LA-ICP-MS zircon U-Pb ages, petrogeochemistry and tectonic significance of the Indosinian basic intrusive rocks in the Tengxian region, southeastern Guangxi

The basic intrusive rocks in the Tengxian region, southeastern Guangxi occur as N-E-orientated beads along the Lingshan-Tengxian fault, including the Sanmentan, Dongsheng, Longcun, Tangcun and Hanchi intrusive rock masses, and consist dominantly of norite, gabbro norite, gabbro and quartz gabbro diorite. The LA-ICP-MS zircon U-Pb ages are dated at 230.0±0.9 Ma for hornblende norite from the Sanmentan rock masses and 236.5±1.3 Ma for quartz hornblende norite from the Dongsheng rock masses. Geochemically, these intrusive rocks are characterized by low Mg and high Ti and Fe contents. The total REE contents are relatively low and highly variable, with ΣREE amounts of (43-189)×10^-6,δEu values from 0.79 to 1.63 showing positive Eu anomalies. The primitive mantle-normalized trace element distribution patterns display the geochemical signatures of continental volcanic arc calc-alkaline basalts characteristic of the highly enrichment of the large-ion lithophile elements(LILE) Rb, Ba and Th and slightly enrichment of the elements Ce, P and Sm, indicating "three uplifts" features and the "valley" shape distribution of the high field strength elements(HFSE)Ta, Nb, Zr and Hf against the background of weak enrichment. The results of research have reflected that the basic intrusive rocks in the Tengxian region were formed during the Middle Triassic, and are assigned to the continental volcanic arc calc-alkaline basalts in the active epicontinental arc environments, and represent the geological records of the Indosinian epicontinental orogenic belts in southeastern Guangxi.