西秦岭二长花岗岩岩体群同源性研究

摘要

对西秦岭二长花岗岩岩体群(又称“五朵金花”)的岩体地质、岩相学及地球化学等方面的研究表明:5个岩体均具有较为清晰的侵入顺序:早期为闪长岩浆侵入,中期和晚期为二长花岗岩浆侵入,分别形成黑云二长花岗岩和二云二长花岗岩侵入体,其岩性成分表现为从早至晚从偏基性→偏酸性演化特征；从每个岩体来讲,显示出由东向西变细的矿物粒度变化和由北面向南成分逐渐变酸的特点.早期样品为高钾钙碱系列和钾玄岩系列,中期样品主要为钾玄岩系列,而晚期样品主要集中于高钾钙碱系列.早期次样品落入钾质和钠质的过渡区,中期和晚期样品则多数落入钾质区.各岩体组成具有相似的稀土和微量元素分布特征,在球粒陨石标准化稀土元素配分图上,轻稀土富集,具有中等亏损的负Eu异常.岩体Rb-Sr同位素年龄值介于181～232.9 Ma,K-Ar同位素年龄值介于178～248.8 Ma,ANKC值大多小于1.1,属过铝质花岗岩.该岩体群具有喜马拉雅岩型花岗岩的特征,具有同源岩浆的特点.%The homology of the rock mass is analyzed according to the geology, petro-graphic and geochemical along the rock group of adamellite in the western Qinling(commonly called as" Five golden flowers"). It shows that the invasion sequence is clear. The rock mass includes diorite in early phase, biotite adamellite in the metaphase, two-mica monzonitic granites in the late stage. The intrusion has an evolution trend from acidic to alkali with rock forming episode. In the space, the longitudinal lithology is consistent overall, and the structure become thinner from east to west; the transverse structure is similar and the composition is more partial acid to the south. The rock group from the old to the new, they are from the potassium and sodium transition area to potassium, belonging to shoshonitic series and high-K calc-alkaline series. They have similar geochemical features. The REE diagram of the Chondrite-normalized show that they are rich in LREE, and evidently depleted in Eu. The adamellite is formed at 181-232. 9Ma (by Rb-Sr) and 178-248.8Ma (by K-Ar) . Meanwhile, the value of the ANKC is lower than 1.1, with peraluminous granite. They are Himalayan-type granite. Research shows that the rock group of adamellite has homology.