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TUFFACEOUS DEPOSITS IN THE SEDIMENTARY COVER OF THE STRONA-CENERI ZONE AND IN THE VILLAFORTUNA-TRECATE OIL SYSTEM: PETROLOGICAL, GEOCHEMICAL AND GEOCHRONOLOGICAL CHARACTERIZATION
No full textIn the western sector of the Southern Alps, tuffaceous levels are occasionally found in Triassic sedimentary sequences and the age of the related magmatism is still matter of debate. The few available geochronological data on these tuffites (M. San Giorgio area, Lugano, CH) yield Triassic ages (245±1 Ma; U-Pb zircon [1]), which are slightly older than the stratigraphic position. The precise definition of the tuffite age is, however, important for the Triassic evolution of the western Alps. In particular, if the magmatism is synchronous with their stratigraphic position, tuffites might be linked to the Triassic magmatism documented by the Finero area (NE Ivrea-Verbano Zone [2]). However, it cannot be presently excluded that they are the product of erosion and re-deposition of the Permian acid volcanics located at the base of the Mesozoic sedimentary cover [3].In this work, we have considered the tuffaceous deposits occurring within a late Anisian-Ladinian succession in the Mesozoic sedimentary cover of the Strona-Ceneri Zone in the Borgosesia area [3,4] and the tuffites at the same stratigraphic position found in some wells of the Villafortuna-Trecate oil system field (western Po Plain, Piedmont region, NW Italy) [5]. These tuffaceous deposits are constituted by a variable mixture of magmatic and sedimentary components. Available chamical data on the magmatic component suggests a calc-alkaline affinity. Zircons have been separated with conventional methods from four samples, mounted in epoxy resin and characterised under cathodoluminescence (CL). Based on colour, morphology and internal structure, zircons have been divided in two populations. One group is constituted by light-pink coloured zircons with prismatic habits and tight osciscillatory zoning suggesting growth under magmatic conditions. Zircons from the second group are colourless, rounded in shape and with only relics of magmatic zoning. They most likely suffered metamorphic recrystallization.Ongoing ELA-ICP-MS characterizations of both trace elements composition and U-Pb age of these zircons is expected to provide valuable constraints on the geodynamic evolution of the Southern Alps Domain in Permo-Triassic times.References. [1] Mundil, R., Brack, P., Meier, M., Rieber, H., Oberli, F. (1996): Earth and Planetary Science Letters, 141, 137-151; [2] Peressini, G., Mazzucchelli, M., Rivalenti, G., Hofmann, A.W. (2004): Geophysical Research Abstracts, 6, 05072, SRef-ID: 1607-7962/gra/EGU04-A-05072; [3] Carraro, F., Fiora, L. (1974): Riv. It. Paleont. Strat., 80, 167-191; [4] Fantoni, R., Decarlis, A., Fantoni, E. (2004): Atti Tic. Sc. Terra, 44, 97-110; [5] Fantoni, R., Bello, M., Ronchi, P., Scotti, P. (2002): Extended Abstracts Book EAGE Conference Florence
Towards a chronostratigraphic definition of the paroxysmal phase of rifting in the Ligurian Alps (Case Morteo rhyodacites).
No full textTowards a chronostratigraphic definition of the paroxysmal phase of rifting in the Ligurian Alps (Case Morteo Rhyodacites).
