HR: 0800h
AN: V41F-1536    [Abstracts]
TI: Expanding the Inventory of Early Archean Crust: Confirmation of a >3750 Ma Supracrustal Sequence, Nuvvuagittuq Belt, Northern Québec
AU: * Cates, N L
EM: nicole.cates@colorado.edu
AF: Department of Geological Sciences, Center for Astrobiology, University of Colorado, 2200 Colorado Ave UCB 399, Boulder, CO 80309-0399 United States
AU: Mojzsis, S J
EM: stephen.mojzsis@colorado.edu
AF: Department of Geological Sciences, Center for Astrobiology, University of Colorado, 2200 Colorado Ave UCB 399, Boulder, CO 80309-0399 United States
AB: Early Archean supracrustal sequences provide the only direct window into geologic processes that governed the young Earth. Preserved crust of such antiquity is extremely rare and each new discovery has the potential to greatly expand our knowledge on conditions of the emergent biosphere. Currently there are only two well studied locations with supracrustal sequences greater than 3600 Ma: the Isua supracrustal belt (ISB) and the Akilia association, both located in Western Greenland. Here we present new data from a recently described locality (Simard et al., 2003) from Northern Québec, Canada. The Nuvvuagittuq belt (Porpoise Cove), located within the Inukjuak terrane of the Superior Province comprises a volcano-sedimentary sequence composed of mafic extrusives, chemical sediments (including finely laminated banded iron formations), and a potential polymict conglomerate, all intruded by tonalitic orthogneiss. The sequence is multiply deformed and metamorphosed to upper amphibolite/lower granulite facies. Our high resolution mapping (1:40) of a small coastal outcrop with spectacular exposure within the ~10 km² belt has revealed unequivocal cross-cutting relationships between supracrustal units and intrusive orthogneisses, which provide a minimum age for the supracrustal sequence. Ion microprobe U-Th-Pb zircon geochronology on five orthogneisses thus far analyzed yield concordant ²⁰⁷Pb/²⁰⁶Pb ages of ~3760 Ma with Th/U consistent with a magmatic origin. These new geochronology results are somewhat younger than a previously reported multi-grain TIMS age of 3825 Ma (Simard et al., 2003; Nadeau, unpublished thesis) and suggests that this slice of crust is contemporaneous with the early Archean of southern West Greenland.
DE: 1065 Major and trace element geochemistry
DE: 1090 Field relationships (3690, 8486)
DE: 1115 Radioisotope geochronology
DE: 5225 Early environment of Earth
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005