bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismic tomography of the Dead Sea region: thinned crust, anomalous velocities and possible magmatic diapirism
Authors: Rabinowitz Nitzan , Mart Yossi 
Published: April 2008

Abstract

Analysis of first arrivals of P waves from 113 earthquakes in the Dead Sea region and the calculation of a tomographic model indicates anomalous distribution of seismic velocities in the crust and the upper mantle. The seismic tomography model was applied to the lower and intermediate crust and the uppermost mantle there, at depths greater than the detection limits of seismic reflection surveys. At these depths the inversion shows two deep layers, at depths of 10–22 km and 22–32 km. The deeper layer shows average seismic velocity of 7.7 km s
−1
, and the shallower one 6.5 km s
−1
. The model suggests therefore that the Moho under the central Dead Sea is found at depth of 22 km, and the seismic velocity in the upper lithospheric mantle is anomalously low. The velocity of the layer overlying the Moho suggests a modelled layer of composite mineralogy, but high velocity anomalies were encountered in the 10–22 km layer under the boundary faults of the Dead Sea Rift, and a low velocity anomaly under the central Dead Sea is plausible. The probable interpretation of these anomalies is that the mantle under the central Dead Sea is shallow and anomalously hot, and that the lower and intermediate crust under the axial zone of the central and northern Dead Sea is also anomalously hot. Furthermore, it seems probable that magmatic diapirs ascend along the boundary faults of the rift into the intermediate crust. Structural similarity of the upper mantle and the lower crust between the Dead Sea and the northern Red Sea suggests an analogous tectonic regime for these two regions.
Extrusion dynamics of mud volcanoes on the Mediterranean Ridge accretionary complex
Authors: Kopf Achim , Behrmann Jan H. 
Published: April 2008

Abstract

Drilling of two submarine mud domes situated in the Olimpi field on the northern flank of the Mediterranean Ridge accretionary complex has documented episodic eruptive activity over the last 1 to >1.5 Ma. Mud extrusion is related to plate convergence between Africa and Eurasia, having caused backthrust faulting of accreted strata containing overpressured mud at depth. The domes mainly consist of mud breccia with up to 65% of polymictic clasts embedded in a clayey matrix. On the basis of modifications of Poiseuille’s and Stokes’ laws, mud extrusion rates were calculated for Milano and Napoli mud domes. Mud ascent velocities are estimated to be up to 60–300 km a
−1
, and are comparable with those of silicate magmas. Using physical property, structural and flux data of the mud breccias, and compiled data from mud domes on land, the diameter of the feeder channel and the depth of origin for the overpressured muds could be reliably estimated for the first time. Feeder channels are likely to be only a few metres wide. Gas efflux estimates constrain a source depth to
c.
1700 ± 50 m below sea floor in the Olimpi field, which is considerably shallower than estimations made from the thermal maturity of solid organic carbon in the mud breccias. The efflux data suggest that the overpressured muds were not mobilized at décollement depth, but at a shallower level within the accretionary prism. A comparison of mud ascent rates (as determined from Poiseuille flow) and the total volumes of mud extruded indicate that only a fraction of the time span constrained from biostratigraphic data (
c.
1 Ma) is needed to build up the Milano and Napoli mud domes. Durations of 12–58 ka of extrusive activity suggest mud volcanism here to have been a highly episodic phenomenon.
Holocene environmental change in the Yorkshire Ouse basin and its influence on river dynamics and sediment fluxes to the coastal zone
Authors: Macklin M. G. , Taylor M. P. , Hudson-Edwards K. A. , Howard A. J. 
Published: April 2008

