Early Paleozoic metamorphism at two crustal levels and a tectonic model for the Pennsylvania-Delaware Piedmont

Abstract

Research Article| July 01, 1987 Early Paleozoic metamorphism at two crustal levels and a tectonic model for the Pennsylvania-Delaware Piedmont MARY EMMA WAGNER; MARY EMMA WAGNER 1Department of Geology, University of Pennsylvania, Philadelphia, Pennsylvania 19104 Search for other works by this author on: GSW Google Scholar LEEANN SROGI LEEANN SROGI 1Department of Geology, University of Pennsylvania, Philadelphia, Pennsylvania 19104 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1987) 99 (1): 113–126. https://doi.org/10.1130/0016-7606(1987)99<113:EPMATC>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation MARY EMMA WAGNER, LEEANN SROGI; Early Paleozoic metamorphism at two crustal levels and a tectonic model for the Pennsylvania-Delaware Piedmont. GSA Bulletin 1987;; 99 (1): 113–126. doi: https://doi.org/10.1130/0016-7606(1987)99<113:EPMATC>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Two high-grade metamorphic terranes of early Paleozoic age are exposed in southeastern Pennsylvania and northern Delaware. The Wilmington Complex in Delaware was metamorphosed at high temperatures to intermediate-pressure granulite facies during the early Paleozoic. In the West Chester prong, Pennsylvania, a granulite-facies metamorphism of Grenville age was overprinted by a high-pressure, moderate-temperature metamorphism during the Taconic orogeny. We propose a model to account for the different metamorphic conditions in these two terranes. In this model, the Piedmont of northern Delaware and southeastern Pennsylvania was the site of collision between a magmatic arc and the North American continent along an east-dipping subduction zone. The Wilmington Complex was the infrastructure of the arc, whereas the Grenville-age gneisses of the West Chester prong were basement of the North American continent. Between these two relatively rigid plates, there are nappes of remobilized basement and highly deformed forearc-basin and accretion-ary-prism sediments. The North American continent underthrust the hot infrastructure of the volcanic arc, resulting in the high-pressure (9-11 kb), moderate-temperature (650–700 °C), metamorphic overprint on Grenville assemblages of the West Chester prong. The Wilmington Complex was metamorphosed at moderate pressure (6–7 kb) and high temperature (∼800 °C) during the early Paleozoic, under the conditions of the high geothermal gradient that existed at the base of the volcanic arc. The intervening sediments and remobilized basement are all at amphibolite grade, but the grade is highest (above second sillimanite isograd) everywhere adjacent to the structurally overlying Wilmington Complex, suggesting that the isograds in the sediments are inverted beneath the Wilmington Complex. Uplift of this doubled thickness of crust was rapid enough that the gneisses of the West Chester prong were never heated above 700 °C. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.