AbstractThe Early to Late Cretaceous Mundwara alkaline complex (comprising the Musala, Mer and Toa plugs) displays a broad spectrum of alkaline rocks closely associated in space and time with the Deccan Large Igneous Province (DLIP) in NW India. Petrology and Nd-Sr isotopic data on two youngest and altogether compositionally different lamprophyre dykes of the Mundwara alkaline complex are presented in this paper to understand their petrogenesis and also to constrain the magmatic processes responsible for generation of the rock spectrum in the complex (pyroxenite, picrite ankaramite, carbonatite, shonkinite, olivine gabbro, feldspathoidal and foid-free syenite). The two lamprophyre dykes occurring in the Mer and the Musala hills are referred to as basaltic camptonite I and camptonite II, respectively. The basaltic camptonite-I is highly porphyritic and contains olivine, clinopyroxene and magnetite macrocrysts embedded within the groundmass of microphenocyrsts composed of clinopyroxene, phlogopite, magnetite and feldspar. Whereas camptonite-II, with more or less similar texture, contains amphibole, biotite, magnetite and clinopyroxene within the microphenocrystic groundmass of amphibole, biotite, apatite and feldspar. Pyroxenes are chemically zoned and display corrosion of the cores revealing that they are antecrysts developed during early stages of magma evolution and later on inherited by more evolved magmas. Mineral chemistry and trace element composition of the lamprophyres reveal that fractional crystallisation was a dominant process. Early segregation of olivine + Cr-rich clinopyroxene + Cr-spinel from a primary hydrous alkali basalt within a magmatic plumbing system is inferred which led to the generation of basaltic camptonitic magma (M1) forming the Mer hill lamprophyre. Subsequently, progressive fractionation of pyroxene and Fe-Ti oxides from the basaltic camptonitic (M1) magma generated camptonitic (M2) magma forming the Musala hill lamprophyre. Both lamprophyre dykes on the Sr-Nd isotopic array reflect plume type asthenospheric derivation which largely corresponds to the Réunion plume and other alkaline rocks of the Deccan LIP. Our study brings out a complex sequence of processes such as crystal fractionation, accumulation and corrosion in the magmatic plumbing system involved in the generation of the Mundwara alkaline complex.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5277073
The geochemical effects of olivine slurry replenishment and dolostone assimilation in the plumbing system of the Franklin Large Igneous Province, Victoria Island, Arctic Canada