1.45 Ga granulites in the southwestern Grenville Province; geologic setting, P-T conditions, and U-Pb geochronology

In the southwestern Grenville province, the parautochthonous Britt domain includes a variety of pre-Grenvillian metamorphic and plutonic rocks that were reworked at upper amphibolite facies during the Grenvillian orogeny. Near Pointe-au-Baril, Ontario, a crustal block containing pre-Grenvillian gran...

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Bibliographic Details
Published in:Geology (Boulder) 1994-03, Vol.22 (3), p.215-218
Main Authors: Ketchum, J. W. F, Jamieson, R. A, Heaman, L. M, Culshaw, N. G, Krogh, T. E
Format: Article
Language:English
Subjects:
absolute age
Britt Domain
Canada
Canadian Shield
Central Gneiss Belt
dates
Eastern Canada
facies
Geochronology
Geology
granulite facies
granulites
Grenville Front
Grenville Province
Grenvillian Orogeny
igneous activity
igneous and metamorphic rocks
mafic composition
Mesoproterozoic
metamorphic rocks
metamorphism
mineral assemblages
nesosilicates
North America
Ontario
orthosilicates
P-T conditions
Petrology
Plate tectonics
Precambrian
Proterozoic
silicates
U/Pb
upper Precambrian
zircon
zircon group
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Summary:In the southwestern Grenville province, the parautochthonous Britt domain includes a variety of pre-Grenvillian metamorphic and plutonic rocks that were reworked at upper amphibolite facies during the Grenvillian orogeny. Near Pointe-au-Baril, Ontario, a crustal block containing pre-Grenvillian granulite facies mineral assemblages and pre-Grenvillian to early Grenvillian tectonic fabrics has been identified. The block is bounded on the northwest and southeast by extensional shear zones that may have isolated it from regional late Grenvillian deformation. Multiequilibria pressure-temperature (P-T) calculations for orthopyroxene-bearing mafic rocks suggest conditions of 625-700°C and 7.2-8.4 kbar for the pre-Grenvillian metamorphism. The granulite facies assemblages were locally overprinted during higher pressure Grenvillian metamorphism, which peaked at 720-775°C and 10.8-11.5 kbar. U-Pb zircon data from migmatitic, mafic supracrustal gneiss indicate metamorphism and leucosome development at ca. 1450-1430 Ma, in agreement with other pre-Grenvillian metamorphic ages for the Central gneiss belt and Grenville Front tectonic zone. An expanding data base on pre-Grenvillian events in the southwestern Grenville province indicates that high-grade metamorphism at ca. 1450-1430 Ma affected a large region of crust and was coeval with widespread felsic to intermediate plutonism.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(1994)022<0215:GGITSG>2.3.CO;2