Late Neoarchean volcanic rocks in the southern Liaoning Terrane and their tectonic implications for the formation of the eastern North China Craton
Late Neoarchean volcanic rocks in the southern Liaoning Terrane and their tectonic implications for the formation of the eastern North China Craton
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辽南地体晚新太古代火山岩及其对华北克拉通东部形成的构造意义
DOI：
10.1016/j.gsf.2019.11.003
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发表时间：
2020
影响因子：
8.9
通讯作者：
Guo Rongrong
中科院分区：
文献类型：
--
作者：
Gao Lei;Liu Shuwen;Wang Maojiang;Bao Han;Guo Rongrong
华北东部辽南地体晚新太古代变质火山岩主要由斜长角闪岩和长英质片麻岩组成，化学分类为玄武岩（1组）、玄武安山岩（2组）、英安岩（3组）和流纹英安岩（4组）。LA-ICP-MS锆石U-Th-Pb定年表明，它们形成于2.53- 2.51Ga。第1组样品的稀土元素（REE）配分模式基本平坦，（La/Yb）N比值较低，（Hf/Sm）N比值范围较窄，其岩浆前体由俯冲板片流体弱交代的亏损地幔楔部分熔融形成。与第1组样品相比，第2组样品显示出强烈的稀土元素分馏模式，具有更高的（La/Yb）N比值和更分散的（Hf/Sm）N比值，表明亏损地幔楔已被强烈交代的板状熔体和流体。第3组样品具有高MgO和过渡族微量元素含量及稀土元素分馏模式，类似于典型的高硅埃达克岩，岩浆前体来自俯冲洋板的部分熔融。第4组样品具有最高的SiO2和最低的MgO和过渡微量元素含量，并来自于下地壳水平的玄武质岩石的部分熔融。将这些拉斑玄武岩至钙碱性火山岩与大量同期闪长质-英云闪长质-奥长花岗闪长质片麻岩相结合，发现晚新太古代火山岩最有可能产生于活动大陆边缘。此外，还讨论了华北地体、冀东-辽西地体、北方-吉南地体、鞍山-本溪陆核（ABN）和沂水杂岩（YSC）共同表明，在新太古代晚期和克拉通期形成了一个完整的、规模更大的陆块。尺度侧向吸积作用是华北克拉通东部的主要动力学机制。
The late Neoarchean metamorphosed volcanic rocks in the southern Liaoning Terrane (SLT) of the eastern North China Craton (NCC) are mainly composed of amphibolites and felsic gneisses and can be chemically classified as basalt (Group#1), basaltic andesite (Group#2), dacite (Group#3) and rhyodacite (Group#4). LA-ICP-MS zircon U–Th–Pb dating reveals that they formed at ~2.53–2.51 Ga. Group#1 samples are characterized by approximately flat chondrite-normalized rare earth element (REE) patterns with low (La/Yb)Nratios and a narrow range of (Hf/Sm)Nratios, and their magmatic precursors were generated by partial melting of a depleted mantle wedge weakly metasomatized by subducted slab fluids. Compared to Group#1 samples, Group#2 samples display strongly fractionated REE patterns with higher (La/Yb)Nratios and more scattered (Hf/Sm)Nratios, indicative of a depleted mantle wedge that had been intensely metasomatized by slab-derived melts and fluids. Group#3 samples are characterized by high MgO and transition trace element concentrations and fractionated REE patterns, which resemble typical high-Si adakites, and the magmatic precursors were derived from partial melting of a subducted oceanic slab. Group#4 samples have the highest SiO2and the lowest MgO and transition trace element contents, and were derived from partial melting of basaltic rocks at lower crust levels. Integrating these tholeiitic to calc-alkaline volcanic rocks with the mass of contemporaneous dioritic-tonalitic-trondhjemitic-granodioritic gneisses, the late Neoarchean volcanic rocks in the SLT were most likely produced in an active continental margin. Furthermore, the affinities in lithological assemblages, metamorphism and tectonic regime among SLT, eastern Hebei to western Liaoning Terrane (EH–WLT), northern Liaoning to southern Jilin Terrane (NL–SJT), Anshan-Benxi continental nucleus (ABN) and Yishui complex (YSC) collectively indicate that an integral and much larger continental block had been formed in the late Neoarchean and the craton-scale lateral accretion was a dominantly geodynamic mechanism in the eastern NCC.