Geochemical characterization and P-T trajectory of amphibolite enclaves from the Central Bundelkhand craton and its tectono-metamorphic evolution

Although the Bundelkhand Craton (BuC) is a notable Archean region in northern India, little is known about its tectono-metamorphic evolutionary history. We present petrography, bulk composition modeling, and geochemical characterisation of garnet-bearing and garnet-absent amphibolites. Both basaltic and andesitic-basalt are the protoliths of the studied amphibolites of BuC. Chondrite normalized rare earth element (REE) patterns indicate enrichment of LREEs over HREEs coupled with negative Nb, Ta, and Ti anomalies that imply a typical subduction-related geochemical signature. Furthermore, our results show a basaltic protolith originated at the active edges of island arcs-type environment. Trace element geochemistry-based discrimination diagrams including Nb/Th vs. Zr/Nb, Zr vs. Zr/Y, and Th/Nb vs. Ce/Nb, as well as high Th/Yb and low Nb/Yb ratios further suggest an island arc setting for the genesis of our studied amphibolites. Our results such as petrography, mineralogy and pseudosection-modelling are consistent and invoke three phases of metamorphism experienced by studied amphibolites.  The pre-peak metamorphic phase was characterized by pressure-temperature (P‒T) values of 6.25–6.5 kbar and 580–590°C for garnet-bearing amphibolites and 5.0–5.8 kbar and 400–450°C for garnet-absent amphibolites. Peak metamorphism took place in garnet-bearing amphibolites at 6.8–7.4 kbar and temperatures between 760 and 805°C, and in garnet-absent amphibolites at 7.0–7.4 kbar and temperatures between 785 and 810°C. P‒T values of 4.45–4.75 kbar and 585–615°C for garnet-bearing amphibolites and 3.1–4.0 kbar and 620–710°C for garnet-absent amphibolites were indicative of retrograde metamorphic processes. The mineral assemblages and P‒T trajectories delineate a clockwise P‒T path for both garnet-bearing and garnet-absent amphibolites from the Babina and Mauranipur regions. This suggests that the rocks were subjected to burial in a subduction tectonic setting within an arc-related environment, followed by a decompression stage that brought them to the surface.