bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some time-space relationships for crustal melting and granitic intrusion at various depths
Authors: Thompson Alan Bruce 
Published: April 2008

Abstract
Crustal melting occurs at the higher grades of metamorphism. Migmatites reflect crustal anatexis without necessary additional heat supply. Granites usually result from crustal melting resulting from ‘hot’ geotherms, or reflect an external heat supply.
The commonest mechanisms of crustal melting are: (i) decompression of crust thickened into mantle in convergent orogens; (ii) asthenosphere upwelled beneth the crust in extensional orogens; (iii) massive invasion or underplating of crust by mantle magma generated by mantle decompression. This paper considers some of the processes governing timescales and lengthscales of these various magmatic events with particular view to determining the intensity and duration of crustal melting, and relationships between the rates of melt extraction, ascent and emplacement.
Emplacement of the Joshua Flat-Beer Creek Pluton (White Inyo Mountains, California): a story of multiple material transfer processes
Authors: Dietl Carlo 
Published: April 2008

Abstract

The Joshua Flat-Beer Creek Pluton (JBP) in the White Inyo Mountains, California, is part of the Inyo batholith, which intruded a Neoproterozoic to Lower Cambrian metasedimentary sequence at about 180–160 Ma ago. Contact metamorphism around the JBP reached hornblende-hornfels- to lower amphibolite-facies conditions. The intrusion consists of three distinct phases. Field relations suggest an intrusion sequence Marble Canyon Diorite-Joshua Flat Monzonite-Beer Creek Granodiorite as nested diapirs. In the Marble Canyon Diorite as well as the Joshua Flat Monzonite the subsequent intrusions led to brecciation and stoping, but also to mingling and mixing between the Joshua Flat Monzonite and the Beer Creek Granodiorite. Fabrics in the contact aureole document several emplacement mechanisms such as stoping and dyking, ductile downward flow, partial melting and magma chamber expansion. The relative importance of the different emplacement mechanisms through time is as follows: the Marble Canyon Diorite probably intruded as dyke/sill, whereas stoping and dyking, ductile downward flow together with assimilation acted during the emplacement of the Joshua Flat Monzonite. Magma chamber expansion represents only the latest stage of intrusion during the emplacement of the Beer Creek Granodiorite into the already existing magma chamber of the JBP. AMS, quartz
c
-axis and strain measurements support the field observations.
Indentation of volcanic edifices by the ascending magma
Authors: Merle Olivier , Donnadieu Franck 
Published: April 2008

Abstract
The process by which magma ascends into and deforms a volcanic edifice is studied by analogue modelling. A control experiment is conducted with a wooden piston moving vertically into a sand cone. This reveals a well-defined fault pattern that makes it possible to draw the main compressive stress trajectory within the cone during the ascent of the piston. This makes it possible to show that the deformational process is that of indentation of the cone by the rigid piston. Experiments with an indenter that is viscous, as in nature, show that the motion of the viscous body is controlled by the first fault created in the cone. This fault serves as a structural guide, making the viscous body deviate from the vertical and resulting in deformation of the flank of the cone, which bulges out. Other major shear faults that were observed in the control experiment are then inhibited and do not form. This result emphasizes that the structural evolution of an indentation process within a brittle cone and at low rate depends on the rheology of the indenter.
Pluton emplacement in the Northern Tyrrhenian area, Italy
Authors: Rossetti F. , Faccenna C. , Acocella V. , Funiciello R. , Jolivet L. , Salvini F. 
Published: April 2008

