辽宁辽河群高家峪组火山岩锆石U-Pb年代学及其地质意义

Zircon U-Pb Geochronology of Volcanic Rocks from Gaojiayu Formation,Liaohe Group,Liaoning Province and Its Geological Significance

处于龙岗地块和狼林地块之间的古元古代辽吉构造带内分布有大量的变质沉积-火山地层,在辽宁地区称为辽河群.对于辽河群沉积时限及其内部各岩组之间关系的认识一直存在分歧.为了限制古元古代变沉积岩(辽河群)的沉积时限及其内部各层位间关系,选择辽东地区高家峪组火山岩进行锆石U-Pb LA-ICP-MS年代学研究.测年结果显示高家峪组代表岩石成岩年龄的岩浆活动有4期2179~2145 Ma、2079 Ma、1985 Ma、1928 Ma.结合前人已发表辽河群火山岩年代学数据显示,辽河群火山活动主要集中在3期:第1期(2210~2140 Ma)早期岩浆活动主要为酸性火山岩,在末期显示双峰式火山岩组合;第2期(2100~2050 Ma)岩浆活动以基性岩浆活动为主;第3期(2000~1960 Ma)岩浆活动也显示双峰式火山岩组合.辽河群火山岩的形成年龄将其沉积时限限制于2229~1928 Ma,沉积作用至少持续了300 Ma.火山岩年代学结果显示,辽河群浪子山组、里尔峪组、高家峪组和大石桥组火山岩形成时代呈现互相交替穿插关系,没有显示规律性的上下有序关系.结合野外辽河群各岩组之间多以韧性剪切带形式接触,认为辽河群各岩组之间不是从底到顶的有序沉积,而是"整体无序,局部有序".

There are a large number of meta-sedimentary-volcanic strata in the Paleoproterozoic Liaoji belt between Longgang block and Langlin block,which is called Liaohe Group.There has been a debate on the sedimentary time of the Liaohe Group and the relationship among its inner groups.In order to solve these problems,the zircon U-Pb LA-ICP-MS geochronology of the volcanic rocks from the Gaojiayu Formation in the eastern Liaoning Province is studied.The dating results show that the magmatic activities of the Gaojiayu Formation can be divided into four stages:2179-2145 Ma,2079 Ma,1985 Ma and 1928 Ma.Combining with the published chronological data,the volcanic activities in the Liaohe Group are mainly concentrated in three stages:the early magmatic activity in the first stage(2210-2140 Ma)is mainly acid volcanic rock,showing bimodal volcanic rock assemblage in the late stage;the second stage(2100-2050 Ma)magmatism is dominated by basic magmatism;the third stage(2000-1960 Ma)magmatism also shows bimodal volcanic rock assemblage.The sedimentary time of the Liaohe Group is limited to 2229-1928 Ma by the age of the volcanic rocks,and the deposition lasts at least 300 Ma.The chronological results show the ages of the of volcanic rocks in the Langzishan Formation,Lieryu Formation,Gaojiayu Formation and Dashiqiao Formation of Liaohe Group are alternant,and there is no regular upper-lower orderly relationship.In combination with the fact that the formations of Liaohe Group in the field mostly contact in the form of ductile shear zone,it is considered that the rock groups of Liaohe Group are not orderly sedimentary from the bottom to the top,but"disordered as a whole and orderly as a part".