吉林省中部地区早古生代英云闪长岩的成因:锆石U-Pb年代学和地球化学证据  

Petrogenesis of the Early Paleozoic tonalite in the central Jilin Province:Evidence from zircon U-Pb chronology and geochemistry

作　　者：裴福萍[1] 王志伟[1] 曹花花[2] 许文良[1] 王枫[1] 

机构地区：[1]吉林大学地球科学学院,长春130061 [2]中国海洋大学海洋地球科学学院,青岛266003

出　　处：《岩石学报》2014年第7期2009-2019,共11页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划(2013CB429802);国家自然科学基金项目(41172057);吉林大学科学前沿与交叉学科创新项目(200903032);中国地质调查局项目(1212011085480;1212011085476)联合资助

摘　　要：本文对吉林省中部地区永吉县张家屯附近出露的早古生代英云闪长岩进行了LA-ICP MS锆石U-Pb年代学、地球化学及锆石Hf同位素的研究,探讨了该英云闪长岩的源区性质及构造背景。张家屯英云闪长岩出露面积约100m2,与其呈沉积接触关系的是具磨拉石建造特点的张家屯组地层。LA-ICP MS锆石U-Pb定年结果显示,张家屯英云闪长岩的形成时代为443±5Ma,即晚奥陶世-早志留世。该英云闪长岩的SiO2含量介于71.5%~72.9%,具有低K2O(0.22%~0.76%)、高Na2O(3.82%~4.49%)和低TiO2(0.30%~0.42%)的特征,属于低钾拉斑系列。其A/CNK值介于0.95~1.25,A/NK值介于1.71~1.94,主体属于I型花岗岩。张家屯英云闪长岩的稀土总量较低(15.3×10-6~23.4×10-6),具有轻重稀土弱分异[(La/Yb)N=5.01~5.60]和较平坦的重稀土分配型式,并具有明显的铕正异常(Eu/Eu*=1.85~2.59)。微量元素显示具有大离子亲石元素(Rb、Ba、Cs、Th)富集和高场强元素(Nb和Ta)亏损的特征。另外,它们具有正的εHf(t)值(+9.92^+13.6)和年轻的两阶段亏损地幔模式年龄(648~911Ma)。张家屯英云闪长岩的地球化学特征与超俯冲带弧前环境的斜长花岗岩的源区相似,可能来源于低压高温条件下大洋堆晶辉长岩的部分熔融,并有俯冲流体的参与。即张家屯英云闪长岩形成于俯冲背景下的岛弧环境,结合晚志留世-早泥盆世张家屯组磨拉石建造的沉积特征,揭示了加里东运动在华北板块北缘东段的存在。Northeast （NE） China is composed of a Paleozoic orogenic collage that is considered to be the eastern segmeht of the Central Asian Orogenic Belt （CAOB）. In the Paleozoic, NE China evolved from amalgamation of multiple microcontinental massifs, such as the Erguna, Xing＇an, Songnen-Zhangguangeai Range, Jiamusi, and Khanka from west to east. The Early Paleozoic tectonic evolutionary history between the microcontinental massifs and the North China Block （NCB） is the key for us to understand the Paleozoic evolution of the NE China. Recently, one of the key issues about the Paleozoic evolutionary history in the eastern segment of the northern margin of the NCB is whether or not the Early Paleozoic accretion belt existed. The previous studies considered that the Early Paleozoic accretion belt existed according to the Early Paleozoic igneous rock belt extending from west to east in the Jilin Province, while others are dubious about the whole idea because they have ascertained that some ＂Early Paleozoic＂ intrusion and strata including volcanic rock formed in the Late Paleozoic or Early Mesozoic based on zircon U-Pb dating. The issue clearly requires high precision data on the crystallization ages and geochemical data of the igneous rocks in this area. We conducted LA-ICP-MS zircon U-Pb dating and whole-rock geochemical analysis on ＂Caledonian granite＂ in the central Jilin Province, with the aim of constraining the tectonic setting of the eastern segment of the northern margin of the NCB during the Early Paleozoic. The study area in this paper is located at the north to the boundary of geosyncline-platform of the NCB, east to the Songliao Basin, west to the Dunhua-Mishan Fault, and south to Changchun-Yanji suture belt. The oldest strata in this area, Zhangjiatun Formation with the characteristics of molasse construction, distributing near the Zhangjiatun village, is composed of amaranth and motley conglomerate rock at the bottom, pebbly sandstone in the middle, and sihstone and red tuffaceous sihstone

关 键 词：早古生代 英云闪长岩 锆石U-PB年代学 地球化学 中国东北 华北板块北缘东段 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]