NSF Award
2418804
Subduction zones are regions where two tectonic plates move towards each other and one of them sinks, or “subducts”, beneath the other. They cause major hazards like earthquakes, volcanic eruptions, and landslides. They are also the main way that surface materials, such as water, are dragged deep into the interior of Earth. Many such effects stem from the chemical changes that subducting rocks undergo as they sink deeper and get hotter. The sinking tectonic plate's temperature, known as the "subduction zone thermal structure," influences these changes. One important avenue of subduction research thus aims to constrain this thermal structure and how quickly it changes. However, because many of the important processes mentioned above occur very deep below the surface, we cannot make direct measurements of the temperature here. To overcome this, the researchers will instead use chemical measurements of rocks that have resurfaced from an ancient subduction zone. By analyzing the chemistry of these rocks, they can measure the extreme pressures and temperatures they experienced when they were deep underground. To do this, they will focus on the western Alps of Switzerland and Italy, which is a well-studied fossilized subduction zone. They will combine measurements of the rocks with computer simulations of this ancient subduction zone, to home in on this subduction zone’s thermal structure. This study will help us understand when, why, and how quickly these temperature changes occur. This project will also support student researchers and benefit society through educational and scientific outreach activities. The team's outreach component will be a subduction-focused workshop at the University of South Carolina. It will bring together geoscientists from the southeastern U.S, with the goal of fostering collaboration and team building.<br/><br/>In this project, the researchers aim to constrain the time-evolving pressure-temperature (P-T) conditions along the well-studied Western Alps paleo-subduction interface, the timescales of metamorphism, and the mechanisms responsible for spatio-temporal variations in this thermal structure and metamorphism. They will combine garnet petrochronology (P-T constraints and geochronology) with P-T-time constraints from the literature to create a series of “snapshots” of the evolving Alpine paleo-subduction P-T conditions. These field-based constraints will be integrated with geodynamic subduction models to help determine the geodynamic mechanisms and parameters needed to explain the Ps, Ts and rates of metamorphism observed in the exhumed rock record. This integrated approach will enable them to test their primary geodynamic hypothesis: A highly time-dependent thermal evolution is causally linked to spatio-temporal dependent changes in the lithology/structure of the downgoing plate and to the significant three-dimensionality of the Alpine subduction zone. The petrochronology work will benefit from the large spatial and temporal subduction rock record offered by the Western Alps, allowing for the sampling and examination of lithologically various exhumed terranes to determine a P-T-time history. Recent advances in the time-dependent modeling of subduction zone thermal structure will enable the team to test the hypotheses within 3-dimensional and “dynamic” models (i.e., with no external forces imposed on the system). An important component of this project is the bi-directional integration of the modeling and the geological observations, wherein a), constraints from the rock record will inform the dominant physical processes that enter the geodynamic modeling, and b), targeted sampling and analysis will be informed by the geodynamic modeling results. This project will also support student researchers and benefit society through educational and scientific outreach activities. The outreach component will be a subduction-focused workshop at the University of South Carolina. It will bring together geoscientists from the southeastern U.S, with the goal of fostering collaboration and team building.<br/><br/>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.