Abstract
Geomorphological, geochemical and geochronological investigations of Holocene fluvial sedimentary sequences have been undertaken within a range of upland, piedmont and lowland valley floor reaches in the Yorkshire Ouse catchment, northern England. The aims of these studies have been to: (a) evaluate the effects of prehistoric and historic land-use change on catchment erosion and sediment delivery to river channels and floodplains; (b) establish the degree to which episodes of river erosion and sedimentation are controlled by climate-related variations in flood regime; and (c) assess the spatial heterogeneity of river response to environmental change and how this is likely to influence short- and long-term sediment storage, as well as sediment transfer to the Humber Estuary. Similar discontinuities in the Holocene alluvial record are evident at many sites in the Yorkshire Ouse catchment, though local differences in river sensitivity to externally imposed change have resulted in a complicated and often unique relationship between river behaviour and environmental change. The large proportion of particulate-borne contaminant metals (resulting predominantly from historical mining) stored in the Vale of York strongly indicates that sediment delivery from the Ouse catchment to the Humber Estuary during the Holocene may have been relatively low. This suggests that the degree of connectivity between river, estuarine and coastal transport systems, as well as spatial and temporal variations in fluvial sediment storage, are the key controls of long-term land-ocean sediment fluxes.
Modelling western North Sea palaeogeographies and tidal changes during the Holocene
Authors: Shennan I. , Lambeck K. , Flather R. , Horton B. , McArthur J. , Innes J. , Lloyd J. , Rutherford M. , Wingfield R. 
Published: April 2008

Abstract

Analysis of cores collected from Late Devensian (Weichselian) and Holocene sediments on the floor of the North Sea provides evidence of the transgression of freshwater environments during relative sea-level rise. Although many cores show truncated sequences, examples from the Dogger Bank, Well Bank and 5 km offshore of north Norfolk reveal transitional sequences and reliable indicators of past shoreline positions. Together with radiocarbon-dated sea-level index points collected from the Holocene sediments of the estuaries and coastal lowlands of eastern England these data enable the development and testing of models of the palaeogeographies of coastlines in the western North Sea and models of tidal range changes through the Holocene epoch. Geophysical models that incorporate ice-sheet reconstructions, earth rheology, eustasy, and glacio- and hydroisostasy provide predictions of sea-level relative to the present for the last 10 ka at 1-ka intervals. These predictions, added to a model of present-day bathymetry, produce palaeogeographic reconstructions for each time period. The palaeogeographic maps reveal the transgression of the North Sea continental shelf. Key stages include a western embayment off northeast England as early as 10 ka
bp
; the evolution of a large tidal embayment between eastern England and the Dogger Bank before 9 ka
bp
with connection to the English Channel prior to 8 ka
bp
; and Dogger Bank as an island at high tide by 7.5 ka
bp
and totally submerged by 6 ka
bp
. Analysis of core data shows that coastal and saltmarsh environments could adapt to rapid rates of sea-level rise and coastline retreat. After 6 ka
bp
the major changes in palaeogeography occurred inland of the present coast of eastern England. The palaeogeographic models provide the coastline positions and bathymetries for modelling tidal ranges at each 1-ka interval. A nested hierarchy of models, from the scale of the northeast Atlantic to the east coast of England, uses 26 tidal harmonics to reconstruct tidal regimes. Predictions consistently show tidal ranges smaller than present in the early Holocene, with only minor changes since 6 ka
bp
. Recalibration of previously available sea-level index points using the model results rather than present tidal-range parameters increases the difference between observations and predictions of relative sea-levels from the glacio-hydro-isostatic models and reinforces the need to search for better ice-sheet reconstructions.
Differential compaction of interbedded sandstone and coal
Authors: Laubach Stephen E. , Schultz-Ela Daniel D. , Tyler Roger 
Published: April 2008

