Petrogenesis and tectonic significance of the Late Permian-Middle Triassic calc-alkaline granites in the Balong region, eastern Kunlun Orogen, China

Numerous calc-alkaline granitoid intrusions in the eastern Kunlun Orogen provide a valuable opportunity to constrain the evolution of the orogen. The age and genesis of these intrusions, however, remain poorly understood. The granitoid intrusions near the Balong region, eastern Kunlun Orogen, consist of granodiorite, diorite and syenogranite. The granodiorite contains crystallized segregations, abundant mafic microgranular enclaves (MMEs) and small quartz diorite stocks. In situ zircon U-Pb dating reveals that the granodiorites and quartz diorites were emplaced between 263 and 241 Ma, whereas the syenogranite was produced at c. 231 Ma. The granodiorite and quartz diorite have a calc-alkaline affinity and are metaluminous and Na-rich, with slightly enriched Sr-Nd isotope compositions. The granodiorite is characterized by fractionated REE patterns, whereas the quartz diorite displays a relatively flat REE pattern. The MMEs are consistent with the granodiorite in terms of incompatible elements and Sr-Nd isotope composition. Compared to the granodiorite and diorite, the syenogranite has higher SiO2, K, Rb, Th and Sr contents and a lower Rb/Sr ratio. The results presented here, when combined with regional geological data, indicate that the granodiorite and quartz diorite were derived from dehydration melting of mafic lower crustal rocks during the N-directed subduction of the Anyemaqen ocean lithosphere in Late Permian-Middle Triassic times, whereas the syenogranite was produced at a higher crustal level in a syn-collisional setting compared to the granodiorite.