Petrography and Geochemistry of Alkaline Rocks from Michni (Warsak), NW Pakistan

Abstract

Petrographic and geochemical features of alkaline rocks in the Michni area (Warsak), NW Pakistan, are being studied. Based on field relationships and petrographic observations, these rocks are classified as Pyroxenite, ijolite series rocks (melteigite ijloite-urtite), Nepheline Syenite, Fenites and Carbonatite. So far, there have been no reports of Carbonatite in the study area. It has been reported for the first time. Ijolites predominate and have a wide variety of texture, with carbonatite intruding as well. Melteigite is found in close contact to ijolite. Pyroxenite was located along the metasediments. The remaining rocks are few and possibly eroded. A petrographic observation enabled the studied rocks to be classified into silica under-saturated rocks, that contain the essential minerals feldspathoids (nepheline that has primarily undergone cancrinite alteration), clinopyroxene, amphibole, carbonate, as well as accessories like titanite, apatite, garnet, carbonate, phlogopite, biotite, etc. whereas clinopyroxenes and amphiboles make up the majority of mafic rocks such as pyroxenites, melteigites and ijolites. Calciocarboantite is the chemical name for the carbonatite, which mostly comprises calcite. Fenitization linked with carbonatite results in altered rocks called fenites. Metasomatism of ijolitic or carbonatitic magma is most likely to be responsible.