Geochemistry of early Paleozoic alkali dyke swarms in south Qinling and its geological significance  

作　　者：张成立 高山 张国伟 柳小明 于在平 

机构地区：[1]The Key Laboratory of Northwest University Continental Dynamics, Ministry of Education and Department of Ge-ology, Northwest University, Xian 710069, China [2]State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, China [3]Department of Geochemistry, China University of Geosciences, Wuhan 430074, China

出　　处：《Science China Earth Sciences》2003年第12期1292-1306,共15页中国科学（地球科学英文版）

基　　金：the Key National Natural Science Foundation of China(Grant Nos.40032010-C,40133020,49732080);Foundations of Higher Visiting Scholarship of High Education Colleges in Western Areas and Backbone Teacher of Ministry of Education of China(Grant No.[2000]143).

摘　　要：The early Paleozoic alkali dyke swarms in the Ziyang-Langao areas of south Qinling are characterized by bimodal volcanic association. They show the patterns of enriched LREE with high fractionation of light and heavy REE and enrichment of incompatible elements in the primitive man-tle-normalized spider-diagrams with peaks of Ba and Nb and valleys of Pb and Sr. The ratios of Ta/Hf are larger than 0.3 and those of Th/Ta less than 1.6, indicating that they were derived from enriched mantle sources closely related to plume. The occurrence of alkali dyke swarm demon-strates an extensional event of crust resulting from deep plume activity in the Qinling orogeny dur-ing early Paleozoic. The rifting extension could not continue due to the short activity of plume. Consequently, no new oceanic basin was formed.The early Paleozoic alkali dyke swarms in the Ziyang-Langao areas of south Qinling are characterized by bimodal volcanic association. They show the patterns of enriched LREE with high fractionation of light and heavy REE and enrichment of incompatible elements in the primitive mantle-normalized spider-diagrams with peaks of Ba and Nb and valleys of Pb and Sr. The ratios of Ta/Hf are larger than 0.3 and those of Th/Ta less than 1.6, indicating that they were derived from enriched mantle sources closely related to plume. The occurrence of alkali dyke swarm demonstrates an extensional event of crust resulting from deep plume activity in the Qinling orogeny during early Paleozoic. The rifting extension could not continue due to the short activity of plume. Consequently, no new oceanic basin was formed.

关 键 词：ALKALI DYKE swarms  rift  activity of plume  early Paleozoic  south Qinling. 

分 类 号：P542.3[天文地球—构造地质学]