Abstract
Cretaceous and Tertiary coal beds in the western United States typically contain subvertical opening-mode fractures (cleat). However, closely spaced normal faults abruptly substitute for opening-mode fractures in coal beneath some sandstone lenses having blunt terminations. Differential forced-fold compaction of coal beds around and beneath lens-shaped sandstone bodies accounts for such shifts in fracture style. Finite element modelling of coal deformation shows that shear stress is augmented in coal layers below abruptly tapering edges of sandstones lenses, favouring fault development, whereas under gradually tapering lenses shear stresses are not sufficiently enhanced to cause shifts in fracture style. Upper Cretaceous Mesaverde Group coal beds in southwest Wyoming have significant variations in fracture style over distances of a few to tens of metres. Because these faults have little or no porosity, the coal that contains them is likely to have low permeability compared to coal having typical (generally porous) opening-mode fractures. Thus, shifting fracture style may affect regional and local gas and water flow in coal beds.
Late Quaternary monoclinal folding induced by caldera resurgence at Ischia, Italy
Authors: Tibaldi Alessandro , Vezzoli Luigina 
Published: April 2008

Abstract

The main structure of the active resurgent caldera of Ischia is uncommonly well exposed. The very young age of the resurgence (<33 ka
bp
) has enabled the uppermost part of the uplifted block to be preserved, whereas the severe erosion on the steep flanks, made up of low-resistant pyroclastic deposits, has resulted in the rest of the resurgent block structure cropping out. The uppermost part is characterized by strata gently dipping at 1–5° in a general south-southeast direction. Along the southern flank of the resurgent block, the strata gradually form a complex double monocline fold with ENE-trending hinge lines. Some tens of metres below the topographic surface, the anticline part of each monocline fold gradually turns into a vertical fault. The middle limb strata are vertical to subvertical. This draping occurred with the aid of at least one main detachment horizon localized inside the pyroclastic succession. Total resurgence here is about 350 m. The opposite northern flank of the resurgent horst, which has experienced maximum uplift of the order of about 900 m, is characterized by a few vertical to subvertical normal faults with draping of strata. These data suggest that the outward-dipping strata commonly found in Quaternary resurgent calderas could represent; (i) the surface expression of forced folding induced by the piston-like uplift of a fault-bounded concealed block; or (ii) the classical doming induced by radial and vertical growth. The fault-bounded horsts sometimes recognized in old, deeply eroded, resurgent calderas could be the forcing block of non-preserved drape folds. These monocline folds could also be disrupted by upward propagation of the bounding faults after an incremental offset beyond the limit of folding of a given volcanic succession.
Stratal fold patterns adjacent to normal faults: observations from the Gulf of Mexico
Authors: Mansfield C. S. , Cartwright J. A. 
Published: April 2008

Abstract
This paper describes the study of a subsurface array of young growth faults from the Gulf of Mexico, using a high-resolution three-dimensional (3D) seismic data set. The seismic data have resolved all of the faults within the survey area in detail, enabling the full three-dimensional structure and displacement patterns of the faults to be accurately mapped. In this paper, special attention is paid to the magnitude and orientation of small ‘drag’ folds that occur in the wall-rock of these faults, ubiquitous throughout the data set and well resolved by the seismic data. The results indicate that in both the footwalls and the hangingwalls the folds occur with variable amplitude, and also that they are small in relation to the dimensions of the respective faults. That is, they are spatially impersistent, often exhibiting rapid changes from normal drag to reverse drag over distances as short as 100 m. Furthermore, strong discordance with the recorded patterns of throw (the vertical component of displacement) suggests that no simple apparent correlation exists with the respective displacement distributions.
By comparison with a number of field and theoretical examples, various mechanisms are discussed to explain the probable origin and variability of these folds. In general, however, evidence for the cause of the folds is limited and remains largely inconclusive. It is suggested that one potential explanation is stratal deformation in the vicinity of points of overlap and linkage between faults in the dip direction (dip linkage). In an earlier study of the fault throw distributions it is has been argued that this is the preferential mechanism by which faults in this part of the Gulf of Mexico enlarged their surface area during growth.
Effects of interlayer slip in model forced folds
Authors: Couples G. D. , Lewis H. 
Published: April 2008

