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U-Pb geochronology and evolution of Mesoproterozoic basement rocks, western Connecticut

By
Gregory J. Walsh
Gregory J. Walsh
U.S. Geological Survey, P.O. Box 628, 87 State Street, Room 324, Montpelier, Vermont 05601, USA
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John N. Aleinikoff
John N. Aleinikoff
U.S. Geological Survey, Box 25046, MS 963, Denver, Colorado 80225, USA
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C. Mark Fanning
C. Mark Fanning
Research School of Earth Sciences, The Australian National University, Mills Road, Canberra ACT 0200, Australia
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Published:
January 01, 2004

Geologic mapping and U-Pb geochronology by ion microprobe on zircon, titanite, and monazite in the New Milford quadrangle, western Connecticut indicate Meso-proterozoic events at ca. 1.3, 1.05, and 0.99 Ga in the Laurentian basement rocks. Pink granite gneiss (1311 ± 7 Ma) intruded a paragneiss sequence during the early stages of the Elzevirian orogeny. During the Ottawan orogeny, syn-tectonic anatexis produced a belt of stromatic migmatite at 1057 ± 10 Ma. Ottawan igneous activity included syn-tectonic intrusion of abundant sills of biotite granite gneiss, dated at 1050 ± 14 and 1048 ± 11 Ma, and intrusion of the Danbury augen granite at 1045 ± 8 Ma. Overgrowths on igneous zircon and metamorphic zircon in hornblende gneiss indicate that terminal Grenville metamorphism occurred at ca. 993 ± 8 Ma.

Late Ordovician syn-tectonic events included intrusion of a leucogranite dike into the Brookfield Gneiss at 453 ± 6 Ma and intrusion of the Candlewood Granite at 443 ± 7 Ma. A monazite age from the Candlewood Granite of 445 ± 9 Ma agrees with the zircon age. A second phase of migmatization in the basement rocks is associated with the injection of numerous granitic leucosomes at 444 ± 6 Ma along the margin of the Candlewood Granite. Titanite ages from 431 to 406 Ma indicate several high-grade heating events from the Silurian to the Early Devonian. The lack of Grenville-age titan-ite in the basement suggests that post-Taconian heating was sufficient to completely reset old titanite in the massif.

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GSA Memoirs

Proterozoic Tectonic Evolution of the Grenville Orogen in North America

Richard P. Tollo
Richard P. Tollo
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James McLelland
James McLelland
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Louise Corriveau
Louise Corriveau
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Mervin J. Bartholomew
Mervin J. Bartholomew
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Geological Society of America
Volume
197
ISBN print:
9780813711973
Publication date:
January 01, 2004

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