Crystal-melt differential behaviour during magma ascent in dykes: insights from 2-D numerical modelling

We
 present
 the
 results
 of
 2D
 numerical
 models
 of
 flow
 in
 a
 two-phase
 medium,
 composed
 by
 crystals
 carried
 by
 a
 viscous
 melt,
 subject
 to
 a
 vertical
 pressure gradient condition.
These simulations of magma migration in a vertical
 dyke
 show
 that
 presence
 of
 crystals
 and
 their
 proportion
 perturb
 the
 flow
 velocity.
As shown in previous analytical studies,
the presence of crystals leads to
 a
 significant
 drop
 in
 vertical
 velocity.
 However
 in
 our
 case,
 this
 global
 displacement
 is
 accompanied
 neither
 by
 obvious
 crystal
 rotation
 nor
 by
 a
 significant
 horizontal
 displacement
 of
 crystals
 towards
 the
 dyke
 centre.
 Moreover,
 our
 results
 show
 that
 separation
 between
 crystal
 and
 melt
 occurs
 under
 certain
 conditions,
 which
 can
 lead
 to
 geochemical
 differentiation
 of
 magmas
 during
 their
 ascent.
 We
 provide,
 through
 a
 quantitative
 parametric
 study,
the
 range
 of 
values 
leading 
to
 crystal-melt 
segregation
 and
 compare 
the
 obtained differentiation rates to natural observations.
 Consequently, our results
 have
 fundamental
 implications
 regarding
 the
 causes
 of
 geochemical
 heterogeneities
 in
 magmatic
 suites.
 They
 provide
 constrains
 on
 differentiation
 processes
 during
 ascent,
 which
 is
 often
 neglected
 in
 comparison
 with
 the
 two
 classical
 end-members
 (i.e.,
 source-related
 processes
 vs.
 emplacement-related processes differentiation

Cartographie de l’occupation et de l’utilisation du sol et modélisation dassymétrique pour une meilleure gestion des risques en répondant à la directive INSPIRE

RESUME. Dans un contexte d’urbanisation et d’augmentation des risques des habitants à cause du changement climatique, les autorités doivent élaborer des plans de gestion pour comprendre, mesurer et cartographier les risques. Cet article traite de l'utilisation des géodonnées, des analyses spatiales et de la télédétection pour développer des méthodes de cartographie d’occupation / utilisation du sol mais aussi de densité de population. Ces cartes sont essentielles dans l’analyse des risques, que ce soit dans l’évaluation des dangers ou dans l’exposition de la population mais elles répondent également aux exigences de la directive européenne INSPIRE et donc aux obligations de l’administration. ABSTRACT. In the context of steady urban population growth and increased risk to these populations due to climate change, cities need to develop management strategies to understand, measure, map and mitigate the challenges and risks. This article deals with the use of geodata, spatial analysis and remote sensing to develop land-cover / land-use mapping and population density methods. These maps are not only essential in the risk analysis, whether in the assessment of hazards or in the exposure of the population, but they also meet the requirements of the European directive INSPIRE and therefore the obligations of the administration.info:eu-repo/semantics/publishe

Dating the exhumation of a metamorphic dome: geological evidence for pre-Eocene unroofing of the Nigde Massif (Central Anatolia, Turkey)

