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2008, Memorie Descrittive della CARTA GEOLOGICA d’ITALIA vol. LXXXII
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301 pages
1 file
During the last 30 years, structural geology had relevant advances thanks to a wealth of data provided by geological and geophysical investigations. In this volume we propose a sort of handbook for basic tectonic features. We review the fundamental mechanics, and the most common features associated to brittle deformation. The main geometries and kinematics of compressional, transpressive, strike-slip, transtensive and extensional tectonic environments are presented. Moreover the migration of rupture along faults and the elementary evolution of diapirs are discussed. Few instances on how tectonics influences sedimentation, compaction, and the sedimentary architecture controls tectonics are highlighted. The structural features are then inserted in a wider geodynamic scenario in which the basic element is the basal decollement, with its depth, temperature, pressure and strain rate. The regional subsidence or uplift is combined with the growth rate of single tectonic features, which may locally increase or decrease the regional motions. This points to the computation for example of the fold total uplift, e.g., the uplift of an anticline minus the regional subsidence rate of the foredeep, that can even exceed the vertical growth rate of the fold. The combination with variable sedimentation rates may further differentiate the growth structures. The geodynamics of subduction zones and rift zones is discussed in the frame of the westward drift of the lithosphere, generating a worldwide asymmetry, which can be recognized as well as between the subduction zones in the Mediterranean realm. Unlike the Apennines, the Alps do not have a coaxial rifting in the hangingwall of the subduction, i.e., a back arc basin as the Tyrrhenian Sea. In this context, the Southern Alps and the Dolomites in particular, are rather the compressive retrobelt of the Alpine orogen, which is associated to the right-lateral transpressive subduction along the E-W trending segment of the belt. The Dolomites were undergoing rifting episodes during the Permo-Mesozoic. Fast subsidence rates during the Ladinian would support a backarc origin in the hangingwall of a W-directed subduction zone, possibly located in the present Pannonian Basin. The Dolomites are located half on the N-trending Trento Horst to the west, and the other half on the Belluno Graben to the east, both extensional features of Permo-Mesozoic age. The Trento Horst determined an undulation in the Alpine thrusting, being located in a recess since the early phases of shortening, generating left-lateral transpression along the western border (Giudicarie system), and right-lateral transpression on its eastern margin (Paleogene WSW-verging thrusts of the central-eastern Dolomites). The adjacent Lombard Graben (and basin) to the west, and the Belluno Basin to the east have rather been the seat of salients. The description of a five days field trip illustrates well exposed examples of tectonic features generated by the Mesozoic rifting and the later Cenozoic Alpine inversion that generated a classic thrust belt with imbricate fan geometry.
Tectonophysics, 1985
Boccaletti, M., Coli, M., Eva, C.
Swiss Journal of Geosciences, 2013
The Lepontine dome represents a unique region in the arc of the Central and Western Alps, where complex fold structures of upper amphibolite facies grade of the deepest stage of the orogenic belt are exposed in a tectonic half-window. The NW-verging Mont Blanc, Aar und Gotthard basement folds and the Lower Penninic gneiss nappes of the Central Alps were formed by ductile detachment of the upper European crust during its Late Eocene-Early Oligocene SE-directed underthrust below the upper Penninic and Austroalpine thrusts and the Adriatic plate. Four underthrust zones are distinguished in the NW-verging stack of Alpine fold nappes and thrusts: the Canavese, Piemont, Valais and Adula zones. Up to three schistosities S1-S3, folds F1-F3 and a stretching lineation XI with top-to-NW shear indicators were developed in the F1-F3 fold nappes. Spectacular F4 transverse folds, the SW-verging Verzasca, Maggia, Ziccher, Alpe Bosa and Wandfluhhorn anticlines and synclines overprint the Alpine nappe stack. Their formation under amphibolite facies grade was related to late ductile folding of the southern nappe roots during dextral displacement of the Adriatic indenter. The transverse folding F4 was followed since 30 Ma by the pull-apart exhumation and erosion of the Lepontine dome. This occurred coevally with the formation of the dextral ductile Simplon shear zone, the S-verging backfolding F5 and the formation of the southern steep belt. Exhumation continued after 18 Ma with movement on the brittle Rhone-Simplon detachment, accompanied by the N-, NW-and W-directed Helvetic and Dauphiné thrusts. The dextral shear is dated by the 29-25 Ma crustal-derived aplite and pegmatite intrusions in the southern steep belt. The cooling by uplift and erosion of the Tertiary migmatites of the Bellinzona region occurred between 22 and 18 Ma followed by the exhumation of the Toce dome on the brittle Rhone-Simplon fault since 18 Ma.
