Learn more about retrogression

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H-J Massonne, in Reference Module in Earth Systems and Environmental Sciences, 2016

Black Kurt Heeled Lining Mules Geiger nbsp;leather Berner Identification of UHP rocks

The discovery of UHP rocks at Earth's surface at a relatively late date in geological science history can be attributed to specific processes. Retrogression of rocks during exhumation can result in a complete overprint of the UHP mineral assemblage, thus, erasing the memory (record) of the UHP event in a metamorphic rock. Therefore, it is important for the geoscientist working with such rocks to look for mineralogical hints at UHP metamorphism (eg, tiny inclusions in resistant garnet porphyroblasts and unusual microfabric textures). Coesite, the indicator mineral that points to UHP, has never been found to be a major constituent of UHP rocks. On the contrary, quartz dominates among the SiO2 polymorphs, even in the best preserved UHP rocks, and coesite commonly occurs only as inclusions in minerals such as garnet and zircon (). Even in such inclusions, coesite is normally partly decomposed to quartz. A typical decomposition fabric is formed of palisade quartz, characterized by lamellae perpendicular to the reaction front. Cracks in the host mineral around the coesite inclusion form due to the volume increase during the decomposition of coesite to quartz. Thus, even completely replaced coesite can be recognized by such features. Tiny coesite relics can be identified by confocal micro-Raman spectroscopy even when the relics are not at the surface of a rock thin section.

Another mineral that is diagnostic for UHP is diamond (). Like coesite it can be easily transformed. During exhumation, unless it is enclosed as tiny grains in resistant porphyroblasts, diamond reacts to graphite. Even when enclosed in such porphyroblasts, diamond rarely survives, but it can react to form pseudomorphs of radially oriented graphite (). Although microdiamonds might not be as widespread in UHP rocks as coesite they are found in all kinds of UHP rocks, from ultrabasic to felsic or silicate- to carbonate-rich rocks, whereas coesite can occur only in felsic to basic rocks when SiO2 is in excess.

Identifying UHP rocks on the basis of coesite is problematic when cracks around quartz inclusions in the host mineral are discernible but no coesite relic or palisade quartz is detectable. Palisade quartz formations may have recrystallized, forming polycrystalline quartz, but this cannot be considered a clear indication for UHP metamorphism. No doubt, there have been a few reports in the literature of UHP rocks as a result of mistaken identification of polycrystalline quartz inclusions as former coesite. Similar inclusions that also contain K-feldspar were considered as pseudomorphs after K-cymrite (KAlSi3O8•H2O), another UHP phase (), but this phase has not yet found in nature. Further doubtful reports of UHP rocks, based on the detection of nano- and microdiamonds, result from contamination during the preparation of rock thin sections. Especially the report of both diamond and moissanite (SiC), typical phases used for lapping and polishing thin sections, indicate contamination when the identification of these phases was solely undertaken on the surface of garnet or zircon regarded as host of enclosed UHP phases.

In contrast to coesite and diamond, which are pure phases, a few chemically complex solid-solution phases also have potential to detect UHP rocks. In fact, these phases, such as garnet and potassic white-mica, can also occur in a low pressure metamorphic rock, but their chemical compositions can lead to the identification of the UHP nature of a rock. This usually requires the precise elucidation of the variable composition of the solid-solution phases and their chronological relationships. A thermodynamic evaluation considering the corresponding bulk-rock composition follows. The degree of uncertainty in determining pressure conditions, for instance, for rocks with Si rich potassic white-mica (phengite) is not below 2 kbar, even when advanced thermodynamic calculation methods and suitable mineral paragenesis are considered. Nevertheless, geothermobarometry considering phengite and/or garnet compositions is a powerful tool and allows determination of P-TWl373 New Trainers Balance nbsp;textile Black Lining wwqT56C conditions in the UHP regime, whereas coesite and diamond can yield only minimum pressures. This is also true for tetrahedrally coordinated Al in clinopyroxene and orthopyroxene, which act as suitable geobarometers in the presence of garnet, especially for ultrabasic rocks lacking phengite.

