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Chronological and geochemical studies of adakites and adakitic rocks are important in understanding the tectonic evolution and geodynamic processes. We present new zircon U–Pb ages, Hf isotope, and geochemical analyses of adakitic rocks exposed in the Baishan area, southeastern Jilin Province, China. These new ages, together with existing age data, indicate that adakitic magmatism in southeastern Jilin Province can be subdivided into four stages: Early–Middle Triassic (251–235 Ma), Late Triassic (221–219 Ma), late Early–early Late Jurassic (176–156 Ma), and Early Cretaceous (ca. 130 Ma). Early–Middle Triassic adakitic rocks occur in a nearly E–W-trending belt within the northern margin of the northeastern North China Craton, indicating a compressional tectonic setting caused by the scissor-like closure of the Paleo-Asian Ocean from west to east. Late Triassic adakitic rocks occur in the Tonghua area and formed in an extensional setting caused by delamination after subduction and collision between the Yangtze Craton and NCC. Late Early–early Late Jurassic adakitic rocks occur in the Baishan and Kaiyuan areas and originated from partial melting of thickened lower crust in a compressional setting related to subduction of the Paleo-Pacific Plate. Early Cretaceous adakitic rocks occur in the Baishan area and were derived from partial melting of thickened lower crust above the subduction zone and delaminated lower crust, indicating that the subducting Paleo-Pacific Plate retreated to the eastern part of southern Jilin Province during the Early Cretaceous (ca. 130 Ma) and that the tectonic setting of the northeastern part of the NCC changed from compression to extension, starting in the east and progressing westward. In summary, the northeastern part of the NCC has been affected by a series of tectonic events during the Mesozoic, such as the closure of the Paleo-Asian Ocean, the collision between the NCC and YC, and the subduction of the Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

This study presents new zircon U-Pb geochronology, geochemistry, and zircon Hf isotopic data of volcanic and subvolcanic rocks that crop out in the Bayanhushuo area of the southern Great Xing’an Range (GXR) of NE China. These data provide insights into the tectonic evolution of this area during the late Mesozoic and constrain the evolution of the Mongol-Okhotsk Ocean. Combining these new ages with previously published data suggests that the late Mesozoic volcanism occurred in two distinct episodes: Early-Middle Jurassic (176-173 Ma) and Late Jurassic-Early Cretaceous (151-138 Ma). The Early-Middle Jurassic dacite porphyry belongs to high-K calc-alkaline series, showing the features of I-type igneous rock. This unit has zircon εHf(t) values from +4.06 to +11.62 that yield two-stage model ages (TDM2) from 959 to 481 Ma. The geochemistry of the dacite porphyry is indicative of formation in a volcanic arc tectonic setting, and it is derived from a primary magma generated by the partial melting of juvenile mafic crustal material. The Late Jurassic-Early Cretaceous volcanic rocks belong to high-K calc-alkaline or shoshonite series and have A2-type affinities. These volcanics have εHf(t) and TDM2 values from +5.00 to +8.93 and from 879 to 627 Ma, respectively. The geochemistry of these Late Jurassic-Early Cretaceous volcanic rocks is indicative of formation in a post-collisional extensional environment, and they formed from primary magmas generated by the partial melting of juvenile mafic lower crust. The discovery of late Mesozoic volcanic and subvolcanic rocks within the southern GXR indicates that this region was in volcanic arc and extensional tectonic settings during the Early-Middle Jurassic and the Late Jurassic-Early Cretaceous, respectively. This indicates that the Mongol-Okhotsk oceanic plate was undergoing subduction during the Early-Middle Jurassic, and this ocean adjacent to the GXR may have closed by the Late Middle Jurassic-Early Late Jurassic. [ABSTRACT FROM AUTHOR]

Introduction: Sialoliths can be removed by sialendoscopy in some cases. But sometimes it fails if the stone is located in the proximal or hilum of Wharton's duct., Aim: To evaluate the clinical efficacy of the sialendoscopy-assisted intraoral incision approach to remove large stones located in the proximal or hilum of Wharton's duct, when sialendoscopy alone fails., Material and Methods: Twenty patients with large stones located in the proximal or hilum of Wharton's duct were included in our study. We used a sialendoscopy-assisted intraoral incision approach to remove large stones located in the proximal or hilum of Wharton's duct when endoscopy failed. The complications and treatment effect were observed., Results: The stones were removed successfully in this way in all patients. Two cases had tongue numbness after the operation, and recovered 3 months later without additional intervention. No swelling or pain appeared during the 3-month to 1-year follow-up. Saliva could be observed from the orifice in 15 patients, with little or none in 5 patients., Conclusions: The sialendoscopy-assisted intraoral incision approach to remove large stones located in the proximal or hilum of Wharton's duct is effective and safe., Competing Interests: The authors declare no conflict of interest., (Copyright: © 2020 Fundacja Videochirurgii.)