Onstraints on timing of the early-Paleoproterozoic magmatism and crustal evolution of the Oulongbuluke microcontinent: U-Pb and Lu-Hf isotope systematics of zircons from Mohe granitic pluton

Abstract

The Olongbuluke micro-continent is composed of a two-fold basement with cover strata. The lower basement is the medium-to high-grade Delingha complex (DC) and the Dakendaban Group, the upper is the low-grade Wandonggou Group. Zircon LA-ICP-MS dating gives U-Pb isotope of 27 zircon grains from the Mohe granite of the DC, of which 26 zircon grains suffered various degree of Pb loss and defined a Concordia with a upper intercept age of 2470 + 19/ - 18Ma. Hf isotope of 25 zircon grains was measured using LA-MC-ICP-MS technique, of which 23 grains crystallized from Mohe granite show Hf i = 0.28129 ∼ 0.28140 (weighted average of 0.28134 ± 0.00003), ε Hf = 2.94 ∼ 6.95 (weighted average of 4.58 + 0.54/ - 0.76), resident time for the felsic crustal reservoir T DM C = 2.54 ∼ 2.75Ga with weighted average of 2.66 ±0.04/-0.02Ga. These data indicate that the Mohe granite pluton was derived from partial melting of the mantle, and the intrusion of the Mohe granite pluton implied a crustal accretion event occurred in Olongbuluke micro-continent at ca. 2.5Ga.