【摘要】 近年来,由于分析手段的不断改进,锂同位素的精确测试才得以实现。锂以其分馏大、中度不相容、易随流体迁移、地表环境与地幔锂同位素特征差异明显等优势,被认为是极具潜力的示踪元素。目前,锂同位素在壳幔物质循环、风化作用、岩浆作用、流体(热液)活动等方面研究中已得到广泛的应用,其中又以俯冲带锂同位素的研究程度最高。本文主要从锂同位素分馏机理、俯冲带锂的行为特征、岛弧岩浆的锂同位素研究以及深俯冲作用过程中锂的行为等方面总结了当前国内外锂同位素的研究进展。更多还原

【Abstract】 Lithium has two stable isotopes,7Li and 6Li,which have the biggest relative mass difference among all isotope pairs except for hydrogen-deuterium.Its potential for mass-dependent fractionation is thus obvious.Unlike the better established light stable isotopic systems(e.g.C,O,S),Li is a trace cation and does not form an integral part of the hydrological,atmospheric or biological cycle.Hence measurements of Li isotopes are likely to provide information rather different from data obtained from more commonly used isotope systems.Lithium isotope is regarded as a potential trace element because Li has many favorable characteristics,such as moderate incompatibility during mantle melting,high mobility in hydrous fluids and a strong isotopic fractionation at low temperatures,which make this trace element a powerful tracer for recycled materials in the mantle.In recent years,studies of Li and its isotopes in the solid earth have been rapidly increasing in number,as there exists great interest in determining the usefulness of the Li isotope system in tracing crust-mantle recycling.Lithium isotopes can be strongly fractionated under different conditions,with δ7Li values ranging from +32‰ in sea water to very low in eclogites(-35‰),which are interpreted as analogs of the dehydrated oceanic crust.Because Li is a fluid-mobile element,it has been held that heavy seawater Li incorporated into altered oceanic crust would move from the slab into the mantle wedge together with other fluid-mobile elements during subduction zone metamorphism and ultimately manifested itself again in island arc lavas.However,studies of island arcs show that Li is decoupled from other fluid-mobile elements,and most island arc lavas(+2‰～+6‰) have δ7Li indistingui-shable from δ7Li of MORB.Several models have been proposed to explain the Li isotopic composition of lavas,such as fluid filtering and fluid-mantle wedge mixing.Thus,the isotopic composition of recycled Li remains a matter of speculation in the subduction zone.更多还原