44 research outputs found
Reconciling the Geology of the Emilia Apennines and Tuscany across the Livorno-Sillaro Lineament, northern Apennines, Italy.
No full textSurface expression of lithospheric faults may vary greatly as they can develop a wide range of geomorphic/topographic features and various kinds of superficial geological/structural mismatchings. The “Livorno-Sillaro Lineament” (Nirta et alii, 2007; Pascucci et alii, 2007; Bettelli et alii, 2012) is one of the most important transverse lineaments of the Northern Apennine orogen. The lithospheric-scale role of this structure has been recognized long time ago by various authors on the base of different geophysical, geological and geomorphic data, although its origin is still not well defined. Also the exact surface characters of this structure are still not well-defined, we think because they are mainly based on old and out-of-date geological data.
We present a review of the more recent stratigraphical and structural data related to the geology across the “Sillaro Lineament”, SL, the northeasternmost segment of the “Livorno-Sillaro Lineament”. Based on a re-examination and reinterpretation of the existing information about the regional geology of the Northern Apennines we conclude that the supposed mismatching of the Ligurian/Subligurian Units on the two sides of this lineament is mainly due to a lack of knowledge and to an inadequate correlation between corresponding units. Nevertheless, we recognize that this structure (along with the Secchia transverse lineament) greatly influenced the growth and the evolution of the oceanic accretionary prism/Ligurian/Subligurian thrust-nappe from the late Eocene to the late Serravallian, and also later on. In particular, we point out that at least the easternmost segment of this structure not only played an important role on the differential growth of the Ligurian/Subligurian accretionary prism-thrust nappe, but that it was responsible for the different amount of translation of the Ligurian Units on both side of the lineament.
Our conclusions and interpretations include:
1) the Sillano/Mt Morello succession, typically cropping out SE of the SL in eastern Tuscany, represents the source rocks of the Ligurian blocks forming the Sestola-Vidiciatico tectonic unit and similar units (e.g., Coscogno-Montepastore tectonic unit: Remitti et alii, 2013) cropping out NW of the SL and along the SL itself;
2) the External Ligurian unit variously named as Samoggia/Val Sillaro/Val Marecchia Varicoloured Shales, AVS, and the overlying lower to middle Eocene turbidites (e.g., Savigno Fm) cropping out in the Emilia Apennines - i.e., NW of the SL – represents a lateral and more internal equivalent of the Sillano/Mt Morello succession. The AVS were extensively present also SE of the SL, as testified by the large klippen in the Romagna Apennines (Savio and Marecchia valleys) and many small klippens in the Umbria area (Umbertide-Gubbio area);
3) along and SE of the SL the AVS form the stratigraphic base of the Mt Morello Fm. Therefore, also this unit is present on both sides of the SL;
4) the pre-middle Eocene Subligurian Units cropping out NW of the SL (Argille e Calcari di Canetolo Fm and Calcari del Groppo del Vescovo Fm) do not correspond to the so called Subligurian Units cropping out SE of the SL (i.e., in Tuscany). The latter are the result of the sedimentation in a particular paleogeographic domain, transitional to the Tuscan domain, absent or not preserved NW of the SL. This seems to represent the only real difference in the geology of the Ligurian/Subligurian thrust nappes NW and SE of the SL.
All the available data show that until the late Serravallian the thrust front of the Ligurian nappe was located in the same position across the SL. However, starting from the early-late Tortonian a differential translation of the Ligurian nappe NW of the SL took place, progressively reaching the present day position. With the exception of the Marecchia area, in the Romagna and Umbria Apennines (SE of the SL), instead, the thrust front of the Ligurian nappe remained more or less in the same position it reached in the late Serravallian. This implies that in the Northern Apennines the transverse SL played also an important role in the different amount of translation of the Ligurian thrust-nappe.
REFERENCES
Bettelli, G., Panini, F., Fioroni, C., Nirta, G., Remitti, F., Vannucchi, P. & Carlini, M. (2012), Revisiting the Geology of the “Sillaro Line”, Northern Aprnnines, Italy. Rendiconti Online Società Geologica Italiana, 22, 14-17.
