辽宁辽阳地区辽河群酸性火山岩锆石U-Pb年代学及其地质意义

发布时间：2018-02-07 14:29

本文关键词： 辽阳辽河群酸性火山岩锆石U-Pb年代学构造背景　出处：《岩石学报》2017年09期 　论文类型：期刊论文

【摘要】：辽宁省辽阳地区出露有大面积的古元古代辽河群地层,在辽河群里尔峪组及高家峪组中识别出一套酸性火山岩。本文通过对酸性火山岩同位素年代学及地球化学研究,用以限定辽河群形成时代,并进一步探讨其形成的动力学背景。这套酸性火山岩岩性包括流纹岩、变流纹质含角砾凝灰岩、角岩化流纹岩和弱硅化流纹岩,对其中6件样品利用LA-ICP-MS锆石U-Pb方法测年。CL图像显示辽河群酸性火山岩中的锆石均具典型的岩浆振荡环带结构和较高的Th/U比值,显示为岩浆锆石。锆石U-Pb年龄可分为3期:2190~2180Ma、2110~2100Ma、1970~1960Ma,结合其中存在继承锆石的结果认为辽河群至少存在3期岩浆活动,将辽河群形成时代限制于2.19~1.96Ga,其形成时代大约持续了230Myr左右。野外接触关系的观察及酸性火山岩的年代学特征从另一个方面揭露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。前人研究表明"辽吉花岗岩"形成年龄为2.16Ga,通过野外观察其与辽河群之间均为构造接触。D1442-1和D1444-2两个样品锆石U-Pb测年结果为2180±12Ma、2190±13Ma,均略早于"辽吉花岗岩",结合其与辽河群野外关系,认为"辽吉花岗岩"应该不是作为沉积基底,而是与辽河群为同一构造运动的产物。辽河群流纹岩Al_2O_3含量16.33%~16.90%,K_2O含量4.62%~4.77%,K_2O+Na_2O含量5.97%~7.54%,含铝指数(A/CNK)比较高为1.27~1.50,为过铝质岩石,显示富铝、高钾特征。此外流纹岩轻稀土富集,重稀土亏损,轻重稀土分馏明显,具有明显的负铕异常,亏损Ba、Sr、Ti,较高的Zr及(Zr+Nb+Ce+Y)含量、10000Ga/Al比值等特点都显示为A型花岗岩,说明其形成于地壳减薄环境。本文在辽河群中识别出一套酸性火山岩与前人在南辽河群识别出的变质流纹岩组成了酸性端元(2201~1960Ma),同时期存在的基性火成岩(2198~1869Ma)为基性端元,证明了辽河群"双峰式火山岩"的存在,暗示辽河群形成于伸展拉张环境。
[Abstract]:A large area of paleoproterozoic Liaohe Group strata were exposed in Liaoyang area, Liaoning Province, and a set of acidic volcanic rocks were identified in Lianyu formation and Gaojiayu formation of Liaohe Group. The isotopic chronology and geochemistry of acidic volcanic rocks are studied in this paper. It is used to define the formation age of the Liaohe Group and to further explore the dynamic background of its formation. This set of acid volcanic lithology includes rhyolite, metamorphic kernel-bearing tuff, keratinized rhyolite and weakly silicified rhyolite. For 6 samples, the LA-ICP-MS zircon U-Pb dating images show that the zircons in the acidic volcanic rocks of the Liaohe Group all have typical magmatic oscillatory zone structure and high Th/U ratio. The zircon U-Pb age can be divided into three phases: 21902 180 Ma-21010 Ma-2100 Ma-1970Ma-1960Ma. combined with the result of inherited zircon, it is concluded that there are at least three magmatic activities in the Liaohe Group, and the results show that there are three phases of magmatic activity in the Liaohe Group. The formation age of Liaohe Group was limited to 2.19 ~ 1.96Ga, which lasted about 230Myr. The observation of field contact relationship and the chronological characteristics of acid volcanic rocks reveal that the Liaohe Group is a set of disordered and locally orderly tectonic strata in another aspect. Previous studies show that the age of formation of Liaoji granites is 2.16Ga, and the zircon U-Pb dating between Liaohe Group and Liaohe Group is tectonic contact. D1442-1 and D1444-2 are 2180 卤12Ma-2190 卤13Ma-zircon U-Pb dating results, which is slightly earlier than that of Liaohe Group. "Liaoji Granite", combined with its field relationship with Liaohe Group, It is considered that "Liaoji granite" should be the product of the same tectonic movement as Liaohe Group, not as sedimentary basement. The Al_2O_3 content of rhyolite in Liaohe Group is 16.33 ~ 16.90 and the content of K _ 2O is 4.62 ~ 4.77 and K _ 2O Na_2O is 5.97 ~ 7.54. The Al content of Liaohe Group is higher than that of Liaohe Group, which is a peraluminous rock, indicating that it is aluminum-rich, and the content of K _ 2O is 5.97 ~ 7.54% higher than that of Liaohe Group. In addition, the rhyolite is characterized by enrichment of light rare earths, depletion of heavy rare earths, obvious fractionation of light and heavy rare earths, obvious negative europium anomaly, depletion of Bajiu SrTiand high Zr and zirconium NB ce Y contents of 10000Ga / Al ratio, all of which show A-type granites. In this paper, a set of acidic volcanic rocks and metamorphic rhyolite identified in the South Liaohe Group have been identified as the basic terminal elements. The acidic end element is composed of the acidic end element, the basic igneous rock, which existed in the same period, and the basic igneous rock, which existed at the same time, and the basic igneous rocks of the same period. In this paper, a set of acid volcanic rocks and metamorphic rhyolite identified in the South Liaohe Group are identified as basic terminal elements. The existence of bimodal volcanic rocks in Liaohe Group suggests that Liaohe Group was formed in extensional and extensional environment.
【作者单位】：中国地质调查局沈阳地质调查中心;吉林大学地球科学学院;辽宁省矿产勘查院;
【基金】：中国地质调查局地质调查工作项目(12120113058400、DD20160048-05、12120113053400)资助
【分类号】：P588.14;P597.3

【相似文献】