Collaborative Research: Evaluating the Exhumation History of the Aleutians with Zircon and Apatite Thermochronology

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Island arcs are chains of volcanic islands that form at subduction zone plate boundaries where one plate is being dragged beneath another, recycling old crust to the Earth’s mantle and creating new continental crust through volcanism. A central question surrounding these systems is whether processes that occur deeply in the subduction zone affect processes that are observed on the surface. This is especially debated for what drives surface uplift and related island arc exhumation and erosion. Uplift and exhumation of island arcs in other localities have been attributed to a variety of factors, from deep tectonic drivers to climate-surface interactions, with exhumation rates and erosion estimates that vary by orders of magnitude. In many locations, the arc exhumation history is difficult to study because it may be overprinted by later thermal or physical processes. The Aleutian Arc is unique in that it includes over 50 islands composed of both active and inactive volcanoes over 1,900 miles from Alaska to Russia, and has limited overprinting by secondary events. In addition, it has a volcanic history that spans 50 million years, so that the ancient magma chambers of past volcanoes are now exposed on the islands’ surfaces today. These plutonic rocks hold a record of past island uplift, exhumation, and erosion that can address key questions regarding: When were the Aleutians uplifted? When and how much has been eroded through time? Was uplift and subsequent erosion constant or cyclical? How does it vary geographically along the length of the arc? Specifically, the answers to these questions will shed light on the link between plate-scale processes and uplift; the timing and magnitude of erosion, contributing sediment and geochemical inputs to North Pacific; and the relationship between plutonic exhumation rates, geochemistry, and emplacement depth. The Aleutians have functioned as a natural laboratory to test fundamental principles regarding subduction zone evolution for more than four decades. This study will make a novel contribution to the existing extensive geochemical and geodynamic research. In terms of Broader Impacts, this award supports a new PI and engages underrepresented minority students and teachers, from the undergraduate through K-12 level. In order to quantify when and by how much the Aleutians experienced surface uplift and erosion, plutonic samples from ~10 islands that span 870 miles of arc length will be analyzed for emplacement depth and subsequent uplift rates. This work will place the exhumation history of the Central Aleutians in the context of 1) driving forces involving regional tectonics and subduction zone processes; and 2) geochemical inputs to the N. Pacific via erosion of arc material. In order to answer these questions, previously sampled and well-characterized plutonic rocks from across the central Aleutians will be characterized by pluton crystallization age, emplacement depth, and 2 or more thermochronometers with different thermal sensitivities (e.g., apatite and/or zircon, (U-Th)/He and/or fission track). Thermochronology techniques, particularly the use of multiple chronometers with different temperature sensitivities within the same sample, can constrain exhumation rates and be used to estimate erosion rates over time. Coupling the thermochronological data with emplacement depth will help constrain the amount of material eroded over that time. The timing and geographic trends revealed by these data can then be related in time and space to previously proposed drivers for uplift, including plate rotation, change in convergence angle and rate, or the development of an accretionary prism.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.