Internal Shortening Research Articles

Thick-skin-dominated orogens; from initial inversion to full accretion: an introduction

Abstract Fifty per cent of orogens have a thick-skin character, and have evolved from passive margin and intra-cratonic rift systems. One group of thick-skin provinces can be found at both pro- and retro-wedges of orogens associated with advancing subduction zones, that is, orogenic wedges whose advance vectors oppose the mantle flow. A second group can be found at pro-wedges of orogens associated with retreating subduction zones, that is, orogens whose advance vectors have the same direction as mantle flow. A third group is formed in intra-plate settings where mechanical strengthening is produced by internal shortening. Thick-skin province development is controlled by driving factors such as individual plate movement rates, overall convergence rates, orogen movement sense with respect to mantle flow, and pro-wedge v. retro-wedge location. These driving factors are themselves constrained by numerous internal and external factors. This introductory chapter focusses primarily on least-deformed case areas in order to understand the role of different factors in controlling the evolution of thick-skin tectonic provinces from the initial inversion stage to full accretion stage.

Abstract 323: Resveratrol Attenuates Pressure Overload-induced Heart Failure

The purpose of this study was to determine whether the potent antioxidant, resveratrol, attenuates the adverse cardiac remodeling and dysfunction in pressure overload heart failure induced by transverse aortic constriction (TAC). Male C57BL6 mice (26-28 g) were subjected to either sham or TAC surgery. One group of TAC mice was given daily resveratrol treatment (oral gavage, 100 mg/kg/body weight (bw) for 28 days starting on day 2 after surgery. Echocardiographic, biometric, and immunohistological analyses were performed on the three groups of mice. All echocardiographic parameters examined (internal diameters, fractional shortening , and ejection fraction) demonstrated significantly greater adverse cardiac remodeling and dysfunction in the TAC compared to the sham mice. These pathological changes were significantly improved by resveratrol treatment. At day 28 fractional shortening was 46.5±2.4%, 26.2±2.0%, and 35±2.6% in the sham, TAC, and TAC + resveratrol mice, respectively. This was reflected by lung weight/bw ratios of 4.2±0.3 mg/g (sham), 8.6±0.9 mg/g (TAC) and 7.2±0.4 mg/g (TAC + resveratrol). Resveratrol treatment also significantly reduced cardiac hypertrophy as determined by the heart weight/bw ratios (sham, 4.8±0.3 mg/g; TAC, 8.7±0.6 mg/g; and TAC + resveratrol, 7.2±0.3 mg/g). Likewise, the TAC protocol significantly increased fibrosis (10.0±1.1%), compared to the sham-operated mice (0.7±0.3%), which was attenuated by resveratrol treatment (3.0±0.5%). Similar results were obtained when cardiomyocyte apoptosis was assessed. Both superoxide dismutase 2 and hypoxia inducible factor 1α were markedly increased in the TAC compared to the sham-operated mice most likely as a compensatory response to increased oxidative stress and hypoxia. These TAC-induced factors were significantly decreased by resveratrol treatment indicating that the resveratrol was acting in place of these stress inducible factors. In summary, these results demonstrate that resveratrol treatment significantly attenuates the adverse cardiac remodeling and dysfunction produced by the TAC protocol in C57/BL6 mice and that this activity is mediated, at least in part, by the inhibition of oxidative stress and hypoxia.

Lengthening z-Osteotomy of the Fibula to Correct Persistent Talar Shift Following Open Reduction Internal Fixation of Ankle Fractures

In cases where ankle fracture union has been compromised by persistent syndesmotic diastasis following open reduction internal fixation, both external rotation and shortening of the fibula have been identified as prominent features. This study reports a technique that uses a z-osteotomy to achieve both lengthening and internal rotation of the fibula to correct persistent talar shift following ankle fracture fixation. Four patients with persistent talar shift following open reduction internal fixation for an ankle fracture received z-osteotomy of the fibula to achieve both lengthening and internal rotation. At the latest clinic review, all 4 ankles exhibited satisfactory clinical and radiological union. All patients have returned to full mobility and are satisfied with the outcome. This study demonstrates the effectiveness of lengthening z-osteotomy of the fibula in correcting persistent talar shift following internal fixation of ankle fractures. Therapeutic Level V.

