Reconsidering the Variscan basement of southern Tuscany (inner Northern Apennines)

2021 ◽  
Author(s):  
Enrico Capezzuoli ◽  
Amalia Spina ◽  
Andrea Brogi ◽  
Domenico Liotta ◽  
Gabriella Bagnoli ◽  
...  
Keyword(s):  
Continental Crust ◽  
Early Carboniferous ◽  
Northern Apennines ◽  
Time Interval ◽  
Structural Studies ◽  
Structural Setting ◽  
Elba Island ◽  
Orogenic Cycle ◽  
Existing Data ◽  
Variscan Basement

<p>The Pre-Mesozoic units exposed in the inner Northern Apennines mostly consist of middle-late Carboniferous-Permian successions unconformably deposited on a continental crust consolidated at the end of the Variscan (i.e. Hercynian) orogenic cycle (Silurian-Carboniferous). In the inner Northern Apennines, exposures of this continental crust, Cambrian?-early Carboniferous in age, have been described in the Northern Tuscany, Elba Island (Tuscan Archipelago) and, partly, in scattered and isolated outcrops of southern Tuscany. In this contribution, we reappraise the most significative succession (i.e. Risanguigno Formation) exposed in southern Tuscany and considered by most authors as part of the Variscan Basement. New stratigraphic and structural studies, coupled with palynological analyses, allow us to refine the age of the Risanguigno Fm and its geological setting and evolution. Based on the microfloristic content, the structural setting and the fieldwork study, we attribute this formation to late Tournaisian-Visean (middle Mississipian) time interval and conclude it is not showing evidence of a pre-Alpine deformation. These results, together with the already existing data, allow us to presume that no exposures of rocks involved in the Variscan orogenesis occur in southern Tuscany.</p>

scholarly journals Reconsidering the Variscan Basement of Southern Tuscany (Inner Northern Apennines)

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 84
Author(s):  
Enrico Capezzuoli ◽  
Amalia Spina ◽  
Andrea Brogi ◽  
Domenico Liotta ◽  
Gabriella Bagnoli ◽  
...  
Keyword(s):  
Continental Crust ◽  
Organic Matter Content ◽  
Matter Content ◽  
Northern Apennines ◽  
Structural Studies ◽  
Middle Mississippian ◽  
Elba Island ◽  
Orogenic Cycle ◽  
Existing Data ◽  
Variscan Basement

The Pre-Mesozoic units exposed in the inner Northern Apennines mostly consist of Pennsylvanian-Permian successions unconformably deposited on a continental crust consolidated at the end of the Variscan orogenic cycle (Silurian-Carboniferous). In the inner Northern Apennines, exposures of this continental crust, Cambrian?-Devonian in age, have been described in Northern Tuscany, Elba Island (Tuscan Archipelago) and, partly, in scattered and isolated outcrops of southern Tuscany. This paper reappraises the most significant succession (i.e., Risanguigno Formation) exposed in southern Tuscany and considered by most authors as part of the Variscan Basement. New stratigraphic and structural studies, coupled with analyses of the organic matter content, allow us to refine the age of the Risanguigno Fm and its geological setting and evolution. Based on the low diversification of palynoflora, the content of sporomorphs, the structural setting and the new field study, this formation is dated as late Tournaisian to Visean (Middle Mississippian) and is not affected by pre-Alpine deformation. This conclusion, together with the already existing data, clearly indicate that no exposures of rocks involved in the Variscan orogenesis occur in southern Tuscany.

scholarly journals Applicability of the dipole-dipole method for structural studies: examples from the Northern Apennines

1998 ◽  
Vol 41 (3) ◽  
Author(s):  
M. Giudici ◽  
L. Alfano
Keyword(s):  
Northern Apennines ◽  
Structural Studies ◽  
Geological Structures ◽  
Vertical Electrical Soundings ◽  
North East ◽  
Field Activity ◽  
Electrical Soundings ◽  
Surrounding Areas

We present some results of a geoelectrical investigation program conducted in the Northern Apennines, namely in the Val d'Aveto and Bobbio window and surrounding areas. Field activity included the execution of more than 50 vertical electrical soundings with continuous polar dipole-dipole spread. We image the geometries of some deep geological structures; in particular we found a resistive background, whose resistivity is different along the geoelectrical profiles. In our interpretation the resistive background consists of subligurid and tuscan units underlying the alloctone Ligurid units in the area surrounding the Val d'Aveto and Bobbio window. The resistive background was not found, at least at the same depths, toward north-east. Therefore, the geoelectrical survey revealed the position of the front of the subligurid and Tuscan nappes toward the plain for a depth of about one kilometer.

