Lithospheric mantle multi-stage metasomatism: Constraints from Sr-Nd-Pb-Mo isotopes of Mesozoic basaltic andesites in the Xing'an Massif

Subduction zones represent primary sites for material exchange between the mantle and crust. Over the long course of geological history, the mantle is frequently subjected to superimposed reworking by materials derived from distinct subduction zones. However, relatively few studies have focused on mantle multi-stage metasomatism driven by different tectonic systems. The Xing’an Massif, situated in the eastern segment of the Central Asian Orogenic Belt, was influenced by the Mongol-Okhotsk and Paleo-Pacific tectonic systems during the Mesozoic. Consequently, systematic analysis of spatiotemporal geochemical variations in Mesozoic igneous rocks across this region provides valuable constraints for deciphering mantle multi-stage metasomatism. Here, we report integrated elemental and Sr-Nd-Pb-Mo isotopic analyses of the Late Triassic and late Early Cretaceous basaltic andesites from the Xing’an Massif. The Late Triassic samples exhibit elevated δ^98/95Mo values (+0.49‰ to +0.56‰), which are significantly higher than the normal mantle value of -0.20‰ ±0.01‰. They also show enrichment in fluid-mobile elements (e.g., Ba, Cs) and high Sr/Nd ratios (34 to 36). Combined with high Ce/Mo ratios (115 to 145) and moderately enriched Sr-Nd-Pb isotopic compositions, these features indicate the mantle source originated from the partial melting of a mantle wedge metasomatized by both serpentinite-derived fluids and sediment-derived melts during the southward subduction of the Mongol-Okhotsk oceanic plate. The late Early Cretaceous basaltic andesites exhibit high δ^98/95Mo values (-0.13‰ to +0.70‰) and pronounced enrichment in fluid-mobile elements, demonstrating geochemical affinities to the Late Triassic rocks. This similarity implies that the late Early Cretaceous mantle source components were inherited from pre-existing Late Triassic metasomatized mantle domains. However, their more enriched Sr-Nd-Pb isotopic compositions than those of Late Triassic counterparts suggest the addition of subsequent sediment melts contributed to their mantle source. Magmatism, tectonism, and paleomagnetic evidence indicate that the eastern segment of the Mongol-Okhotsk Ocean closed during the Middle Jurassic to Early Cretaceous. Therefore, these additional sediment melts should have been derived from the Paleo-Pacific Plate. Collectively, this study identifies the multi-stage metasomatism of mantle by materials derived from different subduction zones, thereby providing new constraints for reconstructing the multi-stage tectonic transition processes and the spatiotemporal extent of their impacts in Northeast Asia.

This work was financially supported by the China National Science and Technology Major Project (No. 2024ZD1001104) and the National Natural Science Foundation of China (No. U2244201).