The Randolph Bromery Spring 2019 Seminar Series: Michael Ackerson

Description

Dr. Michael Ackerson, a geologist at Smithsonian National Museum of Natural History, will give a talk entitled "Partially-molten Granites at 500 °C? Reimagining Crustal Magmatism" for the Department of Earth & Planetary Sciences.

Abstract:

Extracting crystallization temperatures and thermal histories recorded within minerals is critical to understanding granitic magma assembly and elucidating the relationship between silicic plutonic and volcanic systems. Recent work has suggested that magmas may undergo "cold storage" at temperatures cooler than previously thought possible — in some cases these temperature estimates are below the wet solidus. These observations complicate conventional interpretations of magma evolution and require more work to constrain both the thermal and chemical evolution of silicic magmas and the extent of low-temperature processes retained in the rock record.

Here, we utilize Ti-in-quartz thermobarometry combined with diffusion modeling of Ti concentration profiles in quartz to place constraints on the crystallization temperatures and cooling histories recorded in granitic rocks of the Tuolumne Intrusive Suite (TIS) — a compositionally-zoned group of calc-alkaline granitoids in the Sierra Nevada mountains in California. Our results suggest that a significant proportion of quartz within these granites crystallized at temperatures below the granitic wet solidus. These and other results reveal complex super- and sub-solidus crystallization histories recorded in granitic minerals, potentially providing clues to the nature of cold storage and the relationship between plutonic rocks, volcanic rocks, and ore deposits.