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A Preliminary Low-Temperature Exhumation Study of the Central Aleutian Islands, Alaska
  • Anahi Carrera,
  • Emily HG Cooperdock
Anahi Carrera
University of Southern California

Corresponding Author:anahicar@usc.edu

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Emily HG Cooperdock
University of Southern California
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Abstract

Exhumation in continental and oceanic arc settings is linked to tectonic and climatic forces that result in some of the highest topography and erosion rates in the world. Regional exhumation studies of oceanic arcs are sparse due to poor exposure, accessibility, complex inherited structures, and thermal overprinting due to magmatism, reburial, and metamorphism. In contrast, the Aleutian arc has an unusually thick crust, exceptional subaerial exposure of plutons, and limited regional thermal overprinting, providing the ideal conditions for a systematic thermochronology study that investigates the mechanisms that lead to arc exhumation. By analyzing multiple chronometers (apatite and zircon (U-Th)/He, zircon U-Pb) with different temperature sensitivities within the same plutonic sample, we can constrain uplift and erosion rates over ~40 million years of Aleutian arc history. Here, we present preliminary apatite and zircon (U-Th)/He ages from 23 plutonic samples from the islands of Unalaska, Umnak, Atka, Ilak, and Amatignak. These data are part of a larger study where we will analyze a total of 78 samples collected from 11 plutons along >1400 km of the Central Aleutian Islands. Ultimately, this dataset will provide a regional framework to quantitatively assess the various proposed mechanisms for Aleutian arc exhumation, such as; 10° Pacific plate rotation, subduction of the Kula ridge, and/or pluton emplacement, each of which has predictable and testable geographic age trends. The samples analyzed are from plutons that crystallized in the Oligocene to Miocene based on zircon U-Pb dating. Both zircon and apatite (U-Th)/He ages also show an Oligocene to Miocene spread, with a majority of the ages from both chronometers pooling at 7-13 Ma and no particular geographic trend. These preliminary results suggest that a significant exhumation event occurred in the late Miocene, as has been observed in other circum-Pacific arcs. These preliminary data may support the hypothesis that the late Miocene pulse of high plutonism in the Aleutian Islands led to arc exhumation. However, additional samples need to be analyzed to provide an arc-scale view of exhumation timing, trends, and rates of the Central Aleutian arc in order to test possible uplift and erosion scenarios.