七宝山花岗斑岩的地质地球化学特征

来源期刊：中南大学学报(自然科学版)2002年第6期

论文作者：胡祥昭 肖宪国 杨中宝

文章页码：551 - 554

关键词：花岗斑岩;岩石学;地球化学;浏阳七宝山

Key words：granite-porphyry; petrology; geochemistry; Qibaoshan, Liuyang

摘    要：七宝山花岗斑岩岩体产于湖南浏阳境内,出露面积约2 km²,其形态十分复杂,铷、锶、钾、氢同位素年龄为(184~227)×10⁶a,岩石具斑状结构.其矿物成分主要由石英(约35%)、正长石(约30%)、钾长石(约28%)及黑云母(约7%)组成.化学成分中,SiO₂偏低(w(SiO₂)=70%),CaO含量极低,富钾贫钠(m(K₂O)/m(Na₂O)=4.2),铝过饱和(w(Al₂O₃)=15.83%);岩体分异指数高(DI=80),稀土元素总量偏低,w(REE)=(158.31~176.97)×10^-6,轻稀土含量大于重稀土含量,w(LREE)/w(HREE)=16.97~19.02,δE_u为0.88~1.02,无异常,与同熔型花岗岩相当,成矿元素Cu平均含量为1 800 g/t,为世界花岗岩平均含量的90倍,总体富铷贫锶,w(Rb)/w(Sr)=4;岩体Co,Cr,Ni等元素含量高于世界花岗岩中的平均值,岩体属壳幔同熔型成因花岗岩.

Abstract: Qibaoshan granite-prophyry, with 2 km² out cropped area and complicated shape, occurs in Liuyang ,Hunan province. The Rb-Sr and K-Ar isotopic ages vary between 128 Ma and 227 Ma. The rock shows porphyritic texture, and the minerals are mainly quartz (about 35%), orthoclase (about 30%), plagioclase (about 28%) and biotited (about7%). The chemical composition is characterized by abundant Fe, Al, K and lack of Ca, Na (w(K₂O)/w(Na₂O)=4.2) and over-satureated Al with slight lower SiO₂(about 70%) and rare CaO content (about 0.94%). The rock differentiation index is very high (about 80%). The w(REE) is slightly lower (w(REE)= (158.31~176.97)×10^-6) and w(LREE) was obvious higher than w(HREE), the rate of w(LREE) and w(HREE)varies between 16.97 and 19.02. The δ E_u varies from 0.88 to 1.02, corresponding to the value of syntactic granite . Trace-element is abundant in Rb and lack of Sr , the contents of Co, Cr, Ni are higher than the average contents of world granite. The average content of Cu in rock equals 1 800 g/t which is 90 times as much as the average content of world granite. The rock body belongs to crust-mantle miscibility on genetic type.