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Mineralogy and Petrology - We present here a new set of mineralogical and geochemical data from a cluster of east southeast-trending mafic dykes that intrude a lava flow of Sylhet traps. These... 相似文献
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We report for the first time the occurrence of rare phosphate wagnerite as a stable phase from the Mg–Al granulites of Sonapahar. The wagnerite bearing assemblages consist of the spinel, phlogopite, brucite and corundum. The wagnerite appears in the Mg–Al granulites due to the break-down of spinel and fluorapatite. The mineral chemistry of the phases has been discussed from the EPMA data, which reveals that the fluorine content of the wagnerite is relatively low due to the exchange of F to coexisting phases. The major oxide analysis of the rocks show the low content of Ca, which is the requisite for the occurrences of wagnerite. 相似文献
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The geochemistry of the metapelites and basic granulite of Sonapahar has been studied in order to assess the nature of the protolith and their likely tectonic environment. Metapelites contains SiO2 (av. 62.16wt %), K2O+Na2O (av. 4.57 wt%), Al2O3 (av. 16.69 wt%), MgO (av. 5.31 wt%), Mg# av. 0.60 and low TiO2 (av. 0.68 wt%) with low Y (av. 23.48 ppm) and Yb (av. 1.6 ppm) which point to their derivation from andesite source. Metapelites show prominent negative europium anomaly (EuN/Eu* = 0.38–0.54) and fractionated LREE to HREE pattern (LaN/LuN) 17.23 to 56.69. Basic granulites demonstrate low content of SiO2 (av50.95 wt%), Al2O3 (av13.67 wt%), K2O (av 0.58 wt%) and enriched in Fe2O3 t (av 11.42 wt%), MgO (av 7.29 wt%), CaO (av 10.60 wt %), Na2O (av 2.26 wt%), Mg# av. 0.56 and range from calc-alkaline to tholeiitic in nature. The geochemistry of the metapelites and basic granulites advocate that metapelites are derived from arc related andesitic source due to subduction whereas protoliths of basic granulites was originated in rift related volcanism through diapiric movement of hot rising mantle derived basaltic magmas. 相似文献
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