(viii) Blount’s disease

Abstract Blount’s disease is an uncommon disorder of the postero-medial proximal tibial physis, which produces a varus proximal tibia, tibial internal torsion, procurvatum and shortening. Blount described infantile and adolescent types. The precise pathogenesis of the condition remains obscure but associations include an early walking age, obesity, familial tendency and Afro-Caribbean race. It is frequently bilateral. The diagnosis of Blount’s disease follows clinical assessment and radiographs of the knee, which show a progressive varus deformity and typically an increased metaphyseal-diaphyseal angle. The natural history of the condition is adult knee pain, deformity and arthrosis. Treatment is dependent on the age of the child, the stage of the disease and the amount of angular and articular deformity present. Bracing may be used for early stage infantile disease. Surgical treatment options include hemiepiphysiodesis, osteotomy and bar excision. Monitoring of limb alignment and length is required until skeletal maturity.

Treatment of long-segment fracture in middle-up part of femoral shaft with long proximal femoral nail antirotation of AO/ASIF

Objective To investigate the operative method and evaluate the clinical outcomes of long proximal femoral nail ant-rotation(PFNA-long)in treating long-segment fracture in middle-up part of femoral bone.Methods From June 2006 to December 2009,32 cases of long-segment fracture in middleup part of femoral shaft were treated by closed reduction or limited open reduction and fixation with PFNA-long,including 30 males and 2 females with an average age of 3.8.8 years(range,20-69).All patients had closed fractures in shaft of femur.The average time from injury to operation was 4.2 days(range,3 hours to 12 days).All fractures were fixed with the PFNA-long.The patients were followed at 1,2,3,6,9,12 month after surgery,respectively,and next time at least once per year.The clinical outcomes were evaluated according to Harris criteria and radiological examinations.Results The mean operating time of all cases was 55 minutes(range,35-90),and the mean blood loss during surgery was 75.6 ml(ranged,30-150 ml).All patients walked with walking aid 4-7 days after surgery.They were followed up for 9-37 months.All fractures healed after 3.1-5.4 months(mean 3.7 months).No complications such as infection,lower limb vein infarction,cut-out or breakage of the implants occurred.But 2 cases had hip internal reverse-lamb shortening malformation,According to Harris criteria,the clinical results were excellent in 23 cases,good in 7,and moderate in 2,and the excellent and good rate was 93.75%(30/32).Conclusion PFNA-long is an effective and minimally invasive method for long-segment fracture in middle-up part of femoral shaft,with minimally invasive,high fixation-strength and accord with biomechanics characteristics;and with a high rate of bone union,early functional recovery and less complications. Key words: Femoral fractures; Fracture fixation,intramedullary; Internal fixators

Pliocene onset of rapid exhumation in Taiwan during arc–continent collision: new insights from detrital thermochronometry

ABSTRACTThe Coastal Range in eastern Taiwan contains the remnants of the Pliocene–Pleistocene retro‐foredeep basin of the ongoing Penglai orogeny. These sedimentary successions record the earliest exhumation of the Central Range, Taiwan. We dated detrital Plio‐Pleistocene sediments in the Coastal Range using multiple thermochronometers [fission‐track, zircon (U–Th)/He and U/Pb dating] to document changes in exhumation rate through time. Fission‐track grain ages in 2–4‐Myr‐old sediments were not reset by the Penglai orogeny and reflect the early stage removal of the sedimentary cover. This early stage, when exhumation rates were low, could encompass both the accretionary wedge phase of the orogen and the early arc–continent collision. Sediments younger than 2‐Myr‐old yield Pliocene zircon fission‐track grain ages and suggest that exhumation, transport and deposition occurred within 0.4–1.5 Myr. The recorded onset of rapid exhumation in the Pliocene is contemporaneous with other major tectonic changes in the region, including an increase in subsidence rate in both the pro‐ and retro‐foredeep basins and a change in the wedge kinematics from internal shortening to underplating.