Abstract
The post-orogenic extensional processes that affected the inner sector of the Northern Apennine orogenic wedge (i.e. the Northern Tyrrhenian region) were accompanied by the emplacement of chiefly anatectic intrusive rocks of Late Miocene to Mid-Pleistocene age. In this paper, we compare geological and structural data from Messinian-Pliocene monzogranitic intrusions located both offshore (Monte Capanne, Porto Azzurro, Montecristo and Giglio) and onshore (Gavorrano and Botro ai Marmi) in the Northern Tyrrhenian region to constrain modes of pluton emplacement. Offshore, eastward non-coaxial extensional shear zones active both in ductile and brittle conditions accompanied the emplacement of the monzogranitic intrusions, and accommodated extension oriented E-W to WNW-ESE. Onshore, N-S dextral strike-slip faulting was active both during and after the late stage of emplacement of both Botro ai Marmi and Gavorrano plutons, and controlled their rise in coincidence with releasing bends. In our interpretation, the N-S, Late Miocene-Pliocene strike-slip faulting constitutes a secondary shear feature in a context of generalized post-orogenic extension, accommodating in the brittle upper crust the non-coaxial ductile extension in the lower crust. In this framework, N-S strike-slip faults localized the rise of early anatectic magma, generated during regional post-orogenic extension and residing at the base of the extending crust.
Recrystallization salt fabric in a shear zone (Cardona diapir, southern Pyrenees, Spain)
Authors: Miralles L. , Sans M. , Pueyo J. J. , Santanach P. 
Published: April 2008

Abstract
In the southern Pyrenees foreland, the Cardona salt diapir has a 250 m high stem and a small bulb, which is partially exposed. The internal structure of the diapir consists of a main sheath fold divided by a shear zone. This shear zone crosses two salt units with different initial properties. In this paper, a qualitative analysis of the fabric both units crossed by the shear zone and a 3D quantitative morphological and textural analysis of the unit with small grain size were carried out. In this unit, the fabric is characterized by a grain size similar to that of the initial fabric, disappearance of primary structures, a poor grain orientation with the long axis statistically at 20° of the shear boundary, and a strong {100} crystallographic preferred orientation. The unit composed of coarser grains shows a disappearance of primary structures. The fabric changes in both units and the strong decrease in water content during deformation suggest that fluid-assisted synkinematic recrystallization was dominant. The different behaviour of the two studied units on shear deformation also suggests that the initial grain size and water content were the main factors controlling fabric changes.
Holocene sediment storage in the Humber Estuary
Authors: Rees J. G. , Ridgway J. , Ellis S. , Knox R. W. O’B. , Newsham R. , Parkes A. 
Published: April 2008

Abstract

In order to determine the processes that have governed the accumulation and erosion of sediments in the Humber Estuary (English North Sea coast) through the Holocene, the character, volume and source of sediments were studied. Eight sediment suites were identified on the basis of chemostratigraphy, lithostratigraphy and mineralogy. The locally sourced, freshwater, Basal Suite is overlain by the Newland and Butterwick Suites, deposited between
c.
8 and 7.4 cal. ka
bp
in brackish environments behind a morainic barrier at St Andrew’s Dock, Hull. These are overlain by the largely marine, saltmarsh sediments of the Garthorpe Suite, which in turn are overlain, with erosional contact, by the channel sandflat and mudflat deposits of the Saltend, Sunk Island and Skeffling Suites. Most of the Saltend Suite is likely to have been deposited since
c.
4 ka ago, whilst the Sunk Island and Skeffling Suites are likely to have been deposited since Medieval times and from the late eighteenth century onwards, respectively, as indicated by their concentrations of anthropogenic metals. On the coast, the Spurn Suite consists of sediments, associated with a spit system, which are almost entirely marine in origin. The suites show a progressive increase in marine influence; sediments of the oldest suite being entirely from the terrestrial catchment, those of the younger suites from erosion of the North Sea floor and coast. The relationships between suites show that during the last 4 ka the geomorphological evolution of the estuary has been marked by widespread erosion episodes that have led to the partial removal or redistribution of earlier deposits. By modelling the volumes of the suites it can be shown that, of the total volume of the estuarine fill (9.6 km
3
), over half is likely to have been deposited during this period.
Origin, abundance and storage of organic carbon and sulphur in the Holocene Humber Estuary: emphasizing human impact on storage changes
Authors: Andrews J. E. , Samways G. , Dennis P. F. , Maher B. A. 
Published: April 2008

