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Supra-subduction zone extensional magmatism in Vermont and adjacent Quebec; implications for early Paleozoic Appalachian tectonics

Jonathan Kim, Raymond Coish, Matthew Evans and Gregory Dick
Supra-subduction zone extensional magmatism in Vermont and adjacent Quebec; implications for early Paleozoic Appalachian tectonics
Geological Society of America Bulletin (December 2003) 115 (12): 1552-1569

Abstract

Metadiabasic intrusions of the Mount Norris Intrusive Suite occur in fault-bounded lithotectonic packages containing Stowe, Moretown, and Cram Hill Formation lithologies in the northern Vermont Rowe-Hawley belt, a proposed Ordovician arc-trench gap above an east-dipping subduction zone. Rocks of the Mount Norris Intrusive Suite are characteristically massive and weakly foliated, have chilled margins, contain xenoliths, and have sharp contacts that both crosscut and are parallel to early structural fabrics in the host metasedimentary rocks. Although the mineral assemblage of the Mount Norris Intrusive Suite is albite + actinolite + epidote + chlorite + calcite + quartz, intergrowths of albite + actinolite are probably pseudomorphs after plagioclase + clinopyroxene. The metadiabases are subalkaline, tholeiitic, hypabyssal basalts with preserved ophitic texture. A backarc-basin tectonic setting for the intrusive suite is suggested by its LREE (light rare earth element) enrichment, negative Nb-Ta anomalies, and Ta/Yb vs. Th/Yb trends. Although no direct isotopic age data are available, the intrusions are broadly Ordovician because their contacts are clearly folded by the earliest Acadian (Silurian-Devonian) folds. Field evidence and geochemical data suggest compelling along-strike correlations with the Coburn Hill Volcanics of northern Vermont and the Bolton Igneous Group of southern Quebec. Isotopic and stratigraphic age constraints for the Bolton Igneous Group bracket these backarc magmas to the 477-458 Ma interval. A tectonic model that begins with east-dipping subduction and progresses to outboard west-dipping subduction after a syncollisional polarity reversal best explains the intrusion of deformed metamorphosed metasedimentary rocks by backarc magmas.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 115
Serial Issue: 12
Title: Supra-subduction zone extensional magmatism in Vermont and adjacent Quebec; implications for early Paleozoic Appalachian tectonics
Affiliation: Vermont Geological Survey, Waterbury, VT, United States
Pages: 1552-1569
Published: 200312
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 83
Accession Number: 2004-003391
Categories: Igneous and metamorphic petrologyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 3 tables, geol. sketch maps
N44°30'00" - N45°00'00", W73°00'00" - W72°00'00"
Secondary Affiliation: Middlebury College, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200401
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