摘要
过去十几年来,非传统稳定同位素地球化学在高温地质过程的研究中取得了的重大进展。多接收诱导耦合等离子质谱(MC-ICP-MS)的应用引发了稳定同位素分析方法的重大突破,使得精确测定重元素的同位素比值成为可能。本文总结了以Li、Fe和Mg同位素为代表的非传统稳定同位素在岩石地球化学研究中的应用。Li同位素目前被广泛地用于地幔地球化学、俯冲带物质再循环和变质作用的研究中,可以用来示踪岩浆的源区性质和扩散等动力学过程。不同价态的Fe在矿物熔体相之间的分配可以产生Fe同位素分馏,可以发生在地幔交代、部分熔融、分离结晶等过程中。岩浆岩的Mg同位素则大致反映其源区的特征,地幔的Mg同位素组成比较均一,这为研究低温地球化学过程中Mg同位素的分馏提供一个均一的背景。此外,Cl,Si,Cu,Ca,U等等同位素体系也具有广阔的应用前景。对同位素分馏机制的实验研究和理论模拟为理解非传统稳定同位素数据提供了必要的指导。实验表明,高温下具有不同的迁移速度的轻、重同位素可以产生显著的动力学同位素分馏,这一分馏可以在化学扩散、蒸发和凝华等过程中发生;同位素在矿物和熔体以及流体相中化学环境的差异使得不同相之间可以发生平衡分馏。而最近的硅酸盐岩浆的热扩散和热迁移实验则揭示了一种"新"的岩浆分异和同位素分馏机制。沿着温度梯度,硅酸盐岩浆可以发生显著的元素和同位素分异,湿的安山岩可以通过这种方式演变成花岗质成分,因此这个过程可能对陆壳的产生和演化有重大影响。如果温度梯度在岩浆作用中能长期存在,热扩散就可以产生稳定同位素的分馏,这一机制有别于传统的平衡和动力学同位素分馏。而多个稳定同位素体系的正相关关系是示踪热迁移过程的最有力证据。在热扩散过程中,流体承载的物质�
The last ten years have seen big progress and wide applications of a novel field,non-traditional stable isotope（NTSI）geochemistry,to high temperature geo-science studies.Invention of multi-collector-inductively coupled plasma-mass spectrometry（MC-ICP-MS）led to the big breakthrough of analytical methods for heavy stable isotopes.This contribution summarizes Li,Fe,and Mg isotope studies on igneous rocks and minerals,as representative of NTSI geochemistry.Li isotopes have been widely applied to the studies of mantle geochemistry,recycling of subducted materials,and metamorphism to constrain the source of magma and kinetic diffusion process.Fe isotope fractionation is related to partitioning of multi-valent Fe between Fe-bearing phases,which can occur in the course of mantle metasomatism,partial melting,and fractional crystallization.Mg isotopic compositions of igneous rocks most likely reflect the source signatures.Variation of Mg isotopic ratios of mantle peridotites is trivial and this provides a homogenous background for Mg isotope fractionation in low temperature processes.Furthermore,Cl,Si,Cu,Ca,and U isotopes are also promising in the future geochemical studies.Experimental studies and theoretical simulation for the mechanisms of isotope fractionation provide important guidances for understanding the NTIS data.Experimental studies show that light and heavy isotopes have different migration velocity at high temperature processes such as chemical diffusion,evaporation,and desublimation,which could produce significant kinetic isotope fractionation.Equilibrium isotopic fractionation could occur among mineral,melt,and fluid when chemical environment of the isotopes are different between the phases.Recent thermal diffusion and migration experiments on silicate material reveal a ＂new＂ mechanism of magma differentiation and isotope fractionation.Along a temperature gradient in silicate magma,large elemental variation and isotopic fractionation can occur,by which a wet andesite can even be differentiated to
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2011年第2期365-382,共18页
Acta Petrologica Sinica
基金
中国科学院百人计划项目
中国科学院壳幔物质与环境重点实验室经费联合资助