Nirta, G., Principi, G. & Vannucchi, P. (2007), The Ligurian Units of Western Tuscany (Northern Apennines): insight on the influence of pre-existing weakness zones during ocean closure. Geodinamica Acta, 20/1-2, 71-97, doi:10.3166/ga.20.71-97
Pascucci, V., Martini, I.P., Sagri, M. & Sandrelli, F. (2007), Effects of transversal structural lineaments on the Neogene-Quaternary basins of Tuscany (inner Northern Apennines, Italy). In: G. Nichols, E. Williams & C. Paola (Eds.), Sedimentary Processes, Environments and Basins: a Tribute to Peter Friend (pp.155-182). Special Pubblication no. 38 of the International Association of Sedimentologists.
Remitti, F., Balestrieri, M.L., Vannucchi, P. & Bettelli, G. (2013), Early exhumation of underthrust units near the toe of an ancient erosive subduction zone: A case study from the Northern Apennines of Italy. Geological Society of America Bullettin, 125, 1820-1832, ISSN: 0016-7606
Inherited structures and lateral variability along a plate boundary shear zone in a convergent margin: The Sestola-Vidiciatico Tectonic Unit and the Subligurian Units of the Northern Apennines of Italy
No full textMechanical behavior of the shallow part of megathrusts: hints from the Sestola Vidiciatico tectonic Unit (Northern Apennines, Italy)
No full textInternal architecture of the frontal part of subduction accretionary prism: the role of folding in brittle diffuse deformation
No full textFluid history related to the early Eocene-middle Miocene convergent system of the Northern Apennines (Italy). Constraints from structural and isotopic studies
No full textThe late Eocene-middle Miocene erosive plate boundary between the European and
the Adriatic plates is exhumed in the Northem Apennines of Italy. The fossil fault zone is
500 m thick and the outcropping portion exposes the :first 5 km of its depth. At this
plate boundary basai and frontal tectonic erosion incorporated unlithified, fluid-rich sediments
into the fault zone. The deformation and nature of the material along the plate boundary define a
fossil subduction channel. Here we couple a detailed structural analysis of the Apennine subduction
channel, focusing, in particular, on calcite veins, with a stable isotope analysis to characterize
the fluid regime along an active subduction channel.
The 13C and 180 composition of calcite vein and host rock samples within the fault zone
indicates that there is a deep metamorphic source of fluids migrating upward along the subduction
channel, in addition to locally derived fluid components. Dewatering of subducting turbidites
contributes significantly only in the shallowest part of the channel. Structural observations
indicate fluid flow along and across the subduction channel. At deep levels fluid flow is
associated with discrete deformation events on shear faults offset by dilational jogs :filled with
implosion breccias. At intennediate levels deformation is stili cyclic and associated with repeated
crack-and-seal events. At the shallowest levels deformation occurred, while portions of the
subducting material were stili unlithi:fied. Here the deformation was quasicontinuous, without
associated vein development. Both isotope and structural analyses indicate that this erosive
subduction channel behaved as a weak: fault with a vertical maximum principal stres
RETRIEVAL OF TROPOSPHERIC ASH CLOUDS OF MT. ETNA FROM AVHRR DATA
No full textThis paper focuses on three eruptiveevents of the Mt. Etna volcano: July 22nd 1998,April 26th 2000 and the recent eruption of July-August 2001. Such eruptions may be a severethreat to aircraft safety, as in the April 2000event. From the AVHRR visible images theheight of the top of the clouds is estimated,using geometrical methods, knowing bothNOAA satellite and Sun positions. The resultsare then compared with information derivedfrom radio-sounding data etc.. The volcanic ashparticles with diameters of 1-10 mm are notdetectable by aircraft radar but they may beremotely sensed using thermal infrared data.The well-known algorithm, based on theAVHRR channel 4 and channel 5 brightnesstemperatures difference [Prata, 1989; Schneideret al. 1994], is here applied to highlight the ashclouds of Mt. Etna volcano. Even though it wastypically used to detect and follow the volcanicclouds of stratospheric eruptions, here it is succesfullytested for tropospheric plume too.Some good results of this technique are presentedtogether with some basic problems. Thiswork points out that it could be useful to preparea procedure to monitor Mt. Etna eruption cloudsanalysing TIR data. Such a procedure shouldautomatically alert (in real time, using the newMeteosat Second Generation satellite) and indicatethe cloud direction on the basis of atmosphericradio-sounded and/or predicted data
