bluuebunny/crossref_metadata_2025_split huggingface dataset:
A critical assessment of the tectono-thermal memory of rocks and definition of tectono-metamorphic units: evidence from fabric and degree of metamorphic transformations
Authors: Spalla M. Iole , Zucali Michele , Di Paola Silvia , Gosso Guido 
Published: April 2008

Abstract

A correlation procedure of scattered tectonic and metamorphic imprints in the reactivated crust is elaborated from recent analytical work in three Alpine metamorphic complexes. It consists of: interpretation of the time-sequence of tectonic fabrics and test of their kinematic coherence; determination of paragenetic compatibility among the mineralogical support of mesoscopic fabrics; cross-validation of mineral transformation over-prints; construction of
P-T-d-t
paths using a time-sequence of parageneses. The representation of structural and metamorphic information conveys the full tectono-metamorphic history on maps displaying combined tectonic and metamorphic effects. Shape and size definition of metamorphic units, now individuated mainly using their lithological homogeneity and dominant metamorphic imprint, is improved. The analysis of interaction between fabric and metamorphic imprint distributions, proposed in three Alpine examples, shows that the dominant metamorphic imprint does not coincide with
T
max
-
P

T
max

of each inferred
P-T-d-t
loop; the dominant metamorphic imprint is that given by the mineralogical support of the most pervasive fabric. Different metamorphic imprints may dominate in adjacent areas of a single tectono-metamorphic unit (TMU), or equivalent metamorphic imprints may dominate in different TMUs. Therefore, lithostratigraphic setting and dominant metamorphic imprint are inefficient to contour TMUs in terrains with polyphase deformation and metamorphism, without considering multiscale heterogeneity of superposed synmetamorphic fabrics.
Origin of the current stress field in the western/central Alps: role of gravitational re-equilibration constrained by numerical modelling
Authors: Delacou Bastien , Sue Christian , Champagnac Jean-Daniel , Burkhard Martin 
Published: April 2008

Abstract
We interpret the strain and stress fields of the western/central Alpine arc on the basis of 2.5D finite element modelling and a recent seismotectonic synthesis. Models have fixed boundary forces and different crustal geometries, so that they respond to buoyancy forces (variations in gravitational potential energies). The seismotectonic regime, characterized by orogen-perpendicular extension in the high topographic core of the belt and local orogenperpendicular compressional/transpressional deformation in the external zones, appears to be very close to the modelled gravitational regime. Rotation of Apulia has a minor effect on the current strain or stress fields of the Alpine realm. Nevertheless, it could help to explain the orogen-parallel dextral faulting that is observed all along external zones, from the northern Valais to the Argentera external crystalline massif. Our results highlight the consequences for the Alpine realm of ongoing convergence between the African and European plates. Our interpretation is that collision is no longer ongoing and that buoyancy-driven stresses dominate the present-day geodynamics of the western/central Alps.
Submarine slope systems: processes and products
Authors: Flint Stephen S. , Hodgson David M. 
Published: April 2008

Abstract
Understanding of the processes operating on submarine slopes, the preserved depositional products and post-depositional modifications to sediment body geometries through instability and remobilization requires integration of data from modern slopes with information derived from seismic and outcrop studies of ancient slope successions. Although local factors are important, key generic concepts that aid in predicting submarine slope processes and products include: (1) shelf accommodation/lateral sediment supply variations on sediment delivery; (2) the spatial/temporal distribution of characteristic styles/intensities of sediment instability and remobilization; and (3) a generalized model for the stratigraphic development of slope channel complexes, slope fans and the temporal relationships between these major components of slope stratigraphy.
Key remaining problems include bridging the gap between the timescales sampled by Recent to late Quaternary studies and those represented by ancient slope successions. Moreover, present-day highstand conditions may not provide a good analogue for lowstand slope settings. Future research efforts will also concentrate on better calibration of seismic facies to rock facies and linking of physical and numerical (process and forward) modelling techniques at different scales to observational datasets. The future lies in integration of these complementary research directions.
Deposition and stratigraphic architecture of an outcropping ancient slope system: Tres Pasos Formation, Magallanes Basin, southern Chile
Authors: Shultz M. R. , Fildani A. , Cope T. D. , Graham S. A. 
Published: April 2008

