摘要
太和镁铁质-超镁铁质层状岩体位于峨眉山大火成岩省内带,赋存有超大型的钒钛磁铁矿矿床。根据岩石矿物组合、矿物含量及结构特征等,岩体从下向上可划分为下部岩相带、中部岩相带和上部岩相带,并且中部岩相带可进一步划分为Ⅰ~Ⅵ旋回。太和岩体不同层位广泛分布有角闪石,大多数样品角闪石体积分数在1%~3%之间,局部可达5%~10%。岩相学研究显示,角闪石呈嵌晶结构且具有均一的光学特征。结合地球化学组成判别,这些角闪石与幔源岩浆有关,是岩浆演化晚期结晶的产物。下部岩相带角闪石含有相对较高的w(Cr)(3×10^(-6)~112×10^(-6))和w(Ni)(114×10^(-6)~163×10^(-6)),而中部岩相带和上部岩相带都显示较低的w(Cr)(3.81×10^(-6)~28.1×10^(-6))和w(Ni)(0.42×10^(-6)~20.9×10^(-6)),暗示下部岩相带的母岩浆相对原始,是一种富Fe-Ti岩浆。另外,中部岩相带角闪石TiO_(2)变化呈韵律旋回变化,且在Ⅵ旋回中角闪石明显富集Nb并迅速向上降低。同时,角闪石微量元素蛛网图反映中部岩相带的母岩浆显著富集Y、REE、Sr等元素。这些特征暗示中部岩相带的母岩浆是一种演化的岩浆。通过角闪石成分估算的岩浆氧逸度呈旋回变化,从旋回底部到旋回顶部氧逸度逐渐降低,这个特征与角闪石Fe^(3+)/(Fe^(3+)+Fe^(2+))比值变化相似。高氧逸度和岩浆富水是导致磁铁矿早期结晶的关键控制因素。
The Taihe mafic-ultramafic layered intrusion is located in the internal zone of the Emeishan Large Igneous Province.It hosts super-large sized V-Ti magnetite ore deposits.The lower,middle and upper lithofacies zones have been identified from the bottom to the top of the Taihe intrusion based on their mineral assemblages,mineral contents and petrographic textures of various rocks in the intrusion.Especially,the Ⅰ-Ⅵ cycles of intrusive rocks have been further indentified in the middle lithofacies zone.Amphibole is widely distributed in different layered rocks of the Tai intrusion.Most rock samples have amphibole volumetric fractions ranging from 1%to 3%.Minor rock samples have those of 5%-10%.Petrographic studies show that amphiboles have poikilite structure and uniform optical characteristics in various rocks.Combined with their geochemical compositions,these amphiboles are related to the mantle-derived magma and are crystallization products of the evolved magma in the late stage.The amphiboles in the lower lithofacies zone have relatively high contents of Cr(3-112 ppm)and Ni(114-163 ppm),whereas those in the middle and upper lithofacies zones have relatively low contents of Cr(3.81-28.1 ppm)and Ni(0.42-20.9 ppm),implying that the parent magma of rocks in the lower lithofacies zone is relatively close to the primitive magma and is an Fe-Ti-rich magma.Furthermore,TiO_(2) concentrations of amphiboles in the middle lithofacies zone are rhythmic cyclically changed.Especially,Nb contents are clearly high in amphiboles in the Ⅵ cycle of the middle lithofacies zone,but are rapidly decreased in amphiboles of the upper lithofacies zone.Meanwhile,the parent magmas of rocks in the middle lithofacies zone are highly enriched in Y,REE,Sr and other incompatible elements based on trace element spidergrams of amphiboles.These features indicate that parent magma of rocks in the middle lithofacies zone was an evolving magma.The oxygen fugicity of the magma estimated by the composition of hornblende shows a cyclic variation,de
作者
包从法
佘宇伟
路永严
普志坤
李炜
何小虎
何海龙
BAO Congfa;SHE Yuwei;LU Yongyan;PU Zhikun;LI Wei;HE Xiaohu;HE Hailong(Yunnan Planning Design Institute of Land Resources,Kunming Yunnan 650051,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Sciences,Yunnan University,Kunming Yunnan 650500,China)
出处
《矿物学报》
CAS
CSCD
北大核心
2024年第2期178-187,共10页
Acta Mineralogica Sinica
基金
云南省基础研究计划面上项目(编号:202201AT070087)
中国地质科学院地质研究所基本科研业务费项目(编号:J2312)
中国地质科学院基本科研业务费专项经费资助(编号:JKYZD202311)。
关键词
角闪石
氧逸度
太和层状岩体
Fe-Ti氧化物
分离结晶
amphibole
oxygen fugacity
Taihe layered intrusion
Fe-Ti oxides
fractional crystallization
