大别造山带毛屋岩体的解体及古地幔性质的厘定

根据详细的地球化学 (特别是稀土元素地球化学 )的研究资料 ,提出大别造山带毛屋岩体应该解体。毛屋岩体不是由多幕式镁铁 超镁铁质层状堆晶作用形成的一套岩石系列 ,而是由橄榄岩类、含石榴石方辉岩类、榴辉岩类和绿辉石岩类组成的一个混杂岩体。其中含石榴石方辉岩类与绿辉石岩类之间存在成因上的联系 ,含石榴石方辉岩类的原岩是本区原始地幔经约36 %的部分熔融后剩下的残余 ,而绿辉石岩的原岩是由该熔融体结晶的产物。根据含石榴石方辉岩与绿辉石岩之间的成分制约关系 ,对该区古地幔的稀土元素组成和地幔性质进行了反演 ,结果表明 ,该区原始地幔稀土元素成分与球粒陨石中的相似 ,为轻稀土略亏损的平坦型组成模式 ;该区原始地幔矿物成分为橄榄石 (72 8% )、单斜辉石 (12 4% )和石榴石 (14 8% ) ,属含单辉石榴橄榄岩的地幔。

DISAGGREGATION OF MAOWU ULTRAMAFITE AND ITS PRIMORDIAL MANTLE DETERMINATION IN DABIE OROGENIC BELT,CHINA

Based on the detail geochemical research especially REE geochemistry, it is suggested that the Maowu ultramafite should be disaggregated into the complex rocks, which are composed of peridotite, garnet bearing harzburgite, eclogite and omphacitite. Of them, garnet bearing harzburgite connected with omphacitite in the cause of formation. By differential coefficient theory,it was calculated that the garnet bearing harzburgite was the residual after the local primordial mantle had partially melt about 36%, and the primary rock of omphacitite was derived from the crystallization of the very magma. According to the restriction between the garnet bearing harzburgite and omphacitite, the REE contents and mineral components of the primordial mantle are obtained. It was revealed that the REE in the primordial mantle are similar to those of chondrite and shown a slightly LREE depleted flatness pattern. The local primordial mantle consists mainly of olivine (72 8%), clinopyroxene (12 4%) and garnet (14 8%), and is a clinopyroxene bearing garnet peridotite mantle.