Petrology, geochemistry and magnetic properties of Sadara sill: Evidence of rift related magmatism from Kutch basin, northwest India |
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| Authors: | Arijit Ray SK Patil DK Paul SK Biswas Brindaban Das NC Pant |
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| Institution: | aDepartment of Geology, Presidency College, College Street, Kolkata 700073, India;bMagnetic Observatory, IIG, Alibag 402201, Raigad, Maharashtra, India;cDepartment of Earth Science, IIT, Bombay, Powai, Mumbai, Maharashtra, India;dGeological Survey of India, Faridabad, India |
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| Abstract: | Mafic volcanic rocks of the Mesozoic Kutch basin represent the earliest phase of Deccan volcanic activity. An olivine-clinopyroxene-plagioclase-phyric undersaturated basalt occurs as a sill near Sadara in the Pachham upland, Northern Kutch. The Sadara sill is deformed and emplaced along faults. The sill is alkaline in character and is transitional between basalt and basanite. Compared to primitive mantle, the Sadara sill is enriched in Sr, Ba, Pb and LREE but depleted in Nb, Cr, Y, Cs and Lu. Fractional crystallization of olivine and clinopyroxene from an alkaline mafic melt generated by low degree partial melting of mantle peridotite can explain the observed chemical variation in the sill.IRM and L-F test experiments and mineral analyses show titano-magnetite as the major remanence carrying magnetic mineral. AF and thermal demagnetizations of the Sadara sill yielded a mean ChRM direction as D=315.6°, I=−43.0° (α95=9.78; k=25.38) and the corresponding VGP at 25°S; 114.6°E (dp/dm=6.58°/11.6°). The Sadara sill pole is significantly different from those of the Deccan (65 Ma) and the Rajmahal Traps (118 Ma) but is close to the Cretaceous poles of 85–91 Ma rock units from southern India. This suggests a pre-Deccan age for the sill. |
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| Keywords: | Deccan volcanism Kutch (India) Geochemistry Petrogenesis Palaeomagnetism |
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