The circulation of water deep in the earth?s crust underlies a variety of highly significant geological processes, including formation of ore bodies, heat flow in geothermal fields, and the thermal, mineralogical and chemical evolution of crustal rocks and magmas. Most crustal water circulation occurs at depths of less than 10 kilometers because this is the range over which pores and fractures remain open against the pressure of overlying rocks. One of the great challenges to our understanding of this phenomenon is that our tools for measuring the temperatures experienced by rocks in this upper portion of the crust generally provide only semi-quantitative or relative constraints. And, this ambiguity in temperature confounds efforts to define the chemistry of waters that have reacted with rocks. For this reason, our firmest grip on crustal water-rock reaction is confined to narrow (~1 km) haloes of hot rock immediately surrounding intruding magmas, where elevated temperatures drive mineralogical reactions that can be used as rigorous temperature constraints.
This project will re-examine this problem using a recently invented method of thermometry that allows for the precise quantitative measurement of temperatures of water-rock reaction over a wide range of temperatures common to the upper 10 km of the crust. This method, 'carbonate clumped isotope thermometry', is based on the grouping together of rare isotopes of carbon and oxygen into the same molecular groups in minerals such as calcite and dolomite. Analysis of these rare isotopic molecules is technically challenging but enabled by recent innovations in mass spectrometry, and has led to advances in the study of past climates, topography of the earth's surface, temperatures of faults, geologic histories of petroleum deposits, body temperatures of dinosaurs and other problems. The method should also define the isotopic compositions of waters that co-existed with carbonate minerals, letting one 'map' the circulation of fluid at depth. This project will be the first time this tool has been applied to a significant problem in the thermal and chemical evolution of the deep crust.
The study area, Notch Peak, Utah, is exceptionally well exposed and well studied, meaning the results of this project's measurements can be compared to detailed models of the distribution of heat and fluids. An expected outcome of this project is that quantitative, predictive models of temperatures and fluid migration pathways in this environment will be extended out of the narrow belt of hot rocks that surrounds the Notch Peak magmatic intrusion and into the broad surrounding region of more typical crustal rocks. This result could lead to advances in understanding of ore bodies, oil and gas fields, and hydrothermal energy resources.