Abstract

An organic carbon (C
org
) and sulphur (S) storage inventory for Holocene sediments in the Humber Estuary is established; sources of organic matter and their variation over time are identified, and with chronological control, the importance of estuarine sediments as C
org
and S stores is demonstrated. Humber Holocene sediments are grouped into seven widespread environmental facies with statistically significant geochemical data sets: (1)
oak-hazel fenwood
(OHF); (2)
alder carr
(AC), appearing as peats in core; (3)
river channel muds or sands
(Rcm/s); (4)
high saltmarsh
(HSM); (5)
low saltmarsh
(LSM); (6)
intertidal mudflat
(ITMF); and (7) a
sandy
facies (S). Carbon, nitrogen and sulphur (CNS) abundances show that these facies have diagnostic geochemical signatures and δ
13
C values for bulk organic matter exhibit a range of average values: −28‰ (terrestrial peats), −27‰ (HSM), and −24.5‰ (ITMF) reflecting the up core transition from terrestrial peats through saltmarshes to more open marine mudflat environments as regional sea-level rose. Chronology and average sedimentation rates are partly constrained by radiocarbon dates; palaeomagnetic techniques helped define discrete sediment packages and discontinuities (time gaps). Although the Humber Holocene sediment record is not continuous, long-term sedimentation rates (about 1 mm a
−1
) show that sediment accretion kept pace with regional sea-level rise between 6 and 2 cal. ka
BP
. This sedimentation rate, combined with core evidence to allow a geographic reconstruction of the palaeo-Humber (3–2cal. ka
BP
), is used to calculate storage values for C
org
and S in the various environments of the palaeo-Humber. Comparison of the C
org
and S sedimentation and storage terms for the palaeo-Humber with modern values highlights the impacts of reclamation and commercial/urban development in the estuary in the last 300 years. OHF and AC peats, which were the largest C
org
and S stores in the palaeo-estuary, are now absent (reclaimed), while saltmarshes are no longer widespread. Conservative calculations show a net decrease in C
org
deposition from about 3.2 × 10
5
tonne in the palaeo-estuary to no more than 2.5 × 10
3
tonne today, a >99% reduction in potential C
org
storage capacity. The total modern yearly S deposition is approximately 2% of its value 2ka ago. Removal of saltmarsh and associated brackish-freshwater wetland suggests that suspended sediment and associated C
org
and S are currently bypassing former (Holocene) storage areas and may be impacting North Sea biogeochemical cycling.
Sediment provenance and flux in the Tees Estuary: the record from the Late Devensian to the present
Authors: Plater A. J. , Ridgway J. , Rayner B. , Shennan I. , Horton B. P. , Haworth E. Y. , Wright M. R. , Rutherford M. M. , Wintle A. G. 
Published: April 2008

Abstract

The influences of sea-level, climate, human activity and coastal morphology on post-glacial sediment flux and deposition in the Tees Estuary were considered in a multidisciplinary investigation of the Late Pleistocene and Holocene sedimentary record. The following tripartite division was identified using a combination of lithostratigraphic and geochemical data: a Late Glacial laminated clay providing evidence of a former proglacial lake and a proxy record of climate change; an early-mid-Holocene intercalated sequence of tidal silts and clays and peats; and a late Holocene succession characterized by increasing evidence of human activity and metal contamination. Sea-level change has been identified as the main control on sedimentation
via
decelerating sea-level rise and changing tidal dynamics between
c.
8 and 3 ka
bp
. Climate controlled the sequence of rhythmite thickness in the Late Glacial clays, whilst increased wetness after
c.
3 ka
bp
may have encouraged terrestrial sediment influx. Enhanced sediment supply to the coastal zone can also be attributed to increasing human activity in the catchment from the Bronze Age onward, first as a consequence of clearance, and subsequently as a result of mining and industrial expansion. Fine-grained sediment flux has almost exclusively been from the Tees catchment to the coast, extending offshore during rebound-induced collapse and erosion of the Late Glacial lake basin. The only notable onshore sediment flux has been the deposition of marine sands in the outer estuary between
c.
6.5 and 3.5 ka
bp
.
Sedimentary evolution of the north Norfolk barrier coastline in the context of Holocene sea-level change
Authors: Andrews J. E. , Boomer I. , Bailiff I. , Balson P. , Bristow C. , Chroston P. N. , Funnell B. M. , Harwood G. M. , Jones R. , Maher B. A. , Shimmield G. B. 
Published: April 2008

