bluuebunny/crossref_metadata_2025_split huggingface dataset:
Notes and cross-sections illustrating inversion tectonics in the Wessex Basin
Authors: Simpson I. R. , Gravestock M. , Ham D. , Leach H. , Thompson S. D. 
Published: April 2008

Summary
Four cross-sections based on seismic and well data illustrate the Tertiary inversion tectonics in the Wessex Basin. Inversion is concentrated in Early Cretaceous depocentres with Permian and Triassic depocentres undergoing limited uplift. In the Portland—South Wight Basin inversion formed a northward facing monocline with a major reverse fault in the S. In contrast, in the Weald Basin a broad arch of 50 km wavelength was formed. Both basins show an overall uplift of 1.5 km. These variations in inversion style are probably a function of the geometry of the basin-controlling faults and underlying detachments.
The kinematics of inversion in the Danish Central Graben
Authors: Cartwright J. A. 
Published: April 2008

Summary
The Danish Central Graben is a complex mosaic of half-grabens and structural highs that formed during Permo-Triassic and Upper Jurassic rift phases at the confluence of the NW-SE and N-S trending elements of the Central North Sea Rift. The extensional structures forming the margins to the rift were reactivated in a reverse sense in the Late Cretaceous as part of the regional inversion of basins in the southern North Sea. Deposition proceeded throughout the deformation, and thickness variation in the deep marine Chalk succession is directly attributable to compressional deformation of the basin floor. The total shortening across the rift amounts to only a few percent, and the structural expression of the reactivated margins is typically as low amplitude folds with minor associated reverse faulting. Compressional reactivation was restricted to basement faults, and the shallow inclination of the margin faults may have been an important factor in their subsequent reactivation. Zechstein evaporites and overpressured Jurassic shales influenced the development of some of the compressional structures. The orientation of the growth fold axes is consistent with a net convergence in an approximately NE-SW direction. The fold axes are arranged in a segmented pattern which can be related to the underlying basement fabric. This segmentation not only resulted in variations in the amounts and style of shortening along the length of the rift, but seems to have influenced the timing of the deformation. Seismic-stratigraphic analysis of the Upper Cretaceous sequence indicates that the compressional deformation was markedly diachronous. Abrupt changes in the deformational chronology are found to occur across the transverse segment boundaries.
The Permian to Cretaceous structural evolution of the Western Approaches Basin (Melville sub-basin), UK
Authors: Chapman T. J. 
Published: April 2008

Summary
The tectonic-sedimentary evolution of the western part of the Western Approaches Basin (Melville sub-basin) was initiated during early Permian times when synrift clastic sedimentation and volcanism commenced within an ENE trending half-graben. This sequence thickened to the south and onlapped a high to the north. During the Permian an early NNW-SSE basin extension was accommodated on an array of ENE-WSW trending normal faults linked by NNW-SSE orientated transfer faults. This was followed by a period of ENE-WSW extension along the basin axis when the normal and transfer faults of the previous faulting episode swapped roles. This was possibly related to early rifting in the Bay of Biscay. Both sets of faults appear to be controlled to some extent by Variscan thrusts and strike-slip faults within the basement. During the Upper Triassic the ridge in the north subsided allowing a thick sequence of salt to be deposited where there had previously been a topographic high. During Jurassic times sedimentation extended across the Permian-Triassic half-graben into the French sector. This was followed by an episode of rifting and wrench deformation (and inversion?) during which the Permian to Jurassic basin was domed and uplifted. The Cretaceous to Tertiary sedimentation which followed probably resulted from postrift thermal subsidence related to cooling of the continental platform adjacent to the opening Atlantic Ocean. Steep normal and/or strike—slip faults data from the earliest part of this postrifting stage.
Devonian basins of Northern Scotland: extension and inversion related to Late Caledonian — Variscan tectonics
Authors: Coward M. P. , Enfield M. A. , Fischer M. W. 
Published: April 2008

