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New 40Ar/ 39Ar dates from the Caliente caldera complex, Nevada-Utah; at least 10 million years of Tertiary volcanism in one of the world's largest caldera complexes

, : New 40Ar/ 39Ar dates from the Caliente caldera complex, Nevada-Utah; at least 10 million years of Tertiary volcanism in one of the world's largest caldera complexes. Abstracts with Programs - Geological Society of America 32(7): 461

The Caliente caldera complex consists of an 80 km E-W by 35 km N-S area of nested calderas in the southeastern Great Basin. It is bounded on its north and south sides by E-W shear zones that provided magmatic pathways for stratovolcanoes, volcanic domes, breccia pipes, and other volcanic vents. The E-W zones also provided fluid pathways that resulted in adjacent hydrothermal gold deposits of the Delamar, Chief, Easter, Pennsylvania, and Goldstrike mining districts. The E-W shear zones are interpreted as transverse zones, which are broad belts of accommodation that enabled crust north and south of them to extend at different rates, amounts, and methods. The caldera complex is a subsided area, in which extension and magmatic dilation occurred together. Age constraints are provided by 150 argon dates, having one-sigma analytical errors generally less than 0.1 Ma, on sanidine, hornblende, and biotite. Eruptions from stratovolcanoes and their source plutons in the caldera complex were active from 25-22 Ma. Ash-flow eruptions resulted in the Swett (about 23.7 Ma) and Bauers (22.8 Ma) Tuff Members of the Condor Canyon Formation, Hiko Tuff (18.3 Ma), tuff of Teepee Rocks (17.8 Ma), tuff of Dow Mountain (about 17.4 Ma), tuff of Acklin Canyon (17.1 Ma), tuff of Rainbow Canyon (15.6 Ma), tuff of Etna (14.0 Ma), and Ox Valley Tuff (about 13.5 Ma). Associated intrusions, volcanoes, domes, and breccia pipes in the complex and adjacent transverse zones have similar dates. About 17.8-17.4 Ma, magmatism changed from calc-alkaline to more alkalic, younger and bimodal basalt-rhyolite volcanism. This petrologic transition has been linked temporally to the approximate change from more intense pre-basin-range extension to more widely spaced and lower rates of classic basin-range extension.


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