Clumped isotope geochemistry of carbonatites in the north-western Deccan igneous province: Aspects of evolution, post-depositional alteration and mineralisation

Fosu, Benjamin R.; Ghosh, Prosenjit; Viladkar, Shrinivas G.

doi:10.1016/j.gca.2020.01.020

Cited by 16 publications

(5 citation statements)

References 97 publications

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“…For example, carbonatites are commonly susceptible to diagenetic alteration, recrystallization, and closed system isotopic exchange, which reflect in their Δ 47 values. 49,50 However, the pristine δ 18 O values of NBS18 and OLNC (mantle field in Figure 5) imply that their Δ′ 17 O compositions are preserved, despite alteration in Δ 47 values.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…While postdepositional modification of sample Δ′ 17 O values upon isotopic exchange with circulating fluids is a possibility (a common alteration phenomenon in carbonates), the Δ′ 17 O compositions (Figure ) mostly seem to reflect the combination of processes related to the mineral formation, rather than diagenetic modifications. For example, carbonatites are commonly susceptible to diagenetic alteration, recrystallization, and closed system isotopic exchange, which reflect in their Δ 47 values. , However, the pristine δ 18 O values of NBS18 and OLNC (mantle field in Figure ) imply that their Δ′ 17 O compositions are preserved, despite alteration in Δ 47 values.…”

Section: Resultsmentioning

confidence: 99%

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Technical Note: Developments and Applications in Triple Oxygen Isotope Analysis of Carbonates

Fosu

Subba

Peethambaran

et al. 2020

ACS Earth Space Chem.

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Triple oxygen isotope systematics has evolved as a powerful tool in understanding various earth system processes. It has proven reliable in assessing paleoenvironmental conditions from natural archives (e.g., waters, ice cores, biota, sediments, etc.) owing to recent advances in high-precision mass spectrometric analysis. Toward the standardization of triple oxygen isotope analyses in carbonates, we describe a procedure of high-precision Δ′17O analysis of carbonates by a two-step protocol: acid digestion of carbonates to evolve CO2 followed by the catalytic CO2–O2 exchange method. The Δ′17O values of a suite of carbonate reference materials and several carbonates of different origins have been determined with good precision (∼0.007‰). The accuracy of sample Δ′17O values is dependent on the accuracy of Δ′17O composition of the reference CO2 used in determining the effective fractionation (θs) in the experimental setup. The obtained Δ′17O values (λ = 0.528, versus VSMOW) for NBS18-CO2 (−0.119‰) and NBS19-CO2 (−0.169‰) show a difference of 0.050‰, similar to that obtained elsewhere via complete fluorination. The analyzed carbonates mostly conform to equilibrium mass-dependent fractionation laws, but we encountered a suite of samples from cold seeps, caves, and metasomatic environments that have Δ′17O values indicative of disequilibrium fractionation. We show that a combination of clumped isotope composition (Δ47) that provides estimates of formation temperature and triple oxygen isotope ratios in carbonates can help in reconstructing past environments, where paired carbonate data (δ13C−δ18O−Δ47–Δ′17O) and parent water data (δ17O−δ18O−Δ′17O) are particularly useful.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Technical Note: Developments and Applications in Triple Oxygen Isotope Analysis of Carbonates

Fosu

Subba

Peethambaran

et al. 2020

ACS Earth Space Chem.

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“…Petrographic observations of textural equilibrium of carbonates and accessory minerals in association with the presence of graphite as inclusion within carbonates and mineral geothermometers (graphite-magnesite) of Newania carbonatites suggest a crystallization temperature of more than 600°C (Doroshkevich et al, 2010). Temperatures of emplacements of typical carbonatite magmas are~300-700°C which are much higher than temperatures of late-stage hydrothermal fluids (<250°C) (Mitchell and Krouse, 1975;Fosu et al, 2020). Therefore, the estimates of crystallization temperatures of Newania carbonatites indicate that most sulfides would form under magmatic conditions.…”

Section: Sulfur Isotopic Compositions Of the Newania Carbonatitesmentioning

confidence: 98%

Sulfur, carbon and oxygen isotopic compositions of Newania carbonatites of India: implications for the mantle source characteristics

Banerjee

Satish‐Kumar

Chakrabarti³

2021

Journal of Mineralogical and Petrological Sciences

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This study presents first report of the sulfur isotopic compositions of carbonatites from the Mesoproterozoic Newania complex of India along with their stable C and O isotope ratios. The δ 34 S V-CDT (−1.4 to 2‰) and Δ 33 S (−0.001 to −0.13‰) values of these carbonatite samples (n = 7) overlap with the S isotope compositions of Earth's mantle. Additionally, the δ 13 C V-PDB and δ 18 O V-SMOW values of these carbonatites also show overlapping compositions to that of Earth's mantle. Based on these mantle-like stable isotopic compositions of carbonatites along with their higher crystallization temperature (~600°C) compared to a hydrothermal fluid (<250°C), we suggest that the sulfide minerals in these carbonatites were formed under a magmatic condition. The mantle like signatures in the δ 34 S, δ 13 C-δ 18 O, and 87 Sr/ 86 Sr values of these carbonatites rule out possible crustal contamination. Coexistence of the sulfide phase (pyrrhotite) with magnesite in these carbonatites suggests that the sulfide phase has formed early during the crystallization of carbonatite magmas under reducing conditions. Overall restricted variability in the δ 34 S values of these samples further rules out any isotopic fractionation due to the change in the redox condition of the magma and reflect the isotopic composition of the parental melts of the Newania carbonatite complex. A compilation of δ 34 S of carbonatites from Newania and other complexes worldwide indicates limited variability in the isotopic composition for carbonatites older than 400 Ma, which broadly overlaps with Earth's asthenospheric mantle composition. This contrasts with the larger variability in δ 34 S observed in carbonatites younger than 400 Ma. Such observation could suggest an overall lower oxidation state of carbonatite magmas emplaced prior to 400 Ma.

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“…Variations in the C–O isotope data and petrographic observations reveal the coupling of fractional crystallisation and post-magmatic fluid–rock interactions to bulk-rock composition. After emplacement, the resetting of clumped isotope signatures in carbonatites is facilitated by post-magmatic processes in both open and closed systems (Fosu et al , 2020). Banerjee and Chakrabarti (2019) found that the calcite and ankerite carbonatites are characterised by geochemical and Ca, Nd and Sr isotopic variations.…”

Section: Geological Setting and Origin Of The Carbonatitesmentioning

confidence: 99%

Evolution of pyrochlore in carbonatites of the Amba Dongar complex, India.

Viladkar

Sorokhtina

2021

MinMag

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Clumped isotope geochemistry of carbonatites in the north-western Deccan igneous province: Aspects of evolution, post-depositional alteration and mineralisation

Cited by 16 publications

References 97 publications

Technical Note: Developments and Applications in Triple Oxygen Isotope Analysis of Carbonates

Technical Note: Developments and Applications in Triple Oxygen Isotope Analysis of Carbonates

Sulfur, carbon and oxygen isotopic compositions of Newania carbonatites of India: implications for the mantle source characteristics

Evolution of pyrochlore in carbonatites of the Amba Dongar complex, India.

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