Diamond and Coesite After Former Stishovite in Tibet Ophiolites: Is That Myth or Reality?

Details Diamond and Coesite After Former Stishovite in Tibet Ophiolites: Is That Myth or Reality? Diamond and Coesite After Former Stishovite in Tibet Ophiolites: Is That Myth or Reality?

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.v44b..01y&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #V44B-01

Physics

8100 Tectonophysics, 8400 Volcanology

Scientific paper

An extremely controversial theme in the Earth Sciences over the last 30 years has been the origin of chromitite deposits found worldwide within depleted peridotites (harzburgites) of the uppermost mantle in ¨C rock sequences representing former oceanic lithosphere. The majority of workers support a model in which massive chromitites containing Os- and Ir-rich platinum group element (PGE) alloys form by interaction of H2O-saturated boninite melt with harzburgites of the mantle wedge above a subduction zone at comparatively shallow levels in the mantle, from depths of 30-50 km to a maximum pressure of 4.5 GPa (ca.150 km). A second model suggests that the Os/Ir-rich PGE alloys associated with podiform chromitites formed in the very deep mantle, either before formation of Earth's core or, if later, at the core-mantle boundary, and that they have been transported to the surface as xenoliths in deep-rooted mantle plumes. We report the presence of diamond and prismatic coesite associated with metallic grains from chromitite of a Tibetan ophiolite, implying 4 GPa minimum pressure. The microstructure of coesite strongly suggests replacement of stishovite, implying P over10 GPa. This is the first confirmed observation of coesite or diamond in an ophiolite and the occurrence of coesite with the morphology of stishovite is unique. Diamonds have been recovered previously from the Luobusa chromitites, but only as individual grains. Here we describe a composite microdiamond-silicate inclusion in a grain of Os/Ir alloy. Our study also involves examination of grains of Os-Ir, Ni-Fe-Cr-C and CrC alloys, native Si, Fe, Ti and Cr, and chromite separated from massive chromitite ore. Two explanations appear possible: derivation from the deep mantle or meteorite impact, but no direct evidence of shock has been observed. However, at this stage the interpretation should leave open.

Affiliated with

Also associated with

No associations

Rating

Diamond and Coesite After Former Stishovite in Tibet Ophiolites: Is That Myth or Reality? does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Diamond and Coesite After Former Stishovite in Tibet Ophiolites: Is That Myth or Reality?, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Diamond and Coesite After Former Stishovite in Tibet Ophiolites: Is That Myth or Reality? will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-963350