Linking deep-time magmatism to present-day lithospheric architecture through integrating geochemical mapping, geophysical observation, and phase equilibrium modeling

Probing the deep lithosphere is a frontier in solid Earth science. Present-day lithospheric architecture is a time-integrated configuration shaped by long-term geological processes, with magmatism playing a pivotal role. Although petrological inference has long been incorporated into lithospheric investigations and integrated with advanced geophysical methods, the full potential of surface-exposed magmatic rocks remains underexploited, particularly in ancient orogens. Here, we investigate Late Carboniferous to Middle Permian magmatic rocks in the West Tianshan, SW Central Asian Orogenic Belt, using multi-proxy isotopic and elemental spatial imaging together with thermodynamic phase-equilibrium modeling. Radiogenic (Hf-Nd) isotopic mapping reveals two distinct domains: an isotopically depleted domain (IDD) in the north and an isotopically enriched domain (IED) in the south. The lower crust beneath IDD was built through magmatic differentiation of intermediate magmas sourced from an oceanic subduction-modified mantle. In contrast, the lower crust beneath IED formed via the differentiation of sanukitoid magmas derived from an ancient crust-metasomatized mantle, with variable involvement of Tarim supracrustal relaminant. Domain-scale contrasts in Bouguer gravity anomaly and Vs velocity structure indicate marked differences in the modern lower crust’s physical properties. Given the insignificant Mesozoic-Cenozoic lithospheric modification, the systematic spatial correspondence between geochemical proxies and lower-crustal Vs velocity structure links modern lithospheric architecture directly to Late Paleozoic magmatism. Our study provides a reproducible workflow that integrates geochemical information from surface-exposed, deep-time magmatic rocks with geophysical observations to explore lithospheric architecture and its genesis beneath ancient orogens.