Chromitites from an Archean layered intrusion in the Western Dharwar Craton, southern India
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Chromitites from an Archean layered intrusion in the Western Dharwar Craton, southern India. / Santosh, M.; He, Xiao-Fang; Waterton, Pedro; Szilas, Kristoffer; Pearson, D. Graham.
I: Lithos, Bind 376-377, 105772, 01.12.2020.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
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T1 - Chromitites from an Archean layered intrusion in the Western Dharwar Craton, southern India
AU - Santosh, M.
AU - He, Xiao-Fang
AU - Waterton, Pedro
AU - Szilas, Kristoffer
AU - Pearson, D. Graham
PY - 2020/12/1
Y1 - 2020/12/1
N2 - Chromite deposits hosted in a layered ultramafic-maficintrusion in the Archean Chithradurga greenstone belt are part of asuture that divides the Western and Central Dharwar craton blocks insouthern India. Serpentinised ultramafic rocks including dunite,peridotite, and phlogopite-rich clinopyroxenite occur with massivechromitite. The olivine compositions show two distinct groups, one withFo ~91-92 olivines, in the massive chromitite and another group witholivine Fo values of ~95-96, in the serpentinised dunite. The chromiteoccurs as massive chromitite and as an accessory phase in dunite. Theformer are characterized by high Cr# (Cr/(Cr+Al)×100=67-70) and moderateto high Mg# (Mg/(Mg+Fe)=52-66); The latter have a larger variation in Crwhich is likely related to sub-solidus re-equilibration of the chromiteduring the serpentinization event. In the massive chromitites, subsolidusre-equilibration of chromite is less significant or absent. Bulkrockmajor and trace element analyses of the peridotites reveal acomposition less magnesian than depleted mantle rocks, with low TiO2,Na2O, CaO and high Cr, Ni content, a general depletion in Sr andenrichment in Th, U. The chromitites contain varied PGE abundances (ΣPGE= 14-167 ppb) and IPGEs (Ir, Os, Ru) as well as enriched primitive-mantlenormalized PGE patterns (PdN/IrN= 0.004-0.241). These features suggestthe chromitites are cumulates formed from a highly magnesian parentalmagma with komatiitic affinity, derived by large degrees of partialmelting of a refractory mantle protolith, which underwent crustalcontamination. The Re-Os isotope data demonstrate a minimum Re-depletionmodel age (TRD) of 2895 ±24 Ma for the serpentinized dunite (MY11/3), anda more robust age of 3120 ±12 Ma for two chromitite samples, which weinterpret as the best estimate of the magmatic age of this ultramaficintrusion. Abundant zircon grains also occur within these ultramaficrocks with U-Pb ages spanning from ca. 2.9 Ga to ca. 2.4 Ga, with adominant age population in the range 2.8-2.6 Ga. We interpret the upperintercept age at ca. 2.9 Ga to represent the initial crystallization ofzircon in the ultramafic rocks, potentially as a result of meltinfiltration and metasomatism associated with regional granitoid crustformation and related metasomatic activity. The 2.5-2.4 Ga zircon agesreflect a late-stage high-grade metamorphic overprint.
AB - Chromite deposits hosted in a layered ultramafic-maficintrusion in the Archean Chithradurga greenstone belt are part of asuture that divides the Western and Central Dharwar craton blocks insouthern India. Serpentinised ultramafic rocks including dunite,peridotite, and phlogopite-rich clinopyroxenite occur with massivechromitite. The olivine compositions show two distinct groups, one withFo ~91-92 olivines, in the massive chromitite and another group witholivine Fo values of ~95-96, in the serpentinised dunite. The chromiteoccurs as massive chromitite and as an accessory phase in dunite. Theformer are characterized by high Cr# (Cr/(Cr+Al)×100=67-70) and moderateto high Mg# (Mg/(Mg+Fe)=52-66); The latter have a larger variation in Crwhich is likely related to sub-solidus re-equilibration of the chromiteduring the serpentinization event. In the massive chromitites, subsolidusre-equilibration of chromite is less significant or absent. Bulkrockmajor and trace element analyses of the peridotites reveal acomposition less magnesian than depleted mantle rocks, with low TiO2,Na2O, CaO and high Cr, Ni content, a general depletion in Sr andenrichment in Th, U. The chromitites contain varied PGE abundances (ΣPGE= 14-167 ppb) and IPGEs (Ir, Os, Ru) as well as enriched primitive-mantlenormalized PGE patterns (PdN/IrN= 0.004-0.241). These features suggestthe chromitites are cumulates formed from a highly magnesian parentalmagma with komatiitic affinity, derived by large degrees of partialmelting of a refractory mantle protolith, which underwent crustalcontamination. The Re-Os isotope data demonstrate a minimum Re-depletionmodel age (TRD) of 2895 ±24 Ma for the serpentinized dunite (MY11/3), anda more robust age of 3120 ±12 Ma for two chromitite samples, which weinterpret as the best estimate of the magmatic age of this ultramaficintrusion. Abundant zircon grains also occur within these ultramaficrocks with U-Pb ages spanning from ca. 2.9 Ga to ca. 2.4 Ga, with adominant age population in the range 2.8-2.6 Ga. We interpret the upperintercept age at ca. 2.9 Ga to represent the initial crystallization ofzircon in the ultramafic rocks, potentially as a result of meltinfiltration and metasomatism associated with regional granitoid crustformation and related metasomatic activity. The 2.5-2.4 Ga zircon agesreflect a late-stage high-grade metamorphic overprint.
KW - Faculty of Science
KW - Archean chromitite
KW - Ultramafic intrusion
KW - Platinum-group elements
KW - Western Dharwar Craton
KW - Chithradurga greenstone belt
U2 - 10.1016/j.lithos.2020.105772
DO - 10.1016/j.lithos.2020.105772
M3 - Journal article
VL - 376-377
JO - Lithos
JF - Lithos
SN - 0024-4937
M1 - 105772
ER -
ID: 248146219