1,720,966 research outputs found
Papini, Vailati e la "Cultura dell'Anima". Atti dei Convegni di studio Chieti, Maggio 2009 e gennaio 2010
No full textRole of pre-existing topography and overburden on strain-partitioning of oblique doubly-vergent convergent wedges
No full textScaled sandbox modeling was used to analyze the three-dimensional aspects of strain partitioning along obliquely convergent margins that underwent a subduction polarity reversal event. In the experiments, the first phase of shortening produced a preexisting topography that affected wedge kinematics during the second phase. Increasing degrees of obliquity during the first shortening phase produced different amounts of inherited topography and overburden, giving way to different effects on wedge response during the second phase of shortening. During the second phase the models with an inherited heavy overburden show an anomalous orientation for Riedel shears predating the development of a margin-parallel strike-slip fault. These shears are oriented at an angle that is higher than kinematically predicted with respect to the subduction slot, suggesting a transient rotation of the stress applied by the obliquity of subduction. In contrast, experiments with a lighter overburden do not show this inconsistency. In addition, all the models displayed an unexpectedly high accretion rate during the second phase of shortening, which we interpret to be dependent on topographical slope breaks inherited after the first phase of shortening and the critical asymmetrical architecture of doubly vergent wedges
Complex faulting sequences controlled by dynamic topography in 3D experimental deformation of doubly-vergent coulomb wedges
No full textIn this paper sandbox modelling was used to investigate the dynamic effect of localised syntectonic erosion and\or sedimentation on the deformation mechanics of accretionary systems. High obliquity was chosen as the main boundary condition to analyse 3D strain partitioning of a doubly-vergent Coulomb wedge for the particular case in which a subduction po1artv reversal event affected wedge development. In the experiments the first phase of shortening ( P1) produces a preexisting topography affecting wedge development during second phase ( P2). The elevation potential can be varied in the models via sequential events of syntectonic denudation and/or sedimentation performed on distinct sectors of the deforming wedge. Experimental results suggest that the parallelism between the imbricates at the thrust front and the strike-slip fault at the rear of the prism predicted by theoretical models is valid only at steady-state when failure conditions exist everywhere at the basal décollement. Before this stage different velocity fields characterise mass transfer in distinct sectors leading to unexpected wedge behavior during which superficial extension or compression, both located i n the axial zone, predate the full development of a strike-slip fault
The northern Apennines: tracking an ancient polarity reversal event from E-dipping to W-dipping subduction.
No full textThe effect of tectonic overloading on strain partitioning of doubly-vergent Coulomb wedges: a 2D-3D sand-box modelling approach
No full textThe preliminary results of a sand-box experimental program are presented in this paper. The aim of the study is to analyse the effect of a pre-existing load and wedge taper angle on the development and strain partitioning of a doubly-vergent Coulomb wedge. By simulating a subduction polarity reversal, two distinct and interacting thrust systems with opposite vergence were produced, and their relationship evaluated. The presence of previously built topography strongly alters the way in which deformation is distributed inside the wedge. In particular, 2D models indicate that the axial zone inherited from the first phase of contraction diminishes the block uplift concentrated above the step-up shear (or retro-thrust) during the second phase. Therefore, a high accretion rate characterises the initial stages of deformation. In 3D, this accretion produces an anomalously wide prowedge compared to theoretical model predictions for highly oblique convergent settings. Moreover, the whole wedge is not characterised by total strike-slip partitioning on a single fault
The structure of the Aurunci Mountains (Southern Lazio): a balanced cross section and its restoration.
No full textI Monti Ausoni-Aurunci costituiscono la parte sudoccidentale
del dominio della Piattaforma Laziale-Abruzzese, dove affiora una
potente successione carbonatica dal Trias superiore al Cretaceo superiore
di mare sottile, costituita essenzialmente da calcari fangosostenuti,
calcari dolomitici e dolomie (ACCORDI et alii, 1988; CARANNANTE
et alii, 1978; CHIOCCHINI et alii, 1994).
Attraverso una dettagliata analisi di superficie, ottenuta tramite
un rilevamento geologico alla scala 1:25.000, ed una analisi strutturale
alla meso ed alla macro-scala, viene proposta una sezione geologica
bilanciata tra Gaeta e Campodimele. Utilizzando software che
sfruttano il line-length balancing methods, sono stati calcolati i tassi
di estensione e di raccorciamento, che possono essere generalizzati
all’intera struttura studiata. Questa presenta una notevole complessità
strutturale, caratterizzata dalla sovrapposizione delle strutture
distensive, legate all’estensione tirrenica su quelle compressive medio-
mioceniche a vergenza nord-orientale. Nell’area infatti sono riconoscibili
due unità tettoniche principali, sovrapposte mediante un
piano di sovrascorrimento a generale andamento appenninico che
presenta una traiettoria tipo ramp-flat-ramp. Nel settore sudoccidentale
dell’area il sovrascorrimento determina la sovrapposizione dei
termini triassico-giurassici su quelli cenomaniani; mentre nel settore
centrale un piano ausiliario posto alla base del cretacico determina
soltanto un raddoppio della porzione cretacica della successione.
Probabilmente associabili alle fasi finali della deformazione sono infine
i sistemi di faglie normali a direzione prevalentemente appenninica;
mentre parte delle strutture distensive minori mostrano direzioni
antiappenniniche e riattivano in senso normale anche faglie
preesistenti a direzione N-S.
I calcoli di bilanciamento hanno fornito valori di raccorciamento
pari a 6.6 km (32.8%) mentre i valori di estensione calcolati
sono pari a 4.9 km (26.9%)
Effect of unbalanced topography and overloading on Coulomb wedge kinematics: Insights from sandbox modeling
No full textThis study addresses the effect of variable unbalanced topography and overload on the kinematics of a fold and thrust belt developed within a collisional belt that underwent a subduction polarity reversal event. This was done by physical modeling of doubly vergent Coulomb wedges, using sand as an analogue material. During the experimental procedure a preexisting topography was generated by a first phase of subduction in one direction. A second phase of subduction was then initiated in the opposite direction ( simulating a subduction flip). An anomalous, strong frontal growth for the wedge during the second phase was experimentally shown to be dependent upon surface slope breaks and the critical asymmetrical architecture achieved by the wedge at mature stages of deformation. The latter is suggested to be the rule for doubly vergent orogens at steady state, even after a subduction flip. During the experiments, surface processes, like syntectonic erosion and sedimentation, markedly altered mass transfer within the wedge. In particular, lowering the surface slope by syntectonic erosion favored cycling between accretion and underthrusting modes. By contrast, a sudden syntectonic sediment load in the prowedge region promoted prolonged phases of underthrusting, retarding accretion of new imbricates at the prowedge toe. However, at later stages of deformation the prowedge was forced to regain its characteristic minimum critical taper as predicted by theory and did so by the sudden nucleation of long, flat thrust units, rapidly rebalancing the asymmetry between prowedge and retrowedge regions. The experiments suggest that given a fixed critical taper related to time-invariant frictional properties along the wedge bounding surfaces, deformation does vary within the wedge according to time-varying location of normal stress surpluses and unbalanced topography acting on potential failure surfaces. These, in turn, alter the equilibrium between prowedge and retrowedge basal detachments that is here considered to be a major factor controlling the self-regulating dynamics of collisional orogens
THE STRUCTURE OF THE AURUNCI MOUNTAINS (SOUTHERN lAZIO): A BALANCED CROSS SECTION AND ITS RESTORATION
No full textUnbalanced topography. Localised denudation/sedimentation and dynamic strain partitioning in 3D experimental Coulomb wedges: a synopsis.
No full textIn this paper, sandbox modelling was used to investigate the dynamic effect of growing topography on the deformation mechanics of accretionary systems. High obliquity was chosen as the main boundary condition to analyse 3D strain partitioning of a doubly-vergent Coulomb wedge, for the particular case in which a subduction polarity reversal event affected wedge development. In the experiments, the first phase of shortening produces a pre-existing topography affecting wedge kinematics during the second phase. Different degrees of obliquity set for the first phase produced different amounts of inherited topography, thus giving way to variable effects on wedge response to shortening during the second phase. In addition, the elevation potential during second phase could be varied in the models via sequential events of syn-tectonic denudation and/or sedimentation, performed on distinct sectors of the deforming wedge.
Experimental results suggest that both timing and mode of retrothrust activation are crucial factors in influencing critical wedge mechanics as a whole. These may control localisation of compressive stress surpluses in the axial region, thus temporarily suppressing margin-parallel total strike-slip partitioning. Differential disequilibrium characterizing the topographic profile with respect to a given basal/internal coefficients of friction ratio will have a strong impact on the wedge growth history. Moreover, the parallelism between the imbricates at the thrust front and the strike-slip fault at the rear of the prism predicted by theoretical models is valid only at steady-state, when failure conditions exist everywhere at the basal décollement. Before this stage, uneven mechanical conditions at the base of the prowedge region produced an irregular distribution of the velocity fields within the deforming wedge, which caused, in turn, non-collinear mass transfer vectors between the prowedge and retrowedge regions. This led to unexpected wedge behaviour during which superficial extension or compression, both located in the axial zone, predated the full-development of a strike-slip fault
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