Silicic volcanism triggered by increased denudation rates in the Quaternary Andean arc of central Chile between 33°50′-34°30′S

In central Chile (33°50′-34°30′S), the Quaternary arc records a distinctive episode of silicic volcanism (SiO2 >70 wt%) that occurred during latest Pleistocene (0.1–1 Ma). This episode is recorded in several eroded and inactive arc centers distributed mostly along the highest summits of the Andes in the same region covered by the modern arc centers. We report new data including field observations, petrography, whole rock chemical and Sr-Nd isotopic analyses, mineral chemistry and geochronology for the Quaternary Andean arc in the region with emphasis in the latest Pleistocene units (0.1–1 Ma). The silicic episode that the latter units represent constitutes a singularity in the common compositions that characterize in the long term this arc segment, as it is preceded and followed by basaltic andesite-andesite-dacite suite compositions. In addition, it occurs coevally with a period of increased denudation resulting from the major uplift event of the Andean orogen in the area. Geologic field markers, supported by thermobarometric estimations, indicate conservative estimates of denudation of ∼1.5 km during this period in the area which in turn accounts for a significant pressure decrease at upper crustal levels that must have affected the shallow reservoirs that fed the arc volcanoes. For evaluating this, thermodynamic numerical simulations have been run at different pressure conditions in order to describe for such magmatic systems the evolution in terms of major element composition, degree of crystallinity and volatile content with the temperature decrease. Overall, results show that the compositional spectra defined by this arc segment can be reproduced by low pressure (