Abstract Blueschists are sporadically exposed as lenses within the Lancangjiang metamorphic complex, and represent unique components of the Paleo-Tethys. In this paper, we present geochemical and geochronological results of blueschists to decipher their origin and tectonic significance. The whole-rock geochemical analyses revealed strong similarities with ocean island basalt (OIB), and further discrimination diagrams confirm an affinity to a within-plate setting. Combined studies on blueschists using cathodoluminescence (CL) imaging, SHRIMP U-Pb dating of zircon domains and 40Ar/39Ar dating of phengite and glaucophane provide evidence of their magmatic origin and metamorphic evolution. Slightly oscillatory zoned or compositionally homogeneous zircon grains/domains, as well as structureless zircon rims, yield ages from 231.6 ± 3.7 to 225.3 ± 4.8 Ma, recording the blueschist facies metamorphic event. In contrast, the captured zircon grains and cores with a major age peak at ~241 Ma as well as several minor older age peaks indicate the multiple provenance of the zircons. 40Ar/39Ar step heating analyses on single grains of phengite and glaucophane separated from blueschists yield plateau ages ranging from 242.5 ± 1.4 to 228.7 ± 1.5 Ma which are interpreted to reflect high-pressure metamorphism. This study provides geochemical and geochronological constraints on the tectonic evolution of the Paleo-Tethyan ocean, which was closed and subsequently subducted as a result of the collision of the Simao and Baoshan Blocks. During subduction in Trassic (243 to 225 Ma), the protoliths of blueschists underwent blueschist facies conditions.

中文翻译：

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澜沧江变质杂岩古特提斯构造演化——来自青藏高原东南部小黑江-夏云地区蓝片岩SHRIMP U-Pb锆石定年和40Ar/39Ar同位素年代学的证据

摘要 蓝片岩在澜沧江变质杂岩体中零星地暴露为透镜体，代表了古特提斯纪的独特组成部分。在本文中，我们展示了蓝片岩的地球化学和地质年代学结果，以破译它们的起源和构造意义。全岩地球化学分析显示与海岛玄武岩 (OIB) 有很强的相似性，进一步的鉴别图证实了与板块内环境的亲和力。使用阴极发光 (CL) 成像、锆石结构域的 SHRIMP U-Pb 定年以及 phengite 和蓝闪石的 40Ar/39Ar 定年对蓝片岩的综合研究提供了它们的岩浆起源和变质演化的证据。轻微振荡的带状或成分均匀的锆石晶粒/畴，以及无结构的锆石边缘，产生年龄从 231.6 ± 3.7 到 225.3 ± 4.8 Ma，记录蓝片岩相变质事件。相比之下，捕获的锆石颗粒和核的主要年龄峰值在~241 Ma 以及几个较小的年龄峰值，表明锆石的多重来源。40Ar/39Ar 阶梯加热分析从蓝片岩中分离出的单粒菱镁矿和蓝闪石产生的高原年龄范围为 242.5 ± 1.4 至 228.7 ± 1.5 Ma，被解释为反映了高压变质作用。这项研究为古特提斯洋的构造演化提供了地球化学和地质年代学约束，该洋因思茅和宝山地块的碰撞而闭合并随后俯冲。在 Trassic 俯冲期间（243 至 225 Ma），蓝片岩的原岩经历了蓝片岩相条件。捕获的锆石颗粒和核的主要年龄峰值在~241 Ma 以及几个较小的年龄峰值表明锆石的多重来源。40Ar/39Ar 阶梯加热分析从蓝片岩中分离出的单粒菱镁矿和蓝闪石产生的高原年龄范围为 242.5 ± 1.4 至 228.7 ± 1.5 Ma，被解释为反映了高压变质作用。这项研究为古特提斯洋的构造演化提供了地球化学和地质年代学约束，该洋因思茅和宝山地块的碰撞而闭合并随后俯冲。在 Trassic 俯冲期间（243 至 225 Ma），蓝片岩的原岩经历了蓝片岩相条件。捕获的锆石颗粒和核的主要年龄峰值在~241 Ma 以及几个较小的年龄峰值，表明锆石的多重来源。40Ar/39Ar 阶梯加热分析从蓝片岩中分离出的单粒菱镁矿和蓝闪石产生的高原年龄范围为 242.5 ± 1.4 至 228.7 ± 1.5 Ma，被解释为反映了高压变质作用。这项研究为古特提斯洋的构造演化提供了地球化学和地质年代学约束，该洋因思茅和宝山地块的碰撞而闭合并随后俯冲。在 Trassic 俯冲期间（243 至 225 Ma），蓝片岩的原岩经历了蓝片岩相条件。