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See detailFe–Ti–V–P ore deposits associated with Proterozoic massif-type anorthosites and related rocks
Charlier, Bernard ULg; Namur, Olivier; Bolle, Olivier ULg et al

in Earth-Science Reviews (2015), 141(0), 56-81

Magmatic rocks containing economic concentrations of iron, titanium, vanadium and phosphorous are commonly associated with massif-type anorthosites and related rocks. This rock association is part of the ... [more ▼]

Magmatic rocks containing economic concentrations of iron, titanium, vanadium and phosphorous are commonly associated with massif-type anorthosites and related rocks. This rock association is part of the anorthosite–mangerite–charnockite–(rapakivi-)granite suites that are restricted to the Proterozoic. Understanding the geochemistry and emplacement mechanisms of ilmenite, magnetite and apatite ore deposits is crucial for exploration, efficient mining operations and ore processing. This review discusses the controlling factors on the grade of an ore, its mineralogy, and its major and trace element distribution. We present petrogenetic models of currently mined deposits (Lac Tio, Tellnes, Damiao) and discuss the characteristics of minor ore bodies from anorthosite provinces worldwide (Grenville, North China Craton, East European Craton, Rogaland, Laramie). Models of formation of anorthosite and related rocks are presented, as well as the nature of the possible parental magmas of the suite. A mineralogical classification of Fe–Ti ores is proposed: (1) Gabbro-noritic ilmenite ore ± apatite ± magnetite; (2) Ti-magnetite-dominated ore; (3) Nelsonite (Fe–Ti oxides + apatite); and (4) Rutile-ilmenite ore. The stability of ilmenite and magnetite is then critically reviewed and the influence of various factors, particularly oxygen fugacity and crystallization pressure, is examined. We discuss liquidus compositions of Fe–Ti oxides and the behavior of important trace elements such as Cr and V, both of which are sensitive to fO2 variations. Post-cumulus evolution of both oxides can occur due to re-equilibration with trapped liquid, re-equilibration with ferromagnesian silicates, exsolution, oxidation, reaction between ilmenite and magnetite, and metamorphic overprinting. These various processes are described and their effects on the oxide geochemistry are emphasized. Several potential ore-forming processes have been invoked and can explain the formation of huge concentration of ilmenite, ± magnetite, ± apatite. Fractional crystallization can be combined with crystal sorting and plagioclase buoyancy to produce relative enrichment of dense ore minerals. Silicate liquid immiscibility can segregate conjugate Si-rich and Fe-rich melts, the latter being enriched in Fe–Ti–P. Magma mixing can produce hybrid magmas located in a single-phase field of the phase diagram and precipitate a pure ilmenite cumulate. Alternative processes are also described, such as ejection of Fe–Ti-enriched residual melts by filter-pressing and compaction, solid-state remobilization of ilmenite in veins, and hydrothermal transport of Fe and Ti from the host anorthosite followed by concentration in veins and lenticular ore bodies. The magnetic properties of Fe–Ti ore deposits present contrasting signatures, depending on whether the natural remanent magnetization is dominated by hemo-ilmenite or multi-domain magnetite. Micro- and macro-scale deformation features of ore rocks are intimately correlated with magma emplacement, and with ballooning of the anorthosite diapir associated with gravitational sagging of dense ore bodies. Exploration perspectives show that oxide-apatite gabbronorites are interesting targets because ilmenite in these rocks is poorer in Cr and Mg, and because the Ti-resource may be combined with apatite and vanadiferous magnetite. [less ▲]

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See detailWhat is the best way to measure extinction? A reflection from the palaeobotanical record
Cascales - Miñana, Borja ULg; Cleal, Christopher J.; Diez, José B.

in Earth-Science Reviews (2013), 124

Documenting extinction phenomena remains a vital topic in palaeontology, especially in the context of the marine fossil record. It has been widely assumed that the methods that have been developed in ... [more ▼]

Documenting extinction phenomena remains a vital topic in palaeontology, especially in the context of the marine fossil record. It has been widely assumed that the methods that have been developed in these studies are of universal application throughout palaeontology, but there have been few attempts to test them with plant fossils. We explored the adequacy of the most common methods for documenting extinction events and the associated loss of diversity through time by exploring the monographic knowledge of tracheophytes, especially the record of non-flowering seed-plants. The measure of extinctions was addressed by evaluating diversity fluctuations and the corresponding sampling biases, by measuring levels of taxonomic extinctions, and by exploring disruptions to similarity patterns between time units. Results revealed a strong relationship between diversity and sampling effort based on various different sampling proxies. This suggests that it is vital to take into account the effect of sampling bias when trying to use palaeobotanical diversity dynamics to quantify the real scale of extinction. After testing 16 metrics in two different temporal frameworks, by using criteria like the adjustment between the descriptive extinction metric and the derived probabilistic profile, the interpretation of extinction intensity was overall improved by using normalized metrics that discounted short-lived taxa. Results also revealed that sample size has a significant effect on such analyses and must be evaluated independently for each study before data interpretation. Complementarily, the results showed how the main disturbances of diversity curves generally attributed to extinction events are reflected as abrupt reductions of similarity coefficients between successive time units, which are clearly revealed using clustering methods. © 2013. [less ▲]

