Geochemical and Isotopic Constraints of Neoarchaean Fossil Plume for Evolution of Volcanic Rocks of Sandur Greenstone Belt, India
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REE, HFSE and 143Nd/144Nda ta from Sultanpura volcanic rocks vary between CHUR (Chondrite Uniform Rcservoir), primitive mantle and depleted manilc, but appear to be derived from primitive mantle and have been probably contaminated by continental crust. Although the abundance of REE varics from 2 to 12 chondrite, the patterns are smooth and flat with small negative or positive Eu anomalies as artifacts of alteration. Generally positive, but in few samples negative Nb anomalies are also found, with (Ce/Sm)N, and (Gd/Yb)N, being near chondritic. Ti/V, Ti/Zr, Zr/Y, Sc/Y, Nb/La, Nb/Th, Nb/U, MgO/TiO2, MgO/FeO and Al2O3/TiO2, also for many samples are ncar chondritic, εNd=+0.8649±0.00024 resembling CHUR. ThMb, NblU and some other ratios are near to those of Ontong Java and Gorgana plateaus (0.80 Ga) and the tholeiite-komatiitic sequence found in 2.7 Ga Southern volcanic zone, Abitibi belt of Canada and 2.1 Ga Birimian belt of West Africa. Collectively, thcsc data indicate that a mantle plume. derived from an enriched mantle, possibly played an important role in the oceanic volcanic sequence of Sultanpura block. Some of the HFSE follow the olivine control line, whereas other elements following the olivine control line define a narrow array tube. Formation of such array tubes on the plots of some HFSE elements and their ratios, and the scatters of HFSE/REE ratios, probably suggest dynamic melting of the plume during ascent. Entrenchment, mixing of Archaean ocean ridge basalts (AORB), crustal contamination and subduction of such a plume-fed slab may have generated the compositional heterogeneities observed in the Sultanpura metavolcanic rocks.
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