The timing of exhumation of metamorphic rocks and granitoids of the Nigde metamorphic dome, at the southern tip of the Central Anatolian Crystalline Complex, is a matter of debate. According to some authors, the metamorphic rocks are overlain nonconformably by a sedimentary sequence of late Maastrichtian to Late Palaeocene age. In contrast, other authors recently argued that the Nigde dome represents an extensional core complex of Oligocene-Early Miocene age, finally unroofed during late Miocene times. On the one hand, the results Of Our study contradict the latter interpretation. A sedimentary sequence of earliest Eocene to early Middle Eocene age nonconformably overlies the high-grade rocks of the Nigde dome on its southeastern flank. Pebbles from the metamorphic rocks are ubiquitous in the conglomerates of this sequence. As a result, the Nigde metamorphic rocks must have reached the surface before Eocene times. or at the very beginning of the Eocene at the latest. The Uckapth granite, whose crystallization age has been inferred to be Early Miocene, has intruded the metamorphic complex during exhumation. The granite is also found as pebbles within the conglomerates of the Eocene sedimentary sequence and, thus, is actually older than the Eocene. Apatite fission track dates of 12-11 Ma across the Nigde dome do not indicate that the metamorphic rocks were still on their way to the surface at that time; instead, they must reflect a later event, which is most probably heating during late Neogene magmatism. Lastly, there is no ductile-then-brittle extensional detachment in the two areas where it has been invoked, that is, on the western and southern flanks of the dome. An extensional detachment nevertheless exists at the top of the Nidge dome, best documented in its northern part, where the detachment fault superposes a superficial unit made up of massive ophiolitic rocks onto the high-grade metamorphic sequence. Field evidence indicates that this detachment developed before Eocene times. Oil the other hand, our observations do not confirm the nonconformity of the sedimentary sequence dated as late Maastrichtian-Late Palaeocene onto the Nigde high-grade rocks. Field relations show either a tectonic contact between the two, or the direct nonconformity of the Eocene sediments onto the metamorphic rocks. The lack of coarse clasts originating from the Nigde high-grade rocks within the Maastrichtian-Palacocene sequence further suggests that the metamorphic dome did not reach the surface before Late Palaeocene times. These results compare well with available data from the northwestern part of the Central Anatolian Crystalline Complex, suggesting that exhumation has been broadly synchronous on the scale of the massif, as a result of an episode of high magnitude extension that affected the region in Campanian to Palaeocene times

Modélisation spatiale des populations et de l’utilisation du sol comme outil de planification durable des territoires urbains

info:eu-repo/semantics/nonPublishe

SUSTAINABLE AND SMART CITY PLANNING USING SPATIAL DATA IN WALLONIA

Simulating population distribution and land use changes in space and time offer opportunities for smart city planning. It provides a holistic and dynamic vision of fast changing urban environment to policy makers. Impacts, such as environmental and health risks or mobility issues, of policies can be assessed and adapted consequently. In this paper, we suppose that “Smart” city developments should be sustainable, dynamic and participative. This paper addresses these three smart objectives in the context of urban risk assessment in Wallonia, Belgium. The sustainable, dynamic and participative solution includes (i) land cover and land use mapping using remote sensing and GIS, (ii) population density mapping using dasymetric mapping, (iii) predictive modelling of land use changes and population dynamics and (iv) risk assessment. The comprehensive and long-term vision of the territory should help to draw sustainable spatial planning policies, to adapt remote sensing acquisition, to update GIS data and to refine risk assessment from regional to city scale

Inclination shallowing in the Eocene Linzizong sediments from Tibet: correction, possible causes and implications for reconstructing the India-Asia collision

A systematic bias towards low palaeomagnetic inclination recorded in clastic sediments, that is, inclination shallowing, has been recognized and studied for decades. Identification, understanding and correction of this inclination shallowing are critical for palaeogeographic reconstructions, particularly those used in climatemodels and to date collisional events in convergent orogenic systems, such as those surrounding the Neotethys. Here we report palaeomagnetic inclinations from the sedimentary Eocene upper Linzizong Group of Southern Tibet that are ∼20◦ lower than conformable underlying volcanic units. At face value, the palaeomagnetic results from these sedimentary rocks suggest the southern margin of Asia was located ∼10◦N, which is inconsistent with recent reviews of the palaeolatitude of Southern Tibet. We apply two different correction methods to estimate the magnitude of inclination shallowing independently from the volcanics. The mean inclination is corrected from 20.5◦ to 40.0◦ within 95 per cent confidence limits between 33.1◦ and 49.5◦ by the elongation/inclination (E/I) correction method; an anisotropy-based inclination correction method steepens the mean inclination to 41.3 ± 3.3◦ after a curve fitting- determined particle anisotropy of 1.39 is applied. These corrected inclinations are statistically indistinguishable from the well-determined 40.3 ± 4.5o mean inclination of the underlying volcanic rocks that provides an independent check on the validity of these correction methods. Our results show that inclination shallowing in sedimentary rocks can be corrected. Careful inspection of stratigraphic variations of rock magnetic properties and remanence anisotropy suggests shallowing was caused mainly by a combination of syn- and post-depositional processes such as particle imbrication and sedimentary compaction that vary in importance throughout the section. Palaeolatitudes calculated from palaeomagnetic directions from Eocene sedimentary rocks of the upper Linzizong Group that have corrected for inclination shallowing are consistent with palaeolatitude history of the Lhasa terrane, and suggest that the India–Asia collision began at ∼20◦N by 45–55 Ma

