Search

Fault-related folds in fold-and-thrust belts and accretionary prisms are commonly simulated by three end-member classes of geometric models: decollement folding, fault-propagation folding, and fault-bend folding. A given model produces a fold shape that depends on the amount of shortening, the fault shape and, eventually, the fault propagation history. The great variety of geometric solutions implies that the final fold shape is adequate to distinguish among different folding mechanisms only in a limited suite of cases. Additional information to better constrain fold kinematics is provided by the analysis of growth strata patterns, which passively register the progressive evolution of deformation in the substratum. Availability of growth strata pattern templates associated with different geometric and kinematic solutions provides a useful tool for inferring the dominant kinematic pathways of natural thrust-related structures. In this paper, we present growth strata patterns associated with double-edge fault-propagation folding. The influence of the sedimentation rate, the fault shape, and the fault S/P ratio (i.e. slip versus ramp propagation rate) on growth strata architectures are investigated. Geometrical modelling and application to natural examples indicate that double-edge fault-propagation anticlines are characterised by growth triangles on both limbs. Their position and geometry relate to the ramp shape and propagation history, and on the sedimentation rate.

Fault-propagation folding is a common folding mechanism in thrust-and-fold belts and accretionary prisms. Several geometrical models relating the fold shape to the ramp shape have been proposed. In all these models, ramps always emanate from a basal fault and propagate upwards. We have developed a new kinematic and geometric model of fault-propagation folding, named double-edge fault-propagation folding. The model simulates folding at thrust ramps as a function of their nucleation site and propagation history within the folded multilayer. The fold shape depends on the initial length and location of the ramp, its dip, and the S / P ratio (i.e. incremental ramp slip versus propagation) of both the upper and lower ramp tips. This solution increases the geometrical flexibility of fault-propagation folding reducing, for example, the direct dependence between the backlimb dip and the ramp dip, as double-edge fault-propagation folding is characterised by a backlimb panel not necessary parallel to the ramp. Non-parallelism between the ramp and the backlimb is commonly observed in thrust-related anticlines, within fold-and-thrust belts and accretionary prisms. The excess layer-parallel shear imposed by the development of double-edge fault-propagation folding can be easily accommodated by discrete faulting and/or penetrative deformation. The dependence of the fold shape on the fault behaviour provides a tool for including the role of mechanical stratigraphy and environmental conditions of deformation into kinematic models. Natural examples of anticlines that could be modelled by double-edge fault-propagation are presented.

The axial zone of the Ethiopian Rift is made up of Quaternary extensional fractures and normal faults. Field analysis was performed to study the mechanism of development of the normal faults. The collected data show that the normal faults (1) are subvertical at surface, (2) have dilation proportional to the throw, and (3) end laterally as extension fractures, that is, tension fractures which gradually decrease in dilation. The minimum measured opening of normal faults is 2 m and the maximum measured dilation of the extension fractures is 4 m. The minimum measured length of normal faults is 800 m and the maximum measured length of the extension fractures is 400 m. The collected data suggest that the normal faults nucleate from wider extension fractures in the axial zone. When the extension fractures reach critical dimensions (length=∼800 m and dilation=2–4 m, corresponding to a predicted depth of ∼700 m), the shear rupture behavior controls the further propagation of the fractures at depth. This mechanism has close similarities with models previously proposed for fault formation along the oceanic ridge of Iceland. This suggests common rifting processes along diverging plates, independently from the oceanic or continental nature of the lithosphere.

The Ethiopian Rift is characterized by several Quaternary calderas. Remote sensing and field analyses were used to investigate the regional structural control on three calderas (Fantale, Gariboldi, Gedemsa) in the axial part of the rift. These calderas are located along the Wonji Fault Belt (WFB), a zone of Quaternary NNE–SSW normal faults and extensional fractures. The three calderas show E–W elongation and major E–W vent alignments, oblique with regard to the mean NW–SE extension direction. No significant evidence of E–W tectonic structures has been found near the calderas, the only relevant systems being those of the WFB. Conversely, left-lateral E–W-trending faults are present at the rift borders and on the Nubia and Somalia plateaus, implying a predominant pre-rift activity. The E–W fractures were partly reactivated during rifting, possibly controlling the development of the magma chambers. Thus, the E–W elongation of the calderas would be the surface expression of such a control, rather than the result of regional extension. An evolutionary model on the role of different structures on magmatism at different crustal levels within the rift is proposed.

