bluuebunny/crossref_metadata_2025_split huggingface dataset:
Topography and origin of the southern Rocky Mountains and Alvarado Ridge
Authors: Eaton Gordon P. 
Published: April 2008

Summary
The southern Rocky Mountains of the western United States and their structural continuation southward to the Mexican border represent the crest of a bilaterally symmetrical, continental feature of large dimensions, the Alvarado Ridge. It is characterized by long, gentle topographic rises with systematic, concave-upward slopes on which elevation declines in a quasi-exponential manner. The rises were originally blanketed with clastic sediments, a few tens to hundreds of metres thick; their erosional source being at the ridge crest. The blanket on the E rise is well preserved and has been undisturbed for nearly 5 Ma, save for regional Neogene warping and local, near-crest faulting associated with uplift of the ridge.
A comparative study of variations in regional elevation, gravity and crustal thickness suggest that the Alvarado Ridge and its rises are isostatically compensated and that almost none of the compensation involves an Airy crustal root. The flexural rigidity of the lithosphere is likewise believed to play but a minor role in the origin of the regional topography. Instead, the data are interpreted as confirming the hypothesis of distributed lithospheric thinning continuous and non-continuous in nature, and related thermotectonic uplift. Elevation of the ridge crest took place above the axis of an elongate, rapidly developing, asthenospheric bulge along which extensional strain in the shallow crust was limited to a central corridor only 150–200 km wide. The relatively low density and geometrical configuration of that bulge supports the topography. Heat-flow data in the region are in accord with this model.
Extension and its influence on Canadian Cordilleran passive-margin evolution
Authors: Thompson Bob , Mercier Eric , Roots Charlie 
Published: April 2008

Summary
The proto-Pacific margin of North America remained passive for the main part of 1.4 Ga. The stratigraphy that accumulated can be split into four major time-rock sequences; each may be considered a separate passive-margin sequence. The margin, initiated at about 1500 Ma, was remodelled by extensional (rift) episodes. Geological evidence for a 780 Ma extension event is documented here; subsidence analysis supports a 550 to 600 Ma separation event (Bond & Kominz), and stratigraphic and structural evidence from the northern Canadian Cordillera suggests 370 Ma extension. Each event is interpreted as the precursor to, and initiator of, passive-margin sedimentation.
Fold- and thrust-belt trends reflect passive-margin geometry. In the Ogilvie Mountains an abrupt right-angle bend in structural trend was inherited from 775 Ma extension faults.
Timing and style of crustal extension N of the Scottish mainland
Authors: Kirton S. R. , Hitchen K. 
Published: April 2008

Summary
The region immediately to the N of the Scottish mainland and W of Orkney and Shetland may be divided into two areas on grounds of structural style. The two areas are separated by a well-defined NE-SW-trending horst, the Solan Bank High. The northwestern area is dominated by listric normal faults downthrowing to the NW. These faults were initiated at two main stages: late, or post Permo-Triassic (but pre-middle Jurassic) and middle Jurassic. A well-defined NW-SE-trending transfer (strike-slip) fault, termed here the Judd fault, is associated with the middle Jurassic faults. The southeastern area is dominated by listric normal faults down-throwing to the SE. These faults were initially Caledonian thrusts which subsequently relaxed during the Permo-Triassic.
Sedimentary structures associated with extensional fault movement from the Westphalian of NE England
Authors: Fielding C. R. , Johnson G. A. L. 
Published: April 2008

