辽宁本溪连山关地区辽河群浪子山组、里尔峪组形成时代及其地质意义

    The formation ages of the Langzishan and Lieryu Formations in Lianshanguan area, Benxi, Liaoning Province, and its geological significance.

    • 摘要: 辽宁省本溪连山关地区出露大面积的古元古代辽河群地层,在朱家沟典型剖面浪子山组中识别出2层斜长角闪岩,镜下观察其原岩为玄武岩;在连山关及河栏镇里尔峪组中识别出一套酸性火山岩。对浪子山组2件斜长角闪岩样品、里尔峪组2件流纹岩样品测定LA-ICP-MS锆石U-Pb年龄。阴极发光图像显示,样品D020锆石内部结构整体发黑、条痕状吸收程度不等,Th/U值较低,为变质锆石,其1934±45Ma代表了浪子山组的变质年龄。其余3个样品阴极发光图像显示典型的岩浆振荡环带结构和较高的Th/U值,为岩浆锆石。1952±38Ma代表了浪子山组的形成时代,2177±34Ma和2208±12Ma代表了里尔峪组的形成时代。结合前人资料,将辽河群形成时代限制在2.20~1.95Ga,其形成时代持续了250Ma左右。野外接触关系及火山岩年代学特征从另一个方面揭露了辽河群总体为一套无序、局部有序的构造地层,各岩组间不存在上下关系,浪子山组已经不适合置于里尔峪组之下。

       

      Abstract: A large area of the Paleoproterozoic Liaohe Group is exposed in Lianshanguan area, Benxi, Liaoning Province. Two layers of amphibolite and a set of felsic volcanic rocks have been identified in the Langzishanand Lieryu Formations of the Liaohe Group. The samples include two amphibolites and two rhyolites. Zircons from D020 for LA-ICP-MS U-Pb dating have black interior structure, unequal striation absorption and low Th/U ratios, indicating typical metamorphic origin. The age of 1934±45Ma represents the metamorphic age of the Langzishan Formation. Zircons from the other three samples for LA-ICP-MS U-Pb dating have oscillatory zoning and high Th/U ratios, indicating typical magmatic origin. The ages of 1952±38Ma and 2177±34Ma, 2208±12Ma represent the formation age of the Langzishan and Lieryu Formations respectively. In consideration of previous data, the authors hold that the formation age of the Liaohe Group is limited in the range of 2.20~1.95Ga, lasting about 250Ma. Field contact relations and chronological characteristics of volcanic rocks reveal that the Liaohe Group is a series of disordered and locally ordered structural strata, and there is no upper and lower relation between the rock groups. The Langzishan Formation is no longer suitable for being placed beneath the Lieryu Formation.

       

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