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Construction and evolution of the Kodiak Talkeetna Arc crustal section, Southern Alaska

David W. Farris
Construction and evolution of the Kodiak Talkeetna Arc crustal section, Southern Alaska (in Crustal cross sections; from the western North American Cordillera and elsewhere; implications for tectonic and petrologic processes, Robert B. Miller (editor) and Arthur W. Snoke (editor))
Special Paper - Geological Society of America (2009) 456: 69-96

Abstract

The Kodiak Border Ranges ultramafic complex, Afognak batholith, and Shuyak Formation on Kodiak and Afognak Islands together form the lower, middle, and upper portions, respectively, of a Jurassic-Triassic island-arc crustal section. The Kodiak section exhibits structural and geochemical trends similar, but not identical to, the Tonsina-Nelchina segment of the Talkeetna arc, located >500 km to the northeast. Exposed at the base of the Kodiak section is cumulate clinopyroxenite with associated dunite, wehrlite, and layered gabbro. In the inferred middle to upper crust, tonalite and quartz diorite of the Afognak batholith intrude Shuyak Formation basaltic flows, basaltic pillow lavas, and volcaniclastic sedimentary rocks. Despite the fault-bounded nature of the lower crustal and mantle rocks, continuous chemical trends in elements such as MgO, Ni, Cr, Nb, Sr, Y, and rare-earth elements exist across all three units. Modeling of these data suggest that Kodiak arc evolution occurred in two main stages: (1) a gabbroic initial melt underwent fractional crystallization that produced a pyroxenitic root and a gabbroic lower crust, and (2) melt in equilibrium with the gabbroic lower crust underwent assimilation-fractional crystallization to produce mid-crustal plutonic and upper-crustal volcanic rocks. Kodiak Island exposes the oldest and thinnest portion of the Talkeetna arc, with ages from the Afognak batholith ranging from ca. 215-185 Ma. In the eastern and western Talkeetna arc, magmatism migrated northward after ca. 180 Ma in response to inferred forearc erosion. Forearc erosion coupled with differential subduction-channel movement juxtaposed blueschist-facies rocks with middle and lower crustal arc rocks. These processes occurred earlier and to a greater degree in the western Talkeetna arc, causing the arc to split in half, separating the Kodiak and Alaskan Peninsula parts of the Talkeetna arc.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 456
Title: Construction and evolution of the Kodiak Talkeetna Arc crustal section, Southern Alaska
Title: Crustal cross sections; from the western North American Cordillera and elsewhere; implications for tectonic and petrologic processes
Author(s): Farris, David W.
Author(s): Miller, Robert B.editor
Author(s): Snoke, Arthur W.editor
Affiliation: Florida State University, Department of Geological Sciences, Tallahassee, FL, United States
Affiliation: San Jose State University, Department of Geology, San Jose, CA, United States
Pages: 69-96
Published: 2009
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 77
Accession Number: 2010-004834
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch maps
N57°00'00" - N62°49'60", W153°40'00" - W147°00'00"
Secondary Affiliation: University of Wyoming, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 201003
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