We present the results of field investigations carried out at the southern termination of the Priestley Fault, a major Cenozoic right-lateral strike-slip fault system in northern Victoria Land, Antarctica. The Priestley Fault was originally traced from offshore seismic profiles. Its onshore prosecution was inferred from the regional geological picture. Our work provides the first robust dataset on the kinematics and structural architecture of the Priestley Fault. The fault system includes a principal displacement zone (PDZ), where most horizontal displacement is accounted for, and a transtensional splay zone (TSZ) in the southern side consisting of a major basin at the fault tip, the Terror Rift, and minor ones paralleling it cratonward. Part of the strike-slip displacement is transferred by fault splaying from the principal displacement zone to the basin-boundary faults in the transtensional splay zone. The principal displacement zone is characterised by strongly transpressive deformation and this contrasts with the extensional component occurring in the transtensional splay zone. Such a contrast is only apparent because the two regions are kinematically linked. Transfer of the residual right-lateral strike-slip displacement from the tip region of the principal displacement zone to the basin-boundary fault systems of the Terror Rift represents the most effective displacement compensation mechanism at the termination of the Priestley Fault. It provides an additional solution for reducing the well known and still fully unsolved discrepancy between large translations of adjacent crustal blocks and the lack of comparable displacement values in their boundary strike-slip fault systems. The unquestionable evidence of intense Cenozoic brittle deformations in north Victoria Land imposes a re-examination of the regional tectonic framework, commonly interpreted as the mere result of the Early Paleozoic Ross Orogeny.

Recent hydrocarbon discoveries in the Southern Apennines of Italy have focussed attention on the importance of studying fracturing and cataclasis in carbonate rocks because of their fundamental impact on reservoir permeability and connectivity. The Narni Anticline in the central Apennines consists of a stack of easterly-verging carbonate thrust sheets compartmentalized by extensional and strike-slip fault zones. The structure provides afield analogue for studying the evolution of superimposed fold- and fault-related fractures in carbonate reservoir rocks. The fracture pattern at the Narni Anticline developed as a result of three mechanisms: (a) layer-parallel shortening predating folding and faulting; (b) thrust-related folding and further thrust breakthrough; and (c) extensional and strike-slip faulting. Along-strike (longitudinal) fractures developed during progressive rollover fault-propagation folding, and their intensity depends on the precise structural position within the fold: fracture intensity is high in the forelimb and low in the crest. The 3-D architecture of the mechanical anisotropy associated with thrusting, folding, and related fracturing constrained the location and geometry of subsequent extensional and strike-slip faulting. The superimposition in damage zones of a fault-related cleavage on the pre-existing fracture pattern, which is associated with layer-parallel shortening and thrust-related folding, resulted in rock fragmentation and comminution, and the development of cataclastic bands. The evolution of fracturing in the Narni Anticline, its role in constraining thrust breakthrough trajectories and the location of extensional and strike-slip faults, and the final development of low-permeability cataclastic bands, will be relevant to studies of known oilfields in the Southern Apennines, as well as for future exploration.

A sandbox analog modeling research program was used to study the detailed evolution of doubly-vergent thrust wedges. High-resolution multilayers of thin alternating sand and mica layers were used in contractional Coulomb wedge experiments to simulate deformation of anisotropic, brittle upper crustal strata in doubly-vergent orogens. Experiments incorporating syntectonic sedimentation in foreland basins and in piggyback basins were also carried out. Our laboratory models evolved in two main stages: (1) initial high-velocity thrusting in the retrowedge and high-frequency together with low displacement folding and thrusting in the prowedge; and (2) low-frequency, high-displacement synchronous thrusting in the prowedge and low-velocity thrusting in the retrowedge. Transition from stage I to stage II occurred when the growing wedges reached the critical height at which they behaved as a backstop for further prowedge accretion. Addition of syntectonic sediments increased the persistence of stage I and triggered out-of-sequence thrusting in the axial zone of the experimental orogens. Thrust motion was stick-slip. Retrovergent thrusting occurred along a long-lived ramp whose lower tip was located at the subduction slot. Provergent kink bands nucleated at the subduction slot in stage I. In contrast, during the second stage of wedge evolution, kink bands nucleated in a piggyback fashion in the foreland far from the subduction slot and then evolved into high-displacement faults that remained active up until the end of the experiments, at progressively decreasing rates of thrusting. The axial zones of the model wedges were characterized by fast uplift rates during stage I due to backward translation of the belt along the retrovergent, long-lived ramp and due to the localization of deformation close to the subduction slot. Outward migration of the deformation front in the prowedge region during stage II caused the progressive decrease in the rate of the wedge uplift, until it eventually stopped. Analytical models to quantify the Coulomb behavior in the wedges validated the reversal of thrust polarity with increasing shortening, triggered by the buildup of the topographic load during deformation. This thrust polarity reversal highlights problems with the classic concept of back thrusting as a reflection of a significant change in the deformation regime. Our results compare well with the kinematic evolution of natural accretionary prisms and of thrust-and-fold belts such as the Lesser Antilles Arc System, the Mediterranean Ridge, and the Pyrenees.

