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Osmium alloys & the pulse of the Earth

Final Report Summary - OS.EARTH (Osmium alloys & the pulse of the Earth)

This project was aimed at the career integration and cementation of Dr. Arjan Dijkstra, who was appointed as an igneous petrology lecturer and researcher in the Earth Sciences group at Plymouth University, United Kingdom in October 2010. The key research project to achieve this goal focussed on the analysis of osmium-bearing alloys obtained from mantle rocks, but the overall project was also 'reactive', allowing for the initiation of new research aspects in response to new developments such as collaborations with colleagues or other researchers in the field, student-led projects, and new strategic objectives of the department, research unit, or even Plymouth University as a whole (e.g. recent foundation of the new Sustainable Earth Institute).
The background to the main research project was as follows. Current 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 and evidence from the crustal record may be incomplete and biased. 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'.
In this project we studied 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; such events are likely to have been associated with widespread volcanism on Earth. The formation of these alloys can be dated by measuring the different isotope proportions of osmium. In this project we used an innovative, multi-faceted approach, centered on the collection and analysis of a large number of Os alloys from river and beach placer deposits, and from key mantle outcrops worldwide. An exciting results from the project consisted of a fully analysed collection of >300 osmium-bearing alloy grains from the River Rhine, the first of its kind from NW Europe, which confirmed the global nature of major mantle melting super-event around 1.2 billion year ago, an event that was hitherto poorly constrained. Many more samples from new localities (e.g. Shetland Islands, Colombia) are ‘in the pipe-line’ and will hopefully also give a better insight in similar events in the earlier part of Earth history.
Reaching across to other scientific disciplines, this project also targeted alluvial gold placer 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 'signatures' for each alluvial gold deposit. Some initial success was made towards the end of the project in identifying such alluvial gold deposits in Greece and research is underway to test if Os isotopic signatures will allow testing of the hypothesis that Os alloy inclusions in prehistoric gold objects can be used to pinpoint the exact source of prehistoric gold, e.g. of individual coins and cultural artefacts.
In the course of the project, the researcher has been highly active in developing new methodology for fast automated mineralogy analysis using scanning electron microscopy. This new methodology has not only been very useful for the academic research project outlined above which critically relies on finding rare osmium-bearing alloys in mantle-derived rocks and sediments, but is already proving to be very much in demand for more applied research and problem-solving projects together with industry partners, for instance, in mineral liberation analysis in mineral processing, in kimberlite analysis for diamond prospecting, and in mineralogical studies of potential Rare Earth Element resources.
In reference to the overarching aim of career integration and cementation, the researcher has dramatically broadened his expertise, especially in industry-facing projects, in the course of the project,. He has also obtained permanent employment with good prospects for academic promotion, developed a very strong and diverse teaching portfolio, has become a member of the programme management team of the subject area, and has established a research group comprising 3 PhD students and 3-4 Masters students at any one time.