Research program
Relationships between anorogenic and orogenic magma sources and geodynamic implications for the Europe-Africa system.
University Co-ordinator
Università degli Studi di FERRARA -
SCIENZE DELLA TERRA - FERRARA(FE)
Research Unit Leader
Franca SIENA
Description
The proposed research project will be addressed to the reconstruction of compositional variations which affected mantle sources in the central-western Mediterranean area, studying the petrological-geochemical features of basic magmas and associated mantle xenoliths. The Mediterranean area represents in this regard an ideal situation for a comparative study of magma sources of the European and African lithospheric domains which have been juxtaposed during the Cenozoic collisional processes. Research will be focussed on both basic magmas and associated mantle xenoliths from anorogenic volcanic districts located in the central-western Mediterranean and neighbouring areas. This constitutes an innovative and complementary approach since xenoliths, although representing a shallower mantle portion with respect to magma sources, provide fundamental information on the geochemical and isotopic characteristics of the metasomatic agents which affected the lithospheric section as a whole. Moreover, in several localities of the Mediterranean area alkaline anorogenic lavas including xenoliths postdate orogenic magmatic events as for instance in Sardinia, Betic Cordillera (Spain) and Moroccan Mid-Atlas. In these localities it will be interesting to investigate any possible inherited geochemical features of the previous subduction processes. The investigated areas from the European lithosphere will be:- Neogene-Quaternary anorogenic basic volcanism, and associated mantle xenoliths, from Olot, Calatrava e di Tallante (Betic Cordillera) in Spain, and the analogous intra-plate associations from Sardinia; The areas of the Adriatic-African lithosphere under study will be:- anorogenic basic volcanism, and associated mantle xenoliths, from Veneto Volcanic Province (Paleogene), Mts. Iblei (Sicily)(Neogene-Quaternary) and the analogous intra-plate associations from Gharian (Libya) and Mid-Atlas (Morocco).The main scientific objectives may be summarized as follows:- Petrological-geochemical characterization (including thermo-barometric estimates) of mantle sources of basic magmas in the investigated volcanic districts. This will allow a definition of the generation depth of alkaline and subalkaline magmas and, consequently, the vertical distribution of the geochemical components in the concerned lithospheric segment. Preliminary data suggest that EM components, related to subalkaline magmas, seem to be mostly confined in the upper, rigid portion of the lithospheric mantle (Mechanical Boundary Layer), whereas the HIMU-like components, which characterize the most alkaline magmas, prevail in the underlying Thermal Boundary Layer. - Evaluation of the metasomatic effects in mantle xenoliths and identification of agents and mechanisms of both anorogenic and subduction-related metasomatism. The occurrence of amphibole, phlogopite and glass is an important indicator both for metasomatic processes and genetic conditions of basic magmas with variable degree of alkalinity. Moreover the incompatible element distribution, together with the isotopic data, provide fundamental markers for the geochemical components which characterized the metasomatic processes in the concerned mantle section. On this topic systematic studies on the relationships between geochemical components and metasomatic features, both in oceanic (Canary Islands, Gran Comores e Cape Verde) and continental settings (Austria, Ungheria, Romania Antartide, Australia), have been carried out by the U.R. In those study cases where the orogenic magmatic events precede the anorogenic magmatism (Sardinia, Tallante, Morocco), a particular attention will be devoted to recognize the preservation and persistence of subduction related components in mantle xenoliths. In this regard the comparison with an analogous occurrence in the eastern Siberia (currently studied by the UR) where mantle xenoliths are entrained in nephelinitic lavas cutting widespread calc-alkaline terrains will be of particular interest. - Reconstruction of the compositional evolution of the African and European lithospheric mantle and evaluation of a regional geodynamic model accounting for the petrological and geochemical features of magmas and their sources, particularly with regard to the existence and nature of Mediterranean "plume/s".The methodological approach will comprise: 1 – completion of field work and sampling; 2 - petrographic, bulk rock major and trace element analyses (Earth Science Department, University of Ferrara) and mineral chemistry (electron microprobe, CNR Istituto di Geoscienze e Georisorse , Padua; Centro di Microscopia Elettronica, Ferrara University); 3 - ultra-trace analyses by ICP-MS on selected samples and mineral separates (Earth Science Department, University of Ferrara); 4 - in-situ trace element analyses of minerals by ion microprobe and LAM-ICP-MS (CNR Istituto di Geoscienze e Georisorse, Pavia) and the new LAM-ICP-MS requested in this project (Earth Science Department, University of Ferrara);5 – isotope analyses (Sr, Nd, Pb, Hf) of whole rock and/or mineral separates (Earth Sciences Department-CNR, Florence University; School of Earth Sciences, Leeds University; ; Dept. of Geology, Royal Holloway, University of London) on carefully selected samples;6 – data processing and modelling.Research will be subdivided in two phases: - in the first year, completion of field work and sampling is expected, together with basic chemical analyses on bulk rocks and mineral phases of ca 200 samples (xenoliths and their host lavas);- the second year foresees ultra-trace analyses on bulk rocks and mineral phases, as well as isotopes of about 80 highly representative samples.The scientific results will be published in International Journals and presented at national and international meetings.
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