bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of gravity in orogenic belts
Authors: Ramberg H. 
Published: May 2008

Summary
The diapiric and nappe structures of the Caledonides in Scandanavia are briefly discussed and compared with similar structures in other orogenic belts. The buoyancy of sialic basement is discussed and a theoretical treatment of basement buoyancy is outlined. The gravitational spreading of nappes is then considered. Two theoretical models are presented: the first considers the condition of free slip on the base and the second deals with the more realistic situation when the base exhibits coherence.
Dynamic analysis of a small imbricate thrust and related structures, Front Ranges, Southern Canadian Rocky Mountains
Authors: Spang J. H. , Brown S. P. 
Published: May 2008

Summary
The thrust is a hanging-wall imbricate of the Lac des Arcs Thrust within the McConnell Thrust Plate. The small imbricate terminates vertically into a cylindrical, macroscopic kink band and laterally by merging with the Lac des Arcs Thrust. Numerical dynamic analysis of calcite and dolomite twin lamellae gives a near layer parallel maximum principal compression and an extension at a high angle to layering, both in the transport direction. The twinning is considered to be late stage. Reorientation of the principal axes occurs near folds and other minor thrusts in the area.
The microfabric of calcite tectonites from the Helvetic Nappes (Swiss Alps)
Authors: Schmid S. M. , Casey M. , Starkey J. 
Published: May 2008

Summary
The crystallographic orientations of calcite in tectonites from the Morcles Nappe and the Glarus Overthrust have been measured by X-ray texture goniometry. The orientation data are represented by pole figures, inverse pole figures and as orientation distribution functions.
The patterns of preferred orientation observed in the specimens from the Morcles Nappe are correlated with intracrystalline slip mechanisms. The patterns exhibit quasiaxial symmetry and in some cases the axis of symmetry is oblique to the symmetry of the macroscopic fabric. This obliquity is interpreted as the result of a rotational strain path and may be used to infer direction and sense of shear.
Some specimens of the Lochseiten mylonite from the Glarus Thrust show no strong preferred crystallographic orientation. This suggests that grain boundary sliding was the major deformation mechanism.
Very low grade metamorphism with a reverse gradient induced by an overthrust in Haute-Savoie (France)
Authors: Aprahamian J. , Pairis J.-L. 
Published: May 2008

Summary
The observed distribution of metamorphic transformations, using: (1) the metamorphic facies of Taveyanne Sandstones, (2) the mineralogical composition of the argillaceous fraction (which shows index minerals like paragonite, corrensite and allevardite), (3) the crystallinity indices of the illites, enables us to show that a reverse gradient (the maximum of which must be located in the thrust plane) is superimposed on the already known gradient which decreases both towards the top of the series and towards the external part of the chain.
To account for the observed relationships, we propose that heat was produced by friction along the thrust plane; the theoretical implications of such a model are discussed.
It is pointed out that such a reversed metamorphic gradient will only be observed following favourable circumstances of nappe thickness, rate of motion, thermal properties of the rocks and rate of erosion.
Saline horizons acting as thrust planes along the southern margin of the Damara Orogen (Namibia/SW-Africa)
Authors: Behr H. J. , Ahrendt H. , Schmidt A. , Weber K. 
Published: May 2008

Summary
At the S margin and at the base of the Naukluft Nappes of the late Proterozoic-early Palaeozoic Damara Orogen in Namibia so-called ‘Unconformity Dolomites’ are developed along thrust planes of nappes and within imbricate structures. Micro-probe analyses, phase-petrological relationships of the unusual mineral composition of the ‘Dolomite’, the salinity and composition of fluid inclusions as well as other geochemical data prove a saline origin of the ‘Unconformity Dolomite’. These data combined with observations on the relationship of deformation and mineral growth, calculated geothermal gradients and radiometric datings lead to the conception that the ‘Unconformity Dolomite’ is a hot saline intrusion which has already intruded a preexisting nappe pile. After intrusion and rapid crystallization, the rocks directly below the rigid dolomite plate acted as a thrust plane for last nappe movements which brought the Naukluft Nappes into their present position.
Sliding and other deformation mechanisms in a glacier of salt, S Iran
Authors: Talbot C. J. 
Published: May 2008