In the known UHP regions of the world, minerals with specific exsolution fabrics were observed and assigned to UHP conditions. Clinopyroxenes can contain rods of SiO2. Garnets show clinopyroxene and orthopyroxene exsolution lamellae and precipitates (). Both phenomena are explained by introduction of Si into the octahedral site of the corresponding mineral structure at UHP. Subsequent pressure release results in dissolution of the octahedrally coordinated Si and formation of specific minerals. Experimental constraints are only related to garnet, whereby small amounts of majorite component, (Mg,Ca)4Si4O12, can be dissolved in the garnet structure at pressures exceeding 50 kbar. However, the dissolution products, clinopyroxene and orthopyroxene, can form from ordinary garnet by pressure release as well, but in that case, the pyroxenes should contain significant amounts of Tschermak's component, CaAl2SiO6. Titanite in marble from the Kokchetav Massif is yet another example for the likely introduction of Si into the octahedral site. This mineral contains coesite precipitates as dissolution product. Clinopyroxene from UHP areas can also show K-feldspar lamellae, which are interpreted as exsolution from K-bearing clinopyroxene. Such clinopyroxenes, with significant amounts of K2O (> 0.5 wt.%), have been reported from diamondiferous siliceous marbles of the Kokchetav Massif. Experiments have proved that K is introduced into the clinopyroxene lattice at high pressures, but conclusions on the metamorphic pressures of the Kokchetav rocks have so far been only semiquantitative.

Certainly a number of other potential candidates, either minerals or specific mineral assemblages, could serve to diagnose UHP conditions. Experimental studies and calculations of mineral equilibria using thermodynamic data have indicated this possibility. Four examples are presented subsequently, but they are all questionable in regard of the correct interpretion of the causative pressure. In high pressure experiments, TiO2 with α-PbO2 structure is stable at elevated temperatures above 60 kbar instead of rutile (). A nanocrystal of HP-TiO2 was observed in a diamondiferous quartzofeldspathic rock from the Saxonian Erzgebirge, Bohemian Massif. Clinoenstatite lamellae in pyroxenes were reported from the Dabie Shan - Sulu terrain, China. This would point to pressures of 80 kbar and more (). Magnesite and calcite, probably former aragonite, in direct contact or separated by dolomite were observed in the Dabie Shan. This allows the conclusion that the corresponding rocks experienced pressures of at least 60 kbar (). Ilmenite rods in olivine were reported from several ultrabasic rocks of different UHP terrains. Relatively high concentrations of these rods were found in olivine from Alpe Arami, central Alps, and related to depths of more than 300 km as the origin of the corresponding rock.

Mycorrhizas Across Successional Gradients

F.P. Teste, I.A. Dickie, in Mycorrhizal Mediation of Soil, 2017 pH

Soil pH strongly declines during ecosystem development and can range from a pH of approximately 9 in the young developing soil to a pH of approximately 4 in the old nutrient-impoverished soils during ecosystem retrogression (Turner and Laliberté, 2015). Within each main successional type (primary and secondary) soil pH can be even more variable; however, in general a declining pattern remains as soil and plant communities age. The effect of soil pH is perhaps the most influential yet the most complex and interactive factor because it is strongly linked to other soil characteristics. Plant ecologists have been attempting to separate the complex effects of soil pH for some time, but they have only recently been able to elucidate the relative importance of soil pH in environmental filtering of plant communities using advanced statistical approaches such as structural equation modeling (SEM; Grace, 2006; Laliberté et al., 2014).

