Shear zone controlled syn-kinematic emplacement of granites: Multi-scale structural analysis of the Taibai pluton in the Qinling orogen, central China

Understanding granitic pluton emplacement within collisional orogens is essential for deciphering the dynamic coupling between crustal magmatism and regional tectonic evolution. Well-constrained emplacement models are widely established for extensional and transtensional regimes, whereas the mechanical processes controlling magma ascent and intrusion under regional transpression remain poorly documented and hotly debated. The late Mesozoic Taibai pluton, situated between two major ductile shear zones in the Qinling orogen of central China, provides an ideal subject for investigating the interplay between magma emplacement and tectonics. This study integrates multi-scale structural analyses, including macro- to microscopic structural observations, electron backscatter diffraction, and magnetic fabric measurements, geochronology, and Bouguer gravity data, to constrain the emplacement mechanism of the pluton and its relationship with shearing. Structural observations reveal a systematic pattern in fabric distribution: The pluton interior preserves primary magmatic flow fabrics, whereas the margins adjacent to shear zones transition into medium- to high-temperature solid-state deformation features. Magnetic fabrics further highlight a pronounced contrast between the weakly deformed interior and the strongly strained margins, with magnetic lineations consistently aligned subparallel to the shear zones. Furthermore, a prominent low Bouguer gravity anomaly in the southern part of the pluton is interpreted as a deep-seated magma ascent conduit, supporting structural control on emplacement. Zircon U-Pb dating constrains the timing of granite formation to 119−118 Ma, which is synchronous with regional structures, especially the ductile shearing. The temporal synchroneity of magmatism and ductile shearing, combined with the progressive transition from magmatic fabrics to solid-state deformation, demonstrates that pluton emplacement took place during ongoing regional tectonic deformation. Consequently, we propose that the emplacement room of the Taibai pluton was created at the junction of the Taibai and Houzhenzi shear zones with sinistral transpressional kinematics. Subsequent ductile shearing caused pronounced deformation in high-strain domains near shear zone, while the low-strain interior remains largely undeformed. Our findings demonstrate that shearing is critical for both magma emplacement and subsequent deformation, thereby providing new insights into magma-tectonics coupling within orogenic belts.