Platinum enrichment processes in ultramafic massifs of the Uralian Platinum belt, Russia - evidence for mineralization at the magmatic to hydrothermal transition
Final Report Abstract
The Re-Os (187Re->188Os) and the Pt-Os (186Pt->188Os) isotopic systems are the geochronometers of choice to date HSE mineralizations, such as the Pt mineralizations of the Ural-Alaskan-Complexes. More recently, Pt mineralization have also been dated by the Pt-He (190Pt->4He) isotopic system, which - like the Pt-Os isotopic system - is based on the alpha decay of 190Pt. The 187Re-187Os and 190Pt-186Os compositions of Pt-alloys from the Kondyor Zoned Ultramafic Complex (ZUC) analyzed here reveal overprinting for both geochronometers except in one alloy exhibiting the most unradiogenic 187Os/188Os and most radiogenic 186Os/188Os signatures. These signatures reveal an Early Triassic Pt mineralization, when silicate melts/fluids derived from the partial melting of an Archean mantle (likely the Siberian cratonic mantle root) crystallized to form the Kondyor ZUC. In contrast, the 190Pt-4He chronometer supports an Early Cretaceous Pt mineralization for the Kondyor ZUV. 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.
Publications
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(2019). 190Pt-186Os geochronometer reveals open system behavior of 190Pt-4He isotope system. Geochemical Perspective Letters 11, 44-48
Luguet A., Nowell G.M., Pushkarev E., Ballhaus C., Wirth R., Schreiber A. and Gottman I.
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(2019). Pt-Re-Os dating of the Pt-alloys from the Kondyor Zoned Ultramafic Complex (Far East Russia). Goldschmidt abstract 2076
Luguet A., Nowell G.M., Pushkarev E., Ballhaus C., Wirth R. and Schreiber A.
