Miocene to modern hydrothermal circulation and high topography during synconvergent extension in the Cordillera Blanca, Peru

Abstract The Cordillera Blanca detachment in the highest elevations of Peruvian Andes has been accommodating synconvergent extension since late Miocene. Stable isotope analysis synkinematic mica from its exhumed footwall shear zone provides new constraints on deep meteoric-hydrothermal circulation during ductile deformation and regional paleoelevation. Muscovite biotite that deformed and/or grew synkinematically have δ2H values −131‰ to −58‰ −149‰ −98‰ (versus Vienna standard mean ocean water, VSMOW), respectively. value difference between coexisting muscovite is consistent with equilibrium fractionation same fluid at temperature. Calculated water (−107‰ −78‰) these micas are indistinguishable those present-day, deeply circulated (9–11 km) hot spring waters emanating fault. Such low-δ2H fluids indicate meteoric depths brittle-ductile transition cannot be explained by other mechanisms. Average recharge paleoelevation for entering based hydrogen isotopes was 3400 + 500/–700 m (1σ). This near, but ~500 below, present-day elevation catchments feeding modern springs 3965 ± 880 m, ~700 below 4200 700/–900 derived surface thermal water. consistency ancient fault-assisted hydrothermal systems suggests high topography, steep relief, persisted throughout history system.