Coastal neotectonics in Southern Central Andes: uplift and deformation of marine terraces in Northern Chile (27°S)

Neotectonic observations allow a new interpretation of the recent tectonic behaviour of the outer fore arc in the Caldera area, northern Chile (27°S). Two periods of deformation are distinguished, based on large-scale Neogene to Quaternary features of the westernmost part of the Coastal Cordillera: Late Miocene to Early Pliocene deformations, characterized by a weak NE–SW to E–W extension is followed by uppermost Pliocene NW–SE to E–W compression. The Middle Pleistocene to Recent time is characterized by vertical uplift and NW–SE extension. These deformations provide clear indications of the occurrence of moderate to large earthquakes. Microseismic observations, however, indicate a lack of shallow crustal seismicity in coastal zone. We propose that both long-term brittle deformation and uplift are linked to the subduction seismic cycle.     

Current states of stress in the northern Andes as indicated by focal mechanisms of earthquakes

Systematic inversion of double couple focal mechanisms of shallow earthquakes in the northern Andes reveals relatively homogeneous patterns of crustal stress in three main regions. The first region, presently under the influence of the Caribbean plate, includes the northern segment of the Eastern Cordillera of Colombia and the western flank of the Central Cordillera (north of 4°N). It is characterized by WNW–ESE compression of dominantly reverse type that deflects to NW–SE in the Merida Andes of Venezuela, where it becomes mainly strike–slip in type. A major bend of the Eastern thrust front of the Eastern Cordillera, near its junction with the Merida Andes, coincides with a local deflection of the stress regime (SW–NE compression), suggesting local accommodation of the thrust belt to a rigid indenter in this area. The second region includes the SW Pacific coast of Colombia and Ecuador, currently under the influence of the Nazca plate. In this area, approximately E–W compression is mainly reverse in type. It deflects to WSW–ENE in the northern Andes south of 4°N, where it is accommodated by right-lateral displacement of the Romeral fault complex and the Eastern front of the northern Andes. The third, and most complex, region is the area of the triple junction between the South American, Nazca and Caribbean plates. It reveals two major stress regimes, both mainly strike–slip in type. The first regime involves SW–NE compression related to the interaction between the Nazca and Caribbean plates and the Panama micro-plate, typically accommodated in an E–W left-lateral shear zone. The second regime involves NW–SE compression, mainly related to the interaction between the Caribbean plate and the North Andes block which induces left-lateral displacement on the Uramita and Romeral faults north of 4°N.Deep seismicity (about 150–170 km) concentrates in the Bucaramanga nest and Cauca Valley areas. The inversion reveals a rather homogeneous attitude of the minimum stress axis, which dips towards the E. This extension is consistent with the present plunge of the Nazca and Caribbean slabs, suggesting that a broken slab may be torn under gravitational stresses in the Bucaramanga nest. This model is compatible with current blocking of the subduction in the western northern Andes, inhibiting the eastward displacement of slabs, which are forced to break and sink in to the asthenosphere under their own weight.     

Stratigraphic and regional distribution of fractures in Barremian–Aptian carbonate rocks of Eastern Oman: outcrop data and their extrapolation to Interior Oman hydrocarbon reservoirs

The carbonates of the Barremian to Aptian Qishn Formation are outcrop equivalents to major hydrocarbon reservoirs in the Middle East and in Oman specifically. The rocks are exposed in the Haushi–Huqf area of eastern Oman where they are affected by pervasive jointing and localized folding and faulting. Information gathered in the Huqf outcrops can be used to formulate predictions on fracture patterns in adjacent reservoirs. Systematic joints are confined to few meters-thick intervals of widely differing lithologies, which can be correlated over hundreds of square kilometers. Over the entire area, systematic joints are typically more than tens of meters long, have spacings of 4–18 cm and homogeneous morphologies. These joints are interpreted to be of Late Aptian age. The dominant set of joints strikes consistently NW–SE and developed parallel to the causative maximum horizontal compression S_H. The direction of compression is at an high angle to the two major tectonic domains of the region, the subsiding Oman Interior basins and the elevated Haushi-Huqf High. NW–SE compression is proposed to have caused crustal/lithospheric buckling and thereby to have controlled Jurassic to Early Tertiary patterns of vertical movements. In such a scenario, the direction of compression is predicted to be constant over the entire domain. It is thus expected that Qishn carbonates in the subsiding Oman Interior basins also experienced NW–SE compression and developed systematic joints similar to those observed in the Huqf region. In the Neogene, with the establishment of the Zagros stress field, the maximum horizontal compression became roughly N–S, thereby possibly leading to the closure of pre-existing joint systems.     