Summary
The Devonian sedimentary basins of Northern Scotland illustrate the different processes of inversion along reactivated frontal and lateral thrust ramps, and the importance of strike-slip fault movements to late and post-Caledonian tectonics. The basins of the West Orkneys and West Shetland, west of the Great Glen Fault developed by collapse of thickened Caledonian crust during the Devonian. The basins extended in a NW-SE direction on dominantly SE-dipping faults, which curve and become parallel to the earlier Caledonian fabric at depth. The Caledonian structures developed a crustal anisotropy which was subsequently reworked during the later Palaeozoic and Mesozoic by extensional and compressional movements. Hence in the West Orkney and Minches basins, Caledonian structures influenced the kinematics of Early to Middle Old Red Sandstone extension, later (Devonian and Permo-Carboniferous) compression, Mesozoic extension and later Mesozoic-Tertiary compression. During basin extension, minor inversion of early listric normal faults occurred within the basin sediments, driven by gravitational gliding down tilted fault blocks. SE of the Great Glen Fault in eastern Shetland and possibly also the Inner Moray Firth, basins were affected by NE-SW extension during Middle to Upper Devonian times. This is possibly a result of sinistral strike-slip displacements on the Great Glen-Walls Boundary Fault system. This strike-slip episode may have been responsible for inversion of the earlier and more regionally widespread Lower and Middle Devonian basins formed by NW-SE extension. Localized zones of folding in Caithness and the Orkney Islands and wide zones of more intense folding in western Shetland are thought to be related to this deformation. Late Palaeozoic Variscan dextral strike-slip displacements juxtaposed basins along the Great Glen-Walls Boundary fault system which have distinct stratigraphies and structural evolutions and formed separately to the east and west of these faults. This strike-slip deformation inverted basins both to the east and west of the Great Glen Fault. In the East Shetland basins it produced local zones of overturned beds above oblique and frontal ramps. Further subsequent dextral movements in the Mesozoic produced pull-apart basins in the Moray Firth and East Orkneys.
A new tectonic model for the Helvetic nappes
Authors: Dietrich D. , Casey M. 
Published: April 2008

Summary

A tectonic model must be based on geometrical information of both large and small scales. A new model of the Helvetic nappes of western Switzerland has been developed using constraints from:

(1)
The geometric shape of the nappes. Accurate profiles of the Morcles, Diabelerets and Wildhorn nappes show that all three nappes are wedge-shaped and that the axial planes of the major nappe internal folds converge towards the root zone.

(2)
The strain state of the nappes. All the existing pressure shadow fibre data of the region are reviewed and reveal the existence of very steep gradients of increasing strain towards the root zone of each individual nappe.

(3)
The metamorphism of the nappes. A compilation of illite crystallinity data indicates the existence of a vertical gradient of increasing metamorphism, but as well of a horizontal gradient of metamorphism increasing towards the root zone.

A geometrical and finite element compatibility model is presented which best accounts for these data. This model shows the following geometrical features:

(1)
Combinations of simple shear and pure shear deformation to account for the horizontal strain- and metamorphic gradients.

(2)
The heterogeneous simple shear part of the deformation is constant in magnitude from the root zone to the external part of the nappes.

(3)
The pure shear part of the deformation decreases towards the external part of the nappes.

(4)
Varying amounts of overthrust displacement are taken up by distributed ductile shear in the internal part of the nappes and by thrust faulting in the external part.

This model has kinematic implications. We envisage tectonic extrusion from the root zone to be responsible for the pure shear component of the deformation. The nappes formed sequentially being extruded between the underthrusting basement and the backfolded Gotthard massif.
Strain-displacement compatibility and restoration of the Chaînes Subalpines of the western Alps
Authors: Gratier J.-P. , Ménard G. , Arpin R. 
Published: April 2008

