Elemental and Nd-Sr isotopic geochemistry of granitoids from the West Junggar foldbelt (NW China), with implications for Phanerozoic continental growth
Elemental and Nd-Sr isotopic geochemistry of granitoids from the West Junggar foldbelt (NW China), with implications for Phanerozoic continental growth
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DOI：
10.1016/j.gca.2004.09.019
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发表时间：
2005-03
影响因子：
5
通讯作者：
B. Chen;Y. Arakawa
中科院分区：
文献类型：
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作者：
B. Chen;Y. Arakawa
我们报告了来自西准噶尔褶皱带（中国西北部）的两个同时代碰撞后岩浆套（~300 Ma）的元素和 Nd-Sr 同位素数据，即庙沟岩浆套和克拉玛依岩浆套，旨在确定其源区及其对大陆生长的影响。庙沟岩石的成分为二长岩到花岗质，镁含量低（<0.30），HFSE 贫化，同位素成分高度贫化，ISr 范围为 0.7035 至 0.7045，εNd（300 Ma）为 + 8.4 至 + 6.6，年轻 Nd 模型年龄（0.37 - 0.70 Ga）与该地区蛇绿岩的年龄。这些特征表明，庙沟岩石本质上是由早至中古生代形成的新生玄武岩下地壳部分熔融形成的。克拉玛依套房包含从辉长闪长岩到花岗岩的各种岩石类型。这些岩石表现出轻稀土和轻稀土元素的富集以及 HFSE 的贫化，并且其化学成分（例如 Mg# = 0.63–0.41）与庙沟岩组有很大不同，尽管它们在同位素上无法区分。这表明克拉玛依岩套的母岩浆起源于先前在古生代俯冲期间交代的年轻岩石圈地幔的融化。西准噶尔岩浆岩代表了显生宙新生大陆地壳的产生，是由拉张体系中软流圈的上涌引发的。该区域下方的基底主要是“被困”的古生代弧系和洋壳。
We report elemental and Nd-Sr isotopic data for two coeval postcollisional magmatic suites (∼300 Ma), the Miaogou and Karamay suites, from West Junggar foldbelt (NW China), aiming to determine their source regions and implications for continental growth. The Miaogou rocks, monzonitic to granitic in composition, show low Mg# (<0.30) and depletion of HFSE, and are highly depleted in isotopic compositions, with ISrranging from 0.7035 to 0.7045, εNd(300 Ma) from + 8.4 to + 6.6 and young Nd model ages (0.37–0.70 Ga) that coincide with the ages of the ophiolites in the area. These features suggest that the Miaogou rocks were derived essentially by partial melting of a juvenile basaltic lower crust formed in the early to middle Palaeozoic. The Karamay suite contains a variety of rock types from gabbroic diorite to granite. These rocks show enrichment of LREE and LILE and depletion of HFSE, and have chemical composition (e.g., Mg# = 0.63–0.41) rather different from the Miaogou suite, though isotopically they are indistinguishable. This suggests that the parental magma of the Karamay suite originated from melting of a young lithospheric mantle that had previously been metasomatized during the Palaeozoic subduction. The West Junggar magmatic rocks represent production of juvenile continental crust in the Phanerozoic, triggered by upwelling of asthenophere in an extensional regime. The basement beneath the area is dominated by “trapped” Palaeozoic arc series and oceanic crust.