Mycorrhizal ecologists have not been as successful as plant ecologists in drawing firm conclusions on the direct effect of soil pH on fungal communities. We have mostly relied on in vitro studies or soil acidification/liming experiments to draw conclusions on the negative effect of low soil pH on growth of fungi and species diversity (Erland and Taylor, 2002, and references therein). Liming acidic forest soils has produced the opposite effects of acidification experiments, increasing EcM fungal species diversity and creating important shifts in community composition in favor of fungal species with abundant extraradical hyphae (Bakker et al., 2000). This effect may reach an optimum at moderately acidic levels because liming is also commercially used to reduce fungal diversity in the production of truffles (García-Montero et al., 2009).

There are a few studies using natural gradients in soil pH, and these have also shown marked negative effects on EcM fungal diversity with increasing soil acidity (Kumpfer and Heyser, 1986; Lu et al., 1999). In the case of AM fungi, soil pH has been shown to structure these fungal communities (Fitzsimons et al., 2008; Dumbrell et al., 2010; Lekberg et al., 2011) with strong interactive effects of the plant host community characteristics (Meadow and Zabinski, 2012). Drawing cause-and-effect conclusions about the direct effect of soil pH on mycorrhizal fungal communities still remains elusive and requires more studies using SEM or similar approaches.

Fluid Flow

Bruce Hobbs, Alison Ord, in High Heeled Cruz nbsp;leather Boots Lola Lining Ankle Blanco 75qxWw84, 2015

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12.1.1 Evidence for the Influx of Fluids

Etheridge et al. (1983, 1984), following Fyfe et al. (1978), presented a case for large-scale infiltration of fluids during regional metamorphism, particularly at low metamorphic grades including retrogression. Since then a large number of studies (Dipple and Ferry, 1992; Ferry, 1994; Oliver, 1996; Ague, 2011) has supported this concept of extensive infiltration although notable disagreements exist (Yardley, 2009). A classification of fluid flow regimes during deformation and metamorphism given by Oliver (1996) highlights the range of observations. We present a slightly modified version of that classification in Figure 12.1. It differs from that of Oliver in that the presence of closed systems dominated by diffusive flow has been explicitly highlighted together with a thermal overlay which we develop throughout the remainder of this chapter. Another view of this classification with respect to melt segregation and migration is presented by Rushmer (2001).

There is no doubt that some form of fluid infiltration is necessary to promote many metamorphic reactions and in some instances metamorphic rocks have been exposed to high temperatures and pressures with no reactions taking place until H2O (or H+) is introduced (Berner Mules Heeled nbsp;leather Geiger Black Kurt Lining Austrheim, 1987; White and Clarke, 1997, see Figure 12.2; Rubie, 1998; John and Schenk, 2003). There is still some debate as to the role of fluid flow in pore space in high grade rocks (Yardley, 2009) or in some mylonites (Fitzgerald et al., 2006). Some (Oliver, 1996; Ord and Oliver, 1997; Ague, 2011) have emphasised that flow can be channelized so that some parts of metamorphic terrains see low fluid fluxes whilst neighbouring parts are exposed to strongly focussed flow. At high metamorphic grades where partial melting occurs, flow in leucosomes has been proposed (Brown, 2010). For some workers (Etheridge et al., 1983) the concept of thermal convection is important. Although thermal convection is said to be impossible in systems with a lithostatic fluid pressure gradient (Wood and Walther, 1986), it turns out that it is possible, in principle, in some forms of open systems with super-hydrostatic fluid pressure gradients (Zhao et al., 2008; Section 4.2). The question is the following: What form do convective systems take in compartments with lithostatic pressure gradients and are such systems common or even possible under crustal conditions? We explore these concepts in Section 12.5.3.

In Figure 12.3, we present some examples where the influence of fluids is widely proposed. These include grain boundary pore structures in mylonites (Figure 12.3(a)), dissolution seams associated with differentiated crenulation cleavage at low metamorphic grades (Figure 12.3(b)), vein systems (Figure 12.3(c)) and leucosomes in migmatite complexes (Figure 12.3(d)).

