Start |Author Index | View Uploaded Presentations | Meeting Information

2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 13
Presentation Time: 4:45 PM

CRUSTAL CONSTITUENCY OF THE ALLEGHANIAN OROGEN AS REFLECTED BY RADIOMETRIC SEDIMENTARY PROVENANCE PROXIES


BECKER, Thomas1, THOMAS, William1, GEHRELS, George2 and ARONSON, James L.3, (1)Department of Geological Sciences, Univ of Kentucky, 101 Slone Bldg, Lexington, KY 40506-0053, (2)Geosciences, Univ of Arizona, Tucson, AZ 85721, (3)Department of Earth Sciences, Dartmouth College, Hanover, NH 03755, tpbeck2@uky.edu

The Alleghanian orogeny evidently included both dextral shear in the internides and cratonward thrusting in the foreland. The seeming mechanical paradox commonly is explained as the result of a temporal kinematic succession. Analyses of foreland detritus provide insights into the possible succession and timing of events.

A compilation of detrital-zircon and white-mica ages from Pennsylvanian and Permian sedimentary deposits within the Appalachian foreland basin reveal a subtle, but systematic, change in the source of detritus from the Alleghanian orogen. Detrital-zircon populations of both Pennsylvanian and Permian strata in the Appalachian basin are dominated by Grenville ages (950-1300 Ma) and include subordinate late Proterozoic-middle Paleozoic ages (360-570 Ma). The Pennsylvanian-age strata in the Appalachian basin have a significant (~13%) population of Archean (>2500 Ma) and Paleoproterozoic (1600-1900 Ma) detrital zircons, but these older zircons are not represented in Permian sandstones. K-Ar ages of detrital white mica from the Permian Dunkard Group range from 390.8 to 394.9 (+/- 9.2) Ma, indicating that exhumation of the Alleghanian orogen was restricted to shallow levels of the crust.

Geochronologic and petrographic data show a crude correlation between the range of detrital-zircon-age populations and the relative maturity of Pennsylvanian and Permian sandstones. Permian samples have the most restricted range of detrital-zircon ages and are the most feldspathic, suggesting a change in sediment sources through time from one dominated by recycled sedimentary cover to one dominated by primary crystalline sources. The change in composition of the sediment source may be a result of the initiation of cratonward directed thrusting of the Alleghanian crystalline hinterland in the early Permian. The change in source is consistent with a change from oblique collision and dextral shear in the internides to orthogonal collision and cratonward thrusting in the foreland.

Session No. 231

Tectonics III: UHP Terranes, Ribbon Continents, Appalachians, and Mid-Continent
Wednesday, 10 November 2004: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol. 36, No. 5, p.535
© Copyright 2004 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.
Back to: Tectonics III: UHP Terranes, Ribbon Continents, Appalachians, and Mid-Continent
<< Previous Abstract | Next Abstract >>