HR: 13:40h
AN: V43E-01    [Abstracts]
TI: Gigantic Diamondiferous Eclogite from Udachnaya: Mineralogy and Tomography of this Yakutian Xenolith.
AU: * Taylor, L A
EM: lataylor@utk.edu
AF: University of Tennessee, Dept. of Earth & Planetary Sciences 306 EPS Bldg., Knoxville, TN 37996 United States
AU: Ketchum, R
V43E-01 AF: University of Texas, Dept. of Geological Sciences, Austin, TX 78712 United States
AU: Day, J M
EM: jday13@utk.edu
AF: University of Tennessee, Dept. of Earth & Planetary Sciences 306 EPS Bldg., Knoxville, TN 37996 United States
AU: Stepanov, A
V43E-01 AF: Institute of Mineralogy & Petrography, Koptyug Ave., 3, Novosibirsk, 630090 Russian Federation
AU: Carlson, W
V43E-01 AF: University of Texas, Dept. of Geological Sciences, Austin, TX 78712 United States
AU: Liu, Y
EM: yangl@utk.edu
AF: University of Tennessee, Dept. of Earth & Planetary Sciences 306 EPS Bldg., Knoxville, TN 37996 United States
AU: Shatsky, V
V43E-01 AF: Institute of Mineralogy & Petrography, Koptyug Ave., 3, Novosibirsk, 630090 Russian Federation
AB: Diamondiferous eclogites are rare unique xenoliths brought to the surface of the Earth by kimberlites. The Udachnaya pipe of Yakutia contains many such unusual xenoliths, largely because of the freshness of this kimberlite; usually only 30-80 gm portions are collected during the crushing and production process. However, a giant 8.8 kg relatively fresh diamondiferous eclogite was recently recovered from the ore stockpile. There appear to be two, possibly more, different types of eclogites in this one xenolith, one with Group A garnets, the other with Group B. Three-dimensional, high-resolution computed X-ray tomography (HRCXT) of this diamondiferous eclogite, difficult for its size, has successfully imaged the multitude of diamonds (micro up to 2-3 cts) and their textural relationships with co-existing minerals. This is an extension to the tomography and xenolith dissections performed previously on diamondiferous eclogites by our group (e.g., Taylor et al., 2000, Int'l Geol Rev 42; Anand et al., 2004, Lithos 77). 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. The maps obtained from this tomography also form the basis for the delicate dissection of the xenolith, revealing the diamonds as they formed in their mantle host rock. A previous eclogite of 65 g contained 74 macro-diamonds. Inspection of the surface of this 8.8 kg eclogite and examination of the tomographic images indicates that >100 diamonds exist in this eclogite. 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 is further evidence that the diamonds formed after the initial host eclogite, probably from the introduction of metasomatic carbonate-rich fluids.
UR: http://geoweb.gg.utk.edu/Faculty/taylor/taylor.htm
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8180 Tomography (6982, 7270)
DE: 8194 Instruments and techniques
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005