Neoproterozoic Bimodal Intrusive Complex in the Southwestern Tarim Block, Northwest China: Age, Geochemistry, and Implications for the Rifting of Rodinia
Neoproterozoic Bimodal Intrusive Complex in the Southwestern Tarim Block, Northwest China: Age, Geochemistry, and Implications for the Rifting of Rodinia
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DOI：
10.2747/0020-6814.48.2.112
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发表时间：
2006-02
影响因子：
2.6
通讯作者：
Chuan-Lin Zhang;Zheng‐Xiang Li;Xian‐Hua Li;Haimin Ye;Aiguo Wang;K. Guo
中科院分区：
文献类型：
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作者：
Chuan-Lin Zhang;Zheng‐Xiang Li;Xian‐Hua Li;Haimin Ye;Aiguo Wang;K. Guo
本文首次报道了塔里木地块新元古代双峰式侵入杂岩的锆石SHRIMP U-Pb年龄和岩石地球化学特征，并讨论了其构造意义。库地火成杂岩（KIC）的结晶年龄为783 ± 10 Ma。花岗岩和辉长岩混合，表明侵入是同时代的。花岗岩显示：结果表明，该花岗岩具有A型花岗岩的特征：高碱量（Na_2 O + K_2 O = 8- 11wt%），高Zr、Nb、Y和稀土总量，LREE富集明显[（La/Yb）N = 9-59]，Eu负异常显著（δdLEu = 0.17-0.44）。此外，花岗岩样品具有均匀的正εNd（T）值（1.4 ~ 2.1）和中元古代Nd模式年龄（~ 1.3Ga）。因此，我们解释的花岗岩可能产生的区域中元古代弧和/或弧后地壳的部分熔融。KIC辉长岩的地球化学特征类似于板内碱性玄武岩，微量元素和同位素组成表明其为OIB型岩浆源，并受到陆壳混染。野外观察、岩石学和地球化学研究表明，KIC是一个双峰碱性杂岩，由这两种不同起源的岩浆在大陆裂谷中混合而成，可能与Rodinian超大陆下的地幔超柱有关。
We report here the first SHRIMP U-Pb zircon ages and bulk-rock geochemistry for a Neoproterozoic bimodal intrusive complex in the Tarim block and discuss the tectonic implications. The Kudi igneous complex (KIC) crystallized at 783 ± 10 Ma. Granite and gabbro comingled, indicating that the intrusions were coeval. The granite displays: high total alkalis (Na2O + K2O = 8-11 wt%); high abundances of Zr, Nb, Y, and total REE; and strong LREE enrichment [(La/Yb)N = 9-59] with a significant negative Eu anomaly (δdLEu = 0.17-0.44), characteristic of A-type granites. Furthermore, samples of the granite have homogeneous positive εNd(T) values of 1.4 to 2.1 and Mesoproterozoic Nd modal ages (∼1.3 Ga). We thus interpret the granite as probably generated by partial melting of the regional Mesoproterozoic arc and/or back-arc crust. The KIC gabbro is geochemically similar to intraplate alkaline basalts, with trace elements and isotope compositions indicating an OIB-type magma source, variably contaminated by continental crust. Field observations, petrology, and geochemistry indicate that the KIC was a bimodal alkaline complex formed by mixing of these two magma types of different origins in a continental rift, possibly related to a mantle superplume beneath the Rodinian supercontinent.