UMD: Ackerson on Tuolumne quartz

2016 Geology Colloquium Series

Friday, October 14th 2016 at 3:00 pm
in PLS 1140

Mike Ackerson
Carnegie Institution for Science

Low-temperature crystallization of granites recorded in quartz from the Tuolumne Intrusive Suite

The granitic wet solidus is a curve in temperature, pressure and composition space below which silicate melt is not present. Based on the experimentally-determined solidus curves for granitic bulk compositions, it is often assumed that granitic mineral assemblages do not crystallize below ~650-700 °C. However, some experimental data indicate that hydrous peralkaline melts can exist in equilibrium with two feldspars and quartz to temperatures as low as 330 °C. It has yet to be demonstrated whether granitic melts exist in nature to such low temperatures. Ti-in-quartz thermobarometry of granitic rocks in the Tuolumne Intrusive Suite (TIS) of the Sierra Nevada Batholith indicates that quartz in the TIS records crystallization temperatures ~122-227 °C below the commonly accepted (traditional) granodiorite wet solidus. This observation agrees with two-feldspar thermometry of the TIS and demonstrates that for some granitic systems, the tradit! ional granitic wet solidus is not the low-temperature limit of granitic magmatism.

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