期刊
LITHOS
卷 302, 期 -, 页码 427-446出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.lithos.2018.01.029
关键词
Listwaenite; Ophiolitic melange; Shear zone; Zircon U-Pb chronology; Xinjiang
资金
- Natural Science Foundation of China [41672047, 41703053]
Listwaenite lenses in the Sartohay ophiolitic melange (Xinjiang, China) were formed via reactions between serpentinite and metasomatic fluids. First, serpentinite changed into talc schist via the reaction of serpentine + CO2 -> talc + magnesite + H2O. Second, talc schist changed into listwaenite via the reaction of talc + CO2 -> magnesite + quartz + H2O. Magnetite was progressively destroyed during transformation from serpentinite to talc schist, and completely consumed in listwaenite. Zircon crystals 30-100 mu m long, disseminating in talc schist, undeformed listwaenite and mylonitized listwaenite, coexist with talc, quartz and magnesite, while micron-sized zircon grains (<5 mu m in length) occur along the shearing foliation in the weakly deformed listwaenite and mylonitized listwaenite. We postulate that these micron-sized zircon crystals may have grown in-situ from medium-temperature hydrothermal fluids. Concentrations of most trace elements including high field strength elements (HFSE) increase from the undeformed, through the weakly deformed, to the mylonitized listwaenite, showing a positive correlation with the degrees of deformation and proportions of micron-size zircon, apatite, rutile and monazite. The large zircon crystals recovered from talc schist, undeformed listwaenite and mylonitized listwaenite yield similar weighted mean U-Pb ages (302.9 +/- 6.8 Ma, 299.7 +/- 5.5 Ma and 296.5 +/- 3.5 Ma), and are thought to represent the age of formation of the talc schist and listwaenite. These ages are indistinguishable within errors and suggest a rapid transformation from talc schist to listwaenite. Some zircon rims in samples of the undeformed listwaenite and mylonitized listwaenite give much younger apparent U-Pb ages (280-277 Ma), which could be interpreted as a recrystallization age reflecting late-stage shearing in the Sartohay ophiolitic melange. (C) 2018 Elsevier B.V. All rights reserved.
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