1,354,141 research outputs found
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
A sequence stratigraphic approach to a Middle Triassic shelf-slope complex of the Ligurian Alps (Ligurian Briançonnais, Monte Carmo-Rialto Unit, Italy)
No full textThe Mesozoic sedimentary cover belonging to the Monte Carmo-Rialto unit of the Ligurian Briançonnais domain is composed of Scythian clastics and Anisian to Carnian carbonate rocks over 300 m thick. This paper focuses on the stratigraphy of this carbonate complex, its environmental significance and its evolution in light of dynamic stratigraphy. Our facies analysis of limestones and dolomites of the Triassic complex allowed us to reconstruct an environmental model. Data support a distally steepened carbonate ramp of Anisian age evolving to a more diversified Ladinian platform with an oolitic sand-bar belt separating the lagoon from the slope. The Monte Carmo-Rialto slope facies are the only witnesses of deep sedimentation in the Triassic terrains of the Ligurian Briançonnais domain, otherwise represented by shallow-water carbonate deposits. On the basis of facies succession, we have identified nine medium-scale cycles (3rd order sequences) in the study area, comparable to those evidenced in the Briançonnais s.s. domain by the French authors. Small-scale cycles analysis evidenced mainly shallowing-upward trends in the examined sequences; although a few evidences of transgression-related deposits (deepening upward cycles) have been found at the base three sequences, they have been mostly obliterated by dolomitisation and masked by local tectonics. For this reason we can undoubtly distinguish only the part of each sequence belonging to HST, while the TST, though present, still remains a partition that cannot be precisely characterised. In the same way, LSTs are not present in the Monte Carmo-Rialto unit, due to the original relative landward position of the examined area. Sequence stratigraphy analysis indicates different long-term dynamics for the two evolutionary stages of the Triassic Ligurian platform: a general landward backstepping to moderate progradation during the Early Anisian and true progradation during the latest Anisian and Ladinian. In addition, a good fit with the sequences proposed by the SEPM chart has been found, indicating a correspondence for the 3rd order sequences of the Middle Triassic
Towards a chronostratigraphic definition of the paroxysmal phase of rifting in the Ligurian Alps (Case Morteo rhyodacites).
No full textSynrift sedimentation on the northern Tethys margin: an example from the Ligurian Alps (Upper Triassic to Lower Cretaceous, Prepiedmont domain, Italy)
No full textThe Prepiedmont domain succession of the Ligurian Alps is formed by a thick Mesozoic sedimentary cover tectonically detached from its substratum. The Arnasco-Castelbianco unit preserves the most complete record of the Ligurian Prepiedmont, although completely overturned and deformed due to Alpine tectonics. It is composed of carbonate and clastics rocks deposited during the Upper Triassic-to-Lower Cretaceous interval. This paper is focused on the stratigraphy of the Jurassic series and its relationships to the Tethyan rifting. Each term of the sedimentary record is seen as a witness of the several phases through which the rifting took place. An early-rifting phase (Late Hettangian-Early Sinemurian) brought to the formation of a normal fault system affecting the carbonate platform, and favoured the development of condensed sedimentation on pelagic highs. The rapid transition from open-platform carbonate to slope-basin cherty limestones, testifies the increased subsidence of the margin in the Late Sinemurian, during which moderate fault activity is recorded (intraformational breccia horizons). Until the Early Pliensbachian, a tectonic pause brought to the sedimentation of a succession of pelagic carbonates, occasionally interrupted by clastic flows. During the Late Pliensbachian (?)-Toarcian, it followed the rifting phase, evidenced by the large amount of clastics generated by the renewed fault activity. Clastics flowed down into the basin as fluxoturbidites at first, and then they passed to breccias during the maximum tectonic pulse. In the Late Toarcian-Aalenian?, the thermal uplift of the Briançonnais shoulder generated a basinal infill of fine clastics. The following thermal subsidence (Aalenian-Tithonian) favoured the restoration of quiet basinal conditions evidenced by the deposition of radiolarites
Late Triassic-Early Jurassic Paleokarst from the Ligurian Alps and its geological significance (Siderolitico Auct., Ligurian Briançonnais domain)
No full textNel domino Brianzonese ligure, le unità carbonatiche medio triassiche, note come Formazione di Costa Losera e Dolomie di San Pietro dei Monti, sono stratigraficamente seguite da una importante lacuna che segna il passaggio ai calcari neritici di Rio di Nava del Batoniano. Nell’ambito di una classica evoluzione di un margine continentale passivo, una stasi nella subsidenza, seguita da un sollevamento portò ad una erosione della piattaforma triassica in misura progressivamente maggiore procedendo verso le unità più interne, cioè verso la Tetide ligure. Tale erosione, che verosimilmente si verificò su di un substrato tettonicamente controllato, portò alla formazione di sequenze sedimentarie assai diversificate, talora mancanti di tutti i terreni triassici o persino dell’intero tegumento permiano. Nell’area studiata (ed in limitate aree esclusivamente appartenenti alla porzione più esterna dell’unità di Ormea), la lacuna mesozoica è ben più di una semplice superficie di erosione; i depositi ad essa associati (“Siderolitico” Auct.) sono costituiti sia da un corpo di peliti rosse interposto fra le sopracitate unità formazionali, sia da una breccia di origine carsica che penetra profondamente le sottostanti dolomie ladiniche. E’ stata condotta una ricerca stratigrafica di dettaglio su questi depositi, unitamente ad un’analisi delle microfacies e petrografico-composizionale, al fine di determinare le caratteristiche dei paleosuoli e del carsismo, di raccogliere maggiori informazioni sulla loro origine e sull’età. Inoltre, è stato discusso il significato regionale e l’importanza di questi depositi grazie ad un confronto a grande scala con il dominio brianzonese classico e con altre località dell’arco alpino occidentale che mostrano una unconformity del tutto simile. Alla luce dei dati raccolti, per l’evento carsico in esame viene proposta un’età compresa fra il Triassico Superiore e il Lias (sino al Baiociano Superiore ?)
The 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
Tectono-sedimentary evolution of the Tertiary Piedmont Basin (NW Italy) within the Oligo-Miocene central Mediterranean geodynamics
No full textWe analyze the tectono-sedimentary and thermochronometric constraints of the Tertiary Piedmont Basin (TPB) and its adjoining orogen, the Ligurian Alps, providing new insights on the basin evolution in response to a changing geodynamic setting. The geometry of the post-metamorphic faults of the Ligurian belt as well as the fault network that controlled the Oligo-Miocene TPB deposition has been characterized through a detailed structural analysis. Three main faulting stages have been distinguished and dated thanks to the relationships among faults and basin stratigraphy and thermochronometric data. The first stage (F1, Rupelian-Early Chattian) is related to the development of extensional NNW-directed faults, which controlled the exhumation of the orogen and the deposition of nearshore clastics. During the Late Chattian, the basin drowning is marked by mudstones and turbidites, which deposition was influenced by the second faulting stage (F2). This phase was mainly characterized by NE- to ENE-striking faults developed within a transtensional zone. Since the Miocene, the whole area was dominated by transpressive tectonics. The sedimentation was represented by a condensed succession followed by a very thick, turbiditic complex. At the regional scale, this succession of events reflects the major geodynamic reorganization in the central Mediterranean region during the Oligo-Miocene times, induced by the late-collisional processes of the Alps, by the eastward migration of the Apennines subduction and by the opening of extensional basins (i. e., the Liguro-Provençal Ocean)
Towards 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 textU-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
- …
