Mesoproterozoic tectonic-thermal events in the Oulongbuluke Block, NW China: Constraints on the transition from supercontinent Columbia to Rodinia

Abstract

The Oulongbuluke Block, which is one of several ancient micro-continents on the southeast margin of Tarim in NW China, has been considered a nearly extinct fragment of the Tarim Craton. Here, zircon U-Pb, Lu-Hf isotope, petrologic and geochemical studies were carried out on the migmatites, grey felsic gneisses, mafic granulites and augen granitic gneisses from Wulan County on the eastern margin of the Oulongbuluke Block. Macroscopic and microscopic observations show that the felsic migmatite is mainly composed of plagioclase-rich leucosomes and melanosomes. The plagioclase-rich leucosomes with positive Eu and Sr anomalies occur as layers and veins, showing in situ partial melting features. Zircon U-Pb dating and Hf isotope analyses on the melanosome, grey felsic gneisses, mafic granulites and augen granitic gneisses from the Oulongbuluke Block yield three age populations at 1500–1496 Ma, 1454–1443 Ma and 1113–1104 Ma. The ca. 1.5 Ga magmatic zircon cores of the grey felsic gneiss and melanosome possess εHf(t) values between −3.5 and 3.9, with two-stage Hf model ages (TDMC) between 2.4 Ga and 2.0 Ga. The ca. 1.1 Ga zircons from samples of augen granitic gneiss have εHf(t) values of −5.2 to 0.5, and the corresponding TDMC values range from 2.2 to 1.9 Ga. Petrological, geochemical and geochronological data suggest that ca. 1.5 Ga magmatic protoliths of grey felsic gneisses were produced by dehydration melting in predominant lower crust setting and experienced metamorphism and anatexis at 1.45 Ga in a rift setting. The precursor magmas of augen granitic gneisses were derived from partial melting of mafic crustal sources in an active continental margin environment.Comparing the tectonothermal events recorded in the Oulongbuluke Block with those in other cratons, the Oulongbuluke Block, Tarim Craton and North China Craton have similar evolutionary histories before the late Mesoproterozoic, suggesting that they were linked together and involved in the assembly and break-up of the Columbia supercontinent. However, the South China Craton, Qilian Block, Oulongbuluke Block, North Qaidam and Tarim Craton were likely temporarily connected during the late Mesoproterozoic-early Neoproterozoic (1.1–0.9 Ga), which corresponded to the assembly of the Rodinia supercontinent.