The Shelburne Falls arc in western Massachusetts and Connecticut: The lost arc of the Taconian orogeny

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5807763

Karabinos, P ^[1]; Tucker, R D ^[2]

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1. Williams Coll., Williamstown, MA (United States). Dept. of Geology
2. Royal Ontario Museum, Toronto, Ontario (Canada). Geochronology Lab.

The Shelburne Falls arc (SFA) is over 185 km long and comprises the following gneiss-cored domes in western Mass. and Conn.: Shelburne Falls, Goshen, Granville, Granby, Collinsville, Bristol, and Waterbury. Arc related rocks from these domes have been correlated with lithologically similar rocks in the Bronson Hill magmatic arc (BHA) dated previously at 442 to 454 Ma. Current tectonic models of the Taconian orogeny in western New England call for crustal shortening and metamorphism following collision of the BHA and Laurentia. The protolith ages from the BHA, however, present a problem for such models because they are younger than the age of Taconian metamorphism found in many rocks from the region (460 to 470 Ma) and are the same age or slightly younger than the Late Ordovician (Caradocian) emplacement of the Giddings Brook sheet in the Taconian thrust belt. A new U-Pb zircon age of a trondhjemitic gneiss in the core of the Goshen dome indicates crystallization at 474 [+-] 4Ma. Discordant U-Pb analyses of zircon from a trondhjemitic gneiss in the Shelburne Falls dome suggest crystallization at approximately 488 Ma with Early to Middle Proterozoic inheritance, whereas single-grain zircon Pt-207/Pb-206 evaporation ages from the same sample indicate crystallization at 468 [+-] 10 Ma. Thus, the rocks from these two domes are approximately 20 to 30 Ma older than similar rocks from the BHA. Based on available isotopic ages, the authors propose that the SFA is temporally distinct from the BHA and that the SFA may be a southern continuation of the Ascot-Weedon and related arc rocks in Quebec and northern Vermont or a separate arc segment. They suggest that the earliest phases of the Taconian orogeny began with collision of Laurentia and the SFA c. 470 Ma ago or possibly younger. Final accretion of the BHA with the composite Laurentia-SFA terrane was probably not complete until the latest stages of the Taconian orogeny in end Ordovician time.

• OSTI ID: 5807763
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

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