New Developments in the Appalachian-Caledonian-Variscan Orogen
CONTAINS OPEN ACCESS
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.
Geochemical and Nd isotopic constraints on the origin of uppermost Silurian rhyolitic rocks in the northern Appalachians (northern New Brunswick): Tectonic implications
*Corresponding author: jdostal@smu.ca
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Published:May 19, 2022
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CiteCitation
Jaroslav Dostal*, Pierre Jutras, Reginald A. Wilson, 2022. "Geochemical and Nd isotopic constraints on the origin of uppermost Silurian rhyolitic rocks in the northern Appalachians (northern New Brunswick): Tectonic implications", 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
Voluminous bimodal volcanic rocks of the Silurian (ca. 422–420 Ma) Dickie Cove Group in the Ganderia domain of northern New Brunswick, Canada, are subaerial units that were deposited in an extensional setting, with the mafic types corresponding to continental tholeiites. Felsic rocks are rhyolites with calc-alkaline affinities. They exhibit geochemical characteristics that are typical of A2-type felsic magmas, such as enrichments in the incompatible elements Zr, Nb, and Y, as well as high FeO*/(FeO* + MgO) and Ga/Al ratios. Their εNd(t) values are positive (+0.7 to +3.4) but lower than those of the associated basalts. Saturation thermometry has yielded average zircon crystallization temperature estimates for the rhyolites that are well above 900 °C. The geochemical data indicate that the felsic melts were likely sourced from heterogeneous Neoproterozoic lower crust and generated by dehydration melting triggered by heat derived from underplated mafic magma. Parent melts of the rhyolites underwent fractional crystallization in a complex magma chamber prior to eruption. The Nd isotopic data suggest that the lower crust of Ganderia is similar to that of Avalonia in northern mainland Nova Scotia, and that the two microcontinents shared a common Neoproterozoic history and origin as continental blocks rifted from neighboring parts of Gondwana. The tectono-magmatic setting of the Dickie Cove Group volcanic rocks is interpreted as being related to Pridolian, post-Salinic relaxation and slab breakoff, which generated volcanism initially constrained within the Chaleur zone of the Chaleur Bay synclinorium, a large domain of the northern Appalachians. This was followed later in the Pridolian by extensional collapse and widening of the area of magmatic activity, which then prograded into the Tobique zone farther to the southwest.
- absolute age
- Appalachians
- basalts
- calc-alkalic composition
- Canada
- Chaleur Bay
- chemical composition
- continental crust
- crust
- Eastern Canada
- extension tectonics
- fractional crystallization
- geologic thermometry
- Gondwana
- high temperature
- igneous rocks
- intraplate processes
- isotopes
- lithosphere
- lower crust
- magmas
- magmatism
- major elements
- mantle
- Maritime Provinces
- melts
- metals
- monazite
- neodymium
- nesosilicates
- New Brunswick
- North America
- orthosilicates
- P-T conditions
- Paleozoic
- phosphates
- plate tectonics
- Pridoli
- rare earths
- rhyolites
- rifting
- silicates
- Silurian
- slabs
- Sm/Nd
- subaerial environment
- tectonics
- temperature
- terrestrial environment
- tholeiite
- trace elements
- underplating
- Upper Silurian
- volcanic rocks
- whole rock
- zircon
- zircon group
- Ganderia
- Dickie Cove Group