Evolution of the Columbia supercontinent: Insights from the North Qilian Block, NW China

Abstract

The North Qilian Orogenic Belt, NW China, is surrounded by the Tarim and North China cratons to the northwest and northeast, respectively. The North Qilian Block (NQB) is preserved as Precambrian continental fragments in this belt. This block records a series of intense Proterozoic tectono–magmatic events associated with the convergence and breakup of the Columbia supercontinent, providing insights into the location of the block within this supercontinent. This study focuses on the Paleoproterozoic (ca. 1.74 Ga) amphibolites of the Beidahe Group (BDHG), and Mesoproterozoic (1.6–1.2 Ga) basalts of the Aoyougou (AF) and Huashugou (HF) formations of the Zhulongguan Group, all of which outcrop in the NQB.The BDHG amphibolites have island arc basalt-type geochemical affinities with variable εNd(t) (−7.8 to −0.7) and εHf(t) (−9.8 to −2.1) values, that are indicative of the derivation from metasomatized mantle wedge in a continental arc setting. The ocean island basalt-like AF basalts and some HF basalts have depleted and decoupled Nd–Hf isotopic compositions (εNd(t) = 1.8–6.4 and εHf(t) = 2.1–10.7), and high mantle potential temperatures of up to 1642 °C, indicating derivation from a mantle plume in an intracontinental rifting setting. The normal mid-ocean-ridge basalt-like HF basalts originated from depleted asthenospheric mantle in a nascent ocean basin, as indicated by their Nd–Hf isotopic compositions (εNd(t) = 8.6–11.6 and εHf(t) = 14.7–15.2).Combining these new data with the results of previous research, it is suggested that the Paleo–Mesoproterozoic evolution of the NQB involved paleo-oceanic plate subduction, intracontinental rifting, and the development of an embryonic oceanic basin, all of which were responses to Columbia supercontinent aggregation and breakup. The formation ages of the BDHG (ca. 1.74 Ga) and the AF (1.56–1.53 Ga) and detrital zircon ages (1.77 and 1.59 Ga) for the North Qilian Orogenic Belt are similar to those of the North China Craton (1.76 and 1.59 Ga) located to the southwest of the central Columbia supercontinent (i.e., Laurentia). This suggests that the NQB was located to the southwest of the Laurentia with volcanic islands within the Columbia supercontinent.