Detrital zircon double-dating of forearc basin strata reveals magmatic, exhumational, and thermal history of sediment source areas

Abstract

Research Article| January 30, 2019 Detrital zircon double-dating of forearc basin strata reveals magmatic, exhumational, and thermal history of sediment source areas Eva Enkelmann; Eva Enkelmann † 1University of Calgary, Department of Geoscience, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada †eva.enkelmann@ucalgary.ca Search for other works by this author on: GSW Google Scholar Sonia K. Sanchez Lohff; Sonia K. Sanchez Lohff 2University of Cincinnati, Department of Geology, 500 Geology Physics Building, Cincinnati, Ohio 45221-0013, USA Search for other works by this author on: GSW Google Scholar Emily S. Finzel Emily S. Finzel 3University of Iowa, Department of Earth and Environmental Science, 115 Trowbridge Hall, Iowa City, Iowa 52242, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Eva Enkelmann † 1University of Calgary, Department of Geoscience, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada Sonia K. Sanchez Lohff 2University of Cincinnati, Department of Geology, 500 Geology Physics Building, Cincinnati, Ohio 45221-0013, USA Emily S. Finzel 3University of Iowa, Department of Earth and Environmental Science, 115 Trowbridge Hall, Iowa City, Iowa 52242, USA †eva.enkelmann@ucalgary.ca Publisher: Geological Society of America Received: 22 May 2018 Revision Received: 04 Oct 2018 Accepted: 21 Nov 2018 First Online: 31 Jan 2019 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2019 Geological Society of America GSA Bulletin (2019) 131 (7-8): 1364–1384. https://doi.org/10.1130/B35043.1 Article history Received: 22 May 2018 Revision Received: 04 Oct 2018 Accepted: 21 Nov 2018 First Online: 31 Jan 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Eva Enkelmann, Sonia K. Sanchez Lohff, Emily S. Finzel; Detrital zircon double-dating of forearc basin strata reveals magmatic, exhumational, and thermal history of sediment source areas. GSA Bulletin 2019;; 131 (7-8): 1364–1384. doi: https://doi.org/10.1130/B35043.1 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 Subduction along the southern margin of Alaska, USA, has been ongoing since at least the Jurassic. However, the character of the subducting slab has changed through time and has included subduction of normal oceanic crust, a spreading ridge, and an oceanic plateau. The latter two resulted in a change of subduction mode by inducing a shallow subduction angle. Geologic processes and landscape evolution of the overriding plate were affected by these variations in subduction mode and are recorded in the forearc basin strata. We investigate the Cenozoic to modern sediment of the forearc Cook Inlet basin in south-central Alaska. Here we use a double-dating approach that combines fission track dating and U-Pb dating on individual detrital zircon grains. In total we analyzed more than 1700 zircons from Eocene to Pliocene strata and modern river sand that has eroded from the surrounding regions of the Cook Inlet basin. The double-dating approach combined with the existing knowledge of the regional geology allows us to discriminate between magmatic cooled grains of extrusive and shallow intrusive rocks, exhumational cooled grains, and thermal reset grains. We find that the erosion of both shallow and deep intrusive arc rocks dominate the detrital age signal, while syn-depositional extrusive grains are lacking. The erosion of rocks that have been thermally altered during the subduction of a spreading ridge dominates the fission track (FT) age signal. This pattern is particularly prominent in the accretionary prism where ages in the most inboard (older) portion have not been thermally reset, but thermal resetting is prevalent in the outboard (younger) portion located proximal to the Paleocene–Eocene near-trench intrusions. Thermal alteration is also evident in the region of the arc that was affected by the passage of the asthenospheric slab window. The erosional signal of the more inboard arc and backarc region (Alaska Range) is characterized by exhumational FT ages of deep-seated rocks, which currently provide material into the forearc basin. This age signal results from flat-slab subduction of the Yakutat microplate, which transfers stress far inboard and produces significant mountain building and deformation. This exhumational age signal, however, is not recorded in the late Cenozoic strata, suggesting that the modern landscape developed since <3 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.