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A re-appraisal of the stratigraphy and volcanology of the Cerro Galán volcanic system, NW Argentina

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https://ir.library.oregonstate.edu/concern/articles/sj139344n

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  • From detailed fieldwork and biotite ⁴⁰Ar/³⁹Ar dating correlated with paleomagnetic analyses of lithic clasts, we present a revision of the stratigraphy, areal extent and volume estimates of ignimbrites in the Cerro Galan volcanic complex. We find evidence for nine distinct outflow ignimbrites, including two newly identified ignimbrites in the Toconquis Group (the Pitas and Vega Ignimbrites). Toconquis Group Ignimbrites ~5.60-4.51 Ma biotite ages) have been discovered to the southwest and north of the caldera, increasing their spatial extents from previous estimates. Previously thought to be contemporaneous, we distinguish the Real Grande Ignimbrite (4.68 ± 0.07 Ma biotite age) from the Cueva Negra Ignimbrite (3.77 ± 0.08 Ma biotite age). The form and collapse processes of the Cerro Galan caldera are also reassessed. Based on re-interpretation of the margins of the caldera, we find evidence for a fault-bounded trapdoor collapse hinged along a regional N-S fault on the eastern side of the caldera and accommodated on a N-S fault on the western caldera margin. The collapsed area defines a roughly isosceles trapezoid shape elongated E-W and with maximum dimensions 27×16 km. The Cerro Galan Ignimbrite (CGI; 2.08 ± 0.02 Ma sanidine age) outflow sheet extends to 40 km in all directions from the inferred structural margins, with a maximum runout distance of similar to ~80 km to the north of the caldera. New deposit volume estimates confirm an increase in eruptive volume through time, wherein the Toconquis Group Ignimbrites increase in volume from the ~10 km³ Lower Merihuaca Ignimbrite to a maximum of ~390 km³ (Dense Rock Equivalent; DRE) with the Real Grande Ignimbrite. The climactic CGI has a revised volume of ~630 km³ (DRE), approximately two thirds of the commonly quoted value.
  • Keywords: Trapdoor, Caldera collapse, Cerro Galan, ⁴⁰Ar/³⁹Ar, Ignimbrite volumes
  • Keywords: Trapdoor, Caldera collapse, Cerro Galan, ⁴⁰Ar/³⁹Ar, Ignimbrite volumes
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  • Folkes, C. B., Wright, H. M., Cas, R. A. F., de Silva, S. L., Lesti, C., & Viramonte, J. G. (2011). A re-appraisal of the stratigraphy and volcanology of the cerro galán volcanic system, NW argentina. Bulletin of Volcanology, 73(10), 1427-1454. doi: 10.1007/s00445-011-0459-y
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  • 73
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  • 10
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  • This research was funded by an Australian Research Council Discovery Program Grant DP0663560 to the research team led by R. Cas. J.G. Viramonte wishes to thank Agencia de Promoción Científica y Tecnológica, MINCyT, Argentina, Grant PICT BID-1728 OC/AR 38131.
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