Late Permian intermediate and felsic intrusions in the eastern Central Asian Orogenic Belt: Final-stage magmatic record of Paleo-Asian Oceanic subduction?
Late Permian intermediate and felsic intrusions in the eastern Central Asian Orogenic Belt: Final-stage magmatic record of Paleo-Asian Oceanic subduction?
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中亚造山带东部晚二叠世中间和长英质侵入：古亚洲大洋俯冲的最后阶段岩浆记录？
DOI：
10.1016/j.lithos.2018.12.022
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发表时间：
2019-02
期刊：
影响因子：
3.5
通讯作者：
Zhou Zhen Hua
中科院分区：
文献类型：
--
作者：
Ma Xing Hua;Chen Chang Jian;Zhao Jian Xin;Qiao Shi Lei;Zhou Zhen Hua
中亚造山带是古亚洲洋闭合形成的地球上最大的中生代增生造山带之一。然而，古亚洲洋最终关闭的时间仍然存在争议。在这里，我们提出了新的锆石U单键Pb定年，氧逸度估计，全岩地球化学和Sr单键Nd同位素数据在中国东北春华地区的中长英质侵入岩约束其岩石成因和评估的构造意义的演化CAOB东部。锆石U-Pb定年表明，侵入岩形成于晚二叠世（257-261 Ma）.根据其化学成分，可将岩石分为两组：第一组主要由闪长岩组成（例如，辉长闪长岩、闪长岩和英云闪长岩），SiO2相对较低，但MgO含量和Mg#值较高。岩石学和地球化学特征表明，Ⅰ组岩石是幔源岩浆与壳源岩浆混合形成的。第Ⅰ组岩石中的镁铁质微粒包体具有高MgO含量（高达9wt%）和亏损的同位素组成（εNd（t）= +4.3 ~+7.2），可能代表镁铁质端元岩浆来源于交代的岩石圈地幔，随后注入长英质地壳岩浆。与此相反，第II组岩石主要是以高SiO2和低Mg#值为特征的花岗闪长岩，具有高Sr/Y和La/Yb比值。这些岩石可能是由镁铁质下地壳的部分熔融形成的，几乎没有地幔物质的加入。微量元素模拟表明壳内分异以角闪石分馏为主，并导致II I组岩石具有高Sr/Y和La/Yb特征。低的（87 Sr/86 Sr）i（0.70345-0.70485）和正的εNd（t）值（+3.8-+4.6）表明主要是年轻的源区，典型的新底侵的镁铁质下地壳。锆石中Ce ~（4+）/Ce ~（3+）比值表明，Ⅰ组和Ⅱ组岩石的氧化态均较低（FMQ-1.1 ~ FMQ-7.9），表明岩石圈地幔和上覆下地壳烃源岩处于还原状态。淳化岩体具有弧型火成岩的岩石学和地球化学特征，包括丰富的自形含水矿物、钙碱性亲岩性和富集大离子亲石元素（如，Rb、Ba和Pb）和高场强元素（例如，Nb、Ta和Ti），表明它们形成于与俯冲有关的环境中。鉴于该区早三叠世-碰撞花岗岩（235-252 Ma）的产出，晚二叠世（257-261 Ma）的侵入体可能代表了与古亚洲洋俯冲作用有关的岩浆活动的最后阶段，表明古亚洲洋在最东端CAOB的最终闭合发生在二叠纪末。
The Central Asian Orogenic Belt (CAOB), which formed by closure of the Paleo-Asian Ocean, is one of the largest Phanerozoic accretionary orogens on Earth. However, the timing of final closure of the Paleo-Asian Ocean remains debated. Here we present new zircon Usingle bondPb dating, oxygen fugacity estimates, and whole-rock geochemical and Srsingle bondNd isotopic data from intermediate and felsic intrusive rocks in the Chunhua area of NE China to constrain their petrogenesis and assess the tectonic implications for the evolution of the eastern CAOB. Zircon Usingle bondPb dating indicates that the intrusive rocks formed in the late Permian (257–261 Ma). Based on their chemical compositions, two groups of rocks can be identified.Group Ιconsists mainly of dioritic rocks (e.g., gabbroic diorites, diorites and tonalites) with relatively low SiO2but high MgO contents and Mg# values. Petrological and geochemical characteristics show thatGroup Ιrocks were formed by mixing of mantle- and crust-derived magmas. Mafic microgranular enclaves withinGroup Ιrocks have high MgO contents (up to 9 wt%) and depleted isotopic compositions (εNd(t) = +4.3 to +7.2), and probably represent mafic end-member magmas derived from a metasomatized lithospheric mantle, which subsequently were injected into the felsic crustal magmas. In contrast,Group ΙIrocks are mostly granodiorites characterized by high SiO2and low Mg# values, with high Sr/Y and La/Yb ratios. These rocks were probably generated by partial melting of mafic lower crust with little or no addition of mantle materials. Trace element modeling suggests that intracrustal differentiation was dominated by hornblende fractionation and caused the high Sr/Y and La/Yb signatures ofGroup ΙIrocks. Their low (87Sr/86Sr)i(0.70345–0.70485) and positive εNd(t) values (+3.8 to +4.6) suggest predominantly juvenile sources, typical of newly underplated mafic lower crust. The low oxidation states (FMQ–1.1 to FMQ–7.9) for bothGroup ΙandGroup ΙIrocks, as indicated by Ce4+/Ce3+ratios in zircon, imply reducing conditions for the lithospheric mantle and the overlying lower-crustal source rocks. The Chunhua intrusions show petrological and geochemical characteristics of arc-type igneous rocks, including abundant euhedral hydrous minerals, calc-alkaline affinities, and enrichment in large ion lithophile elements (e.g., Rb, Ba, and Pb) and depletion in high field strength elements (e.g., Nb, Ta, and Ti), indicating that they formed in a subduction-related setting. Given the occurrences of Early Triassicsyn-collisional granites (235–252 Ma) in the area, the late Permian intrusions (257–261 Ma) likely represent the final stages of magmatism related to subduction of Paleo-Asian Ocean, signifying that final closure of the Paleo-Asian Ocean in the easternmost CAOB occurred during the end-Permian.
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