32 D28. Volcanology

Monday, 26 October 2020
5:30 PM - 8:00 PM
Meeting Rooms

U-PB AGES OF DETRITAL ZIRCON AND THEIR CORRELATION TO LOCAL TECTONICS OF THE ALTIPLANO-PUNA, CHILE

Paper number: 32-10
Program: Technical Sessions
Time: 7:30 PM – 7:40 PM

Authors

Abstract

The relative contributions of tectonism and volcanism to uplift of the Andean Plateau of the Central Andes are debated. In the region of the Altiplano-Puna Volcanic Complex (22° – 24°S) previous work has suggested a link between a 10-1 Ma ignimbrite flare-up and tectonic uplift of the Altiplano-Puna. We are investigating a series of east-dipping ignimbrite flatirons in the Quebrada Lican, northwest of the Salar de Atacama, Chile, where ignimbrites ranging from 10 to 4.09 Ma are interbedded with gravels. By analyzing the ages of detrital zircon in the gravels, we are able to constrain their relations to the ignimbrites and potential source areas. Three samples were taken from two gravel horizons between a 23 to 33 Ma evaporative unit, the Paciencia Group, and the 8.2 Ma Sifon ignimbrite. Approximately 100 detrital zircon grains from each sample were analyzed using LA-ICP mass spectrometry. The lowest sample was taken from a pink gravel horizon directly overlying the Paciencia Group. Detrital zircon grains yielded U-Pb ages that are 86% Cenozoic but older than 10 Ma, 3% Cretaceous, and 11% Triassic and older. The remaining samples were taken from gravels 28m and 4m below the base of the Sifon ignimbrite, from purple gravel horizons. The lower sample has 7% grains between 8.5 and 10 Ma, 33% Cenozoic in age but older than 10 Ma, and 60% Mesozoic and older. The upper sample has 62% grains between 8.18 and 10 Ma, 17% Cenozoic in age but older than 10 Ma, and 21% Mesozoic and older. The sources of the zircon were not limited to sediments eroded from the Altiplano-Puna to the east and underlying ignimbrites. Early sediments are dominated by Mesozoic and older grains derived from the fossil Cretaceous arc and the Cordillera de Domyeko to the west. The percentage of younger grains increases up-section, indicating a progressively younger source material was being eroded as the ignimbrite flare-up progressed in tandem with uplift of the Altiplano-Puna.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-359483

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