Mathematics – Logic
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........5p&link_type=abstract
Thesis (PH.D.)--PRINCETON UNIVERSITY, 1995.Source: Dissertation Abstracts International, Volume: 56-03, Section: B, page: 1312.
Mathematics
Logic
11
Gis, Crater
Scientific paper
During 1990-1994 the Magellan spacecraft produced high-resolution radar images of the surface of Venus. Detailed mapping using a geographic information system (GIS) records a variety of volcanic and tectonic land forms as digital maps and a database, and allows quantitative spatial analysis of their global distributions. This analysis provides a global chronological framework based on the distribution of impact craters. Even though impact craters on Venus are statistically indistinguishable from a spatially random population, significant variations between crater densities of mapped terrains, and correlations of embayed and fractured impacts with geologic land forms, indicate that relative ages based on crater density can be reliably discriminated for areas defined by geologic mapping that exceed 10 ^7 km^2. The ages are determined relative to an assumed age of 300 Ma based on the mean global crater retention age of 288 ( -100,+300) Ma. The evolution of Venus may be broadly partitioned into emplacement of extensive volcanic plains followed by limited volcanism and tectonism concentrated in a roughly equatorial belt of rifts and large volcanic rises. The volcanic plains, about 65% of the planet, were emplaced over a 50-100 Ma period beginning at least 370 Ma ago. The oldest plains are preserved in the lowland planitiae, and embay complexly deformed highlands called tesserae which are probably the oldest surviving crust. Younger plains are concentrated in areas which developed into the rifts and rises, which contain abundant coronae, fissure flows, and rifts with mean ages of 80-150 +/- 100 Ma, and large constructional volcanoes with a mean age of 75 +/- 45 Ma. During the transition from volcanic plains emplacement to volcanism and deformation in the rifts and rises, area resurfacing rates dropped from ~4 km^2/yr during plains deposition to ~0.5 km^2/yr over the past 150 Ma, based on present mapping. Simulations of this resurfacing history indicate that it is compatible with the random crater distribution.
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