Deformation zone ‘jumps’ in a young convergent setting; the Lengguru fold-and-thrust belt, New Guinea Island

The Lengguru fold-and-thrust belt in West Papua (Indonesia) has all the characteristics of a young orogen involved in a rapidly changing tectonic setting. The analysis of the young wedge shows however that its internal shortening has ceased recently, and that it is nowadays suffering severe extension. Recent topographic data, marine industrial seismic lines and drilling, were used with field observations and measurements to create detailed cross-sections and a new structural map. The study allows us to distinguish two superimposed prisms composed of stacked Mesozoic marine sediments of the Australian margin against a crustal buttress. The construction of these two wedges is younger than 11 Myr. The structures of the Lengguru belt external zones are sealed by an unconformable clastic series, indicating that the construction of the Lengguru prism had aborted suddenly due to a change in the way the Australian and Pacific plate convergence was accommodated. At that time, the internal zones probably started to exhume and the tectonic regime became extensional. Nowadays the internal part of the Lengguru fold-and-thrust belt is undergoing an active east–west extension. We believe that the extension observed in the Lengguru wedge is coeval with a transition from a compressive to a transtensional regime illustrated in the Central Range of Papua, and the onset of the Tarera-Aiduna and Paniai left-lateral faults. The structure of the Lengguru belt therefore results from events occurring over a very short time span; a previous Late Miocene northeast–southwest compression linked to the subduction process, a second from Middle Miocene to Early Pliocene and a Late Pliocene-Quaternary global extension in the whole range. The evolution is compared with that of the Seram wedge and the Misool–Onin–Kumawa continental ridge to the west; where deformation is accommodated at a localized zone which jumps as convergence between Australian and Pacific plate proceeds. This evolution of the belt reflects rapid changes in the accommodation oblique shortening, with the isolated orogenic wedge of Lengguru fold-and-thrust belt left to collapse. This example illustrates the way a long-lasting subduction terminates. At the lithospheric scale, the deformation remains rooted at the suture zone. However at the surface, the shortening is suddenly widespread over a large area during a very short time span (formation of the Lengguru belt) prior to being transferred to another plate boundary.

Geological development of the Central and South Vietnamese margin: Implications for the establishment of the South China Sea, Indochinese escape tectonics and Cenozoic volcanism

The Vietnamese margin forms a key region to the understanding of escape tectonics and the development of the South China Sea (SCS). The existing geological reconstructions of the region are restricted to studies of single basins, are based on limited amounts of geophysical data or analysis of onshore geological features. These models are critically assessed on the basis of interpretation of the most comprehensive 2-D digital seismic database published to date within the area combined with a thorough analysis of existing literature, and a new model is presented. The Vietnamese margin is underlain by a series of Paleogene rift basins established through southeastward extrusion of Indochina. The East Vietnam Boundary Fault (EVBF) forms the almost 1000 km long seaward continuation of the left-lateral Ailao Shan-Red River Shear Zone (ASRRSZ). Toward the southern half of the Phu Khanh Basin the EVBF breaks up into discrete segments and splays into the SE-directed Tua Hoa Fault Zone. Paleogene faults splayed from the EVBF and the Mae Ping Shear Zone and accommodated the coeval motion of these two major left-lateral structural lineaments. During the late Oligocene, basin inversions offshore occurred contemporaneously with initial right-lateral inversion along the Mae Ping Shear Zone and the onset of major uplift of the metamorphic core complexes along the ASRRSZ. It is suggested that a dramatic change of the regional stress pattern occurred in response to the northward movement of India and the effective coupling of the West Burma Block and India, the later resulting in broadening of the indenting continental mass. After the mid-Oligocene, left-lateral movements across the offshore EVBF decreased and eventually ceased. Later, onshore sinistral movements were accommodated by internal shortening and local clockwise block rotations within the Shan-Thai Terrain. Renewed rifting offshore south Vietnam resulted from the jump of the SCS spreading axis and subsequent Neogene southwestward propagation of continental break-up. The Neogene opening of the SCS is viewed as a consequence of a slab-pull associated with subduction of the proto-SCS underneath Borneo as offshore Neogene escape tectonism had virtually ceased. During this phase of rifting, right-lateral transtension is inferred along N to NW oriented fault zones in the Phu Khanh and the Nam Con Son basins. Rifting and by inference seafloor spreading continued until the end of middle Miocene time although at significantly reduced rates during the final 5–10 Ma. Termination of seafloor spreading is marked by a distinct latest middle Miocene unconformity in the Nam Con Son and the southern Phu Khanh basins. Neogene volcanism resulted in the build-up of several magmatic structures across the central and South Vietnamese margin and induced reactivation of older faults in the Phu Khanh Basin. The offshore magmatism heralded widespread volcanism onshore southern Indochina associated with a latest Neogene uplift and denudation event. The uplift led to significantly increased siliciclastic accumulation rates offshore, which repressed widespread carbonate deposition.

