bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cross-faults and differential stretching of hanging walls in regions of low-angle normal faulting: examples from western Turkey
Authors: Şengör A. M. C. 
Published: April 2008

Summary

Large oblique-throw hinge faults orientated at high angles to the strike of major breakaway faults in W Turkey are examined. They exhibit variable displacements which commonly increase towards the breakaway fault with which they seem to be associated and bound cross-blocks that in places have rotated around vertical axes by differing amounts and senses, and are interpreted in terms of the possibility that hanging walls of major low-angle breakaway faults (extensional allochthons), may exhibit differential internal extension accommodated by transverse faults that may or may not rotate around vertical axes. Such transverse faults, here called
accommodation faults
, are different from transfer faults in that they need not offset the main breakaway fault and may accomplish significant map-view distortions of extensional allochthons.

Irrotational accommodation faults may give rise to horst and graben complexes or may create the image of domino-style, uniformly tilted normal and/or thrust faults at high angles to the strike of major breakaways, thus giving rise to the misleading image of extension in two directions in an extensional zone or shortening at high angles to regional extension. Although strike-slip offsets along irrotational accommodation faults need not bear any relation to the magnitude of regional extension, their strikes must at least be sub-parallel to the orientation of regional extension. Real shortening at high angles to regional extension may give rise to rotational accommodation faults. Neither the strike-slip offset along such faults nor their azimuth need bear any simple relationship to the magnitude and orientation of regional extension. Rotational accommodation faults bring about an equivalent rotation of all structures that form along them, such as pull-apart basins, and the hanging wall blocks they delimit, together with their pre-existing structures.

All three kinds of cross-faults, i.e. transfer faults, irrotational and rotational accommodation faults may coexist in any one extensional region and may grade into one another both in space and in time creating a very complicated structural picture and causing irregular subsidence patterns. It is stressed that cross-faults have an extremely important bearing on our understanding of the geometry and evolution of extensional zones, here called
taphrogens
, and that only a three-dimensional consideration of the structure of taphrogens is likely to lead to a satisfactory understanding of their nature.
Deformation, diagenesis and the mechanical behaviour of chalk
Authors: Clayton C. R. I. , Matthews M. C. 
Published: April 2008

Summary
The chalk of England is a highly variable material resulting from numerous deformation processes of which the most important are diagenetic or tectonic in nature. The engineering behaviour of the chalk is influenced greatly by these processes thus giving rise to the necessity of carrying out studies of physical properties to aid the prediction of engineering performance. The results of these studies are of value when examining deformation mechanisms associated with diagenesis and tectonism. In this paper use is made of results obtained from engineering laboratory index tests to study deformation mechanisms associated with early diagenesis and the influence of overburden and tectonism.
A laboratory technique for investigating the deformation microstructures of water-rich sediments
Authors: Maltman Alex J. 
Published: April 2008

Summary
Experimental deformation is a particularly valuable means of investigating the mechanical behaviour of water-rich sediments. Techniques have been developed for preparing and deforming wet sediments in the laboratory and petrographically examining the resulting microstructures. Clays marketed for the ceramic industry are more useful than natural clays because of their consistent properties. They are mixed with sea-water, aged, and consolidated to the desired value either by self-weight or in a simple levered oedometer. Argillaceous sediments with water contents of about 50% and lower are routinely produced. Wetter materials are extremely delicate and vulnerable to non-testing artefacts. In an attempt to circumvent this problem a device has been designed which enables slurries to be sedimented directly on to the base of a triaxial compression cell.
The prepared specimens are tested in a conventional ‘direct’ shear box, or in ‘distributed’ shear which subjects the whole block to shear displacement, or in triaxial compression. The latter tests can be undrained, or partially/intermittently drained, from the top and/or the bottom of the sample.
After testing, slabs are cut from the specimen with a wire-saw and impregnated with Carbowax P.E.G. 8000 to allow thin-section preparation and examination.
Shear zones in argillaceous sediments—an experimental study
Authors: Maltman Alex. J. 
Published: April 2008

