Zircon from the Turga Multiphase Massif with Amazonite Granites (Eastern Transbaikalia) and Its Petrogenetic Significance

Resumo

Zircon from granitoids of the multiphase Turga massif (Eastern Transbaikalia) shows various morphological features and compositions of trace elements. This granitoid massif of the Kukulbey complex is spatially associated with rocks of the Shakhtama monzonitoid complex, whose ages are about 133 and 158 Ma, respectively. Zircon from different granitoid phases of the Kukulbey complex demonstrates a decrease in Hf content and an increase in Th, U, Y, and REE concentrations. The trace element accumulation in zircon and rocks of the main phase of the Turga massif (Li-Li-siderophyllite granites) was accompanied by a significant rise of their crystallization temperature, relatively to the earlier phase. The indicative features of zircon in these granites—the intensive development of specific twinning (up to 30% of all grains) and the presence of contrasting growth zones—confirm the idea of increasing crystallization temperatures and alkalinity of the melt. These features of zircon, together with geochemical composition of rocks, indicate that amazonite granites of the Turga massif belong to the alkaline type of Li–F-bearing granites with a mixed geochemical specialization: on the one hand, Li, Ta, and Nb, which are typical for the ore-bearing (peraluminous rare-metal) Orlovka massif; and on the other hand, Zr, REE, Th, and U, which are more typical for alkaline granites.