Petrographic and Chemical Variations in The Rift-Related Basic Dykes of the Malka Area (Lower Swat), N. W. F. P., Pakistan
Abstract
This paper deals with the petrography, mineral chemistry and rock chemistry of dolerite dykes of Malka area (Lower Swat). These dykes intrude Late Palaeozoic Utla granite and consist of variable amounts of plagioclase (An53-59%), clinopyroxene (augite), illmenite, hornblende, biotite, apatite. Altered varieties show amphibole (calcic), plagioclase (An21-23), Fe-Ti oxides, chlorite and epidote.
Clinopyroxene, amphibole (both primary & secondary) and plagioclase have been studied in detail. Chemical composition of these rocks exhibits transitional character between alkaline and sub-alkaline basaltic composition. Major oxides verses S.I. indicate evolved composition for these rocks. Whereas CMAS model of O'Hara (1968) show the fractionation control of plagioclase and clinopyroxene. Compositions of these dolerite dykes indicate their association with rifting of the northern margin of Indo-Pak plate.
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