Summary
One of the salt glaciers in S Iran is interpreted here as an analogue of a gravity-driven, thrust nappe complex which has overridden its own debris. Fabrics from different parts of the body are interpreted in terms of grain boundary diffusion and dynamic recrystallization, together with tensional separation and sliding along the cubic cleavages of porphyroclasts of clear halite.
Slides generate within the salt as ramps, where the salt glacier slows and thickens to surmount the bedrock obstructions to its general downslope flow. Zones of plastic flow-folds and smaller zones of large-scale crenulation cleavage form upstream of the obstructions and the slides emerge from the downstream end of such zones. Few, if any, ramp directly to the surface and most turn to flats within the salt sheet where they may heal as a result of stress-drop annealing.
The competence of the salt mass is assumed to decrease down its length in response to a decrease in grain size and a relative increase in insoluble grains. Such a decrease in competence accounts for the change in character of the internal deformation of the salt sheet when traced downstream. First the slides and then the crenulation cleavage fail to develop upstream of successive obstructions and eventually all internal folding ceases. Instead, the salt glacier moves over the last few bedrock ridges as accommodation folds and another type of slide appears to form by layer parallel slip.
All the slides in the salt glacier originate near irregularities in its bedrock channel. The slide propagation zones remain stationary and the salt tears as it passes through, and beyond them. Instead of eroding its bedrock, the salt glacier effectively smooths irregularities in its channel by shearing over the infilling bodies of static salt.
The Caledonides of northern Norway: relation between preferred orientation of quartz lattice, strain and translation of the nappes
Authors: Boullier A.-M. , Quenardel J.-M. 
Published: May 2008

Summary

In the area of Birtavarre (eastern Troms) evidence of nappe tectonics exist at all scales. The preferred orientation of the
c
-axis of quartz shows a monoclinic symmetry and consists of a girdle containing
Y
and oblique to
Z
. The obliquity of the girdle-angle ϑ between the
c
-axis girdle and the
YZ
plane-is interpreted in terms of simple shear, and the strain is calculated from these data. The results from this study are: (1) almost all the quartz-bearing samples give a consistent sense of simple shear (movement towards the SE) except for some gneisses supposed to be allochthonous Precambrian. (2) the calculated strain is too low to explain the displacement of the nappes (more than 40 km for a 2 km thick unit):
X/Z
ratio is less than 10 on the average. Possible reasons for this are discussed.
Structure and distribution of fault rocks in the Alpine Fault Zone, New Zealand
Authors: Sibson R. H. , White S. H. , Atkinson B. K. 
Published: May 2008

Summary
The Alpine Fault Zone, which is the dominant strand in a dextral system of transform faults along the boundary between the Indo-Australian and Pacific plates, forms a pronounced lineament about 1 km in width. Within the fault zone, the cross-strike passage from cataclasite through augen mylonite (both derived from largely granitoid basement to the NW) to mylonites derived from the high-grade Alpine Schists on the upthrown south-eastern side, is thought to reflect the original distribution of fault rocks with depth below near-surface gouge zones. Structural data suggest that the fault rocks had their fabrics impressed during the late Cenozoic phase of oblique compression when the Southern Alps were ‘ploughed-up’ along the fault. Mylonitic foliation indicates a dip approaching 50°SE for the fault zone at depth, while penetrative stretching lineations plunge in a direction sub-parallel to the present-day interplate slip vector, consistent with dextral-reverse-oblique shear across the fault zone. Pseudotachylyte friction-melt is fairly widely distributed and can be found cutting all other fault rock types apart from gouge. Models for the evolution of the fault zone are considered.
Uplift rates and thermal structure in the Alpine Fault Zone and Alpine Schists, Southern Alps, New Zealand
Authors: Adams C. J. 
Published: May 2008