Shocks in a box: An analogue model of subduction earthquake cycles with application to seismotectonic forearc evolution

We introduce and test an experimental approach to simulate elastoplastic megathrust earthquake cycles using an analogue model and apply it to study the seismotectonic evolution of subduction zones. The quasi‐two‐dimensional analogue model features rate‐ and state‐dependent elastic‐frictional plastic and viscoelastic material properties and is scaled for gravity, inertia, elasticity, friction, and viscosity. The experiments are monitored with a high‐resolution strain analysis tool based on digital image correlation (particle imaging velocimetry, PIV), providing deformation time series comparable to seismologic, geodetic, and geologic observations. In order to separate elastic and nonelastic effects inherent the experimental deformation patterns, we integrate elastic dislocation modeling (EDM) into a hybrid approach: we use the analogue earthquake slip and interseismic locking distribution as EDM dislocation input and forward model the coseismic and interseismic elastic response. The residual, which remains when the EDM prediction is subtracted from the experimental deformation pattern, highlights the accumulation of permanent deformation in the model. The setup generates analogue earthquake sequences with realistic source mechanisms and elastic forearc response and recurrence patterns and reproduces principal earthquake scaling relations. By applying the model to an accretionary‐type plate margin, we demonstrate how strain localization at the rupture peripheries may lead to a seismotectonically segmented forearc, including a tectonically stable shelf and coastal high (<20% plate convergence accommodated by internal shortening) overlying the area of large megathrust earthquake slip. Fifty to 75% of plate convergence is accommodated by internal shortening in the slope region where earthquake slip tapers out toward the trench. The inner forearc region remains undeformed and represents a basin.

Simulation of steady state and transient cardiac muscle response experiments with a Huxley-based contraction model

A cardiac muscle model is presented with the purpose of representing a wide range of mechanical experiments at constant and transient Ca 2+ concentration. Modifications of a previous model were: weak and power attached crossbridge states, a troponin system involving three consecutive regulatory troponin–tropomyosin units acting together in Ca 2+ kinetics and detachment constants depending on crossbridge length. This model improved cooperativity (Hill coefficient close to 4) and the force–velocity relationship, and incorporated the representation of the four phases of muscle response to length and force steps, isotonic shortening and isosarcometric contractions, preserving previous satisfactory results. Moreover, experimentally reported effects, such as length dependence on Ca 2+ affinity, the decreased cooperativity at higher Ca 2+ concentrations, temperature effects on the stiffness–frequency relationship and the isometric internal shortening due to series elasticity, were obtained. In conclusion, the model is more comprehensive than a previous version because it is able to represent a wider variety of steady state experiments, the mechanical variables in twitches can be adequately related to intracellular Ca 2+, and all the simulations were performed with the same set of parameters.

Initial mechanomyographical signals from twitching fibres of human skeletal muscle

To elucidate the origin of characteristic low-frequency sound of contracting skeletal muscle, propagation properties of mechanical and electrical signals along twitching muscle were studied. From voluntarily twitching muscle in human vastus medialis muscle, mechanical and electrical signals were simultaneously recorded through the skin with microphones and wire electrodes. The initial part of the mechanical signal recorded by the microphone showed transient pressure decrease (negative-going phase) followed by sustained pressure increase (positive-going phase). The mechanical signals obtained over the nerve insertion lacked the negative-going phase. The onset of the positive-going phase appeared 2.5 +/- 0.2 (mean +/- SEM, n = 7) ms behind the onset of spike potential independently of the sensor position. The onset of the negative-going phase propagated along the muscle at a constant velocity of 29.8 +/- 3.4 m s(-1), which was about ten times faster than the propagation velocity of action potentials (3.2 +/- 0.1 m s(-1)). Extrapolation analyses showed that the negative- and positive-going phases originated at the nerve insertion 2.1 +/- 0.3 and 1.6 +/- 0.1 ms behind the generation of muscle action potentials respectively. Local muscle compression blocked the propagation of only the negative-going phase. The negative-going mechanical signal represents a passive process, probably the thinning of the internally stretched segments of the twitching muscle. The positive-going phase, on the other hand, represents an active process, probably muscle thickening due to the internal shortening. Each phase, therefore, would convey information about the mechanical properties of resting and contracting muscle fibres respectively.

