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Tectonic evolution of arcuate mountain belts on top of a retreating subduction slab: The example of the Calabrian Arc
No full textIn this paper, new paleomagnetic results from the Calabrian Arc are presented,
together with a critical review of all paleomagnetic data collected in the last decades in
southern Italy. Our study is focused on the upper Miocene to middle Pleistocene deposits
of the Crati extensional basin, a sector of the arc where an abrupt change in the sense of
paleomagnetic rotations is observed. Paleomagnetic data indicate that the Crati basin
underwent a uniform clockwise (CW) rotation of about 15–20 in its central and southern
part, whereas the northern sector is organized in small-scale fault-bounded blocks, which
rotated independently. We interpret this pattern of deformation as the evidence of the
complex nature of this area, which represents the boundary between two domains
characterized by opposite rotations: the southern Apennines, which rotated
counterclockwise, and the Calabria and Sicily, which rotated CW. Integrating these new
paleomagnetic data with paleomagnetic data from southern Italy, we reconstruct the
history of paleomagnetic rotations through time. Paleomagnetic rotations highlight the
peculiarity of the formation of the Calabrian Arc curvature and imply that either an
oroclinal bending model or a progressive arc model cannot be simply applied to the
Calabrian Arc formation. We describe a realistic tectonic-geodynamic model, where the
progressive curvature of the Calabrian Arc is framed within the space-time evolution of
the Ionian subduction system
Indagini macrosismiche ad alta densità per lo studio del risentimento sismico nella città di Roma
No full textIndagini macrosismiche ad alta densità per lo studio del risentimento sismico nella città di Roma. In “La geologia di Roma: dal Centro Storico alla Periferia
No full textCorrelation between magnetic anisotropy and phyllosilicate preferred orientation for various sedimentary rocks.
No full textThe low and high-field magnetic anisotropy (AMS, HFA) of the various sedimentary and anchimetamorphic rocks was compared to the theoretical anisotropy calculated from the neutron texture goniometry measurements. The studied rocks range from Pliocene to Pleistocene clays and marls of southern Italy to Palaeozoic mudstones and greywackes of the Rhenohercynian Zone of the Czech Republic.The magnetic anisotropy of studied rocks is predominantly carried by the paramagnetic phyllosilicates, i.e. chlorite and, to the minor extent, micas. The orientation tensors of the phyllosilicate (001) planes were calculated from the neutron goniometry pole figures. Subsequently, the principal values of the theoretical anisotropy were calculated from the principal values of the orientation tensor assuming the various anisotropy values for the phyllosilicates grains. As only the paramagnetic anisotropy should be correlated with the preferred orientation of phyllosilicate phases, the HFA was used for the separation of the paramagnetic and ferromagnetic contribution to the magnetic anisotropy.In most cases, the principal directions of the AMS, high-field paramagnetic component (HFP), and the theoretical anisotropy are subparallel (Fig. 1). No systematic deviation of paramagnetic fabric from whole-rock magnetic fabric can be observed.Quantitative correlations were presented in terms of the standard deviatoric susceptibility, k’, and the difference shape factor, U, expressing anisotropy degree and shape, respectively (Fig. 2). The degrees of the theoretical anisotropy, AMS, and HFP correlate very well (correlation coefficient, R > 0.95) implying nearly the same degree of anisotropy for all the employed methods. The correlations of the shapes of respective anisotropies show more significant scatters. Despite this dispersion, the prolate and oblate shapes still remain well defined.This integrated approach enables to establish a more accurate qualitative and quantitative correlation between the phyllosilicate fabric and magnetic anisotropy and yields valuable information about the meaning of the magnetic fabri
The Evolution of the Calabrian Arc: Evidence from paleomagnetic and GPS observations
No full textThe present-day arcuate shape of the Calabrian Arc has been accomplished during Neogene and Early Pleistocene by large and
opposite vertical axis rotations along the two arms of the Arc. Clockwise (CW) rotations have been systematically registered in
Sicily and Calabria, whereas counterclockwise (CCW) rotations were measured in Southern Apennines. Such opposite vertical axis
rotations ceased in the uppermost part of the Lower Pleistocene (about 1 Ma ago) along almost the entire Calabrian Arc and are
not observed in the present-day GPS velocity field. The end of the Calabrian Arc bending during the Quaternary marks a decrease
in the efficiency of the tectonic processes related to the long-lived subduction of the Ionian slab, which caused the halting of the
back-arc opening in the Southern Tyrrhenian Sea
