Collaborative Research: What are the Mechanisms and Timescales of Contact Metamorphism in Long-lived Magmatic and Hydrothermal Systems?

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Researchers from Utah Valley University and University of Utah will reconstruct the thermal history of a long-lived plutonic system to determine how pulsed magmatism affects heat and mass transfer in the Earth's crust. Understanding the movement of heat and mass in the Earth's crust directly improves the understanding of other crustal systems such as geothermal systems, ore bodies, and geological hazards associated with volcanism. Multiple mineral phases with complementary strengths as geochronometers, together with multiple analytical techniques, will be used to produce a high-fidelity temperature (T)-time (t) record for the Alta-Little Cottonwood stock system, Utah, USA. In-situ microanalytical techniques will be used to place analytical results (mineral ages, chemistry) in textural and spatial context in order to connect these analytical results to the geologic processes responsible for the evolution of this magmatic-metamorphic system. The research outcomes could redefine our understanding of both the magmatic and metamorphic processes in these systems and in turn affect how we best utilize thermal and mineral resources and prepare for volcanic hazards. This project will strengthen research at a primarily undergraduate institution. In addition, a summer-school program will broaden participation in Earth Science and disseminate scientific content to middle school students in the context of the Utah Science Core curriculum. The project will address fundamental questions of how incremental pluton emplacement and evolving permeability structures govern the temporal and spatial patterns of (hydro-) thermal metamorphism. Preliminary petrochronology results indicate that hydrothermal alteration of the Alta stock (AS), and possibly also growth of the contact aureole, occurred over ~10 Myr. This project will reconcile the small size of the AS with the large areal extent of its contact aureole (AA) and determine whether emplacement of the Little Cottonwood Stock (LCS) instead drove protracted, episodic hydrothermal and contact metamorphism in the adjacent AS and aureole. The researchers will apply in situ (LASS-ICP-MS) and high precision (CA-TIMS) U-Pb dating of titanite, zircon, and garnet in conjunction with thermal modeling to construct a robust T-t history of the system. They will test whether 1) the AS was a conduit for long-lived, episodic hydrothermal fluid-flow driven by emplacement of the LCS; 2) the hydrothermal system driven by emplacement of the LCS merely overprinted the western portion of the AS; or 3) a younger intrusion is responsible for the protracted hydrothermal systems in both stocks. The results of this project will impact our understanding of the transfer, storage, and crystallization of magmas, timescales of ore-body genesis, isotopic dating of major mineral phases, the timescales of contact metamorphic reactions, heat and mass transfer in orogens, and thermal modeling of magma and hydrothermal conduits.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.