Intrusive relationships within the Barnard Gneiss of southern Vermont: Lithodemic constraints on Ordovician arc tectonics
- Virginia Polytechnic Inst., Blacksburg, VA (United States). Dept. of Geological Sciences
Recent mapping of rocks previously called Bernard Volcanics and Bernard Gneiss, in 4 adjacent quadrangles in southern Vermont has shown that this belt is comprised of at least 8 metaigneous and 2 metasedimentary units which exhibit tremendous across- and along-strike discontinuity. Informally named igneous rock types include fine-grained amphibolite and interlayered felsic segregations (volcanics at South Pond; SPV), fine-grained fuschsite-bearing felsite (NF), and quartz phenocryst felsic volcanics (volcanics at Sunset Lake). These are cut by two hypabyssal intrusives; porphyritic, mafic dikes and sills, displaying fine-grained chilled margins and zoned feldspar phenocrysts (exposed in the town of Williamsville, WMF), and mafic and intermediate to felsic, porphyritic, dikes and sills (Whitneyville locality; WF). These intrusive rocks comprise an igneous complex, itself intruded by: (1) coarse grained, tan-weathering tonalite (Newfane locality, NT) which also intrudes a well layered, chemically similar, felsic unit (Baker Brook locality; BBV): (2) coarse- to fine-grained trondjemite (WHT) containing xenoliths of SPV, WMF, and WF. Relative age relationships between WHT and NT are unclear. Barnard metasedimentary rocks include: quartz-plagioclase granofels (QPG), similar to units in the underlying Moretown Fm., but separated from them by the Acadian South Newfane Thrust. The other sedimentary unit, the Cram Hill Fm., consists of carbonaceous, sulfidic schist with interlayered dark gray quartzite. Throughout the rest of the belt, Cram Hill is interlayered with SPV and QPG and intruded by WF, WMF, and WHT. These relationships suggest that the intrusives were emplaced into a coherent sedimentary and volcanic sequence, including rocks as young as the supposed Silurian-Devonian North field Fm.
- OSTI ID:
- 5879249
- Report Number(s):
- CONF-9303211--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 25:2; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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