The Tyrrhenian margin of Central Italy underwent extension during Pliocene and Quaternary. Extension occurred mainly through NW–SE normal faults, bordering a sequence of Plio-Quaternary basins. These basins are offset by coeval NE–SW faults, which show strike–slip and normal motions and have been interpreted as transfer faults. Plio-Quaternary volcanic activity along the margin occurred along a NW–SE belt, systematically in correspondence with NE–SW transverse systems. The Campi Flegrei Volcanic District (CFVD), on the Southern Tyrrhenian margin, consists of an active NE–SW volcanic ridge developed along NE–SW fractures. We performed a structural field analysis with analogue and mechanical models to investigate the role of transverse structures upon volcanism at Campi Flegrei. Field analysis at Campi Flegrei recognized NE–SW and, to a lesser extent, coeval NW–SE active fractures. Analogue experiments have simulated the development of transfer fault systems in brittle extensional domains. The experiments show that subvertical transfer faults connect offset adjacent normal faults dipping 60°. The mechanical model is based on the stress equations in uniaxial lithostatic conditions and absence of regional stresses. It shows how pre-existing subvertical fractures require the smallest magmatic pressures to be penetrated. For a given magmatic pressure, subvertical fractures might be penetrated more deeply, tapping more easily primitive magmas. These results suggest that the CFVD is located along a NE–SW transfer zone connecting NW–SE regional normal faults. Volcanic activity along such NE–SW trend would be induced by the subvertical dip of the transfer faults. The subvertical dip of transfer faults also suggests an explanation for the emission of the more primitive products along NE–SW systems at Campi Flegrei. These considerations find a wider application on the remaining volcanic districts of the margin, located in the same overall structural setting.

A lithologic investigation has been performed on the Tarn Flat area, Antarctica, based on Landsat-TM and SPOT-XS processed images and on radiometric field data acquired by an EXOTECH radiometer. Results from the field survey, performed during the austral summer 1994-95 expedition, were used to verify the ability of satellite images to discriminate between the main rock. Principal Component transformation allowed to enhance the spectral information of rocks, despite the high band correlation of TM data, while high-pass filtering and TM-SPOT merging allowed a fairly accurate detection of morphologic features. A supervised classification has been carried out on the processed satellite images as a further demonstration of the utility of remote observation to investigate extreme environments.

New geological, geophysical and seismological data produced in the last decade allow an improved definition of the kinematics of the Tyrrhenian Sea-central Apennines-Adriatic Sea system. The integration of these different types of dataset outlines a complex E-W deformational belt running from the Adriatic Sea, at Gargano latitudes, to the Latium-Abruzzi Platform domain (central Apennines). Its possible prosecution in the Tyrrhenian Sea is discussed. This belt has its own seismotectonic characteristics, and divides the Apennines into two zones with different seismotectonic behaviour. All these data were integrated into a multidisciplinary model that results in the introduction of a strike-slip displacement sometimes in Pliocene to Recent times along the central Apennines-Adriatic Sea E-W belt. This relative motion can take for the strike-slip block tectonics observed in the central Apennines as well as for the uplift of Gargano and Tremiti Islands areas, including their seismicity. The displacement is related to a differing behaviour of the chain-foreland systems across this bend and can be justified either by assuming a partially active sinking of the southern Adriatic lithosphere or a slower sinking processes in the northern Adriatic one.

New seismological and structural data from the central Adriatic—Gargano promontory area demonstrate that the current models of an aseismic and slightly deformed Adriatic block have to be revised. A seismically active deformational belt is mapped along two main fault systems, the Tremiti Islands and Mattinata faults. Moreover, geologic and geophysical evidence suggests that a more extensive lithospheric boundary may cut across the central Italian peninsula to the Tyrrhenian basin.

