Geochemistry of the Mafic Metavolcanic Rocks of Mauranipur-Babina Greenstone Belt, Bundelkhand Craton, Central India: Implication for Tectonic Settings During the Archaean

Abstract

In the Bundelkhand craton of the central Indian shield Mauranipur-Babina greenstone belt is exposed along the E-W trending Bundelkhand tectonic zone (BTZ). The supracrustal sequence of this belt consists of metavolcanic and metasedimentary rocks associated with the granitic gneiss. The metavolcanic rocks occur as small isolated outcrops and have undergone greenschist to amphibolite facies of metamorphism. Since this craton underwent a complex history of faulting, folding, and fabric development, the original stratigraphic relationships between different spatially associated units are unknown. On the basis of the geochemical characteristic of these metavolcanics (amphibolites), two different assemblages are identified (1) oceanic assemblage consisting N-MORB, E-MORB and OIB and (2) subduction derived assemblage comprising oceanic and continental arc associations. The N-MORB type amphibolites are characterized by depleted REE patterns with (La/Yb)n = 0.33–0.36, (La/Sm)n = 0.32–0.40, (Gd/Yb)n = 0.91–1.09, ∑ REE = 16.44–22.31 enrichment of Nb relative to Th, La and Ce. The E-MORB type amphibolites show flat REE patterns with (La/Yb)n = 1.06, (La/Sm)n = 0.68, (Gd/Yb)n = 1.43, ∑ REE = 48.70 and positive anomalies at Nb and Zr. The OIB type amphibolite show fractionated REE patterns with (La/Yb)n = 2.72–3.73; (Gd/Yb)n = 2.44–2.74 and (Sm/Yb)n = 2.91–3.28 and high total REE contents (∑ REE = 75.40–99.39 ppm). On PM normalized diagram they display progressive enrichment of incompatible elements. The amphibolites of the subduction derived assemblage show fractionated REE patterns with (La/Yb)N = 4.44–15.79, concave HREE patterns and positive as well as negative Eu anomalies. The elemental ratios of these amphibolites {(Nb/Th)pm = 0.06–0.23, (Nb/La)pm = 0.15–1.05, (Ti/Sm)pm = 0.09–1.14, (Zr/Nd)pm = 0.07–0.69 and (Zr/Sm)pm = 0.14–1.02} are similar to the basaltic rocks occurring in modern subduction related geodynamic settings. The presence of these N-MORB, E-MORB, OIB and IAB in Mauranipur-Babina greenstone belt of Bundelkhand craton suggests the existence of different plate tectonic settings in central part of the Indian shield during the Archaean. Incompatible trace element characteristics suggest the enrichment of Archaean MORB type mantle source by subduction derived components leading to the conversion of the Achaean depleted upper mantle to enriched sub-arc mantle wedge.