Petrological Investigations and Zircon U‐Pb Dating of High Pressure Felsic Granulites from the Yushugou Complex, South Tianshan, China
Petrological Investigations and Zircon U‐Pb Dating of High Pressure Felsic Granulites from the Yushugou Complex, South Tianshan, China
复制标题
DOI：
10.1111/1755-6724.13499
复制
发表时间：
2018-02
期刊：
影响因子：
--
通讯作者：
Lu Zhang;Lifei Zhang;Jianjiang Zhu;B. Xia;Z. Lü;T. Bader
中科院分区：
文献类型：
--
作者：
Lu Zhang;Lifei Zhang;Jianjiang Zhu;B. Xia;Z. Lü;T. Bader
高压麻粒岩作为了解下地壳的窗口，近十年来受到了广泛的关注。榆树沟高压麻粒岩橄榄岩杂岩位于南天山东北缘。前人认为榆树沟橄榄岩与通化山、六黄山超镁铁岩组合为蛇绿岩带。然而，榆树沟高压麻粒岩的变质演化和构造机制仍存在争议。对榆树沟杂岩中两个代表性长英质麻粒岩样品的岩石学研究和相平衡模拟表明，榆树沟杂岩中的岩石经历了两期变质作用。麻粒岩相变质作用（第一阶段）在895-920°C时的P-T条件为9.8-10.4 kbar，由变斑石榴石岩心记录; HP麻粒岩相变质作用（第二阶段）在845-860°C时的P-T条件为13.2-13.5 kbar，基于石榴石边缘钙铝榴石含量的增加和镁铝榴石含量的减少。榆树沟高压长英质麻粒岩记录了一条逆冲P-T轨迹，其特征是温度降低，压力升高。长英质麻粒岩中锆石的LA-ICP-MS同位素研究表明，麻粒岩的原岩年龄为430 Ma，变质边缘的锆石有390 Ma和340-350 Ma两个年龄组，分别代表第I和第II阶段变质事件。提出了一个构造模式来解释这一过程。所研究的长英质麻粒岩来源于深源上盘，第I期麻粒岩相变质作用时间为390 Ma，可能与泥盆纪弧岩浆侵入有关;第II期HP麻粒岩相变质作用时间为340-350 Ma，可能是被俯冲板片捕获并经历高压变质作用的结果。
As a window of insight into the lower crust, high pressure granulite has received much attention since last decade. Yushugou high pressure granulite‐peridotite Complex was located in the northeast margin of Southern Tianshan, NW China. Previous ideas agreed that the peridotite unit in Yushugou, combined with the ultramafic rocks in Tonghuashan and Liuhuangshan, represent an ophiolite belt. However, the metamorphic evolution and tectonic mechanism of the Yushugou high pressure (HP) granulite remain controversial. Petrological investigations and phase equilibrium modelling for two representative felsic granulite samples suggest two stages metamorphism of the rocks in Yushugou Complex. Granulite facies metamorphism (Stage I) with P‐T conditions of 9.8–10.4 kbar at 895–920°C was recorded by the porphyroblastic garnet core; HP granulite facies metamorphism (Stage II) shows P‐T conditions of 13.2–13.5 kbar at 845–860°C, based on the increasing grossular and decreasing pyrope contents of garnet rims. The Yushugou HP felsic granulites have recorded an anticlockwise P‐T path, characterized by the temperature decreasing and pressure increasing simultaneously. The LA‐ICP‐MS isotopic investigations on zircons from the felsic granulite show that the protolith ages of the granlulites are ∼430 Ma, with two age groups of ∼390 Ma and 340–350 Ma from the metamorphic rims of zircon, indicating the Stage I and II metamorphic events, respectively. A tectonic model was proposed to interpret the processes. The investigated felsic granulite was derived from deep rooted hanging wall, with Stage I granulite facies metamorphism of ∼390 Ma, which may be related to the Devonian arc magmatic intrusion; Stage II HP granulite facies metamorphism (340–350 Ma) may due to the involvement of being captured into the subducting slab and experienced the high pressure metamorphism.