9 Structural Geology and Tectonics (Posters)

Tuesday, 23 May 2017
8:30 AM - 5:00 PM
Room 323A/B/C

ROCK AND AGE RELATIONSHIPS OF THE TALKEETNA FOREARC SUBDUCTION COMPLEX IN THE NELCHINA AREA, SOUTHERN ALASKA

Paper number: 9-4
Program: Technical Sessions
Time: 8:30 AM – 5:00 PM

Authors

Abstract

Subduction-zone processes are still poorly understood due to the paucity of exposures and the complexity of rock relationships within the accretionary prism. A remarkably well-preserved exposure of subduction-related rocks is located at the foot of Nelchina glacier in south-central Alaska. Here, the crystalline basement of the Talkeetna volcanic arc contacts the mélange of its related accretionary complex along the Border Ranges fault. I mapped and sampled the mélange exposures of the complex in July 2016. The mélange consists of relatively undeformed argillite, metavolcanic rocks, and chert, as well as a ~100-m-diameter block of pillow basalt. Preliminary x-ray fluorescence data shows that this pillow basalt formed in a within-plate setting, suggesting it is unrelated to Talkeetna arc volcanism. Detailed compositional data from a transect across this basalt will show effects of progressive alteration from core to rim of the block. A zircon U-Pb age of a gabbro from the Talkeetna arc basement is 188.9 ± 2.2 Ma, which is consistent with the age of Talkeetna arc volcanism. A zircon U-Pb age of a felsic dike that crosscuts the mélange is 53.0 ± 0.9 Ma, which is both consistent with the ages of near-trench plutonic rocks across southern Alaska, and sets a minimum age of mélange deformation.

Geological Society of America Abstracts with Programs. Vol. 49, No. 4

doi: 10.1130/abs/2017CD-292817

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.