New Developments in the Appalachian-Caledonian-Variscan Orogen
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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.
U-Pb zircon ages and Sm-Nd isotopic data from the Cobequid Highlands, Nova Scotia, Canada: New contributions to understanding the Neoproterozoic geologic history of Avalonia
*Deceased October 2018
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Published:May 19, 2022
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CiteCitation
Chris E. White, Sandra M. Barr, James L. Crowley, Deanne van Rooyen, Trevor G. MacHattie*, 2022. "U-Pb zircon ages and Sm-Nd isotopic data from the Cobequid Highlands, Nova Scotia, Canada: New contributions to understanding the Neoproterozoic geologic history of Avalonia", 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
Forty-three new U-Pb zircon ages from metasedimentary and igneous rock units throughout the Cobequid Highlands of northern mainland Nova Scotia, Canada, provide new insights into the Neoproterozoic evolution of this long-enigmatic part of Avalonia in the northern Appalachian orogen. Contrasts in ages and rock types resulted in the identification of fault-bounded Neoproterozoic assemblages of units forming the Bass River, Jeffers, and Mount Ephraim blocks. In the Bass River block, quartzite, metawacke, and minor calc-silicate rocks and marble (Gamble Brook Formation) with a maximum depositional age of 945 ± 12 Ma are associated with subaqueous mafic volcanic rocks, siltstone, and ironstone (Folly River Formation) and intruded by 615–600 Ma calc-alkalic subduction-related dioritic to granitic rocks of the Bass River plutonic suite. The contrasting Jeffers block forms most of the Cobequid Highlands and consists mainly of intermediate to felsic volcanic, epiclastic, and minor plutonic rocks. The western and eastern areas of that block yielded ages mainly ca. 607–592 Ma for both volcanic and plutonic rocks, whereas the central area has ages of ca. 630–625 Ma from both volcanic and plutonic rocks and inheritance in overlying Devonian conglomerate. The Mount Ephraim block forms the eastern part of the highlands and includes possible ca. 800 Ma quartzofeldspathic, semipelitic and pelitic gneiss and schist of the Mount Thom Formation, ca. 752 Ma volcanic arc rocks of the Dalhousie Mountain Formation and related 752–730 Ma gabbroic/dioritic to granitic plutons of the Mount Ephraim plutonic suite and Six Mile Brook pluton, as well as ca. 631 Ma granitoid rocks of the Gunshot Brook pluton. The pre–750 Ma high-grade regional metamorphism and deformation and 752–730 Ma subduction-related magmatism recorded in the Mount Ephraim block were previously unrecognized in Avalonia. Evidence from zircon inheritance and Sm-Nd isotopic data in igneous units suggests linkages among these now-separate areas, and comparison with other parts of Avalonia in the northern Appalachian orogen suggests similarity to southeastern New England.
- absolute age
- Appalachians
- Avalonia
- Canada
- Cape Breton Island
- Carboniferous
- Cobequid Fault
- Cobequid Highlands
- correlation
- deformation
- Eastern Canada
- faults
- gneisses
- igneous rocks
- intrusions
- isotopes
- lithostratigraphy
- magmatism
- Maritime Provinces
- metals
- metamorphic rocks
- metamorphism
- metasedimentary rocks
- neodymium
- Neoproterozoic
- nesosilicates
- New England
- North America
- Nova Scotia
- orthosilicates
- Paleozoic
- plate tectonics
- plutons
- Precambrian
- Proterozoic
- rare earths
- samarium
- schists
- silicates
- Sm/Nd
- subduction
- terranes
- U/Pb
- United States
- upper Precambrian
- volcanic rocks
- zircon
- zircon group
- Antigonish Highlands
- Gamble Brook Formation
- Rockland Brook Fault
- magmatic arcs
- Kirkhill Fault
- Caledonia Terrane
- Jeffers Block
- Bass River Block
- Mount Thom Formation
- Mount Ephraim Block