铜陵地区狮子山矿田侵入岩地球化学特征及成岩机制探讨

Geochemical Characteristics and Petrogenesis of the Intrusive Rocks from Shizishan Ore Field,Tongling Region

铜陵地区是长江中下游成矿带中重要的矿集区,以燕山期大规模岩浆-热液活动形成的Cu-Fe-Au多金属矿产为主。以狮子山矿田3类侵入岩体为研究对象,通过手标本和显微镜观察,将狮子山3类侵入岩体定名为辉石闪长岩、石英闪长岩和花岗闪长岩。对区内岩体地球化学组成、同位素资料及年代学数据的分析整理,推测出本区侵入岩的来源与成因:燕山期太平洋板块斜向俯冲欧亚大陆脱水产生的流体交代地幔楔并使其发生部分熔融形成上地幔玄武质岩浆,少部分与地壳物质发生了较低程度同化混染的玄武质岩浆上升侵位形成辉石闪长岩,大部分玄武质岩浆底侵下地壳熔融形成埃达克质岩浆,熔融作用产生的高温可以使中上地壳物质部分熔融形成浅部花岗质岩浆房。大部分埃达克质岩浆快速上升,直接侵位至地壳浅部并与地壳发生少量混染形成石英闪长岩,小部分埃达克质岩浆上升至浅部花岗质岩浆房与花岗质岩浆发生混合,侵位结晶形成花岗闪长岩。

Tongling region is an important ore-concentrated area of metallogenic belt of middle and lower reaches of Yangtze River. The region is rich in Cu-Fe-Au polymetallic mineral resources, which are formed by large-scale Yanshanian magmatic-hydrothermal activities. We selected three kinds of intrusive mass in Shizishan ore field as the objects of study. According to the observation of hand specimen and thin section, we named them pyroxene diorite, quartz diorite and granodiorite. Through the analysis of the magmatie rocks＇ geochemistry, chronology and isotopic data, we speculate that the source of the intrusive rocks in this area and genesis： during Yanshanian period with the oblique subduction of the Pacific plate to Eurasia, dehydration fluid metasomatism the mantle wedge formation of upper mantle partial melting and produce alkaline basaltic magma, a small amount of basaltic magma rising and emplacement, contamination with the earth＇s crust formed pyroxene diorite. Most of the basaltic magma invaded lower crust molten formed adakite magma; high temperature produced by melting effect can make the upper crustal granitic magma chamber material formed by partial melting. Most of adakite magma rose fast, emplaced directly to the earth＇s crust and contaminated with the earth＇s crust, forming quartz diorite, a small number of adakite magma rose to shallow magma chamber and mixed granitic magma, emplaced and formed granodiorite.