Strain and rotation rate from GPS in Tibet, Anatolia, and the Altiplano

Deformation measured by regional GPS networks in continental plateaus reflects the geologic and tectonic variability of the plateaus. For two collisional plateaus (Tibet and Anatolia) and one noncollisional (the Altiplano), we analyze the regional strain and rotation rate by inverting GPS velocities to calculate the full two‐dimensional velocity gradient tensor. To test the method, we use gridded velocities determined from an elastic block model for the eastern Mediterranean/Middle East region and show that to a first order, the deformation calculated directly from the GPS vectors provides an accurate description of regional deformation patterns. Principal shortening and extension rate axes, vertical axis rotation, and two‐dimensional (2‐D) volume strain (dilatation) are very consistent with long‐term geological features over large areas, indicating that the GPS velocity fields reflect processes responsible for the recent geologic evolution of the plateaus. Differences between geological and GPS descriptions of deformation can be attributed either to GPS networks that are too sparse to capture local interseismic deformation, or to permanent deformation that accrues during strong earthquakes. The Altiplano has higher internal shortening magnitudes than the other two plateaus and negative 2‐D dilatation everywhere. Vertical axis rotation changes sign across the topographic symmetry axis and is due to distributed deformation throughout the plateau. In contrast, the collisional plateaus have large regions of quasi‐rigid body rotation bounded by strike‐slip faults with the opposite rotation sense from the rotating blocks. Tibet and Anatolia are the mirror images of each other; both have regions of positive dilatation on the outboard sides of the rotating blocks. Positive dilatation in the Aegean correlates with a region of crustal thinning, whereas that in eastern Tibet and Yunnan province in China is associated with an area of vertical uplift. Rollback of the Hellenic trench clearly facilitates the rotation of Anatolia; rollback of the Sumatra–Burma trench probably also enables rotation about the eastern syntaxis of Tibet.

Investigating the kinematics of mountain building in Taiwan from the spatiotemporal evolution of the foreland basin and western foothills

The Taiwanese range has resulted from the collision between the Luzon volcanic arc and the Chinese continental margin, which started about 6.5 Myr ago in the north, and has since propagated southward. The building of the range has been recorded in the spatiotemporal evolution of the foreland basin. We analyze this sedimentary record to place some constraints on the kinematics of crustal deformation. The flexure of the foreland under the load of the growing wedge started with a 1.5 Myr long phase of rapid subsidence and sedimentation, which has migrated southward over the last 3.5 Myr at a rate of 31 +10/−5 mm/yr, reflecting the structural evolution of the range and the growth of the topography during the oblique collision. Isopachs from the Toukoshan (∼0 to 1.1 Ma) and Cholan (∼1.1 to 3.3 Ma) formations, as well as the sedimentation rates retrieved from a well on the Pakuashan anticline, indicate that the foreland basement has been moving toward the center of mass of the orogen by ∼45–50 mm/yr during the development of the basin. From there, we estimate the long‐term shortening rate across the range to 39.5–44.5 mm/yr. By considering available data on the thrust faults of the foothills of central Taiwan, we show that most (if not all) the shortening across the range is accommodated by the most frontal structures, with little if any internal shortening within the wedge. The range growth appears therefore to have been essentially sustained by underplating rather than by frontal accretion. In addition, only the upper ∼7 to 9 km of the underthrusted crust participates to the growth of the orogen. This requires that a significant amount of the Chinese passive margin crust is subducted beneath the Philippine Sea plate.

Redistribution of the neurosensory retina in inferior limited macular translocation: an evaluation using image registration

The present work aims to demonstrate the role of redistribution of the neurosensory retina (RNR)-that is, retinal tissue stretching and compression-in inferior limited macular translocation (LMT), to perform displacement mapping all over the area centralis, and to try and improve displacement evaluation precision. Using piecewise linear image registration (through Matlab) on indocyanine green angiographic frames, we have evaluated the deformation (on both the retinal and choroido-scleral layer) of a pre-operative grid superimposed on the area centralis, plotted displacement vectors all over the area centralis, and calculated a scale ratio between pre- and post-operative frames. The scale ratio tests whether or not the same physical distance is represented by the same distance on these frames. The choroido-scleral layer is not deformed following surgery. The retinal layer shows areas of stretching and compression, demonstrating the RNR. Displacement vectors feature a rotating pattern around the optic disk (except if a macular fold exists) and a positive naso-temporal gradient. The median scale ratio is 3.8% (2.5% to 5.8%). LMT involves RNR accounting for inferior retinal displacement, despite the supposedly limited internal scleral shortening. Our study confirms that the optic disk temporal edge is the displacement axis (except if a macular fold exists). Our method, unaffected by a non-zero scale ratio, provides more precision than previously published.

