• CHANDAN KUMAR BORAIAHA

      Articles written in Journal of Earth System Science

    • Field, petrographic and geochemical characteristics of Sullya alkaline complex in the Cauvery Shear Zone (CSZ), southern India: Implications for petrogenesis

      CHANDAN KUMAR BORAIAHA KUMAR BATUK JOSHI ANDREW C KERR JAYANT KUMAR PADHI SARBARTHA SHANKAR MISHRA RASHMI CHANDAN

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      Significant, but volumetrically smaller, unmetamorphosed and largely undeformed alkaline magmatic suites have been reported from the Southern Granulite Terrain in southern India. These Neoproterozoic alkaline magmatic rocks occur as lenses, dykes and plugs that are mostly within, or proximal to, major shear zones or transcrustal faults. In this contribution, field, petrographic and whole-rock geochemicaldata of Sullya syenites and associated mafic granulites from the Mercara Shear Zone (MSZ), which separates low-grade (greenschist to upper amphibolite facies) Dharwar Craton and high-grade (granulite facies) Southern Granulite Terrain is presented. The isolated body of the Sullya syenite, similar to other alkaline plutons of the Southern Granulite Terrain, shows an intrusive relationship with the host hornblende-biotite gneisses and mafic granulites. The Sullya syenites lack macroscopic foliations and unlike, other plutons, they are not associated with carbonatites and ultrapotassic granites. Potash feldspar and plagioclase dominates the felsic phases in the Sullya syenite and there is negligible quartz. The studied syenites show evidence of melt supported deformation, but show no evidence of recrystallization. Geochemically,they most resemble the Angadimogar syenites (situated 3 km west of the Sullya syenites) with similar major oxide and trace element concentrations. The petrogenetic studies of the Sullya syenite have indicated that they were generated by mixing of two different sources derived from the partial melting of metasomatized continental mantle lithosphere and lower crustal mafic granulites. This melt source could have been emplaced in a rift-related tectonic setting. The emplacement is considered to becontrolled by shears.

    • Geochemistry of the Precambrian mafic dykes in and around the Western Ghats greenstone belt, Western Dharwar Craton

      CHANDAN KUMAR BORAIAHA

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      The preliminary field, petrographic and whole-rock geochemical data of the mafic dykes in and around the Western Ghats belt (WGB), Western Dharwar Craton (WDC) is presented in this study. The NNW–SSE trending tholeiitic mafic dykes are basalt to basaltic-andesite in composition. The studied dykes are generally LREE enriched and exhibit negative Nb–Ta and Ti anomalies indicating crustal contamination. Petrological modelling shows that the chemical variability of the dykes is primarily due to crystal fractionation and crustal contamination. Rare earth element (REE) modelling suggests that the WGB dykes were likely derived by low-degree partial melting (${\sim}$3.5%) of a garnet-spinel bearing mantle source. The close similarity in the Beld, petrography and geochemical characteristics between the studied dykes and the 2.21 Ga mafic dykes of WDC suggests that the WGB dykes may represent the 2.21-Ga mafic event in the WDC.

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