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Science 23 March 2007:
Vol. 315. no. 5819, pp. 1704 - 1707
DOI: 10.1126/science.1139170
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Reports

A Vestige of Earth's Oldest Ophiolite

Harald Furnes,1* Maarten de Wit,2,3 Hubert Staudigel,4 Minik Rosing,5 Karlis Muehlenbachs6

A sheeted-dike complex within the ~3.8-billion-year-old Isua supracrustal belt (ISB) in southwest Greenland provides the oldest evidence of oceanic crustal accretion by spreading. The geochemistry of the dikes and associated pillow lavas demonstrates an intraoceanic island arc and mid-ocean ridge–like setting, and their oxygen isotopes suggest a hydrothermal ocean-floor–type metamorphism. The pillows and dikes are associated with gabbroic and ultramafic rocks that together make up an ophiolitic association: the Paleoarchean Isua ophiolite complex. These sheeted dikes offer evidence for remnants of oceanic crust formed by sea-floor spreading 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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