Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8911728 | Lithos | 2018 | 57 Pages |
Abstract
Listwaenite lenses in the Sartohay ophiolitic mélange (Xinjiang, China) were formed via reactions between serpentinite and metasomatic fluids. First, serpentinite changed into talc schist via the reaction of serpentineâ¯+â¯CO2â¯ââ¯talcâ¯+â¯magnesiteâ¯+â¯H2O. Second, talc schist changed into listwaenite via the reaction of talcâ¯+â¯CO2â¯ââ¯magnesiteâ¯+â¯quartzâ¯+â¯H2O. Magnetite was progressively destroyed during transformation from serpentinite to talc schist, and completely consumed in listwaenite. Zircon crystals 30-100â¯Î¼m long, disseminating in talc schist, undeformed listwaenite and mylonitized listwaenite, coexist with talc, quartz and magnesite, while micron-sized zircon grains (<5â¯Î¼m 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 (302.9â¯Â±â¯6.8â¯Ma, 299.7â¯Â±â¯5.5â¯Ma and 296.5â¯Â±â¯3.5â¯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 (280-277â¯Ma), which could be interpreted as a recrystallization age reflecting late-stage shearing in the Sartohay ophiolitic mélange.
Keywords
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
Tian Qiu, Yongfeng Zhu,