The genesis of granite mass in the volcanic area of Litang, Chuanxi province: constraints from rock geochemistry and U-Pb zircon dating

The granite complex in the Maohuo area of Litang County is located in the central and western parts of the Yidun-Shaluri island arc in the Sanjiang area; the intrusion is located in the sand slate of the Tumugou Formation in Daocheng District. In this paper, the petrographic analysis of the granodiorite porphyry and biotite monzogranite in the granite complex in the Volcano area is carried out, a systematic study of rock geochemical characteristics and chronology, elucidating the genetic connection between the two in the nature and tectonic background of the source region. Zircon LA-ICP-MS U-Pb dating shows, granodiorite porphyry, medium-coarse-grained biotite monzogranite, the ages of diorite inclusions in biotite monzonitic granites are 220.7 +/- 1.3 Ma, 220.4 +/- 1.6 Ma, and 219.8 +/- 1.4 Ma, three are roughly formed at the same time, and it is a product of late Triassic magmatic activity. Rock geochemical features show that granodiorite porphyry in the granite complex, biotite monzonite granite, scintillation inclusions it has high total alkali, Rb content and relatively low Al2O3, Sr and other content, has a moderately negative europium anomaly, obvious loss of Ta, Nb, Ti and other high field strength elements, and aluminum saturation index < 1.1 is characterized. Combined with geological data granodiorite porphyry, both biotite monzonitic granites are also I-type granites formed in a typical island-arc environment. Combined with rock geochemical characteristics and U-Pb chronology research results, three should be a set of rock assemblages formed by the evolution of a set of magma melting events. Among them, biotite monzogranite and granodiorite porphyry are the products of homologous magma crystallization and differentiation. The diorite enclaves in the biotite monzogranites are the result of their own evolution when the granitic magma undergoes fusion and immiscibility.