Zircon U-Pb ages and geochemical characteristics of Early Indosinian Liuwanshan granites, Guangxi

The Liuwanshan granites consist mainly of cordierite-bearing biotite monzogranite, which can be divided into four emplacement units according to rock structure and the emplacement relationship. LA-ICP-MS zircon U-Pb dating shows that the ²⁰⁶Pb/²³⁸U weighted average ages of zircons from these emplaced units are 252.8±1.9Ma (MSWD=0.92), 249.2±1.9Ma (MSWD=1.2), 248.3 ± 3.2Ma (MSWD=2.1), and 246.8 ± 2.8Ma (MSWD=2.2), respectively. Geochemical data reveal that these granites are characterized by enrichment of large ion lithophile elements (LILE, such as Rb and K) and relative depletion of high field strength elements (HFSE, such as Nb, Ta and Ti), suggesting geochemical characteristics of typical subduction-related arc magmatic rocks. REE distribution patterns show right-inclined shape with obvious Eu negative anomaly and relative enrichment of HREE, which is consistent with crust-source granites distribution patterns. La-La/Sm diagram indicates that the Liuwanshan granites were mainly formed by partial melting and experienced a certain degree of fractional crystallization. Combined with petrochemical characteristics, trace elements geochemeical characteristics and tectonic setting discrimination diagrams, the authors have reached the conclusion that Liuwanshan granites were formed in a tectonic setting of early ocean-continent subduction and later continental collision.