Petrology and geochemistry of metamorphosed basaltic pillow lava and basaltic komatiite in the Mauranipur area: subduction related volcanism in the Archean Bundelkhand craton, Central India

The occurrence of metamorphosed basaltic pillow lava in close association with serpentinized ultramafic rock, metamorphosed basaltic komatiite, volcaniclastic metasediment, and banded iron formation (BIF) in the Mauranipur area is the first explicit evidence for subduction related submarine volcanism in the Archean Bundelkhand craton, Central India. The Mauranipur pillow lava underwent greenschist to amphibolite facies metamorphism while retaining a geochemical signature of its igneous protolith. The pillow lava and associated massive volcanic rock is subalkalic, low-K tholeiitic basalt to basaltic andesite with SiO2 = 51.9-55.9 wt% and Mg/(Mg + Fe-total) X 100 = 63.4-67.2. The rock shows depletion in HFS elements with Nb/Nb* (0.07-0.17), and LIL elements are relatively enriched compared with present-day N-MORB compositions. Chondrite normalized REE patterns for the Mauranipur pillow lava are nearly flat with (La/SM)(N) = 0.9-1.5, (Gd/Yb)(N) = 1.0-1. 1, and Eu/Eu* = 0.81-1.10. The geochemical characteristics of the pillow lava are similar to those of low-K tholeiitic basalt reported from modem intra-oceanic arcs. The associated high-Mg andesite is compositionally similar to basaltic komatiite, enriched in LREE, with (La/SM)(N) = 2.95-6.44, and depicts a nearly flat chondrite normalized HREE pattern with a low MREE/HREE ratio (Gd/Yb)(N) = 1.24-1.58. The basaltic komatiite displays remarkably similar geochemical characteristics to modem boninite. The present study, combined with available geological data, suggests that the supracrustal rocks of the Mauranipur area represent an Archean ophiolite sequence formed in a plate convergent setting.