Linking arc migration, crustal thickness variation, and magmatism in the Early Cretaceous Sikhote–Alin accretionary orogen, NE Asia

Magmatic arc migration, a prevalent feature in accretionary orogens, often aligns with fluctuations in crustal thickness and geochemical properties. Despite their common occurrence, the mechanisms intertwining these processes and their influence on arc magmatism remain largely elusive. The Sikhote–Alin accretionary orogen, as a part of the West Pacific orogenic belt and a long-lived active margin along eastern Eurasia, offers an exceptional window for investigating these dynamics. Our study leverages machine learning-based modelling inversions, revealing a decrease in crustal thickness from 52 ± 9 km to 43 ± 8 km in Northeast Asia during the Early Cretaceous. This thinning was disrupted by two significant thickening events around 130 Ma (peaking at 57 ± 9 km) and 110 Ma (peaking at 56 ± 6 to 59 ± 5 km). The spatial-temporal distribution of magmatism ages indicates an arc migration exceeding 500 km during 135–120 Ma, and a further ~200 km migration around 110 Ma. During the Early Cretaceous (135–120 Ma), the Sikhote–Alin accretionary orogen was predominantly intruded by S-type granitoids, originating from partial melting of pelite-poor, psammite-rich sediments within a thickened accretionary prism, accompanied by muscovite and biotite dehydration. Younger granitoids, with ages of 120–110 Ma were transitional S- to I-type, whereas those aged 110–100 Ma were dominated by I-type, generated through partial melting of igneous rocks in an accretionary prism setting. Linking the data of arc migration, crustal thickness variation, and magmatism, we propose that the arcs in Northeast Asia migrated during 135–120 Ma and around 110 Ma, mainly driven by crustal thinning and accretionary prism emplacement, respectively. Variations in crustal thickness significantly impacted the magmatic evolution by influencing magma transport, the likelihood and location of magma stagnation, and the pressure conditions for magma differentiation. Arc migration events further accentuated the spatial heterogeneity of crustal composition and thickness, ultimately affecting magma sources and evolution.