Summary
Rates of vertical and horizontal movement at the Alpine Fault Zone and within the adjacent Alpine Schists (Haast Schist Group) are deduced from K-Ar age data of metamorphic and mylonitic rocks. The relative contributions of Jurassic-Cretaceous (Rangitata) and Miocene-Recent (Kaikoura) orogenic phases are also estimated.
After Jurassic regional metamorphism, the Haast Schists were uplifted regionally 18–20 km at rates 0.3–0.4 mm/yr until mid-Cretaceous times. No differential vertical movements occurred on the Alpine Fault at this time. During the Miocene-Recent orogeny, a maximum of 10 km uplift, produced mylonitic rocks at the Alpine Fault and brought Alpine Schists (Haast Schist Group) to the surface. Ages of mylonite, blastomylonite and pseudotachylyte indicate intense fault movement was occurring 5–10 Ma ago. Ages as young as 0.7 Ma occur in the adjacent Alpine Schists. From these data, uplift rates at the Alpine Fault for the period late Miocene-Pliocene are in the range 2.5–5 mm/yr and late Pleistocene-Recent, 7–14 mm/yr.
The estimation of horizontal displacements at the Alpine Fault in the Jurassic-Cretaceous and Miocene-Recent orogenic phases depends critically on the reality of a Cretaceous (?) lamprophyre dyke swarm cut by the Alpine Fault. If this is accepted, then about 360 km horizontal movement is pre-Upper Cretaceous and 120 km is younger. If the dyke swarm evidence is dismissed, then a total 480 km displacement on the Alpine Fault is entirely post-Cretaceous and may have occurred during the Miocene-Recent orogenic phase. This is, then, broadly associated with large-scale motions of the Indian and Pacific plates in the late Cenozoic and Quaternary.
Analysis of the age patterns within the Alpine Fault mylonites and the adjacent Alpine Schists support the possibility that a 15 km wide thermal aureole, about the Alpine Fault or at zones of intense shearing within the Alpine Schists, has been created by frictional generation of heat during relatively rapid aseismic shear sustained over the last 5 Ma. This thermal effect has been sufficient to cause complete argon loss from rocks over a 10 km wide zone immediately E of the Alpine Fault.
The internal geometry of nappes: criteria for models of emplacement
Authors: Cooper M. A. 
Published: May 2008

Summary
The geometric and stratigraphic properties of thrust sheets and fold nappes are controlled by the mechanisms by which they were initiated and emplaced. Thrust sheets that have developed by gravity gliding have their internal stratigraphies truncated by the basal thrusts which cut up-section at the trailing edges. In contrast thrust sheets that have developed by gravitational spreading have their internal stratigraphies truncated by the overlying thrust sheets, and their basal thrusts cut up-section at the leading edges. Fold-nappes have complicated geometries and correlation of stratigraphy between successive nappes is difficult. The basic geometric and stratigraphic properties of thrust sheets and fold-nappes developed by different mechanisms may be used as criteria for testing the applicability of these mechanisms to particular areas of orogenic belts. The Valley and Ridge Province of the Appalachians has geometric and stratigraphic properties consistent with thrust sheet development by gravitational spreading. The western nappes of the Central Scandinavian Caledonides are more complex but have properties suggesting development by buoyant upwelling of the orogen infrastructure. There is, however, a lack of detailed cross-sections of orogenic belts based on geophysical and/or borehole data in addition to the geological data. The interpretation of geological data in isolation is often too dependent on subjective information coloured by the mechanism preferred by the individual concerned.
The Moine Thrust Zone: an overview
Authors: McClay K. R. , Coward M. P. 
Published: May 2008

Summary
The geometry of structures within the Moine Thrust Zone are similar to those found in classic thin-skinned tectonic regimes such as the southern Canadian Rocky Mountains. The deformation style and strain patterns along the strike of the Moine Thrust Zone are controlled by the position of the floor (or Sole) thrust. The stacking sequence of thrust nappes is from E to W in the direction of transport. Reactivation of some thrusts has caused reversals in the stacking sequence. The mylonites associated with the Moine Thrust have undergone a long and complex history of progressive deformation.
Detailed descriptions of the Moine Thrust Zone at Loch Eriboll are given and the relationships of the Moine Thrust Zone to other major Caledonian tectonic features of the NW Highlands are discussed.
Tectonic slides in the Caledonides
Authors: Hutton D. H. W. 
Published: May 2008

