辽东黄花甸-苏子沟地区南辽河岩群里尔峪岩组变沉积岩碎屑锆石LA-ICP-MS U-Pb年代学及其地质意义

辽东黄花甸-苏子沟地区南辽河岩群里尔峪岩组主要为一套原岩以含硼火山-沉积夹陆源碎屑岩的变质岩石组成，岩石类型主要为长英质粒状岩石（浅粒岩-变粒岩组合）。前人长期在该活动带上进行深入的研究，在区域构造、地球化学、同位素年代学研究以及构造演化等方面积累了大量资料，取得了一系列重要进展。但是，有关其里尔峪岩组的变质作用时代、沉积时代、源区特征以及辽河岩群乃至整个胶-辽-吉活动带的大地构造属性和形成的构造演化过程长期以来存在着裂谷开启-闭合模式、弧-陆碰撞模式和陆-陆碰撞模式的争论。笔者旨在辽东黄花甸-苏子沟等地区开展1：5万区域地质调查的基础上，选择黄花甸-苏子沟地区里尔峪岩组的透闪斜长变粒岩、电气黑云二长变粒岩和黑云斜长变粒岩为重点研究对象。通过锆石阴极发光图像特征和锆石U-Pb （LA-ICP-MS，下同）年代学测试，综合限定研究区里尔峪岩组变质沉积岩的物质来源、原岩形成时代及变质变形时代。测试结果显示锆石阴极发光图像具核-边结构，核部具振荡环带，Th/U值较高（Th/U=0.02~2.37），表明部分锆石来源于岩浆，少部分锆石来源于后期的变质变形作用。年代学分析结果表明，这些碎屑锆石U-Pb年龄分别得到~1 900 Ma、~2 182 Ma和~2 511 Ma三个主峰值以及~2 030 Ma、~2 076 Ma、~2 110 Ma、~1 900 Ma、~2 312 Ma、~2 452 Ma、~2 715 Ma、~2 796 Ma、~3 537 Ma等8个次峰值。综合前人研究成果，研究区里尔峪岩组的原岩形成时代应晚于~2 030 Ma，其沉积作用应发生于2 030~1 946 Ma；峰期变质作用年龄为~1 900 Ma，变质变形作用应发生于1 837~1 946 Ma。该区里尔峪岩组碎屑锆石的年龄频谱特征显示，其沉积物主要来源于胶-辽-吉活动带内2 000~2 200 Ma的中酸性岩浆岩、辽吉花岗岩及辽河岩群火山岩，少部分来自北侧龙岗地块的太古宙结晶基底。胶-辽-吉活动带至少还存在一期2 000~2 100 Ma的中酸性岩浆活动。

Detrital Zircon LA-ICP-MS U-Pb Geochronology of Metasedimentary Rocksfrom Li'eryu Petrofabric of South Liaohe Group in Huanghuadian-Suzigou Area,East Liaoning and Its Geological Significance

The Li'eryu petrofabric of South Liaohe Group mainly is a set of boron-bearing volcanic-sedimentary metamorphic rocks in Huanghuadian-Suzigou area, East Liaoning. It mainly consists of quartzo-feldspathic rocks (leptite-leptynite unit). After a long-term, depth and extensive geological study in this area, abundant of new data and interpretations of tectonic, geochemisty, isotopic geochronology and tectonic evolution have been obtained. However, their metamorphic time, depositional time, protolith characteristics and tectonic evolution are still controversy. The debates focus on three major tectonic evolution models of Liaohe group and all Jiaodong-Liaoning-Jilin mobile belt in North China Craton, which include continent-arc collision, continent-continent (terranes) collision and rifting models. The Di-Pl leptynite, Tou-Bt two-feldspathic leptynite and Bt-Pl leptynite from Huanghuadian-Suzigou area have been selected as the research objects in this paper, based on the new data about 1:50000 regional geological survey of East Liaoning. The Cathodoluminescence (CL) imaging and LA-ICP-MS U-Pb zircon data are linked to unravel the origin, depositional and metamorphic time of the Li'eryu petrofabric. Zircon grains separated from three samples show core-rim structure. The zircon cores show oscillatory zoning and have high Th/U ratios (Th/U=0. 02~2.37), suggests that some zircons were derived from magma and a small number of zircons from metamorphic deformation in the late stage. The chronological results show that these detrital zircon U-Pb ages respectively have three main peaks at~1 900 Ma,~2 182 Ma and~2 511 Ma, as well as eight secondary peaks at~2 030 Ma,~2 076 Ma,~2 110 Ma,~1 900 Ma,~2 312 Ma,~2 452 Ma,~2 715 Ma,~2 796 Ma and~3 537 Ma. Integrated predecessors' research results, the formation time of original rock from Li'eryu petrofabric should be later than~2 030 Ma; its sedimentation happened at 2 030~1 46Ma; Peak metamorphism age was~1 900Ma and the metamorphic deformation occurred at 1 837~1 946 Ma. The detrital zircon age spectrum characteristics of Li'eryu petrofabric show that the sediments mainly soured from acidic magmatic rocks, Liaoji granite and volcanic rocks of Liaohe group in Jiaodong-Liaoning-Jilin mobile belt with the ages of 2 000~2 200 Ma, and a few of them came from archean crystalline basement of Longgang terrane at its north side. At least, an intermediate-acid magmatic activity with an age of 2 000~2 100 Ma was occurred in the Jiaodong-Liaoning-Jilin mobile belt.