赣南全南正长岩的SHRIMP锆石U-Pb年龄及其对华南燕山早期构造背景的制约  

SHRIMP U-Pb zircon age of the Quannan syenite,southern Jiangxi:Constraints on the early Yanshanian tectonic setting of SE China

作　　者：陈志刚[1] 李献华[1] 李武显[1] 刘敦一[2] 

机构地区：[1]中国科学院广州地球化学研究所,广东广州510640 [2]中国地质科学院地质研究所,北京100037

出　　处：《地球化学》2003年第3期223-229,共7页Geochimica

基　　金：中国科学院知识创新工程重要方向项目(KZCX2-102)

摘　　要：SHRIMP锆石U-Pb年龄测定结果表明,赣南全南正长岩的形成年龄为(161±4)Ma。受地壳混染影响程度最低的正长岩样品具高钾(K2O/Na2O≥1)、富集大离子亲石元素、轻稀土元素和高场强元素(Nb/La≈1.4、Nb/Th≈15)、εNd(t)≈+3.4的特征,属板内“裂谷型”钾质碱性岩(和桂东南地区侏罗纪正长岩类似),而明显不同于“岛弧型”钾质碱性岩。上述结果以及区域岩浆岩组合特征表明,华南内陆侏罗纪的构造环境类似于板内裂谷或“盆岭构造”。The SHRIMP U-Pb zircon results indic ate that the Quannan syenite from sou thern Jiangxi was formed at(161±4)Ma.The least crustal-contaminated syenites are enriched in K 2 O(K 2 O /Na 2 O≥1),LIL,LREE and HFS elements(La /Nb≈1.4,Nb /Th≈15)and display a positiveε Nd (t)value of +3.4.While these geochemic al features are similar to those of the i ntraplate,'rift-type'potassic alkaline rock such as the Ju rassic syenites from SE Guangxi,they differ significantly from those of the'arc-type'potassic alkaline rock.These new re sults,together with the igneous rocks associations of the study area,favor an intraplate extensional /rifting tectonic regime in SE China in the early Yanshanian time,w hich was probably similar to present -day Basin and Range Province in the western United States.

关 键 词：江西 正长岩 SHRIMP锆石U—Pb年龄 形成年龄 轻稀土元素 岩浆岩 岩浆活动 构造环境 中生代 

分 类 号：P588.122[天文地球—岩石学]