Petrogenesis of picrites from the Caribbean Plateau and the North Atlantic magmatic province

We studied the petrography, mineralogy and geochemistry of picrites from three different regions: the island of Curaçao which forms part of a Cretaceous oceanic plateau; Iceland, an active hot spot on the mid-Atlantic ridge; and the early Tertiary volcanic margin off the coast of Greenland, which formed during the rifting that created the Atlantic ocean. Using the compositions of olivine phenocrysts and relations between MgO and FeO, Al2O3 and Ni, we estimated compositions of parental liquids and the proportion of accumulated olivine in each rock. Picrites from Curaçao formed mainly from a liquid with 12 wt.% MgO and they contain up to 55 wt.% excess olivine in the form of phenocrysts. A small proportion of more forsterite-rich olivine grains are xenocrysts from a more magnesian source. Picrites from Iceland formed from a slightly less magnesian liquid but one with also about 12 wt.% MgO and they contain both olivine and plagioclase in the accumulated assemblage. Picrites from the Greenland volcanic margin formed from a liquid that was distinctly more magnesian, with up to 20 wt.% MgO. In some of these rocks the proportion of accumulated olivine was minimal and in these the whole-rock composition is roughly equivalent to the liquid composition. The picrites from the three areas formed under different conditions and through contrasting melting processes. The Curaçao picrites derive from pooled liquids formed through moderate degrees of melting at moderate depths beneath a relatively old and thick oceanic lithosphere. Iceland picrites, on the other hand, formed through advanced fractional melting of mantle that ascended almost to the base of the crust at the mid-ocean spreading center. An unusual combination of relatively high concentrations of incompatible trace elements and high MgO indicates that the Greenland picrites formed by relatively low degrees of melting at greater depths in the mantle

The volcaniclastic series from the Luang Prabang Basin, Laos: A witness of a triassic magmatic arc?

The paleogeographic evolution of South East Asia (SEA) during the early Mesozoic is still poorly understood and a number of models have recently been put forward to account for the geodynamic evolution of SEA. The Luang Prabang Basin (north Laos), located in the core of a "paleogeographic jigsaw" in SEA, recorded a long lasting volcanism that spanned for ~ 35 my from the earliest Triassic up to Late Triassic as evidenced by combined stratigraphic and geochronological (U-Pb/zircon) analyses performed on both volcanic and volcaniclastic series. The volcanic rocks are arc tholeiites and calk-alkaline andesites to dacites. The volcaniclastic rocks contain, in part, volcaniclasts produced contemporaneously with sedimentation. Both the volcanic and volcaniclastic series display geochemical features characteristic of a subduction related volcanism. Therefore, the Luang Prabang Basin documents a magmatic arc in a good agreement with the recent recognition of neighboring ophiolitic rocks in the Luang Prabang area. Following a passive margin setting that prevailed from the late Carboniferous to the late Permian, an active margin then initiated along the western margin of the Indochina Block. This active magmatic arc developed as the result of an east-dipping subduction below the Indochina Block during most of the Triassic, at least from ca. 250 to 215 Ma. Subsequently, this oceanic subduction episode must have been followed by a continental collision of the Indochina Block with the eastern Simao Block, at a period that remains to be defined

Mesozoic emplacement and subsequent deformation of the Cuaro sills and dykes (Uruguay) from anisotropy of magnetic susceptibility.

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