Forsterite reprecipitation and carbon dioxide entrapment in the lithospheric mantle during its interaction with carbonatitic melt: a case study from the Sung Valley ultramafic–alkaline–carbonatite complex, Meghalaya, NE India

Choudhary, Shubham; Sen, Koushik; Kumar, Santosh; Rana, Shruti; Ghosh, S.

doi:10.1017/s0016756820000631

Cited by 11 publications

(1 citation statement)

References 62 publications

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“…In the southern part, Tertiary shelf sediments, Cretaceous Sylhet trap rocks, plume‐related youngest igneous rocks such as mafic to ultramafics, alkaline‐ijolite, and carbonatite formed at ca. 117 Ma in the Meghalaya Plateau (Choudhary, Sen, & Kumar, 2021; Choudhary, Sen, Kumar, Rana, & Ghosh, 2021; Ghatak & Basu, 2013; Ray, Pattanayak, & Pande, 2005; Srivastava, Heaman, Sinha, & Shihua, 2005).…”

Section: Geochronology Geology and Field Relationsmentioning

confidence: 99%

Geochemistry of Proterozoic and Cambrian granites from Meghalaya Plateau, north‐east India: Implication on petrogenesis of post‐collisional, transitional from I‐type to A‐type felsic magmatism

et al. 2021

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The Meghalaya Plateau including the Mikir Hills represents the northeastern extension of the Precambrian Indian Shield and mainly comprises the Proterozoic basement granite gneisses, granites (sensu lato), granulites, metasediments, Cambrian granites, and Mesozoic‐Tertiary lithounits. A new whole‐ rock geochemical dataset of Proterozoic and Cambrian granites is presented and investigated to decipher the petrogenesis of these granites with its implications on understanding the crustal growth history of Meghalaya Plateau. Cambrian granites commonly intrude the Proterozoic basement granite gneisses and Shillong Group of rocks. Both the Proterozoic and Cambrian granites exhibit similar mineral assemblages (Bt ± Amp‐Pl‐Kf‐Qz‐Zrn‐Mag‐Ttn‐Ap ± Ilm), but they are texturally distinct. Microgranular enclaves are ubiquitous in Cambrian plutons but are devoid or rare in the Proterozoic granites. Cambrian granites are medium‐ to coarse‐grained, inequigranular, hypidiomorphic, frequently porphyritic, and undeformed to mildly deformed, whereas Proterozoic granites are medium‐ to coarse‐grained, less frequent porphyritic, and mildly to strongly deformed. Geochemically, the Proterozoic (molar Al2O3/CaO + Na2O + K2O (A/CNK) = 0.86–1.15; FeOt/FeOt + MgO = 0.60–0.93) and Cambrian (A/CNK = 0.77–1.20; FeOt/FeOt + MgO = 0.56–0.90) granites are nearly identical showing strongly metaluminous to moderate peraluminous, magnesian to ferroan, and alkali‐calcic to calc‐alkaline and transitional character between I‐type and A‐type oxidized granites formed in a post‐collision tectonic environment. Comparison of studied granites with experimental melt compositions derived from various protoliths suggests that they are sourced from metabasics to tonalites. Harker bivariate plots demonstrate fractional differentiation as a dominant process in the evolution of these granites. However, occurrence of hybrid microgranular enclaves and geochemical features manifest that the mixing and fractionation of coeval mafic and felsic magmas have also played a key role in the evolution of some Cambrian plutons. A slightly higher zircon saturation temperatures for Cambrian (700–950°C) than the Proterozoic (675–900°C) granites characterize a relatively higher‐T melting regime for the generation of Cambrian than the Proterozoic granites. Petrogenetic modelling constrains that the parental magma to the Proterozoic granites can be generated by about 25.5% melting of heterogeneous lower crustal sources with low maficity, which subsequently had undergone fractional crystallization involving bt‐amp‐pl‐Kf‐qz assemblage. However, parental to Cambrian granites can be produced by about 32% melting of the amphibolitic lower crust that subsequently evolved through synchronous fractional crystallization and mixing with a mantle‐derived mafic melt. The chronological records and the present petrogenetic findings on Proterozoic granites propound a viable geodynamic model that the assembly and growth (thickening) of the Columbia Supercontinent during ca. 1,800–1,600 Ma caused a hi...

