Deep Mantle Recycling Revealed in Diamonds and their Mineral Inclusions (NERC Grant NE/J008583/1)

Three Published Papers; Thomson et al CMP 2014 - Origin of Sub-Lithospheric diamonds from the Juina-5 Kimberlite (Brazil): constraints from Carbon Isotopes and Inclusion Compositions http://dx.doi.org/10.1007/s00410-014-1081-8. Thomson et al Nature 2016 - Slab melting as a barrier to deep carbon subduction http://dx.doi.org/10.1038/nature16174 Burnham et al 2015 - Stable Isotope evidence for Crustal Recycling as recorded by superdeep Diamonds http://dx.doi.org/10.1016/j.epsl.2015.10.023 NERC grant abstract: Natural diamonds are formed at high pressures and temperatures deep within the Earth's interior. When diamonds form, probably from carbonate-rich fluids and melts in the mantle, they sometimes encapsulate small pieces of the minerals that occur at great depth in the Earth. These are called mineral inclusions. The diamonds are then transported from Earth's deep mantle to the surface in uncommon magmas called kimberlites. Diamonds that contain these mineral inclusions are very rare, and offer a truly unique glimpse into what is an otherwise inaccessible portion of the Earth. Some very rare inclusions provide direct samples of lithologies present in the mantle transition zone (400 - 660 km) and the lower mantle (>660 km) - these are often called superdeep diamonds. The chemistry of the inclusions along with mineral phase relations yield important information about the kinds of lithologies they originated in, and constrain the conditions of diamond formation and the depth at which kimberlite magmas form. Thus, superdeep diamonds are very important for studying the types of materials that occur in the deep Earth, for elucidating deep mantle processes, and for understanding how carbon is cycled from the surface to the mantle and back to the surface again - the deep carbon cycle. For example, some diamonds contain materials that are very similar to those occurring near the earth's surface, such as minerals akin to oceanic crust or sediments, and these often have carbon isotopic compositions akin to organic carbon - although this is a controversial subject. From this, we can conclude that surface materials can be transported to great depth, helping to constrain models of mass transfer in Earth by mantle convection. Further, by dating when the diamonds formed, for example by dating of inclusions, we can effectively place time constraints in the geodynamic processes involved in diamond formation and uplift in the mantle. Inclusion-bearing diamonds suitable for study are very hard to come by. We are very fortunate to be in possession of several large suites (over 200 inclusion-bearing diamonds in all!) of diamonds from kimberlite pipes in the famous Juina region of Brazil, a region known for its superdeep diamonds. Our previous study on diamonds from the Juina region has yielded some fascinating results, and has led to a model of material recycling beneath Brazil that we have recently published in the journal Nature and in Contributions to Mineralogy and Petrology. We now wish to extend our investigations by studying new suites of diamonds from Juina to test our current model, and to make high-pressure temperature experiments that will allow us to determine at what depths the inclusions formed and equilibrated, and will provide information needed to constrain the rates at which diamonds were transported in the solid-state mantle, possibly in a mantle plume. Here, we propose a three-year project for a comprehensive mineralogical, geochemical, isotopic and experimental investigation of these unique diamonds and their mineral inclusions.

Identification info

Metadata Language: English (en)

Dataset Reference Date (): 2016-01

Identifier: http://data.bgs.ac.uk/id/dataHolding/13607078

University of Bristol

Professor Michael Walter

(

School of Earth Sciences

)

Wills Memorial Building, Queens Road, Clifton

Bristol

BS8 1RJ

Maintenance and update frequency: notApplicable

GEMET - INSPIRE themes

Geology

BGS Thesaurus of Geosciences

Carbon cycle
Subduction
Geology
Geochemistry
Stable isotopes
Petrology
Diamonds

Keywords

NERC_DDC

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Other constraints: The copyright of materials derived from the British Geological Survey's work is vested in the Natural Environment Research Council [NERC]. No part of this work may be reproduced or transmitted in any form or by any means, or stored in a retrieval system of any nature, without the prior permission of the copyright holder, via the BGS Intellectual Property Rights Manager. Use by customers of information provided by the BGS, is at the customer's own risk. In view of the disparate sources of information at BGS's disposal, including such material donated to BGS, that BGS accepts in good faith as being accurate, the Natural Environment Research Council (NERC) gives no warranty, expressed or implied, as to the quality or accuracy of the information supplied, or to the information's suitability for any use. NERC/BGS accepts no liability whatever in respect of loss, damage, injury or other occurence however caused.

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Topic category

Geoscientific information

End date: 2016-01

Additional information: Thomson et al CMP 2014 refers to NE/J500033/1 Thomson et al Nature 2016 refers to NE/J008583/1 and NE/J500033/1 Burnham et al 2015 refers to NE/J008583/1