Abstract
The Tres Pasos Formation, Magallanes Basin, Chile, represents the deposit of a submarine slope depositional system. The formation is approximately 1500 m thick where exposed in the Ultima Esperanza district of southernmost Chile. It is characterized by a basal turbiditic sandstone unit up to 200 m thick that shows a north-to-south, proximal-to-distal facies evolution from turbidite channel-fill complexes to sheet-like sandstone units. This unit is interpreted as having been deposited at or near the base of slope. Overlying the basal sandstone unit is approximately 500 m of amalgamated mass transport complexes, fine-grained strata, and channelized and non-channelized turbidity current deposits, collectively comprising the middle part of the formation. Mass transport complexes exert a primary control on the character and grain size of turbidite sandstone bodies in the basal and middle part of the formation. In the southern part of the study area, a 300 m thick coarse-grained unit interpreted as a turbidite channel-fill complex partially replaces the middle part. The upper part of the formation is approximately 500 m thick and consists primarily of fine-grained strata. Failure scarps and thin turbidite channel-fill units are present in this upper part, interpreted as upper slope deposits.
Architecture and stratigraphic evolution of multiple, vertically-stacked slope channel complexes, Tanqua depocentre, Karoo Basin, South Africa
Authors: Wild Richard J. , Hodgson David M. , Flint Stephen S. 
Published: April 2008

Abstract
Early Permian deep-water deposits of the Tanqua depocentre, SW Karoo Basin, South Africa, include Unit 5, an extremely well-exposed 100 m-thick lower slope succession. Within the study area, Unit 5 comprises two partially-synchronous, vertically stacked, sub-parallel channel complex sets that lie 8 km apart along strike (the east-trending Klein Hangklip complex set and the NE-trending Groot Hangklip complex set). The detailed time-stratigraphic relationship between deposition in the interchannel areas and channel fill aggradation remains unresolved due to exposure limitations; however, it is suggested that most of the turbidite sheet deposits between the channels represent frontal lower slope splays from earlier slope feeder systems and are not genetically related to the channels. Gravitational instability in the sheet deposits drove a range of deformation processes from low velocity ‘slope creep’ to complete failure and slumping during times of maximum incision and bypass within the slope channels. Following the main phase of aggradation within the channels, periods of spill led to the formation of lateral splays and splay channels, which are distinct from the older frontal splay deposits. Each channel complex comprises two composite channel bodies and is interpreted to represent a fifth order sequence. In the absence of evidence of local (intraslope) tectonic controls, the vertical stacking of the channel complexes is interpreted to be due to fixed shelf edge entry points. Abrupt lateral facies changes along depositional strike, the ubiquity of instability features, the high proportion of sandstone preserved in the channel complexes and the absence of levees supports the interpretation that Unit 5 in the Hangklip area was deposited in a lower slope setting.
Quantitative textural analyses of TOBI sonar imagery along the Almería Canyon, Almería Margin, Alborán Sea, SE Spain
Authors: Sichi Olga Gómez , Blondel Philippe , Gràcia Eulàlia , Dañobeitia Juan José ,   The Hits-2001 Science Party
Published: April 2008

Abstract

Hydrocarbon exploration and the ongoing assessment of potential seismic risks are the main drivers behind the high-resolution mapping of continental margins. The large volume of literature devoted to turbidite systems in particular shows the importance of detailed descriptions of their characteristics and overall geomorphological variability, primarily through the distribution of sediment facies. These descriptions rely mainly on acoustic measurements, which are notoriously difficult to interpret. Textural analyses quantify the second-order statistics of sonar imagery, detecting and quantifying details invisible to the human eye. We show the potential (and limitations) of this approach using high-resolution (6 m) towed ocean bottom instrument (TOBI) sidescan sonar imagery acquired in the Alborán Sea, south of Almería, Spain, during the high resolution imaging of Tsunamigenic structures (HITS) 2001 programme. The imagery is co-registered with EM-12 multibeam bathymetry, topographic parametric sonar (TOPAS) sub-bottom profiles, and localized ground truthing. Our study focuses on the Almería Canyon, a meandering channel system more than 57 km long and transporting large amounts of sediments from the coast down to the Alborán Trough,
c
. 1700 m deep. Textural analyses quantify the variations of sediment processes along the slope of the Almería Canyon. They agree with the results of previous studies, and they can be used to provide new insights in the dynamics and evolution of the canyon.
Mud prone entrenched deep-water slope channel complexes from the Eocene of eastern Turkey
Authors: Cronin Bryan T. , Çelik Hasan , Hurst Andrew , Turkmen Ibrahim 
Published: April 2008