Summary
Finite strain values and trajectories of the sedimentary cover of the French Chaînes Subalpines (Chartreuse, Vercors, Diois, Baronnies) with respect to the stable platform west of these regions were deduced from the strain measurements of a folded and faulted competent layer (Tithonian). The removal of this finite deformation was obtained by a finite element analysis (84 elements of initial size of about 15×15 km) and the finite displacement field of this cover was calculated. Assuming a stable margin (one fixed element, and one line with a constant direction during the progressive deformation) the displacement of the eastern, southern and western limits of the Chaînes Subalpines were estimated. A displacement towards the west, associated with a counterclockwise rotation (15–20°) was found for the Miocene—Present basement thrust of the Belledonne massif. The presence of local heterogeneities (such as Jurassic normal faults) deflect the general E-W displacement along dextral NE-SW and N-S strike-slip faults and induce a displacement of the Chaînes Subalpines towards the southwest. The comparison of the restored depth of the Tithonian with its estimated initial depth reveals an excess of elevation of the Chaînes Subalpines with a maximum value (1000–1500 m) for the Diois—Vercors which might be associated with an external basement thrust under the Chaînes Subalpines.
Southwestward thrusting and tectonics of the western Alps
Authors: Fry N. 
Published: April 2008

Summary

The gross geometry of the western Alps is the result of three processes operating since Eocene times: thrusting to WNW; thrusting to SW; arcuate lithospheric flexure due to loading. In the
external zones
, taken to include the SubBriançonnais domain, these processes are more substantial than earlier phases of Alpine tectonics. In the
internal zones
, these processes rework substantial earlier Alpine structures. A major feature of Alpine thrusting is the preservation of basement topography, which influences the geometry of the thrust system. This is demonstrated by the Digne thrust system W from Remollon and is implicated in both formation and emplacement sequence of the Lower Embrunais-Ubaye nappes, in the Embrunais-Ubaye arc, in the localization of WNW thrust outcrops S of the Pelvoux Massif and perhaps in the southerly derivation of Gres d’Annot sediments. A major (>100 km) phase of SW thrusting affects the Embrunais-Ubaye terrain (continuity of external and SubBriançonnais) before the development of the lower Embrunais-Ubaye nappes and the arcuate deformation of their external floor. All these Embrunais-Ubaye processes are consistent with maintenance of a single 230° transport direction, and with thrusts arising from depth, causing real crustal shortening. Later events with southwestward transport are the emplacement of the combined Parpaillon-Briançonnais thrust stack, the Argentera Massif ‘pop-up’, and the Digne thrust system. Despite circumstantial evidence, there is no substantial contribution to the regional tectonics of the western Alps from strike-slip tectonics, inversion tectonics, gravity tectonics, rotation during thrusting, radial thrusting or arc bending. The dominant features are the maintenance, spanning hundreds of kilometres and tens of millions of years, of the two principal directions of thrust transport (230°; 290°) and the regional continuity of displacements which this implies.
Structural and metamorphic constraints on the tectonic evolution of the upper Pennine Alps
Authors: Ellis A. C. , Barnicoat A. C. , Fry N. 
Published: April 2008

Summary
A series of thrust and shear zone structures in the upper Pennine Alps dissect the area into a number of horsts and duplexes. The diversity of the mineral stretching lineation directions when combined with shear-sense indicators reveals substantial variation in the movement direction both between and within different units, and in some cases at different times within the same unit. The present-day geometry, illustrated in a new block diagram, is controlled largely by backthrusts. These backthrusts have overprinted, and in some cases reactivated, earlier, more ductile forethrusts and cut out all but one of the regional megascopic folds. While this backthrusting renders structural analysis of the early history of the area intractable, study of the petrogenesis of early, high-pressure assemblages yields some data. Deformation during subduction, leading to the subcretion of rock packets onto the over-riding plate is recorded by a ‘hairpin’ in the P-T paths of several units, and by a few relic structures within ophiolite units. The forms of P-T paths for units which have undergone high pressure metamorphism indicates that they underwent similar histories. Geochronological data for this area are as yet of insufficient resolution to decide if the tectonometamorphic events were continuous or episodic.
West-directed décollement of Austro-Alpine cover nappes in the eastern Alps: geometrical and rheological considerations
Authors: Ratschbacher L. , Neubauer F. 
Published: April 2008

