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马德拉斯(Madras)麻粒岩的主要元素和痕量元素地球化学研究使用了帕拉瓦拉姆(Pallavaram)地区64个有代表性的样品,这些样品在地球化学上可以分为四种不同的岩类:变火成岩的辉石麻粒岩类,变辉长岩类和紫苏花岗岩类以及变沉积岩的孔达岩类(Khondalites)。变火成岩类岩石在一起显示了明显的富铁拉斑玄武岩趋势,而与苏格兰刘易斯麻粒岩所显示的总的钙碱趋势相对照。辉石麻粒岩类和变辉长岩之间的地球化学差异表明前者可代表原始玄武岩的液体组份,后者则较近似于堆积岩类。紫苏花岗岩类的大部分在成分上相当于石英二长岩,而缺少中性组份,这就突出了变火成岩组合的双模式性,双模式性在其它太古宙地区是一种常见的特征。根据Ba、Rb、Sr亲石元素和轻稀土元素的丰度,紫苏花岗岩质岩类总体上类似于现代安第斯山的同类岩石。然而其中钇的丰度很低,表明重稀土元素的减少虽然可变但很重要,也表明了石榴石或角闪石在其成因方面的影响。和其它麻粒岩地体一样,在某些岩石类型中K/Rb比值随K_2O减少而有增加的趋势,并记载有K/Rb比值为1700。然而,岩石中的K/Rb比值在矿物学方面有明显的依赖性,那些具钾相的岩石有较低的K/Rb比值。虽然如此,甚至富钾长石的紫苏花岗岩的K/Rb比值仍然高于地壳的平均值。在不同的矿物组合中共存辉石和石榴石电子探针分析提供了一致的温度压力数据 (据几种方法),确定变质结晶作用的条件为720—840℃和9—10千巴。长石温度计表明结晶作用的温度约为680℃。这些温度压力条件与其它前寒武纪麻粒岩相地体所记载的情况是很一致的。
The major elements and trace element geochemical studies of granulite in Madras use 64 representative samples of the Pallavaram region that are geochemically divisible into four Different types of rock: pyroxene magmatites, gabbro and perish granitoids, and metamorphic Khondalites. Temperate igneous rocks together show a clear trend of iron-rich tholeiite basalts in contrast to the trend of total calcium-alkaline shown by Lewis’ granulite in Scotland. The geochemical differences between pyroxene granulites and gabbro indicate that the former can represent the liquid components of the original basalts and the latter more closely resemble the sedimentary rocks. Much of the perillal granitoids are compositionally equivalent to quartz monzogranites and lacking neutrals, highlighting the dual-mode nature of altered igneous assemblages, a common feature in other Archean regions . Based on the abundances of Ba, Rb, Sr lithophile elements and LREEs, the peridotite granites are generally similar to the rocks of the modern Andes. However, the abundance of yttrium is very low, indicating that the reduction of heavy rare earth elements, although variable, is important and shows the effect of garnet or amphibole on their genesis. As with other granulite landforms, the K / Rb ratio tends to increase with decreasing K_2O in some rock types and a K / Rb ratio of 1700 is documented. However, K / Rb ratios in rocks have a clear mineralogical dependence, and those with K phases have a lower K / Rb ratio. Even so, even the K / Rb ratio of peridotite enriched in feldspar feldspar is still above the average value of the crust. The analysis of coexistent pyroxene and garnet electron microprobe analysis in different mineral assemblages provides consistent temperature-pressure data (by several methods), and the conditions for determining metamorphic crystallization are 720-840 ° C and 9-10 kPa. The feldspar thermometer shows that the crystallization temperature is about 680 ° C. These temperature and pressure conditions are consistent with those recorded in other Precambrian granulite facies.