Tectonic interpretations of central Ishtar Terra (Venus) from Venera [formula omitted] and Magellan full-resolution radar images

Abstract

For more than a decade, the mapping of Venus has revealed a surface that has had a complex volcanic and tectonic history, especially in the northern latitudes. Detailed morphostructural analysis and tectonic interpretations of Central Ishtar Terra, based both on Venera 15 16 and Magellan full-resolution radar images, have provided additional insight to the formation and evolution of Venusian terrains. Ishtar Terra, centred at 0°E longitude and 62°N latitude, consists of a broad high plateau, Lakshmi Planum, partly surrounded by two highlands, Freyja and Maxwell Montes, which have been interpreted as orogenic belts based on Venera 15 and 16 data. Lakshmi Planum, the oldest part of Ishtar Terra, is an extensive and complexly fractured plateau that can be compared to a terrestrial craton. The plateau is partially covered by fluid lava flows similar to the Deccan traps in India, which underwent a late stage of extensional fracturing. After the extensional deformation of Lakshmi Planum, Freyja and Maxwell Montes were created by regional E-W horizontal shortening that produced a series of N-S folds and thrusts. However, this regional arrangement of folds and thrusts is disturbed locally, e.g. the compressive deformation of Freyja Montes was closely controlled by parallel WNW-ESE-trending left-lateral shear zones and the northwestern part of Maxwell Montes seems to be extruded laterally to the southwest, which implies a second oblique thrust front overlapping Lakshmi Planum. These mountain belts also show evidence of a late volcanic stage and a subsequent period of relaxation that created grabens parallel to the highland trends, especially in Maxwell Montes.