• AUSAF RAZA

      Articles written in Journal of Earth System Science

    • Carbonate hosted intermetallic compounds in Paleoproterozoic Salumber Ghatol metallogenic belt, Aravalli Craton, Rajasthan, India

      SURESH CHANDER AUSAF RAZA SANTANU BHATTACHARJEE SANJAY DAS

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      Carbonate hosted intermetallic compound in the Umarvaniyan area is localized within the intensively sheared (mylonitised) dolomite in a NW–SE shear zone ($\sim$15 km), belongs to Salumber Ghatol metallogenic belt, in Debari Group of Aravalli Craton, Rajasthan, India. It is characterized by extensive silicification and ferruginisation with hematite, goethite, magnetite and native gold specks. The intermetallic compound within the dolomite is composed of varying proportion of Cu–Zn–Ni–Os–Fe which has been detected by electron probe microanalysis (EPMA) study. The EMPA (WDS) results of the intermetallic compounds also reveal occurrences of intermetallic compounds of Cu–Zn–Ni–Os–Fe and native Au. The occurrence of these non-separable compounds is probably because these metals were formed at very high temperatures and in reducing condition during the evolving shear with low oxygen and low sulfur fugacity. The fast cooling effect thereafter probably made the geochemical environment least conducive for reaction between Cu/Zn/Ni and sulphur or oxygen.

    • Geochemistry of late Archaean Jhiri Granite in the North Delhi Fold Belt: Petrogenesis and implications for crustal growth in Aravalli Craton of the Indian shield

      AUSAF RAZA SHAILENDRA KUMAR GAHLOT PRATEEK GARKHAL HITEN KUMAR JALUTHARIA

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      The Neoarchaean Jhiri Granite (2.53 Ga) occurs as a small pluton in the North Delhi Fold Belt (NDFB) of Aravalli Craton. This pluton is made up of dark grey porphyritic granites with abundant mafic enclaves and shows a quartz monzonite composition. In the present contribution new geochemical data comprising major, and trace elements (including REE) of Jhiri Granite are reported and discussed to draw meaningful interpretations regarding its origin and crustal evolution in the northern part of the Indian shield. Most of the whole rock major and trace-element compositions suggest that the Jhiri Granite belongs to sanukitoid rock series, as well as show close affinities with ‘high-Ti’ sanukitoids. The origin of Jhiri Granite magma may be explained through a two-stage petrogenetic model: (1) melts and fluids derived from subducted oceanic slab and clay-rich terrigeneous sediments acted as metasomatic agents to react with overlying mantle wedge peridotite and were consumed to produce an enriched (metasomatized) assemblage and (2) subsequent melting of this metasomatised mantle source generated the high-Ti sanukitoid magma. The heat for melting of enriched (metasomatized) mantle source could be derived from upwelling mantle as a result of slab break-off and delamination. The wide distribution of sanukitoids in Aravalli and Bundelkhand cratons and similar petrogenetic conditions for their emplacement suggest the major role of subduction–accretion processes in building the ancient cratonic blocks of the Indian shield.

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