Journal of The Virtual Explorer, 2003
In this paper, we recall some aspects of the geology of central Italy, not fully consistent with the interpretation of the Tyrrhenian-Apennine system in the frame of a subduction context. Available near-vertical and deep-sounding seismic profiles across the Apennines of central Italy (e.g. CROP 03 and DSS ʻ78) do not show any evidence of an accretionary wedge above a subducting plane, but rather show a thick-skinned thrust belt with involvement of the overall crust in the deformation and with modest amounts of horizontal shortening. The relatively deep (<90 km) seismicity registered in Central Italy cannot be interpreted in terms of ongoing subduction. In fact, the hypocentral distributions do not mark the underthrusting of the Adriatic continental lithosphere beneath the Tyrrhenian lithosphere, but rather depict a seismogenic west-dipping thrust zone within the Adriatic lithosphere. The presence within the Apennine mountain chain of a carbonatite-potassic melilitite rock association, middle Pleistocene in age, points to a different geodynamic environment than subduction. In fact, this rock association is very rare and exclusively found in intra-continental rift context. The possibility to explain the evolution of the Tyrrhenian-Apennine system applying either a passive or an active (plume-related) rift context as alternative to subduction is briefly addressed. All considering, the evolution of the area is interpreted as the result of a peculiar combination of large-scale plume-induced lithospheric stretching and of local-scale rift push-induced crustal shortening, the latter progressively developed at the outer border of the extending region.
Earth Surface Processes and Landforms, 1993
Earth-Science Reviews, 2010
A new reconstruction of Alpine Tethys combines plate-kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution, from sea-floor spreading through subduction to collision in the Alps. Unlike previous models, which relate the fate of Alpine Tethys solely to relative motions of Africa, Iberia and Europe during opening of the Atlantic, our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record. The motions of these microplates (Adria, Iberia, Alcapia, Alkapecia, and Tiszia) relative to both Africa and Europe during Late Cretaceous to Cenozoic time involved the subduction of remnant Tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces: (1) 131-84 Ma intra-oceanic subduction of the Ligurian part of Alpine Tethys attached to Iberia coincided with Eo-alpine orogenesis in the Alcapia microplate, north of Africa. These events were triggered primarily by foundering of the older (170-131 Ma) Neotethyan subduction slab along the NE margin of the composite African-Adriatic plate; subduction was linked by a sinistral transform system to E-W opening of the Valais part of Alpine Tethys; (2) 84-35 Ma subduction of primarily the Piemont and Valais parts of Alpine Tethys which were then attached to the European plate beneath the overriding African and later Adriatic plates. NW translation of Adria with respect to Africa was accommodated primarily by slow widening of the Ionian Sea; (3) 35 Ma-Recent rollback subduction of the Ligurian part of Alpine Tethys coincided with Western Alpine orogenesis and involved the formation of the Gibraltar and Calabrian arcs. Rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable, retreating Adriatic and African slabs during slow convergence of Africa and Europe. The upper European-Iberian plate stretched to accommodate this slab retreat in a very mobile fashion, while the continental core of the Adriatic microplate acted as a rigid indenter within the Alpine collisional zone. The subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the Alps and Apennines, as well as beneath parts of the Pannonian Basin, the Adriatic Sea, the Ligurian Sea, and the Western Mediterranean. The predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10-30%, indicating that parts of slabs may be superposed within the mantle transition zone and/or that some of this subducted lithosphere became seismically transparent.
