HR: 09:45h
AN: V51E-08 INVITED     [Abstracts]
TI: Evidence of Former Stishovite in Metamorphosed Sediments: Exhumation from >300 km
AU: Liu, L
EM: liuliang@nwu.edu.cn
AF: Department of Geology, Northwest University, Xi'an, 710069 China
AU: Liu, L
EM: liuliang@nwu.edu.cn
AF: IGPP and Dept. of Earth Sciences, University of California, Riverside, CA 92521 United States
AU: Zhang, J
EM: junfeng.zhang@email.ucr.edu
AF: IGPP and Dept. of Earth Sciences, University of California, Riverside, CA 92521 United States
AU: * Green, H W
EM: harry.green@ucr.edu
AF: IGPP and Dept. of Earth Sciences, University of California, Riverside, CA 92521 United States
AU: jin, Z
EM: zmjin@cug.edu.cn
AF: Stat Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074 China
AB: Deep subduction of continental rocks or sediments is difficult because they are buoyant relative to mantle compositions. Nevertheless, it has been shown that during continental collision, such rocks can be subducted to ~200km and returned to the surface. At pressures equivalent to ~300 km, experimental studies indicate that continental rocks will become more dense than ambient mantle and therefore presumably lose their ability to return to the surface buoyantly. We have discovered distinctive aluminum- and iron-bearing oxide inclusions (oriented kyanite and hercynite) in quartz of high-pressure pelitic rocks from the Altyn Tagh, western China that may represent rocks subducted to approximately this point of no return. The inclusions exhibit all of the characteristics of phases exsolved from solid solution except that they have no topotaxy with their host quartz; in many cases, the oriented inclusions cross high-angle quartz grain boundaries with no deviation in their orientations. The abundance of these phases (~1 vol%) is also incompatible with the known solubility of Fe and Al in either quartz or coesite. We have performed laboratory experiments at high pressure and found that these observations are consistent with the possibility that the oxides precipitated from stishovite, which is stable only above ~10GPa. These observations strongly suggest that these pelitic (clay-rich) sediments have been subducted to at least 300 km and returned to the surface.
DE: 3630 Experimental mineralogy and petrology
DE: 3660 Metamorphic petrology
DE: 3924 High-pressure behavior
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005