Geochemical and SHRIMP U-Pb zircon chronological constraints on the Magam-mixing event in eastern Kunlun orogenic belt, China

Abstract

Sr from 0.70859 to 0.70956, and those of their host granites are from 0.70144 to 0.70972; and eNd in MME from -4.5 to -9.2, and in host rocks from -5 to -6.2.These data are roughly similar. Single-grain zircon U-Pb dating for MME, host granodiorite, and related hornblende-gabbro have been conducted in Beijing SHRIMP Center by using SHRIMP II and yielded 241±5Ma, 242±6Ma and 239±6Ma of ages, respectively. The results indicate that the three types of rocks were formed almost in the same event. All these data imply that the granites have the origin of magma mixing. The mixing/mingling event between the crust- and mantle-derived magmas prevailed in the early-middle Triassic epoch in Eastern Kunlun orogeny. And the granitoid host rock and hornblende-gabbro may approximately represent the acid and basic end-members of the mixing with the ratio of about 70% and 30% estimated by SiO 2 , respectively. MME are the incompletely mixed clots of the basic magma injected into the acid magma. Consequently, the injection and reaction of mantle mass and energy into/with the crust play an important role in the origin of granites and the vertical growth of the crust.