Zircon U-Pb Dating and Geochemical Characteristics of Granite Porphyry in Zhanhongshan Area, East Kunlun
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摘要: 在野外调查的基础上，对东昆仑战红山地区花岗斑岩通过锆石U-Pb测年和地球化学研究，获得花岗斑岩成岩年龄为（243.4±1.5）Ma（MSWD=0.99），属中三叠世。岩石地球化学特征显示岩石SiO2为73.82%~75.65%，K2O/Na2O=0.61~0.95，相对富钠，贫MnO（0.05%~0.06%）、P2O5（0.05%）和TiO2（0.17%~0.2%），A/CNK值为1~1.09，平均为1.053，Al2O3为12.02%~13.12%，里特曼指数δ值为1.61~1.89，TFeO/MgO为2.44~2.54，DI为91.2~92.64，表明其为过铝质、钙碱性岩系列的高分异I型花岗岩。岩石稀土总量较低（ΣREE=134.89×10-6~165.65×10-6），LREE/HREE=7.99~8.85，（La/Yb）N=9.9~11.21，轻重稀土分馏明显，表现出轻稀土富集而重稀土亏损的右倾曲线。δEu为0.58~0.66，岩石具大离子亲石元素Rb、Ba及高场强元素U、Th、Pb相对富集，K、P、Ti相对亏损特征。结合岩石成岩年龄、地球化学特征以及区域构造演化，认为其形成于古特提斯洋向北俯冲的碰撞环境。Abstract: Based on the field investigation of granite porphyry in Zhanhongshan area of East Kunlun, zircon U-Pb dating and geochemical study show that the granite porphyry has a diagenetic age of (243.4 ±1.5) Ma (MSWD=0.99), belonging to the Middle Triassic. The geochemical characteristics of the rocks show that the SiO2 ranges from 73.82% to 75.65%, K2O/Na2O=0.61-0.95, relatively rich in sodium, poor in MnO (0.05%~0.06%), P2O5 (0.05%) and TiO2 (0.17%~0.2%). The A/CNK value is 1~1.09, with an average of 1.053. Al2O3 is between 12.02%~13.12%. The values of δ are 1.61~1.89. TFeO/MgO is 2.44~2.54 and DI is 91.2~92.64. All these show that it is a highly fractionated I-type granite of peraluminous and calc-alkaline series. The total REE content of the rocks is low (∑REE=134.89×10-6~165.65×10-6), LREE/HREE=7.99~8.85, (La/Yb)N=9.9~11.21. The fractionation of LREE and HREE is obvious, showing a right dipping curve of LREE enrichment and HREE depletion.δEu is 0.58~0.66. The rocks are characterized by a relative enrichment of large ion lithophiles of Rb, Ba and high field strength elements of U, Th, Pb, whereas a depletion of K, P and Ti. Combined with the diagenetic age, geochemical characteristics and regional tectonic evolution,the authors hold that the rocks formed in the collision environment of the northward subduction of the PaleoTethys ocean.
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Key words:
- granite porphyry /
- zircon U-Pb dating /
- the Middle Triassic /
- East Kunlun /
- Zhanhongshan
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