FIRST DATA IN FAVOR OF THE CRYSTALLIZATION MODEL OF LITHIUM ISOTOPE FRACTIONATION IN THE PEGMATITIC PROCESS

Abstract

The isotopic composition of Li in crystalline rocks of the upper mantle and continental crust differs little from the standard value (δ7Li = −2…+5‰). High-temperature processes of magmatic differentiation do not provoke significant effects of isotope fractionation. However, the Li isotope in seawater appeared unexpectedly heavy (+32 ‰). The most notable δ7Li variations are attributed to low-temperature exogenous processes, such as halmyrolysis of marine basalts, weathering of rocks, and diagenesis of sediments. Trends of the Li isotope fractionation in metamorphic, postmagmatic, and hydrothermal-metasomatic processes in the Earth’s crust are poorly studied.