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Northeastern Section - 36th Annual Meeting (March 12-14, 2001)

Paper No. 7
Presentation Time: 3:50 PM

MAFIC COMPLEXES IN NORTHERN VERMONT AND QUEBEC CORRELATIVES


KIM, Jonathan1, GALE, Marjorie1, LAIRD, Jo2, THOMPSON, Peter2 and BOTHNER, Wallace2, (1)Vermont Geol Survey, 103 S. Main St, Waterbury, VT 05671, (2)Univ New Hampshire, 56 College Rd, Durham, NH 03824-3589, jonk@dec.anr.state.vt.us

Based on geochemical, petrologic, geochronologic, and structural data, four pre-Silurian mafic complexes are mapped in northern Vermont: 1) Belvidere, 2) Tillotson, 3) Worcester, and 4) Warner Hill.

The Belvidere Complex (BC) is composed of ultramafics, amphibolites, greenstones, and muscovite schist. Ultramafics represent the vestige of an ophiolite with dynamothermally metamorphosed amphibolites at the sole that was subsequently assembled with muscovite schist and greenstones at greenschist-facies and emplaced on Hazens Notch Fm albitic schists. Reaction space calculations show BC amphibolite pressures of ~9 Kb whereas grt-hbd temperatures are 550 to 650 C. Barroisitic hbd yields a 505 Ma Ar/Ar plateau age. Tectonic affinities of BC mafic units range from MORB to trans-arc.

The Tillotson Peak Complex (TPC) consists of fault-bounded blueschist+eclogite-facies mafic and pelitic rocks that were juxtaposed with ultramafics and Hazens Notch Fm albitic schists. Blueschist from TPC has MORB tectonic affinity. Thermobarometry from grt-omph pairs ranges from 12 Kb, 520 C to 14 Kb, 620 C. A total fusion Ar/Ar age of 468 Ma was determined from glaucophane. An inferred Taconian fault separates TPC from BC.

The Worcester Complex (WC) consists of mafic schist infolded and faulted against garnet-kyanite grade pelitic schist; both have been overprinted by Acadian greenschist-facies metamorphism. Tectonic affinities of WC mafic rocks range from MORB to trans-arc. Grt-hbd temperatures of 500-520 C were obtained from the WC and reaction space pressures are ~7 Kb. Mg hbd from the WC yielded a 470 Ma Ar/Ar plateau age.

Warner Hill Complex (WHC) greenstones and ultramafics are in fault contact with Ottauquechee Fm black phyllites. WHC greenstones ranges from arc (including boninitic) to MORB tectonic affinities.

Northern Vermont Mafic Complex metamorphic ages are similar to those reported by Tremblay et al. (2000) for the Quebec Dunnage Zone. WC schists may be analogous lithologically and in structural position to those in the Carineault Antiform. WHC boninitic and arc mafics may have analogs in the Quebec ophiolites.

Session No. 13

T5. Geologic Evolution of the Northern Appalachians; the Quebec-Vermont Connection
Monday, 12 March 2001: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol. 33, No. 1, February 2001
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