Petrogenesis of ultramafics in the Neoarchean Veligallu greenstone terrane, eastern Dharwar craton, India: Constraints from bulk-rock geochemistry and Lu-Hf isotopes

Abstract

We report on the bulk-rock geochemistry and Lu-Hf isotope systematics, and infer the petrogenesis of the ultramafic rocks in the Neoarchean Veligallu greenstone terrane, eastern Dharwar craton, India. The ultramafics along with the basalts and adakites yield an age of 2.696 ± 0.054 Ga, consistent with the available SIMS zircon U-Pb age of 2.697 ± 5 Ma, reported for the felsic volcanics, in the literature. The rocks have positive initial εHf (2.696 Ga) = + 3.0 to + 6.5, consistent with an origin from a long term depleted mantle source relative to a chondritic reservoir at ~2.7 Ga. Geochemically, the ultramafic rocks are characterized by high MgO = 23-33 wt. %, Mg# ~ 89, Cr = 2290-3855 ppm and Ni = 604-966 ppm contents; moderate to low SiO2 = 52-49 wt. %, Al2O3 = 9.2-4.7 wt. %, and TiO2 = 0.30-0.14 wt. %. To first order, these chemical compositions broadly resemble komatiites. The rocks exhibit higher than chondrite Al2O3/TiO2 (21-37) ratio, depletions in their middle-REE relative to the heavy-REE i.e. GdN/YbN < 1, and negative Nb, Ti, and positive Zr (Hf) anomalies in a primitive mantle normalized trace element variation diagram. Hence, the Veligallu ultramafics lack the key geochemical characteristics that would indicate a plume origin typically attributed to komatiites. Post-magmatic low grade metamorphism, hydrothermal alteration and element mobility, and /or contamination by Archean upper continental crust cannot be the cause of these geochemical patterns. Further, the calculated liquid evolution lines involving major element chemistry, are inconsistent with a boninitic lineage. Present study suggests that the Veligallu ultramafic rocks may represent melts that mainly evolved through fractional crystallization of orthopyroxene ± olivine. The spatial and temporal association of these ultramafics with the arc basalts, andesites and adakites in the Veligallu greenstone terrane significantly contributes to the

Boninites in the ~3.3 Ga Holenarsipur Greenstone Belt, Western Dharwar Craton, India

“…Precision and accuracy are better than the RSD 3% for the majority of the trace elements. The major and trace element concentrations determined for BHVO-1 are in concurrence with the recommended values in the GEOREM database [16]. An independent analysis of international certified reference material BIR-1, (supplied by United States Geological Survey, Reston, VA, USA), which was run as an unknown, and not part of the calibration, is also provided in Table 4.…”

“…Besides the boninitic rocks reported here from the~3.3 Ga Holenarsipur greenstone belt, boninite-like rocks have also been recognized in the greenstone terranes of Eo-, Meso-and Neoarchean age [5][6][7][8]16]. The origin of boninites, in general, is attributed to a two stage melting process involving depletion of a mantle source due to prior melt extraction events, presumably at a mid-oceanic ridge, in the first stage, followed by partial melting of this depleted source triggered by the fluids/melts derived from the dehydration of subducted altered oceanic crust in the sub-arc mantle, in the second stage.…”

Petrology and Geochemistry of Mesoarchean Sukinda Ultramafics, Southern Singhbhum Odisha Craton, India: Implications for Mantle Resources and the Geodynamic Setting

“…The total REE value of the Katpal ultramafics showed a narrow range of variation from 2.56 to 21.50 ppm, with there was limited REE fractionation. The (Ce/Yb) CN ratios varied from 0.77 to 4.79, LREE values varied from (La/Sm) CN = 0.79 to 3.17 [46], Nuasahi boninite [9], Bababudan komatiite [47], Veligallu ultramafic [48], Sonakhan SHMB [49], Barberton komatiite [50], Pilbara SHMB [51], and Isua boninite cumulate [52]. Bababudan komatiite [47], Veligallu ultramafic [48], Sonakhan SHMB [49], Barberton komatiite [50],…”

“…The data of the Sukinda ultramafic complex are plotted along with different high-Mg rocks of the world for comparison purposes. The data are obtained after Gadwal boninite [103]; OMG boninite [46]; Bastar boninite [104]; Dongargarh boninite [105]; Nuasahi ultramafic [9]; Veligallu ultramafics [48]; Cape Vogel boninite [106], and Isua boninite cumulate [52].…”

Paleoproterozoic ($$\sim$$1.88–1.89 Ga) ultramafic–mafic sills, Cuddapah basin, India—revisited: Implications for interaction between mantle plume and metasomatized subcontinental lithospheric mantle

“…Existence of an ancient subduction event in the Dharwar craton is established through several geochemical and isotopic studies on felsic and mafic volcanic rocks from the Neoarchean greenstone belts (e.g., Manikyamba et al 2005;Ram Mohan et al 2013;Khanna et al 2015Khanna et al , 2016. It is suggested that these Neoarchean felsic (adakiticaffinities and Mg-andesites) and mafic (boninitelike ultramafics) volcanic rocks have their genesis through subduction tectonics.…”