The Miaoershan-Yuechengling complex pluton is the largest granitoid complex in the western Nanling metallogenic belt with a surface exposure of >3000 km². The complex pluton is composed of an early stage granitoid batholith and late stage small intrusions. The early stage batholith contains mainly medium-grained porphyritic mica granite and porphyritic monzonite granite, whereas the late stage intrusions are composed of muscovite granite porphyry and muscovite monzonitic granite. There are many W-Sn-Mo-Pb-Zn-Cu ores in the contact zone between the batholith and strata, forming an ore-rich belt around the batholith. Based on zircon LA-ICP-MS U-Pb ages, the southwestern part of the early stage batholith formed at 228.7 ± 4.1 Ma (MSWD = 2.49), with slightly earlier magmatic activity at 243.0 ± 5.8 Ma (MSWD = 2.62). The Yuntoujie muscovite granite was associated with W-Mo mineralization and has a zircon LA-ICP-MS U-Pb age of 216.8 ± 4.9 Ma (MSWD = 1.44). The Re-Os isochron age of molybdenite from the Yuntoujie W-Mo ore was 216.8 ± 7.5 Ma (MSWD = 11.3). Our new isotope data suggest that the late stage intrusive stocks from the southwestern Miaoershan-Yuechengling batholith were closely associated with W-Mo mineralization from the Indosinian period. These new results together with previous isotope data, suggest that South China underwent not only the well-known Yanshanian mineralization event, but also a widespread Indosinian metallogenic event during the Mesozoic period. Therefore, South China has a greater potential for Indosinian mineralization than previously thought such that more attention should be given to the Indosinian ore prospecting in South China.

A-type granites are conventionally interpreted to be formed in late post-collisional or anorogenic settings. However, we firstly identified an Early Jurassic syn-collisional A-type granite suite in the Qinling orogenic belt: the Baoji granite suite. A comprehensive investigation into its mineralogical, petrological, geochronological, and geochemical characteristics can shed light on the genesis of syn-collisional A-type granites and geodynamic evolution of collisional orogeny. The Baoji granite suite contains two types of rocks: (1) A-type granites including biotite syenite, coarse-grained, porphyritic, and fine-grained syenogranites, and alkali-feldspar granite, and (2) magnesian monzodiorite; both types are coeval, with zircon U–Pb ages of ca. 190 Ma. The A-type granites yield A₁-type trace element signatures and large variations in trace element contents, with Ba contents of 16.9–762 ppm, Sr of 11.0–211 ppm, Rb of 193–645 ppm, and Eu of 0.08–1.24 ppm. Their radiogenic isotope compositions (⁸⁷Sr/⁸⁶Sr_i = 0.70631–0.70637; εNd = −5.18 to −3.84; εHf = −5.01 to +2.76) are similar, and overlap those of Neoproterozoic OIB-like basic volcanics from the South Qinling belt. These characteristics show that the A-type granites originated from the anatexis of OIB-like lower crust and underwent fractional crystallization in a silicic magma reservoir. The monzodiorite has low SiO₂ contents (49.82–53.29 wt.%) and enriched radiogenic isotopic compositions (⁸⁷Sr/⁸⁶Sr_i = 0.70554–0.70638; εNd = −11.0 to −5.28) contains abundant hornblende and biotite (~40%), and exhibits evidence of magma mingling. It also contains two groups of zircon: pristine and unzoned zircon that yields negative Hf isotope compositions (εHf = −9.42 to −3.14), and xenocrystic zircon that yields similar Hf isotope compositions (εHf = −3.54 to +1.85) to the A-type granites. These characteristics demonstrate that the monzodiorite was derived from the differentiation of basaltic partial melts of an enriched mantle source, and mingled with the A-type granitic magma during its ascent and emplacement into a silicic magma reservoir. Along with regional records of the Early Jurassic magmatism, deformation, metamorphism, and sedimentation, the genetic models for the Baoji A-type granites and monzodiorite suggest that the Middle Triassic to Early Jurassic oblique continental collision (ca. 230–190 Ma) produced coupled EW-trending strike-slip and NE-trending extensional faults at crustal levels and Rayleigh–Taylor (gravitational) convective instabilities at mantle depths in the Qinling orogenic belt, which controlled the production of the syn-collisional A-type granite suite. Our work also indicates that the A-type granites can be formed in syn-collisional setting in response to oblique continental collision and the resultant slow foundering of a high-density lithospheric root; therefore, we suggest that the syn-collisional A-type granites are evidence for oblique continental collision.