Summary
Despite the continuing use of the term ‘tectonic slide’ in the Caledonian fold belt of Britain and Ireland for the past fifty years, the concept has found few advocates elsewhere. To many geologists outside the British Isles it remains a subject of some confusion.
A review of the literature suggests that slides are a general term for faults which form in close association with syn-metamorphic regional deformation. They are often related to major folds although this is not a diagnostic feature. Neither is any movement sense implied in the term slide; thus, they may be thrusts, lags, oblique slip etc. Classically, these structures lie along and subparallel to the boundaries of major lithological units but transgress the stratigraphy on a larger scale. Structural analogies with the thrusts of the lower grade or non-metamorphic deformed cover sequences can often be seen in slides. However, they are more commonly and possibly fundamentally the result of differing responses to deformation of contrasting, adjacent lithologies in areas of higher strain and metamorphism.
Estimation of the rate and amount of absolute lateral shortening in an orogen using diachronism and strike slipped segments
Authors: Phillips W. E. A. 
Published: May 2008

Summary

By reference to the Caledonide Orogen, a method is illustrated by which quantitive estimates may be obtained of lateral movements between opposing forelands of a collision orogen. The procedure involves: 1: Identification of a rigid foreland frame (2 plates) bounding the collision orogen and establishing the orientation of the main movement direction between forelands, 2: Measurement along strike of diachroneity in the ending of arc volcanism and of cooling ages for granites; relating this to a rate of migration of collision along strike of the collision suture, and calculation of the rate of plate convergence from this, knowing the angle between the collision suture and the plate movement direction, 3: Recognition of swings in strike which predate collision, and 4: Measurement of lateral offset of dated collision points in the strike slip sector of the curved orogen and calculation from this of the components of lateral shortening around the curve. Application of these methods to the Caledonide Orogen of the British Isles, Scandinavia and E Greenland, gives values for foreland convergence on a trend of 115–295° of 0.88 cm/year between the Lower Caradoc (430 Ma) and Lower Ludlow (
c.
400 Ma). Convergence slowed to 0.75 cm/year on this trend during the Caledonian orogenesis between Lower Ludlow (
c.
400 Ma) and the end of the Middle Devonian (
c.
365 Ma), giving lateral convergences of about 267 km in the E Greenland W Norway region (
c.
22%) and 216 km (
c.
31%) in the paratectonic Caledonides of the British Isles.
Strain within thrust sheets
Authors: Coward M. P. , Kim J. H. 
Published: May 2008

Summary
The finite strains within the thrust sheets of the Moine Thrust Zone in NW Scotland have been factorized into components of simple shear and longitudinal strain. Variations in these strains have been examined in the Cambrian sediments in the Eriboll and Assynt areas and strain maps produced of the Glencoul Nappe, Assynt. There are heterogeneous simple shear strains parallel to the layering resulting from bending of the nappe over a step in the thrust plane and to frictional drag at the base of the thrust. Layer parallel shortening and associated layer parallel thickening occur in the front of the thrust zone at Eriboll, above a decoupling plane in the lower part of the Cambrian sequence. Within the Cambrian rocks of the Glencoul Nappe in Assynt, there is a steady eastward increase in intensity of layer parallel shortening togeather with local anomalous zones characterized by more intense shortening or extension. These anomalous zones overlie shear zones in the Lewisian basement. There are variations in shear strain on the plane which contains the normal to bedding resulting from differential movement of the nappe. These shear strains distort and fold the bedding planes. Combinations of these shear strains and the longitudinal strains result in a wide range of ellipsoid shapes from oblate to prolate and also explain the pattern and sequences of folds in the nappes and mylonite belts. The folds are formed by local variation in shear and longitudinal stress and, hence, there may be no simple correlation of fold phases along, or across, a thrust zone.
Tectonics of the Helvetic Nappes
Authors: Ramsay J. G. 
Published: May 2008

