辽东宽甸和三家子地区花岗伟晶岩的锆石U-Pb年代学及其地质意义  

Zircon U-Pb dating and its geological significance of granitic pegmatites from the Kuandian and Sanjiazi area in eastern Liaoning Province

作　　者：杨红[1] 王伟[1] 刘建辉[1] YANG Hong WANG Wei LIU JianHui(Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China)

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2017年第9期2675-2688,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金重点项目(41430210);中国地质调查局地质大调查项目(DD20160121);中国地质科学院地质研究所基本科研业务经费(J1612;YYWF201703)联合资助

摘　　要：辽东宽甸和三家子地区辽河群中广泛存在花岗质伟晶岩脉或岩体,对其进行研究具有重要的构造意义。本文对两个地区侵入辽河群中的花岗伟晶岩样品进行岩石学、锆石LA-ICP-MS稀土微量元素和U-Pb定年的综合研究,获得侵入不同岩组地层中伟晶岩的原岩年龄,并对其成因和构造环境进行了探讨。花岗伟晶岩主要矿物组合为石英+钾长石±钠长石±电气石±白云母,中粗粒结构或伟晶结构,块状构造。宽甸地区侵入高家峪组大理岩中的二处伟晶岩样品年龄分别为1842±7Ma和1864±8Ma;三家子地区侵入里尔峪组地层的二处伟晶岩样品年龄分别为1876±11Ma和1871±7Ma,侵入大石桥组的伟晶岩岩体年龄为1802±15Ma,侵入盖县组地层的伟晶岩年龄为1740±8Ma。宽甸地区伟晶岩(年龄1.86~1.84Ga)锆石阴极发光具振荡环带,Th/U大多>0.1,稀土配分模式主要显示岩浆锆石的特征,在Ce/Ce*-(Sm/La)_N图解上显示近岩浆锆石区域,花岗伟晶岩脉熔体可能是母岩浆初步结晶分异后的产物,较大保留了母岩浆的性质;三家子地区3个样品(年龄1.87~1.74Ga)锆石微区具低亮度无结构特征、Th/U<0.1,稀土配分模式显示热液锆石特征,在Ce/Ce*-(Sm/La)_N图解上偏热液锆石区域,此花岗伟晶岩脉可能是母岩浆高度结晶分异后的残余热液结晶而成,偏热液性质。三家子1个样品(年龄1.87Ga)锆石具弱振荡环带,ΣREE值较低,Eu/Eu*主要介于0.00~0.60,HREE总量低且平缓,显示深熔成因,其伟晶岩脉熔体可能直接来自含石榴石的原岩部分熔融而成的深熔脉体。本文研究的多期次花岗伟晶岩或与辽吉造山带周围1.89~1.82Ga的S型或I型花岗岩和深熔脉体具有亲缘关系,即大部分伟晶岩可能与1.89~1.82Ga的花岗质岩浆作用有关,一部分则与变质沉积岩系的深熔作用有关。从构造环境来看,辽吉造山带在碰撞后的构造折返过程中,从~1.87Ga到~1.74Ga至少130Myr的时间里�Granitic pegmatites intruded into the Liaohe Group are widely outcropped in the Kuandian and Sanjiazi area in eastern Liaoning Province, study of which is of important tectonic significance. In this study, petrology, zircon LA-ICP-MS trace element and REE analysis and U-Pb dating were conducted, petrogenesis of pegmatites and tectonic settings are then discussed. Granitic pegmatites have the main mineral assemblages of quartz ＋ K-feldspar ＋ albite ＋ tourmaline ～ muscovite with medium-coarse grained texture or pegmatitic texture and massive structure. Two samples of pegmatite intruded into Gaojiayu Formation of the Liaohe Group in Kuandian area achieved U-Pb ages of 1842 ～ 7Ma and 1864 ～ 8Ma. Two samples of pegmatite intruded into Lieryu Formation of the Liaohe Group in Sanjiazi area achieved U-Pb ages of 1876 ～llMa and 1871 ～ 7Ma. Pegmatite intruded into the Dashiqiao Formation and Gaixian Formation achieved U-Pb ages of 1802 ～ 15Ma and 1741 ～ 8Ma, respectively. Zircons of pegmatites from the Kuandian area have oscillating band in the cathodoluminescence （CL） images, REE patterns of magmatic zircons and Th/U ratios of 〉 0. 1, and are close to the magmatic region in the Ce/Ce ＊-（Sm/La） ～ discrimination diagram. The Kuandian pegmatites may be crystallized from residues after the preliminary fraction of parental magma. Zircons of three samples from the Sanjiazi area have weak and textureless CL images, REE patterns resembling hydrothermal zircons and Th/U ratios of 〈 O. 1, and are close to the hydrothermal region in the Ce/Ce＊ - （Sm/La） N discrimination diagram. The Sanjiazi granitic pegmatites may be originated from hydrothermal fluid after the highly fractional crystallization of parental magma. Zircons of one sample from the Sanjiazi area have weak oscillating band, low EREE, Eu/Eu＊ = 0.00 ～ 0.60 and low and flat HREE pattern, which indicates the anatectic origin from the partial melting of garnet-bearing host rock. Granitic pegmatites may have genetic relationships w

关 键 词：胶-辽-吉带 花岗伟晶岩 辽河群 辽吉花岗岩 锆石U-PB定年 

分 类 号：P588.3[天文地球—岩石学]