Abstract

Forced-fold models, constructed from multiple sheets of rock layers and other materials, are deformed, under confining pressure, by the translations and rotations of a steel-block forcing assembly. The first-order response of these models is like that observed in earlier sets of models: an asymmetric fold pair develops over the uplifted edge of the rigid, primary forcing block; the layers translate into the folding area without being pushed; and bending deformation imparts spatially variable strains onto the layered package. The second-order response of the new experiments is quite different from earlier work — the new multilayered models develop temporally variable bending strains caused by the progressive development of interlayer slip on
some
of the layer-layer interfaces. The presence of the layer-parallel slip surfaces reduces the bending resistance, and it causes the resulting folds to be more localized and to have different shapes than in similar experiments where layering is less effective. In the multilayer models, faulting in the layered package is much reduced compared to similar models without multiple layering, and material strains are everywhere smaller in the layers. Layer contractions and elongations of the layering are produced in these forced-fold models as a consequence of the flexure process, without regard to farfield causative loads. The models reveal a progression of deformation consequences that is related to the mechanical effectiveness of the layering. If the understanding of process gained from these models is extended to natural folds, it becomes possible to explain both the observed differences of fold shape and some of the variations in subsidiary deformations.
Geometry of fold arrays in the Silesian-Cracovian region of southern Poland
Authors: Teper Leslaw 
Published: April 2008

Abstract
A zone of deformation characterized by en echelon folds extends along the northeast margin of the Upper Silesian Coal basin in southern Poland. The zone is well exposed by mining in numerous collieries where the deformation involving Upper Carboniferous strata can be observed. Folds and associated faults form a structural pattern consistent with an origin in dextral convergent wrenching on both the principal deep-seated fractures and the subsidiary faults affecting crystalline basement beneath this part of the basin. The zone is cross-cut by sublatitudinal fold belts which, according to their geometrical parameters, seem to result from alternate transcurrent shearing along west-east oriented fractures in the basement, sinistral in one case and dextral in the other. Among folds caused by the concentrated operation of a force couple whose vectors lie in the horizontal plane, there are examples of bending folds (forced folds) in each array resulting from vertical components of movement of deep-seated fault blocks. The dimensions of the folds change with depth, and the axial trend and the inclination of axial surfaces differ with distance from the basement fault trace. The length of fold segments strongly depends on axes orientation. Widely distributed evidence of interlayer slip demonstrates a variable spatial distribution of tectonic-transport direction in the sedimentary sequence. The above-mentioned features and other geometrical attributes of the fold arrays enable the dynamics of the forcing structures during Variscan tectogenesis to be determined and illustrate a hierarchical structure of the basement boundary zones. Examples from the Silesian-Cracovian region suggest that bending folds (forced folds) can sometimes originate in conditions provided by a strike-slip regime.
Complex metamorphic zonation of the Thaya dome: result of buckling and gravitational collapse of an imbricated nappe sequence
Authors: Štípská P. , Schulmann K. , Höck V. 
Published: April 2008

Abstract
The metamorphic isograd geometry and dome structure of the Thaya tectonic window, which emerges through the Moldanubian nappe pile at the eastern margin of the Bohemian Massif, is interpreted as a result of large-scale buckling of an imbricated nappe sequence. This large-scale mechanical instability was initiated by the blocking of passively transported hot viscous rocks to shallow crustal levels. The wavelength and shape of the buckle fold is controlled by the greatest thickness of the uppermost nappe and by the low ratio of strong orthogneiss to weak micaschists in individual nappes. The steep inclinations of the thrust surfaces and the oblique movement of the crustal multilayer minimizes the role of gravity on fold generation. Medium-scale gravitational folds originated at the end of the buckling of the nappes and are associated with the late sliding of the nappes away from the core of the anticline during late exhumation. Thermal, rheological and fold calculations are presented which document and explain the mechanism of folding of large-scale crystalline nappes.
The gravity field of the Karakoram Mountain Range and surrounding areas
Authors: Caporali A. 
Published: April 2008

