Mathematics – Logic
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.p21a..03i&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #P21A-03
Mathematics
Logic
5475 Tectonics (8149), 5480 Volcanism (8450)
Scientific paper
We have conducted geological mapping in four quadrangles under the NASA program of geological mapping of Venus. Two quadrangles portray large equidimensional lowlands (Lavinia, V55, and Atalanta, V4, Planitiae) and two more areas are characterized by a large corona (Quetzalpetlatl corona, QC, V66), and Lakshmi Planum (LP, V7). Geological mapping of these large-scale features allows for their broad comparisons by both sets of typical structures and sequences of events. The Planitiae share a number of similar characteristics. (1) Lavinia and Atalanta are broad quasi-circular lowlands 1-2 km deep. (2) The central portions of the basins lack both coronae and large volcanoes. (3) The belts of tectonic deformation characterize the central portions of the basins. (4) There is evidence in both lowlands that they subsided predominantly before the emplacement of regional plains. (5) Recent volcanism is shifted toward the periphery of the basins and occurred after or at the late stages the formation of the lowlands. The above characteristics of the lowlands are better reconciled with the scenario in which their formation is due to a broad-scale mantle downwelling that started relatively early in the visible geologic history of Venus. The QC and LP are elevated structures roughly comparable in size. The formation of QC is commonly attributed to large-scale mantle positive diapirism while the formation of LP remains controversial and both mantle upwelling and downwelling models exist. QC and LP have similar characteristics such as broadly circular shape in plan-view, association with regional highlands, associated relatively young volcanism, and a topographic moat bordering both QC and LP from the North. Despite the above similarities, the striking differences between QC and LP are obvious too. LP is crowned by the highest mountain ranges on Venus and QC is bordered from the North by a common belt of ridges. LP itself makes up a regional highland within the upland of Ishtar Terra while QC produces a much less significant topographic anomaly on the background of the highland of Lada Terra. Highly deformed, tessera-like, terrain apparently makes up the basement of LP, and QC formed in the tessera-free area. Volcanic activity is concentrated in the central portion of LP while QC is a regionally important center of young volcanism. These differences, which probably can not be accounted for by simple difference in the size of LP and QC, suggest non-similar modes of the formation of both regional structures and do not favor the upwelling models of the formation of LP.
Head James W.
Ivanov Michael A.
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