33-11 Evidence for Cenozoic Deformation in the Porcupine Fault System, Alaska, from fault rock hematite (U-Th)/He thermochronology and microstructural analysis

Session: Going with the Shear - New Insights into Lithospheric Extensional and Strike-Slip Systems (Posters)

Poster Booth No.: 248

Presenting Author:

Allison Kim

Authors:

Kim, Allison E.¹, Odlum, Margo L.², Strauss, Justin V.³, Donaghy, Erin Elizabeth⁴, Rasbury, Emma Troy⁵, McClelland, William C.⁶, Faehnrich, Karol⁷

(1) Scripps Institute of Oceanography, University of California San Diego, La Jolla, CA, USA, (2) Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA, (3) Dartmouth College, Hanover, NH, USA, (4) University of Nevada, Las Vegas, Las Vegas, NV, USA; Dartmouth College, Hanover, NH, USA, (5) Stony Brook University, Stony Brook, NY, USA, (6) University of Iowa, Iowa City, IA, USA, (7) University of Adelaide, Adelaide, Australia; Dartmouth College, Hanover, NH, USA,

Abstract:

The Porcupine Fault System (PFS) is a large-scale fault zone in northeastern Alaska and northwestern Yukon, representing a major boundary that potentially accommodated the translation of the Arctic Alaska terrane along northwestern Laurentia. Previous studies suggest the PFS accommodated terrane translation during the Paleozoic, and it has been proposed that the PFS played a key role in the Cretaceous opening of the Canada Basin. However, kinematically contextualized geo- and thermochronological data from the PFS are needed to understand the Mesozoic-Cenozoic deformation history. Here, we investigate the thermochronology of hematite-coated fault rocks from rocks within and adjacent to the PFS. Sampled rock types consisted of Paleozoic shales and sandstones, with hematite coated fault surfaces containing slickenlines that indicate oblique and/or normal slip kinematics. Apatite (U-Th)/He dates from the fault host rocks range from ~55 - 88 Ma. Eighteen hematite aliquots from two faults within the PFS were microstructurally characterized and targeted for hematite (U-Th)/He (He). Hematite He analysis yielded a range of Miocene–Pleistocene dates from ~0.7 - 8.5 Ma, significantly younger than the apatite He dates from the host rocks. Microstructural analysis of hematite slip-surfaces reveals platy, cataclasite, and botryoidal grain morphologies with grain sizes generally decreasing towards the slip surface, notably with a lack of high-temperature hematite morphologies. These microstructures indicate that the hematite was deformed via brittle deformation mechanisms, including cataclasis and comminution, during or after its formation in the shallow crust. Hematite He closure temperatures calculated from grain size distributions are higher than those of apatite He, supporting that the hematite He dates record precipitation in the shallow crust. Our preliminary findings imply Cenozoic displacement in the PFS continued through the Pleistocene and likely played a role in the formation of large Cenozoic basins in eastern Alaska, such as the Yukon Flats.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.