ALBERT

Beschreibung: In the present paper integrated stratigraphy and structural analyses are aimed at the description of a synsedimentary transpressional tectonic event, driving the onset and development of the Early Pliocene Lascari Basin, located NW of the Madonie Mountains (northern Sicily).Our data show that the transpressive tectonics generated a morphostructural high flanked by a deep and narrow tectonic depression, bounded by steep and tectonically controlled slopes. Within this depression an Early Pliocene fining and deepening upward sedimentary succession was deposited, unconformably overlying the already deformed substrate. The succession is made up of «base-of-slope» breccias, cross-stratified calcarenites, and bathyal limestones deposited in a high-energy palaeostrait setting. The growth geometry that characterizes the stratal pattern of the deposits suggests the activity of a synsedrimentary transpressional event during the Early Pliocene time.The roughly E-W trending Lascari Syncline, where the Early Pliocene syntectonic basin is hosted, belongs to a system of north verging folds, deforming the pre-existing, originally flat thrusts, generated in Langhian-Serravallian time.This paper presents an original interpretation of the stratigraphic and structural evolution of the study sector of the Sicily Fold and Thrust Belt. Our data contribute also to both define the structural style and constrain the timing of transpressional tectonic event in northern Sicily. A brief comparison performed between the data here presented and those coming from adjacent sectors of northern Sicily suggests that the transpressional tectonics in these sectors of the chain was active at least since the latest Tortonian till at least the Late Pliocene.

Beschreibung: The Umbria-Marche Apennines, an arc-shaped fold and thrust belt with eastward convexity and vergence, form the external part of the Northern Apennines. In the middle 1980s, the Umbria-Marche Apennines were interpreted by some as a classical thin-skinned fold-thrust belt, with thrust sheets emplaced in an in-sequence, piggyback mode, from the interior to the exterior of the orogen, over a main, basal detachment in the Triassic evaporites. In the mechanics of this kind of edifice, the folds and thrusts would develop within a prism or tapered wedge, bounded at the base by an undeformed basement with a regional monocline dipping toward the hinterland, and at the top by a topographic and structural slope generally dipping toward the foreland. Other authors saw the Umbria-Marche Apennines as a more complex orogen, with basement involvement, possible tectonic inversions, and out-of-sequence thrusts. In the present paper, the geometry, structure, and tectono-sedimentary evolution of the Umbria-Marche Apennines are compared with the classical thin-skinned model. We suggest that this fold-thrust belt can be divided longitudinally into two sectors. The eastern part of the chain, comprising the high Mesozoic carbonate anticlinal ridges of the axial zone together with the Marche external folds, fits the classical model well, but the western part, comprising the Umbrian Pre-Apennines, shows striking differences. The boundary between the eastern and western parts of the Umbria-Marche Apennines is here termed the Scheggia-Foligno Line (SFL). East of this line, the Eastern Umbria-Marche Apennines show an eastward taper between the undeformed basement, dipping gently west, and an upper surface in which both topographic and structural elevation decrease toward the east. West of the Scheggia-Foligno Line, by contrast, seismic reflection profiles and subsurface data show basement involvement in the thrusting at shallow depths, while both the topographic and structural elevations are anomalously low compared to the more easterly parts of the chain. There is also a notable discontinuity in foredeep-basin evolution at the Scheggia-Foligno Line, with well-developed foredeep basins in the Umbrian Pre-Apennines and the external Marche belt (the Marnoso-arenacea and Marche Plio-Pleistocene, respectively), whereas only thrust-top basins developed in the axial zone, during the Tortonian-Messinian interval. Various mechanisms, not all mutually exclusive, might be invoked to explain the discontinuity at the Scheggia-Foligno Line. These possible explanations include causes of local character, linked to the sedimentary and tectonic evolution of the region, involving episodic departures from steady-state conditions, interrupting the regular growth of the accretionary wedge. However, it also possible that the Western and Eastern Umbria-Marche Apennines represent completely different orogenic systems, with different causes - possibly with the former related to Corsica-Adria collision and the latter due to slab rollback of Adriatic lithosphere. In either case, this study demonstrates the complexity of evolution of the Northern Apennines, with adjacent zones showing abrupt variations in their history and style of deformation, which are difficult to incorporate in a single, unified geodynamic model.

Beschreibung: Our knowledge of subsurface structures often derives from seismic velocities that are measured during seismic acquisition surveys. These velocities can greatly change due to lithological, fracture frequencies and/or effective pressure/temperature variations. However, the influence of such intrinsic lithological properties and environmental conditions at the large scale is poorly understood due to the lack of comprehensive datasets. Here, we analyze 43 borehole-derived velocity datasets of 3 end-member tight carbonate sequences from Central Italy, including massive pure limestone (Calcare Massiccio, CM), thick-layered (20-50 cm) pure limestone (Maiolica, MA), and thin-layered (2-20 cm) marly limestone (Calcareous Scaglia, CS). Our results show that the main rock parameters and environmental conditions driving large scale velocity variations are bedding and paleostresses, while mineralogical composition and current tectonic stress also play a role. For each of the 3 end-members, measured VP values vary differently with depth, as the thin-layered CS units show a clear increase in Vp, while velocity slightly increases and remains constant for the thick-layered MA and massive CM units, respectively. Such observations show that velocities are affected by specific characteristics of lithological discontinuities, such as the thickness of bedding. Counterintuitively, larger Vp values were recorded in the deformed mountain range than in the undeformed foreland suggesting that higher paleo-stresses increase velocity values by enhancing diagenesis and healing of discontinuities. Our results thus demonstrate that large scale velocity variations are strictly related to variation of lithological properties and to the geological and tectonic history of an area. We suggest that such lithological and environmental controls should be taken into account when developing velocity and mechanical models for tectonically active regions of the Mediterranean Area, where earthquakes mostly nucleate and propagate through carbonate formations, and for resource exploration in fractured carbonate reservoirs.

Beschreibung: Published

Beschreibung: 9472

Beschreibung: 1T. Struttura della Terra

Beschreibung: JCR Journal

Beschreibung: Analysis of seismicity can illuminate active fault zone structures but also deformation within large volumes of the seismogenic zone. For the Mw 6.5 2016-2017 Central Italy seismic sequence, seismicity not only localizes along the major structures hosting the mainshocks (on-fault seismicity), but also occurs within volumes of Triassic Evaporites, TE, composed of alternated anhydrites and dolostones. These volumes of distributed microseismicity show a different frequency-magnitude distribution than on-fault seismicity. We interpret that, during the sequence, shear strain-rate increase, and fluid overpressure promoted widespread ductile deformation within TE that light-up with distributed microseismicity. This interpretation is supported by field and laboratory observations showing that TE background ductile deformation is complex and dominated by distributed failure and folding of the anhydrites associated with boudinage hydro-fracturing and faulting of dolostones. Our results indicate that ductile crustal deformation can cause distributed microseismicity, which obeys to different scaling laws than on-fault seismicity occurring on structures characterized by elasto-frictional stick-slip behaviour.

Beschreibung: Published

Beschreibung: 5627

Beschreibung: 4T. Sismicità dell'Italia

Beschreibung: JCR Journal