Fluids associated with metamorphism arise from a number of sources including meteoric sources, connate waters, fluids released by devolatilisation (including decarbonisation, hydrocarbon release from organic material and dehydration of (OH)-bearing minerals), and release of volatiles from crystallising melts. The chemical and isotopic characteristics of these fluids and the roles they play in metamorphic processes are discussed by Hollister and Crawford (1986) and Yardley (2009).

Coherence of the Dabie Shan UHPM Terrane Investigated by Lu–Hf and 40Ar/39Ar Dating of Eclogites

Fraukje M. Brouwer, ... Yuanbao Wu, in Boots Lace up Brown Fashionable Kiomi p7nxtA, 2011

11.4.1 Petrography

The freshest eclogites in Dabie Shan contain garnet and omphacite as major minerals, often accompanied by phengite and locally kyanite and/or zoisite. In some cases prograde glaucophane persists as part of the eclogite facies mineral assemblage. Upon retrogression, omphacite is replaced by amphibole–plagioclase symplectites, and garnet becomes rimmed by amphibole. Different types of eclogite may be recognized in the field: dark fresh eclogite, light fresh eclogite (only found at Bixiling, eastern Dabie), and banded eclogite (Figure 11.2A; Xiong Dian, western Dabie).

Eclogites selected for Lu–Hf geochronology are dominantly Grt+Omp+Qtz/Coe+Phg+Rt±Zo±Ky. Banded eclogite from the Xiong Dian (XD) locality has layers dominated by Grt+Qtz/Coe+Phg, contrasting with layers with mostly Omp and minor Amp and Zo, as well as mixed Grt+Omp+Amp layers. Although sampled in a known UHP belt and partly at established UHP localities, only a few of the freshest eclogites show convincing UHP textures, such as radial cracks in Cpx around a polycrystalline SiO2-inclusion with palisade quartz at its rim (Figure 11.2C). Some eclogites are partially retrogressed, in which case Amp can sometimes be concentrated for 40Ar/39Ar thermochronology. For thermochronology, additional samples were selected among amphibolites with or without garnet that, based on textural criteria (Brouwer et al., 2005), are thought to be products of thorough retrogression of eclogites. Amphibolites contain a mineral assemblage of Amp+Plag+Qtz+sympl+Rt±Grt±Ep/Czo. When garnet is present it is rimmed by Act and symplectites, made up of Amp+Plag probably result from the breakdown of sodic pyroxene.

The eclogites and amphibolites occur as lenses from meter to kilometer scale in a basement dominated by gneisses. Two orthogneiss samples, 07HA02 and 07LT01, are selected for thermochronology. One of the orthogneisses is a layered Qtz+Phg+Plag rock, whereas the other contains additional Kfs, Hbl, and Bt. One amphibole-bearing gneiss (07TH03) occurs as a layered lens surrounded by felsic gneisses. The rock is made up of bands of garnet with minor Qtz and Amp, alternating with layers dominated by Qtz and Ep. Sample 07BX36 is a diorite dyke with large euhedral Hbl in a fine-grained matrix of Pl+Hbl. Samples 07XX23 and 07BX37 (Figure 11.2B) are dolerite dykes of Hbl+Plag±Qtz±sympl. Sample 07XX23 Hbl has thin Act-rims and symplectites made up of Amp+Pl. Detailed descriptions of all samples are listed in the appendix.

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James S. Griffiths, ... David K.C. Jones, in Developments in Earth Surface Processes, 2011

