301 research outputs found
The External Ligurian units (Northern Apennine, Italy): from rifting to convergence of a fossil ocean-continent transition zone
The External Ligurian Units of the Northern Apennine are interpreted as derived from the continent-ocean transition domain at the northern thinned conti- nental margin of the Adria microplate, i.e. the External Ligurian domain. The evolution of this paleogeographic realm from pre-orogenic times to the Eo- alpine and Meso-alpine tectonics is presented here, through a review of stratigraphic, petrological and structural data. The tectono-metamorphic evolution started in the Late Carboniferous-Early Permian (about 290 Ma), with the emplacement at deep crustal levels of the gabbroic protholits of mafic granulites. These lower continental crust rocks subsequentely underwent Permo-Triassic tectonic exhumation and were finally exhumed at shallow crustal levels in mid- dle Jurassic. The latter period was characterized by extensive brittle faulting at shallow crustal levels, giving rise to extensional allochtons formed by stretched slices of upper continental crust (mainly granitoids). At deep structural levels high temperature shearing of ophiolitic gabbros took place. Opening of the Lig- urian Tethys is finally testified by the basalt emplacement and radiolarian chert sedimentation in the Late Jurassic.
During Late Cretaceous, development of Alpine intraoceanic subduction led to the inversion of the External Ligurian domain: the Eo-alpine deformation is recorded by syn-tectonic sedimentation of the Complessi di Base Auct., by development of very low-grade metamorphism and deformation at about 80 Ma. Middle Eocene deformation related with collision and indentation of the Adria with the Alpine accretionary wedge can be subdivided in two main stages: the first one (Ligurian Phase 1) implies large-scale, westward displacement of the EL Units, whereas the second stage (Ligurian Phase 2) is characterized by east- verging structures probably driven by the thinning of the preexisting nappe pile associated with exumation of underplated HP/LT Alpine units
Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica
The switching in deformation mode (from distributed to localized)
and mechanisms (viscous versus frictional) represent a relevant issue in the
frame of crustal deformation, being also connected with the concept of the
brittle–ductile transition and seismogenesis. In a subduction environment,
switching in deformation mode and mechanisms and scale of localization may be
inferred along the subduction interface, in a transition zone between the
highly coupled (seismogenic zone) and decoupled deeper aseismic domain
(stable slip). However, the role of brittle precursors in
nucleating crystal-plastic shear zones has received more and more
consideration being now recognized as fundamental in some cases for the
localization of deformation and shear zone development, thus representing a
case in which switching deformation mechanisms and scale and style of
localization (deformation mode) interact and relate to each other. This
contribution analyses an example of a millimetre-scale shear zone localized
by brittle precursor formed within a host granitic protomylonite. The studied
structures, developed in ambient pressure–temperature (P–T) conditions of low-grade blueschist facies
(temperature T of ca. 300 °C and pressure P ≥ 0. 70 GPa)
during involvement of Corsican continental crust in the Alpine subduction. We
used a multidisciplinary approach by combining detailed microstructural and
petrographic analyses, crystallographic preferred orientation by electron backscatter diffraction (EBSD), and
palaeopiezometric studies on a selected sample to support an evolutionary
model and deformation path for subducted continental crust. We infer that the
studied structures, possibly formed by transient instability associated with
fluctuations of pore fluid pressure and episodic strain rate variations, may
be considered as a small-scale example of fault behaviour associated with a
cycle of interseismic creep and coseismic rupture or a new analogue for
episodic tremors and slow-slip structures. Our case study represents,
therefore, a fossil example of association of fault structures related to
stick-slip strain accommodation during subduction of continental crust
Late Palaeozoic tectonics in Central Mediterranean: a reappraisal
A revision of late Palaeozoic tectonics recorded in Tuscany, Calabria and Corsica is here presented. We propose that, in
Tuscany, upper Carboniferous-Permian shallow-marine to continental sedimentary basins, characterized by unconformities
and abrupt changes in sedimentary facies, coal-measures, red fanglomerate deposits and felsic magmatism,
may be related with a transtensional setting where upper-crustal splay faults are linked with a mid-crustal shear zone.
