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  • Monazite and titanite UPb a...
    Qin, Zheng-wei; Siebel, Wolfgang; Fu, Jian-ming; Wang, Hao; Bao, Bo; Yu, Yu-shuai; Shan, Liang; Lu, You-yue; Wu, Yuan-Bao

    Lithos, 12/2023, Letnik: 460-461
    Journal Article

    The early Paleozoic granitoids of the North Qinling Terrane have been widely viewed as the products of an Andean-type margin related to the long-lasting subduction of the Proto-Tethys (Shangdan) ocean. However, the spatial and temporal distributions of the arc granitoids coupled with subduction-accretion processes are still a subject of debate. Here, we report LA-ICP-MS UPb monazite and titanite ages and trace element concentrations for granites and a paragneiss from the North Qinling Terrane. The results, together with data in the literatures, are used to reconstruct the magmatic evolution related to the subduction of the Shangdan ocean during the early Paleozoic. As revealed by UPb geochronology, subduction-related magmatism in the southern belt of the North Qinling magmatic arc (NQMA) was most active between 423 and 404 Ma, and therefore younger and shorter than previously speculated. The ages are in agreement with a metamorphic monazite UPb age (415 Ma) obtained from the paragneiss, suggesting that crustal anatexis of the NQMA was contemporaneous with the magmatism. Overall, magmatism in the NQMA moved progressively from north to south. This southward propagation is consistent with roll-back of the Shangdan oceanic slab and transition from an oceanic arc into a back-arc basin setting. The timing of magmatism and migmatization as well as high-temperature granulite metamorphism in the NQMA signifies that the Shangdan ocean retreated to the North Qinling Unit before c. 423 Ma. Monazites from NQMA generally show HREE depletion and negative Eu anomalies, and some display the REE tetrad effect. These geochemical features indicated that the NQMA granites were highly fractionated. In addition, the abrupt changes in REE compositions displayed by titanites probably record a mixing event with a mafic magma along the Shangdan suture zone. •U-Pb ages of monazite and titanite suggest younger and shorter arc magmatism at c. 423–404 Ma.•The new age data reveals a southwestward migration of the arc magmatic activity from c. 440 Ma.•A revised tectonic model involving slab roll-back is proposed for the North Qinling orogen during the early Paleozoic.•Monazite is well suited for dating highly evolved granites, whereas titanite could record detailed petrogenetic information.