Triassic-Jurassic thermal evolution and exhumation of the western Gondwana foreland: Thermochronology and basalt thermobarometry from the Argentine Sierras Pampeanas

MARTINA, F.; AVILA, P.; DAVILA, F.M.; PARRA, M.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2021 vol. 105

0895-9811

The geological record of the eastern Sierras Pampeanas province, in the modern Andean broken foreland ofArgentina can be divided into four main events: (1) Proterozoic to early Paleozoic collisional tectonics, (2)middle-late Paleozoic anorogenic magmatism, relief generation and glacial paleovalley formation followed by (3)a classical foreland filling in the Permian and two proximal alluvial sedimentation associated with (3) Cretaceousrifting and (4) Neogene intermontane foreland accumulation. The region lacks Silurian, Triassic and Jurassicrecords, commonly associated with unknown deformation and/or no-sedimentation stages (bypass zone?). In thiswork, we analyzed the Mesozoic (Triassic-Jurassic) Pampean unconformity, using low-temperature thermochronologicalmodelling. After a rapid Carboniferous cooling track, a Triassic reheating followed by a slowJurassic to Cretaceous cooling. Considering that (1) no Triassic basins have been described to date in the easternSierras Pampeanas (i.e., reheating cannot be related to burial), (2) coeval surface heat flows are anomalouslyhigh in western Sierras Pampeanas, in the Ischigualasto basin, and (3) our petrogenetic modelling on Triassicbasalts evidence mantle potential temperatures of ~1350?1400 ◦C (i.e., the heat source cannot be related withan anomalously high basal heat flows and/or mantle plumes); we interpreted the formation of the Mesozoicunconformity as a result of ridge collision and slab window formation, followed by slab rollback. Both processesmight have affected not only the surface heat flow but also triggered a lithospheric thickness reduction, whichdrove isostatic rebound. In this context, the Jurassic history of the unconformity could be associated with coolingby erosion and exhumation until the Cretaceous, when the region was under extension. Our model agrees withother observations like the formation of back-arc hydrocarbon-productive Triassic-Jurassic depocenters to thewest (Cuyo and Ischigualasto basins) and the magmatic evolution, from 28◦ to 34◦ SL, described along theChilean margin.