Abstract
A series of deep-water channel deposits are exposed near Baskil, 50 km west of Elaziğ in eastern Turkey. The use of correlation panels, sedimentary logs, biostratigraphy and mapping revealed that all of the channel elements are found within much larger features. One series of channels from the southern margin of the basin lie, within an entrenched deep-water slope channel complex, over 3 km wide, called the Nohut Channel Complex. This channel complex has three main fill packages. The lower package is a highly disturbed, slumped interval that directly overlies the erosional base of the main channel complex. The slumped interval is interpreted as a series of mass transport complexes, derived from shallow marine or upper slope facies. The second package comprises a mixed carbonate-siliciclastic series, principally of interbedded calcarenites, marls and mudstones. Locally, outer shelf/upper slope offset-stacked channels with calcarenite fills occur. The upper package comprises isolated conglomerate and sandstone filled deep-water channels that are incised into laterally extensive depositional lobes. The coarse-grained fills are dominated by tabular beds. The lobes are comprised of fine-medium grained sandstones. Some of these channels have low aspect ratios (25:1), and are asymmetric in cross-section, suggesting sinuosity. The upper part of this fill package is either incised into by pro-fan delta conglomerate filled channels, or downlapped onto by shelfal calcarenites. A separate series of channels come from the northern margin of the basin, but are interpreted to have developed on an open, deep-water slope or ramp, rather than as an entrenched channel complex. These channels occur in two main sets, collectively referred to as the Aydinlar Channel Complexes. The lower set is characterized by syn-sedimentary foundering of the sand-filled channels within slumped enveloping finer-grained slope sediments. The upper set of channels, dominated by one large sand and gravel-filled fairway, is characterized by large bedforms at the base, passing upwards into stacked conglomerates, mud chip breccias and sandstones. The conglomerate facies is locally injected upwards into the fill or laterally into finer-grained marginal facies. The channel is capped by finer-grained facies, including graded sandstones and siltstones with complete Bouma sequences.
Deformation and submarine landsliding caused by seamount subduction beneath the Costa Rica continental margin — new insights from high-resolution sidescan sonar data
Authors: Hühnerbach V. , Masson D. G. , Bohrmann G. , Bull J. M. , Weinrebe W. 
Published: April 2008

Abstract
Subduction of seamounts at destructive sedimented plate margins results in spectacular deformation of the overriding plate. High-resolution sidescan sonar imagery from the Costa Rica margin show the tracks of five individual seamounts, of which four are described in this paper. These were subducted at various times during the last 690 ka and each represents a different stage in the subduction process. Each subducted seamount leaves a parallel-sided depression in its wake, that can be traced for up to 55 km landward of the deformation front. This wake is created by deformation and uplift of the continental slope as the seamount passes beneath it, followed by collapse due to landsliding as support for the uplifted area is withdrawn. Areas of uplift above seamounts are characterized by complex normal and strike-slip fault patterns. Collapse of the uplift along the trailing edge of the seamount creates a zone of slope failure (landsliding) that migrates upslope (or landward) with the seamount. Landslide processes are dominated by debris flow, but also include sliding of coherent blocks and debris avalanche. Erosion occurs by repeated landslides, which produce a series of overlapping debris flows. Downslope sediment transport typically extends over limited distances, resulting in partial ‘backfilling’ of the scar as its headwall moves up slope. The amount of margin material disrupted by seamount subduction is four to five times the volume of the subducting seamount, of which about three quarters seems to be recycled downslope, backfilling the scar, and nearly one quarter is subducted with the seamount.
Seismic and aseismic weakening effects in transtension: field and microstructural observations on the mechanics and architecture of a large fault zone in SE Tibet
Authors: Edwards M. A. , Ratschbacher L. 
Published: April 2008

