U–Pb Zircon Geochronology and Geochemistry of Granitic Mylonites From Tangdong Fault, Zhuguang Area: Insights Into Middle Triassic Tectono‐Magmatism in South China

The studied granitic mylonites represent ductile deformation characteristics of the Tangdong shear zone with a left‐lateral strike‐slip kinematics. The mylonites contain two‐mica assemblages and are strongly peraluminous (A/CNK = 2.07–6.40). Whole‐rock trace elements (Nb = 18.2–20.4 ppm, Zr = 109–113 ppm, Eu/Eu* = 0.25–0.35), Rb/Sr. ratios (5.01–8.19), and Nb/Ta (4.19–8.10) confirm the protolith as fluid‐altered S‐type granitoids derived from meta‐sedimentary crustal materials. Zircon U–Pb dating yields a crystallization age of 236.6 ± 1.1 Ma (Middle Triassic). Zircon trace elements show flat HREE patterns, negative Eu anomalies (Eu/Eu* ~0.08), and positive Ce anomalies (Ce/Ce* ~8.22), denoting plagioclase breakdown and fluid‐assisted redistribution during fault‐related infiltration Ti‐in‐zircon thermometry yields crystallization temperatures of 685–827 T°C, higher than regional S‐type granites (585–673 T°C), suggesting localized heat flow along the fault zone. Melt depth indicators (Dy/Yb = 0.25–0.42, absence of garnet signature) point to melting at intermediate crustal depths (20–40 km) from metasedimentary sources. The tectno‐magmatic indicators characterize post‐collisional S‐type granitoids emplaced during the compression‐extension transition following the collision between the Indochina Block (ICB) and South China Block (SCB). This study presents a three‐stage evolution model of a ~236 Ma magma emplacement, a ~209 Ma mylonization, and a ~145 Ma reactivation.