HR: 17:15h
AN: V44A-05    [Abstracts]
TI: Thermal structure of the Sulu UHP terrane in the CCSD-main hole from 100 to 300 m constrained by Zr concentration in eclogitic rutile
AU: * Zhang, R Y
EM: ry.zhang@stanford.edu
AF: Stanford University, Dept. of Geological & Environmental Sciences, Stanford, CA 94305- 2115, United States
AU: Iizuka, Y
EM: yiizuka@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, P.O. Box 1-55 Nankang, Taipei, 11529, Taiwan
AU: Xu, Z
EM: xzq@ccsd.cn
AF: Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang, Beijing, 100037, China
AU: Liou, J G
EM: jliou@stanford.edu
AF: Stanford University, Dept. of Geological & Environmental Sciences, Stanford, CA 94305- 2115, United States
AU: Jahn, B
EM: jahn@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, P.O. Box 1-55 Nankang, Taipei, 11529, Taiwan
AB: The core rocks recovered by the main hole (5100 m deep) of the Chinese Continental Scientific Drilling (CCSD) project in the southern Sulu UHP terrane, China are composed of eclogites, various gneisses and minor peridotite cumulates, and were experienced subduction-zone UHP metamorphism. Eclogites are mainly restricted to the upper 100-2000 m; among them, Phn-bearing eclogite is most common, Ky-bearing, and Zo/Ep- bearing eclogites are minor. Rutile, zircon and apatite occur as accessory phases in all eclogite cores. In order constrain thermal structure of the CCSD-MH zirconium concentration in rutile coexisting with zircon and quartz from 22 eclogite cores (each 16-45 points) from 101 to 2774 m were analyzed by electron microprobe. The Zr content of rutile ranges from 30 to 1,000 ppm; most are about 100-400 mm. The Zr-in-rutile geothermometer yields the maximum and average temperatures at 645-875°C and 595-680°C by the calibration of Zack et al. (2004), and 594-755°C and 570-623°C by the calibration of Watson et al. (2006), respectively. The maximum temperature of 700-800°C obtained occurs at 100-530 m and >1600 m, which are very close to the temperature calculated at 3 GPa by Cpx-Grt thermometers. In a shear zone of 870- 1113 m the maximum-T show a small range of 660-690°C, slightly lower than those of eclogites at the top part of 100-530 m, probably due to retrograde metamorphism caused by strong deformation. If the influence of pressure on the Zr-substitution in rutile is considered (Tomkins et al., 2007), the maximum temperature at > 30 kbar would be changed. In general, the Zr-in-rutile thermometer yields slightly low-T in comparison with those of using the Fe-Mg portioning between garnet and clinopyroxene, and only the maximum temperatures may record the temperature of peak stage metamorphism. As the Sulu UHP eclogites and their associated gneissic rocks have been subjected to long duration of 20-40 Ma UHP metamorphism and amphibolite-facites retrograde overprint, the difference of the obtained temperatures from different sample or individual sample may record the different stage of growth and equlibration of minerals.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3651 Thermobarometry
DE: 3654 Ultra-high pressure metamorphism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting