Geochemical systematics of the Mauranipur-Babina greenstone belt, Bundelkhand Craton, Central India: Insights on Neoarchean mantle plume-arc accretion and crustal evolution

Abstract

The Neoarchean Bundelkhand greenstone sequences at Mauranipur and Babina areas within the Bundelkhand Gneissic Complex preserve a variety of magmatic rocks such as komatiitic basalts, basalts, felsic volcanic rocks and high-Mg andesites belonging to the Baragaon, Raspahari and Koti Formations. The intrusive and extrusive komatiitic basalts are characterized by low SiO 2 (39e53 wt.%), high MgO (18e25 wt.%), moderately high Fe 2 O 3 (7.1e11.6 wt.%), Al 2 O 3 (4.5e12.0 wt.%), and TiO 2 (0.4e1.23 wt.%) with super to subchondritic (Gd/Yb) N ratios indicating garnet control on the melts. The intrusive komatiitic suite of Ti-enriched and Al-depleted type possesses predominant negative Eu and positive Nb, Ti and Y anomalies. The chemical composition of basalts classifies them into three types with varying SiO 2 , TiO 2 , MgO, Fe 2 O 3 , Al 2 O 3 and CaO. At similar SiO 2 content of type I and III basalts, the type II basalts show slightly high Al 2 O 3 and Fe 2 O 3 contents. Significant negative anomalies of Nb, Zr, Hf and Ti, slightly enriched LREE with relatively flat HREE and low P REE contents are observed in type I and II basalts. Type III basalts show high Zr/Nb ratios (9.8e10.4), TiO 2 (1.97e2.04 wt.%), but possess strikingly flat Zr, Hf, Y and Yb and are uncontaminated. Andesites from Agar and Koti have high SiO 2 (55e64 wt.%), moderate TiO 2 (0.4e0.7 wt.%), slightly low Al 2 O 3 (7e11.9 wt.%), medium to high MgO (3e8 wt.%) and CaO contents (10e17 wt.%). Anomalously high Cr, Co and Ni contents are observed in the Koti rhyolites. Tholeiitic to calc alkaline affinity of mafic-felsic volcanic rocks and basalteandesiteedaciteerhyolite differentiation indicate a mature arc and thickened crust during the advanced stage of the evolution of Neoarchean Bundelkhand greenstone belt in a convergent tectonic setting where the melts were derived from partial melting of thick basaltic crust metamorphosed to amphibolite-eclogite facies. The trace element systematics suggest the presence of arc-back arc association with varying magnitudes of crust-mantle interaction. La/Sm, La/Ta, Nb/Th, high MgO contents (>20 wt.%), CaO/Al 2 O 3 and (Gd/Yb) N > 1 along with the positive Nb anomalies of the komatiite basalts reflect a mantle plume source for their origin contaminated by subductionmetasomatized mantle lithosphere. The overall geochemical signatures of the ultramafic-mafic and felsic volcanic rocks endorse the Neoarchean plume-arc accretion tectonics in the Bundelkhand greenstone belt.