Listwaenite in the Sartohay ophiolitic melange (Xinjiang, China): A genetic model based on petrology, U-Pb chronology and trace element geochemistry
Listwaenite in the Sartohay ophiolitic melange (Xinjiang, China): A genetic model based on petrology, U-Pb chronology and trace element geochemistry
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Sartohay蛇绿混杂岩中的Listwaenite（中国新疆）：基于岩石学、U-Pb年代学和微量元素地球化学的成因模型
DOI：
10.1016/j.lithos.2018.01.029
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发表时间：
2018
期刊：
影响因子：
3.5
通讯作者：
Zhu Yongfeng
中科院分区：
文献类型：
--
作者：
Qiu Tian;Zhu Yongfeng
新疆萨尔托海蛇绿混杂岩中的利斯特湾岩透镜体是蛇纹岩与交代流体反应形成的。蛇纹岩首先通过蛇纹岩+ CO2→滑石+菱镁矿+ H2O反应生成滑石片岩。滑石片岩经滑石+CO_2 →菱镁矿+石英+H_2O的反应转变为水滑石。磁铁矿在蛇纹岩向滑石片岩的转化过程中逐渐被破坏，并完全消耗在李斯温岩中。长30-100 μm的锆石分布在滑石片岩、未变形的李氏岩和糜棱岩化的李氏岩中，与滑石、石英和菱镁矿共生，而微米级的锆石（<5 μm）沿沿着剪切叶理分布在弱变形的李氏岩和糜棱岩化的李氏岩中。我们推测这些微米大小的锆石晶体可能是从中温热液中原位生长的。大多数微量元素，包括高场强元素（HFSE）的浓度增加，从未变形，通过弱变形，糜棱岩化的listwaenite，表现出正相关的变形程度和微米级的锆石，磷灰石，金红石和独居石的比例。从滑石片岩、未变形的李氏岩和糜棱岩化的李氏岩中回收的大颗粒锆石U-Pb加权平均年龄相近（302.9 ± 6.8Ma、299.7 ± 5.5Ma和296.5 ± 3.5Ma），可以代表滑石片岩和李氏岩的形成年龄。这些年龄在误差范围内难以区分，表明滑石片岩迅速转变为李斯文岩。在未变形的李氏岩和糜棱岩化的李氏岩样品中，一些锆石环给出了更年轻的U-Pb年龄（280-277 Ma），这可以解释为反映Sartohay蛇绿混杂岩中晚期剪切作用的重结晶年龄。
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 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 μm long, disseminating in talc schist, undeformed listwaenite and mylonitized listwaenite, coexist with talc, quartz and magnesite, while micron-sized zircon grains (<5 μm 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 mélange.