The petrogenesis of minette from Luocheng of Northern Guangxi: Geochemistry and U-Pb geochronology

In this paper, the authors conducted detailed study of geochemistry and LA-ICP-MS zircon U-Pb geochronology of lamproites in Luocheng of northern Guangxi, and obtained a zircon age of 248±1 Ma, indicating that the lamprophyre magmatic activity in this area occurred during the Triassic.The potassium content of minette is significantly higher than average content of continental crust.The rock is characterized by rich potassium (K₂O/Na₂O=4.23~136.2) and alkali (K₂O+Na₂O=6.86%~8.03%) and enrichment of light rare-earth elements and large ion lithophile elements as well as depletion of high field strength elements with low La/Nb ratios, Nb/U ratio less than MORB, OIB and the value of the earth's crust, being close to average relevant values of global diving sediments.These results show that the source area might have been the enriched mantle formed by early subduction metasomatism.Combined with regional tectonic background analysis, the authors infer that the diagenetic process of minette from Luocheng in northern Guangxi was as follows:the intracontinental lithosphere of South China experienced stretching and thinning in Mesozoic Triassic (255.5±3.5 Ma), the upwelling of the asthenosphere caused the partial melting of the enriched mantle to form the minettes magma, and the NNE-trending deep fault in the region provided the channel for the magma eruption.