No full textReply to Discussion on ‘Breakup continents at magma poor rifted margins: a seismic v. outcrop perspective’. Journal of the Geological Society, London, 175, 875-882
No full textThe Ivrea-Verbano tectonic evolution: The role of the crust-mantle interactions in rifting localization
No full textThis work aims to review and discuss with new interpretations the tectonic evolution of the Ivrea Verbano Zone (IVZ), to highlight how inheritance from previous orogenic cycles may have driven the Mesozoic Alpine Tethys rifting processes. After the Mesozoic rifting, the IVZ was located at the base of the continental crust of the Adriatic distal margin, before being exhumed at the surface during Alpine orogenesis. Different compositions of the IVZ peridotite massifs, mostly lherzolitic and harzburgitic, reflect upper mantle processes developed since late Proterozoic-early Paleozoic, when a sub-Gondwanian lherzolitic mantle slice (Balmuccia-type) coexisted with a depleted harzburgitic raft (Finero-type). After the buildup of the Variscan chain, in the Carboniferous, the overthickened crust might start to delaminate at its base. Whereas the Balmuccia body behaved as a passive witness of the Paleozoic mantle differentiation, the Finero mantle section underwent pervasive K-metasomatism in late Carboniferous to early Permian, triggered by melting of delaminated lower crustal slabs. Asthenosphere mantle decompression in the early Permian generated basic magmas emplaced in the lower crust. They led to a significant lateral variation of the crustal rheology, which probably drove the subsequent Triassic to Jurassic extensional tectonic pulses to delocalize along weaker zones. The Finero peridotite was characterized by a relatively low density, which was enhanced by the K-metasomatism, thereby promoting its exhumation near one of these weak zones, during a late Triassic-early Jurassic extensional pulse. Thus, the Alpine rift and, in general, magma-poor rift localization can be considered as the final product of deep processes predating the onset of rifting extensional tectonics s.s., which may have promoted crustal excision and mantle exhumation at specific locations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
U-Pb zircon data for tuffaceous layers from the sedimentary cover of the Strona-Ceneri Zone and Po Plain: constraints on the Triassic geodynamic evolution of the Southern Alps.
No full textIn the western sector of the Southern Alps, tuffaceous levels areoccasionally found in the Triassic sedimentary sequences. The direct agecharacterisation of these layers is very limited: in fact, a U-Pb zircon ageof 245±1 Ma is available only for the tuffites from Mt. San Giorgio area(Lugano, CH: [1]), which results slightly older than that expectedaccording to the stratigraphic position. Besides, no geochemicalinformation is presently available for these layers and the geodynamicsetting of the related volcanism is still matter of debate.Thus, with the aim to place further constraints of the geodynamicevolution of the Southern Alps in Mesozoic times and increase theaccuracy of the age record of the sedimentary sequence, we haveperformed a mineralogical, geochemical and geochronological study ontuffaceous deposits outcropping within the Anisian-Ladinian succession ofthe sedimentary cover of the Strona-Ceneri Zone in the Borgosesia area[2,3] and recovered at the same stratigraphic position in wells of theVillafortuna-Trecate oil field (western Po Plain, Piedmont region, NW Italy:[4]). CO2 concentration was determined by Dietrich-Früling calcimeter.XRD data indicate that such tuffaceous deposits are constituted by avariable mixture of magmatic and sedimentary components. Major andtrace element compostions, assessed by means of XRF analysis, suggest acalc-alkaline affinity for the magmatic component. To provide accurategeochronological constraints, zircons have been separated withconventional methods from four tuffaceaous outcrops, namely "Lembo diSostegno", "Lembo di Crevacuore" and "Lembo di Monte Fenera"outcrops, as well as from a buried tuffaceous sample of theVillafortuna-Trecate oil field. Zircons were mounted in epoxy resin andcharacterised under cathodoluminescence (CL). Based on colour,morphology and internal structure, they have been divided in twopopulations. One group is constituted by light-pink coloured zircons withprismatic habits and tight oscillatory zoning suggesting growth undermagmatic conditions. The zircons from the second group are colourless,rounded in shape and with only relics of magmatic zoning, consistent withmetamorphic recrystallization. U-Pb ELA-ICP-MS data point to ages of237±8 Ma and 229±9 Ma for the magmatic growth of the zircons from thetuffites of "Lembo di Crevacuore" and "Lembo di Sostegno", respectively,which are in agreement with their stratigraphic position. The volcanicactivity producing these layers might be linked to the intrusive Triassicmagmatism documented in the Finero Complex (NE Ivrea-Verbano Zone[5,6]). Conversely, the zircons from the "Lembo di Monte Fenera" andVillafortuna-Trecate oil field produce a very large range ofcrystallisation-recrystallisation ages, which span from Proterozoic toPaleozoic to the Permian-Triassic boundary, thus indicating a dominantcontribution of the crystalline basement to the zircon population
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Vertebrate footprints in the case valmarenca pelite (Lower-Middle Triassic) (Briançonnais domain- Ligurian alps).
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