新疆库鲁克塔格地区古元古代深熔混合岩变质作用P-T-t轨迹及其对碰撞造山过程的约束

Quruqtagh is one of the key region for researching early Precambrian geological evolution in the Tarim Block, with prominent Ppaleoproterozoic orosirian geologic events synchronized with collision orogenesisthat which were considered as amalgamation of Columbia supercontinent. In previous studies, a number of research results have achieved on magmatism and metamorphism in supracrustal rock series, and based on the age of the supercontinent was discussed. However, orogenesis and anatiexs which closely relate to supercontinent amalgamation was rarely mentioned. Anatectite, occurred widely in supracrustal rock series, recorded the important information of orogenetic process. In this study, anatiexs in pelite and mafic rocks will be taken as the breakthrough point, to Oobserve and analyze petrographical feature in melanosome of anatectite and mineral inclusion in metamorphic zircon, to ensure the zircon origin and age of the metamorphism and anataxis by characteristics of zircon inner texture, trace element, mineral inclusion and Hf isotope, and to divide and determine the orogenesis evolution episode combining with the anataxis condition and mode, and then to restrict the converging events of supercontinent. The study is significant for early precambrian geological evolution and regional comparison in Tarim Block.

库鲁克塔格是塔里木地块早前寒武地质演化研究关键地区之一，古元古代造山纪地质事件显著，与全球普遍存在的同时代碰撞造山事件同步，被认为是哥伦比亚超大陆聚合的响应。前人在造山纪岩浆作用和表壳岩系变质作用方面取得一些研究成果，并基于此讨论了超大陆聚合时代，而对与超大陆聚合密切相关的造山作用及深熔作用讨论较少。深熔混合岩在库鲁克塔格地区变质表壳岩系中广泛发育，蕴含着碰撞造山带演化的重要信息。本次研究拟以基性岩和泥质岩深熔作用为切入点：观察分析深熔混合岩暗色体及变质锆石所含矿物包裹体岩相学特征，确定各变质阶段矿物组合及测定变质温压条件；通过锆石的内部结构、微量元素、矿物包裹体和Hf同位素等方面特征分析，确定锆石成因，确定变质和深熔作用的时代；再结合深熔作用的条件和方式，划分和确定造山作用演化阶段和时限，进而约束超大陆聚合事件。该项研究对约束塔里木地块早前寒武地质演化及区域对比具有重要意义。

塔里木北缘古元古代造山带的演化模式仍然存在争议。这一不足直接影响了对哥伦比亚超大陆重建的认识。我们对古元古代构造-热事件的产物兴地塔格群，进行了岩相学，相平衡模拟和锆石U-Pb年代学的工作，试图去约束以下几个问题：（1）塔里木北缘古元古代造山演化各阶段的温度-压力条件和P-T轨迹。（2）1.85-1.80变质峰期年龄的意义。（3）古元古代造山带碰撞时限的约束。（4）从变质演化角度约束塔里木北缘古元古代造山演化模式。.我们的研究得到以下结论。1：塔里木北缘兴地塔格群发育巴罗式变质带，高温岩组(泥质麻粒岩NZ-1)经历了顺时针的高温麻粒岩相变质，可能代表了造山带接近根部的位置。而中-下亚群（石榴云母片岩-浅粒岩）同样也经历了角闪岩相的中高压顺时针变质，可能代表了造山带的中部。2：区域上1.85-1.80 Ga的变质年龄峰期代表了兴地塔格群高温岩组减压折返后的冷却事件，而不是之前大部分研究认为的碰撞事件。3：通过对蓝晶石石榴片岩的变质研究和年代学研究，我们约束塔里木北缘在古元古代的碰撞时间在1.92 Ga。4：我们提出了新的塔里木北缘古元古代构造演化模型。分别是＞1.92Ga的俯冲阶段，1.92Ga的碰撞阶段，1.92-1.85Ga的折返阶段和1.85-1.80Ga的折返后冷却阶段。