Sisir Mondal

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Fátima Sá

ISCTE - University Institute of Lisbon (ISCTE-IUL)

Davide Nadali

Università degli Studi "La Sapienza" di Roma

Daniel Hershenzon

University of Connecticut

Salvador Muñoz-Viñas

Universitat Politècnica de València

José Manuel Santos

University of Salamanca

Gülsu Şimşek Franci

Gedik University

Silvia Cecchini

Roma Tre University, Rome, Italy

Aaron Shugar

Queen's University at Kingston

Paula Menino Homem

Universidade do Porto

Saulo Moreno Rocha

Universidade Federal do Ceará

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Petrogenesis of the late Archean Pillow Basalts from the Chitradurga greenstone belt, Western Dharwar Craton (southern India)

Journal of Earth System Science, Apr 12, 2022

The well-preserved exposures of pillow basalts from the late Archean (2.7 Ga) Chitradurga greenst... more The well-preserved exposures of pillow basalts from the late Archean (2.7 Ga) Chitradurga greenstone belt (Western Dharwar Craton) have been studied in detail using petrological, bulk-rock geochemical and isotope data. The pillows are compositionally basalts to basaltic andesites, and constituted of actinolite and plagioclase. The pillows show slight to moderately depleted LREE (La/SmN = 0.6−1.03), and nearly flat HREE patterns (Gd/YbN = 1.03−1.17) that are comparable with MORBs, but have an overall depletion in REEs relative to the latter. The trace-element patterns of the pillows on an N-MORB normalized multi-element diagram, however, are broadly comparable with that of Island Arc Basalts. The pillows were perhaps generated during the initiation of an intra-oceanic subduction zone where a depleted upper mantle (MORB-source) was metasomatized with slab-derived aqueous fluids. The pillows show a whole-rock Sm–Nd errorchron age of 2433 ± 400 Ma, which is within error of the previously reported Sm–Nd age of 2747 ± 15 Ma. The Pb–Pb isochron age (2627 ± 82 Ma) of the pillows is much closer to the previously reported Sm–Nd age, and it may also indicate the 2.62 Ga thermal event associated with felsic magmatism in the Western Dharwar Craton.

Trace-element fingerprints of chromite, magnetite and sulfides from the 3.1 Ga ultramafic–mafic rocks of the Nuggihalli greenstone belt, Western Dharwar craton (India)

Contributions to Mineralogy and Petrology, Jun 1, 2015

LA-ICPMS) of unaltered chromites indicates that the parental magma of the chromitite ore-bodies w... more LA-ICPMS) of unaltered chromites indicates that the parental magma of the chromitite ore-bodies was a komatiite lacking nickel-sulfide mineralization. In the Ga/Fe 3+ # versus Ti/Fe 3+ # diagram, the Byrapur chromites plot in the field of suprasubduction zone (SSZ) chromites while those from Bhaktarhalli lie in the MOR field. The above results corroborate our previous results based on majorelement characteristics of the chromites, where the calculated parental melt of the Byrapur chromites was komatiitic to komatiitic basalt, and the Bhaktarhalli chromite was derived from Archean high-Mg basalt. The major-element chromite data hinted at the possibility of a SSZ environment existing in the Archean. Altered and compositionally zoned chromite grains in our study show a decrease in Ga, V, Co, Zn, Mn and enrichments of Ni and Ti in the ferritchromit rims. Trace-element heterogeneity in the altered chromites is attributed to serpentinization. The trace-element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic Fe-Ti-V-rich magnetite bands in layered intrusions, and magnetites from andesitic melts, suggesting that magnetite crystallized from an evolved gabbroic melt. Enrichments of Ni, Co, Te, As and Bi in disseminated millerite and niccolite occurring within chromitites, and in disseminated bravoite within magnetites, reflect element mobility during serpentinization. Monosulfide solid solution inclusions within pyroxenes (altered to actinolite) in pyroxenite, and interstitial pyrites and chalcopyrites in magnetite, retain primary characteristics except for Fe-enrichment in chalcopyrite, probably due to sub-solidus re-equilibration with magnetite. Disseminated sulfides are depleted in platinum-group elements (PGE) due to late sulfide saturation and the PGE-depleted nature of the mantle source of the sill-like ultramafic-mafic plutonic rocks in the Nuggihalli greenstone belt.

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