The monazite record of metamorphic evolution during the orogenic development of northern Patagonia

Abstract

The tectonometamorphic evolution of Paleozoic basement inliers of Patagonia remains largely elusive and has been poorly constrained even though it represents a key piece to reconstruct the timescales and tectonic processes during early construction of the continental crust. In this work, new monazite electron probe microanalysis (EPMA) Th–U–Pb data are integrated with a review of structural, microstructural, and thermo-barometric information of medium- to high-grade metasedimentary rocks of northern Patagonia, providing constraints on the timescales of Paleozoic orogenic processes. Early to middle Devonian regional metamorphism records high-temperature/low-pressure conditions linked with a retreating accretionary orogen with widespread forearc to retroarc magmatism. After closure of associated extensional basins during a late Devonian compressional stage, changing geodynamic conditions are documented. During the middle to late Carboniferous, progressive crustal thickening linked with the transpressional Gondwanide Orogen gave rise to medium- to high-pressure/high-temperature Barrovian metamorphism. Crustal thickening, possibly linked with flat-slab subduction, favored an inland migration of metamorphism and deformation. Therefore, the arc domain records Permian Buchan-type metamorphism during post-orogenic collapse, whereas coeval Barrovian-type metamorphism associated with crustal shortening occurs in the retroarc domain. This ubiquitous crustal thickening resulting from the Gondwanide Orogeny ultimately contributed to the stabilization of the relatively thin continental crust of northern Patagonia, which resulted from mainly retreating, early to middle Paleozoic subduction.