地质论评2025，Vol.71Issue(4)：1215-1234,20.DOI:10.16509/j.georeview.2024.12.045
Nb-Ta分异的控制因素及其地质意义
Influencing factors of Nb—Ta fractionation and its geological implications
摘要
Abstract
The geochemical properties of niobium and tantalum are similar,but the Nb/Ta ratios of various spheres of the Earth and different geological units are lower than that of chondrites.Different mantle endmembers,continental crust,and mid-ocean ridge basalts also have different Nb/Ta ratios.This review summarizes the Nb-Ta partition coefficients of mineral-melts obtained from a large number of simulation experiments and natural samples.It is found that rutile,amphibole and biotite have relatively high Nb-Ta partition coefficients with silicate melts.The Nb/Ta ratio varies greatly and is controlled by the composition and physical and chemical conditions of the magmatic system.The increase of temperature and water content will lead to the decrease of Nb-Ta partition coefficient between rutile and melt.The Nb-Ta partition coefficient between amphibole,biotite and melt is mainly affected by the degree of polymerization(NBO/T),mineral composition(such as Mg#),and water content.DNb,DTa and DNb/DTa all increase with the decrease of Mg# and water content.Since rutile is considered as an important reservoir mineral of Nb-Ta due to its high Nb-Ta partition coefficients,as well as a necessary residual phase in the formation of Archean TTG magma,its fractional crystallization is often used to explain the Nb-Ta depletion of TTG.However,due to the uncertainty of its distribution coefficient ratio and diffusion effect,it is still controversial whether it can lead to the decrease of Nb/Ta ratio in coexisting melts.Based on experimental simulations of magma evolution in arc magmas and felsic melts,it is demonstrated that the fractional crystallization of amphibole and biotite may lead to the decrease of Nb/Ta ratio in the melt.In the late stage of magma evolution,biotite and muscovite have an enhanced effect on the decrease of Nb/Ta ratio in the melt,and the increase of volatile content such as F will promote the enrichment of Nb-Ta in the melt.The transformation of Ti-rich minerals and fluids control the storage,migration and differentiation of Nb-Ta during the process of subduction,the resultant amphibole and rutile-bearing eclogite formed under high pressure may be an important reservoir of Nb-Ta.关键词
Nb/Ta值/分配系数/地幔端元/TTG/俯冲作用/金红石/角闪石/黑云母Key words
Nb/Ta ratio/partition coefficient/mantle endmembers/TTG/subduction/rutile/amphibole/biotite引用本文复制引用
孙玉洁,李晓彦,张超..Nb-Ta分异的控制因素及其地质意义[J].地质论评,2025,71(4):1215-1234,20.基金项目
本文为科技部重点研发计划项目(编号:2023YFF0804200)的成果. This paper was financially supported by National Key Research and Development Program of China(No.2023YFF0804200) （编号:2023YFF0804200）