Summary
This paper gives a general account of the principal major nappes, fold and fault styles, and minor structural features of the Helvetic Nappes with particular emphasis on research results over the past few years. The principal stratigraphic variations are summarized and their influence on development of tectonic structures described. Measurements of strain variations throughout the nappe pile can be used to evaluate the significance of cleavage and linear fabrics. Pressure solution is a particularly important rock deformation process throughout the whole region and provides the source for the fibrous vein fillings which characterize much of this region.
Fold-and-thrust tectonics in the Helvetic Nappes (E Switzerland)
Authors: Pfiffner O. A. 
Published: May 2008

Summary
The Helvetic Nappes in E Switzerland form an example of décollement nappes. The Säntis Thrust represents both an upper and a lower detachment. In the units underlying this detachment shortening is accomplished by a combination of folding and thrusting and is strongly influenced by the occurrence of 2nd order décollement horizons. Nappe-internal deformation resulted in the reorientation of folds (development of a fold arc) and smoothing out of ramps and flats in thrust surfaces. Two types of folds can be recognized: true buckle folds and folds due to ramps and flats.
The movement direction of the thrust sheets was S-N and fold axes oblique to this direction developed probably due to initially ENE striking ramps. Transverse faults with a strike slip component allow changes in displacement along individual thrust surfaces.
Some observations on the development of thrust faults in the Ultradauphinois Zone, French Alps
Authors: Beach A. 
Published: May 2008

Summary
The Ultradauphinois Thrust Nappe involved a westerly movement of external autochthonous Jurassic and Eocene sedimentary sequences by décollement on the Trias. A complex thrust belt evolved at its southern end as the movement was hindered by the upfaulted Pelvoux basement massif. All of the Jurassic rocks exhibit strong, enetrative ductile strains—in the lowermost thrust slices (most westerly part of the sheet) forward spreading strains (NE-SW stretching) involving a combination of simple and pure shear, and in the uppermost thrust slices a NW-SE stretching and rearward compression as the main nappe continued to move past to the N of the hindrance. As the resistance to movement increased in the S, the completely distributed ductile strain became localized in numerous zones, characterized by the formation of many veins and strong local deformation of these veins. This marks the onset of stratigraphic imbrication and repetition. The progress from penetrative ductile to localized ductile to discrete brittle strain is recorded by the sequence of structures observed in the field. The main discrete, brittle thrust surfaces represent the last major stage in a continuous sequence of deformation.
Gravity sliding in the Maritime Alps
Authors: Graham R. H. 
Published: May 2008

Summary
Fallot’s ‘intercutaneous’ Tinée Nappes are interpreted as gravity slides initiated by uplift of the Argentera Massif and emplaced partly by the ductile deformation of slate horizons, and partly by movement on discrete shear planes. Together, the structures stack between 8 and 11 km of Jurassic and Lower Cretaceous strata—the telescoped cover of the Argentera Massif. The lowest nappe is the furthest travelled.
Sliding on a larger scale may have contributed to shortening in the more external parts of Provence.
Sutures, thrusts and nappes in the Variscan Arc of western Europe: plate tectonic implications
Authors: Matte Ph. , Burg J. P. 
Published: May 2008

Summary
The Variscan Arc of western Europe, convex to the W, links the Iberian and the middle European Variscides. It is characterized by nappes and thrusts with converging vergences towards the inner part of the arc. This is illustrated by two cross-sections, one roughly E-W in northwestern Spain, the other N-S in the French Massif Central. This segment of the Variscan belt appears to be a typical collision belt whose plate tectonic evolution may be explained in the following stages: (i) consumption of a Lower Palaeozoic ocean by an intraoceanic subduction towards the NW, (ii) choking of subduction by underthrusting of continental crust beneath the oceanic lithosphere (obduction), (iii) intracontinental deformation during which the arcuate form results from the progressive impingement of a southern continental promontory (part of Africa?) into the northern Laurasian continent.