内蒙古东北部中二叠统哲斯组砂岩地球化学特征分析及物源区示踪

利用岩石地球化学示踪技术,对内蒙古东北地区中二叠统哲斯组砂岩的物源区和构造背景进行了研究.对研究区中二叠统哲斯组砂岩常量元素、微量以及稀土元素的分析表明,哲斯组砂岩样品的常量元素整体上SiO2、Al2O3、Fe2O3含量高(分别为67.87％ ～71.94％、14.57％～15.61％、2.61％ ～6.20％),CaO、MgO含量低(分别为0.31％ ～0.58％和0.80％～1.93％).微量元素上呈大离子亲石元素Ba、Sr相对富集,高场强元素除Zr、Y外相对较低,并且具有轻稀土元素富集、重稀土元素亏损和明显负Eu异常的特点,其中(La/Yb)n=5.08～8.67,Eu/Eu* -0.56～0.77.认为研究区哲斯组砂岩的物源主要来自于上地壳长英质源区,源岩可能为花岗岩,其物源区的构造背景为大陆岛弧环境.

Geochemical characteristics analysis and provenance tracing of sandstone in Middle Permian Zhesi Formation, northeast Inner Mongolia

Using geochemical methods,the authors investigated the provenance of Middle Permian Zhesi Formation sandstone and its tectonic setting in northeast Inner Mongolia.By analyzing major elements,trace elements and rare earth elements,it is found that the sandstone samples are all characterized by high SiO2, Al2O3,Fe2O3 and low CaO,MgO,with their values being 67.87%～71.94%,14.57%～15.61%,2.61%～6.20%,0.31%～0.58% and 0.80%～1.93% respectively.The upper crust normalized spider diagrams are characterized by enrichment of LILE such as Ba and Sr and depletion of HFSE except for Zr and Y.The trace element analysis demonstrates the obvious enrichment of LREE relative to HREE,with significant Eu anomalies,(La/Yb)n=5.08～8.67,Eu/Eu*=0.56～0.77.The provenance of the Middle Permian Zhesi Formation sandstone in the work area might have been derived from felsic rocks of the upper crust,including granites.The tectonic setting of the provenance of the Middle Permian sandstone in the work area was a continental island arc.