Diffusional mass transfer processes in pitted pebble conglomerates

The diffusional mass transfer of soluble components in pitted pebble conglomerates from the Alpine Molasse and the Carboniferous of northern Spain has been studied using electron microprobes. Two categories of pitted pebble conglomerates are distinguished depending on the presence or absence of an affected zone within the pebble which has suffered volume loss. In these affected zones there is a reduction of mobile components—Ca, Ba, Sr, and sometimes Si, and a concentration of immobile components—Mg, Al, Fe, Mn, Si, K, and Ti. The changes in relative abundances of different elements across these zones are shown to be dependent on the mineralogy of the dissolving pebble. This is interpreted as being partly due to the modification of the stress fields, developed within pebbles due to their composition. Theoretical predictions of the rates of pebble pitting are shown to be in reasonable agreement with natural examples. Most of the deformational structures in these conglomerates were produced by a diffusional mass transfer process such as pressure solution.     

Evolution of intraplate stress fields under multiple remote compressions: The case of the Iberian Chain (NE Spain)

The stress evolution of the central-eastern Iberian Chain during the Tertiary compression has been a matter of discussion during the last decades. In particular, there is not a complete agreement on whether the tectonic evolution is controlled by different external stress fields or it is essentially related to a single stress field with multiple stress perturbations. A systematic procedure to discriminate between these two hypotheses is proposed. The procedure involves statistical computing of local compression directions, identifying and ‘filtering’ stress deviations on outcrop to map scale, and timing of paleostresses. The latter has been interpreted from both analysis of cross-cut relationships of structures and consideration of the palaeostress record through the sequence of syntectonic sedimentary units. The results suggest that a single stress field with multiple perturbations cannot explain the ensemble of compression directions inferred in the region. The final proposed model includes three different, partially superposed Intraplate Stress Fields ISF (NE–SW, ESE–WNW to SSE–NNW, and NNE–SSW ISFs), driven by genetically independent far-field tectonic forces related with the active Iberia plate margins, and showing both local and regional deflection of stress trajectories.     

Brittle deformation in pitted pebble conglomerates

The fracture patterns produced in pitted pebble conglomerates from the Alpine Molasse and the Carboniferous of northern Spain, have been studied in relation to the stress concentrations which were produced in the conglomerates during their deformation. The stress distributions which develop around pebble contacts at different stages of their pitting history have been determined from photoelastic experiments. The development of different types of fracture, having dominantly tensile or shear components, and their distribution within the pebbles, are shown to be related to the mineralogy of the pebbles, the strength of the matrix and the amount of deformation the conglomerate has suffered.     

Active faults, seismicity and stresses in an internal boundary of a tectonic arc (Campo de Dalías and Níjar, southeastern Betic Cordilleras, Spain)

The Betic-Rif Cordilleras, formed by the interaction of NW–SE convergence between the Eurasian and African plates and the westward motion of their Internal Zones, provide a good example of an active tectonic arc. The Campo de Dalías and Campo de Níjar constitute outcropping sectors of Neogene and Quaternary rocks located in the southeastern border of the Betic Cordilleras and allow us to study the recent deformations developed in the internal border of this tectonic arc.The main active faults with related seismicity, representing a moderate seismic hazard, associated to the southeastern Betic Cordilleras boundary, include high-angle NW–SE-oriented normal faults that affect, at least, the upper part of the crust, a main detachment located at 10 km depth, and probably another detachment at 20 km as well. Seismite structures, recent fault scarps with associated colluvial wedges that deform the drainage network and the alignment of the coastline, indicate that the high-angle faults have been active at least since the Quaternary.Paleostresses determined from microfault analysis in Quaternary deposits generally show an ENE–WSW trend of extension. Present-day earthquake focal mechanisms include normal, strike-slip and reverse faulting. Normal and strike-slip focal mechanisms generally indicate ENE–WSW extension, and strike-slip and reverse focal mechanisms are related to NNW–SSE compression.The maximum horizontal compression has a consistently NNW–SSE trend. The deep activity of detachments and reverse faults determines the NNW–SSE crustal shortening related to the Eurasian–African plate convergence. At surface, however, the predominance of normal faults is probably produced by the increase in the relative weight of the vertical stress axis, which in turn may be related to relief uplift and subsequent horizontal spreading. The internal mountain front boundary of the Betic Cordilleras developed through the activity of a set of structures that is more complex than a typical external mountain front, probably as a consequence of a vertical variable stress field that acted on previously deformed rocks belonging to the Internal Zone of the cordilleras.     

