Petrographical indicators of petrogenesis: Examples from Central Indian Ocean Basin basalts

摘要: Petrographical features of the Central Indian Ocean Basin (CIOB) basalts were studied to understand their genetic significance. The fresh basaltic pillows show three textural zones from top glassy (zone A) through intermediate B) holocrystalline interior C), with each characterised by varying assemblages plagioclase and olivine that form different textures. Based on presence morphotypes olivine, CIOB are classified as aphyric, dominant, plagioclase+olivine bearing rarely plagioclase+olivine+augite bearing. mineral phases textures reflect magmatic conditions under which crystallised a tholeiitic magma. Rock-forming minerals such feldspars, pyroxenes amphiboles, among others, tend exhibit morphological compositional variations. Plagioclases in lunar oceanic variety crystal morphologies tabular phenocrysts, skeletal, dendritic, spherulitic swallow-tailed 1-3 . occurrence skeletal quench olivines 3 rocks 1 have been described while Drever & Johnston 4 reviewed earlier studies quenched olivine. morphology large smaller crystals can be related an increase cooling rate host rock suggests systematic progression shapes could reveal information about history 5 Other than sizes, zoned twinned good recorders they formed 6 Thin sections rim single pillow, would distinctive petrographic entities help establish range undercoolings. distinction may simply differences length acicular needles flow interiors 7 spacing between dendrites at known distances rims 8 Generally, chemical compositions, obtained various analytical techniques, utilised arrive genesis basalts. But plagioclases occurring also used clues interpret petrogenetic We examine this aspect