摘要:
锡田岩体位于南岭中西段北东向钨锡A型花岗岩带(由花山、姑婆山、九嶷山、骑田岭岩体组成)北端,主要由晚三叠世和晚侏罗世花岗岩组成。本文对锡田岩体进行了岩石学、岩石地球化学特征研究,研究表明锡田岩体为钾质、高钾质,亚碱性,过铝质的碱钙性岩石,SiO2、(K2O+Na2O)含量较高,微量元素Y富集、Ba、Sr亏损,具较低的87Sr/86Sr值、高ε Nd(t)值(>-8)和低t 模式年龄值等特征;在地球化学判别图解上,锡田岩体显示为A型花岗岩,其晚三叠世花岗岩侵位于印支运动的主碰撞之后,形成于碰撞后伸展构造体制下;而晚侏罗世花岗岩可能与古太平洋板块的俯冲消减引起的拉张环境有关,为后造山花岗岩。在野外地质资料的收集及详细调查的基础上,对岩体的接触关系、接触带特征、分布形态,岩体中发育的流面构造、捕虏体及其边缘向斜进行了研究,结合航片、卫片图像特征,认为锡田岩体以气球膨胀方式底辟上升侵位,而部分晚期的侵入次侵位可能受断裂的控制。
Abstract:
A NE-trending Sn-W bearing A-type granite belt which is composed of Huashan, Guposhan, Jiuyis-han, Qitianling granite batholiths are located in the western-middle part of Nanling Range. The Xitian granite in the north part of this belt is intruded in Late Triassic to Jurassic, with geochemical characteristics of high-K, mild alkaline and peraluminous, higher concentration of SiO2 and (K2O+Na2O), which is also rich in Y and poor in Ba, Sr and characterized by lower (87Sr/86Sr)i, higherε Nd(t) (>-8), lower tDM model age etc. The geo-chemical discriminative chart shows that Xitian grantie is A-type granite, considering to be part of Sn-W bear-ing A-type granite belt in southern Hunan-northern Guangxi region, the formation tectonic setting is that Late Triassic granite invaded after major collision in indisinian movement which was formed in the extend tectonic regime after collision;while Late Jurassic granite is post-orogenic granite, formed probably related to exten-tional environment,which caused by the subduction of the paleo Pacific plate. By means of collecting geology outside data, together with the explanation of contact relationship, contact region characteristic, distribution pattern of rocks, and planar flow structure, xenoliths, peripheral sink developed in the rocks, also combined by the image characteristic in arial photos, suggesting that Xitian granite are intruded in the manner of ballon ex-pand, while partly terminal intrusion probably is controlled by fracture.
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