Ordovician submarine to subaerial volcanism along the western Gondwana margin: records of the Famatinian belt evolution, north-western Sierras Pampeanas, Argentina

Abstract

The Suri-Las Planchadas Volcanic-Sedimentary Complex (SPVSC), northwest of the Sierras Pampeanas in Argentina, comprises an Early to Middle Ordovician (Floian–Dapingian) submarine and subaerial succession with a variety of mafic to felsic volcanic lithofacies. These units include mafic to intermediate submarine massive-hyaloclastic lava flows, dacitic lavas, pyroclast-rich volcaniclastic deposits, intrusions of domes/sills and rhyodacitic—rhyolitic lavas. Along Las Planchadas hill a section of ~ 3 km thickness is exposed showing vertical and lateral variations. The lower part is dominated by massive, pillowed and basaltic to intermediate lavas, autobreccia and hyaloclastic facies, representing the beginning of the volcanic arc activity. The upper almost 2 km of the succession is dominated by subaqueous-resedimented volcaniclastic siltstones, sandstones and breccias with abundant pyroclastic components and rhyodacitic to rhyolitic lava-domes, sills and dykes. Tuff and ignimbrite lithoclasts, abundant shards and pumice fragments were determined in the resedimented deposits. Volcanism in the SPVSC started with submarine eruptions and progressively grew above the wave base, accompanied by a change from mafic to intermediate and felsic members. The eruptive pattern shifted from effusive to explosive, producing a large apron of syn-and post-eruptive volcaniclastic deposits of debris flows and turbidity currents. They are the evidence of variations in composition and volcanic styles and their development contributed to generate an apron surrounding the volcanoes. The apron prograded and aggraded with the evolution of the volcanism culminating in shallow water volcanogenic beds. The final phase was characterized by felsic subaerial or shallow subaqueous explosive volcanism.