Geological Society of America Bulletin, 2011
Terra Nova, 2003
Marine and Petroleum Geology, 2004
A wide sector of the internal portion of the Central Apennines, which comprises the southern Lepini Mtns up to the northern Simbruini Mtns has been investigated through detailed field mapping and integrated with structural analyses. A few small productive oil fields and a large number of hydrocarbon seeps and oil impregnations are located in this sector. This area offers good opportunities for testing the use of structural fieldwork methodologies in order to highlight oil migrating paths, from Triassic source rocks, and prospecting chances for oil field exploitation.The main stages of the structural evolution of the area took place after deposition of the foredeep sediments (Frosinone Fm.), i.e. after Late Tortonian, under a stress field characterised by a NE–SW trending σ1, which was responsible for the early emplacement of major thrust faults present in the area. The Messinian-Early Pliocene thrust-top basin deposits allowed the reconstruction of an in-sequence evolution of the thrust system. The development of out-of-sequence thrusting post-dates these structures leading to a further strong shortening phase in the area during the Pliocene. This phase is characterised by a roughly NNE–SSW trending σ1. Some peculiar tectonic features evidenced by thrust faults with younger-over-older relationships and an inversion of the original stacking of thrust sheets developed during this phase.Successively, a block-faulting tectonic, mainly with NE–SW extension stress field, occurred and dismembered the compressive tectonic edifice.Later on up to the Middle Pleistocene, N–S to NNE–SSW trending dextral strike-slip faults also acted in the area. Associated to the strike-slip tectonics are local volcanic centres as well as necks, whose compositions show a mantle origin, thus indicating deep seating and a possible lithospheric significance of these structures.In the light of this study, the reduced extension of the productive oil area as well as the spotting of oil seeps, may indicate that the migration conditions are not tied to well defined structures but that likely the cross-cutting points among structures facilitate the conditions for an upwards rising of oil. These conditions in particular are achieved at least in two cases: (1) where the Late Triassic source rocks do not have great depth due to normal or reverse faults, or (2) at a major depth when encountered by transcurrent-oblique roughly N–S trending faults—in both cases oil can easily migrate along the damage zone associated to the fault plane.
Tectonics, 1994
The Adriatic region forms an intermediate continental foreland overthrust along its northeastern margin by the southwest vergent Dinaric thrust belt in Eocene-Oligocene time and along its southwestern margin by the northeast vergent Apennine thrust belt in Pliocene-Quaternary time. Orogenic activity within these thrust belts was accompanied by the development of two superposed foredeep basin systems of opposite polarity and different ages. Using well log, biostratigraphic, and seismostratigraphic data, the geometry of this composite basin system was reconstructed along three profiles at beginning of Quaternary, middle Pliocene, beginning Pliocene, and beginning Eocene time. Modeling of reconstructed geometries using a thin elastic sheet approximation yields a range of acceptable effective elastic plate thicknesses for the central Adriatic region of Te=5-10 km for Eocene-Oligocene flexure and Te= 10-15 km for Pliocene-Quaternary flexure (although an upper bound for Te could not be established on one of the three profiles). These results are consistent with a constant effective elastic plate thickness of Te=10 km for the Adriatic lithosphere and preclude the possibility that significant weakening of the Adriatic plate occurred between flexural events. Modeling of incremental deflections between Pliocene and Quaternary time gives results consistent with constant values of Te=10 km in the central Adriatic and Te=15 km in the northern Adriatic and Po Plain and shows little evidence for weakening of the plate during Pliocene-Quaternary time. Thus within the resolution of the data presented in this paper, there is little evidence for viscous relaxation of the lithosphere on time scales between about 2 and 50 m.y. Analysis of bending of an idealized lithosphere with a simple brittle-elasticductile theology, and a low to moderate thermal gradient suggests that the small values of Te observed within the Adriatic region can be readily understood as the result of bending of the lithosphere to unusually high curvature (4 x l0 -6 m -1) and do not require unusually high temperatures within the foreland lithosphere. The same theological model is also consistent with the absence of significant inelastic Paper number 93TC01935 0278-7407/94/93TC-01935510.00 yielding for at least 50 m.y. after the cessation of loading. An apparent unbending of the Adriatic lithosphere began in early Quaternary time, approximately coeval with the cessation of major thrusting within the Apennine thrust belt. The threedimensional pattern of Quaternary