黑龙江省老黑山盆地下白垩统穆棱组砂岩地球化学特征及其地质意义

Geochemical Characteristics and Geological Implications of Sandstones in Muling Formation of Lower Cretaceous,Laoheishan Basin,Heilongjiang Province

为研究黑龙江老黑山盆地下白垩统穆棱组砂岩的源岩属性和源区大地构造背景,在穆棱组进行系统取样,开展地球化学特征和显微镜下分析。研究结果表明:穆棱组砂岩主量元素显示Fe_2O_3的含量小于FeO,CaO的含量大于MgO的含量,稀土元素具有轻稀土富集、重稀土平坦、多数样品的δEu值具有负异常等特征,样品间微量元素的富集和亏损差异明显。相关系列判别图解表明穆棱组源岩未经沉积再循环作用,属于短距离搬运堆积,且源岩主要为来自上地壳的长英质岩石,但存在多个物源。结合砂岩地球化学特征和Dickinson图解及区域构造背景认为,物源区主要形成于印支运动晚期活动大陆边缘构造背景下的再旋回造山源区和基底隆起区,源岩主要来自于晚三叠世—早中侏罗世的长英质火山岩和侵入岩,而少量可能来自于晚二叠世的变质岩。

The Laoheishan Basin is located in Heilongjiang Province,northeast of China,the coal and oil shale are developed in Muling Formation of Lower Cretaceous. Systematic sampling was made and sandstones of Muling Formation in the Laoheishan Basin were analyzed. The results show that the major elements of sandstones in Muling Formation has the characteristics of Fe_2O_3 less than the FeO,but CaO more than MgO. And the rare earth elements of sandstones show an enrichment in light rare earth elements,a flat trending in heavy rare elements and a negative europium anomaly in most samples. However,there is a significant difference in the enrichment and loss of trace elements between samples. Related discriminations indicate that the source rocks of sandstones were carried and accumulated in short distance which mainly came from felsic rocks of the upper crust without experiencing deposition and recycling. Through the judgment combined with the geochemical characteristic,Dincksion diagram of sandstones and the study of regional tectonic setting,sandstones of Muling For-mation have several provenances,and source region majorly was formed in the recycled orogeny and basement uplifted provenances under the tectonic background of active continental margin at the end of Indo-China Movement. Source rocks mostly came from felsic volcanic rocks and intrusive rocks during late Triassic to early-middle Jurassic,with a little probably from metamorphic of late Permian.