Active right-lateral strike-slip fault zone along the southern margin of the Japan Sea

We describe an active right-lateral strike-slip fault zone along the southern margin of the Japan Sea, named the Southern Japan Sea Fault Zone (SJSFZ). Onshore segments of the fault zone are delineated on the basis of aerial photograph interpretations and field observations of tectonic geomorphic features, whereas the offshore parts are interpreted from single-/multichannel seismic data combined with borehole information. In an effort to evaluate late Quaternary activity along the fault zone, four active segments separated by uplifting structures are identified in this study. The east–northeast-trending SJSFZ constitutes paired arc-parallel strike-slip faults together with the Median Tectonic Line (MTL), both of which have been activated by oblique subduction of the Philippine Sea plate during the Quaternary. They act as the boundaries of three neotectonic stress domains around the eastern margin of the Eurasian plate: the near-trench Outer zone and NW–SE compressive Inner zone of southwest Japan arc, and the southern Japan Sea deformed under E–W compression from south to north.     

内蒙古大青山煤田晚古生代砾岩的沉积特征

大青山煤田晚古生代地层中有 1 4层沉积砾岩。其中,晚石炭世地层中赋存 8层,二叠世 6层。通过对这些砾岩层的野外测量、室内岩矿鉴定等综合分析研究,查明晚石炭世的砾岩几乎全是稳定的单成分砾岩,石英砂岩和燧石质砾石的含量高达 93 %以上,砾石最大扁平面均向南倾,倾角在 5° - 1 0°之间,与砾岩伴生的粗粒石英砂岩发育大型低角度双向交错层理,萨胡环境判别参数等特征表明晚石炭世砾岩为滨海环境下的产物。二叠世的砾岩则主要是复杂成分的砾岩,尤其是早二叠世晚期及晚二叠世初期形成的 2层砾岩中砾石种类达 1 5种,以中酸性火山岩和火山碎屑岩砾石为主,并含较多量的变质岩和中酸性侵入岩砾石,砾岩层各种特征表明二叠世砾岩为河流相产物。大青山煤田晚古生代沉积砾岩的形成与北部造山带的隆升密切相关,它们是前陆盆地的沉积产物。     

Mesozoic extension in the Basque–Cantabrian basin (N Spain): Contributions from AMS and brittle mesostructures

In this work we analyse and check the results of anisotropy of magnetic susceptibility (AMS) by means of a comparison with palaeostress orientations obtained from the analysis of brittle mesostructures in the Cabuérniga Cretaceous basin, located in the western end of the Basque–Cantabrian basin, North Spain. The AMS data refer to 23 sites including Triassic red beds, Jurassic and Lower Cretaceous limestones, sandstones and shales. These deposits are weakly deformed, and represent the syn-rift sequence linked to basins formed during the Mesozoic and later inverted during the Pyrenean compression. The observed magnetic fabrics are typical of early stages of deformation, and show oblate, triaxial and prolate magnetic ellipsoids. The magnetic fabric seems to be related to a tectonic overprint of an original, compaction, sedimentary fabric. Most sites display a NE–SW magnetic lineation that is interpreted to represent the stretching direction of the Early Cretaceous extensional stage of the basin, without recording of the Tertiary compressional events, except for sites with compression-related cleavage.Brittle mesostructures include normal faults, calcite and quartz tension gashes and joints, related to the extensional stage. The results obtained from joints and tension gashes show a dominant N–S to NE–SW, and secondary NW–SE, extension direction. Paleostresses obtained from fault analysis (Right Dihedra and stress inversion methods) indicate NW–SE to E–W, and N–S extension direction. The results obtained from brittle mesostructures show a complex pattern resulting from the superposition of several tectonic processes during the Mesozoic, linked to the tectonic activity related to the opening of the Bay of Biscay during the Early Cretaceous. This work shows the potential in using AMS analysis in inverted basins to unravel its previous extensional history when the magnetic fabric is not expected to be modified by subsequent deformational events. Brittle mesostructure analysis seems to be more sensitive to far-field stress conditions and record longer time spans, whereas AMS records deformation on the near distance, during shorter intervals of time.     

