Sedimentary response to the non-synchronous closure of Paleo-Asian Ocean: evidence from U-Pb ages and Hf isotopic compositions of detrital zircons from the Linxi Formation, NE China

Abstract

ABSTRACT The Linxi Formation is widely deposited in eastern Inner Mongolia (NE China), especially along northern parts of the Solonker-Xar Moron Suture (SXMS) in the eastern Central Asian Orogenic Belt, yet its depositional age and provenance remain ambiguous. We studied the petrography, geochronology, and Hf isotopes of two sandstone samples from this formation, and estimated the depositional age and the provenance of the Linxi Formation, and further constrained the evolution of the Paleo-Asian Ocean (PAO). Based on detailed field observations and measurements, we. Zircons from rocks of the Linxi Formation are mainly composed of detrital zircons of magmatic origin. The determined ages of detrital zircons range from 233 ± 2 Ma to 1365 ± 14 Ma, and indicate that the provenance of the Linxi Formation experienced at least four tectonic-thermal events between 1365 and 233 Ma: Neoproterozoic (ca. 1365–543 Ma), Early Palaeozoic (ca. 512–426 Ma), Late Palaeozoic (ca. 418–251 Ma), and Early Mesozoic (ca. 249–233 Ma). The youngest detrital zircon, with a U-Pb age of 233 ± 2 Ma, defines the maximum depositional age of the Linxi Formation. The εHf (t) values of dated zircons from the sandstone samples have a large range (−7.8–15.0). The four dominant age groups and the range in εHf (t) values are widely found in the Xing’an Block and Songnen-Zhangguangcai Range, which imply that the source of the Linxi Formation had an affinity with northeastern China. These data together with previous geochronological data (from west to east along the SXMS) on the crystallization and depositional ages of detrital zircon suggest that the Linxi Formation was deposited in different tectonic settings: convergent, collisional, and extensional. This study provides further evidence and constraints for the non-synchronous closure of the PAO.