Abstract

Fault-zone surveying and microstructural analyses focus on a transtensionally strained section of a >100 km-long, 5–15 km-wide, active, sinistral strike-slip W-E fault — the Damxung-Jiali Shear Zone (DJSZ). Deformation fabric superposition, palaeostress and neotectonic measurements reveal a progressive dominance of the transtension coaxial component. Vertical flattening and broadening of the DJSZ results in a 10–20 km-wide pull-apart depression with reciprocal emergence of flanking highlands that expose abandoned fault-zone domains that are hundreds of metres by tens of km in size. Polylithological fault rocks preserve a suite of frictional and viscous deformation to
c.
350 °C. Amongst the fault strands, intensity and distribution of grain size reduction from comminution, widespread solution transfer, intragranular plasticity and recrystallization is heterogeneous. A regular pattern of pseudotachylite-coated surfaces short-cutting strong volcanic mylonite domains between weak creeping calcite domains indicates seismic with aseismic strain, and is interpreted as velocity-weakening evidence. Re-brecciation of solution-transfer accommodation-assisted S-C-cataclasite domains document switches from frictional to viscous strain and back again. The co-location of brittle and plastic constituent behaviour for varied fault lithologies plus our interpretations on deformation temperatures suggests major overlap for the frictional and viscous depth ranges. This indicates a very broad and strongly velocity- and fluid-dependent ‘brittle-ductile’ transition.
Electrical conductivity images of active and fossil fault zones
Authors: Ritter O. , Hoffmann-Rothe A. , Bedrosian P. A. , Weckmann U. , Haak V. 
Published: April 2008

Abstract
We compare recent magnetotelluric investigations of four large fault systems: (i) the actively deforming, ocean-continent interplate San Andreas Fault (SAF); (ii) the actively deforming, continent-continent interplate Dead Sea Transform (DST); (iii) the currently inactive, trench-linked intraplate West Fault (WF) in northern Chile; and (iv) the Waterberg Fault/Omaruru Lineament (WF/OL) in Namibia, a fossilized intraplate shear zone formed during early Proterozoic continental collision. These fault zones show both similarities and marked differences in their electrical subsurface structure. The central segment of the SAF is characterized by a zone of high conductivity extending to a depth of several kilometres and attributed to fluids within a highly fractured damage zone. The WF exhibits a less pronounced but similar fault-zone conductor (FZC) that can be explained by meteoric waters entering the fault zone. The DST appears different as it shows a distinct lack of a FZC and seems to act primarily as an impermeable barrier to cross-fault fluid transport. Differences in the electrical structure of these faults within the upper crust may be linked to the degree of deformation localization within the fault zone. At the DST, with no observable fault-zone conductor, strain may have been localized for a considerable time span along a narrow, metre-scale damage zone with a sustained strength difference between the shear plane and the surrounding host rock. In the case of the SAF, a positive correlation of conductance and fault activity is observed, with more active fault segments associated with wider, deeper and more conductive fault-zone anomalies. Fault-zone conductors, however, do not uniquely identify specific architectural or hydrological units of a fault. A more comprehensive whole-fault picture for the brittle crust can be developed in combination with seismicity and structural information. Giving a window into lower-crustal shear zones, the fossil WF/OL in Namibia is imaged as a subvertical, 14 km-deep, 10 km-wide zone of high and anisotropic conductivity. The present level of exhumation suggests that the WF/OL penetrated the entire crust as a relatively narrow shear zone. Contrary to the fluid-driven conductivity anomalies of active faults, the anomaly here is attributed to graphitic enrichment along former shear planes. Once created, graphite is stable over very long time spans and thus fault/shear zones may remain conductive long after activity ceases.
High-temperature and pressure seismic properties of a lower crustal prograde shear zone from the Kohistan Arc, Pakistan
Authors: Burlini L. , Arbaret L. , Zeilinger G. , Burg J.-P. 
Published: April 2008

