Ediacaran initial subduction and Cambrian slab rollback of the Junggar Ocean: New evidence from igneous tectonic blocks and gabbro enclave in Early Palaeozoic accretionary complexes, southern West Junggar, NW China
Ediacaran initial subduction and Cambrian slab rollback of the Junggar Ocean: New evidence from igneous tectonic blocks and gabbro enclave in Early Palaeozoic accretionary complexes, southern West Junggar, NW China
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DOI：
10.1017/s0016756821000376
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发表时间：
2021-05
影响因子：
2.3
通讯作者：
W. Liao;Bao-Fu Han;Yan Xu;An-Yi Li
中科院分区：
文献类型：
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作者：
W. Liao;Bao-Fu Han;Yan Xu;An-Yi Li
西准噶尔增生杂岩南部的4块埃达克质火成岩和2块非埃达克质火成岩的锆石U-Pb年龄和全岩化学数据为准噶尔洋作为古亚洲南部的一部分的初始俯冲和后续退缩过程提供了进一步的约束。唐巴勒最古老的埃达克二长岩为非埃达克质石英二长岩侵入，形成于549 Ma，铁热克霍拉最年轻的埃达克质闪长岩形成于520 Ma。埃迪卡拉纪-寒武纪岩浆作用呈现北向年轻的趋势。高SiO_2埃达克质岩石具有高的锶(300-663ppm)和低的Y(6.68-12.2ppm)，锶/Y=40-84，镁的NO。=46-60，而非埃达克质岩石具有较高的Y(13.2-22.7ppm)和Yb(2.32-2.92ppm)，镁氮。=36-40。辉长岩中镁含量高(14.81-15.11%)，钴含量高(45-48ppm)，铬含量高(1120-1360ppm)，镍含量高(231-288ppm)，镁含量高。=72-73。所有样品都表现出相似的大离子亲石元素(LILE)和轻稀土元素(LREE)的富集性，以及Nb、Ta、Ti和不同程度的Zr、Hf的亏损，表明它们形成于与俯冲有关的环境。埃达克质岩是由俯冲洋板的部分熔融形成的，但熔体受到地幔楔体和板片流体的改造，非埃达克质岩石可能来自中下弧地壳的部分熔体，辉长岩来自板片流体改造的地幔楔体。岩浆作用可能是在埃迪卡拉纪初始俯冲和准噶尔大洋寒武纪板块回滚过程中产生的。
Abstract New zircon U–Pb ages and whole-rock chemical data from four adakitic and two non-adakitic igneous rocks as tectonic blocks in the southern West Junggar accretionary complexes, northwestern China and one gabbro enclave in adakitic block provide further constraints on the initial subduction and following rollback process of the Junggar Ocean as part of southern Palaeo-Asian Ocean. The oldest adakitic monzonite in Tangbale is intruded by the non-adakitic quartz monzonite at 549 Ma, and the youngest adakitic diorite in Tierekehuola formed at 520 Ma. The Ediacaran–Cambrian magmatism show a N-wards younger trend. The high-SiO2 adakitic rocks have high Sr (300–663 ppm) and low Y (6.68–12.2 ppm), with Sr/Y = 40–84 and Mg no. = 46–60, whereas the non-adakitic rocks have high Y (13.2–22.7 ppm) and Yb (2.32–2.92 ppm), with Mg no. = 36–40. The gabbro has high MgO (14.81–15.11 wt%), Co (45–48 ppm), Cr (1120–1360 ppm) and Ni (231–288 ppm), with Mg no. = 72–73. All the samples show similar large-ion lithophile element (LILE) and light rare earth element (LREE) enrichment and Nb, Ta, Ti and varying Zr and Hf depletion, suggesting that they were formed in a subduction-related setting. The adakitic rocks were produced by partial melting of subducted oceanic slab, but the melts were modified by mantle wedge and slab-derived fluids; the non-adakitic rocks were likely derived from partial melts of the middle-lower arc crust; and the gabbro originated from the mantle wedge modified by slab-derived fluids. The magmatism could have been generated during the Ediacaran initial subduction and Cambrian slab rollback of the Junggar Ocean.