Summary
Experimental deformation of water-rich argillaceous sediments has shown that they deform not by pervasive homogeneous flow, as has sometimes been surmised in the past, but by intense slippage within very narrow, discrete zones of shear. These shear zones enable large total strains to be accomplished whilst leaving the bulk of the material undisturbed. Macroscopically the zones are shiny, finely-grooved planes which may be stepped where sub-structures intersect them. Under the microscope the zones are seen to result from pronounced particle reorientation into sub-parallelism with the zone margins, presumably by slippage at the grain scale. The zones commonly curve and anastomose, and various sub-fabrics may be discernible. Although the details vary, the shear zones are strikingly consistent throughout the range of experimental conditions.
In specimens with 15% water content, the shear zones lack cohesion and are analogous to shear fractures in brittle rocks. Between approximately 15–45% water content the same overall geometry persists, but the shear zones maintain cohesion. At greater water contents, up to at least 60%, the clay sediments are extremely weak and although they may appear to be undergoing pervasive flow, microscopic examination reveals that even here arrays of short, narrow zones of concentrated displacement are being generated.
Sediment deformation structures and the palaeotectonic analysis of sedimentary basins, with a case-study from the Carboniferous of northern England
Authors: Leeder Michael 
Published: April 2008

Summary
There is a close link between syn-sedimentary faulting caused by earthquakes of magnitude >5 and accompanying ‘soft’ sediment intrafolial deformation in active neotectonic settings. Certain of these intrafolial structures may also be produced by purely sedimentary processes and are termed ‘autokinetic’. Those caused by earthquake-induced stresses are termed ‘allokinetic’. Although certain structures may be caused by either mechanism, it appears that large amplitude dewatering pipes and recumbent-folded cross stratification are likely to be predominantly allokinetic in origin. These structures may be used to define the Allokinetic Deformation Number which can be systematically mapped out in particular lithofacies over outcrops in a sedimentary basin. Results of this mapping are then combined with data on lithofacies thickening and stacking (tectonically-controlled architecture), hangingwall rollover deformation etc., to establish an interdisciplinary outline of palaeotectonic evolution. This methodology of palaeotectonics is tested in the suspected extensional terrain of the Northumberland Basin with encouraging results.
Syn-diagenetic deformation of a turbiditic succession related to submarine gravity nappe emplacement, Autapie Nappe, French Alps
Authors: Labaume Pierre 
Published: April 2008

Summary
The Autapie Nappe (French Alps) consists of a Late Cretaceous ‘Helminthoid Flysch’ turbiditic succession. It was emplaced in the external Alps during the Late Eocene under the form of a gravity submarine nappe sliding in a turbiditic foreland basin. The syn-diagenetic gravity spreading of the Helminthoid Flysch succession resulted in a pervasive extensional disruption of the sandstone and mudstone layers related to decollements in the marlstone and claystone layers. The deformation regimes and mechanisms testify to: (i) the incomplete and inhomogeneous lithification of the sediments, and (ii) the occurrence of pore pressure gradients and, possibly, excess pore pressure during the deformation. In particular, the critical state of lithification of the sandstone allowed the occurrence of an unusual chronology of deformation mechanisms, the ‘brecciation’ resulting from a partial loss of cohesion of the sandstone in high speed escaping pore-water (ductile, ‘soft-sediment’ behaviour) post-dating calcite-filled veins (brittle, ‘rock’ behaviour). Similar deformation style might be expected to occur at modern convergent margins.
Nephelinites and carbonatites
Authors: Le Bas M. J. 
Published: April 2008

Summary
Carbonatites found in strongly alkaline intra-plate petrographic volcanic provinces are associated with olivine-poor nephelinites and with phonolites. Olivine-rich nephelinites occur in basanitic and alkali basalt provinces, normally without carbonatites. These igneous provinces are marked by epeirogenic crustal uplift.
Nephelinites, ijolites and carbonatites form discrete magmatic events within individual complexes and correspond to the silicate-carbonate conjugate immiscible liquids observed in the laboratory. Carbonate liquids of variable alkali content can separate from both nephelinitic and phonolitic liquids. The silicate liquids give rise to pyroxenites, ijolites, nepheline syenites and nephelinitic pyroclast-rich strato-volcanoes. The carbonate liquids lose alkalis and fractionate to sövite, alvikite and ferrocarbonatite, each with increasing incompatible-element content. Further fractionation of carbonatite magma can produce mineralizing fluids rich in rare-earth elements, F, Ba, U and Th. Dolomite carbonatite forms only in the deeper parts of carbonatitic complexes, perhaps at depths greater than 2 km. Explosive carbonatite volcanism can occur giving widespread carbonate tuffs, rarely with lavas.
Fenitization characterizes ijolite-carbonatite intrusive complexes. Syenitic fenites containing alkali feldspars, sometimes perthitic, are formed as aureoles 500 m wide around ijolites in granitic terranes, with nepheline syenite commonly formed as a contact-reaction rock. The feldspar-rich syneitic fenite aureoles which develop around the early carbonatites usually contain pure orthoclase or pure albite.
Hawaiian alkaline volcanism
Authors: Clague David A. 
Published: April 2008