Abstract

Holocene sediments of the north Norfolk coast (NNC) between Weybourne and Hunstanton have been studied using geophysical, sedimentological, biofacial and dating techniques. New cores and refraction seismic data have defined the topography of the pre-Holocene surface and show that the NNC sediment prism is underlain by an east-west trending Quaternary trough, probably a palaeo-river-valley. The age of the Holocene fill has been dated using radiocarbon and luminescence dates, while sedimentation rates were constrained by, and compared with, modern rates using radionuclide data. The Holocene sediments are divided into a sandy-barrier lithofacies association (LFA), and a muddy-silty-peat back-barrier LFA. The oldest Holocene sediments are peats, formed on an undulating till surface. These peats were forming by 11-10 cal. ka
bp
and continued to form until at least 7 cal. ka
bp
in a number of places. As Holocene sea-level rose, marine mudflat and saltmarsh environments began to form between 7 and 6 cal. ka
bp
east of Holkham and around 6 cal. ka
bp
or younger west of Holkham. A marked erosion surface between the barrier and back-barrier LFA in the Holkham to Burnham Overy area is imperfectly dated at <3 cal. ka
bp
, but suggests the sediment prism has thinned by about 3 km over 6 to
c
. 3cal. ka
bp
. This surface probably records the westward progress of laterally migrating tidal channels that caused back-barrier sediment erosion, along with shoreface processes, as sea-level rose. Small-scale regressive and transgressive saltmarsh sequences occur at different elevations along strike but cannot be correlated, suggesting that the control on saltmarsh and mudflat development is autocyclic rather than allocyclic. Generally, transgressive and regressive events are related to disposition of coastal barriers and these are superimposed on a general facies evolution governed by regional sea-level change. Predictions about how this barrier coastline might respond to increased rates of regional sea-level change caused by global warming, or climatic events like increased storminess, require an understanding of how specific segments of the coastline have responded over millennial time-scales. This longer-term evolution provides the baseline information for decision making and management strategy. It is likely that sandy sediment supply is limited on the NNC and this implies that the barriers will continue to move landward, probably at increased rates relative to today, suggesting that parts of the NNC will become more vulnerable to erosion and flooding.
The geometries and deep structure of the northern North Sea rift system
Authors: Odinsen Tore , Christiansson Peter , Gabrielsen Roy H. , Faleide Jan Inge , Berge Anker M. 
Published: April 2008

Abstract

The enormous quantity of commercial reflection seismic lines across the North Sea Basin have made the area one of the most thoroughly studied continental settings in the world. Further insight in the deep architecture of the crust is provided by
c.
10 000 km deep reflection seismic data. Unfortunately, these unique databases have rarely been combined systematically to constrain possible tectonic models for the area. This paper is built on a full integration of high-quality commercial lines (7 s twt) and the deep (15 s twt) NSDP84-1 and -2 lines. The deep lines have been post-stack reprocessed and depth-converted. A number of deep wells have provided stratigraphic control along the lines. The overall reflective pattern in the lines divides the crust in three, with a reflective upper and lower crust separated by a less reflective middle crust. The lateral changes in reflectivity matches the observed variation in crustal thickness, where the thinnest crust coincides with the Viking Graben area with a total crustal thickness of 21–24 km, increasing to 30–36 km in the platform areas. The lower crust is seen as an undulating 4–10 km thick band with shallow dipping reflections, with a Moho that consists of reflections with variable lateral thickness and amplitude, rather than one single strong reflection. The structural analysis shows that the crust is cut by a number of large normal faults with varying geometries. It is assumed that some of these major faults are long-lived features rooted in old basement grains. The most spectacular normal faults developed during the Permo-early Triassic extensional phase, but were often reactivated during the Jurassic extensional phase, and with continued minor fault movement into the Cretaceous thermal cooling period. Integration of commercial and deep reflection seismic sections shows that three detachment levels are present within the crust. These levels, which control changes in fault geometries, are believed to represent lateral rheological interfaces combined with or intersected by long-lived zones of weaknesses. The uppermost level is represented by supra-basement low-angle normal faults controlled by gravity and/or lithological changes during extension. An intra-basement (middle crust) level between 5 and 7 s (twt) coincides with decreasing dip of the larger basin bounding faults. The lower crust is the deepest detachment level, which probably exerts control on the geometric changes of the upper-mantle shear zones and the largest crustal normal faults.
Crustal stress in and around Norway: a compliation of
in situ
stress observations
Authors: Fejerskov Morten , Lindholm Conrad , Myrvang Arne , Bungum Hilmar 
Published: April 2008

