晋冀蒙高级地体石榴石基性麻粒岩地质特征及其构造意义

在晋、冀、蒙交界处的高级变质岩区,沿孔兹岩系和怀安麻粒岩杂岩的接触带上广泛发育石榴石基性麻粒岩,其主要特征: 1)以透镜状、岩脉状分布于孔兹岩系和麻粒岩杂岩的接触带上; 2)和孔兹岩系及麻粒岩杂岩的接触关系为侵入或韧性剪切接触; 3)具斜方辉石-单斜辉石-角闪石-斜长石-石榴石的矿物组合及围绕石榴石发育斜长石和角闪石或斜方辉石的交生结构,部分还可见到斜方辉石后成合晶定向排列; 4)在孔兹岩和麻粒岩的接触带上还有透镜状的角闪辉石岩、脉状的斜长岩; 5)具等温降压的PT轨迹,并有200-300MPa的压力降,具有陆-陆碰撞的特征; 6)同位素年龄资料显示,岩石的定位年龄约为1800Ma.因此,石榴石基性麻粒岩是下地壳深源岩浆在吕梁运动时沿不同地体的对接带上侵的深源侵入体,并和孔兹岩岩片、 (超)基性岩体一同构成复杂的具混杂岩性质的构造岩浆杂岩带,其出现部位能指明不同地体的对接部位.

THE GEOLOGIC FEATURES AND TECTONIC SIGNIFICANCE OF GRANET-BEARING BASIC GRANULITE IN JIN-JI-MENG (SHANXI-HEBEI-INNER MONGOLIA) HIGH-GRADE TERRAIN

There are many garnet - bearing basic granulites occurring along the contactbetween the khondalite suite and the granulite complex in Jin - Ji - Meng (Shanki - Hebei - InnerMongolia) high - grade tearrain. The geologic features are follows: 1) The rocks are occurred aslens or dike along the contact between the khondalite or granulite complex. 2) The contact of thegarnet- bearing basic granulite with the khondalite suite or granulite complex is intrusive orductile shear contact, the hanging wall is khondalite or granulite. 3) The mineral assemblage ofthe garnet - bearing basic granulite is Opx - Cpx - Hb - Pl - Gt, and the potrographically markedfeature of most rocks is the corona of sympleclitic intergrowth of Pl + Hb /Opx surroundinggarnet, sonme of them are oriented. 4 ) There are also occurred ultrabasic - basic rocks aspyroxeulite and anorthosite with the garnet - bearing basic granulite. 5) It has a isothermaldecompression (ITD) path and about 200 - 300Mpa decompression, which suggest continent -continent collision and a rapid uplifting. 6) The isotopic ages of the rocks show that the garnet -bearing basic granulite is intruded at l800 Ma. In brief, the garnet - bearing basic granulite isintrusive gabbro which intruded into the lower crust when the Luliang movement (1800Ma). Ithas a significance for indicating the regional tectonic boundary taken each other by two terrain.