7 Geomorphological Interpretation

The surface morphology of landslides A–E suggests the forms of movements are generally planar in the lower zones of the landslides, which produced the benches A2, B2 and possibly C2. However, there appears to have been upslope retrogression possibly on quasi-rotational failure surfaces that gave rise to benches A1, B1 and possibly C1. The limited borehole data available along the direction of movement for landslide C1 (Figure 14.5) allow the use of the Glauconitic Marl as a marker horizon to show that bench C1 had been subject to nearly 15 m of vertical displacement. However, whether bench C1 failed as a single ‘foundered’ block or if there were several rotated blocks within the bench could not be determined during the mapping. The main planar movements appear to have taken place along a shear surface in the Gault Clay, and it is possible that the failure was a non-rotational block slide with a now-infilled graben. The lower components of the slide movements in the vicinity of bench C2 could not be disentangled from the coombe rock solifluction debris. This suggests that the main movements of landslide C were contemporaneous with the deposition of the coombe rock, indicating a Late Glacial age. Landslides A and B are likely to be similar in age with landslide B probably slightly older than A, but the indications are that landslides D and E occurred later, and indeed landslide D shows signs of relatively recent movements.

Trace Element and O-Isotope Composition of Polyphase Metamorphic Veins of the Ile de Groix (Armorican Massif, France)

Afifé El Korh, ... Alexey Ulianov, in Boots Lace up Brown Fashionable Kiomi p7nxtA, 2011

9.6 Host Rock Composition

9.6.1 Major Elements

Massive and banded rocks are generally basic in composition, with low SiO2 and high AlKurt Geiger Heeled nbsp;leather Mules Berner Lining Black 2OBlack Berner nbsp;leather Mules Kurt Geiger Lining Heeled 3 and FeBerner Lining nbsp;leather Geiger Black Kurt Heeled Mules 2O3 contents (Table 9.2ons Gold California Lining Of Colors nbsp;textile Slip wvAqa1z). MgO and Na2O contents are higher in massive rocks than in banded rocks, while K2O content is lower. The loss-on-ignition (LOI) value correlates with increasing degrees of retrogression. The values are particularly high in albitic greenschists, indicating high fluid infiltrations during the retrograde albitization. Aegerine–jadeite-bearing eclogite GR 30b and massive blueschist with jadeite pseudomorphs GROA 45 have high Na2O contents and low MgO contents, resulting from a strong metasomatism under HP–LT conditions (Spandler & Hermann, 2006). Micaschist GROA 104 displays high SiO2, Al2O3, and K2O contents and low MgO and Na2O contents (Table 9.2).

9.6.2 Trace Elements

In the multi-element diagrams (Figure 9.4A and B) normalized to N-MORB (Sun & McDonough, 1989), the patterns of massive eclogites, blueschists, and albitic greenschists indicate that their composition is close to E-MORB (Sun & McDonough, 1989), with significant variations in the LILE content (Figure 9.4A). LILE and Pb enrichment of massive eclogites and blueschists is related to the presubduction hydrothermal alteration. The lower LILE contents in albitic greenschists result from the breakdown of phengite during retrogression and their loss during LILE mobilization by fluids (El Korh et al., 2009). The studied banded rocks are similar to the E-MORB pattern (Figure 9.4B) in terms of the HREE contents and show strong LILE enrichment, making them similar to the Global Ocean Subducting Sediment (GLOSS; Plank & Langmuir, 1998). They are interpreted as being volcano-sedimentary in origin and having experienced a presubduction hydrothermal alteration. Micaschist GROA 104 corresponds to the GLOSS, containing 76% of terrigeneous material (Plank & Langmuir, 1998).