Late orogenic deformation of the shallowest portion of an orogenic wedge: coeval activity of extensional and compressional tectonics in the western Northern Apennines (Italy)
No full textIn the Northern Apennines of Italy the Ligurian and Subligurian Units (LSU) were involved, since the Late Cretaceous, in the accretionary and orogenic processes related to the convergence between Europe and Adria. Since early Miocene the Ligurian Units completely overthrusted the Subligurian Units (REMITTI et alii, 2011) and both units stacked together (i.e. the LSU) translated towards NE, above the Tuscan-Umbrian foredeep deposits, until they reached the present-day topographic front in the NW portion of the Northern Apennines. In the NE-facing side of the western Northern Apennines the present-day geometry of the LSU does not reflect neither the shape of the late Cretaceous-middle Eocene oceanic accretionary wedge (MOLLI, 2008 and references therein) nor the shape acquired during the late Oligocene, when the early orogenic collisional phases produced a wedge whose geometry tapered out towards the foreland area, i.e. to the E-NE. In fact, at present, geologic evidences indicate that the LSU have a shape whose thickness ranges from less than 1 km at the main ridge zone (SW) up to more than 3,5 km along the NE slope of the chain and then tips out again few km N of the Northern Apennines topographic front, underneath the Pleistocene-to Recent sediments of the Po Plain foredeep. Therefore, the LSU thickness increases towards its NE external tip and tapers out again in the subsurface of the Po Plain. These data imply the activation of thinning processes in the inner portion of LSU and thickening processes in the central portion of LSU; these thinning and thickening processes have to be related to the post-early Miocene progressive emplacement of the LSU over the foredeep units and to the late orogenic extensional and compressional tectonics affecting the Northern Apennines (ARGNANI et alii, 2003, BOCCALETTI et alii, 2011). In particular, the thinning processes have been identified as being of tectonic nature in the innermost portion (mainly low- and high-angle normal faults: ARTONI et alii, 2006, BETTELLI et alii, 2002, VANNUCCHI et alii - 2008) and of sedimentary nature (mass-wasting deposits) (ARTONI et alii, 2010, PAPANI et alii, 1987, REMITTI et alii, 2011) in the outermost portion of the study area. The observed thickening in the central portion of the LSU body has been interpreted as a tectonic doubling caused by the late Miocene-Recent (?) thrusting which affected the whole Apennine orogenic wedge (CAMURRI et alii, 2001; CARLINI et alii, submitted) or, alternatively, as an accumulation zone of large scale and deep-seated gravitational processes (ARTONI et alii, 2006). In order to put new constraints on the timing and modes of thinning and thickening of the LSU we focussed on the western portion of the Northern Apennines, comprised between the main ridge, the Ceno and the Secchia rivers and the Apenninic topographic front. Here we adopted a multidisciplinary approach taking into account field evidences, low temperature thermal and thermochronological data (i.e. vitrinite reflectance, clay mineral analyses, apatite fission-tracks), numerical modelling of the cooling ages through the use of Pecube finite element code (BRAUN, 2003), results from recently published works on the evolution of the external slope of the chain, and a new interpretation of seismic lines and boreholes data. This multidisciplinary approach allowed us to: 1) build a 3D representation of the LSU present-day geometry; 2) constrain to the late Miocene-early Pliocene (in the innermost portion) and to the late Miocene-Pleistocene (?) (at the Apenninic front) the thinning of the LSU; 3) identify the tectonic exhumation and consequent denudation of the foredeep units as one of the main causes which triggered the thinning processes since late Miocene; 4) define first estimates of exhumation rates affecting the LSU and the underlying foredeep units. These results allow us to give new insights, temporal and spatial constraints on the interplay between shallow (< 4 km) and deep (< 20 km), compressional and extensional tectonics which appear to be acting at the same time and at different depths within the study area since late Miocene to Recent
Tectonic and sedimentary evolution of the frontal part of an ancient subduction complex at the transition from accretion to erosion: the case of the Ligurian wedge of the Northern Apennines, Italy