The remnants of the latter can be found in the deep-well logs of Pontremoli and Larderello-Travale in northern and
southern Tuscany respectively. In Calabria (Sila, Serre and Aspromonte), a continuous pre-Mesozoic crustal section
is exposed, where the lower-crustal portion mainly includes granulites and migmatitic paragneisses, together with
subordinate marbles and metabasites. The mid-crustal section, up to 13 km-thick, includes granitoids, tonalitic to
granitic in composition, emplaced between 306 and 295 Ma. They were progressively deformed during retrograde
extensional shearing, with a final magmatic activity, between 295 ± 1 and 277 ± 1 Ma, when shallower dykes were
emplaced in a transtensional regime. The section is completed by an upper crustal portion, mainly formed by a
Palaeozoic sedimentary succession deformed as a low-grade fold and thrust belt, and locally overlaying mediumgrade
paragneiss units. As a whole, these features are reminiscent of the nappe zone domains of the Sardinia Variscan
Orogen. In Corsica, besides the well-known effusive and intrusive Permian magmatism of the “Autochthonous”
domain, the Alpine Santa Lucia Nappe exposes a kilometer-scale portion of the Permian lower to mid-crust, exhibiting
many similarities to the Ivrea Zone. The distinct Mafic and Granitic complexes characterizing this crustal domain
are juxtaposed through an oblique-slip shear zone named Santa Lucia Shear Zone. Structural and petrological data
witness the interaction between magmatism, metamorphism and retrograde shearing during Permian, in a temperature
range of c. 800–400 °C. We frame the outlined paleotectonic domains within a regional-scale, strain–partitioned,
tectonic setting controlled by a first-order transcurrent/transtensional fault network that includes a westernmost fault
(Santa Lucia Fault) and an easternmost one (East Tuscan Fault), with intervening crustal domains affected by extensional
to transtensional deformation. As a whole, our revision allows new suggestions for a better understanding of
the tectonic framework and evolution of the Central Mediterranean during the late Palaeozoic
Design and performance of a Martian autonomous navigation system based on a smallsat constellation
Deciphering the genesis and evolution of the Martian polar caps can provide crucial understanding of Mars' climate system and will be a big step forward for comparative climatology of the terrestrial planets. The growing scientific interest for the exploration of Mars at high latitudes, together with the need of minimizing the resources onboard landers and rovers, motivates the need for an adequate navigation support from orbit. In the context of the ARES4SC study, we propose a novel concept based on a constellation that can support autonomous navigation of different kind of users devoted to scientific investigations of those regions. We study two constellations, that differ mainly for the semi-major axis and the inclination of the orbits, composed of 5 small satellites (based on the SmallSats design being developed in Argotec), offering dedicated coverage of the Mars polar regions. We focus on the architecture of the inter-satellite links (ISL), the key elements providing both ephemerides and time synchronization for the broadcasting of the navigation message. Our concept is based on suitably configured coherent links, able to suppress the adverse effects of on-board clock instabilities and to provide excellent range-rate accuracies between the constellation's nodes. The data quality allows attaining good positioning performance for both constellations with a largely autonomous system. Indeed, we show that ground support can be heavily reduced by employing an ISL communication architecture. Periodic synchronization of the clocks on-board the constellation nodes with terrestrial time (TT) is enabled through the main spacecraft (the mother-craft), the only element of the constellation enabling radio communication with the Earth. We report on the results of numerical simulations in different operational scenarios and show that a very high-quality orbit reconstruction can be obtained for the constellation nodes using a batch-sequential filter or a batch filter with overlapping arcs, that could be implemented on board the mother-craft, thus enabling a high level of navigation autonomy. The assessment of the achievable positioning accuracy with this concept is fundamental to evaluate the feasibility of a future positioning system providing a global coverage of the red planet
Growth of a sinkhole in a seismic zone of the northern Apennines (Italy)
Sinkhole collapse is a major hazard causing substantial social and economic losses. However, the surface deformations and sinkhole evolution are rarely recorded, as these sites are known mainly after a collapse, making the assessment of sinkhole-related hazard challenging. Furthermore, more than 40% of the sinkholes of Italy are in seismically hazardous zones; it remains unclear whether seismicity may trigger sinkhole collapse. Here we use a multidisciplinary data set of InSAR, surface mapping and historical records of sinkhole activity to show that the PrĂ di Lama lake is a long-lived sinkhole that was formed in an active fault zone and grew through several events of unrest characterized by episodic subsidence and lake-level changes. Moreover, InSAR shows that continuous aseismic subsidence at rates of up to 7.1mmyr-1occurred during 2003-2008, between events of unrest. Earthquakes on the major faults near the sinkhole do not trigger sinkhole activity but low-magnitude earthquakes at 4-12 km depth occurred during sinkhole unrest in 1996 and 2016. We interpret our observations as evidence of seismic creep at depth causing fracturing and ultimately leading to the formation and growth of the PrĂ di Lama sinkhole
