摘要
通过对羌塘盆地火山岩(含少数侵入岩)的锶(Sr)、钕(Nd)和铅(Pb)同位素地球化学的研究,获得中、新生代不同类型火山岩和花岗岩类Sr同位素比值大多数为0.706～0.710,ε_(Nd)值为-0.54～-8.1,均为负值,^(206)Pb/^(204)Pb值为17.1493～19.0313,^(207)Pb/^(204)Pb值为15.4350～15.666,^(208)Pb/^(204)Pb值为37.566～39.072。根据同位素地球化学特征,中生代火山岩物质主要来源于富集地幔区和下地壳,原始岩浆为壳幔混合型,可能与造山带的岛弧—活动陆缘环境有关。早第三纪火山岩岩浆来自富集幔源区,与大陆拉张环境有关。第四纪火山岩形成于高钾熔岩区内,与俯冲环境有关。总之,本区的火山岩中生代为造山带火山岩,新生代(主要为早第三纪)为大陆裂谷带火山岩。
Sr, Nd and Pb isotope geochemical studies have been made of the volcanic rocks (including some intrusive rocks) in the Qiangtang basin on the Qinghai-Tibet plateau. The Sr isotope ratios of different types of Meso-Cenozoic volcanic rocks and granites range mostly from 0. 706 to 0. 710 and the ε_(Nd) values are all negative, ranging from -0. 54 to -8. 1; the ^(206)Pb/^(204)Pb, ^(207)Pb/ ^(204)Pb and ^(208)Pb/^(204)Pb ratios are 17. 1493～19. 0313, 15. 4350～15. 666 and 37. 566～39. 072, respectively. According to these isotope geochemical data, the authors suggest that the materials of Mesozoic volcanic rocks were mainly derived from the enriched mantle and the lower crust, and that the primary magma might be of the crust-mantle mixing type and possibly related to the island arc-active continental-margin environment of an orogenic belt. The magma of Paleogene volcanic rocks was derived from the enriched mantle source area and associated with a continental extensional environment. Quaternary volcanic rocks were originated in a high-K lava area and related to a subduction environment. Therefore the Mesozoic and Cenozoic (mainly Paleogene) volcanic rocks in the study area are represented by volcanic rocks of the orogenic belt and those of the continental rift zone respectively.
出处
《地质论评》
CAS
CSCD
北大核心
1999年第S1期946-951,共6页
Geological Review
基金
中国石油天然气集团公司 青藏"九五"科技攻关项目中"羌塘盆地火成岩综合研究"的成果
关键词
青藏羌塘盆地
中、新生代
火山岩
同位素地球化学
Qiangtang basin
Qinghai-Tibet plateau
Mesozoic
Cenozoic
volcanic rock
isotope geochemistry