Summary
Hawaiian volcanoes erupt alkalic lavas during three of four eruptive stages. Stage 1 is characterized by submarine eruption of alkalic basalt and basanite followed by tholeiitic basalt which is exclusively erupted during stage 2. Stage 3 consists of a post-caldera-collapse capping of alkalic basalt and related differentiates. Stage 4 consists of post-erosional eruptions of alkalic basalt, basanite, nephelinite and melilitite. Eruption rates and volumes increase from stage 1 to stage 2 and then decline through stages 3 and 4. Stage 1 and 4 lavas contain deep-seated lherzolite xenoliths (even some garnet-bearing xenoliths in stage 4 lavas) whereas stage 2 lavas contain only very shallow cumulates, veins, dykes and sills; stage 3 lavas contain mainly dunite, wehrlite and various cumulates. The xenolith assemblages reflect the development of magma storage reservoirs which act as hydraulic filters in removing any xenoliths entrained below the magma storage reservoirs. The development of the magma storage system is a direct response to varying magma supply rates during the four eruptive stages.
Trace-element, isotopic and rare-gas data all indicate that Hawaiian lavas are generated from heterogeneous sources consisting of at least three distinct compositions. Mixing of the sources or of partial melts derived from these sources is inevitable; however, the characteristics of the mixing end-members are not well constrained. In a general way, early and late lavas are generated by small degrees of melting of sources enriched with less incompatible elements, whereas the voluminous shield tholeiites are generated by large degrees of melting of sources enriched with more incompatible elements.
The petrology, chemistry and crystallization history of the Velasco alkaline province, eastern Bolivia
Authors: Fletcher C. J. N. , Beddoe-Stephens B. 
Published: April 2008

Summary
The Velasco alkaline province consists of an early volcanic suite, a series of 14 interfering circular and elliptical alkaline plutons, numerous dykes and a silicified carbonatitic complex. The alkaline rocks, excluding the dykes, are restricted to a narrow NE-trending belt that has been traced for nearly 80 km.
The plutons can be divided into two groups defined by the silica-oversaturated or silica-undersaturated character of the rock units within each pluton. It has been possible to deduce from textural relationships and whole-rock and mineral chemistry that the two groups can be derived from a single pulaskitic magma type, in turn producible by minor fractionation of a mantle-derived trachytic parent. Sr isotopic data indicate that the trend from pulaskite through quartz syenite to granite was developed by progressive crustal contamination due to slow rates of emplacement. In contrast, the undersaturated trend towards foyaite shows no evidence of crustal influence, the plutons probably being emplaced at a greater rate. These plutons exhibit marked sub-vertical crystal layering parallel to the intrusion walls suggesting that crystal-fluid processes were responsible for the fractionation trend.
A separate strongly undersaturated magma batch is represented in the Velasco province and occurs as a melasyenitic dyke-swarm. Some dykes are strongly enriched in rare-earth elements (REE), concentrated in the mineral britholite, and indicate interaction with a hydrous phase enriched in REE.
Tertiary alkaline magmatism in Trans-Pecos Texas
Authors: Barker Daniel S. 
Published: April 2008

Summary

Alkaline magmatism in far W Texas extended from 48 to 16 Ma ago, peaking in volume during the interval 37-26 Ma when all the felsic rocks were emplaced. Primitive magmas are rare, if not entirely lacking, but
ne-
and {ol+hy}-normative hawaiite and mugearite liquids (Ni <120 ppm; 100Mg/(Mg+Fe)<66) erupted through the entire time span. These evolved through
ne
-normative and
q
-normative trachytes to phonolite and rhyolite, including peralkaline varieties of both. Mafic
q
-normative rocks are distinctly subordinate.

