Chromitites from an Archean layered intrusion in the Western Dharwar Craton, southern India

doi:10.1016/j.lithos.2020.105772

Lithos

Volumes 376–377, 1 December 2020, 105772

https://doi.org/10.1016/j.lithos.2020.105772 Get rights and content

Highlights

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ReOs TRD and TMA ages of chromitites in ultramafic rocks from Dharwar Craton show 3.1 Ga.
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Zircon from these rocks preserve tectonic events at 2.9 Ga and ca. 2.5 to 2.4 Ga.
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Geochemical features suggest high magnesian parent magma with komatiitic affinity.
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The refractory mantle derived magma witnessed crustal contamination.

Abstract

Chromite deposits hosted in a layered ultramafic–mafic intrusion in the Archean Chithradurga greenstone belt are part of a suture that divides the Western and Central Dharwar craton blocks in southern India. Serpentinised ultramafic rocks including dunite, peridotite, and phlogopite-rich clinopyroxenite occur with massive chromitite. The olivine compositions show two distinct groups, one with Fo ~91–92 olivines in the massive chromitite, and another group with olivine Fo values of ~95–96, in the serpentinised dunite. The chromite occurs as massive chromitite and as an accessory phase in dunite. The former is characterized by high Cr# (Cr/(Cr + Al) × 100 = 67–70) and moderate to high Mg# (Mg/(Mg + Fe) = 52–66); The latter shows a larger variation in Cr which is likely related to sub-solidus re-equilibration of the chromite during the serpentinization event. In the massive chromitites, sub-solidus re-equilibration of chromite is less significant or absent. Bulk-rock major and trace element analyses of the peridotites reveal a composition less magnesian than depleted mantle rocks, with low TiO₂, Na₂O, CaO and high Cr, Ni content, a general depletion in Sr and enrichment in Th, U. The chromitites contain variable PGE abundances (ΣPGE = 8-244 ppb) with enrichments of Os, Ir and Ru, relative to Pt and Pd . These features suggest that the chromitites are cumulates formed from a highly magnesian parental magma with komatiitic affinity, derived by large degrees of partial melting, , which underwent crustal contamination. The Re single bond Os isotope data demonstrate a minimum Re-depletion model age (TRD) of 2895 ± 24 Ma for the serpentinized dunite (MY11/3), and a more robust age of 3120 ± 12 Ma for two chromitite samples, which we interpret as the best estimate of the magmatic age of this ultramafic intrusion. Abundant zircon grains also occur within these ultramafic rocks with U single bond Pb ages spanning from ca. 2.9 Ga to ca. 2.4 Ga, with a dominant age population in the range 2.8–2.6 Ga. We interpret the upper intercept age at ca. 2.9 Ga to represent the initial crystallization of zircon in the ultramafic rocks, potentially as a result of an early stage of metamorphism and hydrothermal alteration. The 2.5–2.4 Ga zircon ages reflect a late-stage high-grade metamorphic overprint.

Graphical abstract

Introduction

Chromitites and their host rocks provide important constraints on mantle-derived magmas, and are also important indicators of tectonic setting. Chromium is relatively immobile during hydrothermal processes, and chromite is only a minor phase produced during closed-system cotectic crystallization of mafic parent magma (e.g., Irvine, 1977). Chromite has been shown to be a robust petrogenetic tool to characterize diverse settings (Mondal et al., 2007; Mukherjee and Mondal, 2018; Rollinson et al., 2010). This is largely because the chemical composition of chromite is controlled by mantle-melting processes that are characteristic of specific tectonic environment (e.g., Barnes and Roeder, 2001 and references therein).

Chromitites of Archean age are known from a variety of ultramafic–mafic intrusions worldwide (McCallum, 1996; Rollinson, 1997; Stowe, 1994; Szilas et al., 2018). The nearly exclusive association of Archean chromitite with ultramafic–mafic intrusions provide an important window for understanding the secular changes in the early Earth's evolving tectonic systems (Hutchinson, 1981; Rollinson et al., 2017; Stowe, 1994). Chromitite within layered intrusions, such as the well-known Bushveld and Stillwater complexes, host most the world's economic chromium reserves and additionally contain significant platinum group element (PGE) mineralization. The origin and evolution of such chromitite deposits are therefore of prime interest (e.g. González-Jiménez et al., 2014; Junge et al., 2014; Spandler et al., 2005). However, the formation age and tectonic setting of chromitites in the greenstone belts of Western Dharwar remains debated (Mukherjee and Mondal, 2018). In particular, the lack of high-resolution in-situ dating methods has placed limitations on understanding the formation age of the chromitites and their subsequent metamorphic history.

In this study, we investigate chromitites from an Archean layered intrusion in the southern part of the Chithradurga greenstone belt, a suture that divides the Western and Central Dharwar craton blocks in southern India (Jayananda et al., 2020, and references therein). We present results from petrology, mineral chemistry, bulk-rock geochemistry (including platinum-group element data), Re single bond Os geochronology plus in-situ zircon UPb and Hf isotopes, and zircon trace element data from chromitites and the ultramafic host rocks. Our objective is to constrain the formation age, and identify the nature of the parental magma with the aim of reconstructing the tectonic setting. We also attempt a comparison with other similar Archean chromitite occurrences.

Section snippets

Regional geology of the Dharwar Craton

The Dharwar Craton in southern India (Fig. 1) is one of the oldest cratonic blocks on the globe and provides a window to evaluate crustal evolution in the early Earth (Jayananda et al., 2018, Jayananda et al., 2020; Wang and Santosh, 2019, and references therein). This craton comprises vast areas of TTG (tonalite-trondhjemite-granodiorite) gneiss, two generations of greenstone sequences and at least three generations of potassic to calc-alkaline granitoid intrusions (Bhaskar Rao et al., 1992;

Analytical methods

We carried out detailed petrographic studies, quantitative mineral chemical analysis using electron microprobe, bulk rock major, trace and Rare Earth Element (REE) Analysis, PGE analysis by Nickel Sulphide-Fire Assay (NiS-FA), zircon U single bond Pb, REE and LuHf analysis and ReOs isotope and isotope dilution PGE analysis (HPA-ID). The detailed analytical techniques, related references, and the precision and accuracy are reported in Appendix A. The results from these studies are reported in the following

Petrography

The chromite in the studied samples can be divided into two types: 1) chromite in serpentinised peridotite occurring as an accessory phase (Fig. 4a-b,f); and 2) chromite as the major phase in chromitite (Fig. 4c-e). Accessory chromite is subhedral to anhedral in shape, fine- to medium-grained, and shows zoning textures with corroded margins, typically surrounded by a chlorite rim (Fig. 4f). Chromite modal proportions are variable (5–10 vol%) in the chromite-bearing peridotite sample, MY11–3.

Petrogenesis and tectonic setting

The composition of chromite in this study generally shows a high-Cr, low-Al character. Chromite in serpentinised dunite sample MY11/3 is an exception, showing clear zoning (Fig. 4f) and a variable in composition in Al, Ti, Cr. Elevated Fe and lower Mg contents, along with the presence of amphibole, talc, and chlorite suggest this is a consequence of amphibolite grade metamorphism. The chromite in MY11–3 shows enrichment in Fe³⁺ and overlaps with the field of ferritchomit and metamorphic

Conclusions

1. Consistent whole rock Re single bond Os TRD and TMA ages, and Hf mantle depleted ages measured in zircon, suggest formation of ultramafic rocks in the Archean Chithradurga greenstone belt at ~3.1 Ga. These rocks then underwent at least two major tectonic events at ca. 2.9 Ga, and at ca. 2.5–2.4 Ga, the latter corresponding to amphibolite-facies metamorphism. These events reset the zircon ages and substantially modified mineral chemistry.

