Chromian spinel compositions from Madawara ultramafics, Bundelkhand Craton: Implications on petrogenesis and tectonic evolution of the southern part of Bundelkhand Craton, Central India

Abstract

Madawara ultramafic complex (MUC) in the southern part of Bundelkhand Craton, Central India comprises peridotite, olivine pyroxenite, pyroxenite, gabbro, and diorite. Coarse‐grained olivine, clinopyroxene (Cpx), amphibole (Amp), Al‐chromite, Fe‐chromite, and magnetite with rare orthopyroxene (Opx) are common minerals in peridotite. Chromites are usually coarse‐grained euhedral found as disseminated crystals in the olivine matrix showing both homogeneous and zoned texture. Al‐chromite, primarily characterizes Cr‐spinels and its subsequent fluid activity and alteration can result in the formation of Fe‐chromite, chrome magnetite, and magnetite. Mineral chemistry data suggest that Al‐chromite is characterized by moderately high Cr2O3 (38.16–51.52 wt.%) and Fe2O3 (3.22–14.51 wt.%) and low Al2O3 (10.63–21.87 wt.%), MgO (1.71–4.92 wt.%), and TiO2 (0.22–0.67 wt.%), whereas the homogeneous Fe‐chromite type is characterized by high Fe2O3 (25.54–47.60 wt.%), moderately low Cr2O3 (19.56–37.90 wt.%), and very low Al2O3 (0.06–1.53 wt.%). Subsequent alteration of Al‐chromite and Fe‐chromite leads to formation of Cr‐magnetite and magnetite. The Cr# of Al‐chromite varies from 55.12 to 76.48 and γFe3+# from 8 to 19, whereas the ferrian chromite has high Cr# varying from 94.27 to 99.53 while its γFe3+# varies from 38 to 70. As a whole, the primary Al‐chromite shows low Al2O3, TiO2 contents, and high Fe#, Cr# values. Olivines have forsterite ranging from 75.96% to 77.59%. The bulk‐rock geochemistry shows continental arc geochemical affinities indicated by the high concentration of large‐ion lithophile elements and U, Th relative to the low concentration of high‐field strength elements. These petrological and mineralogical as well as primary Al‐chromite compositions plotted in different discrimination diagrams suggest an arc environment that is similar to Alaskan‐type intrusion.

Evolution of Bundelkhand Craton

“…schist, sericite, mafic and ultramafic rocks (Farooqui and Singh, 2006;Singh and Slabunov, 2016;Slabunov et al, 2017;Mohanty et al, 2018;. Here, the thickness of quartzite outcrop is 300 m and it is characterized by fuchsite and hematite-bearing quartz arenite with schist and lesser quartz pebble conglomerate Slabunov, 2015, 2016).…”

“…The MUC lies at the southern fringe of BuC and has been established as a potential source for platinum group elements (PGEs) in north central India Farooqui and Singh, 2006;Prakash et al, 2009;Farooqui and Singh, 2010;Singh et al, 2011;Balaram et al, 2013;Satyanarayanan et al, 2010Satyanarayanan et al, , 2014Satyanarayanan et al, , 2015Singh et al, 2018). Here, variously altered and metamorphosed (± deformed) mafic and ultramafic rocks (metadunite, metaperidotite (± hornblende), metapyroxenite (± olivine), gabbro and diorite) occur as ~E-W-trending lensoidal bodies, distributed in about 400 sq km area and are togetherly, known as MUC Farooqui and Singh, 2006;Singh et al, 2011;Satyanarayanan et al, 2014;Mohanty et al, 2018;Ramiz et al, 2018;Singh et al, 2018). An integration of field, petrography and bulk rock geochemistry have been carried out in MUC to understand its petrogenesis and tectonic setting (Mohanty et al, 2018;Ramiz et al, 2018).…”

“…Here, variously altered and metamorphosed (± deformed) mafic and ultramafic rocks (metadunite, metaperidotite (± hornblende), metapyroxenite (± olivine), gabbro and diorite) occur as ~E-W-trending lensoidal bodies, distributed in about 400 sq km area and are togetherly, known as MUC Farooqui and Singh, 2006;Singh et al, 2011;Satyanarayanan et al, 2014;Mohanty et al, 2018;Ramiz et al, 2018;Singh et al, 2018). An integration of field, petrography and bulk rock geochemistry have been carried out in MUC to understand its petrogenesis and tectonic setting (Mohanty et al, 2018;Ramiz et al, 2018). About 400 m thick low-lying ridge is the largest outcrop of ultramafic exposed in the south east of Madawara Village (Mohanty et al, 2018).…”

“…An integration of field, petrography and bulk rock geochemistry have been carried out in MUC to understand its petrogenesis and tectonic setting (Mohanty et al, 2018;Ramiz et al, 2018). About 400 m thick low-lying ridge is the largest outcrop of ultramafic exposed in the south east of Madawara Village (Mohanty et al, 2018). The rocks of this complex are mainly confined between the Madawara Shear in north and the Sonrai-Girar Shear in south and have undergone greenschist to lower amphibolites facies metamorphism Satyanarayanan et al, 2014;Ramiz et al, 2018).…”

“…In general, the contacts between ultramafic rocks and Bundelkhand granite-gneisses are sheard and mylonitized in the area Ramiz et al, 2018). Recent geochemical studies have shown that rocks of this region are enriched in light rare earth elements (LREEs) and LILEs as compared to HREEs and HFSEs favouring the continental arc setting for the MUC (Mohanty et al, 2018;Ramiz et al, 2018). However, Satyanarayanan et al (2015) have reported that the MUC are depleted in Cu, Al, Ca and V.…”