Transition from a contractional to an extensional regime occurred between 32 and 30 Ma ago, after which Trans-Pecos magmatism was almost exclusively mafic. Major- and trace-element compositions show gradation south-westward to the calc-alkaline rocks of the Sierra Madre Occidental in western Mexico, which were erupted from 35 to 28 Ma ago. This compositional gradient suggests that the alkaline and calc-alkaline rocks were all related to subduction of the Farallon plate. The Trans-Pecos province is not a continental rift, and probably is not a product of back-arc spreading. Peralkaline phonolites and rhyolites in Texas and calc-alkaline rhyolites in Mexico were erupted at the same time and probably in the same stress regime, and their compositional differences must reflect differences in source rocks and conditions of melting.
Tertiary and Quaternary volcanism in the Massif Central, France
Authors: Downes Hilary 
Published: April 2008

Summary
Continental alkaline volcanics of the French Massif Central range in age from 65 Ma to 3450 years BP and can be divided by geography and age into 20 separate areas. There is no correlation between the age of an area and the geographic locality.
Two magma series are present: a silica-undersaturated basanite-tephrite-phonolite series and an alkali basalt-trachyandesite-trachyte-rhyolite series, the evolved members of which are silica-saturated. Rare nephelinites are also found. Primitive magmas of both main series may be derived from 2%–20% partial melting of a mantle enriched with light rare-earth elements with variable amounts of garnet in the residue; nephelinites were formed from a source which was isotopically and chemically distinct.
Fractional crystallization of observed phases accounts for the diversity of intermediate and evolved products. Amphibole fractionation in basalts at depth causes the trend towards silica saturation, while alkali feldspar fractionation dominates the final stages of crystallization. Removal of small quantities of sphene and zircon explains trace-element depletions in trachytes, phonolites and rhyolites.
Up to 30% crustal contamination has occurred in the evolved magmas but contamination is generally absent from their basaltic parents. Sr, Nd and Pb isotope data indicate that the most probable contaminant is undepleted meta-sedimentary granulite-facies lower crust. Variations in Sr and Nd isotope ratios also constrain petrogenetic hypotheses such as amphibole fractionation and magma mixing.
Mineralogical disequilibrium, compositional banding and emulsification textures indicate extensive magma mixing. Some flows are homogeneous hybrid lavas in which only the unusual composition and rare mineral disequilibria indicate the mode of formation.
Geochemistry and Tectonic Setting of Early Proterozoic Volcanic Rocks in Northern Ostrobothnia, Finland
Authors: Honkamo M. 
Published: April 2008

Summary
In northern Ostrobothnia, the Proterozoic Karelidic supracrustal rocks overlie Archaean rocks of the Prekarelidic basement complex. The Karelidic rocks are marine metasediments and marine metavolcanic rocks. The metasedimentary units of the schist area include arkose-quartzites, conglomerates and turbiditic metagreywackes. The associated metavolcanic rocks are mafic lavas with carbonate and chert intercalations.
Despite regional metamorphism of amphibolite facies the chemical composition of the metalavas is well within the limits of modern volcanic suites. Chemically, the metalavas are basaltic tholeiites. On discrimination diagrams based on major element contents the metalavas fall in fields of low-potassium tholeiites (LKT) and oceanic tholeiites. Trace element patterns are intermediate between LKT and mid-ocean ridge basalts (MORB). Field and chemical data permit different interpretations of the plate-tectonic setting of the northern Ostrobothnia basin. There is evidence suggesting marginal basin setting as well as an initial intra-continental rifting environment setting.
Intra-Arc Rifting and Massive Sulphide Mineralization in an Early Proterozoic Volcanic Arc, Skellefte District, Northern Sweden
Authors: Vivallo Waldo , Claesson Lars-Åke 
Published: April 2008

