Variation scale and heterogeneity of the lead isotope composition in sulfides from hydrothermal fields of the Mid-Atlantic Ridge: Evidence from high-precision MC-ICP-MS isotopic data

Чернышев, И. В.; Бортников, Н. С.; Чугаев, А. В.; Голубев, В. Н.; Fouquet, Yves; Amplieva, E. E.; Stavrova, Olga O

doi:10.1134/s1028334x11040106

Cited by 3 publications

(1 citation statement)

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“…Although within-deposit variations in the metamorphosed VMS deposits are sometimes significant, within each isotopic group no systematic variation is observed between pyrite-rich, chalcopyrite-rich and bornite-rich samples (Table S1). This is in line with what reported in modern seafloor VMS deposits, in which different sulphide minerals typically have similar Pb isotope compositions (e.g., Fouquet & Marcoux, 1995;Andrieu et al, 1998;Chernyshev et al, 2011). Therefore, the observed Pb isotope trends are unlikely to be related to isotope fractionation between ore minerals during metamorphism.…”

Section: Isotopic Evolution During Alpine Metamorphismsupporting

confidence: 90%

Lead isotope systematics in ophiolite-associated sulphide deposits from the Western Alps and Northern Apennine (Italy)

Nimis¹,

Omenetto²,

Stasi³

et al. 2018

ejm

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We report Multi-Collector-ICP-MS analyses of Pb isotopes for hydrothermal deposits in ophiolitic units of the Western Alps (hereafter, WA) and Northern Apennine (hereafter, NA). The deposits include (i) volcanogenic massive sulphides formed on the seafloor of the Mesozoic Piemonte-Liguria ocean, which were subjected to subduction-(blueschist to eclogite facies) and collision-related (greenschist facies) metamorphism during the Alpine orogenesis (WA) or escaped Alpine metamorphism (NA), and (ii) post-collision veins cutting the metamorphic oceanic units. The unmetamorphosed sulphides have a MORB-like Pb isotope signature. Sulphides that re-crystallised under eclogitic conditions incorporated an old continental Pb component, which was released from gangue minerals or neighbouring sediments by dehydration reactions at the blueschist-eclogite transition. Our data suggest a limited mobility of sulphide-hosted metals in the subducted oceanic crust up to eclogite-facies conditions. Sulphides in the blueschist-facies and, possibly, eclogite-facies units incorporated further continental Pb derived from oceanic metasedimentary host-rocks containing a continent-sourced terrigenous component during subsequent greenschist-facies metamorphism. Some of the post-collision veins show isotopic similarity with the massive sulphides contained in the same ophiolitic units, suggesting derivation of metals from similar sources (i.e., ophiolites and/or associated metasediments). In the Saint-Véran syn-metamorphic vein deposit, a complex Pb isotope pattern suggests mixing of fluids derived from local retrogressed blueschist-facies rocks with farther-travelled fluids discharged by or reacted with deeper, eclogitic units.

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Section: Isotopic Evolution During Alpine Metamorphismsupporting

confidence: 90%