Abstract

Anastomosing shear zones exposed in the lower crust of the Kohistan palaeoisland arc in Pakistan have parageneses indicating increasing pressure during deformation. Therefore, they represent a rare example of strain localization during crustal thickening. We investigated the seismic properties of a sheared gabbro with constant bulk chemistry across one of these shear zones. The compressional wave velocity was measured at confining pressures of up to 0.5 GPa and temperatures of up to 600 °C. The density, the average V
p
(compressional P-wave velocity) and the acoustic impedance at room temperature increase from the undeformed protolith through the strain gradient to the intensely sheared mylonite. The seismic anisotropy is largest for the strain gradient.

The
V
p
dependence of the velocities on temperature is much higher in the mylonite than in the protolith. The acoustic impedance contrast between protolith and mylonite is high enough to generate seismic reflections at low temperatures, but not at high temperatures. This suggests that the seismic reflectivity may also depend on the temperature. Consequently, ductile shear zones can be detected in reflection profiles of crusts with low geothermal gradients, and may be transparent in crusts with high geothermal gradients.
Damage and recovery of calcite rocks deformed in the cataclastic regime
Authors: Schubnel A. , Fortin J. , Burlini L. , Guéguen Y. 
Published: April 2008

Abstract

Compressional and shear wave velocities have been measured during the experimental deformation of Carrara marble and Solnhofen limestone in the cataclastic regime, both in dry and wet conditions at room temperature. Measurements were performed under hydrostatic conditions (up to 260 MPa confining pressure and 10 MPa pore pressure) during triaxial loading (at the constant strain rate of 10
−5
s
−1
) as well as during differential stress relaxation. During a full cycle, our results show that the seismic velocities first increase as effective mean stress increases. However, when the stress onset of cataclastic deformation was reached, elastic velocities showed rapid decrease due to stress-induced damage in the rock. During stress relaxation tests we observed an increase of elastic velocities with time, which suggested a fast ‘recovery’ of the microstructure. A substantial and rapid drop in the velocities occurred when reloading, suggesting that the previous ‘recovery’ was only transient. Subsequent relaxation tests showed other marked increases in velocities. These experimental results suggests that during the deformation of low-porosity calcite-rich rocks, dilatant (crack opening and frictional sliding) and compaction micro-mechanism (pore closure) compete. Evolutions of elastic properties (mainly sensitive to crack density) and macroscopic volumetric strain (more sensitive to porosity) are therefore not systematically correlated and depend on the strain rate, the solid stress conditions and the pore pressure.
The effect of grain size and melt distributions on the rheology of partially molten olivine aggregates
Authors: Bruhn David , Kohlstedt David L. , Lee Kyong-Ho 
Published: April 2008

Abstract
Grain size distribution affects the distribution of melt in partially molten rocks, as melt is partitioned into the finer grained regions. As the creep strength of partially molten rocks depends on melt fraction, grain size distribution affects rheology in two ways: in the diffusion-creep regime the strength of the rock decreases with decreasing grain size; and by affecting the melt distribution, grain size distribution affects rock strength in the dislocation and the diffusion-creep regimes. To investigate this effect on partially molten dunites, we deformed synthetic aggregates of olivine + mid-ocean ridge basalt (MORB) with varying grain size distributions and melt fractions. We found that samples with bimodal grain size distributions did not obey the flow law derived for samples with a uniform grain size distribution. In the samples with bimodal grain size distributions the finer grained parts are enriched in melt, reducing the relative melt fraction in the coarser grained parts. The stress exponent is close to 1 for lower stresses for samples with non-uniform grain size distributions, while it is close to 3 for samples with a uniform grain size distribution. Electron backscatter diffraction (EBSD) analysis shows crystallographic preferred orientation (CPO) well developed in all samples. Microstructural investigation shows that partitioning of the liquid out of the coarser grained part of the aggregate into the finer grained part leads to a localization of the strain into the weaker, finer grained and melt-enriched part. By treating the two parts as mechanically different phases that deform at a uniform stress, we are able to approximate the rheological behaviour of the aggregates with bimodal grain size distribution.