HR: 0800h
AN: V11A-1415    [Abstracts]
TI: An exotic terrane in the Sulu UHP region, China
AU: * Chu, W
EM: wchu@pangea.stanford.edu
AF: Dept. of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94305 United States
AU: Zhang, R
EM: zhang@pangea.stanford.edu
AF: Dept. of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94305 United States
AU: Tsujimori, T
EM: tatsukix@pangea.stanford.edu
AF: Dept. of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94305 United States
AU: Liou, J G
EM: Liou@pangea.stanford.edu
AF: Dept. of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94305 United States
AB: The Haiyangsuo region of about 15 km2 along the coast in the NE part of the Triassic Sulu UHP terrane occurs three major rock types: amphibolitized metagabbro, gneiss and granitic dikes. Three different gneisses were observed in the field: A) Light color felsic gneiss is the dominant country rock and contains Qtz, Pl, Ms and Bi. B) Dark color plagioclase-amphibole gneiss occurs as thin layers within country rock; C) Granulite facies rock occurs as discontinuous lens. The amphibolitized metagabbros intrude into the gneisses as massive bodies (several m to hundreds of m in size) and thin dikes. Both metamorphic intrusives and gneisses are cross-cut by granitic dikes. The amphibolitized metagabbro was divided into three types: coronal metagabbro, transitional rock and garnet amphibolite: 1) Coronal metagabbro preserves gabbroic texture and primary assemblage of Opx+Cpx+Pl+Amp+Ilm. Most pyroxene grains are partially rimmed by thin corona of Amp+Ab+Qtz. Garnet occurs as fine-grained coronas at interface between plagioclase, pyroxene or ilmenite. 2) Transitional rocks contain similar assemblage and texture but most orthopyroxenes were partially or totally replaced by Amp+Qtz; garnet increases in content and size. Some gabbroic textures are preserved, but calcic plagioclase was replaced by zoisite, albite and muscovite. 3) Garnet amphibolite occurs at the margins of intrusive bodies and boudins where only minor relict clinopyroxenes preserve. Garnet coronal chains are not clear any more. Granitic dikes show pronounced deformation with mylonitic texture and contain 40-50% quartz porphyroclasts. Zircon separates from 2 metagabbros, 4 gneisses and 1 granitic rock were dated by using Stanford SHRIMP-RG. Metagabbroic zircons are angular and fractured shapes. The upper-intercept ages of gneisses rang from 1730 to about 2400 Ma, indicating variable protoith age. The 2 garnet amphibolites have upper-intercept ages 1734$\pm$5Ma and 1735$\pm21$Ma respectively. They are much older than the protolith ages (680-850 Ma) of the Sulu eclogite and country rock. At least two possible metamorphic events are indicated by the lower-intercept ages. One metagabbroic rock has a lower-intercept age of 842$\pm$37 Ma; this records a garnet amphibolite metamorphic event. One gneiss and one metagabbroic rock yield lower-intercept ages of about 340$\pm$25 Ma, suggesting a second metamorphic event. The granitic dike has upper-intercept age 749$\pm$43 Ma and lower-intercept age 150$\pm$17 Ma. All these petrological and geochronological results indicate that the Haiyangsuo region is not part of the Triassic Sulu UHP terrane.
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting