The origin and response of zircon in eclogite to metamorphism during the multi-stage evolution of the Huwan Shear Zone, China: Insights from Lu–Hf and U–Pb isotopic and trace element geochemistry
The origin and response of zircon in eclogite to metamorphism during the multi-stage evolution of the Huwan Shear Zone, China: Insights from Lu–Hf and U–Pb isotopic and trace element geochemistry
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DOI：
10.1016/j.gr.2012.05.008
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发表时间：
2013-03
影响因子：
6.1
通讯作者：
T. Peters;John Cammerer Ayers;Shan Gao;Xiaoming Liu
中科院分区：
文献类型：
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作者：
T. Peters;John Cammerer Ayers;Shan Gao;Xiaoming Liu
湖湾剪切带（HSZ）位于上丹缝合线上，与古生代秦岭造山带和中生代红安-大别造山带并置，是一条含榴辉岩的逆压扭带。该地区保留了一个复杂的历史，在相邻的造山带之间架起了桥梁。同时对雄店和苏家河榴辉岩样品的锆石颗粒进行微量元素、U-Th-Pb和Lu-Hf同位素分析，确定了晚石炭世至早二叠世的高压变质作用，时间约为283 ~ 306Ma。观察到锆石晶粒对变质套印的响应过程分为两个阶段：(1)流体催化界面耦合溶解-再沉淀的初始阶段，包括非理想固溶体钍（ThSiO4）端元的析出和高度不相容组分（LREE和Pb）的损失；(2)在高压条件下，锆石耦合溶解、粗化和与石榴石平衡生长的第二阶段。发现元古代全岩Sm-Nd和锆石颗粒Lu-Hf同位素证据，挑战了雄店和苏家河榴辉岩形成于早古生代地幔熔融和洋壳生成的传统解释。我们认为湖湾剪切带不包含早/中古生代洋壳的确凿证据，而是类似于北秦岭地区的元古代地壳成分，并与商丹缝合线的形成有关。在古生代秦岭造山运动和中生代大别造山运动期间，我们提出了一个更简单的地球动力学模型，其中包括华北地块南缘地形的连续辐合和增生。
The Huwan Shear Zone (HSZ) is an eclogite bearing transpressive wrench zone located along the Shangdan Suture that juxtaposes the Paleozoic Qinling and Mesozoic Hong'an–Dabie orogenic terrains. The region preserves a complex history that bridges the gap between adjacent orogenic terrains. Simultaneous in-situ trace element, U–Th–Pb and Lu–Hf‐isotope analysis of zircon grains from samples of the Xiongdian and Sujiahe eclogite identify a late Carboniferous to early Permian period of high pressure metamorphism, ca. 283 to 306Ma. Zircon grains are observed to respond to metamorphic overprint via a two stage process: (1) An initial prograde stage of fluid catalyzed interface coupled dissolution–reprecipitation, involving exsolution of a non-ideal solid solution thorite (ThSiO4) end member and loss of highly incompatible components (LREE and Pb), (2) A second stage of coupled zircon dissolution, coarsening, and new rim growth in equilibrium with garnet at high pressure conditions. We identify Proterozoic whole rock Sm–Nd and zircon grain Lu–Hf isotopic evidence which challenges the traditional interpretation that the Xiongdian and Sujiahe eclogite formed in response to early Paleozoic mantle melting and oceanic crust generation. We argue the Huwan Shear Zone contains no conclusive evidence of early/middle Paleozoic oceanic crust, but rather Proterozoic crustal components analogous to those found in the Northern Qinling Terrain and associated with formation of the Shangdan Suture. We present a simpler geodynamic model involving continuous convergence and accretion of terrains onto the southern margin of the North China Block during the Paleozoic Qinling and Mesozoic Dabie orogenies.