伊通盆地基底火成岩的LA-ICP-MS锆石U-Pb 定年及其地质意义

为了确定伊通盆地基底的形成时期，对伊通盆地6 个基底火成岩样品进行了LA-ICP-MS 锆石 U-Pb 定年研究。锆石的阴极发光（CL）图像显示，6 个基底火成岩岩心的锆石自形程度较好，且具有典型 的岩浆生长震荡环带。定年结果表明：岔路河断陷的C24 井2 484.2 m 处的黑云母二长花岗岩形成于 （176.8 ± 1.7）Ma，C17 井3 153.0 m 处的碎裂岩化条纹长石二长岩形成于（171.8 ± 3.2）Ma；鹿乡断陷的X5 井、L2 井以及莫里青断陷的Y3 井和Y53 井基底火成岩分别形成于（170.3 ± 3.4）Ma，（169.1 ± 4.5）Ma， （247.2 ± 3.4）Ma 和（186.6 ± 2.5）Ma 。伊通盆地基底火成岩其他锆石定年结果表明，伊通盆地基岩（花岗 岩）的年龄主要为170～336 Ma，其中绝大多数形成于燕山期，少量形成于海西期；各断陷的花岗岩分布存 在差异，岔路河断陷与鹿乡断陷花岗岩基本形成于燕山期，而莫里青断陷花岗岩则在海西期、印支期及燕 山期均有形成。

LA-ICP-MS U-Pb dating of zircon from basement igneous rocks in Yitong Basin and its significance

In order to determine the formation period of Yitong basement accurately, six zircon samples are selected to carry out the study on LA-ICP-MS U-Pb dating of zircon. Zircons from the basement igneous rock are euhedral in shape and show the typical oscillatory zoning with magmatic origin. The dating results indicate that the biotite-monzonitic granite at the depth of 2 484.2 m in C24 well in Chaluhe fault depression formed in （176.8±1.7）Ma, the crack lithification perthitr monzonite at the depth of 3 153.0 m in C17 well formed in （171.8±3.2）Ma, the basement igneous rocks in X5 and L2 wells in Luxiang fault depression respectively formed in （170.3±3.4）Ma and （169.1±4.5）Ma, and the basement igneous rocks in Y53 and Y3 wells in Moliqing fault depression respectively formed in（247.2±3.4）Ma and（186.6±2.5）Ma. In combination with other U-Pb dating, it is considered that the age of basement igneous rocks in Yitong Basin is mainly of 170～336 Ma, and the most formed in Yanshanian, and a little formed in Hercynian. The distribution of granite in each fault depression is different. The most of granites in Chaluhe and Luxiang fault depression formed in Yanshanian, while in Moliqing fault depression the granites formed in Hercynian, Indosinian and Yanshanian.