Geology of the Uranius group volcanic constructs: Uranius Patera, Ceraunius Tholus, and Uranius Tholus

Uranius Patera, Ceraunius Tholus, and Uranius Tholus (three small construct s in the northeast Tharsis region) date to the Late Hesperian Epoch and def ine the earliest phases of constructional volcanism in the Tharsis province . All three volcanoes are interpreted as shields, built by effusive eruptio ns of low-viscosity lavas, presumably basalt. Ceraunius Tholus and Uranius Tholus also record pyroclastic volcanism in the form of mantling deposits o n their hanks; Uranius Patera either did not experience pyroclastic volcani sm or the deposits were subsequently buried by later effusive eruptions. Tr oughs observed on the flanks of Ceraunius Tholus and Uranius Tholus are int erpreted to have been formed by fluvial surface runoff. These constructs ar e coeval with other small edifices in western Tharsis province and are coev al with plains volcanism in the southern Tharsis, Syria, and Sinai regions. (C) 2000 Academic Press.