Revised deformation history of the central Andes: Inferences from Cenozoic foredeep and intermontane basins of the Eastern Cordillera, Bolivia

Investigation of Cenozoic deformation, sediment accumulation, and provenance in the Eastern Cordillera of Bolivia at 17–21°S indicates major shortening (60–140 km) and foredeep development followed by limited internal shortening and intermontane basin development. Contrasting histories of shortening, deposition, sediment dispersal, and detrital composition distinguish a formerly extensive Paleogene foredeep exposed along an eastern belt of synclines from a zone of principally Neogene intermontane basins in the central Eastern Cordillera. New40Ar/39Ar ages of 25–17 Ma for interbedded tuffs reveal latest Oligocene–early Miocene accumulation in intermontane basins at rates <80 m/Myr, several times lower than Andean foredeeps. Although poorly dated, foredeep evolution probably coincided with middle Eocene–Oligocene deformation and denudation in adjoining regions to the west. A mid‐Cenozoic transition from foredeep to intermontane conditions may be attributable to emplacement of a basement‐involved tectonic wedge beneath the Eastern Cordillera. In this interpretation, wedge emplacement drove flexural foredeep subsidence from roughly 40 to 25 Ma, whereas subsequent accumulation occurred in localized internally drained basins in elevated intermontane areas. Regardless of the regional subsurface structural geometry,40Ar/39Ar ages define a 25–21 Ma onset of intermontane sedimentation that signifies the termination of major upper crustal shortening over large parts of the Eastern Cordillera and possibly the age of initial shortening in the Interandean and Subandean zones to the east. In contrast to several popular models, the revised tectonic history presented here suggests significant pre‐Neogene shortening in the Eastern Cordillera and underscores the large uncertainties in estimates of long‐term shortening rates in the Andes.

Thrust sequences and evolution of the external sector of a fold and thrust belt: An example from the Southern Apennines (Italy)

Abstract The Southern Apenninic chain was built up from the late Oligocene–early Miocene to the middle Pleistocene. It consists of an upper wedge composed of strongly deformed deep marine and carbonate platform successions and a buried thrust and fold belt in the carbonate rocks of the Apulian Platform. This paper analyzes the frontal part of the Southern Apennines, where contractional structures display complex geometries related to progressive incorporation of accreted material, internal shortening and gravitational processes. Late normal faults, which hinder the interpretation of contractional structures in other sectors of the chain, are scarcely represented in the frontal part of the Southern Apennines. This allows a detailed analysis of thrust and fold geometry. In particular it is possible to recognize the relationships between gravity-driven nappes, foreland-vergent thrusts and backthrusts. New field observations allow us to depict a detailed structural framework of this area and to construct regional cross-sections, which illustrate the inferred evolution of the frontal sector of the Apenninic chain. The chronological constraints are given by the age of thrust-top basins and foredeep deposits of middle–late Miocene to Pleistocene age. Deepening of the decollement level during thrusting creates complicate overprinting relationships connected to the deformation of the older thrust surfaces. The inferred evolution can be summarized in two stages. During the first stage shortening of the wedge was associated to emplacement of thin thrust sheets, interpreted as gravity-driven nappes, before sedimentation of middle–late Miocene thrust top basins. The second stage, of middle Pliocene–middle Pleistocene age, was characterized by folding and breaching of the pre-existing structures, related to deep thrusting in the Apulian Platform. The examples shown suggest the presence of transfer zones and lateral ramps to explain lateral variations in thrust geometry and shortening amount. The along strike geometry of non-cylindrical structures provides a valuable tool to decipher the tectonic evolution of the thrust belt. The proposed scheme is well suited to interpret the structural setting of thin-skinned thrust and fold belts characterised by change in the geometry of the thrust systems through time.