Abstract

In-situ
rock stresses yield information about geodynamic processes in the crust, and are important input data for almost all kinds of geomechanics work. Compilations of rock stress measurements, such as the World Stress Map, have been used to characterize the regional stress field. On the basis of new data from the Norwegian region, a map of the maximum horizontal stress (
σ
H
) direction, for both on- and offshore Norway, has been established. Four main stress provinces with different regional stress trends are identified. The Barents Sea and northern Norway province exhibits a very consistent N-S
σ
H
direction, with high horizontal stresses. In the Norwegian Sea and mid-Norway province the
σ
H
direction has rotated towards NW-SE. Also here, high horizontal stresses are measured and a compressional regime appears. In the northern North Sea and western Norway province the
σ
H
direction is more scattered. A WNW-ESE direction dominates, but a NNE-SSW trend, parallel to the major structures in the area, also appears. The stress regime is primarily compressional, but in the Stord area normal faulting earthquakes are observed. The southern North Sea province yields a very scattered
σ
H
direction. However, a NW-SE trend, which aligns with the stress system in western Europe, is identified. The high variation, both laterally and with depth, indicates near-isotropic horizontal stresses and influence by local features. The different stress determination techniques applied (overcoring, borehole breakouts and earthquake focal mechanisms) yield approximately the same stress orientation, and regional and internal variation, although they cover different depth intervals. They further manifest high horizontal stresses in the Norwegian area, generally exceeding the vertical stress. This indicates the presence of compressional tectonic stresses penetrating deep into the crust. The first-order stress pattern in Norway and adjacent offshore regions show a rotation in
σ
H
direction from N-S in the Barents Sea to WNW-ESE in the North Sea. This rotation can be explained by the ridge push effect alone, but other effects may also be contributing factors. The increased scatter in
σ
H
direction in the south is believed to be due to changes in the tectonic stress magnitudes, or related to relative changes in angle between the continental margin and the ridge push force.
Crustal stress in and around Norway: an evaluation of stress-generating mechanisms
Authors: Fejerskov Morten , Lindholm Conrad 
Published: April 2008

Abstract

Recent stress observations from
in situ
measurements and earthquake focal mechanisms in the Norwegian onshore and offshore areas are evaluated with the aim of characterizing the most important mechanisms for the present stress field in and around Norway. The evaluation is based on a set of stress indicators that include both shallow measurements (overcoring and borehole breakouts) and deep data (earthquake focal mechanisms). Computer simulations of simple stress-generation models were used to constrain the relative importance of different stress-generating mechanisms. The ridge push force associated with sea-floor spreading in the North Atlantic is considered to be the primary source of the compressional stress field observed in Norway. Regional influences from the continental margin density contrast, topography and flexure induced by sediment loading are of limited lateral extent, but are important in reorienting the stress field in certain areas. The observed tectonics and stresses are generally also in accord with tectonics expected from Fennoscandian uplift.