德国Münchberg地块榴辉岩的岩石学研究

PETROLOGY OF THE ECLOGITES FROM MNCHBERG MASSIF, GERMANY

Ｍüｎｃｈｂｅｒｇ地块是一个角闪岩相变质的结晶基底，构造推覆于极低级变质古生代火山－沉积岩之中．榴辉岩呈透镜状或互层状产于斜长角闪岩、片麻岩和大理岩之中．榴辉岩的原生矿物组合是石榴石、绿辉石、石英和金红石，可含少量蓝晶石、多硅白云母和黝帘石，峰期变质作用的温度为６００～７００℃，压力＞２．５ＧＰａ，接近柯石英的稳定范围．在榴辉岩的抬升过程中经历了从榴辉岩到角闪岩相、绿片岩相和葡萄石绿纤石相退变质作用．退变质作用的早期为近等温降压过程，晚期为降压和快速降温过程．

Münchberg Massif is an amphibolite facies metamorphic crystalline basement, and thrusts tectonically on a very low_grade Paleozoic volcano_sedimentary sequence. In this Massif, the eclogites occur as lenses and layers within the amphibolite, gneiss and marble. The primary mineral assemblages of the eclogite are garnet, omphacite, quartz and rutile, with minor kyanite, phengite and zoisite. The peak metamorphic pt conditions are 600～700℃ and >2.5GPa, approaching the stable condition of coesite. The eclogites have been subjected to retrograde metamorphism from eclogite facies, to amphibolite facies, to greenschist facies and prehnite pumpellyite facies during the uplift. The retrogressive pt path shows features of isothermal decompressing in the early stage and decreasing temperature and pressure in the late stage.