bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geodynamic model for Alpine intra-plate compressional deformation in Western and Central Europe
Authors: Ziegler P. A. 
Published: April 2008

Summary
The Mesozoic grabens and wrench induced troughs of Western and Central Europe developed in response to Triassic to Early Cretaceous intra-plate tensional stresses which affected the Arctic — North Atlantic and the Tethys borderlands during the rifting phases preceding the opening of the respective oceans. During the Alpine orogeny, collision-related compressive stresses exerted on the foreland induced the reactiviation of pre-existing fracture systems, and caused the inversion of Mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present Alpine deformation front. The structural style of these inversion structures is indicative of compression and transpression. Total crustal shortening is unlikely to exceed a few tens of kilometres. These displacements require a coupling between the foreland and the orogen at the Alpine A-subduction zones and, within the foreland, a decoupling at intra-crustal levels between the crust and mantle and/or at deeper lithospheric levels.
Rift basin evolution in Africa: the influence of reactivated steep basement shear zones
Authors: Daly M. C. , Chorowicz J. , Fairhead J. D. 
Published: April 2008

SummaryPhanerozoic rift basin evolution in Africa has been strongly influenced by the pre-existing basement structure inherited from Precambrian tectonics. Two modes of basement reactivation may be identified; the largely dip-slip reactivation of gently dipping shear zone and thrust structures and the largely strike-slip reactivation of steep shear zones and faults. In particular, crustal scale steep basement shear zones have exercised a profound control on rift basin formation on a regional scale. Such shear zone structures are seen to govern the location, trend and structural style of rifts and appear to constrain the orientation of displacements generating the rifts. The shear zones are relatively narrow, high strain zones formed during ductile deformation. They occur as steep, crustal scale ramps that define a pronounced mechanical anisotropy within the African continental crust. These structures are difficult to reactivate by dip-slip movement and thus tend to act as major strike-slip transfer zones during later extensional events. This paper discusses examples of the steep shear zone-rift relationship from three of the rift systems of Africa: the Upper Palaeozoic (Karoo) rifts of Central Africa, the Mesozoic rifts of the Sudan and the Cenozoic rifts of East Africa. These discussions indicate that steep shear zones are sites of rift nucleation and play a fundamental role in the mechanisms of rift propagation and subsequent continental breakup.
Alpine tectonics — an overview
Authors: Coward Mike , Dietrich Dorothee 
Published: April 2008

Summary
This overview summarizes aspects of 150 years of research in Alpine tectonics and in particular introduces the tectonic setting for the more detailed papers in this volume.
The Alpine Mesozoic ocean, Tethys, formed as a large elongate pull-apart basin in the Jurassic, as a consequence of the opening of the Atlantic and of the movement of Africa towards the east relative to a fixed Europe. The NNE trending Tethys was bounded by WNW trending transforms, by the European/Iberian margin in the W and by the Adriatic promontory of Africa in the E, and its shape determined the present day configuration of the arcs of the Alpine chain. The closing of this ocean and the collision tectonics began during the Cretaceous, as Africa moved to the NE relative to Europe and as the N Atlantic gradually opened, to drive Iberia and the southern part of the European plate to the E. Subduction of oceanic crust and adjacent continental crust led to high pressure metamorphism of Cretaceous age. Ophiolites were obducted over the southern continental margin, but after collision the shear sense reversed so that the Austro-Alpine nappes of the African Adriatic promontory overthrust Europe in a WNW direction. During the main Tertiary deformation the overall anticlockwise rotation of Africa led to a change-over from N to NW and WNW-directed collisional structures. The E-W striking sector of the Alps in Switzerland and Austria is therefore a diffuse transpressive dextral shear belt, approximately reworking the northern transform boundary of Tethys, modifying it by compression related to the rotation of the African Adriatic promontory.
Approximately 250 km of European lithosphere were involved in the building of the western Alps. As Alpine nappes consist largely of rock material confined to the upper crust, a large amount of lower crust and lithospheric mantle of the two continental blocks must be duplicated and/or subducted during the Alpine collision history.
Delamination and asymmetric lithospheric thickening in the development of the Tyrrhenian Rift
Authors: Channell J. E. T. , Mareschal J. C. 
Published: April 2008

