郯庐断裂带张八岭隆起段晚中生代岩浆岩继承锆石U-Pb年代学:源区属性及构造意义  

Inherited zircon U-Pb geochronology of the Late Mesozoic igneous rocks from the Zhangbaling uplift segment of the Tan-Lu Fault Zone: Magma source affinity and its tectonic implications

作　　者：谢成龙[1] 陈娟[1] 刘友勤 朱晓超[1] 牛漫兰[1] 向必伟[3] 

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009 [2]云南地质工程勘察设计研究院,昆明650041 [3]安徽大学资源与环境工程学院,合肥230601

出　　处：《岩石学报》2016年第4期976-1000,共25页Acta Petrologica Sinica

基　　金：国家自然科学青年基金项目(40902064);面上基金项目(41472194)联合资助

摘　　要：大别与苏鲁造山带之间的郯庐断裂带张八岭隆起段,构成了华北与扬子板块之间的断裂边界。该边界带的深部结构状态长期以来存在着不同的认识。本文利用张八岭隆起带沿线出露的晚中生代岩浆岩中继承锆石U-Pb年代学信息,结合地球物理资料及Nd、Pb、Hf同位素资料,分析了其深部的岩浆源区属性及结构状态。张八岭隆起带北段晚中生代岩浆岩继承锆石年龄以1.9-2.7Ga为主,最大峰值年龄为2.5Ga;南段继承锆石年龄以2.2-2.6Ga为主,峰值年龄也为2.5Ga;郯庐断裂带庐江段则以含大量新元古代锆石为特征,在0.7Ga形成显著的分布峰值,并有早元古和少量太古代年龄信息。分析结果表明,张八岭隆起带北段的晚中生代岩浆岩源区为华北下地壳,南段的源区兼有华北和扬子陆壳的信息,而更南部庐江段则以扬子地壳源区为特征。电法剖面揭示,郯庐断裂主边界在张八岭隆起带下向南东倾斜,从而深部存在华北地壳;而南部庐江段转变为向北西陡倾,从而深部皆为扬子地壳。郯庐断裂深部产状特征支持其印支期应为斜向汇聚边界。而其中三叠纪继承锆石的缺失指示隆起带上变质岩应为原地岩石,而非来自大别造山带。The Zhangbaling uplift segment of the Tan-Lu Fault Zone between the Dabie and Sulu orogenic belts constitutes a fault boundary between the North China and Yangtze plates. Deep texture of the boundary belt remains controversial for a long time. In this paper,we use geochronology data of inherited zircon from the Late Mesozoic igneous rocks along the belt,combined with geophysical and Nd,Pb,Hf isotope data,to analyze magma source affinity and its deep texture. The inherited zircon U-Pb ages of the Late Mesozoic igneous rocks from the northern part of the Zhangbaling uplift mainly range from 1. 9 to 2. 7Ga,and the peak age is about2. 5Ga,ages from the southern party mainly range from 2. 2 to 2. 6Ga,and the peak age is also about 2. 5Ga,but ages from the Lujiang part have a distribution of peak at 0. 7Ga,and also have Early Proterozoic and a small amount Archean information. These data show that the magma source is lower crust of the North China Plate for the Late Mesozoic igneous rocks in the northern part,mixture of the North China and Yangtze plates for the southern part and lower crust of the Yangtze Plate for the Lujiang part. Electrical profiles show that the Tan-Lu main boundary fault dips SE below the Zhangbaling uplift belt whereas it dips NW steeply below the Lujiang part,leading to the presence of the North China crust below the Zhangbaling uplift belt and only Yangtze crust below the Lujiang part. The deep attitudes of the Tan-Lu Fault Zone are consistent with features of the Indosinian oblique convergence boundary. The lack of Triassic inherited zircon suggests that metamorphic rocks in the Zhangbaling uplift belt belong to autochthonous rocks,rather than from the Dabie orogenic belt.

关 键 词：郯庐断裂带 张八岭隆起带 岩浆岩 继承锆石 晚中生代 深部结构 

分 类 号：P588.3[天文地球—岩石学]