Paleoproterozoic transition in tectonic regime recorded by the Eastern Block of the North China Craton: evidence from detrital zircons of the Langzishan Formation, Jiao-Liao-Ji Belt

摘要

The Eastern Block of the North China Craton records Paleoproterozoic oceanic plate subduction, the opening and subsequent closure of a back-arc basin, and a following collisional orogenic event to generate the Jiao-Liao-Ji Belt (JLJB). However, the processes involved in the initiation of subduction remain unclear. This study presents U-Pb age and trace elemental data for detrital zircons from the Langzishan Formation, the lowermost sedimentary unit within the JLJB, to constrain the provenance, depositional age, and depositional environment of this formation as well as the processes involved in the Paleoproterozoic transition in tectonic regime recorded by the Eastern Block. The U-Pb ages of these detrital zircons yield one major age peak at ca. 2529, and three minor age peaks at ca. 2700, ca. 2347, and ca. 2198 Ma. Provenance analysis indicates that the Langzishan Formation was derived from basement rocks in the Longgang Block with minor contributions from early magmatic rocks within the JLJB. Detrital zircon age contribution further suggests that the deposition of the Langzishan Formation was in a passive continental margin and commenced no earlier than 2205 Ma. Combining with previous research on the widespread distribution of magmatic and sedimentary rocks that formed in convergent settings in this area, this study suggests that the Eastern Block records a transition in tectonic regime at ~2205-2170 Ma, from passive continental margin to active continental margin settings, most likely as a result of the re-initiation of global plate tectonic cycling during the early history of the Earth.