Acasta Gneiss Complex
The Acasta gneiss complex in northwestern Canada contains some of the oldest dated rocks on earth and the oldest dated using U-Pb in zircon. They therefore potentially preserve clues to the nature and history of earth’s oldest crust. The geology of the gneisses reflects a complex multistage history of magmatism, metamorphism, and deformation over more than 400 million years, and the entire complex should be viewed as a small fragment of Hadean to Archean continental crust. The gneisses are compositionally diverse and range from granite and tonalite to gabbro and serpentinized ultramafic rocks. The oldest published crystallization age is 4.031 +/− 0.003 Ga. There are isotopic and inherited zircon data consistent with the involvement of crust as old as 4.2 Ga. There is no single age of the Acasta gneiss complex (Bowring and Williams, 1999).
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