摘要
北秦岭晚古生代—晚中生代花岗岩类的Ｎｄ，Ｓｒ同位素研究表明：具低放射成因Ｐｂ同位素组成的花岗质岩基主要是南秦岭基底变质岩深熔的产物；而具高放射成因Ｐｂ同位素组成的原地、半原地型花岗岩类是北秦岭丹凤群有关岩石深熔和交代作用形成的产物．它们都可分为Ｉ型和Ｓ型，并可同时共存，岩浆源区中都有基性岩石物质的加入，其区别是基性岩类物质对Ｉ型花岗岩类的贡献分数较大，具有较小的亏损地幔模式年龄；由于岩浆源区中不同物质组成的混合，花岗岩类的亏损地幔模式年龄并不代表真实的壳幔分异事件的年龄．从新元古代到晚中生代，Ｉ型花岗岩类的ｄ（ｔ）和ＴＤＭ具逐渐变小的趋势，反映了地壳中基性岩石物质发生深熔作用的时间逐渐变晚，而Ｓ型花岗岩类的ｄ（ｔ）增大，ＴＤＭ变小，反映了基性岩石物质加入比例的增大。
Geochemical characteristics of Sr,Nd and Pb isotopes in Late Paleozoic-Mesozoic granitoids from Northern Qinling belt show that granitoid batholiths with lower ratios of radiogenic lead isotopes are anatectic products of mixture of metabasalts and metasediments from the basement of the Southern Qinling belt,due to subduction of southern Qinling basement beneath the northern Qinling during continent-continent collision.Innate or subautochthonous granitoids intruding into the Danfeng Group were produced via anatexis and metasomatism of related metavolcanics and metasediments in Danfeng Group under high temperature and pressure in response to the collision.The granitoids can be classified into S-and I-types according ε Nd (t) , ε Nd (t) and T DM .S-type and I-type granitoids may coexist in a multiple batholith.The metabasalts were involved in formation of the two types of granitoids.I-thpe granitoids anre characterized by higher ε Nd (t) and lower T DM compared to S-type granitoids.Because of mixing,the Nd model ages of these granitoids might not represent real crust-mantle separation event.From Neoproterozoic to Mesozoic, ε Nd (t) and T DM of I-type granitoids showed decreasing trend,which reflects decreasing age of fractionation event of metabasalts; ε Nd (t) increases and T DM decreases for S-type granitoids,which indicates increasing involvement of metasediments and suggests stronger magmatism during collision.
出处
《地球科学（中国地质大学学报）》
CSCD
北大核心
1996年第5期481-486,共6页
Earth Science-Journal of China University of Geosciences
基金
地质矿产部壳幔体系组成
物质交换及动力学开放研究实验室基金
国家自然科学基金
关键词
花岗岩
钕
锶
铅
同位素
地球化学
Late Paleozoic
Mesozoic
granitoid
Nd-Sr isotopes
magma source
Northern Qinling.
