Eoarchean crust is not that rare: Widespread pre-3750 Ma supracrustal rocks from the Nuvvuagittuq supracrustal belt, northern Québec.

Details Eoarchean crust is not that rare: Widespread pre-3750 Ma supracrustal rocks from the Nuvvuagittuq supracrustal belt, northern Québec. Eoarchean crust is not that rare: Widespread pre-3750 Ma supracrustal rocks from the Nuvvuagittuq supracrustal belt, northern Québec.

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.v11d0615c&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #V11D-0615

Biology

0406 Astrobiology And Extraterrestrial Materials, 0419 Biomineralization, 1040 Radiogenic Isotope Geochemistry, 1065 Major And Trace Element Geochemistry, 1115 Radioisotope Geochronology

Scientific paper

Geochemistry and U-Pb ion microprobe zircon geochronology guided by high-resolution mapping (1:50 scale) supports a minimum age of ca. 3750 Ma for supracrustal rocks from the Nuvvuagittuq supracrustal belt (NSB) in the Inukjuak domain of the northern Superior Province (Minto Block), Québec (Canada). Field relations, mineralogy and geochemistry at the Porpoise Cove locality describe a supracrustal succession of mafic amphibolites and ultramafic rocks, finely banded quartz-magnetite units with intermixed coarse-grained ferruginous quartz-pyroxene rocks, and quartz-biotite schists that superficially resemble polymict meta- conglomerates with large (up to 10 cm) deformed polycrystalline quartz and mafic clasts. All units preserve sharp lithological contacts. Narrow (dominantly trondhjemitic) orthogneiss sheets locally preserve intrusive contact relationships to the supracrustal enclave. The enclave is strongly deformed and the full deformation history appears to be shared by all units with later modifications from leucogranitoid intrusions. The quartz- biotite schists record complex zircon growth at 3500 and 2800 Ma, interpreted to reflect metamorphic events. Zircons separated from orthogneisses in the enclave including one sheet that transects a banded quartz- pyroxene(magnetite) unit yield magmatic 207Pb/206Pb ages of ca. 3750 Ma. These ages are slightly younger than earlier provisional reports for an NSB orthogneiss from Porpoise Cove. The Nuvvuagittuq supracrustals are the oldest rocks thus far reported for the Minto Block, they are locally abundant in the Inukjuak domain, they overlap in age with the ca. 3.7-3.83 Ga Isua supracrustal belt and Akilia association rocks in West Greenland, and represent an important new data set for exploration of the early Earth. Every year more and more pre-3.6 billion year old rocks of sedimentary origin are discovered. This means that our understanding of this pivotal time period will surely continue to grow.

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