102,660 research outputs found
Mesozoic Igneous event into the Baldissero mantle peridotite (Ivrea-Verbano Zone, NW Italy)?
No full textSRef-ID: 1607-7962/gra/EGU04-A-03966A suite of diorite dykes occurring into the Baldissero mantle peridotite (Southern Ivrea-Verbano Zone) shows an unusual geochemistry, characterised by high mg# values in bulk rock and mineral phases and a positive correlation of this parameter with incompatible element concentration. The dykes, in spite of their fine-grained texture, contain large amounts of cumulus phases. Their geochemical characteristics may be explained by melt flow, accompanied by crystallisation and reaction with the ambient peridotite, of a hydrous basaltic melt. The least evolved melts in this process are those that have the lowest incompatible element concentration and mg#. Reactionswith the ambient peridotite are very limited and consists of olivine dissolution and orthopyroxene crystallisation, so that an orthopyroxenite (orthopyroxene, spinel, minor olivine and clinopyroxene) rim, less than 0.5 cm thick, may appear at the contact. Very smooth geochemical gradients, which extend for a few cm inside the ambient peridotite, may be present. The age of dyke intrusion is currently constrained by: a) a two point mineral (plagioclase + clinopyroxene) best fit calculated from Sm-Nd isotopic data which yelds a slope corresponding to an age of 180 +/- 26 Ma, with a Ndi = 0.512804 and epsilon Ndi = 7.8 (Obermiller, 1994); b) Re-Os model ages (Re depletion model age) between 140 and 190 Ma calculated on whole rock samples of the ambient peridotite. Other isotopic determinations are in progress. More indications of Mesozoic ages, obtained in other parts of the Ivrea-Verbano Zone, are reported in Lu et al. (1997) and Peressini et al. (2004).The presence of remarkable episodes of Mesozoic magmatism in the Ivrea-Verbano Zone furnishes new constraints for the understanding the post-Variscan geodynamic evolution of the Europa-Adria lithosphere.ReferencesLu M., Hofmann A.W., Mazzucchelli M., Rivalenti G. (1997) Chem. Geol. 140, 223-235.Obermiller W.A. (1994) Unpub. PhD thesis, J. Gutenberg-Universität Mainz, 192 pp.Peressini G., Mazzucchelli M., Rivalenti G., Hofmann A.W. (2004). This Congress
Mesozoic Magmatism in the Ivrea-Verbano Zone and its geodynamic implications.
No full textabs. 10.1474, 01-0560.In the Southern Alps, Mesozoic magmatism is well documented in the Dolomite region and in the Lombard Pre-Alps. In the western portion of the Southern Alps, the Mesozoic magmatic activity has received much less attention.In the present study we report a review of geochronological evidences of the existence of Mesozoic magmatism in the portion of the Southern Alps west of the Lugano lake. The Mesozoic events are exclusively located: a) south of the Cremosina fault system; b) in the northeasternmost portion of the Ivrea-Verbano Zone.a) A suite of diorite-norite dykes occurring into the Baldissero mantle peridotite (Southern Ivrea-Verbano Zone) has been recently recognized. The age of dyke intrusion is currently constrained by: a) a two point mineral (plagioclase + clinopyroxene) best fit calculated from Sm-Nd isotopic data which yields a slope corresponding to an age of 18026 Ma, with a Ndi = 0.512804 and Ndi = 7.8 (Obermiller, 1984, PhD Thesis Un. Mainz, Germany); b) Re-Os model ages (Re depletion model age) between 140 and 190 Ma calculated on whole rock samples of the ambient peridotite (Mazzucchelli et al., 2004, EGU04 Geophys. Res. Abs., 6, 03966). Moreover a number of acid tuff layers from mm to several meters in thickness are present in the Mesozoic sedimentary cover of the Southern Alps from the Lugano to Biella area. They occur in the Crevacuore and Sostegno sedimentary succession, in the Villafortuna-Trecate oil field, and in the sedimentary cover of Monte San Giorgio (Ticino, Switzerland). In the Monte San Giorgio occurrence, high-resolution U-Pb zircon age gives 241±0.8 Ma (Mundil et al., 1996, Earth Planet. Sci. Letters, 141, 137-151). b) In the Basic Complex cropping out in the Finero and Val Grande area, most of the isotopic data invariably give