Payenia volcanic province in the Southern Andes: An appraisal of an exceptional Quaternary tectonic setting

Abstract

The Southern Volcanic Zone of the Andes has a Quaternary basaltic province along the retroarc which has a unique tectonic setting. The Payenia volcanic province covers an area larger than 40,000km2 between 33°30' and 38° South latitudes, with an estimated volcanic volume of about 8387km3 erupted through more than 800 volcanic centers in the last ~2Ma. The mainly basaltic province developed above the San Rafael Block is subdivided in three segments characterized by the Cerro Nevado, Llancanelo, Payún Matru, Tromen and Auca Mahuida volcanic fields, together with hundreds of minor monogenetic basaltic centers. The analysis of the different segments shows the formation of a common basalt plateau with intraplate signature from south to north between 2.0 and 1.7Ma, which reached the 35°S to the north. Above this plateau monogenetic centers as Nihuil Vn. 1.433Ma and Cerro Chato at 1.352Ma are developed, followed by the large polygenetic center of Cerro Nevado (3980ma.s.l.) at 1.320Ma. This plateau was broken by a series of normal faults that produced volcanic cone alignments such as the NNW-trending Mancha Jarilla lineament in the central part at about 1.0Ma. Extension shifted to the eastern margin of the San Rafael Block, which concentrates tens of monogenetic centers between 0.9 and 0.7Ma. Extension then migrated towards the foothills in the west, where many monogenetic cones were erupted through NW-trending normal faults between 0.5 and 0.435Ma. The collapse of the large Diamante Caldera at 0.445Ma coincides with that period. Subsequent volcanism was concentrated in (1) the Payún Matru volcanic field, with the eruption of Cerro Payén between 0.272 and 0.261Ma; the Payún Matru shield volcano, with polygenetic eruptions at least since the last 0.233Ma and with the caldera formation bracketed between 0.168±0.004Ma and 0.082±0.001Ma, followed by several eruptions until 7000yrs, and even historical ones; and in (2) the Tromen volcano, where younger than 0.2Ma eruptions took place and historical eruptions were reported. The understanding of these eruptions in time and space, combined with geophysical data, indicates the geometry of an important crustal attenuation beneath Payenia, associated with a hot sublithosphere. The Late Miocene uplifted San Rafael Block collapsed in the Early Pleistocene as a consequence of the steepening of the subducted slab, and the injection of hot asthenosphere produced the Quaternary Payenia volcanic province. Melts of the lower crust along the Principal Cordillera at these latitudes are responsible for the Quaternary calderas, ignimbritic flows and rhyolitic volcanism that express the crustal delamination of the Andes. The Payún Matru volcanic field concentrates this asthenospheric flow in the Present.