大别山超高压变质带中型花A岗岩确定及成因探讨

大别山超高压带中变质花岗岩特征：（１） 岩石组合较单一，以二长花岗岩（ 原岩） 为主，缺乏中基性岩和正长岩类；（２） 具鳞片花岗变晶结构，片麻状构造，保留残存的岩浆岩组构；（３） 与榴辉岩及其它超高压变质岩石有明显侵入接触关系，并可见有其捕虏体；（４） 岩石化学表现为富硅、富碱、贫钙、贫镁等特征，一般地ＳｉＯ２ ＞ ７６ ％ ，（ Ｎａ２ Ｏ＋ Ｋ２ Ｏ） ＞ ８ ％ ，ＣａＯ＜ ０ ．５ ％ ，ＭｇＯ ＜ ０ ．４ ％ ；（５） 痕量元素表现为Ｚｒ 、Ｙ、Ｎｂ 、ＲＥＥ 含量高，Ｓｒ 、Ｓｃ 、Ｖ、Ｎｉ 等低；（６） 变质矿物组合为斜长石＋ 石英＋ 钾长石＋ 白云母＋ 石榴石＋ 绿帘石，属于低角闪岩相。（７） 锆石Ｕ － Ｐｂ 同位素年龄值为６８５ ±４１ Ｍａ 。大别山超高压变质带中变质花岗岩为Ａ 型花岗岩，更接近Ａ２ 亚类。变质Ａ 型花岗岩的确定，对进一步认识大别山的大地构造演化、榴辉岩等超高压变质带的形成、折返机制等提供了重要地质依据。

THE DETERMINATION AND GENESIS OF METAMORPHOSED A-TYPE GRANITESOF THE DABIE ULTRAHIGH PRESSURE BELT

The metamorphosed granites of the Dabie UHPMB are characterized by:(1)single rock association dominated by adamellite(protolith)lacking intermediate-basic rock and syenite;(2)scale granoblastic texture, gneissic structure and the remains of igneous rock texture and structure; (3)evident intrusive contact relationship with eclogite and other ultrahigh pressure metamorphosed rocks and their xenoliths; (4)petrochemically rich silicon and alcali and poor calcium and magnesium with SiO2>76%, (Na2O+K2O)>7%, CaO<0.5%and MgO<0.4%; (5)trace elements of high content of Zr, Y,Nb and REE and low content of Sr, Sc,V , Ni, etc.;(6)amphibolite facies of metamorphosed mineral association of plagioclase+quartz+potassium feldspar+mica+garnet+epidote. Based on the above characteristics of the metamorphosed granites in the Dabie ultrahigh pressure belt, they are thought to be A-type granites, close to A2 subtype, which provide important geological basis for further recognition of the tectonic evolution, the formation of eclogite and other ultrahigh pressure metamorphosed belts and exhumational mechanism of the Dabie Mts.