HR: 0800h
AN: V41E-1518    [Abstracts]
TI: In-situ Study of Multiple Chromite Inclusions in Udachnaya Diamonds, Siberia
AU: * Liu, Y
EM: yangl@utk.edu
AF: Planetary Geosciences Institute, Department of Earth & Plaentary Sciences, University of Tennessee, Knoxville, TN 37996 United States
AU: Taylor, L A
EM: lataylor@utk.edu
AF: Planetary Geosciences Institute, Department of Earth & Plaentary Sciences, University of Tennessee, Knoxville, TN 37996 United States
AU: Floss, C
V41E-1518 AF: Laboratory for Space Sciences, Physics Department, CB 1105, Washington University, St. Louis, MO 63130 United States
AU: Logvinova, A M
V41E-1518 AF: Institute of Mineralogy & Petrography, Russian Academy of Science-Siberian Branch, Novosibirsk, 630090 Russian Federation
AU: Sobolev, N V
V41E-1518 AF: Institute of Mineralogy & Petrography, Russian Academy of Science-Siberian Branch, Novosibirsk, 630090 Russian Federation
AB: Diamonds are time-capsules from the mantle containing mineral inclusions in their pristine state and, as such, reveal unique information on the otherwise unaccessable portions of the Earth. Chemistry of multiple mineral inclusions (DIs) in a single diamond potentially records the temporal and spatial variation of the environment of diamond formation. Several studies have been conducted on multiple inclusions in single Russian diamonds, with highly significant results such as heterogeneity in chemistry of 35 eclogitic garnets and 5 pyroxene inclusions in a single diamond from the Mir pipe (Sobolev et al. 1997, Int Geol Rev 40). Unfortunately most studies of DIs are performed on inclusions that are won from their diamond hosts by either burning or cracking/picking of the diamonds, thereby destroying the relative ages of the multiple inclusions. This paper reports the numerous chromite inclusions that occur in the P/U-type diamonds from the Udachnaya pipe, some of which display differences in chemistry, not totally explainable by magmatic processes. The diamonds in this study were examined through a small ``window'' polished into the diamond. The relative positions of the chromite inclusions were examined and a plane was noted where at least 3 chromites would be exposed simultaneously. As this plane was approached by polishing, the diamond was further tilted on the goniometric dop (holder) so as to possibly bring other chromites into this new slightly different plane. By such a detailed polishing technique, up to 7 DIs could be exposed on a single polished surface of the diamond at one time. Cathodoluminescence (CL) imaging of the polished diamond revealed the relative ages of the DIs. Due to defects and/or N<sub>2</sub> aggregation in diamond, zones with variable degrees of brightness are displayed parallel to one another, much like tree rings. Both major- and trace-element chemistry of the DIs are determined. This methodology of study of DIs while they are still within their original positions in the diamonds is referred to as the ``In-Situ Technique''. Out of thousands of diamond grains, we found nine diamond crystals (10-60 mg) with multiple inclusions (chromites ± olivine ± orthopyroxene). Composition of chromites as well as associated olivine and pyroxene in different CL zones of a single diamond reveals `non-systematic' variations of these DIs with respect to their relative ages. These differences represent different chemistry of the minerals at the time of their encapsulation, largely controlled by the nature of the metasomatic fluids, which also directly cause the further growth of the diamond.
DE: 1025 Composition of the mantle
DE: 3621 Mantle processes (1038)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005