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Section: Geochronology Geology and Field Relationsmentioning

confidence: 99%

Geochemistry of Proterozoic and Cambrian granites from Meghalaya Plateau, north‐east India: Implication on petrogenesis of post‐collisional, transitional from I‐type to A‐type felsic magmatism

et al. 2021

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Metasomatic ijolite, glimmerite, silicocarbonatite, and antiskarn formation: carbonatite and silicate phase equilibria in the system Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–O2–CO2

Anenburg,

Walters

2024

Contrib Mineral Petrol

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Silicocarbonatites are carbonatite rocks containing > 20% silicate minerals. Their formation is not well understood due to low silica solubility in carbonatite melts and negligible amounts of silicate minerals on carbonatite melt cotectics at upper crustal conditions. We explore whether silicocarbonatites can be thought of as antiskarns: rocks formed by leaching of SiO2 from siliceous wall rocks by carbonatite melts, and its deposition as solid silicate minerals by reaction with chemical components already present in the carbonatite melt. Solid state thermodynamic modelling at 1–5 kbar and 500–800 °C predicts that calcite–dolomite–magnetite assemblages will transform to dolomite-free silicocarbonatites with an increase in silica contents. In sodic systems, the formation of aegirine and alkali amphiboles suppresses silica activity despite elevated silica contents. Therefore, dolomite remains stable, but Fe3+ is consumed, firstly from magnetite breakdown, and secondly by coupled Fe oxidation and reduction of CO2 to CO, CH4, and graphite, particularly at higher pressures. Despite a net increase in Fe3+/Fe2+, the system evolves to increasingly lower oxygen fugacity. In aluminous systems, nepheline indicates high temperatures whereas alkali feldspars form at lower temperatures. Modelling of potassic systems demonstrates stability of mostly phlogopite-rich biotites, leading to Fe2+ increase in all other carbonate and silicate phases. We find that perthites are expected in high pressures whereas two feldspars are more likely in lower pressures.Aspects of the clinopyroxene natural compositional trend (diopside to hedenbergite to aegirine) of carbonatite systems can be explained by silica contamination. Ferrous clinopyroxenes typically require low alumina and are predicted in potassic or low temperature sodic systems, primarily at mid to high pressures. Silica contamination permits the formation of silicocarbonatite-like assemblages in a way that is not limited by SiO2 solubility in carbonatite melts. Glimmerites and clinopyroxene-rich rocks (such as the ijolite series) that often occur around carbonatite rocks at the contact with silica-oversaturated wall rocks can be explained as the extreme end of silica contamination of carbonatite melts. Therefore, these clinopyroxenites and glimmerites can form solely via metasomatic processes without the presence of a silicate melt.

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Early Cretaceous ultramafic-alkaline-carbonatite magmatism in the Shillong Plateau-Mikir Hills, northeastern India – a synthesis

2022

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A comprehensive mineralogical, geochemical and isotopic review of six ultramafic-alkaline-carbonatite magmatic intrusions of the Shillong Plateau (Sung Valley, Jasra, Swangkre-Rongjeng, and Mawpyut) and Mikir Hills (Samchampi-Samteran and Barpung) is presented here, using the published data. These intrusions emplaced ca. 115–102 Ma ago, thus are significantly younger than the tholeiitic flood basalts erupted in Rajmahal-Sylhet province (ca. 118–115 Ma). The intrusive lithologies vary from ultramafic (dunites, clinopyroxenites, melilitolites) to mafic (ijolites, gabbros sensu lato, shonkinites), to felsic (syenites, nepheline syenites) and carbonatites (mostly calcite-rich varieties). The volcanic-subvolcanic facies (lamprophyres, phonolites) are not abundant. The range of chemical compositions of the magmatic phases in the various assemblages is notable; the intrusive rocks are thus the result of crystallization of magmas from variably evolved, independent liquid-lines-of descent, generally of alkaline/strongly alkaline lineages and sodic-to-potassic in affinity. The large variations of the Sr–Nd isotopic ratios of the silicate intrusive rocks (sensu lato) suggest a role of shallow-level crustal contamination during their formation. The carbonatites of the Sung Valley and Samchampi-Samteran have different isotope ratios than the associated silicate rocks, have some isotopic affinity with the Group I tholeiitic basalts of Rajmahal Traps and have an ultimate genesis in a carbonate-bearing lithospheric mantle.

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Forsterite reprecipitation and carbon dioxide entrapment in the lithospheric mantle during its interaction with carbonatitic melt: a case study from the Sung Valley ultramafic–alkaline–carbonatite complex, Meghalaya, NE India

Cited by 11 publications

References 62 publications

Geochemistry of Proterozoic and Cambrian granites from Meghalaya Plateau, north‐east India: Implication on petrogenesis of post‐collisional, transitional from I‐type to A‐type felsic magmatism

Geochemistry of Proterozoic and Cambrian granites from Meghalaya Plateau, north‐east India: Implication on petrogenesis of post‐collisional, transitional from I‐type to A‐type felsic magmatism

Metasomatic ijolite, glimmerite, silicocarbonatite, and antiskarn formation: carbonatite and silicate phase equilibria in the system Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–O2–CO2

Early Cretaceous ultramafic-alkaline-carbonatite magmatism in the Shillong Plateau-Mikir Hills, northeastern India – a synthesis

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