Tectonic studies, upper mantle studies, tectonic settings of diamond deposits

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The two main themes of the planned research are the tectonic settings of diamond deposits, in particular primary diamond deposits occurring in kimberlites and other igneous rocks, and problems of diamond storage in the Earth's lithosphere. The first theme involves studying the various hierarchies of tectonic controls on primary diamond deposits, including the formation of the diamond-bearing source rocks in the roots cratons, the preservation of diamonds until they are transported to the surface, and the regional and local structural controls of kimberlite formation and near-surface emplacement. This research will focus mainly on the kimberlites of the Slave and Superior Provinces of the Canadian Shield, where deep-crustal and upper mantle geophysical data were collected by the LITHOPROBE and POLARIS programs. The second theme involves laboratory studies of diamonds from the Slave Province and South Africa to investigate whether intracrystalline strain in brown diamonds indicates that these deformed diamonds were stored metastably in the lithosphere. The possibility of metastable storage is suggested by recent advances in high-pressure, high-temperature (HPHT) treatment of natural diamonds which have shown that brown diamonds can be transformed (annealed?) into yellow or white diamonds after a relatively short period (as little as 20 minutes) of treatment under conditions that only slightly overstep the minimum pressure and temperature of the diamond stability field. The proposed research is designed to test the annealing hypothesis and its implications for xenolith and xenocryst-based upper mantle models in which it is commonly assumed that diamond-bearing assemblages were transported from depths corresponding to the pressures of the diamond stability field. The results may have a profound impact on current models for area selection in diamond exploration.