Summary
Late tectonic extensional basins are superimposed on the continental collision suture at certain points along the Alpine belt. The onset of extension in these basins (Alboran, Tyrrhenian, Pannonian and Aegean) postdates the continental collision by only a few million years. In the case of the Tyrrhenian region, the rifting of the collision suture is accompanied by contemporaneous shortening in the Sicilian/southern Apennine thrust belt. We use finite element models to test whether the rapid evolution of the collision suture into a zone of rifting, and the development of closely juxtaposed regions of compression and extension, can be explained by a mechanism involving collision-induced delamination of continental mantle lithosphere. With delamination underway, the models predict the development of a region of contraction flanked by regions of extension, but no appreciable migration of the delamination front. Investigation of various initial lithospheric geometries shows that a uniformly thickened lithosphere will not readily delaminate, and that delamination is triggered if crustal and lithospheric thickening are offset. Asymmetric, or offset, lithospheric thickening produces an asymmetry in underlying mantle flow which gives rise to extension which is largely restricted to one side of the region of compression. The juxtaposition of extension and shortening in the Tyrrhenian/Calabrian region, as well as the greater degree of extension in the Tyrrhenian relative to the Ionian basin, may be a result of asymmetric lithospheric thickening in the initial collision suture.
Oolitic ironstones as event-stratigraphical marker beds within the Upper Devonian of the Ardenno-Rhenish Massif
Authors: Dreesen Roland 
Published: April 2008

Summary
Seven stratigraphically distinct, Clinton-type oolitic ironstones occur in the Upper Devonian of the Ardenne shelf, south of the London-Brabant Massif. They occur at the lithofacies boundary of succeeding lithological units and represent condensed deposits associated with hardgrounds and shoaling upward sequences. Microfacies analysis points to storm-generated concentration, removal and subsequent transport of the ferruginized allochems. The ironstones represent excellent marker beds which can be traced over several tens of kilometres on the palaeoshelf. Conodonts provide further evidence for the allochtonous character of the allochems and have enabled precise dating and correlation of each ironstone level with synsedimentary volcanic and tectonic events in the Rhenish Massif. Although the source of the iron is still a matter of discussion, lateritic weathering is not accepted here; instead, volcanism and evapotranspiration processes might represent potential sources for the iron in the studied ironstones.
Ironstones in the Mesozoic passive margin sequence of the Tethys Himalaya (Zanskar, Northern India): sedimentology and metamorphism
Authors: Garzanti E. , Haas R. , Jadoul F. 
Published: April 2008

Summary
The sedimentary succession of the Zanskar continental terrace comprises Triassic (Quartzite Series), Jurassic (Ferruginous Oolite) and Cretaceous (Giumal Sandstone) shelf siliciclastic units, all of which contain either chamositic ironstones or glauconitic greensands associated with reworked phosphorites. Ironstones are found above major unconformities at the top of shoaling arenaceous sequences, and generally mark the rapid transition from shallow-marine sands to highstand offshore pelites or pelagic foraminiferal limestones. Petrographical and sedimentological features of condensed intervals indicate deposition by transgressive fronts. During sea-level rise, high-energy waves mixed ferruginous and phosphatic grains formed in the course of earlier starved stages at low sedimentation rates, with detritus from shoreline and paralic sources reworked during stepwise coastal retreat. The timing of ironstone deposition apparently coincides with breakup stages affecting the Indian continental margin.

Ironstones are also important metamorphic markers in the Tethyan sedimentary zone, which has undergone intense fold-thrust deformation at very low to low metamorphic grade during the Tertiary Himalayan orogeny. In the Triassic iron oolites of central Zanskar, the occurrence of stilpnomelane suggests upper anchimetamorphic conditions (
c.
300° C). In the Cretaceous greensands, however, K-rich glauconite is only peripherally replaced by incipient stilpnomelane growth, pointing to metamorphic conditions comparable to lower prehnite-pumpellyite facies (
c.
260° C).
Cadomian magmatism in the North Armorican Massif
Authors: Brown Michael , Power G. M. , Topley C. G. , D’Lemos R. S. 
Published: April 2008

