Fault-Driven Differential Exhumation in a Transpressional Tectonic Setting: A Combined Microstructural and Thermochronologic Approach From the Liquine-Ofqui Fault System, Southern Andes (39°S)

Abstract

Crustal deformation in transpressive tectonic settings is partitioned across fault-bounded tectonic blocks whose borders may represent ideal loci for enhanced rock exhumation. Field and petrographic analysis, geothermobarometry, zircon U-Pb geochronology, and zircon and apatite (U-Th)/He thermochronology were applied to intrusive and metamorphic rocks to investigate exhumation patterns of fault blocks delimited by the Liquine-Ofqui Fault System (LOFS), Southern Andes (39 degrees S). Our integrated analyses document the relative influences of magmatism, fault-driven differential exhumation, and fault-controlled geothermal flow along the LOFS. Magmatism was concentrated in the Early to Late Jurassic (similar to 182-151 Ma), Early Cretaceous (similar to 116-104 Ma), and Miocene (similar to 17-6 Ma). Dextral mylonitic deformation was most likely coeval with the Miocene pulse of magmatism. Tectonic exhumation occurred across a positive flower structure during the Late Miocene to Early Pleistocene (similar to 6-2 Ma), and affected kilometric-scale tectonic blocks bound by N-striking, steeply dipping faults of the LOFS. Fault-controlled geothermal flow occurred from the Early Pleistocene to the present-day (similar to 1.5 Ma-present). Our results suggest that individual faults not only facilitate exhumation of tectonic blocks but also act as pathways for long-term hydrothermal fluid