HR: 0830h
AN: T31F-0898    [PDF]
TI: Microstructural analysis of the ultrahigh-pressure Sulu terrane, eastern China
AU: * Leech, M L
EM: mary@geo.stanford.edu
AF: Stanford University, Geological and Environmental Sciences, Stanford, CA 94305-2115 United States
AU: Webb, L E
EM: lewebb@syr.edu
AF: Syracuse University, Earth Sciences, 204 Heroy Geology Laboratory, Syracuse, NY 13244-1070 United States
AU: Yang, T
EM: yangtn@cags.cn.net
AF: Chinese Academy of Geological Sciences, Institute of Geology, Baiwanzhuang Road, Beijing, 100037 China
AU: Xu, Z
EM: xuzhiqin@ccsd.org.cn
AF: Chinese Academy of Geological Sciences, Institute of Geology, Baiwanzhuang Road, Beijing, 100037 China
AB: We applied techniques of microstructural analysis to oriented samples from eclogites and host gneisses of the Sulu UHP terrane of eastern China to understand the exhumation process. Our field observations of top-to-the-(W)NW sense of shear in exhumation related fabrics are corroborated by microstructural kinematic indicators such as C'-type shear band cleavage, mica fish, sigma clasts, and quartz fabrics. The top-to-the-(W)NW sense of shear is recorded through the continuum of retrograde metamorphism from eclogite-facies conditions. Microboudinage of amphibole and zoisite parallels the stretching lineation and strain shadows with recrystallized quartz occur around porphyroclasts. Eclogite bodies displaying mesoscopic deformation fabrics are commonly dominated by symplectite textures at microscopic scale, suggesting static recrystallization occurred after deformation was partitioned into surrounding host gneisses as exhumation progressed. Syntectonic albite porphyroblasts from retrograde mafic schists interlayered with host gneisses contain hornblende and rutile-rich inclusion suites. This internal foliation is continuous with the external foliation defined by biotite. Locally, recovery of quartz and feldspar in host gneisses indicate that temperature outlasted deformation. Upper greenschist-facies mylonitic fabrics are preserved in the NW limb of a large SW-NE trending antiform near the Yantai-Qingdao-Wulian detachment zone. These data support a single stage of exhumation of the UHP unit from mantle to upper mid-crustal depths. U-Pb SHRIMP dating and 40Ar/39Ar thermochronology will reveal the ages of ultrahigh-pressure metamorphism and constrain the timing of cooling and deformation associated with exhumation.
DE: 3660 Metamorphic petrology
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8025 Mesoscopic fabrics
DE: 8030 Microstructures
DE: 8100 TECTONOPHYSICS
SC: Tectonophysics [T]
MN: 2003 Fall Meeting