A review on the tectonic evolution of the Paleozoic-Triassic basins from Patagonia: Record of protracted westward migration of the pre-Jurassic subduction zone

Abstract

The Paleozoic-Triassic Patagonian basins, at present comprising the Andean hinterland and structural basement of active basins, document a pre-Jurassic evolution associated with accretionary processes at the paleo-Pacific convergent margin. The Early Cambrian basins constitute the earliest record for the emplacement of the Terra Australis Orogen in northern Patagonia and preserve metavolcanic strata derived from an extensional magmatic arc. Together, pre-Jurassic basins document the Early Cambrian to Late Triassic oceanward migration of the trench-forearc system, evidencing that slab retreat was the common subduction setup. Tectonostratigraphy of these basins can be divided into three major sequences, from east to west: (i) early-middle Cambrian, (ii) Silurian-Carboniferous and (iii) Late Permian-late Triassic, which are separated by angular unconformities, evidencing large deformational pulses (advancing stages?) at Early Ordovician, early-middle Permian, and Late Triassic-Early Jurassic times. The Early Cambrian basins are mainly represented in the North Patagonian Massif by the Nahuel Niyeu forearc basin and the El Jagüelito backarc basin, which were closed and metamorphosed during the Early Ordovician. The Silurian-Devonian clastic sequences of the Atlantic region and Malvinas Islands evolved in an intracontinental rift setting and were deformed in the Permian when thrust tectonics took place at the continental scale, while the contemporaneous trench-forearc system represented in western Patagonia was governed by slab dynamics and accretion of oceanic material. During the final Pangea assembly (Permian-Triassic), the Antarctic Peninsula crustal block formed part of Patagonia as evidenced the detrital zircons record in the Permian-Triassic arc-flank basins. Deformation and metamorphism of these late Paleozoic-early Mesozoic basins could have occurred during the latest Triassic-Early Jurassic Chonide event.