桂东南大容山晚二叠世花岗岩锆石U-Pb年龄和Sr-Nd-Hf同位素特征及其地质意义

摘要

The petrogenesis and geodynamic processes of the Darongshan granite have been a subject of much controversy. In this paper, the authors report U-Pb ages and Sr-Nd-Hf isotopes for the Darongshan granite in southeastern Guangxi. LA-ICP-MS U-Pb zircon analysis yielded 206Pb/238U weighted mean age of 253.6±2.1Ma, 256.4±1.8Ma and 256.8±2.8Ma for three granite sam⁃ples respectively, indicating that these granites are of Late Permian origin rather than the Early-Middle Triassic origin. They have relatively high εNd(t) values (-9.18~-13.4) and younger Nd model ages (tDMc=1.55~1.84Ga), which are consistent with εHf(t) val⁃ues (-5.5~-6.7) and Hf model ages (TDM2=1.64~1.71Ga), suggesting an lower crustal source mixed with the Paleo-Mesoproterozoic materials. Combined with previous studies, the authors hold that the Darongshan granitic magmatism might have been related to anatexis of the lower crust due to the subduction/collision between Indosinian block and South China plate during the Hercynian to Indosinian period.%对桂东南大容山花岗岩进行了详细的锆石U-Pb定年及Sr-Nd-Hf同位素研究，3个花岗岩样品获得的206Pb/238U年龄加权平均值分别为253.6±2.1Ma、256.4±1.8Ma和256.8±2.8Ma，暗示其形成于晚二叠世，而不是早—中三叠世；岩体的εNd(t)和εHf(t)值均为负值,分别集中于-9.18~-13.4和-5.5~-6.7之间，对应的两阶段Nd模式年龄(tDMc )和Hf模式年龄（TDM2)分别为1.55~1.84Ga和1.64~1.71Ga，表明岩体物质的源区主要为古元古代—中元古代的壳源物质。结合区域已有的研究成果，认为其形成可能与华南板块和印支地块之间在海西期—印支期的俯冲/碰撞拼合有关。