Abstract

This review concerns intrusive magmatism related to the Cadomian orogeny in the northeastern part of the Armorican Massif of France. The Cadomian orogeny is interpreted to represent tectono-thermal activity in a continental margin above a subduction zone. The North Armorican Shear Zone (NASZ) separates two major Cadomian terranes, the North Armorican Composite Terrane (NACT) and the Central Armorican Terrane (CAT). The amalgamation of three terranes within the NACT (the St Brieuc Terrane (SBT), the St Malo Terrane (SMT) and the Mancellian Terrane (MT)) around 540 Ma by sinistral transpression is a key element in the Cadomian orogeny. Cadomian plutonic complexes intrude the
c.
2000 Ma Icartian Gneisses and form the local basement to, and are emplaced into the Brioverian succession. Cadomian magmatism spans approximately 275 Ma, from
c.
700 Ma to
c.
425 Ma.

Early Cadomian foliated plutonic complexes occur within the Guernsey-La Hague structural block of the SBT; they represent volcanic arc granites derived in a subduction zone environment. Late Cadomian post-tectonic plutonic complexes within the Guernsey—La Hague structural block were emplaced
c.
500 Ma, exhibit a variety of ‘mixed magma’ features and have a normal to mature continental arc geochemistry. To the southeast, the Jersey structural block within the SBT represents a higher structural level as well as a greater distance away from the probable trench site. Here, the late Cadomian posttectonic plutonic complexes were emplaced during Cambrian and Ordovician-Silurian times and represent mature continental arc activity, probably associated with the decay of the Cadomian subduction zone system after transpressional terrane accretion.

The St Malo Terrane, to the southeast, represents an inverted intra- or behind-arc basin. The migmatite belts within this terrane developed by crustal anatexis. Emplacement of homogeneous diatexites and leucogranites synkinematically with sinistral strike-slip movement along shear belts generated by the transpressive terrane accretion allows this event to be dated at
c.
540 Ma.

The Mancellian Terrane, further to the southeast, comprises low-grade Brioverian metasediments into which has been emplaced the Mancellian Batholith, a late Cadomian post-tectonic series of predominantly granite complexes. These complexes have the geochemical features of volcanic arc granites.

Overall, Cadomian magmatism represents
c.
275 Ma of plutonic activity broadly related to subduction beneath a continental margin. The early part of the Cadomian orogenic cycle includes volcanic-arc plutonic suites and basaltic volcanic rocks with associated feeder dykes. The peak of the Cadomian orogeny involves intra- or behind-arc basin inversion with concomitant mid-crustal anatexis and sinistrally transpressive terrane accretion
c.
540 Ma. The late evolution begins with andesite-rhyolite volcanism and calcalkaline plutonism occurs over a period of
c.
100 Ma during the decay of the Cadomian subduction zone system.
Sedimentation dynamics and redox iron-cycling: controlling factors for the apatite—glauconite association on the East Australian continental margin
Authors: O’Brien G. W. , Milnes A. R. , Veeh H. H. , Heggie D. T. , Riggs S. R. , Cullen D. J. , Marshall J. F. , Cook P. J. 
Published: April 2008

Abstract
Detailed sedimentological and geochemical studies of phosphorites and sediments from the East Australian continental margin have shown that both apatite and glauconite are forming at a transition zone between relict, iron oxyhydroxide-rich, organic-poor (TOC<0.3%) outer shelf (200–350 m) sediments and relatively rapidly accumulating, iron oxyhydroxide-deficient, organic-rich (TOC>0.8%) deep water (460–650 m) sediments. The interaction between sediment mixing and Fe-P cycling processes (between the pore waters and the solid phase) appear critical to the formation of modern phosphorites in this area. The phosphate nodules form within the anoxic zone in the sediments at depths of approximately 10–18 cm below the sediment-seawater interface. Nodules which remain in the sediment mixed layer after they form continue to accumulate both P and Fe for up to 60 ka; during this time their apatite and iron oxyhydroxide contents more than double and the nodules become denser and more lithified. Apatite and glauconite formation are favoured by periods of high sea-level and low current velocities, as these conditions allow a relatively high organic carbon input to the sediments and thereby the maintenance of anoxia at shallow depths within the sediments. During periods of low sea-level and high current velocities, the carbon flux into the sediments decreases and the sediments become oxic. Consequently the Fe-cycling processes cease and apatite and glauconite formation stops: the glauconite is progressively transformed to goethite, and phosphorite nodules are concentrated into lag deposits and ferruginized. Alternations of high and low sea-level cycles eventually result in the formation of the massive ferruginous Neogene phosphorites that mantle much of the outer shelf. The iron enrichment processes observed in the modern to Neogene phosphorites on the East Australian continental margin provide explanations for many of the features seen in ferruginous Neogene deposits in the world’s oceans.
Quartzite rheology under geological conditions
Authors: Paterson M. S. , Luan F. C. 
Published: April 2008

