峨眉山玄武岩结构面类型及成生规律

Types and formation law of structural planes of Emeishan basalt in Sichuan,China

通过研究中国西南地区峨眉山玄武岩地区修建的部分水电站的基础地质资料,以及东岩区、中岩区和西岩区峨眉山玄武岩产出的区域地质背景、岩石学、岩相学和地球化学特征,划分出峨眉山玄武岩的结构面类型,分别是:由不同软弱夹层构成的喷发间断结构面、岩浆侵入使围岩发生蚀变而形成的侵入、蚀变结构面,以及地表岩体由于风化卸荷而形成的风化卸荷结构面。根据不同岩区玄武岩的地质地球化学特征和形成环境,探讨了这些结构面的成生规律和分布特点。东岩区玄武岩喷发旋回多,凝灰岩和沉积岩夹层多而厚,结构面以凝灰岩夹层形成的层间错动带、冷凝收缩形成的柱状节理、火山爆裂式喷发形成的集块岩、火山角砾岩夹层构成的结构面为主;中岩区在大地构造上处于攀西裂谷核心地带,岩浆活动频繁,构造运动和变质作用异常强烈,侵入、蚀变结构面和风化卸荷结构面大量出现;西岩区由于玄武岩喷发环境为海相,燕山晚期和喜马拉雅期构造活动强烈,以枕状构造结构面、蚀变结构面和构造结构面最为发育。

This paper studies the basic geological data of some hydropower stations built on the Emeishan basalt in the southwest of China and the regional geological background and the characteristics of petrology,petrography and chemistry of the Emeishan basalt in the eastern,western and middle basalt areas.It identifies the structural plane types of the Emeishan basalt.They are the structural planes of the different weak interbeds,the invasion and alteration structural planes of the wall rock alteration by magma intrusion,and the weathering relaxation structural planes formed by the surface rock mass because of weathering relaxation.Based on the geological geochemical characteristics and the formation environment of the basalts from different areas,this paper discusses the generative regularities and distribution features of these structural planes.In the eastern basalt area,there are many eruption cycles of basalt,many and thick tuff and sedimentary rock interlayers,and the main structural planes are consist of the inter-laminar dislocation band formed by tuffaceousinterbeds,the columnar joint of condensation and shrinkage,and the agglomerate and volcanic breccia interbeds formed by volcanic burst eruption.In the middle basalt area located in the Panxi rift focal area in geotectonic,there are frequent magmatic activities,extremely intensive tectonic movements and metamorphism,and a large number of structural planes of invasion,alteration,weathering and relaxation.In the western basalt area,because the basalt eruption environment is marine,having the violent tectonic activities of Yanshan and Xishang period,the pillow structural plane and alteration and tectonic structural plane develop best.