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2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 9
Presentation Time: 1:30 PM-5:30 PM

MICRO-PHASES AND MICROSTRUCTURES IN CLINOPYROXENE MINERALS FROM A RAPIDLY SUBDUCTED AND EXHUMED HIGH PRESSURE METAMORPHIC TERRAIN: HRTEM AND X-PEEM INVESTIGATIONS


XU, Huifang1, FRAZER, Bradley H.2, FU, Bin1, LIAO, Xiao-Zhou3, YEREDLA, Rakesh Reddy1, ABRECHT, Mike2, VALLEY, John W.1 and GILBERT, P.U.P.A.4, (1)Department of Geology and Geophysics, Univ of Wisconsin, Department of Geology and Geophysics, University of Wisconsin, Madison, WI 53706, USA, Madison, WI 53706, (2)Synchrotron Radiation Center, University of Wisconsin, 3731 Schneider Dr, Stoughton, WI 53589, (3)School of Aerospace, Mechanical & Mechatronic Engineering, The University of Sydney, Sydney, 2006, Australia, (4)Department of Physics, University of Wisconsin, 1150 University Avenue, Madison, WI 53706, hfxu@geology.wisc.edu

Microstructures and micro-inclusions in minerals can provide information about the genesis and evolutionary history of host rocks. High-resolution TEM (HRTEM) and X-ray PhotoElectron Emission Microscopy (X-PEEM) are useful tools for studying microstructures and microchemistry of minerals, which can provide spatially resolved chemistry about micro-phases and interfaces in minerals. The sample for this study is from a garnet clinopyroxenite, a high pressure metamorphic rock in northern Dabie Mountains of China. The terrain hosting the sample was a product of the Triassic continental collision between the Sino-Korean and Yangtze cratons in East-central China. Previously, the rock was considered as a product of an ultra-high pressure metamorphism (Tsai & Liou, 2000, Am. Mineral. v.85, p.1-8). Recent study also shows that the eclogite-facies rocks re-equilibrated under granulite-facies conditions (Fu, et al., 2003, Lithos, v.70, p.293-319). The clinopyroxene (Wo39En37Jd14Ac6Fs4) crystals contain micron to sub micron silica-rich (> 75% SiO2 ) precipitates, some of them CO2 (L)-bearing, in the core and exsolution lamella of a second generation pyroxene in the rim. HRTEM and X-PEEM results indicate that silica-rich glass precipitates are uniformly distributed and that the (Fe,Mg)-rich pyroxene lamellae and have P21 /c symmetry (the symmetry for pigeonite, not orthopyroxene). We suggest that the Al-bearing exsolution lamellae formed metastably (quickly). The silica-rich micro-phases inside the host pyroxene probably formed during fast transformation from amphibole into pyroxene, which may indicate rapid subduction of the continental plate. The preservation of silica-rich glass precipitates and the formation of (Fe,Mg)-rich clinopyroxene lamella indicate very fast cooling of the host rock. Our results indicate that the host rock (in paleo-continent plate in the Dabie Mountains) had experienced extremely rapid subduction and exhumation.

Session No. 118--Booth# 99

T101. Petrologic Mineralogy—The Study of Minerals in Context (Posters): In Honor of Charles V. Guidotti
Monday, 23 October 2006: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol. 38, No. 7, p.293
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