The Basin and Range landscape of Nevada has been shaped by crustal extension over the past tens of millions of years. This extension is accommodated by widespread faulting and synchronous magmatism, which has generated hazardous earthquakes, resulted in many plutons (i.e., crystalized magma bodies) associated with valuable ore deposits, and contributed to the high crustal temperatures that provide geothermal energy potential across the state. In this study, the principal investigators are investigating the styles and magnitudes of the crustal stretching and the relationship between faulting and pluton emplacement. In particular, different styles of crustal deformation affect the cooling of initially hot plutons and the regional geothermal gradient. The rate of crustal cooling directly impacts the extensional style, the overall strength of the crust, and the potential distribution of future earthquakes. The goal of this work is to reconstruct the tectonic and thermal histories of this part of the Basin and Range crust by investigating a tilted pluton that provides a unique exposure of the vertical compositional and paleo-thermal profile of the crust. This work has implications for understanding the tectonic and magmatic evolution of the Basin and Range, the crustal strength and depth of local earthquakes, and the linkage between tectonic and magmatic activities to high crustal temperatures and geothermal energy. In addition to the research goals of the project, important societal outcomes of the award including supporting the training of a graduate student in an important science, technology, engineering and mathematics (STEM) discipline. It is also advancing the research efforts of two early-career investigators. Participants of this project are also involved in public outreach programs at the University of Nevada, Reno thereby contributing to increased public science literacy and public engagement with STEM. These efforts include dissemination of cutting-edge research results with the public via outreach events including the annual Earth Science Week event at the Nevada Bureau of Mines and Geology. The development of digital mapping techniques, and the implementation of adaptive education via virtual reality mapping for students who may have physical disabilities that impair traditional field techniques and education, thereby contributing to the full participation of persons with disabilities in STEM education. Finally, this research echoes the recent community vision on the future challenges and opportunities in tectonics research and promotes the community effort to advance the knowledge of structural geology and tectonics
The project quantifies tectonic and thermal histories during the emplacement and subsequent cooling of the Miocene Searchlight pluton in the Colorado extensional corridor near Las Vegas to better understand the extensional faulting process. The PIs characterize structures and fabrics within the pluton to test the hypothesis that "the pluton experienced flow-like footwall rotation during simple-shear extension." This extensional mechanism makes specific predictions to be tested by constraining the nature of the observed fabrics, deformation kinematics within the pluton and wallrock, and cooling history through an integrated structural, numerical modeling, and thermochronology study. The working hypothesis is that the footwall rotation during simple-shear extension is a more effective crustal cooling mechanism than pure-shear modes of extension because rotation advects the hotter parts of the pluton toward the Earth's surface to cool. Rapid cooling increases the rheological strength of the upper crust and can act as a negative feedback to cease further rapid extension via brittle faulting. Various complementary methods are used in this study including (1) digital field mapping to characterize the fabric patterns, local shear sense, and contacts within the Searchlight pluton, (2) advanced microscopic study by electron backscatter diffraction to determine the nature, temperature, style, and kinematics of fabrics, (3) state-in-art computational simulations to construct and refine analytical/numerical thermo-kinematic models of footwall tilting and associated crustal cooling that will predict cooling histories to be tested via thermochronology, and (4) apatite and zircon (U-Th)/He thermochronometry to constrain the cooling history. This project sheds light on structural/tectonic processes linking transient thermal and rheological evolution of the crust with deformation mechanisms from grain to outcrop to regional scales. Thermochronology and modeling explore the thermal evolution during the extensional process and impacts on crustal rheology. The derived cooling rates, together with detailed structural analysis, constrain the geologic strain rates in the Basin and Range and new robust estimates for the timing and rates of Miocene extension in the Colorado extensional corridor. This study also sheds light on linkages between surface heat flux, ore formation, and hydrothermal systems.
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.
