HR: 1330h
AN: V42A-0321    [PDF]
TI: Diamondiferous Peridotite Tomography: Precursor to Xenolith Dissections.
AU: * Taylor, L A
EM: lataylor@utk.edu
AF: University of Tennessee, Planetary Geosciences Institute, 306 GS Bldg., Knoxville, TN 37996 United States
AU: Taylor, D S
AF: University of Tennessee, Planetary Geosciences Institute, 306 GS Bldg., Knoxville, TN 37996 United States
AU: Anand, M
EM: anandm@utk.edu
AF: University of Tennessee, Planetary Geosciences Institute, 306 GS Bldg., Knoxville, TN 37996 United States
AU: Ketcham, R
EM: ricjk@maestro.geo.utexas.edu
AF: University of Texas, Dept. of Geological Sci., Austin, TX 78712 United States
AU: Carlson, W
EM: wcarlson@mail.utexas.edu
AF: University of Texas, Dept. of Geological Sci., Austin, TX 78712 United States
AU: Sobolev, N V
EM: sobolev@uiggm.nsc.ru
AF: Intitute of Mineralogy & Petrography, Koptyug Ave. 3, Novosibirsk, 630090 Russian Federation
AU: Pokhilenko, N
AF: Intitute of Mineralogy & Petrography, Koptyug Ave. 3, Novosibirsk, 630090 Russian Federation
AB: Three-dimensional, high-resolution computed X-ray tomography (HRCXT) of diamondiferous peridotite xenoliths from Siberia has successfully imaged diamonds and their textural relationships with co-existing minerals. This is an extension to the tomography and xenolith dissections performed previously on diamondiferous eclogites (e.g., Taylor et al., 2000, Int'l Geol Rev 42; Anand et al., 2003, 8th Int'l Kimb Conf). Spatial relationships between diamonds and their surroundings provide clues to the processes that control diamond crystallization. These relationships can be determined by rotating and viewing the 3-D model at different perspectives and orientations to look for specific associations/alignments. It is possible to render some of the phases transparent and display only one or two minerals at a time. Then by rotating the model, it is possible to look for spatial relationships between different crystals of the same mineral or different minerals. The maps obtained from the tomography form the basis for the delicate dissections of the xenoliths, revealing the diamonds as they formed in their mantle host rocks. Diamondiferous peridotites appear to be sparse carriers of diamonds compared to eclogites, where one unusual eclogite of 65 g contained 74 macro-diamonds. Although kimberlites always contain considerably more peridotite xenoliths than eclogites, the diamond population may actually be more indicative of eclogitic origin. The diamonds appear to be preferentially located in zones with a prominent sub-planar fabric of secondary mineralization - i.e., zones of increased permeability. Diamond was never observed in direct contact with any fresh, primary minerals. Also, there is insufficient sulfide mineralization to call upon an immiscible-sulfide melt as the diamond-forming medium. The association of the diamonds with secondary minerals strongly suggests that the diamonds formed after the initial host peridotite or eclogite, perhaps in conjunction with introduction of metasomatic fluids.
DE: 3640 Igneous petrology
DE: 3660 Metamorphic petrology
DE: 3694 Instruments and techniques
DE: 8180 Tomography
DE: 8194 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting