bluuebunny/crossref_metadata_2025_split huggingface dataset:
Linking growth episodes of zircon and metamorphic textures to zircon chemistry: an example from the ultrahigh-temperature granulites of Rogaland (SW Norway)
Authors: Möller Andreas , O’Brien Patrick J. , Kennedy Allen , Kröner Alfred 
Published: April 2008

Abstract

In-situ
U-Th-Pb analyses by ion-microprobe on zircon in intact textural relationships are combined with backscatter and cathodoluminescence imaging and trace element analyses to provide evidence for growth episodes of zircon. This approach helps: (a) to unravel the polymetamorphic history of aluminous migmatitic and granitoid gneisses of the regional contact aureole around the Rogaland anorthosite-norite intrusive complex; and (b) to constrain the age of M
2
ultrahigh-temperature (UHT) metamorphism and the subsequent retrograde M
3
event. All samples yield magmatic inherited zircon of
c.
1035 Ma, some an additional group at
c.
1050 Ma. This suggests that loss of Pb by volume diffusion in non-metamict zircon is not an important factor even under extreme crustal conditions. Furthermore, the identical inheritance patterns in aluminous (garnet, cordierite ± osumilite-bearing) migmatites and orthogneisses indicate a metasomatic igneous instead of a sedimentary protolith for the migmatite. Results for the M
1
metamorphic event at
c.
1000 Ma
BP
are consistent in all samples, including those from outside the orthopyroxene-in isograd. The latter do not show evidence for zircon growth during the M
2
metamorphic episode.

Zircon intergrown with or included within M
2
metamorphic minerals (magnetite, spinel, orthopyroxene) give an age of 927 ± 7 Ma (2
σ, n
= 20). The youngest observed results are found in zircon outside M
2
minerals, some overgrown by M
3
mineral assemblages (late garnet coronas, garnet + quartz and orthopyroxene + garnet symplectites) and yield a slightly younger pooled age of 908 ± 9 Ma (2
σ, n
= 6). These textures are relative time markers for the crystallization of zircon overgrowths during discrete stages of the UHT event. These youngest age groups are consistent with the emplacement age of the Rogaland intrusive complex and the last magmatic activity (Tellnes dyke intrusion), respectively. This is direct and conclusive evidence for UHT metamorphism in the regional aureole being caused by the intrusions, and corrects earlier notions that the events are not linked. Trace element behaviour of zircon (Tb/U and Y content) has been tracked through time in the samples and shows variations both within and between samples. This heterogeneous behaviour at all scales appears to be common in metamorphic rocks and precludes the use of ‘rules of thumb’ in the interpretation of zircon chemistry, but chemical tracers are useful for recognition of zircon growth or recrystallization during metamorphism.
Improving precision of Sm-Nd garnet dating by H
2
SO
4
leaching: a simple solution to the phosphate inclusion problem
Authors: Anczkiewicz Robert , Thirlwall Matthew F. 
Published: April 2008

Abstract

Sm-Nd garnet geochronology is often hampered by the presence of submicroscopic inclusions of rare earth element-rich phosphates, which lower age precision, lead to inaccurate ages or make dating impossible. We propose a single-step sulphuric acid leaching technique as a very efficient tool in eliminating phosphate inclusions, which helps to achieve more precise and more accurate Sm-Nd garnet dates. Examples from silimanite grade metapelites demonstrate the much higher efficiency of this method in comparison with previously proposed techniques based on HF and HCl.
147
Sm/
144
Nd ratios obtained on garnets leached by sulphuric acid were twice as high as those obtained by HF and HCl leaching. This led to age precision better than 3% for Tertiary samples. Comparison of leached and unleached nearly inclusion-free garnets from high pressure granulites, demonstrates that there is no Sm/Nd fractionation induced by H
2
SO
4
leaching. Our new technique eliminates phosphates, but does not attack garnet. This considerably reduces the necessity for hand-picking and lowers the amount of sample required for analysis making Sm-Nd garnet dating a more easily applied geochronometer.
The use of dynamic reaction cell ICP mass spectrometry to facilitate Rb-Sr age determination
Authors: Vanhaecke F. , De Wannemacker G. , Balcaen L. , Moens L. 
Published: April 2008

Abstract

By using a set of granitic whole rock samples, originating from the Regensburg Forest (Germany) and dated (approximately 350 Ma old) previously by means of thermal ionization mass spectrometry (TIMS), the capability of dynamic reaction cell (DRC) inductively coupled plasma mass spectrometry (ICPMS) for Rb-Sr age determination was demonstrated. With DRC-ICPMS, chemical separation of Sr from Rb during the sample pretreatment is no longer required as interference-free determination of the
87
Sr/
86
Sr isotope ratio can be accomplished by monitoring the signals of the SrF
+
adduct ions, formed as a result of the selective reaction between the Sr
+
ions extracted from the ICP and the reaction gas CH
3
F. The mass discrimination was established to depend strongly on the matrix composition. This drawback could be overcome by using the United States Geological Survey reference material G-2 as an external standard. Results obtained by DRC-ICPMS (age and initial
87
Sr/
86
Sr ratio) showed an excellent agreement with both (a) experimental values obtained by means of quadrupole-based and sector field ICPMS after isolation of Sr via cation exchange chromatography and (b) TIMS literature values. In addition, DRC-ICPMS offers a smaller combined uncertainty on the isotope ratio results as a result of (a) an improved internal isotope ratio precision (<0.1% RSD when also using Ne as an additional non-reactive collision gas) and (b) the fact that, in contrast to quadrupole-based and sector field ICPMS, no correction for the remaining overlap between the signals of
87
Sr
+
and
87
Rb
+
is required.
Melt segregation rates in migmatites: review and critique of common approaches
Authors: Kriegsman Leo M. , Nyström Annika I. 
Published: April 2008

Abstract
The rate of melt segregation in regional migmatite terrains can be estimated by various lines of research. Firstly, the segregation rate of a melt batch, with a volume below the melt percolation threshold, cannot exceed the melt production rate and is therefore limited by the heating rate derived from geothermometry and geochronology (method A). Other estimates come from physical models for melt percolation (method B) and from the degree of (dis)equilibrium reached between melt and source rocks (method C). The first method is restricted by the current time resolution of isotopic techniques. Results from the second and third approaches depend heavily on assumed values of melt viscosity and other parameters (B); on the correct recognition of (dis)equilibrium trace element distributions (C); and on the migmatization model used (B and C).

The validity of method C is undermined by the mathematical equivalence of trace element models for five different scenarios: (1) disequilibrium melting (with or without melt escape) followed by
in situ
crystallization of non-segregated melt; (2) equilibrium melting, followed by equilibrium crystallization and major melt escape; (3) disequilibrium melting, followed by equilibrium crystallization and minor melt escape; (4) pervasive retrograde re-equilibration; and (5) subsolidus differentiation. Hence, trace element data in support of model 1 (implying fast melt segregation rates) are equally consistent with models 2 to 4 (implying slow melt segregation rates), and even with melt-absent model 5. The level of trace element saturation reached during accessory phase dissolution into melt may not provide better answers, as it is largely controlled by textural constraints, e.g. shielding of accessories by porphyroblasts.

We conclude that the way forward is to directly couple microtextural and microgeochemical information with time constraints. This requires high-resolution (space and time) geochronology, possibly with more advanced methods than presently available.
40
Ar/
39
Ar ages in mantle xenolith phlogopites: determining the ages of multiple lithospheric mantle events and diatreme ascent rates in southern Africa and Malaita, Solomon Islands
Authors: Wartho Jo-Anne , Kelley Simon P. 
Published: April 2008

Abstract
Kimberlites are extraordinary natural phenomena, ascending through the Earth’s lithosphere, entraining xenoliths, to erupt at the surface within hours to days of their inception deep within the lithospheric mantle. With the realization that some Ar/Ar phlogopite grain core ages may be indicative of geological events, we have undertaken high spatial resolution Ar/Ar dating of phlogopites in xenoliths and megacrysts from Kimberley, Monastery and Letseng in southern Africa, and Malaita, in the Solomon Islands, to est whether other mantle phlogopite cores may yield meaningful ages.
Modelling of Ar diffusive loss profiles from phlogopite grain boundaries to cores provides information on both the eruption age and the duration of outgassing within the kimberlite magma, and hence yields estimates on diatreme ascent rates. The ascent durations are very similar for all of the southern African pipes studied, yielding durations of 0.9–6.9 days, assuming an average kimberlite magma temperature of 1000 °C. These can be compared to estimates from phlogopite xenoliths from Siberian diamond-bearing kimberlites yielding ascent durations of 2–15 hours (assuming the same magma temperature).
The Tertiary Grès de Ville of the Barrême Basin: feather edge equivalent to the Grès d’Annot?
Authors: Evans Martin J. , Elliott Trevor , Apps Gillian M. , Mange-Rajetzky Maria A. 
Published: April 2008

Abstract
The Tertiary Grès de Ville in the Barrême Basin of the French Alps is conventionally considered to be the feather edge equivalent to the Grès d’Annot to the east. Both units accumulated in a province of thrust-sheet-top basins behind the initial thrust front and were supplied from a southerly hinterland (Maures-Esterel/Corsica-Sardinia). The units are also partially coeval, with the Grès de Ville being equivalent to the youngest part of the Grès d’Annot. However, the units accumulated in structurally distinct sub-basins that were separated by a fold (the St Lions anticline) that was growing at the time of Grès de Ville deposition. The Grès de Ville accumulated close to storm wave base, whereas deposition of the Grès d’Annot was notably deeper, indicating that the Barrême Basin was structurally higher than the Grès d’Annot Basin. There is also evidence that the Grès de Ville and the Grès d’Annot were fed by separate sediment transport paths linked to different drainage basins in the hinterland. It is therefore an oversimplification to regard the Grès de Ville as a feather edge to the Grès d’Annot; instead it should be regarded as an independent element of the fill of the Barrême Basin.
Three-dimensional stratigraphic modelling of the Grès d’Annot system, Eocene-Oligocene, SE France
Authors: Euzen T. , Joseph P. , Du Fornel E. , Lesur S. , Granjeon D. , Guillocheau F. 
Published: April 2008

Abstract
The Eocene-Oligocene Grès d’Annot series of SE France is a well-known turbidite system for sand-rich gravity deposits. The Grès d’Annot were deposited in several parallel and tectonically controlled elongated sub-basins in the western Alps foreland setting. Regional stratigraphic correlation is used to reconstruct and simulate in three dimensions the large-scale geometry and facies distribution of the Grés d’Annot in the Annot and Trois Evêchés sub-basins. The input parameters of the model are the accommodation, the sediment supply and the transport parameters. These are estimated from the geological model and subsequently adjusted in order to fit the simulation with selected sedimentological sections. From the analysis of the three-dimensional simulated block and of the adjusted input parameter set, an interpretation is proposed in which the relative contribution of external factors controlling the stratigraphic architecture are estimated. The first-order parameters that control the large-scale stratigraphic architecture are the initial basin physiography, the basin-floor deformation and the sediment supply variations through time and space. Small-scale folding and large-scale flexuration of the substratum control the confinement of the system and the available space for sedimentation. Sediment supply and water discharge variations through time are responsible for high frequency (fourth-order) and low frequency (third-order) stratigraphic cycles. This interpretation fits well with a model of a flood-dominated fluvio-turbidite ramp system in which physical continuity exists between the fan delta and the basinal turbidites. In such a tectonically active and confined basin, third- and fourth-order stratigraphic cyclicity might respectively result from uplift-denudation cycles and climatic variations through time. Tectonic activity in the source area may also be responsible for the migration of the main feeding system.
The character and origin of thick base-of-slope sandstone units of the Peïra Cava outlier, SE France
Authors: Lee Simon E. , Amy L. A. , Talling P. J. 
Published: April 2008

Abstract
Many hydrocarbon reservoirs occur within confined turbidite systems in which the depositional pattern of turbidity currents has been strongly influenced by basin-floor topography. In certain settings basin-floor topography may cause the development of anomalously thick (tens of metres) sandstones that are potentially excellent reservoir units. Southern exposures of the Peïra Cava outlier (Eocene-Oligocene; Annot Sandstones) provide well-exposed outcrops of such decametre-thick sandstone bodies. These units are located close to basin margins and downstream from an inferred topographic break-in-slope. Several base-of-slope sandstone bodies are examined that illustrate a common sedimentary theme of a complex basal unit, comprising laterally pinching or inter-fingering debrite and turbidite, abruptly overlain by a single, thick normally graded turbidite deposit. One of these sandstone bodies pinches out laterally over less than several hundred metres and sits within a deep (>20 m) ‘spoon shaped’ erosional scour. The scour is similar to morphological features observed in modern base-of-slope settings recently imaged using high-resolution submarine bathymetric surveys. Several different process interpretations may explain the occurrence of such sandstone bodies including remobilization of newly deposited sediment off basinmargins and enhanced deposition due to flow across a break-in-slope. A submarine channel interpretation is not consistent with the field observations. However, these units do share a number of similar features to channels that could lead to the misinterpretation of reservoir geometry.
The Grès d’Annot in the Annot syncline: outer basin-margin onlap and associated soft-sediment deformation
Authors: PuigdefàBregas Cai , Gjelberg John , Vaksdal Monica 
Published: April 2008

Abstract
The Grès d’Annot onlap on the outer basin margin has been extensively studied, but a number of important issues and critical outcrops remain controversial. A new geological map of the Annot syncline is here presented, supplemented with structural and sedimentological field observations. The mapped onlap traces in Annot reveal a curved, east-concave surface, with distinct westward shift of the successive onlap lines. The inferred onlap direction at Chalufy is to the SW, the only orientation compatible with the movement of the normal fault near Cabane des Abeurons. The similarity of the onlap relations between the areas of Annot and Chalufy, together with the structural features of the Annot syncline, support the concept of a common outer basin margin, rather than of a northern confinement of the Annot turbidites. The margin-onlap setting involved a specific style of syndepositional deformation. As a large, high-density turbidity current arrived on the basin-flank slope, it rapidly decelerated, thickened and dropped its coarse load, while being simultaneously deflected away from the slope. The associated normal stress and overpressure caused sub-horizontal injection and de-lamination of the soft substrate, with the tangential strain curling up the detached substrate slice into an overturned synclinal structure. The process provides an efficient way to incorporate fragments of mudstone and thin-bedded sandstone within the still moving highly-concentrated flow, eventually constituting the chaotic intervals within ‘tri-partite’ beds as the examples observed at the Braux section.
Onlap stratal architectures in the Grès d’Annot: geometric models and controlling factors
Authors: Smith Ru , Joseph Philippe 
Published: April 2008

Abstract
Onlap terminations of deep-marine sandstones in the Grès d’Annot, SE France, exhibit a range of styles, from abrupt onlap to feathering ‘aggradational onlap’ geometries. These are well exhibited in the large exposure of southward onlap terminations at Montagne de Chalufy, on the southern end of the Trois Evêchés Massif (Alpes de Haute Provence). These stratal architectures are here simulated by geometrical models that are governed simply by bounding slope gradients and the ratio of coeval slope to basinal aggradation rates. In cases of no coeval deposition on bounding slopes, pure onlap results. In cases of high slope aggradation rates relative to basinal aggradation rates, a feathered geometry results with successive sandstone beds onlapping against successively younger slope drapes. The cyclicity of alternating sand-rich and sand-poor packets seen at Chalufy results in a stepped climbing trajectory of successive slope base positions, with climb angle equal to bounding slope angle when mud-poor sandy flows deposited sandstone bodies with abrupt onlap, and climbing more steeply when slope drapes are deposited. An implication of this result is that any zones of facies change and palaeocurrent swing that are related to distance from bounding slope will exhibit a comparable vertical trajectory through time. The two end member termination types can be compared with the convergent-baselapping and convergent-thinning seismic facies used in the Gulf of Mexico subsurface and elsewhere. The convergent-baselapping seismic facies may include both abrupt onlap and intervals of feathering aggradational onlap if the presence of slope drapes is not resolvable by the frequency content of the available seismic data.
Key controls on the characteristics of turbidite systems
Authors: Bouma Arnold H. 
Published: April 2008

Abstract
Four main controls (tectonics, climate, sedimentary characteristics and processes, and sea-level fluctuations) commonly interact with each other and do so at varying intensities. This results in a wide variety of basin types and shapes, timing of transport within the sequence stratigraphy framework, transport and depositional processes, grain size ranges, and distribution of sediment within a basin. Two major end members of turbidite systems can be recognized: coarse-grained/sand-rich and fine-grained/mud-rich. Coarse-grained fans typically belong to active margin settings. They prograde gradually into a basin and show a decrease in thickness and grain size in the downflow direction. The sediment source is near the coastline, and the turbidite basins are commonly small to medium in size. The fine-grained fans occur on passive and active margins, prograde rapidly into a basin, and deposit most of the input sand in the distal fan as oblong sheet sands. Tectonically confined basins normally have their sediment source nearby, and therefore will be filled with coarse-grained fans. Most of the open (unconfined) basins are medium to large in size, have their sediment source far from the coast, and therefore lose the coarser fractions during continental transport. Diapirically controlled basins are small- to medium-sized confined basins that have a fine-grained turbidite fill, but may not reveal the bypassing of the majority of the sand to the outer fan because of the abundance of sediment transport to the basin.
Present morphology and depositional architecture of a sandy confined submarine system: the Golo turbidite system (eastern margin of Corsica)
Authors: Gervais Anne , Savoye Bruno , Piper David J. W. , Mulder Thierry , Cremer Michel , Pichevin Laetitia 
Published: April 2008

Abstract

The modern sandy Golo turbidite system (500 km
2
) is located in a confined basin on the eastern margin of Corsica. The Golo turbidite system is fed by a single river, which supplies coarse sand derived from active weathering of the neighbouring mountains. The late Quaternary deposits have been imaged using a closely spaced grid of 1000 km of sparker seismic-reflection profiles (line spacing close to 1.6 km, vertical resolution of 2m). The turbidite system is composed of four non-coalescent fans that were at times active simultaneously and of two small deposits onto the slope. The resulting sedimentation pattern is characterized by stacked turbidite deposits. At a regional scale, there is a continuum of fan morphologies and geometries from south to north. The use of both seismic and sedimentary facies, together with mapped seismic geometry of sedimentary bodies, allowed definition of four architectural elements: (1) submarine valley (canyon and gully), (2) sandy channel, (3) muddy levee, and (4) sandy lobe. Some of these architectural elements can be recognized at a scale that is comparable to outcrop examples. Features such as progressive lateral migration and avulsion, or complex longitudinal evolution (progradation and retrogradation), can also be accurately described. Despite the active tectonics along the studied margin, the main variations in sedimentation appear to be controlled by eustatic changes, pre-existing seafloor topography, and sediment source characteristics. The general pattern of sedimentation is controlled by the influence of a confining slope, leading to the predominance of aggradation and to specific morphology and architecture of sedimentary bodies.
Multiple terraces within the deep incised Zaire Valley (ZaïAngo Project): are they confined levees?
Authors: Babonneau N. , Savoye B. , Cremer M. , Bez M. 
Published: April 2008

Abstract
Terraces have been frequently observed and described along turbidite valleys. Many interpretations have been aimed at determining the origin of these structures, including a tectonic origin, succession of infilling and incision processes, channel-wall slumps, or inner levee aggradation. The Zaire submarine valley presents a complex structure with multiple terraces bordering a deep incised meandering thalweg. The detailed analysis of the morphology, the seismic structure and the recent sedimentation (in cores) along the Zaire upper-fan valley show that terraces are inner levees confined within the incised valley. Many terraces correspond to the infilling of abandoned meanders, and aggrade by deposition of turbidite sequences due to current overflows. The major process affecting the initiation and the development of terraces inside the valley is the vertical incision of the thalweg, simultaneously with meander migration.