扬子西北缘碧口块体花岗质岩体锆石U-Pb年龄、Hf同位素特征及其地质意义  

Zircon U-Pb Ages and Hf Isotope Characteristics of the Granitic Plutons in Bikou Terrane,Northwestern Yangtze Block,and Their Geological Significance

作　　者：平先权[1] 郑建平[1] 熊庆[1] 张志海[1] 夏冰[1] 

机构地区：[1]中国地质大学地球科学学院,武汉430074

出　　处：《吉林大学学报（地球科学版）》2014年第4期1200-1218,共19页Journal of Jilin University：Earth Science Edition

基　　金：国家自然科学基金项目(91214204)

摘　　要：对扬子西北缘碧口块体中白雀寺和大安花岗质岩体进行了锆石 U-Pb 定年及 Hf 同位素研究。结果表明，白雀寺岩体的年龄分2组：（855±6）Ma（n＝23）和（917±14）Ma（n＝3）。前者εHf （t）为3．8～10．4，一阶段 Hf 模式年龄为1．00～1．27 Ga；后者εHf （t）为2．0～8．1，一阶段 Hf 模式年龄为1．14～1．40 Ga。而大安岩体给出了6组不同的年龄：（854±10）Ma（n＝3）、（801±7）Ma（n＝3）、（702±10）Ma（n＝3）、（565±6）Ma（n＝1）、（246±7）Ma（n＝1）和（207±2）Ma（n＝1）。其εHf （t）为-12．6～11．4（t ＝854 Ma），一阶段和二阶段 Hf 模式年龄分别为0．95～1．90 Ga 和1．02～2．55 Ga。白雀寺和大安岩体的侵位年龄分别为（855±6）Ma 和（854±10）Ma，代表了扬子西北缘碧口块体内的一次重要岩浆事件，前者主体来源于中元古代新生陆壳源区，而后者主要来源于中元古代新生陆壳与晚太古代地壳物质的混合源区。此外，白雀寺岩体中（917±14）Ma 的年龄代表新元古代早期的岩浆活动，而大安岩体中年轻的年龄可能记录着岩体后期所经历的复杂热改造事件。The Baiquesi and Daan granitic plutons on the northwestern margin of the Yangtze block have been investigated by zircon U Pb dating and Hf isotope analysis.Research results indicate that U-Pb ages of zircons in the Baiquesi pluton can be divided into two groups：（855±6）Ma （n=23）and （917± 14）Ma （n=3）.TheεHf （t）values of the former are 3.8 10.4,and the one-stage Hf isotope model age varies from 1.00 to 1.27 Ga;TheεHf（t）values of the latter are 2.0 8.1,and the one-stage Hf isotope model are 1.14 1.40 Ga.However,the ages of the Daan pluton can be divided into six＆amp;nbsp;groups：（854±10）Ma （n=3）,（801±7）Ma （n=3）,（702±10）Ma （n=3）,（565±6）Ma （n=1）, （246±7）Ma （n=1）and （207±2）Ma （n=1）.TheεHf（t）values of the Daan pluton are -12.6 11.4 （t=854 Ma）,and the one-stage Hf isotope model ages and the two-stage Hf isotope model ages are 0.95 1.90 Ga and 1.02 2.55 Ga.The Baiquesi and Daan plutons were emplaced at （855±6）Ma and （854 ± 10）Ma,respectively,which reflect a significant magmatic event in Bikou terrane,northwestern margin of Yangtze block,and the former was mainly derived from the Mesoproterozoic juvenile crustal source,while the latter was products of two end-member mixing magmas respectively sourced from the Mesoproterozoic juvenile crustal and the Neoarchean old crustal.In addition,the （917±14）Ma which is larger than the intruding age of the Baiquesi pluton represents the record of the Early Neoproterozoic magmatism.Ages which are smaller than the intruding age of Daan pluton probably record the subsequent modifications of other thermal events.

关 键 词：碧口块体 花岗质岩体 锆石U-PB年龄 HF同位素 扬子西北缘 岩石学 

分 类 号：P588.1[天文地球—岩石学]