Clinopyroxene compositions in the Deccan and Rajmahal Traps and their bearing on magma types and evolution

摘要: Abstract Electron probe analyses of clinopyroxenes from several areas the Deccan and Rajmahal Traps consisting mostly subalkalic alkalic basalts, picritic basalts a few dolerite dykes have been obtained. Evaluation data indicate absence pigeonite that occur in close spatial association with mild or strongly such as Rajpipla, Navagam central Kachchh. Co-existence augite pigeonite, however, has noticed basalts/dykes number localities Sagar, Igatpuri, Kalsubai, Triambak, Pavagarh Girnar besides one sample Rajmahal. Diopside, salite, wollastonite-rich compositions dominate basanites foidites Kachchh whereas chrome-diopside salite are main types picrite basalt samples Anila, Botad Paliyad Saurashtra akin to those found contiguous east borehole flows at Dhandhuka Wadhwan studied detail previously. Compositional variations zoned differentiation parental magma also mixing different (subalkalic alkalic) Rajpipla Based on host-rock chemistry, total alkalis-silica plot, CIPW norms, estimated temperatures eruption – thermometry, it inferred clinopyroxene compositions, especially incidence appear be very sensitive bulk chemistry host rocks, their Na 2 O, K SiO , iron TiO contents. Non-quadrilateral cationic components clinopyroxenes, Al tetrahedral octahedral positions together Si, Na, Ti Cr abundances useful discriminate inferences ferric component them. ternary olivine–clinopyroxene-quartz plot polybaric conditions crystallization evolution (e.g. Pavagarh, Anila Kachchh) which could breach olivine–clinopyroxene-plagioclase thermal divide exists part between under atmospheric conditions.