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Analisi strutturale e cinematica lungo la Linea delle Giudicarie Nord, tra la Val di Sole e la Val di Non (Trentino Occidentale)
No full textThe development of the North Giudicarie fault zone (Insubric Line, Northern Italy)
No full textThe kinematics of transpressive fault zones is generally characterized by a variable degree of strain partitioning. This process is enhanced by the presence of older faults, which partition the simple shear strain component more easily. The North Giudicarie line can be taken as a good example of strain partitioning because it is a left-lateral transpressive fault developed during the Oligocene-Miocene along an inherited normal fault system of late-Triassic to Cretaceous age. This paper analyzes two main points related to the kinematics of the North Giudicarie line: (1) the role of the inherited faults in the development of the North Giudicarie fault zone, and (2) the mechanisms of strain partitioning. These processes have been analyzed by structural analysis and detailed mapping of the North Giudicarie fault zone. The main tectonic contact of the North Giudicarie line is a northwest dipping reverse fault, which juxtaposes the Austroalpine basement rocks against the Southalpine cover. Oligocene foliated tonalites, together with basement- and limestone-derived mylonites, are found along the main fault plane. The brittle fault zone, up to 1 km thick, is mostly developed within the Southalpine cover rocks. This area is made up of several tectonic lenses, up to 1 km thick and several km long, bounded by anastomosing faults characterized by a normal offset. North-striking faults (e.g., the Trento-Cles line) branch from the North Giudicarie fault zone. Thrusting along the North Giudicarie line and left-lateral strike-slip along the anastomosing faults and the Trento-Cles line has been documented from shear-sense indicators observed in mylonites and small-scale fault surfaces. Stratigraphic data reveal that the Trento-Cles line reactivated pre-existing late Triassic or jounger normal faults. Therefore, it is suggested that the left-lateral slip component took place more easily along inherited faults. Deformation and metamorphic features of mylonites, and the estimated emplacement depth of the Oligocene foliated tonalites, can give a bulk estimate of the vertical displacement along the North Giudicarie line. The calculated thrust slip (similar to 21 km) is lower than the cumulative left-lateral slip along the whole Giudicarie fault system, as inferred from published regional data
Strike-slip movements and thrusting along a transpressive fault zone: the North Giudicarie line (Insubric line, northern Italy)
Full text linkThis paper analyzes the kinematic evolution and the deformation partitioning within an important transpressive fault zone located in the central part of the Alpine chain. The North Giudicarie line is a NNE trending fault which offsets the dextral Insubric line with an apparent left-lateral displacement of about 70 km. The main fault plane of the North Giudicarie line dips about 35 degrees-45 degrees to the NW. The footwall is characterized by N-S striking strike-slip faults, which reactivate extensional faults of Early Jurassic to Late Cretaceous age. The early deformation history of the North Giudicarie line is revealed by basement- and limestone-mylonites. Shear sense of mylonites indicates on average top-to-the-east thrusting. These movements took place during the late Oligocene-early Miocene, when the Insubric line was active as a right-lateral strike-slip fault. Therefore, in this time span the North Giudicarie line can be interpreted as a dextral transpressive bend of the Insubric line. Mylonites have later been overprinted by brittle faults related to top-to-the-SE thrusting of middle-late Miocene age. During this event the shape of the Insubric line was strongly modified by left-lateral transpression along the Giudicarie fault zone. Deformation was partitioned between prevailing compression along the Giudicarie line and left-lateral strike-slip movements along the N-S striking faults. These faults transferred the strike-slip component of the Giudicarie line into a wider area of the central southern Alps
Thrust sequences and evolution of the external sector of a fold and thrust belt: example from the Southern Apennines (Italy)
No full textThe Southern Apenninic chain was built up from the late Oligocene–early Miocene to the middle Pleistocene. It consists of an upper wedge composed of strongly deformed deep marine and carbonate platform successions and a buried thrust and fold belt in the carbonate rocks of the Apulian Platform. This paper analyzes the frontal part of the Southern Apennines, where contractional structures display complex geometries related to progressive incorporation of accreted material, internal shortening and gravitational processes. Late normal faults, which hinder the interpretation of contractional structures in other sectors of the chain, are scarcely represented in the frontal part of the Southern Apennines. This allows a detailed analysis of thrust and fold geometry. In particular it is possible to recognize the relationships between gravity-driven nappes, foreland-vergent thrusts and backthrusts. New field observations allow us to depict a detailed structural framework of this area and to construct regional cross-sections, which illustrate the inferred evolution of the frontal sector of the Apenninic chain. The chronological constraints are given by the age of thrust-top basins and foredeep deposits of middle–late Miocene to Pleistocene age. Deepening of the décollement level during thrusting creates complicate overprinting relationships connected to the deformation of the older thrust surfaces. The inferred evolution can be summarized in two stages. During the first stage shortening of the wedge was associated to emplacement of thin thrust sheets, interpreted as gravity-driven nappes, before sedimentation of middle–late Miocene thrust top basins. The second stage, of middle Pliocene–middle Pleistocene age, was characterized by folding and breaching of the pre-existing structures, related to deep thrusting in the Apulian Platform. The examples shown suggest the presence of transfer zones and lateral ramps to explain lateral variations in thrust geometry and shortening amount. The along strike geometry of non-cylindrical structures provides a valuable tool to decipher the tectonic evolution of the thrust belt. The proposed scheme is well suited to interpret the structural setting of thin-skinned thrust and fold belts characterised by change in the geometry of the thrust systems through time
An exposed cross-section of the late Hercynian upper and intermediate continental crust in the Sila nappe (Calabria)
No full textUpper to intermediate levels of
continental crust, as shaped by Late Hercynian
metamorphism and magmatism, are exposed in the
Sila nappe (Calabria, S. Italy) after Tertiary
tectonics. Direct observation of the crustal section
reveals a composite metamorphic block dominated
by low- to high-grade metapelites and meta-arenites,
intruded centrally by granitoids. The average
thickness of granitoids, estimated on cross-sections
and by geobarometry, reaches 9 ± 2 km. Their
composition changes with depth from leucogranite
to tonalite with increasing colour index. The
estimated bulk composition of the Sila nappe is
characterised by higher contents of A1203, REE and
Th and lower contents of CaO and Sr than is typical
of upper continental crust, reflecting abundant
metapelite in the Sila nappe. Comparisons between
metasedimentary rocks from the upper and
intermediate levels indicate that intracrustal
differentiation was determined by anatexis, which
favoured A1203 , REE and Th enrichment in
medium- to high-grade metapelites. Distribution of
REE, Th and Zr was connected to the fate of
monazite and zircon during crustal anatexis. Melting
reactions involved mainly muscovite whereas
biotite, enclosing most accessory phases, often
remained stable in the residue. Consequent passive
enrichment of Th in medium- to high-grade restitic metapelite determined an unusual increase in
radiogenic heat production with depth.
Compositional data suggest a connection between
leucogranite genesis and anatexis of intermediate
crust. The composition of leucogranites is similar to
that of crustal melts generated by muscovite
dehydration melting reactions. The extremely low
concentrations of Sr and Ba and high Rb contents
are comparable with those of Himalayan
leucogranites
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