Genesis of adakitic granitoids by partial melting of thickened lower crust and its implications for early crustal growth: A case study from the Huichizi pluton, Qinling orogen, central China
Genesis of adakitic granitoids by partial melting of thickened lower crust and its implications for early crustal growth: A case study from the Huichizi pluton, Qinling orogen, central China
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DOI：
10.1016/j.lithos.2015.09.017
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发表时间：
2015-12
期刊：
影响因子：
3.5
通讯作者：
Zhen Qin;Y. Wu;W. Siebel;Shan Gao;Hao Y. C. Wang;M. Abdallsamed;Wenxiang Zhang;Saihong Yang
中科院分区：
文献类型：
--
作者：
Zhen Qin;Y. Wu;W. Siebel;Shan Gao;Hao Y. C. Wang;M. Abdallsamed;Wenxiang Zhang;Saihong Yang
埃达克质岩石常被认为是解开太古代TTG成因和早期地壳生长的关键。北秦岭灰池子岩体中的花岗岩具有类似埃达克岩的高Sr/Y和（La/Yb）N比值。其相对较高的SiO2，K2 O和Na 2 O和非常低的MgO，Cr和Ni含量的范围内的高SiO2埃达克岩和早太古代TTG和成分相似的实验熔体来自变玄武岩源。新的西姆斯锆石U-Pb定年结果将灰池子岩体的侵位年龄限定在422 ± 5 Ma。灰池子岩体岩石样品的εNd（t）和锆石εHf（t）值与NQ单元新元古代变基性岩相似。结合正常的类地幔δ 18 O同位素值，这些埃达克岩最好的解释是新元古代基性岩壳根的部分熔融，由于俯冲的商丹洋。区域地质资料表明，地壳可能增厚了约。灰池子岩体侵位前的490 Ma弧碰撞过程。我们的研究结果证实，在高压条件下，板片俯冲触发的镁铁质岩浆的底侵作用及其随后的熔融可能是早期大陆地壳形成的重要机制。
Adakitic rocks are often considered as a key to deciphering the genesis of Archean TTGs and the early crustal growth. Granites from the Huichizi pluton in the North Qinling (NQ) unit have high Sr/Y and (La/Yb)Nratios similar to adakites. Their relatively high SiO2, K2O, and Na2O and very low MgO, Cr, and Ni contents are in the range of high-SiO2adakites and early Archean TTGs and are compositionally similar to experimental melts derived from metabasalt sources. New SIMS zircon U–Pb dating constrains the emplacement age of the Huichizi pluton at 422 ± 5 Ma. Rock samples from the Huichizi pluton have εNd(t) and zircon εHf(t) values similar to the Neoproterozoic metabasalts in the NQ unit. In combination with their normal mantle-like δ18Ozirvalues, these adakites are best explained by partial melting of the Neoproterozoic mafic crustal root due to subduction of the Shangdan ocean. Regional geological data suggest that the crust was probably thickened by a ca. 490 Ma arc-collision process prior to the emplacement of the Huichizi pluton. Our results confirm that underplating of mafic magma and its subsequent fusion triggered by slab subduction under high pressure conditions could be an important mechanism for the formation of early continental crust.