Our knowledge about the geological history of the Earth is almost exclusively derived from studies of the Earth's crust, the ~35 km ultra-thin skin covering our planet. There are indications that most of the continental crust has been produced during a few, short-lived bursts - so-called 'super-events' - throughout Earth history, but the issue is controversial. If true, these global events almost certainly had a major impact on the development of the atmosphere, on the evolution of life on Earth and on the formation of world-class mineral deposits. Processes in the Earth's mantle must have played a major role in these proposed 'super-events'.
The aim of this project is to study the vital clues about the large-scale melting events in the history of the Earth that are preserved within the mantle in the form of tiny grains of alloys of the element osmium (Os). Os alloys form when parts of the mantle are melted to a high degree. The formation of these alloys can be dated using the different isotope proportions of osmium. An innovative, multi-faceted approach - already tested by pilot studies – is proposed. The goal is to collect a large number of Os alloys from key river and beach placer deposits worldwide, followed by Os isotope analysis using time- and cost-effective methods, thus constructing a global record of the history of mantle melting. This will allow for a rigorous and systematic testing of the mantle super-event hypothesis.
Reaching across to other scientific disciplines, this project will also target some alluvial gold deposits that were already exploited by man in pre-historic times, as the Os isotope distributions of Os alloys mixed with this gold will not only yield new data on the global mantle super-events, but can also be used to define the characteristic Os isotope signature for the deposit. Such signatures will allow testing of the hypothesis that Os alloy inclusions in prehistoric gold objects can be used to pinpoint the source of the gold.
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