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Harald Furnes,1*Maarten de Wit,2,3Hubert Staudigel,4Minik Rosing,5Karlis Muehlenbachs6
A sheeted-dike complex within the 3.8-billion-year-old Isuasupracrustal belt (ISB) in southwest Greenland provides theoldest evidence of oceanic crustal accretion by spreading. Thegeochemistry of the dikes and associated pillow lavas demonstratesan intraoceanic island arc and mid-ocean ridgelike setting,and their oxygen isotopes suggest a hydrothermal ocean-floortypemetamorphism. The pillows and dikes are associated with gabbroicand ultramafic rocks that together make up an ophiolitic association:the Paleoarchean Isua ophiolite complex. These sheeted dikesoffer evidence for remnants of oceanic crust formed by sea-floorspreading of the earliest intact rocks on Earth.
1 Centre for Geobiology and Department of Earth Science, University of Bergen, Bergen, Norway. 2 Africa Earth Observatory Network (AEON) and Department of Geological Sciences, University of Cape Town, Rondebosch 7700 South Africa. 3 GeoForschungsZentrum (GFZ)Potsdam, Telegraphenberg, Potsdam, Germany. 4 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0225, USA. 5 Nordic Centre for Earth Evolution and Geological Museum, University of Copenhagen, 1350, Københagen K, Denmark 6 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada.
* To whom correspondence should be addressed. E-mail: harald.furnes{at}geo.uib.no
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