Lithos 85 (2005) vii – viii www.elsevier.com/locate/lithos
Introduction
Carbonatites plus: A special issue arising from the dEuroCarbT ESF network
This issue follows from the final field workshop of the EuroCarb European Science Foundation network on mantle carbon and carbon cycling, held in Lanzarote and Fuerteventura, Spain in September 2003. Some of the papers were originally presented there as abstracts, short talks or discussion topics, which can be accessed on www.nhm.ac.uk/hosted_ sites/eurocarb/workshops/canary.html. Highlights not written up here included a report of a new discovery of carbonatite in central Spain, at Calatrava, and a lively debate on the role of plumes in forming carbonatites. The original aims of the Eurocarb network included: understanding the Earth’s solid carbon cycle through the mantle and relating it to the carbon cycle at the surface, encouraging those working on carbonatites to think more globally and consider carbonatites in the context of other mantle-derived carbon, and bringing together scientists working on different aspects of carbon. Each of four field workshops and two conference sessions had a particular theme related to the overall aims and also acted as a forum for research in progress. The EuroCarb workshops certainly encouraged much discussion and debate, both formal and informal. They provided an invaluable forum to bring together scientists from different backgrounds to discuss carbon related topics and gave young researchers the opportunity to take part in high level discussions with the key senior researchers in the field; literally in the field in many cases, at the most relevant carbonatite-alkaline rock outcrops in Europe. 0024-4937/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2005.05.001
The discussion topics were wide ranging but the main interest of most participants remained carbonatite magmatism as reflected in this set of papers. Other forms of mantle-derived carbon are also considered here: carbon-bearing species, and especially, hydrocarbons in the Khibiny complex, Kola Peninsula are reviewed by Nivin et al. and carbonates in Italian lamprophyre dykes are described and discussed by Vichi et al. The perennial problems of carbonate magmatism still remain: whether carbonatites and associated silicate rocks have separated by fractionation and/or immiscibility in the crust or have travelled as discrete carbonate and silicate magmas from the mantle; the relationship between carbonatites and other mantle rocks such as kimberlites, alno¨ites and lamprophyres; the prevalence of calcite carbonatite, even in direct mantle-derived material rather than the experimentally predicted dolomite carbonatite; the understanding of the relevance of the Oldoinyo Lengai natrocarbonatite; the role of alkalis in carbonate melts, and the evolution of magmas and fluids associated with carbonatites. A recent advance that we would highlight is the recognition of more localities with extrusive carbonatite, including the extrusive carbonatites in Italy, subject of the third dEuroCarbT workshop. A review of extrusive carbonatites is provided here (Woolley and Church) and two further contributions dealing with specific localities emphasize the importance of melilitite associated with extrusive carbonatite magmatism (Bailey et al.), and discuss element partition between
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Introduction
pristine silicate glass and carbonatite at Oricola, Italy and the implications for immiscibility processes (Stoppa et al.). A particular pattern that is emerging is the frequency with which carbonatite and silicate magmas are co-erupted. At the Italian workshop, direct mantle derivation of carbonatite won a dstraw pollT but everyone agreed that more then one mechanism for generating carbonatite magma is possible, and none argued with immiscible separation of carbonate and silicate in some cases. Several other papers here tackle the spatial and temporal relationship between carbonatite and associated silicate rocks. The availability of spatially resolved trace element analysis is promising for unravelling intricate magma chamber processes and potential new approaches to magma mixing and mingling problems. The paper by Brassinnes et al. uses a trace element approach to study the relationship between silicates and carbonatites at Vuoriyarvi, Russia and concludes they may have formed from a single magma batch. Melt and fluid inclusion studies are attracting much interest, with a contribution here describing combined silicate–carbonate melt inclusions in apatite phenocrysts in a phonolitic nephelinitic bomb from the Vulture volcano, Italy (Solovova et al.). Calcite–dolomite phase relations are reviewed by Gittins et al. who argue that although there is mineralogical bimodality in carbonatites — most are either calcite or dolomite carbonatites with few intermediates — there is such no compositional division because much of the Mg is hosted by Mg– Fe silicate minerals in the intermediate compositions. Moving to deeper mantle processes, the review of Kola alkaline magmatism by Downes et al. concludes that production of all magmas was triggered by a single event that caused melting of carbonated garnet peridotite mantle and produced a spectrum of ultramafic, alkaline and carbonatite magmas, with pockets of phlogopite metasomatised lithosphere responsible for producing temporally associated kimberlite. The single event is postulated to be a plume, emphasizing the role of carbonatite magmatism in understanding mantle processes. Other fundamental questions about the deep Earth carbon cycle also remain to be answered and are not tackled in this volume. It is established that some carbonates are carried down deep into the mantle with
subducting slabs, and that carbonate species will remain stable in the mantle to great depths. It is also well accepted that at least some of the carbon returns to the surface, in the form of eclogitic diamonds, for example and therefore by implication some carbonatites must also consist of more or less recycled material. The problems, then are to define how much carbon is primordial and how much is recycled, and the paths and processes by which the carbon moves through the deep Earth and returns to the surface. Much still remains to be done. For more information on EuroCarb — including workshop abstracts, field guides and reports, see www.nhm.ac.uk/hosted_sites/eurocarb. Acknowledgements The editors would like to thank all those who generously gave their time to review manuscripts, including Yu. Amelin, F. Andrade, D.S. Barker, F. Castorina, R. Clocchiatti, A.F. Cooper, J.B. Dawson, M. Frezzotti C. Harris, A.P. Jones, J. Keller, B.A. Kjarsgaard, S. Klemme, L.N. Kogarko, G.R. Lumpkin, G. Markl, U. Masi, R.H. Mitchell, K.R. Moore, A. Mu¨ller, P.H. Nixon, M.P. Smith, A.R. Woolley, P.J. Wyllie, A.N. Zaitsev. We are very grateful to Daniel Demaiffe for the editorial handling of the paper by Stoppa et al. and to Stephen Foley, Lithos principal editor and Patricia Masar at Lithos for their help in preparation of this volume. We would also like to express our thanks to the EuroCarb co-ordinating committee members, and especially chairman, A.P. Jones, the other workshop convenors, including M. Munoz. C. de Ignacio and J. Sagredo in the Canary Islands, Spain, and ESF staff, Svenje Mehlert, Catherine Lobstein, and Louise Kennedy. Frances Wall* Gianluigi Rosatelli Francesco Stoppa The Natural History Museum, Department of Mineralogy, Cromwell Road, London SW7 5BD, United Kingdom E-mail address:
[email protected]. *Corresponding author. Tel.: +44 207 942 5623; fax: +44 207 942 5537.
