Cenozoic Italian magmatism – Isotope constraints for possible plume-related activity |
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| Institution: | 1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China;3. Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China;1. Dipartimento di Scienze della Terra, dell''Ambiente e delle Risorse, University of Naples Federico II, Largo S. Marcellino 10, 80138 Naples, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Napoli Osservatorio Vesuviano, Via Diocleziano 328, 80124 Naples, Italy;3. Dipartimento di Fisica e Geologia, University of Perugia, Via A. Pascoli, 06123 Perugia, Italy;4. Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Palermo, Via U. La Malfa 153, 90146 Palermo, Italy;5. Dipartimento di Scienze dell''Ambiente e del Territorio e di Scienze della Terra, University of Milano-Bicocca, Piazza della Scienza 4, 20126 Milan, Italy;1. Dipartimento di Scienze della Terra, dell''Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Largo S. Marcellino 10, 80134 Napoli, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia, sezione di Napoli Osservatorio Vesuviano, Via Diocleziano 328, 80124 Napoli, Italy;3. Departamento de Geoquímica, Petrologia i Prospecció Geològica, Facultat de Geologia, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain;4. Dipartimento di Ingegneria Civile, Design, Edilizia e Ambiente, Seconda Università degli Studi di Napoli, Via Roma 29, 81031 Aversa, CE, Italy;1. Department of Natural Resources Management and Agricultural Engineering, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece;2. Department, of Geology & Geoenvironment, Section of Economic Geology & Geochemistry, National University of Athens, Panepistimiopolis, 15784 Athens, Greece;3. California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA 91125, USA |
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| Abstract: | Assessment of the isotope systematics and the magmatotectonic history of mainly Cenozoic igneous rocks from Italy shows them to be inconsistent with subduction-related magmatism. We attempt to fit these data into an alternative model involving long-term, recurrent plume activity that extended over a period of about 100 Ma, that involved mantle expansion and subsequent mixing between isotopically-distinct, mantle components. Sr, Nd and Pb isotopic compositions of Cenozoic Italian igneous rocks, rather than being random, reflect binary mixing involving a common end-member similar to FOZO. Most isotopic data from along the entire length of Italy, from the Aeolian Islands to the Alpine belt, define a Main Italian Radiogenic Trend (MIRT), characterized by mixing between FOZO and a highly radiogenic Sr, mantle end-member (ITEM, ITalian Enriched Mantle). Data from the Adria foreland, Sicily and the south-western Tyrrhenian Sea and Sardinia deviate from MIRT suggesting mixing with other components, perhaps HIMU and EM1. Both the absence of pure DMM, and the presence of isotopic end-members not recognized in present-day consuming-plate margins are incompatible with subduction-related models. Two models are discussed, one in which ITEM is attributed to melting of pre-Alpine sediments/upper continental crust entrained in a FOZO-like mantle and the other to widespread metasomatic activity involving deep-seated plume activity. In the latter, the widespread nature of FOZO is attributed to a late Triassic–early Jurassic plume that preceded the opening of the Alpine Tethys and led to modification of the lithosphere and/or asthenosphere. Late Jurassic–early Cretaceous plume activity produced mantle expansion and the opening of the Alpine Tethys. A new phase of plume activity started during the Oligocene with the opening of the western and central Mediterranean Basins. Stretching and large-scale extension of the Mediterranean lithosphere was caused by the progressive eastward growth and volume increase of a plume head trapped within the Transition Zone. Plume-generated fluids/melts enriched in K–Ca–CO2–H2O, produced mantle sources capable of generating widespread alkaline, mafic, and carbonatitic magmatism. Lithospheric unloading controlled the Tyrrhenian and peri-Tyrrhenian magmatic activity. |
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