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See detailPlant biodiversity changes in Carboniferous tropical wetlands
Cleal, Christopher J.; Uhl, Dieter; Cascales - Miñana, Borja ULg et al

in Earth-Science Reviews (2012), 114(1-2), 124-155

Using a combination of species richness, polycohort and constrained cluster analyses, the plant biodiversity of Pennsylvanian (late Carboniferous) tropical wetlands ("coal swamps") has been investigated ... [more ▼]

Using a combination of species richness, polycohort and constrained cluster analyses, the plant biodiversity of Pennsylvanian (late Carboniferous) tropical wetlands ("coal swamps") has been investigated in five areas in Western Europe and eastern North America: South Wales, Pennines, Ruhr, Saarland and Sydney coal basins. In all cases, species richness expansion followed an essentially logistic curve typical of that associated with ecologically closed habitats, with niche saturation being achieved in about three million years. The resulting steady-state ("climax") coal swamp vegetation had a local-scale (within an area of c. 0.1ha) species diversity in South Wales of 16±7 and Simpson Diversity Indices of 4.53±2.55, which are very similar to values obtained from studies on North American coal swamp vegetation. Landscape diversity (within an area 105km2) varied between 50 and 100 species in the lower to middle Westphalian Stage, falling to about 40-50 species in the upper Westphalian Stage. Regional-scale diversity (within an area>105km2) is difficult to estimate but was at least 120 species. Species turn-over was typically very low, at about 4 species per million years, but there were a number of intervals of more rapid species turn-over in the early Langsettian, late Duckmantian, early Bolsovian and middle Asturian times, which are recognised today as biozonal boundaries. The swamps were mostly subject to ecological stasis during early and middle Westphalian times, although they contracted locally in response to drying of substrates. Later in Westphalian times, however, the swamps were subject to regional-scale changes in composition and aerial extent, probably in response to climate change. The coal swamps had a much lower species diversity compared to modern-day tropical rain forests. © 2012 Elsevier B.V.. [less ▲]

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See detailLate Frasnian - Famennian climates based on palynomorph analyses and the question of the late Devonian glaciations.
Streel, Maurice ULg; Caputo, MV; Loboziak, S et al

in Earth-Science Reviews (2000), 52(1-3), 121-173

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See detailReconnaissance of the general circulation of the North-Western European Continental Shelf by means of a three-dimensional turbulent closure model
Delhez, Eric ULg

in Earth-Science Reviews (1996), 41(1-2), 3-29

The general circulation of the North-Western European Continental Shelf is investigated by means of a three-dimensional macroscale mathematical model. Results corresponding to typical winter and summer ... [more ▼]

The general circulation of the North-Western European Continental Shelf is investigated by means of a three-dimensional macroscale mathematical model. Results corresponding to typical winter and summer conditions are described in detail. Prominent features are explained from a dynamic point of view by referring to the main forcing factors of the macroscale circulation on the North-Western European Continental Shelf: seasonal mean wind stress and atmospheric pressure, large a scale sea surface slope, non-linear interactions of the higher frequency processes and density differences. The role of the bottom topography is also highlighted. The largest seasonal variations are mainly due to the occurrence of a thermal stratification in summer over large parts of the shelf. In such conditions, there is only a weak interaction between the surface and bottom layers that have therefore significantly different dynamics. [less ▲]

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See detailHierarchy and scales in marine ecohydrodynamics
Nihoul, Jacques ULg; Djenidi, Salim ULg

in Earth-Science Reviews (1991), 31(3-4), 255-277

Recent investigations reveal, in marine ecosystems, an ecohydrodynamic hierarchical organization resulting from the different rates of ecological processes confronted to a multi-scale physical environment ... [more ▼]

Recent investigations reveal, in marine ecosystems, an ecohydrodynamic hierarchical organization resulting from the different rates of ecological processes confronted to a multi-scale physical environment. Major marine hydrodynamic processes are briefly analyzed here in an ecohydrodynamic perspective, emphasizing the effects they have on ecosystems at different levels of hierarchy and identifying appropriate “spectral windows” for modelling. A case study application to the Northern Bering Sea's Summer Ecohydrodynamics is given in illustration. [less ▲]

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See detailModelling the general circulation of shelf seas by 3Dk-ε models
Nihoul, Jacques ULg; Deleersnijder, Eric; Djenidi, Salim ULg

in Earth-Science Reviews (1989), 26(1-3), 163-189

One examines the modifications which must be made-and the limitations which must be set-to classicalk-ε models to extend their application to the simulation of marine mesoscale, synopticscale and ... [more ▼]

One examines the modifications which must be made-and the limitations which must be set-to classicalk-ε models to extend their application to the simulation of marine mesoscale, synopticscale and macroscale processes which compose the weather-like and general circulations of the sea. The case of the general circulation—for which sub-grid scale fluctuations include such semi-organized motions as tides and storm surges-is discussed in more detail. A 3Dk-ε model appropriate to the study of the general circulation in a shallow stratified sea is presented and illustrated with the results of a simulation of the general summer circulation in the Northern Bering Sea, made in the scope of the NSF ISHTAR (“Inner Shelf Transfer and Recycling”) Program. [less ▲]

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