Generation of lithium-bearing pegmatite deposits within the Songpan-Ganze orogenic belt, East Tibet

Abstract

As the largest lithium ore deposits in China, the Jiajika and Markam lithium pegmatites formed in the Songpan-Ganze orogenic hinterlands, East Tibet. The lithium pegmatites, hosted in the Upper Triassic turbiditic metasedimentary rocks, were related to granitic intrusions currently expressed as gneiss domes. Combined previous studies with new field observations, drilling data and geochemical and geochronological results from Jiajika and Markam gneiss domes, we determined that both gneiss domes, related to lithium ore deposits, are characterized by cored granites and mantling high-medium temperature/middle-low pressure metamorphic rocks intruded by numerous lithium-bearing pegmatites. We confirm that the granitic plutons within the gneiss domes were mainly intruded at ∼227-215 Ma during crustal shortening associated with Upper Triassic orogeny. The gneiss domes are metamorphic core complex generated by magmatic diapirism or a combination of top-to-the-south ductile detachment and diapirism, respectively, during the Late Triassic to Early Jurassic (∼216-170 Ma).Our synthesis indicates that the lithium-bearing pegmatites occur mainly in the staurolite-andalusite metamorphic zones of both core complexes, and that they were produced by strong differentiation of parental S-type, calc-alkaline and peraluminous granites.We suggest that the Markam gneiss dome formed between ∼212 and 170 Ma, as indicated by the age of the Markam detachment, the crystallization ages of the lithium-bearing pegmatites and the associated metamorphic events. In contrast, formation of the Jiajika gneiss dome was initiated at least by ∼216-214 Ma, as indicated by ages of the lithium-bearing pegmatite veins and other mineralization ages. Therefore, we suggest that the lithium-bearing pegmatites were emplaced during formation of the gneiss domes, and that the deformation, metamorphism, magmatism and mineralization in the eastern Songpan-Ganze orogenic belt are spatially and temporally related to the exhumation stage of the Indosinian orogeny.