HR: 0800h
AN: V11A-1405    [Abstracts]
TI: An unusual clinopyroxenite nodule from the northeastern Sulu ultrahigh-pressure metamorphic (UHPM) terrane, East China: Its P-T path and implications for subduction erosion
AU: * Yang, T
EM: yangtn@cags.net.cn
AF: Key Laboratory for Continental Dynamics, MLR, Institute of Geology, Chinese Academy of Geological Science, Baiwanzhuang Rd. #26, Beijing, 100037 China
AU: Zeng, L
EM: lzeng@ccsd.org.cn
AF: Key Laboratory for Continental Dynamics, MLR, Institute of Geology, Chinese Academy of Geological Science, Baiwanzhuang Rd. #26, Beijing, 100037 China
AB: Pyroxenite consisting only of clinopyroxenes is rare. We present bulk composition and microtexture observation data on a garnet-pyroxenite nodule enclosed within a granitic gneiss in Rongcheng, northeastern Sulu UHPM terrane to (1) reconstruct its protolith; (2) estimate its P-T path; and (3) its implications for the continent-continent subduction and collision dynamics. Bulk composition analyses and micro-textural observations demonstrated that the Rongcheng garnet-pyroxenite originally was a mono-mineralic pyroxenite consisting only of clinopyroxene. Prograde and/or retrograde metamorphic reactions have led to the formation of pyroxenes that are surrounded by an interconnected network of garnets. Within the pyroxenes that consist of clinopyroxene and solid exsolutions, four sets of garnet lamellae occur strictly along four crystallographic planes. Hydrous minerals such as amphibole and epidote were formed at later stages of retrograde metamorphism. The P-T conditions determined for the pyroxenite indicate it has undergone a P-increasing and/or T-decreasing earlier stage and an isothermal decompression later stage metamorphism, followed by the latest stage metamorphism of decreasing both in P and T. The last two stages experienced by the pyroxenite are similar to those of the nearby eclogites from the northeastern Sulu UHPM terrane. The Rongcheng pyroxenite and granitic gneiss host may belong to the hanging wall of the Sulu subduction zone. This observation also suggests that parts of the Northern China Block (NCB) might have been dragged into deeper mantle due to subduction erosion during the continent ­Ccontinent subduction and collision between the NCB and the Southern China Block (SCB), and then returned to the surface together. This interpretation is significant to resolve some differences in geologic features between the northeastern and southwestern Sulu UHPM terrane.
DE: 8102 Continental contractional orogenic belts
DE: 3660 Metamorphic petrology
DE: 1020 Composition of the crust
DE: 1025 Composition of the mantle
DE: 0330 Geochemical cycles
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting