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Durham University

Department of Earth Sciences

Profile

Publication details for Dr Geoff Nowell

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

Author(s) from Durham

Abstract

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.