Glass and Mineral Chemistry of Northern Central Indian Ridge Basalts:Compositional Diversity and Petrogenetic Significance

The glass and mineral chemistry of basaits examined from the northern central Indian ridge （NCIR） provides an insight into magma genesis around the vicinity of two transform faults： Vityaz （VT） and Vema （VM）. The studied mid-ocean ridge basalts （MORBs） from the outer ridge flank （VT area） and a near-ridge seamount （VM area） reveal that they are moderately phyric plagioclase basalts composed of plagioclase （phenocryst [An60-90] and groundmass [An35-79]）, olivine （Fo81-88）, diopside （Wo45-51, En25-37, Fs14-24）, and titanomagnetite （FeOt -63.75 wt% and TiO2 -22.69 wt%）. The wholerock composition of these basalts has similar Mg# [mole Mg/mole（Mg＋Fe2＋）] （VT basalt： -0.56-0.58; VM basalt： -0.57）, but differ in their total alkali content （VT basalt： -2.65; VM basalt： -3.24）. The bulk composition of the magma was gradually depleted in MgO and enriched in FeOt, TiO2, P2O5, and Na2O with progressive fractionation, the basalts were gradually enriched in Y and Zr and depleted in Ni and Cr. In addition, the ∑REE of magma also increased with fractionation, without any change in the （La/ Yb）N value. Glass from the VM seamount shows more fractionated characters （Mg#： 0.56-0.57） compared to the outer ridge flank lava of the VT area （Mg#： 0.63-0.65）. This study concludes that present basalts experienced low-pressure crystallization at a relatively shallow depth. The geochemical changes in the NCIR magmas resulted from fractional crystallization at a shallow depth. As a consequence, spinel was the first mineral to crystallize at a pressure 〉10 kbar, followed by Fe-rich olivine at 〈10 kbar pressure.

A New Report of Serpentinites from Northern Central Indian Ridge(at 6°S)—An Implication for Hydrothermal Activity

Serpentinites from the inside corner high （6°38.5′S/68°19.34′E） from the Northern Central Indian Ridge （NCIR） are comprised mainly of high Mg-rich lizardite and chrysotile pseudomorphs with varying morphologies. ＇Mesh rim＇, ＇window＇, ＇hourglass＇ and ＇bastite＇ are the most common textures displayed by both chrysotile and lizardite. Numerous chrysotile veins in association with cross cutting magnetite veins indicate an advanced stage of serpentinisation. The relatively high abundance of chrysotile and lizardite suggest their close association and formation at a temperature below 250℃. Abundant ＇mesh rim＇ and ＇bastite＇ texture and variegated matrix reveal that the present serpentinites might have formed due to the interaction of harzburgite and seawater. Positive Eu anomaly （Eu/Eu^＊ up to ＋3.38）, higher La/Sm （up to 4.40） and Nb/La （up to 6.34） ratios suggest substantial hydrothermal influence during the formation of the serpentinites.

A Petrogenetic Model of Basalts from the Northern Central Indian Ridge:3-11°S

Mid-Ocean Ridge Basalts （MORB） from the Northern Central Indian Ridge （NCIR） were recovered between latitudes 3° and 11° S and are olivine tholeiite with higher abundances of K and Rb. They are of typical transitional MORB （T-MORB） variety and appear to have been generated from an enriched-mantle peridotite source. The primitive NCIR MORBs having Mg^# 〉 0.68 are the product of partial melting at an estimated pressure of - 1 GPa. It is inferred that the magma was subsequently modified at a pressure 〉 1 GPa by crystal fractionation and spinel was the first mineral to crystallize followed by separation of relatively Fe-rich olivine with subsequent decrease in pressure. During progressive fractionation at lower pressure （between 1-0.5 GPa）, the bulk composition of the magma became systematically depleted in MgO, and enriched in ∑FeO, TiO2, P2Os and Na20. There was, however, limited gradual depletion in Al2O3 and CaO and concomitant enrichment in K20. With the progressive fractionation these basalts became gradually enriched in V, Co, Y, Zr and to some extent in Sr, and depleted in Ni and Cro In addition, the T_JtEE of the magma also increased with fractionation, without any change in （La/Yb）n value.

Spectral characteristics of banded iron formations in Singhbhum craton,eastern India:Implications for hematite deposits on Mars

Banded iron formations （BIFs） are major rock units having hematite layers intermittent with silica rich layers and formed by sedimentary processes during late Archean to mid Proterozoic time. In terrestrial environment, hematite deposits are mainly found associated with banded iron formations. The BIFs in Lake Superior （Canada） and Carajas （Brazil） have been studied by planetary scientists to trace the evolution of hematite deposits on Mars. Hematite deposits are extensively identified in Meridiani region on Mars. Many hypotheses have been proposed to decipher the mechanism for the formation of these deposits. On the basis of geomorphological and mineralogical studies, aqueous environment of deposition is found to be the most supportive mechanism for its secondary iron rich deposits. In the present study, we examined the spectral characteristics of banded iron formations of Joda and Daitari located in Singhbhum craton in eastern India to check its potentiality as an analog to the aqueous/marine environment on Mars. The prominent banding feature of banded iron formations is in the range of few millimeters to few centimeters in thickness. Fe rich bands are darker （gray） in color compared to the light reddish jaspilitic chert bands. Thin quartz veins （〈4 mm） are occasionally observed in the handspecimens of banded iron formations. Spectral investigations have been conducted in VIS/NIR region of electromagnetic spectrum in the laboratory conditions. Optimum absorption bands identified include 0.65, 0.86, 1.4 and 1.9 μm, in which 0.56 and 0.86 μm absorption bands are due to ferric iron and 1.4 and 1,9 μm bands are due to OH/H2O. To validate the mineralogical results obtained from VlS/NIR spectral radiometry, laser Raman and Fourier transform infrared spectroscopic techniques were utilized and the results were found to be similar. Goethite-hematite association in banded iron formation in Singhbhum craton suggests dehydration activity, which has altered the primary iron oxide phases into the secondary iron oxide phases. The optimum bands identified for the minerals using various spectroscopic techniques can be used as reference for similar mineral deposits on any remote area on Earth or on other hydrated planetary surfaces like Mars.