An integrated study of onshore and offshore geology of the Ross Sea region (namely, Victoria Land, north of Ross Island, and the Ross Sea, Antarctica) has revealed a complex, post-Eocene tectonic framework. Regional NW-SE right-lateral, strike-slip faults are the outstanding feature of this framework and overprint an older Mesozoic extensional event, responsible for formation of N-S basins in the Ross Sea. The Cenozoic framework includes kinematic deformation and reactivation along the NW-SE faults, including formation of pull-apart basins, both positive and negative flower structures, and push-up ridges. N-S extensional faults are well developed between NW-SE faults and indicate E-W extension during the Cenozoic, produced by the NW-SE right-lateral strike-slip motion together with regional crustal extension. NNW-SSE compression, induced by the right-lateral, strike-slip kinematics, is indicated by locally inverted NE-SW faults and basins. The evolution, geometry, and location of the Rennick Graben and the Lanterman Range fit well into this model. Variations in the deformational style across the region can be linked to corresponding variations in the bulk crustal rheology, from brittle behavior in the west, to ductile deformation (at subseismic-scale resolution) near the Eastern Basin. A semibrittle region that favors N-S clustering of Cenozoic magmatic activity lies in between. In this region, Cenozoic volcanoes develop at the intersections of the NW-SE and the major N-S faults. The NW-SE faults cut almost continually from the Ross Sea to East Antarctica through lithospheric sectors with different rheology and thickness. At least two of the NW-SE faults correspond to older Paleozoic terrane boundaries in northern Victoria Land. The NW-SE faults link in the Southern Ocean with major transform faults related to the plate motions of Australia, New Zealand, and Antarctica.

""\\"Regional geodynamics is responsible of a series of effects. that notably include tectonics and seismicity. They in turn control. the morphology of the surface of the planet. The regional. dimension of the peri-Tyrrhenian orogen reveals that its. evolution is deeply involved in a lithospheric scale dynamics. As. a result, we expect different observable and\\\\\\\/or measurable effects. at the various scales from the outcrop evidences to the subcontinental. deformation corridors. Effects at the various scales. not necessarily are directly related, and their relations should be. carefully understood taking into account both their geometry and. spatial distribution. A classical example is represented by an en. echelon system. Each single fracture is the effect of a local. extension, yet their spatial distribution shows that these local. stresses are the effect of a larger scale shear zone with a different. orientation.. Remotely sensed images proved the existence on the Earth. surface of linear features with dimensions spanning over three. order of magnitude: from hundreds of meters to thousand of. kilometers. Such features are referred to image lineaments and. are generally related to alignment of morphological features in. continental environment such as onshore crests, ridges, valleys. and troughs. In the oceans lineaments relate to the scars. associated to the seafloor spreading and fracture zones. Synthetic. scale images of tectonically active regions revealed the existence. of groups of regional scale lineaments on the earth surface. appearing as image textural anisotropies. They clusters around. preferential orientations to form lineament domains. These. domains occupies well defined areas to form lineament swarms.. Lineament domain analysis on regional scale images of the. Earth surface proved a useful tool to investigate regions. characterized by active tectonics (Wise et al., 1985; Funiciello et. al., 1977; Cianfarra & Salvini, 2008).. Both the Tyrrhenian Sea and the Apennines are geodynamic. blocks within the collisional puzzle between Africa and Europe. in the Central Mediterranean area.. In this work we explore the possible relations between these. two blocks by lineaments analysis. The found lineament domains. were interpreted as reflecting the structural grain of these two. geodynamic regions. Lineament detection was done by using. original automatic methods. Domains were identified by. statistical analysis. This work analyses lineaments detectable by. simulating different directions of lighting condition on the. DEMs. This allowed to properly evaluate the influence of the. light condition changes in the lineaments produced by. morphological features. The comparison among the analyses. showed that the different lighting conditions induce rotations of. few degrees of the mean azimuth of each lineament domain. This. rotation relate to the result of two contrasting effects: tectonics,. that tends to enhance linear morphologies, and erosion that. progressively smoothes them. Lineament domains characterised. by small rotations relate to morphologies where the tectonic. processes prevail on the erosional ones. Lineament domains. therefore have rotations inversely proportional to their tectonic. activity.\\"""