Plio-Pleistocene rear-arc volcanism in the Southern Volcanic Zone: Eruptive styles of the Varvarco Volcanic Field

Abstract

The Varvarco Volcanic Field (VVF) is located in the southern part of the Las Loicas Trough, as part of the Late Pliocene-Early Pleistocene rear-arc volcanic belt in the Transitional Southern Volcanic Zone (34.5–37°S). Its volcanic products show an elliptical distribution, elongated parallel to NW-SE main structures that regionally controlled the Las Loicas Trough. A detailed field and petrographic study was carried out to identify main lithofacies and establish its eruptive styles. The VVF magmatic evolution is initially characterized by a voluminous explosive stage represented in the area by dense and dilute pyroclastic density currents (PDC) deposits (massive lapilli tuffs, cross-stratified lapilli tuffs and diffuse-stratified tuffs). Afterwards, it evolved into an effusive stage represented by basaltic lava flows (coherent basalts), associated with Hawaiian to Strombolian eruptive style, which constitutes most of the VVF volume. The final stage of the VVF history was linked to a stratovolcano-type activity where both effusive (coherent basalts and andesites, and rhyolitic coulees) and explosive lithofacies (such as massive lithic breccias and massive lapilli tuffs) are described. Within this stage, the uppermost effusive levels were intruded by dacitic and rhyolitic domes and basaltic dykes. Available ages allow to conclude that the VVF emplacement was developed during Plio-Pleistocene times, linked to the re-steepening of the Nazca plate, after the Late Miocene Payenia shallow subduction regime.