大别山东部榴辉岩带中的变质花岗岩及其大地构造意义

大别山高－超高压变质带中的变质花岗岩类是碱性花岗岩。它以其下列特征与本区未变质花岗岩和围绕它的低压花岗质片麻岩相区别：（１）有标型矿物多硅白云母和长石的石榴石反应边；（２）主要为花岗变晶结构但有残留的岩浆结构，岩体边部有片麻状构造；（３）与超高压围岩之间有残留侵入接触关系，两者共同受到第二期褶皱影响；（４）化学成分富硅和富碱，Ｋ２Ｏ和Ｎａ２Ｏ含量变化不定，大部分样品的Ｎａ２Ｏ大于Ｋ２Ｏ含量，Ｋ２Ｏ＋Ｎａ２Ｏ总量大于７％；（５）矿物组合表明变质级为角闪岩相；（６）Ｒｂ－Ｓｒ等时线年龄１８１Ｍａ（全岩，黑云母）；（７）其中常有高－超高压变质岩相的捕虏体。这些特征表明，这里的变质花岗岩类是高－超高压变质带折返到中地壳时侵入其中并随之共同变质变形的，因此是高－超高压变质带的特殊成员。这对理解超高压变质带的折返速率是非常重要的。

Meta granitoid from the High Ultrahigh Pressure Metamorphic Belt in the Dabie Mountains and Its Tectonic Significance

The metagranitoid found in the high ultrahigh pressure metamorphic belt ( HP UHPMB ) in the Dabie Mountains is alkali meta granite.It can be distinguished from the unmetamorphosed Mesozoic granite and the low pressure gneiss by the features: (1) the key metamorphic minerals:phengite and coronal garnet around albite; (2) mainly granoblastic with relic magmatic texture and gneissic structure on the margin;(3) deformed together with it's HP UHPMB country gneiss during second generation of fold; (4) chemically rich in SiO 2 and Na 2O,sometimes K 2O, the sum of Na 2O and K 2O content is more than 7%;(5) mineral assemblage showing amphibolite metamorphism; (6) chronologically being 181.Ma ( Rb Sr, Wr Bi ); (7) with UP UHPM rocks as xenolith. By these features it is concluded that the metagranitoid was occurred during the exhumation and as the special member of the UHPMB. It is very important for understanding the exhumation rate of the UHPMB.