Triassic high-Mg adakitic andesites from Linxi, Inner Mongolia: Insights into the fate of the Paleo-Asian ocean crust and fossil slab-derived melt–peridotite interaction
Triassic high-Mg adakitic andesites from Linxi, Inner Mongolia: Insights into the fate of the Paleo-Asian ocean crust and fossil slab-derived melt–peridotite interaction
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DOI：
10.1016/j.chemgeo.2012.03.019
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发表时间：
2012-10
期刊：
影响因子：
3.9
通讯作者：
Yongsheng Liu;Xiaohong Wang;Dong-bing Wang;Detao He;K. Zong;Changgui Gao;Zhaochu Hu;H. Gong
中科院分区：
文献类型：
--
作者：
Yongsheng Liu;Xiaohong Wang;Dong-bing Wang;Detao He;K. Zong;Changgui Gao;Zhaochu Hu;H. Gong
通过对内蒙古-大兴安岭造山带林西地区三叠纪高镁埃达克质安山岩的体相元素、同位素组成、单颗粒锆石U-Pb年龄和微量元素组成的研究，探讨了该地区的岩石成因及其对中生代地壳生长的指示意义。林西高镁铝榴石具有典型的高SiO2埃达克岩特征，具有高Mg#、高Cr、Ni含量。发现了具有反环带的粗单斜辉石（cpx）斑晶，这些cpx斑晶具有较低的Mg#和Ni含量和较高的不相容元素含量（例如，Zr和La）与它们的地幔和轮辋进行比较。块体岩石Sr-Nd同位素组成（87 Sr/86 SrI =0.70382-0.70396，εNd（t）=3.2-4.5）属于洋中脊玄武岩（MORB）和现代俯冲相关埃达克岩。LA-ICP-MS单颗粒锆石U-Pb测年结果表明，火山喷发时间约为2000年。238 Ma。结合构造背景和前寒武纪锆石年龄谱，这些特征表明，临西HMA可能来自俯冲的古亚洲洋壳板片，其沉积物来自华北板块，并与地幔中的橄榄岩混染。锆石微量元素年龄变化表明，洋壳形成于石炭纪-早二叠世，约于晚二叠世俯冲。270-260Ma。俯冲洋板的熔融和橄榄岩的混杂作用可能始于约1000年。250毫安。临西海侵带位于华北陆缘与IMDOB的Solonker缝合带之间的南加积带，可能是石炭纪-二叠纪固结的产物。这意味着，林西HMAs可能是来自俯冲后的化石大洋板片的部分熔融，和俯冲相关的熔融可能会被推迟，如果板片俯冲下一个老的，冷克拉通。虽然我们不确定的真实范围的化石洋板，临西HMAs的成因基本上是一个俯冲板片的熔融滞后于俯冲的快照，和熔融的化石洋板可能发挥了重要作用的中生代地壳生长在IMDOB。
Bulk element and isotopic compositions, single zircon U–Pb ages and trace element compositions of the Triassic high-Mg adakitic andesites (HMAs) from the Linxi area in the Inner Mongolia–Daxinganling orogenic belt (IMDOB) were studied to understand the area's petrogenesis and implications for Phanerozoic crustal growth. The Linxi HMAs are characterized by typical features of high-SiO2adakite with high Mg# and high Cr and Ni contents. Coarse clinopyroxene (cpx) phenocrysts with reverse zoning were found. These cpx phenocrysts have cores with lower Mg# and Ni contents, and higher incompatible element contents (e.g., Zr and La) compared with their mantles and rims. Bulk rock Sr–Nd isotopic compositions (87Sr/86SrI=0.70382–0.70396 and εNd(t)=3.2–4.5) fall in the range of mid-ocean ridge basalts (MORB) and modern subduction-related adakites. Single zircon U–Pb dating by LA-ICP-MS suggests an eruption at ca. 238Ma. Combined with the tectonic setting and Precambrian zircon age spectrum, these features suggest that the Linxi HMAs could be derived from the subducted Paleo-Asian oceanic slab with sediments shed from the North China Craton and hybridized by peridotite in the mantle. Trace element-age variations of zircons indicate that the oceanic crust was formed during Carboniferous–early Permian times, and then subducted during ca. 270–260Ma. Melting of the subducted oceanic slab and hybridization by peridotite could have been initiated at ca. 250Ma. It is suggested that the southern accretionary zone between the North China Craton and the Solonker suture in the IMDOB, where the Linxi HMAs are located, could have been consolidated by Carboniferous–Permian times. This implies that the Linxi HMAs could have been derived from partial melting of a fossil oceanic slab after the subduction, and subduction-related melting might have been delayed if the slab was subducted under an old, cold craton. Although we are unsure of the true extent of the fossil oceanic slab, the genesis of the Linxi HMAs is essentially a snapshot of the melting of a subducted slab lagging behind subduction, and melting of the fossil oceanic slab could have played an important role in the Phanerozoic crustal growth in the IMDOB.