The Tongde dioritic pluton (Sichuan, SW China) and its geotectonic setting: Regional implications of a local-scale study

The Tongde intrusive complex, is located in the southern part of the mid-Neoproterozoic intrusive chain that borders the western margin of the Yangtze craton. The Tongde intrusion is made up of diorite, quartz diorite and minor gabbro. The Tongde pluton intruded the Neoproterozoic Yanbian Group, and was intruded by the Gaojiacun mafic-ultramafic complex. SHRIMP U-Pb zircon dating yielded the age of 825 ± 7 Ma. The rocks of the Tongde pluton show arc-type geochemistry and calc-alkaline affinities. The Tongde pluton does not show contact aureole and its peripheral zone (up to 2 km wide) is gneissic, which indicates the metamorphism of the intrusion along with the Yanbian Group, probably during the accretion of a marginal basin to the Yangtze craton. The lack of metamorphism in the adjacent Gaojiacun complex constrains the age of the accretion to ca. 810-830 Ma. The gneissic texture reported from other mid-Neoproterozoic intrusions in the western part of the Yangtze craton (e.g. Yuanmou, Guandaoshan, Shaba, Miyi, Kangding) indicates widespread compression, consistent with an Andean-type geotectonic setting and supporting the existence of the mid-Neoproterozoic Jinning orogeny.