A mid-Palaeozoic ocean–continent transition in the Mazongshan subduction–accretion complex, Beishan, NW China: new structural, chemical and age data constrain the petrogenesis and tectonic evolution

2020 ◽  
Vol 157 (11) ◽  
pp. 1877-1897 ◽  
Author(s):  
J.-X. Wang ◽  
K.-X. Zhang ◽  
Brian F. Windley ◽  
B.-W. Song ◽  
X.-H. Kou ◽  
...  
Keyword(s):  
Continental Crust ◽  
Early Carboniferous ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Published Data ◽  
Zircon Age ◽  
The North ◽  
Tectonic History ◽  
Central Asian ◽  
Tectonic Mélange

AbstractAccretionary orogens contain key evidence for the conversion of oceanic to continental crust. The late tectonic history and closure time of the Palaeo-Asian Ocean are recorded in the Mazongshan subduction–accretion complex in the southern Beishan margin of the Central Asian Orogenic Belt. We present new data on the structure, petrology, geochemistry and zircon U–Pb isotope ages of the Mazongshan subduction–accretion complex, which is a tectonic mélange with a block-in-matrix structure. The blocks are of serpentinized peridotite, basalt, gabbro, basaltic andesite, chert and seamount sediments within a matrix that is mainly composed of fore-arc-trench turbidites. U–Pb zircon ages of two gabbros are 454.6 ± 2.5 Ma and 434.1 ± 3.6 Ma, an andesite has a U–Pb zircon age of 451.3 ± 3.5 Ma and a tuffaceous slate has the youngest U–Pb zircon age of 353.6 ± 5.1 Ma. These new isotopic ages, combined with published data on ophiolitic mélanges from central Beishan, indicate that the subduction–accretion of Beishan in the southernmost Central Asian Orogenic Belt lasted until Late Ordovician – Early Carboniferous time. Structure and age data demonstrate that the younging direction of accretion was southwards and that the subduction zone dipped continuously to the north. Accordingly, these results record the conversion of oceanic to continental crust in the southern Beishan accretionary collage.

The high pCO2 Caprese Reservoir (Northern Apennines, Italy): Relationships between present- and paleo-fluid geochemistry and structural setting

2013 ◽  
Vol 351 ◽  
pp. 40-56 ◽  
Author(s):  
Gabriele Bicocchi ◽  
Franco Tassi ◽  
Marco Bonini ◽  
Francesco Capecchiacci ◽  
Giovanni Ruggieri ◽  
...  
Keyword(s):  
Northern Apennines ◽  
High Pco2 ◽  
Fluid Geochemistry ◽  
Structural Setting

The cooling, deformation and exhumation history of the late Miocene syn-tectonic Porto Azzurro pluton in a regional transfer zone (Elba Island, Italy)

2020 ◽  
Author(s):  
Andrea Brogi ◽  
Richard Spiess ◽  
Alfredo Caggianelli ◽  
Antonio Langone ◽  
Fin Stuart ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Northern Apennines ◽  
Contact Metamorphism ◽  
Pluton Emplacement ◽  
Vertical Permeability ◽  
Extensional Tectonic ◽  
History Of ◽  
Elba Island ◽  
Exhumation History ◽  
Transfer Zone

<p>In extensional tectonic settings, stretched terrains are often associated to lithosphere partial melting and widespread magmatism with plutons emplaced in the thinned crust. Emplacement of felsic magmas, at upper crustal levels, represents the final stage of the magma transfer from profound to shallow depth. In this framework, a mostly vertical permeability controls the magma uprising migration, as induced by dominant transcurrent crustal structures. Nevertheless, the interplay between extension and prolonged heat transfer favors uplift and progressive exhumation of the magmatic bodies, during their cooling.</p><p>In this presentation, we show an example of a felsic magmatic intrusion, the Porto Azzurro pluton (inner northern Apennines), emplaced in an extensional tectonic setting and mainly controlled by a regional transfer zone related to the opening of the Tyrrhenian Basin. This is exposed in the eastern Elba Island (Tuscan Archipelago). The hosting rocks of the Porto Azzurro pluton are mainly represented by micaschist, paragneiss and quartzite, affected by contact metamorphism and intense fluid circulation. We have analysed the structures that assisted the pluton emplacement and the ones that deformed the pluton itself during its cooling, from melt-present to brittle conditions, based on the integration among fieldwork, micro-structural, petrological and EBSD analyses. Furthermore, new U/Pb geochronological data on zircons and (U-Th)/He on apatite fission track refined the age of the pluton emplacement and its cooling, adding new data about the pluton history. Existing petrological analyses of the hosting rocks allowed us to better constrain the time-evolution of the thermal perturbation, permitting to frame the deformation and exhumation history of the Porto Azzurro monzogranite in the context of the Neogene extensional tectonics affecting the inner Northern Apennines.</p>

HP-LT metamorphism in Elba Island: Implications for the geodynamic evolution of the inner Northern Apennines (Italy)