2. Chromite compositions, high Fo number olivine, bulk-rock

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank Editor-in-Chief Prof. Michael Roden and two anonymous referees for comments and suggestions which helped to improve this paper. We thank Dr. K. Sajeev and team for help to M. Santosh during field work. This work was supported by Foreign Expert grants from China University of Geosciences Beijing, P.R. China.

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Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland
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Citation Excerpt :
The Dharwar Craton of southern Peninsular India, one of the largest Archean Cratons of the world, preserves variably metamorphosed igneous and sedimentary remnants of ancient proto-continents and ocean basins, and thus provides a ubiquitous time window to thermo-tectonic transition of Precambrian Earth. The geological, geochemical and geochronological evidence from the granite-greenstone terranes of Dharwar Craton provides a potential archive of polychrononous accretionary and collisional orogens that can be equated with the ancient orogenic records of worldwide Archean Cratons in terms of global tectonic evolution (Gao and Santosh, 2020; Jayananda et al., 2018; Manikyamba et al., 2021; Santosh et al., 2020; Sotiriou et al., 2022; Wang et al., 2019). These offer the most conspicuous and sustainable paradigms fingerprinting the validity of the uniformitarian principle endorsing modern style subduction tectonics in Archean and a transitional evolution of early Earth from Hadean-stage stagnant lid convection to short-term episodic style of subduction tectonics concurrent with gradual cooling of mantle and thickening of lithosphere.
Subduction initiation in the Early Earth and the onset of plate tectonics are topics of wide interest in understanding the formation and evolution of continents and supercontinents on our planet. Here we report results from integrated petrological, geochemical and geochronological (Zircon UPb ages) studies on an ultramafic-mafic complex from the Bondla-Usgao-Durigini (BUD) sectors of Goa to address its petro-tectonic evolution and correlation with Neoarchean crustal growth processes and cratonization events. The ultramafic-mafic cumulate sequence from BUD sectors of Goa comprising dunite, peridotite, troctolite, olivine gabbro and gabbro represents a dismembered crustal section of oceanic lithosphere formed either in a MOR or SSZ fore-arc extensional regime. The geochemical attributes marked by boninitic-IAT trend, depleted to enriched mantle compositions, selective enrichment in fluid-mobile LILE and LREE over HFSE enunciate a multistage petrogenetic evolution associated with a SSZ fore-arc tectonic setting. The ocean-continent transition featured by the geochemical signatures can be translated in terms of oceanic crust formation in a juvenile extensional fore-arc in a SSZ setting, its maturation and accretion at active continental margin during Neoarchean ocean basic closure and arc-continent collision. The studied ultramafic-mafic suite fingerprints the transition of depleted mantle wedge to a LILE-LREE enriched metasomatized one through influx of subduction components and hydrous arc magmatism typical of SSZ oceanic lithosphere formed above a nascent subduction zone. The magmatic precursors of the studied lithologies were derived from a transitional depleted to enriched mantle regime marked by hydration and metasomatism of a depleted MOR-type mantle by the influx of subduction-derived fluids. Zircon grains in the peridotite sample yield positive εHf(t) of +3.2 to +7.6, together with T_DM^C of 2610–2877 Ma suggesting depleted mantle source. The gabbro sample shows positive εHf(t) values of +3.7 to +6.3 and T_DM^C age of 2731–2868 Ma also attesting to depleted mantle source. Zircon UPb ages of 2602.42 ± 0.82 Ma for peridotite and 2479–2684 Ma for gabbro represent the magma emplacement time and Neoarchean-early Paleoproterozoic melt activity. The highly variable ages from zircon grains in the studied samples might suggest multiple stages of metasomatism and melt-rock interaction in a long-lived sub-continental lithospheric mantle. The tectonic evolution can be equated with Neoarchean global subduction-accretion-collision and arc-continent amalgamation events. This study deciphers a 2.6–2.5 Ga Neoarchean oceanic crust formation and magmatic response to subduction initiation, arc maturation and accretion processes correlatable with global crustal growth processes and amalgamation of western Dharwar Craton (WDC) and Antongil-Masora blocks into the Greater Dharwar Craton (GDC).