Summary
Although differential subsidence and extension has been well established as a control on sedimentation for the Dinantian of N England, the continuation of this tectonic regime into Silesian times is less well demonstrated.
The Westphalian (Upper Carboniferous) Coal Measures of the Durham coalfield in NE England, which were deposited on an essentially flat, deltaic plain, display abundant evidence of a subtle structural control on sedimentation. Medium-scale (hundreds of square kilometres) patterns of sedimentation, notably the disposition of major fluvial channel belts, were at times strongly controlled by active, ENE-WSW- and E-W-trending fault lines. The faults represent a response to a broadly N-S directed tension and many resulted from the reactivation of earlier, Caledonide crustal weaknesses.
The effects of such tectonic activity may be seen spectacularly at field-outcrop scale. At an opencast coal mine in southern Co. Durham close to the major Butterknowle fault, an exposed Upper Westphalian A sequence displays a plethora of tectonically associated structures. These include gravity slides, various dewatering structures, claystone dykes, convoluted and internally chaotic sandstone beds, desiccation cracks and signs of vertical drainage in an originally waterlogged paleosol profile, and abrupt bed thickness changes. The existence and orientation of two minor channels on the ESE side of the fault line, and other palaeoflow data, support the hypothesis that the Butterknowle fault displaced downward the area to its ESE at this time.
Fractures across the area of the opencast site were found to contain high concentrations of galena, sphalerite, pyrite/marcasite and other minerals which were apparently introduced at the time of formation of the N Pennine orefield (Carboniferous-Permian).
The thermal and mechanical development of the Wessex Basin, southern England
Authors: Karner Garry D. , Lake Stuart D. , Dewey John F. 
Published: April 2008

Summary
The Wessex Basin of southern England is an E-W-trending Late Palaeozoic to Tertiary extensional basin formed on Early Palaeozoic Variscan crust. Extension occurred over a protracted period from Late Carboniferous to Cretaceous times resulting in the evolution of four main depocentres or sub-basins; the Channel basin, Winterborne-Kingston Trough, Vale of Pewsey, and Weald basins. Each sub-basin was controlled fundamentally by the normal reactivation of basement thrust faults and wrench or transfer faults. The basement faults represent primary structures associated with the fold-and-thrust terrain of the Devonian-Carboniferous Variscan Orogeny. Subsequent, but synchronous, reactivation of both thrust and transfer faults tended to compartmentalize the basement, leading to discrete depocentres and the production of general, rhomboidal-shaped, sub-basins (characteristic of pull-apart basins in strike-slip terrains).

To investigate the thermo-mechanical properties of the lithosphere during basin formation, 50 boreholes within the Wessex Basin were back-stripped to isolate the driving tectonic subsidence responsible for basin formation. The resultant driving subsidence is characterized by a gentle, sometimes negative, exponential form, with superimposed rapid, discrete, subsidence events. As the geological development of the Wessex Basin was characterized by polyphase extension and the utilization of crustal detachments, the lithospheric model used to determine
δ
(crustal extension above the detachment) and
β
(stretching below the detachment) included the effects of depth-dependent stretching and finite re-rifting. From the back-stripping analysis, the basin-wide-averaged upper-crustal extension and lower-crustal/sub-crustal lithospheric stretching were 11 and 5% respectively. The distribution of
δ
is strongly influenced by the location of growth faults, and hence basement thrust-fault reactivation, suggesting that
δ
is reflecting the brittle failure and collapse of hanging wall blocks. Repeated slip and block collapse resulted in the polyphase extension responsible for renewed basin subsidence. In contrast,
β
is uniformly distributed across the basin, suggestive of a ductile failure of the lower crust and responsible for the low-magnitude thermal subsidence. Strain compatibility between the upper-crust and lower-crust/sub-crustal lithosphere is maintained partly within the basin (5%), and partly external to the basin. As the Variscan basal thrust was the fundamental relay (in the sense of Wernicke) responsible for the Wessex Basin formation, we postulate that strain balancing induced a cumulative (essentially thermal) isostatic uplift (of ≈ 60 m) under the northern margin of the Armorican Massif.
The Devonian basins of western Norway: tectonics and kinematics of an extending crust
Authors: Seranne Michel , Seguret Michel 
Published: April 2008

Summary
The Devonian basins of western Norway represent shallow to deep exposures of a synthetic extensional sedimentary basin and provide field evidence for ductile extensional deformation within the basin fill and for the evolution of a brittle low-angle fault and ductile shear zone along the basal contact. The motion along this low-angle (5–25°) detachment is synchronous with both deposition and tilting (25°) of the huge (up to 25-km thick) overlapping coarse detrital Middle Devonian series. Such a geometry requires a minimum dip-slip offset of 50 km.
The structural data are consistent with fault-rock associations along the basal contact and with the prograde greenschist metamorphism observed in the southern basin: deeper and deeper levels are observed from N to S. Except along the highly sheared and retrogressed basal shear zone, the footwall remained unaffected by deformation during basin development.
We discuss three crustal models for basin development and propose that the displacement along the basal contact of the basins is transformed into pervasive ductile flow within the lower crust both at some distance to the side of the basin and beneath the basin.
Deformation processes in unconsolidated sands
Authors: Owen G. 
Published: April 2008

