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Le magmatisme acide Plio-Pleistocène de la Marge
Tyrrhénienne (Italie Centrale) : Géochronologie,
Pétrogénèse et Implications Géodynamiques.

Abstract : The Italian Neogene magmatism is characterized by a large petrological and
geochemical variety, covering almost all the magmatic rocks pattern known worldwide. Most
of the geodynamic models are based upon the recent widespread Quaternary volcanism,
comprising mafic to intermediate lavas. In contrast, the felsic magmatism which corresponds
to the first manifestations of the Tyrrhenian margin is much less voluminous, outcrops
without or with few associated mafic-intermediate rocks, and is less known.
The goals of this thesis are: (1) to precise the age of these manifestations, (2) to better
understand the origin of this magmatism (determinating the sources) and, (3) to insert these
constraints in the general framework of the Italian magmatism and the opening of the
Tyrrhenian Sea. A combined geochronological and petro-geochemical study has thus been
carried out on felsic Tuscan edifices (San Vincenzo, Roccastrada and Amiata) and the Ponza
and Palmarola islands (Pontine Archipelago, Campanian area, Gaeta gulf).
Twenty-five K-Ar datings (Cassignol-Gillot technique) have been performed on the
Ponza and Palmarola islands rocks. The beginning of the volcanic activity of Palmarola has
been dated for the first time at 1.64 ± 0.02 Ma; the obtained Quaternary (Pleistocene) age is in
contradiction with the Pliocene age which was proposed on stratigraphical criteria.
Concerning Ponza, a new rhyolites episode had been recovered at 3.1-2.9 Ma. Between
Pliocene and Pleistocene, the volcanism changed from orogenic calc-alkaline in Ponza to a
transitional magmatism in Palmarola whose chemical signature approaches those of intraplate
alkaline magmatism. This occurred in only 1.3 Ma. A petrogenetic model is proposed for the
magma of Ponza and Palmarola from new mineralogical and isotopic data. It implies
fractional crystallization coupled with more or less strong crustal contamination, from
different mantle liquids.
Accurate and reproducible ages have been obtained for the Tuscan Province edifices
(San Vincenzo, Roccastrada and Amiata). New Sr, Nd and Pb isotopic data confirmed the
hybrid character of Monte Amiata volcano in terms of sources, between the Tuscan and the
Roman provinces. Based on our new ages, we propose a new possible scenario for its
volcanological evolution.
The principal component analysis of the lead isotopic data set of all the studied felsic
manifestations has permitted to identify the two main source components at the origin of these
rocks. The dominant component is mantellic and corresponds to a mixing between DM and
HIMU end-members, while the second is an enriched crustal-derived end-member. The
southernmost felsic rocks (Pontine) show the strongest influence of the DM+HIMU
component. Thus, even with so differentiated rocks and at so small scale (central Italy), we
find the general trend of the whole Italian peninsula and Sicily derived from the isotopic study
of mafic rocks, which shows a general DM+HIMU mixing plus a crustal-derived endmember.
The influence of the DM+HIMU end-member increases from North to South of
Italy.
When extended at the scale of the whole Tyrrhenian margin, the PCA allows identifying two
source domains delimitated by a major lithospheric discontinuity, the 41 Parallel Line, and in
which the evolution of the components is different. The northern domain characteristics could
be controlled by a lower lithosphere delamination, whereas in the southern domain they might
be due to the fast slab roll-back. In both domains, the invoked processes would trigger the
upwelling of asthenospheric material.
Complete list of metadatas

https://tel.archives-ouvertes.fr/tel-00138852
Contributor : Anita Cadoux <>
Submitted on : Wednesday, March 28, 2007 - 7:59:56 AM
Last modification on : Wednesday, October 14, 2020 - 4:00:38 AM
Long-term archiving on: : Friday, September 21, 2012 - 1:30:10 PM

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Citation

Anita Cadoux. Le magmatisme acide Plio-Pleistocène de la Marge
Tyrrhénienne (Italie Centrale) : Géochronologie,
Pétrogénèse et Implications Géodynamiques.. Géochimie. Université Paris Sud - Paris XI, 2005. Français. ⟨tel-00138852⟩

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