Ultrahigh pressure metamorphism and tectonic evolution of southwestern Tianshan orogenic belt, China: a comprehensive review
Ultrahigh pressure metamorphism and tectonic evolution of southwestern Tianshan orogenic belt, China: a comprehensive review
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DOI：
10.1144/sp474.12
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发表时间：
2018-09
期刊：
影响因子：
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通讯作者：
Lifei Zhang;Yang Wang;Lijuan Zhang;Z. Lü
中科院分区：
文献类型：
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作者：
Lifei Zhang;Yang Wang;Lijuan Zhang;Z. Lü
中国西南天山发现了一条巨型大洋型超高压变质带。岩石学研究表明，西南天山造山带的超高压变质岩包括镁铁质榴辉岩和蓝片岩、泥质石榴石多硅白云母片岩、大理岩和蛇纹岩。保存完好的柯石英包裹体常见于榴辉岩、石榴石多硅白云母片岩和大理岩中。在超高压变质蛇纹岩中发现了钛斜绿泥石和钛软骨石。根据P-T假剖面计算和锆石U-Pb联合定年，将其划分为4个阶段：约320 Ma前冷俯冲至超高压条件，峰值超高压约为30kbar(500°C)；305 Ma前热减压至Tmax阶段，峰温约600℃(22kbar)；220 Ma前从角闪岩榴辉岩相向绿帘角闪岩相变质早期冷折返；末次构造折返由绿帘角闪岩相向绿片岩相变质。结合同时代低压高温变质带中同俯冲弧形花岗岩333~326 Ma和S型花岗岩280~260 Ma，提出了天山超高压变质带晚寒武世至早三叠世的构造演化。
Abstract Recently, a huge ultrahigh-pressure (UHP) metamorphic belt of oceanic type has been recognized in SW Tianshan, China. Petrological studies show that the UHP metamorphic rocks of SW Tianshan orogenic belt include mafic eclogites and blueschists, pelitic garnet phengite schists, marbles and serpentinites. The well-preserved coesite inclusions are commonly found in eclogites, garnet phengite schists and marbles. Ti-clinohumite and Ti-chondrodite have been identified in UHP metamorphic serpentinites. Based on the P–T pseudosection calculation and combined U–Pb zircon dating, the P–T–t path has been outlined as four stages: cold subduction to UHP conditions before c. 320 Ma whose peak ultrahigh pressure is about 30 kbar at 500°C; heating decompression from the Pmax to the Tmax stage before 305 Ma whose peak temperature is about 600°C at 22 kbar; then the early cold exhumation from amphibolite eclogite facies to epidote-amphibolite facies metamorphism before 220 Ma; and the last tectonic exhumation from epidote amphibolite facies to greenschist facies metamorphism. Combining with the syn-subduction arc-like 333–326 Ma granitic rocks and 280–260 Ma S-type granites in the coeval low-pressure and high-temperature metamorphic belt, the tectonic evolution of Tianshan UHP metamorphic belt during late Cambrian to early Triassic has been proposed in this paper.