Summary
Deformation in unconsolidated sands requires the action of a deformation mechanism to reduce sediment strength and a driving force to induce deformation. Deformation mechanisms include liquefaction and fluidization and are reflected in the style of deformation and grain orientation fabrics. They are initiated by a trigger, including groundwater movements, wave action and seismic shaking. Driving forces include gravitational body force, unevenly distributed loads, unstable density gradients and shear forces, and are reflected in the geometry of deformation. These components are combined to produce a genetic classification of soft-sediment deformation processes and structures.
Non-destructive determination of Young’s modulus and its relationship with compressive strength, porosity and density
Authors: Allison R. J. 
Published: April 2008

Summary
The Grindosonic apparatus, new equipment capable of indirectly determining rock compressive strength, is discussed. This utilizes the principle that elasticity theory can be applied to rock masses (Attewell & Farmer 1976; Selby 1982) and directly measures the fundamental vibration frequency of a rock sample of regular dimensions following shock excitation. Dynamic Young’s modulus and a variety of other parameters can be established.
Samples of Upper Cretaceous Chalk and Upper Jurassic Portland Limestone are used to demonstrate the apparatus and its application. Test specimens were prepared and analysis conducted on material extracted at a number of locations throughout the Isle of Purbeck in Dorset, UK. Samples suitable for deformation in triaxial compression were also prepared and correlations drawn between compressive strength, dynamic Young’s modulus, porosity and density.
Morphology and microstructures of hydroplastic slickensides in sandstone
Authors: Petit Jean-Pierre , Laville Edgard 
Published: April 2008

Summary
The High Atlas Mountains (Morocco) provide local basins with good Triassic exposures. Basin formation was induced by normal and strike-slip synsedimentary faults, either sealed by Mesozoic and Cenozoic rocks, or reactivated during Alpine orogeny. Thus the Triassic outcrops in these fault zones show not only slickensides obviously due to rupture and friction mechanisms in brittle material (reverse and strike-slip faulting during Alpine orogeny), but also ‘hydroplastic’ slickensides due to faulting in incompletely lithified sediments (normal and strike-slip faulting during Mesozoic pull-apart basin formation).
Microstructural and morphological comparison between these two types of slickensides enable us to describe various specific criteria for ‘hydroplastic slickensides’.
Soft-sediment microfaulting related to compaction within the fluviodeltaic infill of the Soria strike-slip basin (northern Spain)
Authors: Guiraud Michel , Séguret Michel 
Published: April 2008

Summary
As much as 8 km of fluvio-deltaic strata accumulated in the Sorio strikeslip basin during the Late Jurassic-Early Cretaceous (Wealdian). The strata were bent in a huge syn-sedimentary syncline related to the development of an extensional half-graben in the basement. The alluvial plain siltstones and clays are cut by a large number of microfaults of a special type in regard to their geometry and their morphoscopic characters. The fault surfaces concave upward dip at 10°–40° to bedding with a strong dispersion of fault plane strikes, providing a characteristic circular pattern. They are closely spaced and cut the material into small bi-pyramidal cone-shaped units with axes normal to bedding.
The fault surfaces are glossy with a metallic glint and a fine striation without crystallization. From electron microscopic observations, this is due to phyllite re-orientation. Along the fault planes the displacement is always dip-slip and slight.

Analysis of fault striation populations by a computer-aided method gives a unique stress tensor responsible for the striation with the maximum compressive stress σ
1
normal to the bedding plane along the whole section of the synsedimentary syncline and a
R
ratio (
R
= (σ
2
− σ
3
)/(σ
1
− σ
3
)) close to 0.

