Original paper

Late Proterozoic to Early Cambrian sedimentation and magmatism at the western Gondwana margin: metasedimentary rocks in the Sierras Norte de Cordoba (Argentina)

von Gosen, Werner; Prozzi, César

Abstract

Studies of clastic metasedimentary rocks in the Sierras Norte de Córdoba (Argentina) indicate a two-stage history of sedimentation, magmatism and initial tectonics. The basal clastic pile of rocks (Lower Unit) is recorded by coarse conglomerate and sandstone which overlie, and partly alternate with, rhyolite to rhyodacite. The conglomerates contain pebbles and partly boulders of acid magmatic rocks and widely distributed sandstone and siltstone derived from the local succession and a sedimentary cover sequence. They can be interpreted as fluvial to alluvial fan sediments presumably deposited during active normal fault tectonics accompanied by acid volcanism. It is assumed that a younger thick sandstone-siltstone succession with local intercalations of conglomerate and rhyolite to dacite (Upper Unit) was deposited under continuing subsidence. Its pebbles and clasts contents indicate an increasing influence of deformed and metamorphosed clastic successions along withacid magmatic rocks in the source areas. Measured cross-bedding broadly suggests sedimentary transports from eastern source areas. For the clastic sediments and intercalated acid volcanic rocks a Late Proterozoic-Early Cambrian age is reasonable, and the sedimentary succession can be interpreted as a time equivalent of the Puncoviscana Formation sensu lato of northwest Argentina. The geotectonic setting is interpreted as clastic sedimentation at the western pre-Andean Gondwana margin accompanied by acid volcanism. A passive margin development is proposed that might have followed an initial stage of rifting.