HR: 16:30h
AN: V54B-03    [Abstracts]
TI: Coesite After Stishovite in a Tibetan Ophiolite: Primary Evidence of Deep Mantle Plume?
AU: * Yang, J
EM: yangjsui@ccsd.org.cn
AF: Key Laboratory of Continental Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037 China
AU: Dobrzhinetskaya, L
EM: larissa@ucr.edu
AF: Department of Earth Sciences, University of California, Riverside, Riverside, CA 92521 United States
AU: Bai, W
EM: yangjsui@ccsd.cn
AF: Key Laboratory of Continental Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037 China
AU: Fang, Q
EM: yangjsui@ccsd.cn
AF: Key Laboratory of Continental Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037 China
AU: Robinson, P T
EM: p.robinson@ns.sympatico.ca
AF: Key Laboratory of Continental Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037 China
AU: Robinson, P T
EM: p.robinson@ns.sympatico.ca
AF: Department of Earth Sciences, Dalhousie University, Halifax, Halifax, B3H4J1 Canada
AU: Green, H
EM: hgreen@ucrac1.ucr.edu
AF: Department of Earth Sciences and Institute of Geophysics and Planetary Physics, University of California, Riverside, Riverside, CA 92521 United States
AB: The Luobusa massif is situated within the Yarlung-Zangbo suture zone, the largest ophiolite belt in Asia, which is of great interest because of its geodynamic location along the great Himalayan suture defining the geological boundary between Asia and India The massif marks the closure of the Neo-Tethyan ocean in the Early Tertiary (~65Ma). Podiform chromitites within the Luobusa ophiolite of Tibet have been reported to contain diamonds and other unusual minerals, some of which suggest very great depths of formation (Yang et al., 2003, Progress in Natural Science, 13, 528-531). However, the unusual setting (an ophiolite terrane lacking significant metamorphic overprint) has resulted in some skepticism concerning these claims. On a larger scale, similar claims have been made over the last 30 years for other rocks of similar tectonic settingś"Bird and Weathers, 1975, Earth Planet. Sci. Lett. 28, 51-64). Here we report the `smoking gun' that establishes that parts of the mantle section of the Luobusa ophiolite originated at a minimum depth of ~300 km and possibly much more. The critical observation is coesite pseudomorphic after stishovite in contact with Fe-Ti alloy included in chromitite. This is the first observation of coesite in an ophiolite and the occurrence of coesite with the morphology of stishovite is unique. Coexisting titanium oxide containing >30 atom% SiO2 suggests formation under lower mantle conditions, reopening the dialog concerning possible mantle plume origin of some peridotite massifs incorporated in ophiolites worldwideś"Bird et al., 1999 Earth Planet. Sci. Lett. 170, 83-92 ).
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005