加拿大纽芬兰岛Indian Head Range地块格林威尔期二长花岗岩年龄、Nd⁃Hf同位素特征——块体属性与演化新证据

Age and Nd⁃Hf isotopic characteristics of the Greenville monzogranite in the Indian Head Range block,Newfoundland,Canada:New evidence for block attributes and evolution

加拿大阿巴拉契亚造山带纽芬兰岛Humber带基底地块属性及地壳生长演化是近年来关注的科学问题,尤其是岛内西南部的Indian Head Range地块,其年龄组成与同位素特征研究对区域基底构造属性划分与对比至关重要。本文对Indian Head Range地块内的二长花岗岩岩体进行了锆石U⁃Pb定年,得到其^(206)Pb/^(238)U加权平均年龄值为1149±4 Ma,代表该岩体的侵位年龄。这一定年结果表明该岩体具有中元古代晚期的年龄,为该地块格林威尔期岩浆事件的存在提供了新的年龄证据。Nd⁃Hf同位素分析结果显示,该二长花岗岩岩体εNd值为-2.3,εHf值介于+1.93~+3.65之间,两阶段Hf模式年龄介于1.84~1.73 Ga之间。结合前人研究,我们认为Humber带内各地块发育约1.5 Ga、1.15 Ga和1.0 Ga的3期花岗质岩浆事件,它们具有相似的Hf模式年龄值,暗示它们均来源于古元古代新生地壳物质的再造。带内格林威尔基底地块均为原地基底,且与劳伦大陆远端东部边缘具有一致的岩浆-构造演化史。以上研究对Humber带内格林威尔基底地块的亲缘性及地壳生长提供新的制约,并为阿巴拉契亚造山带内古老微陆块的溯源对比提供依据。

The basement properties and crustal growth of the Humber belt of Newfoundland Island in the Appalachi⁃an orogenic belt,Canada,have been the focus in recent years.In particular,the age composition and isotopic char⁃acteristics of the Indian Head Range block in the southwestern part of Newfoundland are significant for dividing and comparing the tectonic attributes of the regional basement.In this paper,the zircon U⁃Pb dating of the monzogranite pluton in the Indian Head Range block shows that the pluton has a late Mesoproterozoic age(1149±4 Ma),which provides new age evidence for the existence of the Greenville magmatic events in the block.The results of the Nd⁃Hf isotope study show that theεNd value of the monzogranite is-2.3,theεHf value varies from+1.93 to+3.65,and the tDM2 age ranges from 1.84 to 1.73 Ga.Combined with previous studies,the authors believe that three stages of granitic magmatic events of~1.5 Ga,~1.15 Ga,and~1.0 Ga occurred in each block in the Humber belt,which have similar Hf model ages,suggesting that they all originated from the reconstruction of Pal⁃eoproterozoic juvenile crustal materials.The Greenville basement blocks in the Humber belt are all in⁃situ base⁃ments,and have the same magmatic⁃tectonic evolution history with the eastern margin of the far end of Laurentian continent.The results of this study provide new constraints on the affinity and crustal growth of the Greenwell base⁃ment in the Humber belt,and provide a basis for the traceability and comparison of ancient micro⁃continents in the Appalachian orogen.