Summary
The Austro-Alpine unit of the eastern Alps constitutes a thrust belt characterized by multiple deformations under changing external stress regimes during the Alpine orogeny. Problems arise in recognizing direction and geometry of initial detachment tectonics and flow behaviour of mylonites accompanying detachment thrusts.
In the first part of this article, we analyse the actual distribution of Austro-Alpine cover sediments as acquired during the Alpine orogeny and studied detachment thrusting on three sections through thrust systems occupying different vertical positions in the Austro-Alpine stack. In the second part, we study ductile rock flow in mylonites along individual thrusts in the basement-cover décollement zone.
The ramp-flat geometry, the dip of frontal ramps, and the imbrication of youngest sediments at the leading edge of thrust systems show that detachment is directed towards the W or NW and is, thus, in agreement with displacement directions derived from the analysis of microstructures in ductile mylonites of the Austro-Alpine unit. This direction deviates from the current N-ward hypothesis of Alpine décollement.

Cover imbrication occurred along brittle thrust faults, whereas broad belts of mylonites accompany the basement-cover detachment thrusts. Mylonite generation may have started under differential stress conditions as high as 100 MPa. Stress relaxation was achieved in monomineralic rocks mainly by geometric softening, producing highly ordered phyllosilicate, quartz and calcite textures, and, in polymineralic rocks, by pressure solution and grain boundary sliding mainly along quartz-phyllosilicate and phyllosilicate-phyllosilicate contacts. Imposed strain rates range from 10
−11
sec
−1
to 10
−15
sec
−1
, and ductile flow lasted up to 8 Ma.
Plate-scale kinematics and compatibility of crustal shear zones in the Alps
Authors: Lacassin R. 
Published: April 2008

Summary
Crustal-scale thrusts of the western Alps are characterized by W to WNW directed movements of several hundreds of kilometres. In the internal zones, prominent lineations mark these slip directions. In the central Alps, coeval right-lateral strike slip (Insubric fault) and N-NNW vergent thrusting (Helvetic and more external thrusts) occurred during the upper Tertiary, on crustal-scale faults. It is proposed that WNW directed convergence between NW Apulia and Europe was accommodated mainly by the combination of movements on three first-order faults: in the central Alps, this oblique convergence is partitioned in two components (thrust and strike slip) at a deep fault bifurcation; in the western Alps, it accounts for the observed thrusts. This direction of convergence in the western and central Alps is markedly different from the coeval relative motion of Africa and Europe (N to NNW directed convergence). It implies either specific movements of Apulia with respect to Africa, or the lateral extrusion of NW Apulia during the indentation of the African promontory during the collision.
A review of palaeomagnetic and magnetic anisotropy results from the Alps
Authors: Heller F. , Lowrie W. , Hirt A. M. 
Published: April 2008

Summary
Numerous palaeomagnetic studies in the Alpine region have documented the effects of tectonic displacement and rotation. Regions in the southern Alps are characterized by palaeomagnetic directions which are more similar to directions predicted by the African path of apparent polar wander than by the Eurasian path. Attempts to define the extent of the region with this African affinity are found in the internal zone of the western Alps, and also in the Lepontine of southern Switzerland, yet directions with European affinity have been reported from S of the Insubric Line. Although the northern calcareous Alps are of southern Tethyan origin, palaeomagnetic directions reveal that these allochthonous units have undergone substantial rotations, in some places clockwise and in others anticlockwise, during emplacement. Several palaeomagnetic studies in the eastern and central Alps show rotated directions due to strong local tectonic effects. In the western Alps, European style directions are found in the undeformed rocks of the Dôme de Barrot and the external Dauphinois zone, whereas directions from the internal zone tend to have African affinity.
Deformation produces not only a deflection of the stable palaeomagnetic vector in a rock. If the deformation is penetrative, grain rotations falsify the palaeomagnetic vector. Preferential grain alignment caused by deformation produces a magnetic anisotropy which can be measured easily and quickly in many rocks. Analogously to the strain fabric, the magnetic fabric can be described by an anisotropy ellipsoid. Several studies in the Alps have confirmed that the principal axes of the magnetic anisotropy are aligned with the corresponding axes of the strain ellipsoid. In deformed Permian red beds in the Alpes Maritimes the anisotropy ellipsoid changes shape and orientation like the strain ellipsoid during progressive deformation. A good qualitative agreement between magnetic fabric and petrofabric is also found in Jurassic shales and slates from the Dauphinois zone of the western Alps, where magnetic lineations often correspond to the direction of nappe transport. In strongly deformed Permo—Triassic red beds from the Lower Glarus nappe complex in central Switzerland the quantitative relationship between strain and magnetic fabric was used to derive equivalent strain ellipsoids in rocks that had no conventional strain markers. In the eastern Alps, the sense of motion on the Insubric Line has been postulated from magnetic fabric observations. Magnetic anisotropy results have been used in attempts to correct palaeomagnetic vectors for the effect of deformation. This technique may be viable in weakly deformed rocks, but it fails in strongly deformed samples; the limits of its applicability have not yet been determined satisfactorily.
Mineral genesis in ironstones: a model based upon laboratory experiments and petrographic observations
Authors: Harder Hermann 
Published: April 2008