Abstract
The problems associated with extrapolating laboratory measurements on quartzite rheology to geological conditions are discussed, with special reference to the question of equilibration with respect to the effect of water. Some new results on synthetic specimens crystallized from wet amorphous silica are presented in the expectation that water equilibration is more closely attained in these than in natural quartz specimens. These results and earlier ones from the literature are collated and used to arrive at limits on quartzite flow strength under geological conditions.
Deformation mechanics in analogue models of extensional fault systems
Authors: McClay K. R. 
Published: April 2008

Abstract
Scaled analogue models of fault structures are powerful tools for investigating the progressive development of extensional deformation. The results of a wide ranging programme of extensional modelling are briefly reviewed and are analysed in terms of the deformation mechanics and rheological behaviour of the modelling materials. Extensional models have been constructed using homogeneous dry quartz sand with isotropic behaviour; sand and dry china clay mixtures; with behaviour controlled by competency; and sand with dry vermiculite mica flakes to simulate anisotropic systems. Rheological tests show that these materials deform by Navier-Coulomb failure with friction angles between 30° and 35°. Extensional faults developed within the models are dilatant granular shear zones, whose widths are grain-size dependent, being widest in the sand models and narrowest in faults cutting the fine-grained clay layers. Initial fault-bedding cutoff angles are high, 60°–70°, but during progressive deformation shear strains may change this, depending upon the boundary conditions of the model. Measurements of angular shear strains within domino fault arrays show significant zones of shear either parallel to the basal detachment or parallel to bounding faults. Small bulk dilations are found in most models as a result of grain packing rearrangements during extension. The primary extensional architecture of the models is controlled by the underlying detachment configuration. Despite limitations to the models, it is believed that the rheologies, the modelling materials and the deformation mechanics within the models realistically simulate brittle deformation of sedimentary rocks in the upper crust.
Evidence for global (glacial-eustatic) control over upper Carboniferous (Pennsylvanian) cyclothems in midcontinent North America
Authors: Heckel Philip H. 
Published: April 2008

Abstract
At least 20 Middle/Upper Pennsylvanian (Westphalian D/Stephanian A, B) major marine cyclothems, each consisting of a thin transgressive limestone, thin offshore dark phosphatic shale, and thick regressive limestone member, extend along outcrop for 600 km from the northern shelf region of Iowa, Missouri and Kansas, to the basinal region of central Oklahoma. Each is correlated lithostratigraphically throughout a gridwork of long cores in the northern region beneath Pleistocene cover, and in good exposures southward. This correlation is confirmed biostratigraphically, along the entire outcrop belt using a combination of conodonts, fusulinids and ammonoids. Most of the cyclothems are separated by thin terrestrial deposits with paleosols, but only rare deltas, for about the northern half of the outcrop distance, which rules out delta shifting as a general control for the vertical alternation of terrestrial and marine deposits across the broad shelf. On the northern shelf, all major cyclothems are traced across the cratonic Forest City basin and over the adjacent Nemaha uplift with little change, which rules out local differential tectonics as a general cause. Presence of Gondwanan glacial deposits at this time, in conjunction with the estimated frequencies of these Pennsylvanian cycles within the Milankovitch band of Earth’s orbital parameters (which control variation in solar heating of the mid-latitudes), indicate that glacial eustasy, rather than distant orogenic movements, was the main control over the cyclothems.
Carboniferous geology of the Southern North Sea Basin and controls on hydrocarbon prospectivity
Authors: Leeder Michael R. , Hardman Martin 
Published: April 2008

