Trace-element composition and origin of granitoids from the Shakhtama complex and Kukul'bei rare-metal complex (Aga zone, Transbaikalia)

The paper gives major-element and extended trace-element descriptions of plutons from the Shakhtama complex in the Aga tectonic zone (Transbaikalia). They are composed of hornblende–biotite gabbrodiorites, monzonites, diorites, and granodiorites. It has been found that they were initially enriched in granitophile (including ore-forming) trace elements. This suggests consanguinity between the intrusions of the Shakhtama complex (J2–J3) and the ore-bearing Kukul'bei rare-metal complex of granites and leucogranites (J3) (Aga zone, Transbaikalia). Since granitophile elements are incompatible, their content in granitoids with an elevated mafic content from the Shakhtama complex is substantially less above the clarke than that in the rare-metal granites and leucogranites from the Kukul’bei complex, which ended postcollisional magmatism in the Aga zone. Analysis of normalized REE patterns for the granitoids from both complexes has revealed their magmatic heterogeneity. It has been demonstrated that the Kukul'bei granite and leucogranite intrusions in the western Aga zone are granitic differentiates of granitoid magma chambers associated with the Shakhtama complex, which were initially enriched in granitophile trace elements. The granites from the rare-metal intrusions of the Kukul'bei complex (in the eastern periphery of the Aga zone) are not directly related to the magma chambers of the Shakhtama complex. They are magmatic melts, which might result from the deep-level selective melting of metamorphosed rocks enriched in volatile trace elements. It has been confirmed that there is no direct genetic relation between the majorand trace-element compositions of the granitoids and their metallogeny and ore content.The granitophile rare-metal specialization of the intrusions in Mesozoic Transbaikalian gabbrodiorite–monzonite–granodiorite and leucogranite complexes is the major evidence supporting the theory of the formation of late- and postcollisional magma chambers associated with deep faults, which were initially enriched in volatile and incompatible trace elements.