The Secondary Minerals from the Pillow Basalt of Salsette-Mumbai, Deccan Volcanic Province, India

Secondary minerals occur within the tholeiitic basalts of Salsette Island in greater Mumbai region, as well other localities Deccan Volcanic Province (DVP). However, secondary show remarkable differences with respect to their mineral speciation and precipitation sequence, which are both due unique geological environment. The region is built up by subgroup, represents youngest sequence DVP. It formed subsequently main phase DVP activity Danian time (62.5 61.5 Ma), course India–Laxmi Ridge–Seychelles breakup. part subgroup consists basaltic flows pillows, pillow breccia, hyaloclastite, contact brackish fresh water a lagoonal In some places, intertrappeans represented fossiliferous shallow sediments. On top, trachytic rhyolitic subaqueous volcaniclastics occur, dioritic bodies have intruded nearby. Due differing fluid rock interactions, several distinctly different developed void spaces hyaloclastite breccia interpillow matrix cavities. highly permeable an open system, where pronounced occurred early at higher temperatures. contrast, cavities were temporally closed system contained, for example, more low-temperature zeolites. genesis can be summarized follows: During initial cooling volcanic rocks about 62 Ma, first mineralization chlorite, laumontite I, quartz, calcite I. Ongoing magmatic caused reheating prehnite–pumpellyite facies conditions. generally decreasing temperatures, range 270–180 °C, babingtonite, II, prehnite, julgoldite, yugawaralite, ilvaite, pumpellyite, gryolite developed. contained SiO2 + Al2O3 +FeO MgO CaO, minor MnO Na2O, was predominately mineralized decomposition glass. Further temperature decreases zeolite conditions okenite scolecite, heulandite, stilbite, finally chabazite 180 °C less than 100 °C. As FeO, MgO, then absent, interaction plagioclase indicated. According Rb-Sr K-Ar ages on apophyllite-K, third II late Eocene Oligocene (30–40 Ma). new hydrothermal additionally K2O, temperatures 50–100 expected.