Paleo-Mesoarchean crustal growth and reworking in the western Dharwar Craton, southwestern India: Evidence from trondhjemitic gneiss and granitic gneiss
2021, Precambrian Research
Paleo-Mesoarchean felsic orthogneisses are widely exposed in the southern part of the western Dharwar Craton (WDC), southern India shield. The felsic orthogneisses studied in this paper from the WDC can be divided into two groups based on their geological, geochronological, and geochemical data: the 3.4–3.3 Ga trondhjemitic gneiss (including trondhjemitic veins) and the ∼3.1–3.0 Ga granitic gneiss. The 3.4–3.3 Ga trondhjemitic gneiss is characterized by high contents of SiO₂ (70.4–73.1 wt%), Na₂O (5.49–5.91 wt%) and Sr (647–740 ppm), high ratios of Na₂O/K₂O (4.7–7.7) and Sr/Y (53–106), but relatively lower Mg# values (32–39), and Cr (9.5–28.7 ppm) and Ni (1.34–5.33 ppm) concentrations, as well as insignificant Eu anomalies, fractionated REE patterns and mostly positive zircon ε_Hf(t) values (+0.8-+5.9). These data indicate that the trondhjemitic gneiss was derived from partial melting of juvenile mafic crust in a relatively moderate-shallow depth, with residual mineral assemblage of garnet, amphibole and clinopyroxene, implying crustal growth event at 3.4–3.3 Ga. By contrast, the ∼3.1–3.0 Ga granitic gneiss is characterized by relatively lower contents of Na₂O (3.82–4.63 wt%) and Sr (96.9–291 ppm), low ratios of Na₂O/K₂O (1.4–1.7) and Sr/Y (3.02–8.65), as well as significantly negative Eu anomalies and negative to positive zircon ε_Hf(t) values (-5.6-+4.5). Therefore, the granitic gneiss was probably derived from partial melting of pre-existing crustal rocks, suggesting a prominent crustal reworking event at ∼3.1–3.0 Ga. This study emphasizes that the western Dharwar Craton is dominated by Paleoarchean (3.4–3.2 Ga) crustal growth event and a strong crustal reworking event in early Mesoarchean (∼3.1–3.0 Ga), though the Mesoarchean crustal growth event is discernible, evidenced by regional ∼3.0 Ga TTG rocks. The early Mesoarchean (∼3.1–3.0 Ga) crustal reworking event, represented by series of potassium-rich granites, is also reported in other Archean cratons, and thus it may have global significances.

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Research ArticleChromitites from an Archean layered intrusion in the Western Dharwar Craton, southern India

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Regional geology of the Dharwar Craton

Analytical methods

Petrography

Petrogenesis and tectonic setting

Conclusions

Declaration of Competing Interest

Acknowledgements

Lithos

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Precambrian Res.

Gondwana Res.

Lithos

Australia. Geochim. Cosmochim. Acta

Gondwana Res.

Precambrian Res.

Chem. Geol.

Chem. Geol.

Chem. Geol. Elsevier B.V

Precambrian Res.

Geochim. Cosmochim. Acta

Gondwana Res.

Lithos

Precambrian Res.

Precambrian Res.

Geosci. Front.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Gondwana Res.

Ore deposits associated with mafic magmas in the Kaapvaal craton

Mineral. Deposita

Variations in chemical compositions of chrome spinels from Hongguleleng ophiolites, Xianjing, China and their significance

Acta Mineral. Sin.

Chromite in Komatiites, 1. Magmatic Controls on Crystallization and Composition

J. Petrol.

Deformed chromitite layers in the Coobina intrusion, Pilbara craton, Western Australia

Econ. Geol.

Research Article
Chromitites from an Archean layered intrusion in the Western Dharwar Craton, southern India