Late Paleoproterozoic tectonic evolution of the Olongbuluke Terrane, northern Qaidam, China: Constraints from stratigraphy and detrital zircon geochronology

Abstract

The late Paleoproterozoic tectonic processes of the Olongbuluke Terrane in the northern Qaidam of northwestern China remain unclear due to rare contemporaneous metamorphic and magmatic records. The sedimentary succession of the Quanji Group preserves detailed geological information of erosion, transportation and deposition, which is pivotal for constraining the late Paleoproterozoic tectonics of the Olongbuluke Terrane. The Quanji Group comprises conglomerate-sandstone of nearshore facies and mudstone-dolomite of tidal flat facies in the lower and upper sections, respectively, displaying an upward fining and transgression sequence. Together with featured sedimentary structures, the facies assemblage and vertical sequence suggest that the Olongbuluke Terrane has experienced a basin evolution of initial rifting, rifting climax and passive continental margin during ∼1780–1640 Ma. Four samples collected from the low to top positions within the profiles yield quite similar detrital zircon age patterns with two distinct clusters of 2510–2216 Ma and 2062–1728 Ma. These detrital zircon ages coincide with those of magmatism–metamorphism in the basement of Olongbuluke Terrane, suggesting the detritus were sourced from the Olongbuluke Terrane itself. The zircons with ages of 2510–2216 Ma display εHf (t) ratios from −2.29 to +6.81 and corresponding TDM2 ages of ∼3.1 to 2.5 Ga, suggesting they were originated from reworking of the Meso- to Neoarchean juvenile crust with mantle inputs or mantle derived rocks. In comparison, the zircons with ages of 2062–1728 Ma exhibit εHf (t) ratios ranging from −17.4 to −0.1 and TDM2 ages of ∼3.6 to 2.5 Ga, indicating their origin in partial melting of the Paleo- to Neoarchean crust. The two sets of zircons display TDM2 ages with three peaks of ∼2.9 Ga, ∼2.7 Ga and ∼2.5 Ga. Comparing with those of the other main blocks all over the world, all the above detrital zircon U-Pb ages and TDM2 ages together with the late Paleoproterozoic tectono-stratigraphic processes suggest that the Olongbuluke Terrane has a Precambrian tectonic affinity close to the western North China Craton.