The architecture of brittle postorogenic extension: Results from an integrated structural and paleomagnetic study in north Calabria (southern Italy)
No full textAn integrated structural and paleomagnetic
study was carried out on Neogene-
Quaternary clastic sedimentary sequences
exposed in north Calabria to defi ne the
brittle postorogenic evolution of the inner
sector of the Calabrian arc. The structural,
mineralogical, and magnetic fabric data
presented in this paper suggest that the postorogenic
basins of north Calabria originated
and developed under an extensional tectonic
regime that has been active since the middle
Miocene. Results were used to defi ne the spatial
and temporal evolution of the extensional
fault systems in the framework of extensional
processes active in the backarc region of the
southeastward-migrating Apennine subduction
system. Our data indicate that regional
backarc extension operated in the brittle
crust, and the data trace a continuous evolution
from low- to high-angle extensional
faulting. Paleomagnetic data show that this
continuous extensional process was accompanied
by complex interactions among faultbounded
crustal blocks. In fact, the extensional
domain is subdivided into different
structural compartments, separated by the
adjustment in the fault strike imposed by the
regional rotation pattern
Late folding-related magnetic foliation in the active Ferdows (northeastern Iran) thrust-fold system
No full textIn this work we present new AMS and structural results from the Ferdows active fold-thrust system (Lut block, Central Iran). AMS analyses show that the Miocene units of the Upper Red Formation have a well defined magnetic fabric of tectonic origin, with both magnetic lineation and magnetic foliation oriented parallel to the regional fold axes. In most of the cases the magnetic fabric, acquired when the bedding was still horizontal, is related to different degrees of LPS shortening. In some other cases, the magnetic foliation is vertical and oblique to the bedding, suggesting that in the Ferdows thrust-fold structure a cleavage system, not visible at the outcrop scale, has been developed as a consequence of later shortening related to the activity of the thrust system, responsible of the recent earthquakes in the area. Results from this study establish a relationships between the recent tectonics of the area and the evolution of the magnetic fabric and demonstrate that a well defined magnetic fabric of pure tectonic origin can also develop in poorly deformed rocks lacking field evidence of pervasive internal deformation. (C) 2015 Elsevier Ltd. All rights reserved
Paleomagnetism of the Neogene-Quaternary sequences of the Crati Basin (Calabria, Southern Italy): tectonic implications
No full textStarting from middle Miocene, the inner sector of the Calabria Arc (southern Italy) was characterised by the deposition of clastic sedimentary sequences, unconformably lying on the orogenic nappe edifice. Still debated is the interpretation of the tectonic context controlling sedimentation in Mio-Pleistocene times and different tectonic models have been proposed: (i) models considering the clastic successions as filling piggy-back or perched basins during the eastward migrating Apennine compressional phases; (ii) models invoking a late Miocene compressive tectonic inversion of an early extensional tectonic phase; and (iii) models proposing the continuous control of extensional processes on the formation and evolution of the tectonic depressions filled by sedimentary sequences. An integrated structural and paleomagnetic study has been carried out on the middle Miocene-Pleistocene sediments filling the Crati basin, northern Calabria. Extensive paleomagnetic sampling of 35 sites has been performed in the clay deposits of distinct ages cropping out throughout the basin. Reliable paleomagnetic data were gathered from 29 sites.Structural and AMS data showed that extensional tectonics was the main factor controlling basin formation and evolution. No evidence for compressional deformation was recognised and it is reasonable to infer that Tyrrhenian extension was a continuous process, active in Calabria since Middle Miocene onward. Paleomagnetic results provide evidence for a differential tectonic evolution occurred in the Crati Basin. The southern sector underwent a homogeneous 25° clockwise rotation. In the central sector of the basin, paleomagnetic vectors show different sense and amount of rotations and altogether, reveal for this sector small scale rotations related to faults bounded blocks. The northern sector is, on the contrary, characterised by a 20° anti-clockwise rotation. These data suggest that this area underwent a complex tectonic evolution during crustal extension and can not be considered tectonically homogeneous. Moreover, evaluation of the deformation history of this area has to take into account the local control exerted by tectonic structures inducing rotation on fault bounded blocks and the influence of the time-space migration of the fault activity
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