Peninsular terrane basement ages recorded by Paleozoic and Paleoproterozoic zircon in gabbro xenoliths and andesite from Redoubt volcano, Alaska

Research Article| January 01, 2012 Peninsular terrane basement ages recorded by Paleozoic and Paleoproterozoic zircon in gabbro xenoliths and andesite from Redoubt volcano, Alaska Charles R. Bacon; Charles R. Bacon † 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA †E-mail: cbacon@usgs.gov Search for other works by this author on: GSW Google Scholar Jorge A. Vazquez; Jorge A. Vazquez 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA2U.S. Geological Survey, Stanford–USGS Ion Microprobe Laboratory, Green Earth Sciences Research Building, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Joseph L. Wooden Joseph L. Wooden 3Department of Geological and Environmental Sciences, Stanford University, Stanford–USGS Ion Microprobe Laboratory, Green Earth Sciences Research Building, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Charles R. Bacon † 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA Jorge A. Vazquez 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA2U.S. Geological Survey, Stanford–USGS Ion Microprobe Laboratory, Green Earth Sciences Research Building, Stanford, California 94305, USA Joseph L. Wooden 3Department of Geological and Environmental Sciences, Stanford University, Stanford–USGS Ion Microprobe Laboratory, Green Earth Sciences Research Building, Stanford, California 94305, USA †E-mail: cbacon@usgs.gov Publisher: Geological Society of America Received: 04 Nov 2010 Revision Received: 11 May 2011 Accepted: 13 May 2011 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2012 Geological Society of America GSA Bulletin (2012) 124 (1-2): 24–34. https://doi.org/10.1130/B30439.1 Article history Received: 04 Nov 2010 Revision Received: 11 May 2011 Accepted: 13 May 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 Charles R. Bacon, Jorge A. Vazquez, Joseph L. Wooden; Peninsular terrane basement ages recorded by Paleozoic and Paleoproterozoic zircon in gabbro xenoliths and andesite from Redoubt volcano, Alaska. GSA Bulletin 2012;; 124 (1-2): 24–34. doi: https://doi.org/10.1130/B30439.1 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 Historically active Redoubt volcano is an Aleutian arc basalt-to-dacite cone constructed upon the Jurassic–Early Tertiary Alaska–Aleutian Range batholith. The batholith intrudes the Peninsular tectonostratigraphic terrane, which is considered to have developed on oceanic basement and to have accreted to North America, possibly in Late Jurassic time. Xenoliths in Redoubt magmas have been thought to be modern cumulate gabbros and fragments of the batholith. However, new sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages for zircon from gabbro xenoliths from a late Pleistocene pyroclastic deposit are dominated by much older, ca. 310 Ma Pennsylvanian and ca. 1865 Ma Paleoproterozoic grains. Zircon age distributions and trace-element concentrations indicate that the ca. 310 Ma zircons date gabbroic intrusive rocks, and the ca. 1865 Ma zircons also are likely from igneous rocks in or beneath Peninsular terrane basement. The trace-element data imply that four of five Cretaceous–Paleocene zircons, and Pennsylvanian low-U, low-Th zircons in one sample, grew from metamorphic or hydrothermal fluids. Textural evidence of xenocrysts and a dominant population of ca. 1865 Ma zircon in juvenile crystal-rich andesite from the same pyroclastic deposit show that this basement has been assimilated by Redoubt magma. Equilibration temperatures and oxygen fugacities indicated by Fe-Ti–oxide minerals in the gabbros and crystal-rich andesite suggest sources near the margins of the Redoubt magmatic system, most likely in the magma accumulation and storage region currently outlined by seismicity and magma petrology at ∼4–10 km below sea level. Additionally, a partially melted gabbro from the 1990 eruption contains zircon with U-Pb ages between ca. 620 Ma and ca. 1705 Ma, as well as one zircon with a U-Th disequilibrium model age of 0 ka. The zircon ages demonstrate that Pennsylvanian, and probably Paleoproterozoic, igneous rocks exist in, or possibly beneath, Peninsular terrane basement. Discovery of Pennsylvanian gabbro similar in age to Skolai arc plutons 500 km to the northeast indicates that the Peninsular terrane, along with the Wrangellia and Alexander terranes, has been part of the Wrangellia composite terrane since at least Pennsylvanian time. Moreover, the zircon data suggest that a Paleoproterozoic continental fragment may be present in the mid-to-upper crust in southern Alaska. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.