loss after cessation of the core dynamo. The northern hemisphere was resurfaced by early Hesperian volcanic plains, which were subjected to an episode of contractional deformation of nearly global extent. Open issues include the mechanisms of crustal formation, any connection between the crustal thickness dichotomy and Tharsis, the cause of the dynamo shut-down, the Noachian-Hesperian volcanic flux history, and its links to volatile outgassing and climate change.
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