Zircon LA-ICP-MS Dating of Granites from the Southeastern Zongnai Mountain Alax and Its Geochemical Characteristics

There are many types of granites around the southeastern Zongnai Mountain rock mass in Alax, the types of rocks, the characteristics of source rocks, and tectonic setting by using the LA-ICP-MS zircon geochronology, petrographic observation, geochemical methods (major, trace and REE elements) of granites and diorites from southeastern Zongnai Mountain rock in Alax are discussed. The rocks are mainly alkaline-calc-alkaline metaluminous granites and diorites. LA-ICP-MS zircon U-Pb dating yielded ages of 236.6±0.95 Ma to 249.7±2.6 Ma for the plagioclase and biotite granite and 268.4±0.69 Ma for the gneissic granite. Therefore, these rocks were formed mainly during the late Variscan and early Indosinian periods and are characteristic of multi-stage intrusions. The values of TiO₂, A/CNK, A/NK, 10000*Ga/Al, etc. and the abnormal elements Ba, Ta, Sr, Eu, etc. indicate that these granites are I-type granites. Major, trace and rare earth elements indicate that these rock are mainly derived from volcanic arc crust and locally derived from the collision zone. Due to the subduction of oceanic crust in the southeastern Zongnai mountain, arc margin orogenic granite intrusions and other variations were formed with continental margin arc characteristics. LA-ICP-MS zircon ages provide timing constraints for the subducted oceanic crust and conclude that the collision time is earlier than 236.8±1.9 Ma.