Reciprocal regulation of PKA and rac signaling
Activated G protein-coupled receptors (GPCRs) and receptor tyrosine kinases relay extracellular signals through spatial and temporal controlled kinase and GTPase entities. These enzymes are coordinated by multifunctional scaffolding proteins for precise intracellular signal processing. The cAMP-dependent protein kinase A (PKA) is the prime example for compartmentalized signal transmission downstream of distinct GPCRs. A-kinase anchoring proteins tether PKA to specific intracellular sites to ensure precision and directionality of PKA phosphorylation events. Here, we show that the Rho-GTPase Rac contains A-kinase anchoring protein properties and forms a dynamic cellular protein complex with PKA. The formation of this transient core complex depends on binary interactions with PKA subunits, cAMP levels and cellular GTP-loading accounting for bidirectional consequences on PKA and Rac downstream signaling. We show that GTP-Rac stabilizes the inactive PKA holoenzyme. However, β-adrenergic receptor-mediated activation of GTP-Rac–bound PKA routes signals to the Raf-Mek-Erk cascade, which is critically implicated in cell proliferation. We describe a further mechanism of how cAMP enhances nuclear Erk1/2 signaling: It emanates from transphosphorylation of p21-activated kinases in their evolutionary conserved kinase-activation loop through GTP-Rac compartmentalized PKA activities. Sole transphosphorylation of p21-activated kinases is not sufficient to activate Erk1/2. It requires complex formation of both kinases with GTP-Rac1 to unleash cAMP-PKA–boosted activation of Raf-Mek-Erk. Consequently GTP-Rac functions as a dual kinase-tuning scaffold that favors the PKA holoenzyme and contributes to potentiate Erk1/2 signaling. Our findings offer additional mechanistic insights how β-adrenergic receptor-controlled PKA activities enhance GTP-Rac–mediated activation of nuclear Erk1/2 signaling
Deciphering the tectono-stratigraphic evolution of the East Pisco Basin (southern Peru): new insights from the geological mapping of its central portion
The Cenozoic fill of the East Pisco Basin (EPB) preserves the sedimentary record of several episodes of deformation of the forearc crust along the Peruvian margin. The 1:50,000 scale geological map presented here covers an area of about 1,000 km2 lying astride the Ica River and, by establishing a first-order tectonostratigraphic frame for the exposed mid-Eocene–upper Miocene succession, contributes to our understanding of the timing and mode of basin filling and deformation. In the study area, deposition initiated onto the PaE0 nonconformity during the middle Eocene time and continued under an extensional regime until early Oligocene time, with a break in deposition recorded by the OE0 unconformity separating the Paracas and Otuma sequences (megasequence P). During this time interval, a single forearc Pisco Basin extended between an offshore outer forearc high and the Western Cordillera. An Oligocene relative sea-level fall, probably resulting from a combination of tectonic inversion and multiple events of eustatic lowstand, led the Pisco Basin to become subaerially exposed. Evidence for this phase of deformation is recorded by the conspicuous CE0 angular unconformity interposed between megasequences P and N. The oldest normal fault populations documented here consist of NNW- and ENE-trending faults largely predating the CE0 erosional hiatus. This widespread extensional faulting was accompanied by the exhumation of the Outer Shelf High-Coastal Cordillera, which segmented the earlier, Paleogene Pisco Basin into the present-day inner EPB and outer West Pisco Basin. Different tectonic processes have been invoked to explain the Oligocene uplift of the extensional Peruvian forearc basins and formation of the Outer Shelf High, including crustal thickening by underplating at an erosive margin or inversion by propagation of basement-rooted, westverging thrust faults. By earliest Miocene time, uplift ceased and subduction erosion and thinning of the overriding plate resulted in renewed subsidence, rise in relative sea level, and marine transgression over the CE0 unconformity with deposition of the lower Miocene Chilcatay and middle to upper Miocene Pisco composite sequences (megasequence N). The early Miocene phase of extension and associated subsidence was followed by a late Miocene contractional tectonic event, with shortening being accommodated by: (i) oblique-slip (reverse plus dextral) reactivation of inherited NE-trending extensional faults, and development of associated fault-parallel hanging-wall anticlines; and (ii) renewal tectonic uplift of the southwestern basin margin, as suggested by the fanning geometry of the northeast-dipping strata of the Pisco composite sequence and their progressive onlap on top of the basement towards the northeastern, internal margin of the basin
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