We expect that the results of this work will provide a new perspective on the chemical and isotopic character of Earth’s mantle, on the interaction between oceanic crust and mantle and the origin of ophiolites and their mineral deposits, particularly podiformchromitites.  The presence of many unusual minerals in oceanic peridotites and chromitites indicates a greater degree of heterogeneity in the mantle than previously thought and we expect to determine the sources of these minerals, where they reside in the mantle and how they are incorporated into ophioliticperidotites and chromitites.  We expect to determine if these minerals are widespread in oceanic mantle as well in ophiolites.  Likewise, we hope to identify the source of the light carbon isotopes found in the ophiolitic diamonds and moissanite grains.  In combination with seismic tomography, we expect to clarify the role of subduction in transporting crustal minerals into the mantle where they are mixed with UHP and highly reduced minerals and to gain a better idea of the nature and composition of the mantle transition zone.  

This work should also provide crucial information on how the unusual minerals are preserved in the mantle and carried to shallow depths far beyond their stability fields.  Such information will provide a much better understand of T, P and redox conditions in the upper mantle.  Ultimately, we expect to be able to combine all of the new data into a dynamic model that can resolve existing questions about the origin of ophiolites and their tectonic environment of formation, the nature and extent of melt-rock reaction in the upper mantle and the role it plays in changing mantle mineralogy and in the formation of podiformchromitites. 

We may not be able to answer all of the outstanding questions raised by the new finding of UHP, highly reduced and crustal minerals in the mantle but we expect to develop a more complete and detailed understanding of mantle processes.  Interpretation of the data will be on-going but final conclusions and models will need to integrate the entire new dataset.  For example, as we examine more ophiolites from year to year, we will have a better idea of the extent to which of the unusual minerals occur in oceanic mantle and their relationship to ophiolites from different orogenic belts and different tectonic environments. Continued study of the diamonds, particularly their C-isotopic and trace element compositions and the nature of their inclusions, should give a much better understanding where and how they are formed in the oceanic mantle.  By this study, we expect to have a complete geochemical database on the investigated ophiolites and a means of fingerprinting podiformchromitites to determine the nature of the magmas from which they were derived.  We will see the compilation, integration and interpretation of the new data and development of new models.  New results and new insights will be published as they become available, with final publications being available shortly after the end of Year 5.

Application of this work 

A major application of this work will be to illucidatethe origin and mode of formation of podiformchromitite, the major source of chromium for many countries.  These bodies are not particularly abundant in ophiolites and are certainly not uniformly distributed.  By the end of Year 3, we expect to have a much better understanding of the processes involved in chromitite formation, which determine their compositions and their locations within specific orogenic belts and specific ophiolites.   These findings should be very useful in developing more efficient exploration models. This work will also spur the application of a wide range of analytical techniques to the nano-scale investigation of a wide range of minerals.

Societal benefits 

Two major societal  benefits will accrue from  this project:

1) Collaboration among scientists with a wide range of knowledge and expertise.  The synergy that arises from such a collaboration is crucial to understanding such a large and complex problem as the nature and evolution of Earth’s mantle.  Each participant brings a wide range of experience and existing knowledge to different aspects of the problem that will be essential in integrating the results into coherent and meaningful models.  All of the participants in this project have worked in large collaborative programs previously and fully understand the value of personal interaction.  It is expected that scientists in a number of underdeveloped countries will have opportunities for sharing information, learning new techniques and making long-lasting contacts with members of this group. 

2) Education and capacity-building among students and young professionals, particularly in countries where such opportunities are currently limited.  Training of students and young scientists will be a major aspect of this project.  Such activities are already taking place in the pilot projects currently underway.   New findings are presented in workshops and symposia, individuals are given the opportunity to work alongside experienced professionals, and both students and young professionals are welcomed into the analytical laboratories where they learn new techniques and develop on-going relationships with the scientists and technicians involved.