Coesite After Stishovite in a Tibetan Ophiolite: Primary Evidence of Deep Mantle Plume?

Details Coesite After Stishovite in a Tibetan Ophiolite: Primary Evidence of Deep Mantle Plume? Coesite After Stishovite in a Tibetan Ophiolite: Primary Evidence of Deep Mantle Plume?

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.v54b..03y&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #V54B-03

Mathematics

Logic

1031 Subduction Zone Processes (3060, 3613, 8170, 8413), 1032 Mid-Oceanic Ridge Processes (3614, 8416), 3060 Subduction Zone Processes (1031, 3613, 8170, 8413), 3613 Subduction Zone Processes (1031, 3060, 8170, 8413), 8170 Subduction Zone Processes (1031, 3060, 3613, 8413)

Scientific paper

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 setting "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 worldwide "Bird et al., 1999 Earth Planet. Sci. Lett. 170, 83-92 ).

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