论文部分内容阅读
印度南部 Tamil Nadu,Madras 地区典型紫苏花岗岩产地的太古代麻粒岩是由一套基性和酸性两种形式的正片麻岩组成的,并伴随有沉积变质片麻岩(孔兹岩系).紫苏花岗岩是一种主要的岩石类型。基性麻粒岩表现出一种具有明显富铁拉斑玄武岩的特点,伴随着稀土元素(REE)浓度的增加,并出现了铕(Eu)负异常.这些特点被认为是反映了辉石——斜长石组合在氧逸度(fo_2)低的条件下的低压分离结晶作用。超 Fe—Mg 质麻粒岩可能代表着这个过程的堆积物.酸性麻粒岩(紫苏花岗岩)一般是富 K_2O 的,而在大多数麻粒岩相地段占主要地位的酸性片麻岩则显然不同,K_2O 都低。然而,紫苏花岗岩中 REE 丰度具有在富 K 和贫 K 的两种太古代片麻岩中所观察到的整个范围。在这个地区大量前麻粒岩相钾质伟晶岩的出现,表明在原来钾含量较少的岩石组合中产生了钾质交代作用。微量元素产生了这样一个模式,即在麻粒岩相变质事件之前产生了酸性片麻岩的交代作用和局部熔融。这种事件的顺序是与地壳深部变质流体的成分的波动有密切的关系.
Archean granulites from the origin of the typical peridotite granite in the Tamil Nadu, Madras region of southern India are composed of a set of both orthogneiss and acid forms of orthogneiss, accompanied by metamorphic gneisses (khondalites) Perilla is a major rock type. The basic granulite shows the characteristic of a distinct iron-rich tholeiite with the increase of REE concentration and the occurrence of the negative Eu anomaly, which is considered to be a reflection of the pyroxene- Low pressure separation and crystallization of plagioclase combination under low fo_2 oxygen rate. The ultra-Fe-Mg granulite may represent a deposition of this process.Acological granulite (Perillaite) is generally K 2O rich, whereas the acidic gneisses that predominate in most of the granulite facies Obviously different, K2O are low. However, REE abundance in peridotite has the entire range observed in two Archean gneissts that are K-rich and K-poor. The presence of a large number of pregranulitic kappa-pegmatites in this area indicates the generation of potassic metasomatism in the original rock assemblage with less potassium content. The trace elements produce a pattern of metasomatism and local melting of the acid gneiss prior to the granulite facies metamorphism. The sequence of such events is closely related to the fluctuations of the composition of the metamorphic fluid in the deep crust of the crust.