东秦岭北部富碱侵入岩钕、锶、铅同位素特征及构造意义

Nd, Sr, Pb isotopic geochemistry of the alkali- rich intrusive rocks in East Qinling, central China and its tectonic significance

东秦岭北部富碱侵入岩主要分布在陕西省洛南与河南省卢氏-确山一带，岩石有碱性岩、碱性花岗岩和石英正长岩三大类。岩石Nd、Sr和Pb同位素地球化学的研究表明,该区富碱侵入体的源区应是以下地壳为主，并通过碰撞造山作用带入少量地幔和上地壳物质。源区同位素组成横向与垂向的不均一性说明华北块体存在成熟的下地壳层，而北秦岭块体是造山带环境。古大陆边缘经历了多次裂解作用和多期碱性岩浆活动；碱性岩浆是在减压扩容环境中再次熔融侵位，形成于松弛和张性构造环境。

The alkali- enriched intrusive rocks in the northern part of East Qinling, central China are mainly located in Luonan- Lushi- Queshan area, and their occurrences are controlled by a regional tectonic zone. The intrusive rocks are characterized by multiple alkali- rich complex intrusions. Based upon systematic petrographic and geochemical studies, the intrusive rocks are divided into three types, i.e. alkaline rock, alkali granite and quartz syenite. The tectogenesis and the mechanism of alkali- rich magmatic emplacement in this area are discussed on the basis of a detailed study on the petrochemistry and Nd, Sr, Pb isotopic geochemistry of the alkali- rich intrusive rocks. This indicates that multiple splitting and multiple phases of alkaline magmatic activity have been taken place on the paleocontinental margin. Analysis of rock assemblages, structure and magma source and physical- chemical conditions shows that alkali magma can derive from crust and may be formed in a post- orogenic flabby and extensional structural environment.