Source: IGCP 649   Publish Time: 2015-04-28 19:48   3177 Views   Size:  16px  14px  12px

 Activity by years

Our general plan is to focus, in each of the first four years, on one specifically chosen ophiolite, which has a well-exposed mantle section that we have not yet investigated for the presence of diamonds and related minerals. We will not only hold a field excursion, workshop (conference) and training course in that locality, but we will also collect samples of perdiotite and chromitite for study by ourselves and IGCP collaborators as part of the project. The latter will help us achieve one of our major scientific goals by investigating whether UHP and other unusual minerals occur in normal MORB-type mantle lithosphere, or only in SSZ–generated ophiolites. Each year, we also plan to organise ophiolite–related sessions in international conferences (i.e. American Geophysical Union, European Geosciences Union, Goldschmidt Conference) in order to publicise the project, share any new achievements and enhance the collaboration among the project participants and other scientists. The meeting in Year 5 will be different: it will be held in Beijing and the field excursion will be to the Loubusaophiolite in Tibet where ophiolitic diamonds were first discovered and where a continental deep drilling project recently drilled through the diamoniferous mantle section. The aim of the final meeting will be to consolidate and present the work already done and prepare a final, high-quality publication on the outcome of the project.

Our plan for the five years of the project is given in more detail below:

Year 1 (2015)

The mid-Cretaceous Troodosophiolite is the most important ophiolite historically, having been the first ophiolite proposed to have formed at an ocean ridge, and then been the focus of the debate on the precise setting of ophiolites with subduction signatures. It has many chromite mines, some of which were mined until relatively recently and its chromite reserves, though small, provide a strategic resource. It also hosts other resources or potential resources, including Cu, Au and PGEs. It has been studied extensively since the 1960s, and its internal structure and tectonic fabric are well known. It has excellent exposures from lavas, through sheeted dkes and plutonic rocks to upper mantle rocks which include highly depleted harzburgite, dunite, lherzolite and, as noted, chromitite deposits.

The Troodosophiolite is thus ideally suited for the first meeting: it is logistically and politically straightforward, easy to access, and allows the whole ophiolite sequence to be viewed by participants who may not be fully familiar with ophiolites. Yet it is important for us scientifically as investigation for diamonds has not yet been carried out. Additionally, of the organisers and collaborators of the project, Professors Yildirim Dilek, Paul Robinson and Julian Pearce all have worked, taught and published extensively on the Troodos Massif. They will use their extensive contacts to organize a field conference in collaboration with the local geologists in the Geological Survey Department in Nicosia. The training course for students and young professionals, in particular, will focus on the basics, namely the classification and tectonic settings of ophiolites, and the formation of crust and upper mantle at ocean ridges. The recent volume of Elements (February 2014) contains a number of articles by the proponents of this project and these will form the basis of the course.

Year 2 (2016)

Our choice of meeting location in Year 2 is Havana, Cuba, with a field trip to the Northern Cuban ophiolite belt. As with the Troodos Massif, this ophiolites are Cretaceous in age and contains many podiformchromitite localities and a number of bodies large enough to mine though, unlike the Troodos Massif, mining is still active. Importantly for the science of this project, some chromites are high-Cr (more SSZ-type) while others are high-Al (more MORB-type)so providing an opportunity to link the presence or absence of diamonds to ophiolite type and hence setting. The ophiolite belt is part of a larger Cuban fold belt comprising deformed and metamorphosed nappes emplaced during the Late Cretaceous and earliest Teriary. The main mantle rocks are tectonisedharzburgite with minor dunites, and a Moho transition zone, cumulate gabbros and sheeted dykes are all exposed. Prof. W. Griffin, project co-proponent was co-author of a recent paper on chromites from one of the mining districts. Project collaborator, Angelica Castro, from the Institute of Geology and Palaeontology in Havana has offered to organise the meeting and run a related field trip to the key mantle localities. The planned training course will focus on the composition and texture of mantle rocks with key contributions by collaborators, Adolf Nicolas, Harry Green and Hans-Peter Schertl.

Year 3 (2017)

The third workshop is planned to be held in Rangoon, Myanmar, with a field excusion to Jurassic ophiolite in the Myitkyina region of Myanmar. topic. The ophiolite in the Myitkyina region represents a suprasubduction zone (SSZ) ophiolite type, and consists of mantle peridotites, andesite-basalt lava flows, leucogabbro and gabbro, olivine pyroxenite and plagioclase-bearing pyroxenite, and plagiogranite intrusions. Jurassic ophiolites are important world-wide and the workshop will address the distribution, settings and characteristics of ophiolites of this age. Because Myanmar has been closed to visiting geologists for some time, this will provide international participants with an opportunity to see a relatively unstudied part of the Earth, and also to collect samples for the study of diamonds and other UHP minerals. Prof.KyaingSein, vice president of Myanmar Geosciences Society, has offered to organise the workshop and field excursion. The training course will focus on the global distribution of ophiolites, in keeping with the workshop theme. A special issue on the same topic is planned for Lithos after the conference.

Year 4 (2018)

We plan to carry our Year 4 activities in Australia and the surrounding region, thus providing an opportunity for scientists in the Southern Hemisphere to become more involved in the project. The workshop will be held in the ARC Centre of Excellence for Core to Crust Fluid Systems Lab (CCFS) in Australia hosted by Prof. William L Griffin. It will focus on the reasons for the presence of diamonds in ophiolites, incorporating geodynamic, geochemical and petrological modelling, a particular strength of many Australian institutions. Mantle dynamic processes will also be the subject of the training course. The related field excursion will be to New Caledonia, north of Australia, which hosts one of the most extensive exposures of ophioliticperidotites on Earth (the Massif du Sud). The mantle rocks are ultra-depleted harzburgitetectonite overlain by extensive dunites (including rare chromitites) and then a Moho transition zone and pyroxene-dominated lower crust and have been interpreted as having formed in a subduction initiation setting with progressively increasing subduction influence. Scientifically, it is important to determine whether diamonds are preserved in this type of setting, where mantle flow mechanisms and drivers are likely to have be quite different from those in Tethyanophiolites. The excursion is logistically straightforward and we have contacts (Meffre, Ferre) who can provide advice and perhaps more. By the time of this meeting, we will also be able to make use of materials from several other field trips to the ophiolite that have been run, or will be run (e.g. IODP Exp 351 post-cruise meeting).

Year 5 (2019)

For the final year, we aim to hold the meeting in China, where the PI will be able to provide significant logistic and financial support. The meeting will be held in Beijing and focus on the results of the project to date. The training course will focus on the mineralogy of the UHP minerals, of which the CAGS in Beijing hosts the world’s best collection. Key contributors will be co-proponents Jingsui Yang, Paul Robinson and Larissa Dobrznetskaya. The field excursion will take place in Tibet, where Loubusa represents the ‘birthplace’ of ophiolitic diamondstudies and related UHP minerals. Participants will have an opportunity to see these ophiolites in the field through an excursion along the Xigazeophiolite belt, finishing at the Loubusa locality. This meeting will also lead a publication on the theme of ophiolitic mantle and its UHP inclusions, likely as a thematic issue of one of the main international journals.