Articles written in Journal of Earth System Science

    • Subduction–collision processes and crustal growth in eastern Dharwar Craton: Evidence from petrochemical studies of Hyderabad granites


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      The granite batholiths of eastern Dharwar Craton, which are showing intrusive relationship with TTGs, exposed in the eastern part of Telangana state at University of Hyderabad, Gachibowli ($9.30 \rm{km}^{2}$), are studied for their petrographic and geochemical characteristics compared with their counterparts in EDC and evaluated their petrogenesis. These are predominantly microcline and quartz with subordinate plagioclase, exhibiting intergranular and perthitic textures. Geochemically, they are strongly peraluminous to slightly metaluminous in nature with high Alumina Saturation Index (ASI) ranging from 0.86 to 1.11 indicating the role of plagioclase in their genesis. Their alkali-calcic to alkalic nature, narrow range of Modified Alkali-Lime Index ($\rm{MALI; Na_{2}O+K_{2}O -CaO}$), and low Fe-number reflect their similarities with the I-type Cordilleran granites. Prominent negative Europium anomalies, high Sr, Rb, Rb/Sr and low Sr/Y ratios indicate moderate to low pressure partial melting of pre-existing TTG with residual plagioclase in the source. We suggest, the melting of older TTGs through crustal anataxis process formed these granites and the sanukitoid melts supplied the required heat for the melting of TTG to evolve into granites. The genesis of these granites supports reworking of older crust, crustal differentiation during syn-collisional stage and marks the stabilization of continental crust in the Dharwar Craton during the Neoarchean time.

    • Understanding the role of chalcophile-siderophile elements in the petrogenesis of metabasalts of Kudremukh greenstone belt, western Dharwar Craton, India: A Platinum group elements geochemical perspective


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      The Meso-Neoarchean Kudremukh greenstone belt (KGB) of Western Dharwar craton comprises predominant metabasalts associated with banded iron formations (BIFs). The metabasalts are characterized by moderate MgO (7.23–8.97 wt.%), Ni (48–374 ppm), Cr (33–188 ppm) with a wide variation in $\Sigma$PGE (21.8–215.7 ppb) contents with 15.8–115.9 ppb Pd, 3.7–105.2 ppb Pt and 0.7–8.5 ppb Rh. Among IPGE group, Iridium, Osmium and Ruthenium range from 0.2–5.9, 1.4–7 and 1.8–7.8 ppb, respectively. These metabasalts are relatively enriched in $\Sigma$PPGE (21.8–215.7 ppb) than $\Sigma$IPGE contents (3.6–18.6 ppb). Their Pd/Ir (7.6–100.7) and Pd/Pt (0.8–5.5) ratios correspond to moderate to lower degree of melting. The abundance of PGEs in Kudremukh metabasalts is dominantly controlled by sulphide and chromite fractionation trend of the parent magma. Sulphur undersaturated nature of the parent magma is evidenced through the relationship of Pd vs. Cu. Further,̄ the Cu/Pd ratios of the studied volcanics (Cu/Pd = 1277–5747) is lower than primitive mantle (Cu/Pd = 7000), indicating early sulphide removal and S-undersaturation during magmatic differentiation. PGEs geochemistry of the studied rocks suggest early removal of sulphide melts followed by pronounced sulphide fractionation and the mantle melting episode is followed by metasomatism of the refractory mantle wedge by the fluids/melts derived from the subducting slab in a convergent margin setting.


      $\bullet$ PGE systematics on the metabasalts from Kudremukh greenstone belt, western Dharwar Craton, India.

      $\bullet$ The KGB metabasalts are characterised by low- moderate degrees of partial melting and high degrees of sulphide fractionation.

      $\bullet$ PGE geochemistry of the KGB metabasalts infers the early sulphur undersaturated nature of magmas.

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