Ediacaran separation of the North Qilian Block from the Central Qilian Block, NW China: Evidence from detrital zircon U-Pb geochronology

Abstract

The Precambrian stratigraphic archive of the North Qilian Accretionary Belt (NQAB) is crucial for understanding the tectonic evolution of the Proto-Tethys Ocean. Although various tectonic evolution models of the NQAB have been proposed, no consensus has yet been reached due to the ambiguous Precambrian chronostratigraphic framework and tectonic nature of this belt. In this study, we present LA-ICP-MS U-Pb dates of detrital zircons from the Precambrian iron-formation-bearing Jingtieshan and Zhulongguan groups in the northwestern NQAB. The new results, together with the published dates, indicate that the depositional ages of the two groups are 1400–1230 Ma and 740–580 Ma, respectively. Meanwhile, the Precambrian stratigraphic sequences and detrital zircon age distributions show strong similarities to their age-equivalent units in the western Central Qilian Block (CQB), demonstrating a close tectonic affinity between them in Precambrian. The provenance shift in early Paleozoic, together with the Ediacaran ophiolite suites and associated rift-related basaltic rocks in the NQAB, indicates that the previously identified North Qilian Block, where the Jingtieshan and Zhulongguan groups deposited, was separated from the CQB by continental rifting and subsequent ocean spreading during the late Ediacaran. These findings shed new lights on the tectonic evolution of the Proto-Tethys Ocean in the Neoproterozoic.