Abstract
The Andes Mountains provide an ideal natural laboratory to analyze the relationship between the tectonic evolution of a subduction margin, basin morphology, and volcanic activity. Magmatic output rates in Cordilleran-style orogenic systems vary through time and are characterized by high-flux magmatic events alternating with periods of low or no activity. The Neuquen Basin (34°S–40°S) of south-central Argentina is in a retroarc position and provides a geological record of sedimentation in variable tectonic settings. Strata ranging in age from Middle Jurassic to Neogene were sampled and analyzed to determine their detrital zircon U-Pb age spectra and Hf isotopic composition. When all detrital zircon data are combined, results indicate that significant pulses in magmatic activity occurred from 190 to 145 Ma, and at 129 Ma, 110 Ma, 67 Ma, 52 Ma, 16 Ma, and 7 Ma. The eHf values were highly evolved when the arc initiated at 190 Ma and transitioned into intermediate and juvenile values between ca. 160 and 150 Ma. There was a large shift toward more juvenile Hf isotopic values at 16 Ma that is consistent with renewed extension in the backarc during the Neogene. Overall geochemical trends in the Neuquen Basin section of the Andean arc are different from those observed in the central (21°S–26°S) and southern Andean arc (41°S–46°S), suggesting a segmented margin with variable tectonic settings and arc processes controlling magmatic output and chemistry along strike.
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