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前言碧口群变质火山岩带位于秦岑地槽和扬子地台两个大地构造的交界处。按李春昱对中国大陆板块构造的研究,岩带北侧为秦岑第二俯冲带,南侧为龙门山康滇地轴俯冲带(图1)。区内岩石主要有超基性岩及一套变质火山岩系。用数学地质方法研究火山岩化学组分的区域变化,对认识该区火山喷发特征及构造环境都十分有益。然而由于作者手头资料有限,本文仅对碧口群东段陕西省境内约两千余平方公里范围内的碧口群火山岩化学成份区域变化作初步研究,不妥之处请批评指出。
Bikou metamorphic volcanic rock belt is located in Qin Cen trough and the Yangtze platform two earth structures at the junction. According to Li Chunyu’s study on the tectonics of the Chinese mainland, the northern side of the rock belt is the second Qinchuan subduction zone and the south side is the Longmen Shan Kangdian subduction zone (Figure 1). There are mainly ultrabasic rocks and metamorphic volcanic rocks in the area. Using mathematical geologic methods to study the regional variation of volcanic rocks chemical composition is very useful for understanding volcanic eruptions and tectonic setting in this area. However, due to the limited data available at hand, this article only studies the changes of the chemical composition of the volcanic rocks in the Bikou volcano in Shaanxi Province within the area of about 2,000 km in the eastern section of Bikou Group.