华南基底变质岩的铌钽赋存状态及对铌钽富集和分异的指示  

Occurrence of niobium-tantalum in basement metamorphic rocks in the South China Block and indication for niobium-tantalum enrichment and differentiation

作　　者：毛志奇 于津海[1] 蔡元峰[1] 孙涛[1] 夏浪 苟树林 MAO Zhiqi;YU Jinhai;CAI Yuanfeng;SUN Tao;XIA Lang;GOU Shulin(State Key Laboratory of Critical Earth Material Cycling and Mineral Deposits,School of Earth Sciences and Engineering,Nanjing University,Nanjing,Jiangsu 210023,China)

机构地区：[1]南京大学地球科学与工程学院,南京大学关键地球物质循环与成矿全国重点实验室,江苏南京210023

出　　处：《地质学报》2025年第4期1289-1311,共23页Acta Geologica Sinica

基　　金：国家自然科学基金重点项目(编号91962221)资助的成果。

摘　　要：华南板块东南部的华夏地块和江南造山带是我国前寒武纪基底和显生宙铌钽等稀有金属矿床重点分布地区。显生宙铌钽等稀有金属成矿作用是否与前寒武纪基底成分有关,以及基底变质岩中铌钽等稀有金属的赋存状态如何影响部分熔融产生的岩浆中铌钽含量和比值是重要的基础科学问题。本文详细分析了华夏地块和江南造山带各种基底变质岩中变质矿物的Nb-Ta含量。结合全岩地球化学、矿物成分、矿物含量、变质温度和部分熔融模拟,本研究揭示了各种变质矿物的Nb-Ta含量和变化的规律,讨论了不同条件下不同矿物熔融对熔体Nb-Ta富集的影响。分析结果显示,黑云母是华南变质岩中最富集Nb-Ta的造岩矿物,Nb和Ta平均含量分别为64.1×10-6和4.93×10-6,对Nb和Ta的相容性相似。白云母的Nb-Ta富集能力略弱,在固相线下更相容Nb,平均Nb/Ta比值为16.9,是潜在的高Nb/Ta储库。辉石、角闪石、石榴子石和长石等造岩矿物的Nb-Ta含量很低,不会对体系Nb-Ta富集和分异产生明显的影响。固相线下黑云母和白云母的Nb-Ta含量、Nb/Ta比值以及与全岩的分配系数主要受控于寄主岩成分、矿物组合、矿物晶体化学成分以及变质温度。云母中的Nb-Ta含量和与全岩的分配系数与变质温度呈良好的线性正相关,与矿物含量呈反相关,体现了矿物含量效应。当云母发生部分熔融后,其化学成分和分配系数发生变化,Nb-Ta含量快速下降,不再受控于固相线下的影响因素,这种转变被称之为“熔融效应”。根据对南岭地区一个二云母片岩的部分熔融模拟,可以得出熔体的Nb-Ta富集和分异程度主要取决于原岩Nb-Ta含量、熔融矿物组合、氧逸度以及熔融程度。高的氧逸度和压力能有效促进Nb-Ta在熔体中的富集。模拟结果显示在0.6GPa和FMQ+2条件下,熔体的Nb和Ta含量最高分别达45.1×10-6和3.44×10-6,相比于原岩富集�The Cathaysia Block and the Jiangnan Orogenic Belt in southeastern South China Block are important areas for the distribution of Precambrian basements and Phanerozoic Nb-Ta and other rare-metal deposits.Understanding the relationship between rare-metal mineralization and Precambrian basement composition,and how rare-metal occurrence in basement metamorphic rocks influences Nb-Ta contents and Nb/Ta ratios in magma generated by partial melting are important fundamental scientific problems.This study analyzes the Nb and Ta contents of different minerals in metamorphic rocks from the Cathaysia Block and Jiangnan Orogenic Belt.Combining whole-rock geochemistry,mineral compositions,mineral proportions,metamorphic temperature,and partial melting modeling,we identify the key factors controlling the Nb-Ta contents and variations in biotite,muscovite,and other metamorphic minerals.We also discuss the influence of melted minerals on Nb-Ta contents in melts under different conditions.Our results show that biotite is the most Nb-Ta-enriched rock-forming mineral in the metamorphic rocks of South China,with mean Nb and Ta contents of 64.1×10-6 and 4.93×10-6,respectively,exhibiting similar compatibility between Nb and Ta.Muscovite is another Nb-Ta-rich metamorphic mineral,albeit with slightly lower concentrations than biotite.Under subsolidus conditions,Nb is more compatible than Ta in muscovite,resulting in a high Nb/Ta ratio of 16.9,which makes it a potential reservoir of high Nb/Ta.Pyroxene,amphibole,garnet,and feldspar have low Nb and Ta contents and make little effect on the Nb-Ta enrichment and differentiation in the system.The Nb-Ta contents and Nb/Ta ratios of biotite and muscovite,as well as their partition coefficients with bulk rocks,are mainly controlled by host-rock composition,mineral assemblage,mineral composition,and metamorphic temperature.Nb-Ta contents and partition coefficients of biotite and muscovite show positive correlations with metamorphic temperature and inverse correlations with mineral proportions,

关 键 词：华南板块 基底变质岩 变质矿物铌钽含量 部分熔融和分离结晶模拟 

分 类 号：P595[天文地球—地球化学]