HR: 0800h
AN: V41C-0712    [Abstracts]
TI: Coupled Sm-Nd and Lu-Hf geochronology constraints prograde garnet growth in ultrahigh- pressure eclogites from the Dabie orogen
AU: Cheng, H
EM: chenghao@mail.tongji.edu.cn
AF: State Key Laboratory of Marine Geology, Tongji University, Shanghai, 200092, China
AU: Cheng, H
EM: chenghao@mail.tongji.edu.cn
AF: Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori, 682-0193, Japan
AU: * King, R
EM: rlking@wsu.edu
AF: Department of Geology, Washington State University, Pullman, Washington, 99164, United States
AU: Nakamura, E
EM: eizonak@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori, 682-0193, Japan
AU: Vervoort, J
EM: vervoort@wsu.edu
AF: Department of Geology, Washington State University, Pullman, Washington, 99164, United States
AU: Zhou, Z
EM: zhouzy@mail.tongji.edu.cn
AF: State Key Laboratory of Marine Geology, Tongji University, Shanghai, 200092, China
AB: Ultrahigh-pressure eclogites from the Dabie orogen formed over a spread rang in temperature (~{}600 oC to >700 oC) have been investigated with combined Sm-Nd and Lu-Hf geochronology. Three eclogites, sampled from Zhujiachong, Huanghzhen and Shima, yield Sm-Nd ages of 222.5 ± 4.4 Ma, 217.8 ± 4.2 Ma and 224.2 ± 5.6 Ma and corresponding Lu-Hf ages of 240.0 ± 5.0 Ma, 224.4 ± 1.9 Ma and 230.8 ± 5.0, respectively. Well-preserved major- and trace element growth zoning in garnets in the Zhujiachong eclogite suggest the Lu-Hf age mostly reflects early garnet growth and garnet growth is estimated to have occurred over a time interval of ~{}22 Myr. Whereas, despite of the preserved element growth zoning in garnets in the Huangzhen eclogite, combined texture study reveal that the obtained Lu-Hf age was skewed towards the last garnet growth episode rather than an average estimate of the overall growth span. The narrow time interval of less than 6 Myr defined by the difference between Sm-Nd and Lu-Hf ages indicates a short growth period response to the final garnet growth episode and thus a rapid cooling stage. In contrast, the rather flat element zoning in garnets in Shima eclogite suggests the obtained Sm-Nd and Lu-Hf ages are cooling ages. Furthermore, Hf isotope disequilibrium was observed in several meters scale. The new Lu-Hf ages point an initiation of prograde metamorphism prior to ~{}240 Ma and the exact peak metamorphism timing is subjected to specific samples are largely range between ~{}220 to ~{}230 Ma.
DE: 1115 Radioisotope geochronology
DE: 3654 Ultra-high pressure metamorphism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting