GEOCHRONOLOGY AND GEOCHEMISTRY OF THE JURASSIC GRANODIORITE IN JIANGJIATUN, TUQUAN COUNTY OF INNER MONGOLIA
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摘要: 对姜家屯花岗闪长岩进行的同位素年代学及岩石地球化学研究显示，花岗闪长岩LA-ICP-MS锆石U-Pb加权平均年龄为154.8±1.8 Ma，表明该侵入体是晚侏罗世形成的.岩石学及地球化学数据显示其属于高钾钙碱性系列，具A型花岗岩特征.岩石高硅（SiO2=66.08%~67.80%）、富碱（K2O+Na2O=7.35%~7.97%）、富铝（Al2O3=14.5~15.23）、贫镁（MgO=1.08%~1.62%）、贫钙（CaO=2.05%~3.04%）、低钛（TiO2=0.56%~0.67%），轻稀土富集，重稀土相对亏损，稀土配分曲线呈右倾型，具明显的负铕异常，轻稀土分馏较好.微量元素亏损Sr、Ba、Ta、Nb，而Th、Zr、Hf、Pb相对富集，在微量元素原始地幔标准化蛛网图上显示明显Sr、Ba、Ti负异常的特征.综合这些特征认为，姜家屯花岗闪长岩是受古太平洋板块俯冲影响，造山后岩石圈伸展剪薄环境下的产物.Abstract: Study on the isotopic chronology and lithogeochemistry of the Jiangjiatun granodiorite in Tuquan County, Inner Mongolia, indicates that the LA-ICP-MS zircon U-Pb weighted average age for the rock body is 154.8±1.8 Ma, which represents Late Jurassic. The petrological and geochemical data shows the granodiorite, belonging to high-K calc-alkaline series and A-type granite, is characterized by high SiO2 (66.08%-67.80%), rich alkali (K2O+Na2O=7.35%-7.97%), rich Al2O3 (14.5-15.23), poor MgO (1.08%-1.62%), poor CaO (2.05%-3.04%) and low TiO2 (0.56%-0.67%). The REE pattern curves are right-dipping with evident negative Eu anomalies and well LREE fractionation. The primitive mantle normalized trace element spidergrams show distinct negative Sr, Ba and Ti anomalies, depletion of Sr,Ba, Ta and Nb,and relative enrichment of Th,Zr,Hf and Pb. From the above, it is thought that the Jiangjiatun granodiorite is the product of post-orogenic lithosphere extension and shear thinning background affected by the subduction of Paleo-Pacific Plate.
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Key words:
- granodiorite /
- lithogeochemistry /
- Late Jurassic /
- Jiangjiatun /
- Inner Mongolia
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