Anticorrelation between low δ13C of eclogitic diamonds and high δ18O of their coesite and garnet inclusions requires a subduction origin
Daniel J. Schulze et al., Dept. of Earth Sciences, University of Toronto, Mississauga, Ontario L5L 1C6, Canada. Posted online 20 Feb. 203; http://dx.doi.org/10.1130/G33839.1.
Daniel J. Schulze and colleagues analyze the isotopic composition of diamonds with tiny garnet and silica inclusions from three diamond mines (in Venezuela, Australia, and Botswana) and find that their compositions are unlike material typical of the upper mantle, but identical to material that would be predicted to occur on the ancient ocean floor. Although many other workers have explained similar values in diamonds as due to crystallization of the diamonds from mantle fluids, the carbon in the diamonds is also equivalent to carbon of biologic origin. The oxygen isotope composition of the tiny minerals in the diamonds is also unlike that from typical mantle material and has only been observed elsewhere in rocks that have been altered on the ocean floor. This pairing, which Schulze and colleagues have documented for the first time, is a fundamental observation that can only be explained by the formation of these diamonds through subduction of rocks altered on the sea floor, mixed with biologic carbon, beneath the continents into the field of diamond sta
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