Syn- and post-collisional granitoids in the Central Tianshan orogen: Geochemistry, geochronology and implications for tectonic evolution
Syn- and post-collisional granitoids in the Central Tianshan orogen: Geochemistry, geochronology and implications for tectonic evolution
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DOI：
10.1016/j.gr.2011.01.013
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发表时间：
2011-09
影响因子：
6.1
通讯作者：
Yunpeng Dong;Guowei Zhang;F. Neubauer;Xiaoming Liu;C. Hauzenberger;Ding-wu Zhou;W. Li
中科院分区：
文献类型：
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作者：
Yunpeng Dong;Guowei Zhang;F. Neubauer;Xiaoming Liu;C. Hauzenberger;Ding-wu Zhou;W. Li
中国中天山带东段花岗岩类十分丰富，它们不仅是壳幔相互作用的标志，而且可用于追踪造山带的构造演化历史。在中天山米市沟地区，已识别出白云母花岗岩（MG）、黑云母二长花岗岩（BMG）、黑云母花岗岩（BG）和碱性花岗岩（AG）四种侵入岩体。MG具有明显的S型亲合性，强过铝质，铝饱和指数高，Rb、Th、U和LREE正异常，Ba、Nb、Sr、P、Ti和Eu负异常强烈。因此，MG的岩浆来源于加厚的陆壳熔融，其主要成分是前志留纪陆岛弧侵蚀的沉积物。锆石U-Pb年龄为424.5 ± 2.6Ma，对MG和地壳增厚的年龄起着制约作用。BG和BMG花岗岩类具有I型地球化学特征，并与俯冲弧密切相关。二者均为钙碱性过铝花岗岩，LREE明显富集，Eu负异常，Ba、Nb、Ta、Sr、P、Ti亏损，Rb、Th、U、Nd、Zr、Sm富集。这些特征表明它们是陆壳下部与俯冲带上地幔楔成分输入的混合岩浆源。LA-ICPMS锆石U-Pb年龄为411 ± 4.7Ma和402 ± 3.4Ma，分别代表了BG和BMG花岗岩类的形成年龄，也表明南天山洋壳俯冲作用也发生在早泥盆世。AG为典型的A型花岗岩，亏损Nb、Ta、Sr、P、Ti和Y。认为AG形成于板内构造环境，与天山造山带碰撞后伸展塌陷的大陆隆起和裂陷带有关。锆石U-Pb年龄为290 ± 5.1Ma，代表了AG的形成时代和伸展塌陷裂陷时代。
The eastern part of the Central Tianshan Belt in China is characterized by abundant granitoids, which are not only indicators of the interaction between crust and mantle but also can be used for tracking the tectonic evolutionary history of the orogen. Four granitic plutons, muscovite granites (MG), biotite monzonitic granites (BMG), biotite granites (BG), and alkali granites (AG), have been recognized to have intruded in the Mishigou area, Central Tianshan Belt. The MG has pronounced a S-type affinity, which is strongly peraluminous with a high aluminum saturation index, and displays positive Rb, Th, U and LREE anomalies with a strong negative Ba, Nb, Sr, P, Ti and Eu anomalies. Therefore, the magma of the MG is considered to have been derived from melting of thickened continental crust, which is composed mainly of the sediments eroded from a pre-Silurian continental island-arc. The U–Pb zircon age of 424.5±2.6Ma constrains the age of MG and crust thickening. The BG and BMG granitoids display I-type geochemical features and have affinities to subduction arcs. Both of them are characterized by calc-alkaline peraluminous granites with a significant LREE enrichment and a negative Eu anomaly, as well as a depletion in Ba, Nb, Ta, Sr, P and Ti and an enrichment in Rb, Th, U, Nd, Zr and Sm. These characteristics indicate that they were derived from a mixed magma source between lower continental crust and the input of components derived from the mantle wedge above the subduction zone. The LA-ICPMS zircon U–Pb ages of 411±4.7Ma and 402±3.4Ma represent the formation ages of the BG and BMG granitoids, respectively, which also constrain that the subduction of the South Tianshan oceanic crust also occurred during Early Devonian time. The AG shows a typical A-type granite affinity with depletion of Nb, Ta, Sr, P, Ti and Y. It is interpreted that AG was formed in a within-plate tectonic setting, and related to continental up-doming and rifting zones as a consequence of the extensional collapse after the collision of the Tianshan orogen. The U–Pb zircon age of 290±5.1Ma represents the formation age of the AG, and the time of the extensional collapse and rifting.