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Multi‐scale intracontinental deformations were developed in response to the tectonic evolution of the southern Longmenshan tectonic belt (LMS) on the eastern margin of the Tibetan Plateau. Detailed studies, including field structural analysis and anisotropy of magnetic susceptibility (AMS), were conducted on sedimentary rocks in the foreland basin of the southern Longmenshan tectonic belt (FBSL) in order to better understand the tectonic evolution of the southern LMS. Field observations show that FBSL deformations are mainly characterized by broad and gentle folds in a NE–SW direction and shallow thrust faults. At least two sedimentary discontinuities and two‐stage deformations occurred after the deposition of Cretaceous strata. Samples of magnetic fabrics from the Qionglai–Changshiba profile were characterized by the triaxial magnetic susceptibility ellipsoids common in sedimentary rocks. The magnetic fabrics of the profile represent a weak deformation that was associated with layer‐parallel shortening before folding and mainly reflect the Mesozoic–Cenozoic NW–SE convergence. There are also the following atypical magnetic fabrics: magnetic foliation that is oblique to the bedding and that was associated with layer‐parallel simple shearing during folding; and magnetic lineation that is to varying degrees oblique to the strike of bedding and represents a superposition of structures. Based on the correlation results of magnetic fabrics for samples of different ages, a tectonic superposition since the Late Indosinian Orogeny was found in FBSL. By combining field structural analysis and magnetic fabrics, it was suggested herein that the FBSL is a propagation product of Mesozoic–Cenozoic deformations of southern LMS to the southeast, which therefore experienced a composite superposition of deformations. This finding provides the basis for a comprehensive understanding of the southern LMS and may shed light on the uplift of the eastern margin of the Tibetan Plateau and the tectonic response of its eastern boundary. [ABSTRACT FROM AUTHOR]

Internal structures of the pluton may provide key information on magma emplacement mechanism and the relationship with regional tectonics. We present a case study on the Late Triassic Gaoqiao pluton from South Qinling Belt, which was emplaced under a syn‐collisional setting. Multi‐approaches including zircon U–Pb geochronology, field and microstructural observations, anisotropy of magnetic susceptibility analysis was conducted to reconstruct the growth process of the pluton and to investigate the internal structures. Zircon U–Pb geochronology reveals that the pluton is a composite intrusion which was constructed by two successive units with distinct ages (~220 and ~210 Ma). Field observations show that the Gaoqiao pluton and its country rocks recorded abundant evidences of syn‐plutonic deformations, indicating a syn‐tectonic emplacement. Microstructural observations show that the internal fabrics were mainly acquired during the stage from magma flow to high‐T solid‐state deformation. The fabric distributions display 'onion‐skin' patterns on the pluton scale, which are characterized by zoned foliations and lineations. Combined with the syn‐collisional convergence setting, we propose a tectonic‐controlled incremental growth model for the pluton, in which the pluton was successively constructed by the Fujiahe unit and the Hetaoping unit, and the emplacement process of the pluton was controlled by the regional deformation with sinistral transpressional kinematics. Furthermore, the internal fabric patterns of the Gaoqiao pluton were probably formed by tectonic‐controlled helical magma flow, which appears to be common in fabric formation of many other plutons with similar features. [ABSTRACT FROM AUTHOR]

The Liziyuan goldfield is located along the northern margin of the western part of the Qinling Orogen (WQO). The goldfield consists of five gold-only deposits hosted by metavolcanic rocks, and one polymetallic (Au–Ag–Pb) deposit hosted by the Tianzishan Monzogranite. As the Liziyuan goldfield appears to be spatially and temporally related to the Jiancaowan Porphyry, the study of the deposit provides a crucial insight into the relationship between tectonic-magmatic events and gold metallogenesis in the WQO. In this paper, we present whole-rock major and trace element geochemistry, and in situ zircon U–Pb and Lu–Hf isotopic data from the Tianzishan Monzogranite and Jiancaowan Porphyry. The two granitic plutons are enriched in LILEs and LREEs, depleted in HFSEs and have zircon εHf(t) values between −14.1 and −5.1 for the Tianzishan Monzogranite and between −21.0 and −8.4 for the Jiancaowan Porphyry. These characteristics indicate that the granites are derived from the crust. The Tianzishan Monzogranite has LA-ICP-MS zircon U–Pb ages of 256.1 ± 3.7 to 260.0 ± 2.1 Ma, which suggests that it was emplaced in the WQO during the convergence of the North and South (Yangtze) China cratons in the early stage of the Qinling Orogeny. In contrast, the porphyry has a LA-ICP-MS zircon U–Pb age of 229.2 ± 1.2 Ma, which is younger than the peak collision age, but corresponds to the widespread Late Triassic post-collisional granitic plutons in the WQO. The Tianzishan Monzogranite has somewhat higher Sr contents (196–631 ppm), lower Y (2.23–19.6 ppm) and Yb (0.20–2.01 ppm) contents, and a positive Eu/Eu* averaging 1.15. These characteristics suggest the pluton was derived from partial melting of the thickened crust. In contrast, the relatively higher MgO content (0.85–2.08 wt%) and Mg no. (43.4–58.2) of the Jiancaowan Porphyry indicates that insignificant amounts of subcontinental lithospheric mantle-derived mafic melts were involved in the generation of the magma. The Liziyuan goldfield is hosted by faults in greenschist-facies metamorphic rocks. Fluid inclusion studies suggest that gold was precipitated from CO2-rich, low-salinity and medium temperature fluids. This feature is consistent with the other orogenic gold deposits throughout the world. The field relationships and zircon U–Pb ages of the two granitic plutons suggest that gold mineralization is coeval with or slightly younger than the emplacement of the Jiancaowan Porphyry. Therefore, both the porphyry and deposit formed during the post-collisional stage of the Qinling Orogen. [ABSTRACT FROM PUBLISHER]