Abstract
The thick sequences of Upper Palaeozoic strata present in the Southern North Sea Basin were probably deposited on a basement of Caledonian low-grade metamorphic rocks intruded by numerous late-Caledonian granitoids which form part of the subsurface extension of the Mid-European Caledonides linking the English Lake District and Northern Pennines to the Ardennes. This basement, along with the better known onshore areas of the British Isles and Ireland was intensely fragmented during late Devonian to mid-Carboniferous times by a major phase of extensional tectonics.
Active fault-bounded tilted blocks developed in the Dinantian with deposition of fluviatile redbeds, marine carbonate/deltaic clastic cycles and deltaic coastal plain facies. These are penetrated by a number of wells on the southern flanks of the Mid-North Sea High, but details of basin geometries and facies distributions remain unclear.
Crustal stretching appears to have given way to thermal subsidence by early to mid-Namurian times. This was coincident with a major climatic change, probably forced by glacial expansion in Gondwanaland. The major drainage system that resulted dominated sedimentation in the SNSCB, punctuated by numerous marine transgressions of undoubted glacio-eustatic origins. Within this broad depositional framework, Namurian facies were closely controlled by basement tilt block topography, with good evidence for a gradual southerly migration of the active fairways of fluviodeltaic sandbodies. Westphalian facies were dominated by the interplay between glacio-eustatic and sedimentary processes on a vast low-gradient alluvial plain with much less pronounced tectonic control.
By late-Westphalian B times a phase of basin inversion caused the gradual elevation of the area as a retro-arc foreland basin. Vadose diagenesis and pedogenesis occurred in the fluviatile facies of the so-called Barren Red Measures (BRM). With continued compressive deformation a series of over 50 NW-SE orientated folds, some associated with thrusts, developed. Significant erosion and truncation of these inversion anticlines was accompanied by the deposition of the BRM facies in characteristic growth fold basins, with marked onlap around the basin margins. The Carboniferous play in the SNSCB has been greatly influenced by the subsequent Mesozoic/Cenozoic geological history of the basin, including periods of subsidence and uplift. We demonstrate that variations in original detrital mineralogy and various diagenetic processes have exerted significant controls upon Carboniferous reservoir quality.
Late Jurassic half-graben control on the siting and structure of hydrocarbon accumulations: UK/Norwegian Central Graben
Authors: Roberts Alan M. , Price John D. , Olsen Terkel Svava 
Published: April 2008

Abstract

The late Jurassic structure of the Central Graben is discussed, both in terms of the extensional features developed at this time and their subsequent controls on younger inversion structures. The regional kinematics of the North Sea rift suggest that during the late Jurassic the Central Graben opened approximately orthogonally to the main NNW—SSE fault-trend within the basin. Some evidence that Triassic extensional faults were reactivated at this time is seen towards the basin margins, and a significant Triassic extensional history is inferred. The late Jurassic basin comprises the axial
c.
100 km of the Central Graben (
s.l.
). The basin axis is offset progressively to the SE by both transfer zones and discrete transfer faults. Footwall uplift of the basin margins during extension provided the source for the Upper Jurassic reservoir sands encountered by exploration drilling. These sands were probably preferentially fed into the basin at transfer zones in the margins. Salt structures are ubiquitous within the Central Graben, and their siting is everywhere controlled by the underlying fault-block topography. Salt structures form preferentially towards the crests of half-graben or buttressed against their boundary faults. Inversion structures in the Norwegian sector reactivated, with a reverse sense of displacement, late Jurassic extensional faults. A model is proposed which shows the two main inversion structures (Feda Graben, Norway; Tail End Graben, Denmark) to be detached on antithetic reverse faults riding in the salt. These faults terminate at tip-folds within major salt walls. The geometry of the inversion structures can be understood only when considered together with the geometry of the underlying late Jurassic half-graben.