deflection makes it difficult to attribute this phenomenon to local depositional processes and suggests that unbending reflects a fundamental change in the subduction process in early Quaternary time. Our preferred interpretation is that unbending is the result of a diminution of forces acting on the subducted Adriatic lithosphere at mantle depths. The Dinaride and Apennine orogenic belts have formed in response to local accommodation of convergence between the Eurasian and African plates in Cenozoic time. Between these two thrust belts lies an intermediate continental foreland lithosphere, overthrust from the northeast by the Dinaric nappes and from the southwest by the Apennine nappes. This intermediate foreland currently underlies the northern Adriatic Sea and the Po Plain of Italy and is referred to here as the Adriatic lithosphere or Adriatic fragment (many authors also refer to it as Apulia, particularly in discussions of southern Alpine tectonics). The basement of the Adriatic fragment forms a central high and deepens to the northeast and to the southwest toward the opposing thrust belts. The Moho lies at 25-to 35-km depth in the northern Adriatic Sea and deepens to the west [Finetti et al., 1966; Giese and Morelli, 1975; Cermak, 1978]. The foredeep basin along the northeastern side of the Adriatic Sea and the Dinaride thrust belt of Yugoslavia developed contemporaneously with southwest vergent thrusting in the Dinaric Alps in Eocene-Oligocene time. Thrusting involved Mesozoic and Paleozoic sedimentary rocks as well as Cenozoic sedimentary rocks deposited in the internal (northeastern) parts of the foredeep basin. The amount of shortening recorded in the Dinaride thrust belt increases southward, reaching several hundreds of kilometers in the southern Dinarides (for a summary, see Burchfiel [1980]). External to (southwest of) the Dinaric thrust belt, late Cretaceous to early Eocene(?) reefs indicate a shallow marine environment within much of the Dinaric foreland. These carbonate rocks are overlain by Eocene to Miocene clastic deposits that fill the foredeep basin and thicken toward the northeast, reaching a maximum thickness of 5-6 km. Subsidence of the foredeep basin and thrusting within the Dinarides ceased probably by Oligocene time. Eocene to Miocene sedimentary rocks in the foredeep are overlain by Pliocene sedimentary rocks associated with the development of the Apennine foredeep basin. Pliocene development of the Apennine thrust belt and western Adriatic foredeep basin postdates tectonic activity in the Dinarides. Northeast directed thrusting in the Apennine thrust belt occurred throughout Miocene and Pliocene time in response to southwestward subduction of the Adriatic lithosphere beneath the mountain belt [Civetta et al., 1978; Mantovani et al., 1992]. The thrust belt migrated to Southern ps Po Plain D 200 km Tyrhennian Sea 28o Kruse and Royden: Bending of the Adriatic Lithosphere the east throughout middle and late Miocene time, transporting sedimentary rocks originally deposited on the Adriatic plate and stripped from their basement during thrusting [e.g., Ogniben et al., 1975; Bally et al., 1986; Cooper, 1988]. The present Apennine-Po foredeep basin was formed in Pliocene-Quaternary time, but remnants of older foredeep basins can be found within the thrust belt itself [e.g., Patacca and Scandone, 1989]. The present basin thickens uniformly to the southwest, containing up to 8 km of Pliocene-Quaternary sediments [Ogniben et al., 1975; Pieri and Groppi, 1981]. At least 60-170 km of shortening is estimated to have occurred across the central Apennines in Pliocene-Quaternary time [Bally et al., 1986]. Evidence pointing toward significant west dipping subduction of the Adriatic lithosphere beneath the Apennine thrust belt includes palinspastic restorations that show up to several hundred kilometers of shortening across the belt [Bally et al., 1986] and the presence of arc volcanism along the Italian peninsula [Barberi et al., 1974]. A narrow, northwest-dipping Benioff zone exists west of the southernmost portion of the Apennines and the Calabrian arc, with hypocenters to 600-km depth [Gasparini et al., 1982]. West of the Apennine mountains, late Miocene-Pliocene extension within the overriding plate has Publ., 414, 1-13, 1981. Royden, L., Flexural behavior of the continental lithosphere in Italy: Constraints imposed by gravity and deflection data, J. Geophys. Res., 93, 7747-7766, 1988. Royden, L., E. Patacca, and P. Scandone, Segmentation and configuration of subducted lithosphere in Italy: An important control on thrust belt and foredeep basin evolution, Geology, 15, 714-717, 1987. Royden, L. H.,The tectonic expression of slab pull at continental convergent boundaries, Tectonics, 12, 303-325, 1993. Ruggieri, G., D. Rio, and R. Sprovieri, Remarks on the chronostratigraphic classification of lower Pleistocene, Boll. Soc. Geol. Ital., 103, 251-259, 1984. Sclater, J. G., and P. A. F. Christie, Continental stretching: An explanation of the post-mid-Cretaceous subsidence of the central North Sea basin, J. Geophys. Res., 85, 3711-3739, 1980.
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