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    Intermediate to felsic middle crust in the accreted Talkeetna arc, the Alaska Peninsula and Kodiak Island, Alaska : an analogue for low-velocity middle crust in modern arcs

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    Article (4.611Mb)
    Data Set S1: Multigrain chemical abrasion-TIMS U-Pb zircon data. (17.06Kb)
    Data Set S1: Multigrain chemical abrasion-TIMS U-Pb zircon data. (55Kb)
    Data Set S2: Laser ablation-ICP-MS U-Pb zircon data. (6.021Kb)
    Data Set S2: Laser ablation-ICP-MS U-Pb zircon data. (43.5Kb)
    Additional file information (4.147Kb)
    Table S1: Modal mineralogies used to calculate seismic velocities. (1.202Kb)
    Table S1: Modal mineralogies used to calculate seismic velocities. (18Kb)
    Date
    2010-05-08
    Author
    Rioux, Matthew  Concept link
    Mattinson, James  Concept link
    Hacker, Bradley R.  Concept link
    Kelemen, Peter B.  Concept link
    Blusztajn, Jerzy S.  Concept link
    Hanghoj, Karen  Concept link
    Gehrels, George  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/3876
    As published
    https://doi.org/10.1029/2009TC002541
    DOI
    10.1029/2009TC002541
    Keyword
     Talkeetna arc; Arc; Alaska 
    Abstract
    Seismic profiles of several modern arcs have identified thick, low-velocity midcrustal layers (Vp = 6.0–6.5 km/s) that are interpreted to represent intermediate to felsic plutonic crust. The presence of this silicic crust is surprising given the mafic composition of most primitive mantle melts and could have important implications for the chemical evolution and bulk composition of arcs. However, direct studies of the middle crust are limited by the restricted plutonic exposures in modern arcs. The accreted Talkeetna arc, south central Alaska, exposes a faulted crustal section from residual subarc mantle to subaerial volcanic rocks of a Jurassic intraoceanic arc and is an ideal place to study the intrusive middle crust. Previous research on the arc, which has provided insight into a range of arc processes, has principally focused on western exposures of the arc in the Chugach Mountains. We present new U-Pb zircon dates, radiogenic isotope data, and whole-rock geochemical analyses that provide the first high-precision data on large intermediate to felsic plutonic exposures on Kodiak Island and the Alaska Peninsula. A single chemical abrasion–thermal ionization mass spectrometry analysis from the Afognak pluton yielded an age of 212.87 ± 0.19 Ma, indicating that the plutonic exposures on Kodiak Island represent the earliest preserved record of Talkeetna arc magmatism. Nine new dates from the extensive Jurassic batholith on the Alaska Peninsula range from 183.5 to 164.1 Ma and require a northward shift in the Talkeetna arc magmatic axis following initial emplacement of the Kodiak plutons, paralleling the development of arc magmatism in the Chugach and Talkeetna mountains. Radiogenic isotope data from the Alaska Peninsula and the Kodiak archipelago range from $\varepsilon$Nd(t) = 5.2 to 9.0 and 87Sr/86Srint = 0.703515 to 0.703947 and are similar to age-corrected data from modern intraoceanic arcs, suggesting that the evolved Alaska Peninsula plutons formed by extensive differentiation of arc basalts with little or no involvement of preexisting crustal material. The whole-rock geochemical data and calculated seismic velocities suggest that the Alaska Peninsula represents an analogue for the low-velocity middle crust observed in modern arcs. The continuous temporal record and extensive exposure of intermediate to felsic plutonic rocks in the Talkeetna arc indicate that evolved magmas are generated by repetitive or steady state processes and play a fundamental role in the growth and evolution of intraoceanic arcs.
    Description
    Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Tectonics 29 (2010): TC3001, doi:10.1029/2009TC002541.
    Collections
    • Geology and Geophysics (G&G)
    Suggested Citation
    Tectonics 29 (2010): TC3001
     

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