The orientation of the stress tensor, the
R
= 0, i.e. σ
2
= σ
3
and the morphological aspect of the fault surfaces similar to shear planes affecting present cohesive soils lead us to conclude that this deformation is related to compaction in cohesive clays contemporaneous with water escape structures in sandstones. This deformation occurs in the evolution of the basin fill from soft sediments to metamorphosed rocks.
Comparative studies of gravity tectonics in Quaternary sediments and sedimentary rocks related to fold belts
Authors: Pedersen S.A. Schack 
Published: April 2008

Summary
Two different modes of gravity tectonics have been active as deformation mechanisms in the Quaternary of Denmark, namely ‘gravity gliding’ and ‘gravity spreading’. Examples of gravity gliding can be found in the fairly slowly moving coherent landslides which characterize many coastal cliffs with lithologies intercalated with Tertiary marine clay or Quaternary interglacial clay. The gravity spreading mechanism generated folds and dislocation structures characteristic of glacial tectonics, mainly during the Weichselian glacier advances of the Pleistocene glaciation. Imbricate dislocation structures formed by diapiric rise of water-saturated clay into sand occur. This structure type is proposed to be characteristic for the gravity spreading model.
Analysis of these gravity deformed Quaternary deposits serve as a model for structures occurring in large-scale tectonic settings. Among the megascopic tectonic settings mentioned, two regions are discussed. Firstly, the transverse thin-skinned thrust fault belt in the southern part of the North Greenland Fold Belt is demonstrated to contain the characteristics of a gravity gliding system. Secondly, the gravity spreading structures of the glacio-dynamic deformations in Denmark are suggested to have a megascopic equivalent in the plate-tectonic convergence zone of the Barbados Ridge.
Genesis and diagnostic value of large-scale gravity-induced penecontemporaneous deformation horizons in Quaternary sediments of the Kleszczów Graben (central Poland)
Authors: Brodzikowski Krzysztof , Hałuszczak Andrzej , Krzyszkowski Dariusz , Van Loon Antonius J. 
Published: April 2008

Summary
Gravity-induced soft-sediment deformations are quite common throughout the Tertiary and Quaternary infilling of the Kleszczów Graben. Only a limited number of horizons, however, are characterized by the abundant occurrence of large-scale load casts, ball-and-pillow structures, convolute lamination and related structures. It appears that the structures started to develop at a metadepositional stage and that the process was favoured by unstable density gradients. The further development was rather complicated, but endogenic activity in the graben must have played a role, though mainly as a trigger mechanism.
Mantle metasomatism—perspective and prospect
Authors: Bailey D. K. 
Published: April 2008

Summary

Mantle replenishment in lithophile elements has been discerned in the patterns of trace elements and isotopes in lavas. One replenishment process is identified as metasomatic replacement, seen in ultramafic xenoliths brought up in high-velocity alkaline eruptions. Thus alkaline magmatism provides the best
prima facie
evidence of metasomatism and open-system conditions in the upper mantle. The list of added lithophile elements includes the following: H, C, F, Na, Al, P, S, Cl, K, Ca, Ti, Fe, Rb, Y, Zr, Nb, Ba and rare earths. Some metasomatism may be due to wall-rock alteration near magma bodies, but the evidence for metasomatism prior to melting opens the possibility that the process is a precursor to alkaline magmatism, giving the necessary source enrichment in lithophile elements. In some igneous provinces the metasomatism is widespread, intensive and pervasive; in others it appears as veining of variable intensity. Metasomatism as a large-scale process is best indicated by the widespread distribution of alkaline magmatism in space and time: volatile flux through the lithosphere would then be the necessary precursor of metasomatism and magmatism.

Volatile activity, metasomatism and melt enrichment clearly widen the scope for mafic magma generation in the mantle, but some long-standing problems of the alkaline associations (and indeed the calc-alkaline) also call for re-examination in terms of volatile activity in the lithosphere mantle. These include the diversity of magmas, the generation of large felsic volumes, and composition gaps in magma series. Experiments show that felsic minerals are stable to 30 kb, indicating the possibility of felsic-melt generation in the upper part of the mantle. A combination of volatile flux and melt percolation along geotherms that intersect the solidus at depths of less than 80 km would lead to enrichment and metasomatism, providing distinct mantle sources for felsic magmas. Initial (or residual) melts from such a region, as distinct from those from greater depths, would be constrained by equilibria involving felsic minerals. Thus an igneous cycle could generate a bimodal association, with felsic melts forming in the upper regime and the mafic melts originating at depths below the range of felsic-mineral stabilities. Such a magma system is consistent with the observed eruptive characteristics, explains the typical ultramafic nodule and megacryst suites in the alkali olivine-basalt association and is free of difficulties with relative volumes of melts, with eruption timing and with rapid changes in erupted compositions.
The genesis of alkaline magmas with emphasis on their source regions: inferences from experimental studies
Authors: Edgar A. D. 
Published: April 2008

