New Developments in the Appalachian-Caledonian-Variscan Orogen

New analytical and field techniques, as well as increased international communication and collaboration, have resulted in significant new geological discoveries within the Appalachian-Caledonian-Variscan orogen. Cross-Atlantic correlations are more tightly constrained and the database that helps us understand the origins of Gondwanan terranes continues to grow. Special Paper 554 provides a comprehensive overview of our current understanding of the evolution of this orogen. It takes the reader along a clockwise path around the North Atlantic Ocean from the U.S. and Canadian Appalachians, to the Caledonides of Spitsbergen, Scandinavia, Scotland and Ireland, and thence south to the Variscides of Morocco.
Evolving views of West Avalonia: Perspectives from southeastern New England, USA
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Published:May 19, 2022
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CiteCitation
M.D. Thompson*, S.M. Barr, J.C. Pollock, 2022. "Evolving views of West Avalonia: Perspectives from southeastern New England, USA", New Developments in the Appalachian-Caledonian-Variscan Orogen, Yvette D. Kuiper, J. Brendan Murphy, R. Damian Nance, Robin A. Strachan, Margaret D. Thompson
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ABSTRACT
Southeastern New England is largely composed of Ediacaran granitoid and related volcanic rocks formed during the main phase of arc-related magmatism recorded in West Avalonian lithotectonic assemblages extending through Atlantic Canada to eastern Newfoundland. In situ Lu-Hf analyses presented here for zircons from the Dedham, Milford, and Esmond Granites and from the Lynn-Mattapan volcanic complex show a restricted range of εHf values (+2 to +5) and associated Hf-TDM model ages of 1.3–0.9 Ga, assuming felsic crustal sources. The most evolved granites within this suite lie in a belt north and west of the Boston Basin, whereas upfaulted granites on the south, as well as the slightly younger volcanic units, show more juvenile Hf isotopic compositions. Similar inferences have been drawn from previously published Sm-Nd isotopic signatures for several of the same plutons. Collectively, the isotopic compositions and high-precision U-Pb geochronological constraints now available for southeastern New England differ in important respects from patterns in the Mira terrane of Cape Breton Island or the Newfoundland Avalon zone, but they closely resemble those documented in the Cobequid and Antigonish Highlands of mainland Nova Scotia and New Brunswick’s Caledonia terrane. Particularly significant features are similarities between the younger than 912 Ma Westboro Formation in New England and the younger than 945 Ma Gamble Brook Formation in the Cobequid Highlands, both of which yield detrital zircon age spectra consistent with sources on the Timanide margin of Baltica. This relationship provides the starting point for a recent model in which episodic West Avalonian arc magmatism began along the Tonian margin of Baltica and terminated during diachronous late Ediacaran arc-arc collision with the Ganderian margin of Gondwana.
- absolute age
- Avalon Zone
- Avalonia
- Baltica
- Canada
- Cape Breton Island
- Cobequid Highlands
- crust
- Dedham Granodiorite
- Eastern Canada
- Ediacaran
- granites
- hafnium
- igneous rocks
- ion probe data
- isotopes
- laser methods
- lithostratigraphy
- lutetium
- Maine
- Maritime Provinces
- mass spectra
- Massachusetts
- metals
- metamorphic rocks
- metasedimentary rocks
- metavolcanic rocks
- neodymium
- Neoproterozoic
- nesosilicates
- New Brunswick
- New England
- Newfoundland and Labrador
- Nova Scotia
- O-18
- orthosilicates
- oxygen
- plate tectonics
- plutonic rocks
- Precambrian
- Proterozoic
- rare earths
- Rhode Island
- samarium
- SHRIMP data
- silicates
- spectra
- stable isotopes
- Tonian
- U/Pb
- United States
- upper Precambrian
- volcanic rocks
- zircon
- zircon group
- Antigonish Highlands
- Gamble Brook Formation
- Mira Terrane
- Boston Basin
- detrital zircon
- Westboro Formation
- Milford Granite
- magmatic arcs
- Esmond Granite
- Caledonia Terrane