2015 ◽  
Vol 91 ◽  
pp. 13-25 ◽  
Author(s):  
Caterina Bianco ◽  
Andrea Brogi ◽  
Alfredo Caggianelli ◽  
Giovanna Giorgetti ◽  
Domenico Liotta ◽  
...  
Keyword(s):  
Northern Apennines ◽  
Geodynamic Evolution ◽  
Elba Island

scholarly journals PROBLEMATIC ASPECTS OF THE FORMATION OF THE UKRAINIAN SEGMENT OF THE CARPATHIANS

2019 ◽  
Vol 3 (180) ◽  
pp. 5-24
Author(s):  
Myroslav Palyuk ◽  
Volodymyr Shlapinsky ◽  
Albert Medvedev ◽  
Bohdan Rizun ◽  
Myroslav Ternavsky
Keyword(s):  
Continental Crust ◽  
Block Structure ◽  
Time Interval ◽  
Vertical Movements ◽  
The Carpathians ◽  
Differential Development ◽  
Flysch Carpathians ◽  
Outer Carpathians

In the paper a model of the formation of the folded-covering-block structure of the Carpathians at a time interval that envelops Late-Hercynian and Alpine events is substantiated. Moreover, this concerns the Outer Carpathians, but the whole Carpathians arch was characterized without going into details, a critical estimate is expressed for application of such terms as terrains, accretion prism, suture, subduction and Transcarpathian fault. It is shown that formation of the Carpathians occurred through several stages under the influence of different-directed, manly horizontal, movements, as a result of which was destruction of early formed Hercynian continental crust, laying of geosynclinals troughs, formation and further transformation of the basement of the Flysch Carpathians, its collision with Eurasian continental edge, underling of the latter under flysh complex. After completion of these processes mainly vertical movements took place that lineally formed the structure of the Carpathians as folded-covering-block one. As a result of the last event (Pliocene-Pleistocene), a differential development of intensive fracturing occurred with the influx of hydrocarbons and filling traps formed up.

A Pyrenean-like model for the Variscan belt in NW Africa : insights from thermometry-based Raman spectroscopy study in the Khenifra Basin

2020 ◽  
Author(s):  
Rémi Leprêtre ◽  
Andrea Schito ◽  
Rachid Ouchaou ◽  
Mohamed El Houicha ◽  
Francis Chopin
Keyword(s):  
Raman Spectroscopy ◽  
Thermal Structure ◽  
Early Carboniferous ◽  
Variscan Orogeny ◽  
Time Interval ◽  
Short Time Interval ◽  
Variscan Belt ◽  
Single Event ◽  
Maximum Temperatures ◽  
Short Time

<p>The Variscan belt in NW Africa is an intracontinental belt, resulting from far-field compressional stress during the closure of the Rheic Ocean between the Late Carboniferous and the Early Permian. In the classical view, this orogen building was preceded by a pre-orogenic stage, namely the Eo-variscan stage, suggested to have occurred at the Late Devonian-Early Carboniferous transition.</p><p>This view is now questioned, for multiple reasons. A first structural reason aims at re-interpreting the so-called Eovariscan features as extensional ones. Indeed, although many structures have been described, their integration into a compressional setting is not straightforward. A second reason is geodynamical, since this peculiar stage is bracketed between two general extensional phases recorded at the scale of NW Africa, and this leaves a very short time interval to proceed to a compressional phase that is geodynamically not integrated until today. At last, a third reason stems from early findings from metamorphic works in the Western Meseta that demonstrated the occurrences of previously unnoticed high geothermal gradients inside numerous Early Carboniferous basins (Chopin et al., 2014 ; Wernert et al., 2016 ; Delchini et al., 2018 ; Lahfid et al., 2019).</p><p>In this work, we sampled the Khenifra Basin within the easternmost part of the Western Meseta, where the Eovariscan deformation was defined (Allary et al., 1972). We carried on structural observations into the basement and sampled both the Ordovician basement and the Middle(?)-Late Visean series of the basin, which is thought the be extensional. Maximum temperatures reached by the 77 sampled rocks were obtained from the analysis of organic matter with the use of the Raman spectroscopy. The examination of this new dataset demonstrates that the Ordovician series acquired temperatures through a single event, consistently with their common record of the Eovariscan deformation. Instead, the unconformable Visean series on top of the basement show a pronounced basinal asymmetry, from low temperatures (< 160°C) to temperatures equivalent to the Ordovician ones (> 250°C). The Visean series do not record the Eovariscan deformation, and their thermal structure was acquired before the Variscan event, regarding their repartition within the basin. The examination of the different hypotheses for the timing of the maximal temperature acquisition (Variscan, compressional Eovariscan and extensional Eovariscan) leads to a single option only compatible with an extensional Eovariscan context.</p><p>The renewal on the knowledge about the early stages of the Variscan orogeny in NW Africa allows us to consider a Pyrenean-like model for the formation of this intraplate belt, resulting from the inversion of hot Early Carboniferous rifted basins.</p>

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