华北克拉通北部迁安紫苏花岗岩LA-ICP-MS锆石U-Pb定年、地球化学及地质意义  

Zircon U-Pb geochronology and geochemistry of charnockitic rocks from Qian'an in the northern part of North China Craton: Implications for petrogenesis and tectonic setting

作　　者：韩鑫[1] 裴磊[1] 郑媛媛[1,2] 刘俊来[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]河南省地质矿产勘查开发局第二地质勘查院,郑州450000

出　　处：《岩石学报》2016年第9期2823-2838,共16页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划"973"项目(2012CB416806);中国地质调查局项目(12120114026901)联合资助

摘　　要：紫苏花岗岩是太古宙高级变质地体的主要物质组成,对其开展岩石成因与年代学研究,可深入理解早期大陆生长及其机制。本文以迁安紫苏花岗岩为窗口,探讨其成因与机制,通过精确的LA-ICP-MS锆石U-Pb测年获得其成岩年龄为2544±22Ma,指示了新太古代晚期的一次岩浆活动。岩石变质年龄为2475±87Ma,证明随后的高级变质作用年龄范围为2439-2501Ma。岩石地球化学研究表明：迁安紫苏花岗岩SiO2=59.14%-66.97%,MgO=1.62%-3.12%,富Ba（574×10-6-1572×10-6）,LREE（（La/Yb）N=22.3-79.0）,亏损HFSE,不存在Eu负异常（δEu=1.76-3.43）,其高Sr/Y值（85-179）与（La/Yb）N值指示了与TTG的相关性。结合样品地球化学特征及锆石U-Pb年龄分析,并与本区域大地构造背景相结合,迁安紫苏花岗岩可能是角闪岩相条件下偏中性含水玄武质原岩高温部分熔融的产物,应当形成于地幔柱背景。Charnockite, one of the dominant lithologies in many Precambrian high-grade metamorphic terranes around the world, provides important clues for the history and mechanism of early crustal growth. However, its genesis is still debated. Charnoekitic rocks in Qian＇ an are outcropped in eastern Hebei, in the northern part of the Eastern Block of the North China Craton. LA-ICP-MS U-Pb dating of zircon grains from the charnoekitic rocks shows that 22 dated spots can be subdivided into two groups. A first group of 6 spots with a weighted mean age of 2544 ± 22Ma is suggested to represent the ages of magrnatic crystallization. Another group of 16 spots is interpreted to represent a later thermal event, attesting to a major phase of a metamorphism during 2439 -2501Ma, with a weighted mean age of 2475 ± 87Ma, subsequent to the Late Neoarehean magmatism. The charnockitic rocks have SiO2 of 59. 14% -66. 97%, MgO of 1.62% - 3.12%, with enrichment in Ba （ 574× 10^ -6 - 1572 × 10 ^-6 ）, LREE （ （La/Yb） N = 22. 3 - 79. 0） and depletion in HFSE, and weak or no negative Eu anomalies （δEu = 1.76- 3.43 ）. In general, their high Sr/Y （ 85 - 179） and （La/Yb） N values are attributed to their TFG affinities. Combined geochemical and zircon U-Pb age analysis, and field and petrographic observations suggest that the charnockitic rocks from Qian＇ an were originated from high-temperature melting of moderately hydrous basaltic source rocks at amphibolite facies. A mantle plume model is favored from the geochemical characteristics, which well explains the petrogenesis of charnockites, and many other geological features in the Eastern Block of the North China Craton as well.

关 键 词：锆石U-PB定年 地球化学 迁安紫苏花岗岩 华北克拉通 地幔柱 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]