Seismicity wedge beneath the Upper Rhine Graben due to backwards Alpine push?

The distribution of hypocentres in the Upper Rhine Graben area is re-examined, and discussed with respect to the present day tectonic framework. Most earthquakes occur within a N60° striking wedge, located on top of a Moho dome. This wedge is limited by the surface and at depth, by a plane which, in the south of the dome, coincides with the SE dipping Conrad discontinuity. In depth, the seismicity shows a normal distribution the maximums of which are located on a surface dipping 6° towards SE, parallel to the south-eastward dipping Conrad and Moho. This surface outcrops along the north-western edge of the uplifted crystalline Vosges and Black-Forest. The main shocks in earthquake swarms in the region often occur in the vicinity of this surface and along pre-existing N–S to NE–SW Variscan or Tertiary faults and show focal mechanisms of strike-slip. In contrast, part of the aftershocks show focal mechanisms of reverse faulting associated with SE–NW striking compression. The seismic wedge and the north-westward rising seismic surface suggest initiation of crustal ramp, which starts at the south-eastern rim of the Conrad dome and which may become a thrust plane if SE–NW compression continues. In the south-eastern edge of the graben and above the south-eastern ridge of the Moho dome, where evidences for extension have been found, we identify clustering of hypocentres along a surface that strikes N150°, parallel to the main compression and dipping towards NE. Dominant normal faulting mechanisms along this surface suggests initiation of a normal, probably listric fault. At depth, the onset of the future fault plane is located on top of the NW–SE striking ridge of the lower crust and Moho, which act as a an indenter. In addition to thrusting of the whole wedge towards NW, increasing of NW–SE compression would lead to the formation of a half graben at the place of the present Sierentz depression.     

From continental margin extension to collision orogen: structural development and tectonic rotation of the Hengchun peninsula, southern Taiwan

As a result of oblique collision, the Taiwan orogen propagates southward. The Hengchun peninsula in the southern tip of the Taiwan Central Range, preserving the youngest, the least deformed and the most complete accretionary prism sequences, allows therefore better understanding of the tectonic evolution of Taiwan orogen. On the Hengchun peninsula, four main stages of paleostress can be recognized by the analysis of brittle tectonics. After recording the first two stages of paleostress, rocks of the Hengchun peninsula (the Hengchun block) have undergone both tilting and counterclockwise rotation of about 90°. The structural boundaries of this rotated Hengchun block are: the Kenting Mélange zone in the southwest, the Fongkang Fault in the north, and a submarine backthrust in the east. The angle of this rotation is principally calculated by the paleomagnetic analysis data and a physical model experiment. Through a systematic back-tilting and back-rotating restoration, the original orientations of the four paleostress stages of Hengchun peninsula are recognized. They are, from the ancient to the recent, a NW–SE extension, a combination of NW–SE transtension and NE–SW transpression, a NE–SW compression, and finally a combination of NE–SW transtension and NW–SE transpression. This result can be explained by a phenomenon of stress axes permutation, instead of a complex polyphase tectonism. This stress axes permutation is caused by the horizontal compression increase accompanying the propagation of the accretionary prism. Combining the tectonic and paleomagnetic data with paleocurrent and stratigraphic data enables us to reconstruct the tectonic evolution of the Hengchun peninsula. This reconstruction corresponds to the deformation history of a continental margin basin, from its opening to its intense deformation in the accretionary prism.     

Tectonics and crustal structure of the Campania continental margin: relationships with volcanism

Summary ¶The crustal structure of the Campania continental margin is synthesized from outcrop, seismic reflection and gravimetric data. Outcrop and subsurface geological data reveal the presence of NE–SW faults, E–W faults and NW–SE faults. An older extensional event occurred along NW–SE faults and was followed by the main extensional event linked to the activity of NE–SW normal faults. The latter were active between 700 and 400ka producing half-grabens filled by more than 5km of Quaternary deposits. The stratigraphic signature of these tectonic events corresponds to a Lower Pleistocene marine unconformity-bounded unit overlain by Middle Pleistocene rocks belonging to a transgressive-regressive cycle. A crustal section of the Campania margin displays an asymmetric linked fault system characterized by a 10–12km-deep main detachment level, listric normal faults and rollover anticlines. Structural and stratigraphic data document that the inception of volcanic activity at Vesuvius occurred at 400ka, just after the main extensional event, and the volcano is located at the margin of a rollover anticline.Received June 26, 2002; revised version accepted November 9, 2002     