Summary
The Skellefte district in northern Sweden consists mainly of pyrite-rich massive sulphide deposits intercalated in an early Proterozoic volcano-sedimentary sequence. The volcanic activity was predominantly submarine, and gave rise to abundant felsic rocks with minor mafic volcanic rocks and rare andesitic volcanism. A few dykes and volcanic flows of high Mg-Cr basalts, probably komatiitic, are also found within the volcanic pile.
The geochemistry of the volcanic rocks is of subalkaline character and displays slightly tholeiitic to calcalkaline differentiation trends. The Ti, Zr, Y, Cr and rare-earth contents of the basaltic and andesitic rocks are consistent with a subduction related volcanic arc setting.
The bimodal nature of the volcanic suite, the presence of highly primitive basaltic rocks and the abundance of felsic pyroclastic material suggests that rifting occurred within the volcanic arc. Long periods of tensional stress predominated and favoured the extrusion of large volumes of felsic pyroclastics and the formation of tectono-volcanic depressions. The convergence in time and space of a thick volcanic sequence with high permeability, a high geothermal gradient related to the rising of basaltic magma, and synvolcanic faulting resulted in extensive hydrothermal activity. The hydrothermal activity caused regional alteration of the volcanic rocks and locally deposition of pyrite-rich massive sulphide deposits within local, tectonically controlled, depressions.
Volcanic Geochemistry of the Northern Segments of the Circum-Superior Belt of the Canadian Shield
Authors: Baragar W. R. A. , Scoates R. F. J. 
Published: April 2008

Summary
The northern segment of the early Proterozoic Circum-Superior Belt extending from the Ungava region of Quebec (Cape Smith Belt) through the islands of eastern Hudson Bay to northeastern Manitoba (Fox River and Thompson Nickel Belts) is distinguished by an extraordinary magmatic assemblage composed of two principal suites; komatiitic and tholeiitic. The older tholeiitic suite comprising basaltic flows and dolerite sills associated with a stable-shelf sedimentary sequence lies next to the Superior Craton in the Ungava-Hudson Bay region and is adjoined on its outboard side by the komatiitic suite of predominantly pillowed lavas. Their relationships are obscured by faulting but the presence of sills of the komatiitic suite at a number of levels in, and folded with, the tholeiite-sedimentary assemblage is evidence of its younger age. In northeastern Manitoba a discrete tholeiitic suite is absent and komatiitic flows and sills, in part differentiated to tholeiitic compositions, are associated directly with siliceous sediments of apparent continental provenance.
The komatiitic suite differs from its Archaean counterparts in that magma compositions rarely exceed about 16–18% MgO, yet spinifex texture (albeit clinopyroxene-olivine) like that of Archaean komatiites is one of its distinctive features. It is typically developed in the upper parts of certain layered (differentiated) flows that are otherwise little distinguished from the majority of layered flows common to the komatiitic sequence.

The tholeiitic suite is little differentiated but the komatiitic suite ranges from olivine- to clinopyroxene- and in places to plagioclase-phyric lavas through both long- and superimposed short-range stratigraphic intervals. Differentiation in the komatiitic suite is effectively represented by declining MgO/CaO ratios through the olivine fractionation stage (to about 1) then by increasing contents of oxides of the less refractory minerals, notably A1
2
O
3
, through clinopyroxene and clinopyroxene-plagioclase fractionation. The short-range variation is attributable to fractionation in the layered flows which are interpreted as principal surface distributors of lava and the long-range variations to major high-level sills as represented by those exposed in the Fox River Belt.
Proterozoic Volcanism in the Flin Flon Greenstone Belt, East-Central Saskatchewan, Canada
Authors: Gaskarth J. W. , Parslow G. R. 
Published: April 2008

Summary

Proterozoic basaltic and rhyolitic volcanics, and associated gabbros and ultramafic bodies from the Saskatchewan part of the Flin Flon-Snow Lake greenstone belt are all chemically tholeiitic. Both within-plate-MORB and volcanic arc tectonomagmatic environments are indicated by ‘discriminant’ plots (TiO
2
-Zr, Cr-Y, Zr-Ti/100-3Y) and MORB-normalized diagram patterns. Rocks with the various environmental ‘signatures’ are closely associated and there appears to be a continuum of compositions between the various types. The geochemistry is compatible with an origin from a single source within a small marginal basin.

Massive, Cu-Zn-Pb, sulphide deposits occur within volcanics with an arc-type ‘signature’ and associated rhyolitic bodies. Gold appears to have some geometrical association with the boundary between arc-type and within-plate-type volcanics though much is in later fractures. The concentration of mineral deposits in this part of the greenstone belt where there are volcanics showing transitional tectonomagmatic characteristics is thought to be significant.