1,721,331 research outputs found
Shaping mobile belt by small scale convection
No full textMobile belts are long-lived deformation zones composed of an
ensemble of crustal fragments, distributed over hundreds of kilometres
inside continental convergentmargins1,2.TheMediterranean
represents a remarkable example of this tectonic setting3: the region
hosts a diffuse boundary between the Nubia and Eurasia plates
comprised of a mosaic of microplates that move and deform independently
from the overall plate convergence4. Surface expressions
of Mediterranean tectonics include deep, subsiding backarc basins,
intraplate plateaux and uplifting orogenic belts. Although the
kinematics of the area are now fairly well defined, the dynamical
origins ofmany of these active features are controversial and usually
attributed to crustal and lithospheric interactions. However, the
effects of mantle convection, well established for continental
interiors5–7, should be particularly relevant in a mobile belt, and
modelling may constrain important parameters such as slab coherence
and lithospheric strength. Here we compute global mantle
flow on the basis of recent, high-resolution seismic tomography to
investigate the role of buoyancy-driven and plate-motion-induced
mantle circulation for theMediterranean.Weshowthatmantle flow
provides an explanation for much of the observed dynamic topography
and microplate motion in the region. More generally,
vigorous small-scale convection in the uppermost mantle may also
underpin other complex mobile belts such as the North American
Cordillera or the Himalayan–Tibetan collision zone
Exhumation of high-pressure rocks driven by slab rollback
No full textRocks metamorphosed under high-pressure (HP) and ultra high-pressure (UHP) conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities. In the Mediterranean realm, their occurrence in several belts related to a single subduction event shows that the burial–exhumation cycle is a recurrent transient process. Using the Calabria–Apennine and Aegean belts as examples, we show that the exhumation of HP rocks is associated in time and space with the subduction of small continental lithosphere blocks that triggers slab rollback, creating the necessary space for the exhumation of the buoyant continental crust thatwas deeply buried just before. The buoyancy force of the subducted crust increases until this crust detaches from the downgoing slab. It then exhumes at a rate that depends directly on the velocity of trench retreat to become part of the overriding plate. Heated from below by the asthenosphere that flows into the opening mantle wedge, the exhumed crust weakens and undergoes core-complex-type extension, responsible for a second stage of exhumation at a lower rate. The full sequence of events that characterizes this model (crust–mantle delamination, slab rollback and trench retreat, HP rock exhumation, asthenosphere heating and core-complex formation) arises entirely from the initial condition imposed by the subduction of a small continental block. No specific condition is required regarding the rheology and erosion rate of HP rocks. The burial–exhumation cycle is transient and can recur every time a small continental block is subducted
Bending of the Bolivian orocline and growth of the central Andean plateau: Paleomagnetic and structural constraints from the Eastern Cordillera (22-24°S, NW Argentina)
No full textWe report new paleomagnetic and structural data
from late Cretaceous to Mio-Pliocene continental
sandy/silty sedimentary rocks from the Eastern
Cordillera (central Andes). Here, N–S to NNE–
SSW ridges hosting Paleozoic basement and upper
Cretaceous continental red beds overthrust thick
adjacent Cenozoic basins. Pretilting (and likely
primary) reliable directions gathered at 15 sites
document 45.9 ± 9.4, 30.1 ± 23.9, and 15.4 ±
19.3 clockwise (CW) rotations with respect to South
America occurring after the late Cretaceous (80 Ma),
Oligo-Miocene (20–30 Ma), and late Miocene-
Pliocene (5–10 Ma), respectively. Conversely, four
upper Cretaceous sites from the walls of a N–S leftlateral
strike-slip fault (Yavi–Abra Pampa fault) yield
a null rotation. About 20 km to the west, flower
structures and subvertical syntectonic strata dated at
14.26 ± 0.19 Ma are exposed along the subparallel
Abra Moreta left-lateral strike-slip fault. Relying on
data from the literature on the period when
deformation began, we suggest that since Eo-
Oligocene times (30–40 Ma) the Eastern Cordillera
has undergone a regional CW rotation of 40–50,
synchronous with crustal shortening and large-scale
bending of the Andean salient. The CW rotation is
possibly still active today, as documented by regional
GPS data from the Andes. Since 15 Ma ago, the
activity of N–S left-lateral strike-slip faults induced
counterclockwise rotations along the fault zone,
locally annulling the regional CW rotation. In
agreement with a previous model, we speculate that
mid-Miocene strike-slip activity accommodated the
progressive southward spreading of the Altiplano-
Puna high-altitude plateau, laterally migrating from the
overthickened crustal region of the salient apex
A review of the role of subduction dynamics for regional and global plate motions
No full textSubduction of oceanic lithosphere and deep slabs control several aspects
of plate tectonics. We review models of subduction dynamics that have been studied
over the last decade by means of numerical and analog experiments. Regional models
indicate that trench rollback, trench curvature, and back-arc deformation may be
explained by fl uid slabs that are ~250–500 times stiffer than the upper mantle. Slab
width and, more importantly, rheology determine the role of viscous bending, poloidalsinking
fl ow and toroidal-rollback stirring, and interactions of the slab with the
higher viscosity lower mantle. Several of these contributions can be represented by
a local sinking velocity. Back-arc deformation may then result from an imbalance if
larger-scale plate forcing leads to deviations of the convergence rate from the local
equilibrium. Lateral viscosity variations (LVVs) are also key for understanding plate
driving forces. The realism of global circulation computations has advanced and
such models with weak zones and other LVVs have lead to an improved match to
observed plate tectonic scores. Those include the correlation with plate motions, the
magnitude of intraplate deformation, and oceanic to continental plate velocity ratios.
Net rotation of the lithosphere with respect to the lower mantle may be caused
jointly by regional slab forcing and the stirring effect of cratonic keels. However,
slab models have so far only produced net rotations that are small compared to
recent hotspot reference-frame models. Progress in the next years will likely come
from a better understanding of slab strength, which is still uncertain since large-scale
subduction zone observables and laboratory results do not put strong constraints on
slab rheology. Importantly, circulation models with an improved representation of
convergent margins will help to close the gap between regional and global approaches
to subduction, and to better understand the potential role of the overriding plate
Paleomagnetic evidence for no tectonic rotation of the Central Italy Tyrrhenian margin since Upper Pliocene
No full textThe influence of paleogeography on thrust system geometries: an analogue modelling approach for the Abruzzi-Molise (Italy) case history
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