3D structural model of the Polish Basin

A 3D structural modelling of the Permian–Mesozoic Polish Basin was performed in order to understand its structural and sedimentary evolution, which led to basin maturation (Permian–Cretaceous) and its tectonic inversion (Late Cretaceous–Paleogene). The model is built on the present-day structure of the basin and comprises 13 horizons within the Permian to Quaternary rocks. The analysis is based on 3D depth views and thickness maps. The results image the basin-scale symmetry, the perennial localization of the NW–SE-oriented basin axis, the salt movements due to tectonics and/or burial, and the transverse segmentation of the Polish Basin. From these observations, we deduce that salt structures are correlated to the main faults and tectonic events. From the model analysis, we interpret the stress conditions, the timing, and the geometry of the tectonic inversion of the Polish Basin into a NW–SE-oriented central horst (Mid-Polish Swell) bordered by two lateral troughs. Emphasis is placed on the Zechstein salt, considering its movements during the Mesozoic sedimentation and its decoupling effect during the tectonic inversion. Moreover, we point to the structural control of the Paleozoic basement and the crustal architecture (Teisseyre–Tornquist Zone) on the geometry of the Polish Basin and the Mid-Polish Swell.     

Quaternary neotectonics of the Somogy Hills, Hungary (part I): Evidence from field observations

Quaternary and directly underlying Late Miocene (Pannonian) outcrops were analysed by structural, tectono-morphologic and sedimentologic methods to describe the main fault directions, to separate mass movements from faulting and folding and to separate earthquake-induced sediment deformations from other (e.g. periglacial) effects in the Somogy Hills. This is a gentle hilly area elevated at 200–300 m above sea level, located immediately south of Lake Balaton, Hungary.

Quaternary outcrops showed several consistent directions of faulting, and co-depositional seismic activity. Three different Mohr-sets of faults/joints could be differentiated in Quaternary sediments. The three sets are considered Late Quaternary since all cut young loess sections and have morphological expressions.

On the basis of the microtectonic measurements and morphotectonic investigations, the following sequence of Quaternary events can be proposed:

1. A (W)NW–(E)SE compression and perpendicular extension would create E–W to WNW–ESE oriented right lateral, NNW–SSE to N–S oriented left lateral shear zones, and NW–SE striking normal faults. Some of these can be evidenced in morphology and among the individual fault measurements. Some reactivated faults might suggest that this field is a relatively older one, but fresh topographic elements suggest that this stress field might be operational sub-recently.

2. A second stress field with NNW–SSE extensional and ENE–WSW oriented compressional directions could be separated. This stress field could create NNE–SSW and NW–SE oriented shear fractures and ENE–WSW oriented conjugate normal faults. Flat thrusts giving ENE directed shear may also be active under this field.

3. A third stress field might be proposed with N–S compression and perpendicular extension directions. This would create NE–SW and NW–SE oriented shear fractures, which are observed in the measured fault data. It is remarkable that the NE–SW faults are all steep, subvertical, and give a very well defined fault set. Based on the fresh topographic expression, this stress field is also sub-recent.

The different sub-recent stress fields and related fault patterns might succeed each other or might alternate through time. The first and third deformations have fresh topographic expressions and cannot play synchronously. The observed features suggest a compressionally active neotectonics of the study area.     

Far field effects of Alpine plate tectonism in the Iberian microplate recorded by fault-related denudation in the Spanish Central System

