Evolving heavy mineral assemblages reveal changing exhumation and trench tectonics in the Mesozoic Chugach accretionary complex, south-central Alaska

Abstract

Research Article| May 01, 2012 Evolving heavy mineral assemblages reveal changing exhumation and trench tectonics in the Mesozoic Chugach accretionary complex, south-central Alaska Peter D. Clift; Peter D. Clift † 1School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK †E-mail: pclift@lsu.edu; current address: Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA. Search for other works by this author on: GSW Google Scholar Nico M. Wares; Nico M. Wares 1School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK Search for other works by this author on: GSW Google Scholar Jeffrey M. Amato; Jeffrey M. Amato 2Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA Search for other works by this author on: GSW Google Scholar Terry L. Pavlis; Terry L. Pavlis 3Department of Geology and Geophysics, University of Texas, El Paso, Texas 79968, USA Search for other works by this author on: GSW Google Scholar Malcolm J. Hole; Malcolm J. Hole 1School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK Search for other works by this author on: GSW Google Scholar Caleb Worthman; Caleb Worthman 2Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA Search for other works by this author on: GSW Google Scholar Erik Day Erik Day 3Department of Geology and Geophysics, University of Texas, El Paso, Texas 79968, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Peter D. Clift † 1School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK Nico M. Wares 1School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK Jeffrey M. Amato 2Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA Terry L. Pavlis 3Department of Geology and Geophysics, University of Texas, El Paso, Texas 79968, USA Malcolm J. Hole 1School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK Caleb Worthman 2Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA Erik Day 3Department of Geology and Geophysics, University of Texas, El Paso, Texas 79968, USA †E-mail: pclift@lsu.edu; current address: Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA. Publisher: Geological Society of America Received: 16 Aug 2011 Revision Received: 03 Nov 2011 Accepted: 29 Nov 2011 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2012 Geological Society of America GSA Bulletin (2012) 124 (5-6): 989–1006. https://doi.org/10.1130/B30594.1 Article history Received: 16 Aug 2011 Revision Received: 03 Nov 2011 Accepted: 29 Nov 2011 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Peter D. Clift, Nico M. Wares, Jeffrey M. Amato, Terry L. Pavlis, Malcolm J. Hole, Caleb Worthman, Erik Day; Evolving heavy mineral assemblages reveal changing exhumation and trench tectonics in the Mesozoic Chugach accretionary complex, south-central Alaska. GSA Bulletin 2012;; 124 (5-6): 989–1006. doi: https://doi.org/10.1130/B30594.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Gulf of Alaska is one of the largest accretionary complexes on Earth. In this study, we examined the earliest phase of accretion in the Mesozoic McHugh Complex and Valdez Groups, exposed in SE Alaska. The oldest preserved fragment, the Mesomélange assemblage, is Jurassic (ca. 160–140 Ma) and consists of an ∼3-km-thick structural package of strongly deformed shaley materials with slices of oceanic cherts and basalts. Heavy minerals indicate dominant erosion from a magmatic arc source uplifted after the collision of the Wrangellia and the Talkeetna oceanic arc. A tectonic erosion event affected the forearc just prior to ca. 120 Ma and was likely caused by seamount collision, ridge subduction, or both. This was followed at 105 Ma by mass wasting of sandstone and conglomerates, preserved as the Graywacke-Conglomerate assemblage (ca. 105–83 Ma). Heavy minerals indicate continued flux from arc sources, but with significant changes suggesting a larger, more diverse catchment area. Erosion of deeper crustal sources provided high-Mg diopside and garnets to the trench. Faster sediment flux was caused by rock uplift triggered by final accretion of the Wrangellia-Peninsula terrane to North America. The start of large-scale accretion in Alaska roughly coincided with the initiation of Shimanto Complex accretion in Japan and can be understood as primarily linked to sediment supply driven by plate-margin tectonics rather than climatically induced erosion onshore. 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