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190Pt-186Os geochronometer reveals open system behaviour of 190Pt-4He isotope system.

Luguet, A. and Nowell, G.M. and Pushkarev, E. and Ballhaus, C. and Wirth, R. and Schreiber, A. and Gottman, I. (2019) '190Pt-186Os geochronometer reveals open system behaviour of 190Pt-4He isotope system.', Geochemical perspectives letters., 2 . pp. 44-48.


Platinum Group Minerals are typically dated using the 187Re-187Os and 190Pt-186Os isotope systems and more recently using the 190Pt-4He geochronometer. The 187Re-187Os and 190Pt-186Os compositions of Pt-alloys from the Kondyor Zoned Ultramafic Complex (ZUC) analysed here reveal overprinting for both geochronometers except in one alloy exhibiting the most unradiogenic 187Os/188Os and most radiogenic 186Os/188Os signatures. These signatures argue for an Early Triassic mineralisation, when silicate melts/fluids derived from the partial melting of an Archean mantle crystallised to form the Kondyor ZUC while the 190Pt-4He chronometer supports an Early Cretaceous mineralisation. We propose that Kondyor ZUC represents the root of an alkaline picritic volcano that constitutes the remnants of an Early Triassic island arc formed during the subduction of the Mongol-Okhotsk ocean seafloor under the Siberia craton. After the Early Cretaceous collision of Siberia with the Mongolia-North China continent, the exhumation of deep-seated structures - such as the Kondyor ZUC - allowed these massifs to cool down below the closure temperatures of the Pt-He and K-Ar, Rb-Sr isotope systems, explaining their Early to Late Cretaceous ages for the Kondyor ZUC.

Item Type:Article
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Available under License - Creative Commons Attribution Non-commercial No Derivatives.
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Publisher statement:Copyright © The Authors Published by the European Association of Geochemistry under Creative Commons License CC BY-NC-ND 4.0
Date accepted:28 August 2019
Date deposited:07 November 2019
Date of first online publication:22 October 2019
Date first made open access:07 November 2019

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