Abstract

A ‘blank on the map’ only 60 years ago, the Karakoram Range has been explored and surveyed with greater difficulty than the Himalaya and Tibet due to its rugged terrain and extensive glaciation. In the past ten years we have succeeded in doubling the number of gravity stations. A substantial improvement in coverage and overall quality was obtained by concentrating on previously unsurveyed areas and by validating older data with more accurate measurements. Our data were merged with earlier data, converted to full Bouguer anomalies and gridded. The resulting Bouguer anomaly map defines very precisely the gravimetric low associated with the Nanga Parbat-Haramosh syntaxis, and the huge negative anomalies between the Karakoram Fault and the Main Karakoram Thrust. Large negative values are now visible also in the Ghujerab-Khunjerab areas. Correlation of the topography and Bouguer anomaly shows that a plate of flexural rigidity with
D
= 2 × 10
24
Nm fits the coherence data in the Karakoram at all but two distinct frequency ranges centred at wavelengths of 80 and 300 km. In a rheologically layered lithosphere developing a buckling instability under horizontal compression, the observed spectral features of the topography and Bouguer gravity anomalies constrain the depth of the competent layers to be in the range 13–20 km and 50–75 km respectively.
Mafic sheets from Indian plate gneisses in the Nanga Parbat syntaxis: their significance in dating crustal growth and metamorphic and deformation events
Authors: Treloar P. J. , George M. T. , Whittington A. G. 
Published: April 2008

AbstractIndian plate, granulite facies, migmatitic basement gneisses exposed within the Nanga Parbat syntaxis host at least two generations of mafic sheets. In the southern part of the syntaxis, concordant sheets yield Palaeo-Proterozoic model ages of 2.2–2.6 Ga, which probably date early stages of continental growth. In the northern part of the syntaxis the sheets include a suite of discordant, silica-saturated or oversaturated sub-alkaline basalts extracted from a slightly depleted sub-continental mantle. Nd model ages and an imprecise Sm-Nd isochron yield an age of emplacement at between 1.6 and 1.8 Ga. That these dykes cross-cut granulite facies migmatitic fabrics implies that peak metamorphism in the Indian plate gneisses was, at latest, Meso-Proterozoic and not Tertiary in age. Zircon and amphibole ages published elsewhere suggest that this metamorphism was probablyc.1850 Ma in age. That the basement gneisses were refractory by the Tertiary has implications for the derivation of leucogranite sheets during the Neogene. Although the gneisses experienced a Tertiary-aged metamorphism, it was to lower temperatures than the Meso-Proterozoic metamorphism. Unless the gneisses were rehydrated during the Tertiary, the leucogranites need to have been sourced from more fertile rocks underplating the granulite facies basement complex.
Tectonics of the SW margin of the Nanga Parbat-Haramosh massif
Authors: Edwards M. A. , Kidd W. S. F. , Khan M. A. , Schneider D. A. 
Published: April 2008

Abstract

We present an analysis of the tectonic evolution of the southwestern portions of the Nanga Parbat massif, Pakistan Himalaya, based upon detailed mapping and structural analyses from the Bunar, Biji, Diamir, Airl, Niat and SW Rupal valleys. Mainly metasedimentary cover rocks of the Indian plate are divided into upper and lower cover. There is a marked structural thinning of the cover in the main Bunar valley from south to north, and this is attributed to a major frontal ramp in the original Main Mantle Thrust (MMT). A hitherto unmapped shear zone, the Diamir Shear Zone, is identified, that is associated with a syn-kinematically intruded belt of granitic rocks, the Jalhari Granite. The shear zone is a several kilometre thick, generally W-vergent, ductile to brittle shear zone that is associated with local overturning of the entire MMT section, typified by the Gashit Fold.
40
Ar/
39
Ar cooling ages from across the area indicate a steep cooling age gradient across the Diamir Shear Zone from >40 to <5 Ma. The Diamir Shear Zone is mechanically linked to part of the Raikhot Fault System and, together, they are seen to be a crustal-scale reverse fault that has allowed relative uplift and overthrusting of the core of Nanga Parbat.