Transcurrent displacement of tectonic terranes in the central Appalachian Piedmont
- Temple Univ., Philadelphia, PA (United States). Dept. of Geology
The metamorphic Piedmont of southeastern Pennsylvania is crosscut by a significant system of steeply dipping ductile shear zones with late- to post-orogenic transcurrent displacement. Geologic evidence suggests that at least some of these shear zones are responsible for hundreds of kilometers of dextral displacement, juxtaposing lithologic units with very different origins and tectonic histories across relatively narrow deformation zones. As a result, the present distribution of lithologies does not reflect Taconic (or earlier) collision at this place on the Laurentian margin. Type-section Wissahickon schist, exposed in the Philadelphia terrane, was metamorphosed to amphibolite facies before or during the Taconic orogeny. This terrane, bounded to the west by the Rosemont shear zone and to the north by the Cream Valley-Huntingdon Valley shear zone system, has been translated southwestward with respect to autochthonous Laurentian lithologies by dextral displacement on these shear zones since peak metamorphism of the schist. Published Late Ordovician ages from the Rosemont shear zone provide a minimum age for peak metamorphism of Wissahickon schist and a maximum age for displacement on the younger Huntingdon Valley-Cream Valley shear zone system. Therefore, peak metamorphic mineral assemblages in Wissahickon schist cannot be used to constrain Taconic collision models for this part of the Appalachians; rather, these mineral assemblages record evidence of (possibly earlier) orogeny elsewhere.
- OSTI ID:
- 6819397
- Report Number(s):
- CONF-9404221-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 26:4; Conference: 43. annual meeting of the Southeastern Section of the Geological Society of America, Blacksburg, VA (United States), 7-8 Apr 1994; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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