THE CHOIYOI SILICIC LARGE IGNEOUS PROVINCE OF ARGENTINA AND CHILE AND ITS POSSIBLE INFLUENCE ON PERMIAN ENVIRONMENTAL DEGRADATION AND MASS EXTINCTION

MAHONEY, J.B.; GROVE, M.; KIMBROUGH, D.L.; GIAMBIAGI, L. B.; MESCUA, J. F.

Denver

Congreso; Geological Society of America General Meeting in Denver; 2016

The Permo-Triassic Choiyoi magmatic province of central and southern Argentina and Chile (23°-42°S) has an aerial extent of ~664,000 km2 and dominant rhyolite-ignimbrite composition that rank it amongst the largest silicic large igneous provinces on earth. Twenty-five new laser ablation ICP-MS zircon ages from Choiyoi volcanic rocks in two key Argentina transects in central Mendoza (32°S) and San Juan (33°S) define a strongly episodic history of magmatism with a major peak in volcanic activity at 266±3 Ma. This includes ~266 Ma emplacement ages throughout >1 km thick sections in each transect that attest to rapid generation and emplacement of silicic magmas. Volcanic alkali feldspars (anorthoclase) from the same samples are compositionally unmixed. These altered feldspars yield highly scattered 40Ar/39Ar results similar to those produced from previous K-Ar and Ar-Ar dating efforts in the area. The pronounced 266±3 Ma flareup in Choiyoi magmatism is corroborated by detrital zircon U-Pb age peaks in middle Triassic and Neogene sedimentary basins as well as a compilation of published zircon U-Pb ages. This peak in Choiyoi magmatism represents a short duration outburst of silicic volcanic activity that overlaps with several major events occurring around this time that include Olson?s mass extinction, the Kamura cooling event, a decline in diversity of fusulinoids, carbon isotope excursions as well as other phenomena, external causes for which have gone unrecognized. These events precede the two closely spaced major mass extinction events that close out the Paleozoic Era, the Permo‐Triassic and Guadalupian?Tatarian mass extinctions which are each associated with major flood basalt eruption, the Siberian Traps (253‐250 Ma) and the Emeishan Traps (260‐257 Ma), respectively. The Choiyoi flareup at 269-263 Ma was therefore the first in a sequence of three closely spaced LIP magmatic events that may have collectively contributed to sustained environmental instability driving Middle and Late Permian extinction events.