ABSTRACT: Style and Distribution of Volcanism on Venus: Recent Magellan Results

HEAD, JAMES W., Brown University, Providence, RI

Analysis of Magellan images covering over 90% of the surface confirm that volcanism is a widespread and fundamentally important process in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows and sinuous rilles with lengths up to many hundreds of kilometers). Large lava outpourings with flow unit volumes measured in the 102-103 cubic kilometers range have been observed in several environments. Thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, and local pyroclastic activity have also been documented. Most features observed are consistent with basaltic compositions; however, a number of large pancake-like dom s are morphologically similar to rhyolite/dacite domes on Earth and may have formed from evolved magmas. At least one of these features is observed in the vicinity of the Venera 8 landing site; geochemical analyses from this site suggest the presence of more evolved magmas. In other environments, anomalously long flows and sinuous channels suggest that extremely high effusion rates and/or very fluid magmas (perhaps komatiites?) may be present. Volcanism in general, and some specific associations of volcanic features, are closely linked to various tectonic settings (coronae, linear deformation zones of both extensional and compressional origin, mountain belts, upland rises, highland plateaus, and tesserae). Global distribution of volcanic features contrasts to the linear belts of Earth an shows an area of anomalously high concentration in the Beta/Atla/Themis region covering about 20% of the total surface of the planet. Impact crater distribution and density indicate that the surface is geologically young (average age <1 Ga). Reflectivity data suggest that Maat Mons in Atla Regio may be active today. Resurfacing rates due to volcanism appear to be low (<2 cubic kilometers/yr) and are comparable to intraplate extrusive rates on the Earth. Crustal formation appears to take place primarily by serial volcanism and associated intrusion. The global data support the existence of an altitude-dependent effect on volcanic style.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)