Chronlogical framework of basement beneath the Xianmgzhong Basin: Evidence by U-Pb ages of detrital zircons from Xikuangshan

The systematic LA-ICP-MS U-Pb dating on detrital zircons from Late Paleozoic sedimentary rocks in Xikuangshan mining area, Xiangzhong Basin, shows that their concordant ages ranging from 3400Ma to 350Ma. On the age spectrum, these zircons can be divided into several groups with different ages, indicating the existence of physical responses to major pre-Indosinian tectonic events in Central Hunan. According to age structure of zircons within different periods of time, together with regional tectonic evolution, the basement-cover framework of Xiangzhong Basin, from bottom to top, was established as crystalline basement (>1.9Ga), metamorphic basement (1.90.54 Ga), low (or non) metamorphic basement (0.540.41Ga), and surface sedimentary cover (<0.41Ga) Combined age spectrum of these strata, as well as corresponding tectonic histories, formation environment of each material layer within the basement-cover frame also has been discussed. Moreover, by comparing age structure of zircons in lamprophyre with zircons in sedimentary rocks, and combined with field geological observations and previous studies, the majority of zircons within the lamprophyre were suggested as residual grains during the melt formation, but not xenocrysts captured from wall rocks during the melt (or dyke) ascending. Most of those zircons were crystalized in 840 700Ma suggest the lamprophyre melt formed at middle-upper metamorphic basement beneath this basin, and thus the position of material-providing layer for lamprophyre melt and other relative fluids is well definited within the basement-cover frame. These works will provide important evidences for further understanding about coupling relationship between magmatism and superlarge-scale Sb mineralization in Xikuangshan.