Distribution of the Pacific/North America motion in the Queen Charlotte Islands‐S. Alaska plate boundary zone

We present GPS data that constrain the distribution of the relative Pacific/North America motion across the Queen Charlotte Islands‐Alaska Panhandle margin (NW North America). Velocities from a network of 22 campaign and permanent sites indicate that the Pacific/North America transpressive motion is mostly accommodated along the locked Queen Charlotte‐Fairweather Fault. A significant portion (6–7 mm/yr) of the relative plate motion is taken up by distributed dextral shear across a ∼200 km wide region of the margin. Two models have been proposed to describe how the Pacific/North America convergence is accommodated off the Queen Charlotte Islands: Internal shortening vs. underthrusting of the Pacific plate. Although the GPS data cannot discriminate between the models, they provide strong constraints on the convergence distribution. The significant non‐transient motion of GPS sites along the central British Columbia‐southern Alaska margin has implications for seismic hazard and tectonic evolution models of the Canadian Cordillera.

Present-day crustal deformation in China constrained by global positioning system measurements.

Global Positioning System (GPS) measurements in China indicate that crustal shortening accommodates most of India's penetration into Eurasia. Deformation within the Tibetan Plateau and its margins, the Himalaya, the Altyn Tagh, and the Qilian Shan, absorbs more than 90% of the relative motion between the Indian and Eurasian plates. Internal shortening of the Tibetan plateau itself accounts for more than one-third of the total convergence. However, the Tibetan plateau south of the Kunlun and Ganzi-Mani faults is moving eastward relative to both India and Eurasia. This movement is accommodated through rotation of material around the eastern Syntaxis. The North China and South China blocks, east of the Tibetan Plateau, move coherently east-southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year, respectively, with respect to the stable Eurasia.

Reconstruction of continental margin architecture deformed by the contraction of the Lagonegro Basin, southern Apennines, Italy

Thrust propagation through previously rifted continental margins may result in fold and thrust belts whose structure is strongly controlled by the inherited basin architecture, as it occurs in southern Italy. The Lagonegro units of the southern Apennines comprise a deformed pelagic basin succession showing variable stratigraphic characteristics, mainly lateral variations in both facies and thickness, interpreted to be due to a complex basin topography related to a Triassic rifting event. In contrast to previous studies, cross-section balancing and restoration indicate that the Lagonegro units exposed in the high Agri Valley area suffered relatively limited internal shortening (8 km, i.e. 35%). Early deformation of these rocks, later incorporated into a large-displacement thrust sheet, was dominated by folding around (present-day) roughly north–south-trending axes. The attainment of a regional décollement level was favoured by an early mild inversion of the basin, producing a roughly similar structural elevation of both hanging-wall and footwall successions to Mesozoic faults. Most of the contractional deformation was accommodated by buckling of the Mesozoic syn-rift strata between synsedimentary faults, which represented major mechanical interfaces. Early strain localization in the Lagonegro Basin ahead of the active thrust front was most probably mechanically controlled by a faulted crustal segment which originally lay, within the continental margin, between two massive carbonate platforms.

Timing and magnitude of rotations in the frontal thrust systems of southwestern Sicily

We report new paleomagnetic and anisotropy of magnetic susceptibility (AMS) results from upper Tortonian to middle Pleistocene sediments which were deposited upon and adjacent to active thrust structures in southwestern Sicily. The data show that the Plio‐Pleistocene sediments from the Belice and Menfi basins (covering the Saccense shelf limestones) underwent any internal shortening after the early Pleistocene (Santernian), as well as any net rotation. Sediments around this area (which overlie basinal Meso‐Cenozoic successions) record systematic rotations: one upper Tortonian site to the west is ∼30° counterclockwise rotated, while to the east, lower Pliocene to middle lower Pleistocene sites within the Gela Nappe domain show 25° to 56° clockwise (CW) rotations. These data show that the ductile basinal sediments were bent and rotated around the rigid Saccense carbonates during the thin‐skinned southward propagation of the orogenic front. We document here that the coastal sediments from the southwestern Gela Nappe underwent both a post middle early Pleistocene ∼30°CW rotation and a post middle Pleistocene E–W to ESE–WNW flattening (revealed by AMS). Our data then constrain to the late Pleistocene‐Holocene the age of the last shortening episode occurring in the southwestern Gela Nappe front. Pleistocene rotations of similar amount also characterize the Sicanian domain, implying that it was incorporated in the Gela Nappe wedge during the recentmost episodes of deformation. This evidence allows us to better understand the very large (up to 114°) post Mesozoic rotations reported by Channell et al. [1980, 1990] for the Sicanian limestones, as related to both Miocene (or older?) deformational episodes and the Plio‐Pleistocene evolution of the Gela Nappe.