Summary
Although mineral assemblages of ironstones vary widely, with hematite and goethite being the main components of red deposits and berthierine and siderite predominating in green deposits, the bulk major and minor elemental chemical compositions for both types of deposits are very similar. This indicates that the source material and physico — chemical conditions at the site of deposition must have been almost identical and that the different mineral associations probably developed during early diagenesis.

Data from experimental studies including iron clay mineral synthesis throw light upon the post-depositional processes. It is demonstrated that berthierine can be synthesized from iron hydroxides in solution with initial SiO
2
concentrations of 5–9ppm, low concentrations of Mg and K, and with ferrous iron dominant.

Decay of organic matter causes changes of Eh towards reducing conditions, which destabilizes the iron-rich particles and leads to both increased concentration of ferrous ions in the pore solution and the release of silicic acid ions. pH and concentration of silicic and carbonic acid controls whether berthierine or siderite is formed. In red deposits the concentration of organic material is low, suggesting that the presence and amount of organic material is a controlling influence.
The formation of goethitic ooids in condensed Jurassic deposits in northern Switzerland
Authors: Gehring A. U. 
Published: April 2008

Summary
Goethitic ooids from condensed sequences close to the Middle/Upper Jurassic boundary in the Swiss Jura mountains were analysed for texture and chemistry. The sequences are characterized by discontinuities of sedimentation and reworking, which indicate a marine aerobic depositional environment. The ooids consist mainly of isometric goethite particles with apatite and clay mineral flakes. The coexistence of these mineralogical phases can be explained by different adsorption processes due to electrostatic forces or ligand exchange reactions. Both types of processes are discussed and illustrated schematically.
Minette-type ironstones
Authors: Siehl A. , Thein J. 
Published: April 2008

Summary

Oolitic ironstones occur in various sedimentary environments: shallow marine to deltaic, lacustrine, fluviatile and pedogenic. Distinction between formational and depositional environment is not always possible. Most of the marine and fluvial minette-type ironstones consist of reworked ferruginous coated grains deposited in agitated water, but there exist also indicative structural features of
in situ
formation in the supporting medium of lateritic and hydromorphic environments. In the zone of oscillating groundwater repeated leaching and subsequent concretionary precipitation of hydrated ferric oxides take place, according to the prevailing Eh/pH-conditions and microbial activity. The moderate Al substitution of goethite from hydromorphic environments corresponds to the observed range in oolitic ironstones. The authors therefore assume erosion, reworking and subsequent fluviomarine redeposition of soil derived ooids to be the major processes of generating minette-type ironstones. Postdepositional diagenetic changes may convert the aluminous, silica-rich ferric oxides into berthierine in reducing environments if the chemical bulk composition of the primary goethite is similar. Since any aquatic milieu with appropriate fluctuations of Eh and pH can produce ferruginous coated grains, marine iron ooids associated with hardgrounds and areas of low sediment input can also occur. But there, release of ferrous iron, transport in saline interstitial waters and fixation of ferric hydroxides — usually with very low Al-substitution — take place in a much smaller scale, unable of generating the huge iron accumulations of minette-type ore deposits.