Lithium isotopic disequilibrium of minerals in the spinel lherzolite xenoliths from Boeun, Korea

Spinel lherzolite xenoliths found in Boeun, Korea, have protogranular to porphyroclastic textures and are enclosed in a Miocene alkali basalt. The lithium concentration and isotopic compositions of olivine, clinopyroxene, and orthopyroxene separates from the spinel lherzolite, and whole rocks of the spinel lherzolites and alkali basalt were determined by inductively coupled plasma mass spectrometry (ICP-MS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The lithium concentrations of the olivines and orthopyroxenes range from 2.2 to 5.0 ppm and from 2.1 to 6.4 ppm, respectively. In contrast, the clinopyroxenes have larger lithium concentrations, from 2.0 to 8.4 ppm, which reflect their preferential lithium enrichment. The lithium isotopic compositions (delta Li-7) of olivines (-5.4 to +3.5 parts per thousand), orthopyroxenes (-11.4 to -0.1 parts per thousand), and clinopyroxenes (-14.4 to -4.7 parts per thousand) range far beyond the average mantle composition of +4 +/- 2 parts per thousand. The lithium isotopic composition of the host rock, alkali basalt (3.4 parts per thousand), is within the range of the intraplate and oceanic island basalts. The spinel lherzolites from Boeun exhibits strong elemental and isotopic disequilibria due to the different lithium and lithium isotope diffusion velocities in the olivine, orthopyroxene, and clinopyroxene minerals after eruption and magma cooling. (C) 2010 Elsevier B.V. All rights reserved.