Crustal anatexis and ductile superimposition in the Culai Mountain region, western Shandong Province: Constraints on the Neoarchean tectonic framework of the eastern North China Craton

Objective Western Shandong is located in the core area of the eastern North China Craton and represents a typical Archean basement exposure. It extends as an overall NW–SE trending linear belt. This area preserves not only multiple phases of magmatic records spanning the early to late Neoarchean but also abundant anatectic–rheological structures overprinted by ductile deformation fabrics. These features are of great significance for understanding the Neoarchean tectonic evolution of the North China Craton. The Culai Mountain region is one of the most promising areas for such geological studies. Situated in the core of the tectonic belt (Belt B) of western Shandong, it is characterized by well-developed anatexis and ductile deformation. This makes it an ideal location for investigating the spatial and temporal relationships between crustal anatexis and ductile deformation. Methods In this study, we selected a representative migmatite outcrop at the Huangshiya Village and conducted systematic field structural analyses, petrographic observations, and LA–ICP–MS zircon U–Pb geochronology. Results Field observations show that the structural lineaments in this region exhibit an overall NW–SE orientation. Numerous felsic melts developed within the amphibolites, mainly as bands along the foliation, with a few occurring in a network-like or disseminated pattern. Flow folds are well-developed. Petrographic observations demonstrate that quartz grains are distributed along the irregular, corroded boundaries of K-feldspar and plagioclase, containing small melt pockets, bead-like quartzs, and melt films. These features collectively indicate intense anatexis in the region. The newly generated melts reduced the overall rock strength, making it more susceptible to subsequent ductile deformation. Concurrently, NE–SW-oriented horizontal compressive stress further promoted NW–SE regional extension, consistent with the nearly vertical foliation and sub-horizontal mineral stretching lineations observed in the amphibolite. This suggests a deformation regime dominated by near-oblate strain. To constrain the timing of the regional deformation, we conducted LA-ICP-MS zircon U-Pb dating on representative pre-, syn-, and post-tectonic samples of the area. The results indicate that the residual amphibolite records a melt crystallization age of ~2503 Ma, representing the timing of the regional anatexis event. The syn-tectonic monzogranite yields a crystallization age of ~2497 Ma, reflecting a syn-tectonic magmatic event, while the undeformed pegmatite veins formed at ~2465 Ma, bracketing the regional ductile deformation at 2497-2465 Ma. Conclusion In summary, the western Shandong region experienced intense anatexis in the late Neoarchean, which was rapidly overprinted by near-oblate strain-dominated shortening deformation under NE–SW-oriented horizontal compressive stress. The anatexis further facilitated the development of NW–SE-directed ductile deformation. The superimposition of these two events ultimately shaped the structural pattern of the Neoarchean crust of the western Shandong region. [ Significance ] This study provides new constraints that improve the understanding of the Neoarchean tectonic framework and structural patterns of the western Shandong region.