Iapetan secrets slowly revealed
The Ordovician closing of the Iapetus Ocean is well documented in western New England and eastern New York. A series of major Taconian thrusts bring pelitic, mafic, and ultramafic rocks over Grenville basement and its Proterozoic Z to Ordovician shelf, slope, and rise cover sequences. Attendant metamorphism (470-460 Ma) is high- to medium-P facies series in northern VT, medium-P in MA, and low-P at the MA/CT/NY boundary. Relict high-P metamorphism occurs locally in MA and CT. The eastern extent of Taconian metamorphism is poorly understood due to the strong overprint of Acadian metamorphism (390-380 Ma) but appears to lie W of the Bronson Hill Anticlinorium (BHA). Taconian rocks are separated from upper Ordovician to Devonian (.) pelitic, calcareous, and mafic rocks in the Connecticut Valley Gaspe Synclinorium (CVGS) by a zone, variously interpreted as an unconformity +/- slip or fault zone. These rocks structurally overlie Grenville (.) basement as folded nappes and are intruded by 385-375 Ma peraluminous granite. Acadian metamorphism is low-P in Ne VT and medium-P farther S. Further 40Ar/39Ar age spectrum studies of amphibole combined with detailed mapping, fabric, and petrologic studies are required to refine the mapping of P, T, and time of metamorphic events and to delimit more precisely terrane boundaries. Tectonic boundaries occur between Iapetan stratigraphic packages and appear crosscut by Taconian isotherms and isobars. Although the RMC separates rocks of distinct lithology, structure, and metamorphic history, it is probably not a terrane boundary.
- Research Organization:
- Univ. of New Hampshire, Durham (USA)
- OSTI ID:
- 6460453
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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