QG2井熔结火山碎屑岩锆石定年及其地质意义

U-Pb Zircon Dating of the Mesozoic Welded Pyroclastics in the QG2 Well and Its Geological Significance

摘要: 辽河坳陷西部凹陷齐家潜山的Qg2井钻遇一套含油性较好的火山岩，通过岩石学和地球化学特征研究，认为是一套典型的壳源酸性钙性岩类，确定为爆发相的熔结角砾凝灰岩。该套火山岩形成时代和地层归属一直存在较大分歧，当时根据区域资料将其归为中生界早白垩纪义县组，但缺乏精确的年代学证据。为了进一步确定该套火山岩的形成时代和地层层位，笔者先是利用LA-ICP-MS锆石原位U-Pb定年方法，获得了熔结角砾凝灰岩的喷发年龄为168.9 ± 1.1 Ma，喷发时代为中生代中侏罗世，与辽西建昌盆地、河北承德盆地以及北京西山马兰村的的髫髻山组的火山岩在形成时代和岩性特征上具有可比性，因此，该套火山岩地层层位确定为髫髻山组，修正了以往对该套火山岩地层归属的观点，为下一步研究该类火山岩油气藏的空间展布奠定了基础。

Abstract: The QG2 Well drilled into a suite of volcanic rocks with good oil-bearing property, which is located in Qijia buried hill, the western sag of Xialiaohe Concave. According to the results of petrography and geochemistry, this suite of volcanic rocks is identified as a suit of classical acid calcareous rock of crust source type, a lava tuff breccia with explosive faces. However, there has been a long debate on the formation age and stratum layer of this suite of volcanic rocks. Based on the regional geological data, it is previously classified into Yixian Formation of Early Cretaceous, but lack of precise chronological evidence. In order to accurately determine its formation age and stratum layer, we performed LA-ICP-MS. Our results indicated that this suite of volcanic rocks was formed at 168.9 ± 1.1 Ma in the period of Middle Jurassic, which is comparable to Tiaojishan Formation in Jianchang Basin of Western Liaoning Province, Chende Basin of Hebei Province, Malan Village of Western Hills of Beijing. So its stratum was defined as Tiaojishan Formation. The result revised the stratigraphical division of this suite of volcanic rocks. This opens the door for further study the distribution of oil and gas in this type of volcanic rocks.