Triassic or Early Jurassic ages. The Basic Complex in this area shows an antiformal structure, constituted by various cumulus rocks and gabbroic lithotypes (Internal Gabbro, Hornblende Peridotite and External Gabbro Units). At the core of the antiform, in tectonic contact with the rocks of the Complex, a mantle phlogopite-bearing peridotite occurs, whose metasomatic imprint was attributed to crustal components, deriving from a subducting slab. The age of metasomatism is Mesozoic [207 Ma - U/Pb on zircons from chromitites (Von Quadt et al., 1992, Ivrea-Verbano Zone Workshop, U.S. Geol. Survey Circular 1089, Abs., 20.); 226-177 Ma - Rb/Sr internal isochrons on amphibole and phlogopite pairs (Hartmann & Wedephol, 1993, Geochim. Cosmochim. Acta, 57, 1761-1782); 220 Ma - Ar/Ar on phlogopite (Hartmann & Wedephol, 1993)]. Magmatic, subeuhedral, pink crystals with oscillatory zoning in CathodoLuminescence (CL) from the External Gabbro Unit has been recently dated with SHRIMP (Peressini et al., 2005, this session). Magmatic growth of the zircons took place at 232±2 Ma and was overprinted at 214±5 Ma by a second event, dated by the rim-recrystallization ages. These ages are well in accordance with the literature data reported for the Basic Complex. In spite of the similar ages, the Basic Complex does not record any evidence of the metasomatic agent which affected the mantle peridotite. The Finero Basic Complex is in tectonic contact, marked by a high-temperature ENE shear-zone, with the Permian (Peressini et al., 2005, this session) relatively anhydrous mafic-ultramafic sequences occurring in Val Sesia and on the right side of the Val d'Ossola.Presently, the evidences of Mesozoic magmatism in the westernmost sector of the Southern Alps are confined by tectonic lineaments to the southernmost and northernmost portion, respectively. This put new constraints for the comprehension of the geodynamic reconstruction of the whole Southern Alps
The Italian journal of geosciences is increasing its appeal among geoscientists
No full textThis is an Editorial of the new Editorial Board of the Italian Journal of Geosciences, composed by Marco Balini (Milan), Hugo Bucher (Zürich), Simonetta Cirilli (Perugia), Laura Crispini (Genoa), Maurizio Mazzucchelli (Modena), and Giulio Ottonello (Genoa), which underlines the progress in the appeal of the journal among Geoscientists
Forme di vita / forme del corpo: studi di caso.
No full textLa nozione di “forma di vita”, in semiotica, appare al tempo stesso evidente e confusa. Vagliata e discussa da parecchi anni, viene utilizzata da molti studiosi in più occasioni e con diversi scopi. Funziona come un tipico termine ombrello. Parallelamente, molti nodi problematici relativi alla scienza della significazione, pur avendo palesi tangenze con tale nozione, sembrano volerne o poterne fare a meno, dichiarandola in contumacia fuori corso.The notion of "life form", in semiotics, appears at the same time evident and confused. Sieved and discussed for several years, it is used by many scholars on several occasions and for different purposes. It works like a typical umbrella term. At the same time, many problematic questions relating to the science of signification, despite having obvious links with this notion, seem to want or be able to do without it, declaring it in absentia out of course
T(T)over-bar deformations with N = (0,2) supersymmetry
No full textWe investigate the behavior of two-dimensional quantum field theories with N = (0,2) supersymmetry under a deformation induced by the "T (T) over bar" composite operator. We show that the deforming operator can be defined by a point-splitting regularization in such a way as to preserve N = (0, 2) supersymmetry. As an example of this construction, we work out the deformation of a free N = (0,2) theory, compare to that induced by the Noether stress-energy tensor and argue that, despite their apparent difference, they are equivalent on shell. Finally, we show that the N = (0,2) supersymmetric deformed action actually possesses N = (2,2) symmetry, half of which is nonlinearly realized
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