华南早侏罗世辉长岩的矿物学特征及其成岩与成矿意义

Mineralogical Characteristics of the Early Jurassic Gabbroic Intrusions in South China and Their Implications for Petrogenesis and Mineralization

南岭地区发育一条近EW向早侏罗世火山-侵入岩带,在赣南-粤北地区出露该时期的程龙、车步和霞岚辉长岩体,其中霞岚辉长岩体发育中国东南部唯一的钒钛磁铁矿矿床,查明该区辉长岩体深部成矿潜能具有重要的找矿意义。系统的岩石学和矿物学研究表明,霞岚岩体岩石组合为橄榄辉长岩、辉长岩和角闪辉长岩,车步岩体为辉长岩和角闪辉长岩,程龙岩体为角闪辉长岩。橄榄石仅出现在霞岚辉长岩中(Fo=65.4%~61.6%);单斜辉石出现在霞岚岩体(Mg^(#)=66~85)和车步岩体(Mg^(#)=67~77);斜长石在上述岩体中均出现,但成分不同(霞岚:An=46.80%~83.60%;车步:An=32.40%~71.70%;程龙:An=7.90%~55.60%)。程龙、车步和霞岚岩体的形成温度分别为930℃,907~1167℃和950~1144℃;压力分别为0.42 GPa,0.47 GPa和0.64 GPa;氧逸度(logfO_(2))分别为-12.23~-10.1、-11.75~-11.11和-11.93~-9.55。本次研究通过与典型层状Bushveld岩体进行对比,建立了华南早侏罗世岩浆房岩石组合概念模型:从霞岚→车步→程龙岩体剥蚀程度依次减弱,各岩体在岩石组合和矿物成分上的差异是由剥露水平的不同造成的。同时利用单斜辉石和铁钛氧化物的Cr_(2)O_(3)含量、斜长石FeO^(T)含量变化以及Rhyolite-MELTS模拟结果并结合区域航磁资料,探讨了上述岩体深部成矿潜能。

A near-EW-trending Early Jurassic volcanic-intrusive rock belt was developed in the Nanling area,South China.The gabbroic intrusions formed during this period in the Southern Jiangxi and Northern Guangdong include the Chenglong,Chebu,and Xialan plutons,among which the Xialan pluton hosts the only V-Ti-magnetite deposit in Southeastern China.Exploring the deep ore-forming potential of the gabbroic intrusions in this area is important for prospecting.Systematic petrological and mineralogical studies indicate that the rock assemblage of the Xialan pluton is composed of olivine gabbro,gabbro,and hornblende gabbro.Tthe Chebu pluton is composed of gabbro and hornblende gabbro,while the Chenglong pluton contains only hornblende gabbro.Olivine only occurs in the Xialan pluton(Fo=65.4%-61.6%),Clinopyroxene occurs in the Xialan(Mg^(#)=66-85)and Chebu plutons(Mg^(#)=67-77);and plagioclase occurs in all of the above plutons(Xialan:An=46.80%-83.60%;Chebu:An=32.40%-71.70%;Chenglong:An=7.90%-55.60%).The formation temperatures of the Chenglong,Chebu,and Xialan plutons are 930℃,907-1167℃,and 950-1144℃,respectively,formation pressures are 0.42 GPa,0.47 GPa,and 0.64 GPa,respectively,and oxygen fugacity(logfO_(2))is-12.23 to-10.1,-11.75 to-11.11,and-11.93 to-9.55,respectively.A conceptual model for the rock assemblages of the Early Jurassic magma chamber in South China was established by comparing it with the typical layered Bushveld intrusion.We propose that the different levels of exhumation resulted in the differences in rock assemblage and mineral composition of the plutons,i.e.,a gradual decrease in the denudation degree of the Xialan,Chebu,and Chenglong plutons.Furthermore,the deep mineralization and ore prospecting potential of the above plutons was discussed on the basis of the Cr2O3 contents of the clinopyroxenes and Fe-Ti oxides,the changes in the total iron(FeOT)content of plagioclase,as well as the Rhyolite-MELTS simulation results,and regional aeromagnetic data.