No full textSubduction can be either associated with accretion or removal of material from the overriding plate. These two processes can coexist or alternate in time along the same margin. Theirinception has the potential to change the dynamic equilibrium of a margin wedge resulting in the development of out-of-sequence thrusts, normal and strike-slip faults or large submarine landslides in the frontal part of the subduction zone.In this work we investigate the effects of the transition from frontal accretion to frontal erosion on the stability of a subduction complex through the study of a fossil example from the Northern Apennines.New structural data suggest that in the Aquitanian the removal and underthrusting of the toe of the wedge, formed by both the accreted sediments of oceanic affinity and the overlying wedge-top basin fill (i.e., the Subligurian Units), implied a process of frontal tectonic erosion. The presence, on top of the subduction complex, of a complete succession of mid-late Eocene to late Miocene slope apron sediments - i.e., the Epiligurian succession - allowed to reconstruct the sedimentary response to thisevent.In the Aquitanian large areas of the wedge were denudated of the lower-slope sedimentary cover through extensive gravitational mass movements. The subsequent deposition of a thick body ofsubmarine debris flow has been documented. The mass-wasting deposits are interpreted as the sedimentary response to the underthrusting of the frontal part of the Ligurian subduction complex formed by the Subligurian Units
Frictional properties of fault zone gouges from the J-FAST drilling project (Mw 9.0 2011 Tohoku-Oki earthquake)
No full textSmectite-rich fault gouges recovered during Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project (J-FAST)) from the plate boundary slip zone of the 2011 M-w 9.0 Tohoku-Oki earthquake were deformed at slip velocities of 10 mu ms(-1) to 3.5ms(-1) and normal stresses up to 12MPa. Water-dampened gouges (1) are weaker (apparent friction coefficient, * 0.1ms(-1)). A significant amount of amorphous material formed in room-humidity experiments at low- and high-slip velocities, likely by comminution and disordering of smectite. Our results indicate that the frictional properties of water-dampened gouges could have facilitated propagation of the Tohoku-oki rupture to the trench and large coseismic slip at shallow depths
New thermal constraints on a shallow fossil subduction channel from the Northern Apennines of Italy
No full textHere we present new thermal constraints (with special regard to vitrinite reflectance, Illite percentage in Illite- Smectite mixed-layers and Kübler Index) derived from both XRD analysis of clay and optical analysis of organic matter dispersed in sediments incorporated in the Apennine erosive subduction channel. This study has the goal to define the distribution of maximum paleo-temperatures in different portion of the subduction channel as well as in the units representing its footwall and hanging wall. We then discuss the results with regards to the time-spacetectonic evolution.In the Northern Apennines of Italy, two tectonic units have been recently recognized as an ancient shallow subduction channel. The subduction channel is represented by the Sestola-Vidiciatico Tectonic Unit and its lateral equivalent, the Subligurian Units. The channel started to form at the transition from subduction to collision between the European and the Adria plates and it was active at least until the middle Miocene. The subduction channel is presently sandwiched between the former oceanic accretionary wedge - the Ligurian thrust nappe - and the underlying Adria sedimentary units deformed by folds and thrusts. The channel has a thickness of about 500 m and is representative of a portion ranging from the shallow diagenetic environment to temperatures of around 150°C, a critical temperature recognized in most of the subduction zones as coincident with the up-dip limit ofseismogenesis.The main component of the subduction channel is represented by material incorporated through frontal tectonic erosion removing the toe of the Ligurian/Subligurian wedge. This toe consisted of former accreted oceanic sediment and their slope deposits, the latter often reworked through gravitational processes. Basal tectonic erosion is shown by blocks of Ligurian rocks tectonically incorporated in the subduction channel. These blocks aregenerally located in the upper part of the mélange.Preliminary data from the clay mineral analysis from the Sestola-Vidiciatico Tectonic Unit and Subligurian Units indicate I% in I/S in a range between 80 and 90% and KI between 0.63 and 0.77. The analysis of organic matter gives Ro% generally in the mature stage of hydrocarbon generation with estimated paleo temperatures between 80°C and 140°C. The data from the footwall are highly variable -from thermally immature to mature- and allow to detect the changes in thickness of the hangingwall and the channel, i.e. the overthrust Ligurian wedge and the Sestola-Vidiciatico Tectonic Unit and Subligurian Units
