Research program
Relationships between anorogenic and orogenic magma sources and geodynamic implications for the Europe-Africa system.
University Co-ordinator
Università degli Studi di NAPOLI "Federico II" -
SCIENZE DELLA TERRA - NAPOLI(NA)
Research Unit Leader
Vincenzo MORRA
Description
Starting from 1993, members of this project work on the genesis and evolution of the post-Precambrian volcanic rocks of Madagascar. Some of the results of this research have been published on major journals (see reference list) and presented in major congresses, and other papers are close to being submitted. We are intended to continue this systematic study in order to achieve full understanding of the alkaline magmatism of Madagascar, in particular the volcanism of the central-northern part of the island.The Madagascan volcanism took place above a continental lithosphere that did not suffer any major episode of tectonometamorphic reworking at least since late Precambrian. Therefore, the subsequent history was simple, and not influenced by the repated orogenic/anorogenic cycles observed in the Mediterranean area, particularly in Sardinia and peninsular Italy.The available geochronological data indicate that the late Cenozoic volcanism postdates the major Cretaceous volcanic event by ca. 60-70 Ma. The source areas of the two volcanic events are probably overlapping, mainly in northern Madagascar. The areal distribution of the plutonic and volcanic complexes of central/northern Madagascar follows in most cases the pattern of rift zones in the Precambrian crust, trending north-south and northwest/southeast. The main goal of this project is the best definition of the petrological and geochemical characteristics of the outcropping igneous rocks and the mantle sources involved in the late Cenozoic event, in order to understand genesis and evolutionary processes ruling in the province. This will be linked to the tectonic events and features of northern Madagascar. The aim of this project cannot be disjointed by a better knowledge of the ages of the different igneous centers and the variation of these ages with the geographic position and the tectonic events.All these informations will allow a general overview and regional correlations of the volcanism with regional geology of the area. Another interesting topic will be the study of the relationships between the mantle source of the Cretaceous and late Cenozoic volcanic rocks, and their evolution with time. There may be the possibility that the Cretaceous magmatism influenced the mantle source of the late Cenozoic volcanics. A major impulse to this direction will be also given by the study of the mantle ultramafic nodules found in Madagascan mafic alkaline rocks, that will give us direct information about the mantle lithosphere beneath northern Madagascar. This study will be carried out in a joint venture with the Ferrara research unit.Major emphasis will be given to the chemical and isotopic relationships between the mantle sources of the Madagascan alkaline volcanics and the volcanics at similar or identical serial affinity found in the Mediterranean area (Sardinia, peninsular Italy). We will try to distinguish andy hotspot influence in both volcanic environments.We need of at least one new field trip in order to sample rock units completely unknown to the recent literature, due to excessive difficulties of sampling in recent times. We need of these samples as they are basic to achieve full understanding of the chemical variations in the province. We strongly need of the assistance of researchers of Malagasy Universities, with their expertise in the field and logistics.On the basis of the strong experience of the members of this project, we want to: 1) complete sampling of the igneous rocks of the Ampasindava peninsula (igneous intrusions with their associated dyke swarm), and very carefully selected sardinian volcanic rocks; 2) complete the sampling of the enormous Massif d'Ambre volcanic complex, of neighbouring areas, and of the Itasy volcanic field. For these areas, very little is known about age, magmatological characteristics, petrographic types and mantle sources involved.The project will be organized as follows:I yeara) a field trip for sampling (4 persons/ one month, abou 100-150 samples) in the areas of Massif d'Ambre, Ampasindava peninsula and Itasy. We would like to remind that we will need of the collaboration of researchers of Malagasy universities, in particular those of the Antsiranana University, who will organize the field trip in detail.b) Petrographic characterization of the samples through study in thin section.c) Mineral chemical analyses (about 200-400 analyses), obtained by utilizing electron microprobes located at Naples, Rome and Firenze Universities;d) Whole-rock chemical analyses utilizing an XRay Fluorescence spectrometer, Atomic Absorption Spectrophotometer (Naples) , and Inductively Coupled Plasma Mass Spectrometer (Ferrara and eventually Nancy, France).II yeare) Pb, Sr and Nd isotopic analyses of very carefully selected samples after obtaining all the whole rock chemical analyses. The Pb isotopic determinations will be carried out at the SOEST (Hawaii University) laboratories, with the collaboration of Dr. John Mahoney and the Sr-Nd isotopic determinations will be carried out at Firenze University.f) On the freshmost samples of every igneous complex we will carry out Ar-Ar age determinations in the laboratory of Dr. Robert Duncan at Oregon State University. Dr. Duncan is one of the most important specilaista of the volcanism in the Indian Ocean area, and is expert also on the Madagascan volcanism.g) Elaboration of the data and production of scientific papers.
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