Apatite fission track analysis was performed on 56 samples from central Spain to unravel the far field effects of the Alpine plate tectonic history of Iberia. The modelled thermal histories reveal complex cooling in the Cenozoic, indicative of intermittent denudation. Accelerated cooling events occurred across the Spanish Central System (SCS) from the Middle Eocene to Recent. These accelerated cooling events resulted in up to 2.8±0.9 km of denudation in the western Sierra de Gredos and 3.6±1.0 km in the central and eastern Gredos (assuming a paleogeothermal gradient of 28±5 °C and a surface temperature of 10 °C). The greatest amount of denudation (5.0±1.6 km) occurred in the Sierra de Guadarrama. Accompanying rock uplift was 4.7±1.0 and 5.9±1.6 km in the eastern Gredos and Guadarrama, respectively. Most denudation in the Gredos occurred from the Middle Eocene to the Early Miocene and can be related to the N–S stress field, induced by the Pyrenean compression. In the Guadarrama, the greatest denudation was Pliocene to Recent of age and seems related to the ongoing NW–SE Betic compression. The fact that the formation of the E–W trending Gredos coincides with the N–S Pyrenean compression and the creation of the present day morphology of the NE–SW trending Guadarrama with the younger NW–SE Betic compression, indicates that they record the far field effects of Alpine plate tectonics on Iberia. The trend of pre-existing lineaments was of major importance in influencing the style and magnitude of these of far field effects.     

Analysis of solution lineations in pebbles: Kinematical vs. dynamical approaches

Solution lineations in conglomerates, resulting from indentation of non-soluble grains of the matrix into the surface of soluble pebbles, make up a morphological and genetic continuum with gradual transition between orthogonal stylolites, oblique slickolites and parallel striations. The distributions of incidence angles of matrix grains have been analyzed in individual pebbles in order to discern their kinematical or dynamical meaning. As a general rule, they fit theoretical models of flow trajectories determined by the bulk strain (kinematical hypothesis). In contrast, they are not consistent with dynamical hypotheses based upon relationships with stress vectors. In particular, they do not fit the model of frictional sliding, which would give rise to a sharp discontinuity between slickolites parallel to the maximum principal stress σ₁ and true striations parallel to the resolved shear stress τ. Therefore, solution lineations all around a pebble cannot be considered as an analogue of multiple fault slip data, and they should not be generally analysed by methods of stress inversion based upon Bott's principle. Under certain conditions (high pebble solubility; active pressure-solution processes able to accommodate the strain rate; earlier cementation), the solution lineations tend to be parallel to each other and to the maximum shortening/compression axis. They therefore assume a double kinematical and dynanical meaning, and the deformation involves maximum volume reduction.     

Salt movements in the Northeast German Basin and its relation to major post-Permian tectonic phases—results from 3D structural modelling, backstripping and reflection seismic data

The NW–SE-striking Northeast German Basin (NEGB) forms part of the Southern Permian Basin and contains up to 8 km of Permian to Cenozoic deposits. During its polyphase evolution, mobilization of the Zechstein salt layer resulted in a complex structural configuration with thin-skinned deformation in the basin and thick-skinned deformation at the basin margins. We investigated the role of salt as a decoupling horizon between its substratum and its cover during the Mesozoic deformation by integration of 3D structural modelling, backstripping and seismic interpretation. Our results suggest that periods of Mesozoic salt movement correlate temporally with changes of the regional stress field structures. Post-depositional salt mobilisation was weakest in the area of highest initial salt thickness and thickest overburden. This also indicates that regional tectonics is responsible for the initiation of salt movements rather than stratigraphic density inversion.Salt movement mainly took place in post-Muschelkalk times. The onset of salt diapirism with the formation of N–S-oriented rim synclines in Late Triassic was synchronous with the development of the NNE–SSW-striking Rheinsberg Trough due to regional E–W extension. In the Middle and Late Jurassic, uplift affected the northern part of the basin and may have induced south-directed gravity gliding in the salt layer. In the southern part, deposition continued in the Early Cretaceous. However, rotation of salt rim synclines axes to NW–SE as well as accelerated rim syncline subsidence near the NW–SE-striking Gardelegen Fault at the southern basin margin indicates a change from E–W extension to a tectonic regime favoring the activation of NW–SE-oriented structural elements. During the Late Cretaceous–Earliest Cenozoic, diapirism was associated with regional N–S compression and progressed further north and west. The Mesozoic interval was folded with the formation of WNW-trending salt-cored anticlines parallel to inversion structures and to differentially uplifted blocks. Late Cretaceous–Early Cenozoic compression caused partial inversion of older rim synclines and reverse reactivation of some Late Triassic to Jurassic normal faults in the salt cover. Subsequent uplift and erosion affected the pre-Cenozoic layers in the entire basin. In the Cenozoic, a last phase of salt tectonic deformation was associated with regional subsidence of the basin. Diapirism of the maturest pre-Cenozoic salt structures continued with some Cenozoic rim synclines overstepping older structures. The difference between the structural wavelength of the tighter folded Mesozoic interval and the wider Cenozoic structures indicates different tectonic regimes in Late Cretaceous and Cenozoic.We suggest that horizontal strain propagation in the brittle salt cover was accommodated by viscous flow in the decoupling salt layer and thus salt motion passively balanced Late Triassic extension as well as parts of Late Cretaceous–Early Tertiary compression.     

