| The Chongzuo Liutang area exposes the northernmost rhyolite and dacite of the contemporaneous Beisi Formation volcanic rocks. This paper obtained high-precision LA-ICP-MS zircon U-Pb ages of 247.8±1.4 Ma and 248.0±1.4 Ma for these rocks. Statistical analysis indicates that volcanic rocks of the Beisi Formation and Banba Formation in southwestern Guangxi Province were formed at 240~248 Ma and 248~ 250Ma, respectively, which were the products of the early Triassic tectonic movement. The geochemical analysis shows that the volcanic rocks of the Beisi Formation have high SiO2 and alkali (Na2O+K2O) contents, extremely low MgO, MnO and CaO contents. The rhyolite and dacite REE contents both have right-inclined LREE enrichment patterns, respectively, δEu values are 0.44~0.48 and 0.48~0.55, Moreover, they are enriched in Rb, K, Th, U, Pb and Nd contents, and are depleted in Ba, Sr, P, Nb, Ta and Ti contents, etc. The Hf isotope study shows that the rhyolites have εHf(t) values ranging from -14.1 to -4.4 and TDM2 values ranging from 1553Ma to 2169 Ma, and the dacites have εHf(t) values of ranging from -16.2 to -7.8 and TDM2 values ranging from 1774Ma to 2296Ma, it can be concluded that the volcanic rocks in this paper were originated from partial melting of Paleoproterozoic metasedimentary rocks. Based on comprehensive study, the Early-Middle Triassic volcanic rocks in southwestern Guangxi are interpreted to have formed in a ?continental margin arc setting? associated with the subduction of the Paleo-Tethys Ocean. These rocks, together with the ?Early-Middle Triassic island arc volcanic rocks? in the Funing-Napo-Chongzuo-Pingxiang area and the ?Babu-Cao Bang ophiolitic melange belt?, constitute an ?oceanic crust subduction-accretion complex-arc system. Thus, the Liutang area volcanic rocks constrain the spatial extent and temporal limits of Paleo-Tethys oceanic subduction in southwestern Guangxi. |