Summary

Experimental studies bearing on the genesis of alkaline magmas are reviewed, with emphasis on alkaline mafic-ultramafic magmas and the nature of their mantle sources. In contrast with previous experiments on simplified systems mainly at low pressures, more recent experiments under mantle pressures have resolved some of the problems of the earlier work. Inadequacies of petrogenetic schemes based on the model pyrolite mantle source for the generation of alkaline magma are also partly resolved by recent studies which suggest that with increasing alkalinity the possibility of deriving mafic-ultramafic magmas from a dry lherzolitic mantle source, or one with H
2
O as the only volatile, becomes increasingly difficult. The addition of CO
2
and H
2
O to the source regions allows generation of magmas such as olivine melilitites, but few magmas of the olivine leucitite kindred can be generated from lherzolitic sources. Such magmas appear to be partial melts of clinopyroxenite or orthopyroxenite sources containing both volatiles. Preliminary experimental modelling of mantle metasomatism suggest that this process may readily occur.

Experiments on felsic alkaline rocks with emphasis on liquid immiscibility and halogens and experiments aimed at solving specific problems are briefly considered.
The nature and origin of lamprophyres: an overview
Authors: Rock Nicholas M.S. 
Published: April 2008

SummaryLamprophyres are ‘alkaline rocks’ because they carry high alkalis at a given percentage of SiO2, together with one or more of normativene, lcorac, modal foids, and Na-K-Ti-rich amphiboles or pyroxenes. They reach higher whole-rock H2O, CO2, Sr and Ba contents than other silicate igneous rocks. Contents of related element subsets in amphiboles (Ti, Ba), K-feldspars (Ba, Fe3), phlogopites (Ti, Ba, Fe3) and pyroxenes (Ti, Al, Fe3) include among the highest values known in nature for these minerals. ‘Primitive’ minerals (diopside, forsterite) commonly coexist with ‘evolved’ minerals (albite + orthoclase, quartz). Four well-defined ‘branches’ of the lamprophyre ‘clan’ have distinctive compositions:calc-alkaline (shoshonitic) lamprophyres(minettes etc.), alone among lamprophyres, have mixed alkaline-calc-alkaline affinities;alkaline lamprophyres(camptonites etc.) are basanitic to nephelinitic and, alone among lamprophyres, usually have Na < K;ultramafic lamprophyres(alnöites etc.) are the most Si poor and Ca rich of silicate igneous rocks, and grade into carbonatites;lamproites(orendites etc.) are uniquely rich in K, Rb, Ba, Th, Mg, Cr and Ni at mainly ‘andesitic’ SiO2contents, and carry a suite of diagnostic minerals (wadeite etc.). Each branch comprises at least four rock types which resemble each other much more than rock types of other branches; however, some rock types can be grouped into slightly distinct ‘families’ within one branch (e.g. phlogopitic and madupitic lamproites). A case can be made for including kimberlites as a fifth branch of the lamprophyre clan. Synoptic plots and tables, based on some 5000 major, trace-element and mineral analyses, are presented, to aid identification and classification. Lamprophyres are far more common than generally stated, occurring worldwide in more tectonic settings than many other alkaline rocks and throughout the geological record. They may approximate intratelluric magma compositions. Nearly all represent primitive magmas, and many represent primary magmas. Some represent parental magmas to a wide range of hydrous alkaline intrusive suites: calc-alkaline lamprophyres to potassic pyroxenite-diorite-shonkinite-syenite-granite plutons (Cortlandt); alkaline lamprophyres to hornblendic gabbro-syenite plutons (Monteregian Hills); and ultramafic lamprophyres to ijolite-carbonatite complexes (Fen).