HR: 0800h
AN: T21A-0513    [Abstracts]
TI: Diamond Synthesis and Carbon Solubility in a Hydrous Granitoid System
AU: * Renfro, A
EM: tashalex@earthlink.net
AF: University of California, Riverside, 900 University Avenue, Riverside, CA 92521
AU: Dobrzhinetskaya, L P
EM: larissa@ucr.edu
AF: University of California, Riverside, 900 University Avenue, Riverside, CA 92521
AB: An increasing number of UHP metamorphic terranes incorporated in collisional orogenic belts have been identified since the first discovery of diamonds within felsic metamorphic rocks of Kokchetav massif, Kazakhstan, extending up to $\sim$4000 km in length in the Dabie-SuLu-Qinling belt of China. Some have suggested that all orogenic belt diamonds formed from a carbonate or calc-alkaline melt similar to those derived from kimberlitic pipes, or alternatively that they formed from a carbon-enriched silicate melt with a granitoid bulk chemistry composition. Another group has suggested that orogenic belt diamonds crystallized from a COH-rich supercritical fluid. While the diversity of the minor components accompanying the SiO$_{2}$-dominated inclusions from Kokchetav diamonds, as well as the presence of cavities bearing traces of a former fluid, suggest the idea of diamond growth from a COH fluid, a Si-rich melt as a source for diamond formation cannot be ruled out. Although many experiments were performed on diamond synthesis and on the petrology of diamond-bearing rocks, no consensus has been reached as to which of the mentioned growth media is correct to explain orogenic belt diamond formation. We report here the results of an experimental program undertaken to determine the critical point of the Si-Al-K-C-H$_{2}$O system (and thus, to distinguish a melt environment from a fluid one) and to provide an understanding of how diamond is crystallized in hydrous subducted felsic continental crust. Carbon solubility in these systems was qualitatively determined based on the observed diamond growth rates. Experiments were performed at in a Walker-style multianvil apparatus at P=7 GPa and T=1500-1700$\deg$C with SiO$_{2}$ ranging from 90 wt. %, imitating diamondiferous quartzite, to 62 wt. %, imitating a wide range of feldspathic diamondiferous gneisses. An additional parameter, oxygen fugacity, was also varied to test its affects on the solubility of carbon in Si-rich melt/fluid.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3630 Experimental mineralogy and petrology
DE: 3660 Metamorphic petrology
DE: 3694 Instruments and techniques
DE: 3699 General or miscellaneous
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting