Neoproterozoic intrusions along the northern margin of South Qinling, central China: Geochemistry, zircon ages, and tectonic implications
Neoproterozoic intrusions along the northern margin of South Qinling, central China: Geochemistry, zircon ages, and tectonic implications
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中国中部南秦岭北缘新元古代侵入岩：地球化学、锆石年龄和构造意义
DOI：
10.1016/j.precamres.2019.105406
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发表时间：
2019
影响因子：
3.8
通讯作者：
CHEN Fukun
中科院分区：
文献类型：
--
作者：
NIE Hu;YE Ri-Sheng;CHENG Hong;ZHU Xi-Yan;CHEN Fukun
本文报道了中国中部南秦岭北部新元古代侵入岩中出露的全岩锶-钕同位素组成、锆石颗粒的U-Pb年龄和Hf同位素组成。岩石成分多样，侵位时代约为751-714 Ma。根据它们不同的地球化学特征，可识别出四个成分群。高钛辉长岩为拉斑玄武岩，SiO_2、MgO含量较低，FeOT、TiO_2含量较高，富含大离子亲石元素，无Nb、Ta负异常。这些辉长岩具有较高的εND(T)值(+1.9~+5.3)，与EMORB或OIB的成分相似，表明其起源于软流圈地幔。低钛辉长岩为钙碱性，具有较高的SiO_2和MgO，较低的FeOT和TiO_2含量。这些辉长岩具有典型的弧状微量元素特征和εND(T)值，变化范围为−3.2~+6.0，与受俯冲改造的非均质岩石圈地幔部分熔融的来源一致。I型花岗岩的元素组成和NdHf同位素组成表明，地幔岩石和地壳岩石都有重要贡献。S型花岗岩起源于变质沉积岩的部分熔融作用，其同位素组成与南秦岭基底的副片麻岩相似。在相对较低的压力和较高的温度下，地幔和地壳岩石的广泛熔融表明新元古代为伸展环境。我们的资料结合已有的基岩和新元古代火成岩资料，约束了扬子地块北缘和南秦岭的地壳演化，其中约800 Ma以前沿扬子地块北缘的俯冲导致了弧陆碰撞，导致斗岭杂岩基岩的高级变质作用。随后旷日持久的大陆裂谷作用与罗迪尼亚超大陆的解体有关。
We report whole-rock Sr–Nd isotopic compositions and U–Pb ages and Hf isotopic compositions of zircon grains from Neoproterozoic intrusive rocks exposed in northern South Qinling, central China. The rocks have diverse compositions and were emplaced at ca 751–714 Ma. On the basis of their distinct geochemical signatures, four compositional groups are recognized. High-Ti gabbros are tholeiitic, with low SiO2 and MgO, and high FeOT and TiO2 contents, and exhibit enrichment in large-ion-lithophile elements and absence of Nb and Ta negative anomalies. These gabbros have high εNd(t) values of +1.9 to +5.3 that are similar to the compositions of EMORB or OIB, implying an origin from asthenospheric mantle. Low-Ti gabbros are calc-alkaline and have high SiO2 and MgO, and low FeOT and TiO2 contents. These gabbros have typical arc-like trace-element signatures and εNd(t) values that vary from −3.2 to +6.0, consistent with derivation from the partial melting of heterogeneous lithospheric mantle that was modified by subduction. Elemental and Nd–Hf isotopic compositions of I type granitoids imply significant contributions from both mantle and crustal rocks. S-type granites originated from the partial melting of metasedimentary rocks with isotopic compositions similar to paragneisses of the basement in South Qinling. The extensive melting of both mantle and crustal rocks under relatively low pressures and high temperatures suggests an extensional environment during the Neoproterozoic. Our data, in combination with existing data from basement rocks and Neoproterozoic igneous rocks, constrain the crustal evolution of the northern Yangtze Block and South Qinling, in which subduction along the northern margin of the Yangtze Block prior to ca 800 Ma led to arc–continent collision, inducing high-grade metamorphism of the basement rocks of the Douling Complex. Subsequent protracted continental rifting was related to breakup of the supercontinent Rodinia.