Spatial and temporal relationships between compression, strike-slip and extension in the Central Venezuelan Andes: Clues for Plio-Quaternary tectonic escape

The geometry of tectonic structures, attributed to the Neogene–Quaternary time interval, is described in the active setting of the Venezuelan Andes. Our methodology is based on the analysis of radar satellite and Digital Elevation Model imagery, complemented by structural fieldwork and the compilation of seismotectonic data to make a structural analysis on a regional scale. Radar images provide first class data for morphostructural analysis in areas of dense vegetation and frequent cloud covering, like the Venezuelan Andes. We focused our analysis in the Burbusay–Río Momboy and Boconó faults corner located in the central part of the belt.We have described three stages of deformation during the Neogene–Quaternary. The first one, Mio-Pliocene in age, is a NW–SE compression responsible for the uplift of the Venezuelan Andes. The second tectonic stage corresponds to a strike-slip regime of deformation marked by shearing along the Boconó, Burbusay and Valera faults, which separates two triangular wedges in the larger Trujillo block. This strike-slip faulting-dominated compressional-extensional tectonic regime allowed the Trujillo crustal block to move towards the NE. Wrenching has therefore started at some point between the Pliocene and the Quaternary. These two tectonic events are consistent with ongoing strain partitioning in the Venezuelan Andes. The third stage corresponds to extensional deformation limited to the Trujillo block and is still active today. Extension is associated with the motion of crustal blocks moving relative to each other, probably above the upper-lower crust boundary. Such extensional deformation can be understood considering that the crust extends and stretches at the same time as it moves towards the NE. The combination of both horizontal lateral motion and extension is characteristic of a tectonic escape process. The northeastward escape of the Trujillo block, which belongs to the larger North Andes block, occurs as a result of the combination of the NW–SE intracontinental convergence between the South-American plate and the Maracaibo block, and the presence to the north of the Caribbean oceanic plate considered as a free boundary. We have showed that the kinematics of the Caribbean plate offers not only a favorable environment, but may also be considered as the driving force of the tectonic escape of the North Andes block.     

Late Tertiary–Quaternary tectonics of the Southern Apennines (Italy): New evidences from the Tyrrhenian slope

This paper summarises the results of combined structural and geomorphological investigations we carried out in two key areas, in order to obtain new data on the structure and evolution of the Tyrrhenian slope of the southern Apennines. Analysis by a stress inversion method [Angelier, J., 1994. Fault slip analysis and paleostress reconstruction. In: Continental Deformation. P.L. Hancock Ed., Pergamon Press, Oxford, 53–100] of fault slip data from Mesozoic to Quaternary formations allowed the reconstruction of states of stress at different time intervals. By integrating these data with those deriving from the stratigraphic and morphotectonic records, chronology and timing of the sequence of the deformation events was obtained.The tectonic history of the region can be related to four deformation events. Structures related to the first event, that was dominated by a strike-slip regime with a NW–SE oriented σ1 and was active since Mid–Late Miocene, do not significantly affect the present day landscape, as they were strongly displaced and overprinted by subsequent deformation events and/or deleted by erosion. The second and third events, that may be considered as the main responsible for the morphostructural signature of the region, are comparable with the stretching phases recognised offshore and considered to be responsible for the opening and widening of the Tyrrhenian basin. In particular, the second event (with an E–W oriented σ3), took place in the Late Miocene/earliest Pliocene and was first dominated by a strike-slip regime, that was also responsible for thrusting and folding. Since Late Pliocene, it was dominated by an extensional regime that created large vertical offsets along N–S to NW–SE trending faults. The third event, that was dominated by extension with a NW–SE oriented σ3, started in the Early Pleistocene and was responsible for formation of the horst-and-graben structure with NE–SW trend that characterises the Tyrrhenian margin of the southern Apennines. The fourth deformation event, which is characterised by an extensional regime with a NE–SW trending σ3, started in the late Middle Pleistocene and is currently active.