Spatial-temporal distribution of volcanism in the 25-28°s segment of the andean central volcanic zone

Abstract

The present contribution describes and analyses the spatial–temporal distribution and main features of the volcanic rocks, with emphasis in pyroclastic deposits, located in the 25–28°S segment of the Central Andes. We built a new database, based on our own field studies and compilation from the literature, where we discriminate the different pyroclastic units. We find that the pyroclastic deposits cover an area of at least 7770 km2 and are distributed mainly along N–S to NNE–SSW, NW–SE to WNW–ESE and NE–SW trends. The spatial distribution of these deposits has varied with time: those > 14.5 Ma are concentrated west of 69°W; during 14.5–11.5 Ma explosive magmatism shifted east of 67°W; the deposits < 11.5 Ma became more dispersed. The main explosive activity occurred during the 26–18 Ma, 14.5–11.5 Ma and ≤ 5.3 Ma intervals. For pyroclastic deposits, dacitic compositions dominate during the Miocene, whereas rhyodacitic and rhyolitic compositions are more abundant since the Pliocene. In the 25–28°S segment of the CVZ there is no clear migration pattern of the magmatism, except for the well-known eastward migration occurred at ca. 26 Ma.Moreover, we find that a) basement lithology or composition or mechanical features influenced distribution of volcanic activity; b) the NE–SW alignment of < 2.5 Ma caldera complexes coincides with the maximum depth of the Moho discontinuity and may be a further indicator of delamination processes in the Puna–Eastern Cordillera/Pampean Ranges border; and c) intense explosive volcanism concentrated during the 14–11.5 Ma interval along the eastern Puna border, which coincides in time with a peak in deformation and in space with the contact between basement units with different mechanical properties. No relationship between magmatic activity and azimuth or convergence rate between South American and Nazca plates are found, except for a peak in convergence rate at ~ 26 Ma.