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

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. Seismic profiles of several modern arcs...

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Bibliographic Details
Published in:Tectonics
Main Authors: Rioux, Matthew, Mattinson, James, Hacker, Bradley R., Kelemen, Peter B., Blusztajn, Jerzy S., Hanghoj, Karen, Gehrels, George
Format: Article in Journal/Newspaper
Language:English
Published: American Geophysical Union 2010
Subjects:
Arc
Online Access:https://hdl.handle.net/1912/3876
Description
Summary: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. 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 ...