Earthquake Thermodynamics and Phase Transformations in the Earth's Interior

Eugeniusz Majewski, in International Geophysics, 2001

13.1 Introduction

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The goal of this chapter is to describe the thermodynamic aspects underlying the behavior of faults during earthquake processes. The faulting processes of earthquakes have been studied scientifically for more than a century. During this period, interest in faulting has, like the faults themselves, evolved and changed. Periods of activity and progress have alternated with periods of stagnation and even of retrogression when misleading concepts have become part of accepted knowledge. The past decade, however, has seen major progress in this branch of science. New theories have been developed that have explained many facts previously unknown; improved measurement techniques have enabled these theories to be tested and have produced new results still to be elucidated. In this chapter, we are concerned with the molecular structure of a fault zone. Especially, we are interested in determining a measure of the knowledge an external observer gains with respect to the occurrence of breaking bonds in the fault zone during an earthquake process. We formulate a fault entropy. This simple concept allows us to interpret a faulting mechanism from the point of view of the information thermodynamics. We relate the fault entropy with the seismic moment, which gives a physically meaningful description of earthquake size. In this way, we connect macroscopic fault properties with microscopic properties of fault rocks. And, finally, it is not merely convenient, but also necessary, to investigate stochastic faulting processes instead of deterministic faults when we want predictions that are applicable to computation and measurements. To this end, the information entropy provides us with statistical interpretations of fracture mechanisms in the fault. Moreover, this approach leads to a more general formulation of faulting processes in terms of statistical thermodynamics.

Geochronology of the Alpine UHP Rhodope Zone

Anthi Liati, ... C. Mark Fanning, in Boots Lace up Brown Fashionable Kiomi p7nxtA, 2011

10.3 Selection of the Most Relevant Geochronological Data for the Rhodope Zone

The complexity and interaction of individual processes involved in the formation of HP and UHP rocks in mountain belts (usually multiple episodes of magmatism, metamorphism, deformation, and fluid–rock interaction) result in small-scale heterogeneities, such as chemical zonation or development of multiple growth domains of minerals used in radiometric dating. Thus, polymetamorphic rocks are often characterized by local equilibrium, including isotopic compositions. This feature has a significant impact on the geochronological results acquired by commonly used geochronometers (K–Ar, Ar–Ar, Rb–Sr, Sm–Nd, Lu–Hf), which are mostly based on large mineral separates, zoned minerals, and whole rocks and are sensitive to retrogression. Moreover, as many HP and especially UHP rocks are characterized by high peak temperatures, the K–Ar and Rb–Sr isotope systems cannot date the peak. Thus, radiometric dating of micas, garnets, pyroxenes, and amphiboles, which are rock-forming minerals that can provide P–T conditions for metamorphism, can be problematic, as they have relatively low closure temperatures, may be zoned, and/or show only local isotopic equilibrium even within a single thin section. The latter feature results in the commonly encountered problem of isotopic disequilibrium within and amongst dated minerals with the Rb–Sr, Sm–Nd, and Lu–Hf systems.

It is also worth noting that closure temperatures depend largely on the cooling rates, grain size, and action of fluids (e.g., Berner Kurt Mules Black Heeled Geiger nbsp;leather Lining Kelley, 2002; Scherer et al., 2000). Thus, especially for (U)HP rocks, which are characterized by steep P–T paths (i.e., small temperature variations for high depth differences) and usually strong retrogression, closure temperatures of minerals in the conventional sense may not even be applicable, while fluid-induced recrystallization is the predominant mechanism responsible for the disturbance of isotopic systems and partial or complete age resetting (Villa, 1998; see Section 10.6).

Given these complexities, the dating technique that meets with closest approximation the requirements for dating (U)HP-HT rocks is the ion microprobe SIMS technique. This technique uses the U–Pb isotopic system on the robust mineral zircon and is at the same time a high-resolution beam technique able to resolve within grain age zonation. It is preceded by cathodoluminescence (CL) imaging for the visualization of the internal structure of the sectioned zircons and is promising and reliable for this type of rocks, as zircon largely responds to metamorphic recrystallization at the high temperatures and pressures suffered by a major part of the Rhodope metamorphic rocks. As zircon can survive very high temperatures it usually retains a memory of previous metamorphic and/or magmatic events. Although zircon does not usually participate in metamorphic reactions and therefore its formation cannot be directly linked to a particular stage of metamorphism, this issue can be often satisfactorily solved by using mineral inclusions and REE compositions of the analyzed zircon domains (e.g., Rubatto, 2002; Hoskin & Schaltegger, 2003, and references therein).

Determination of the time of metamorphism in the Rhodope has first been approached by K–Ar and Ar–Ar dating of mica and hornblende and implied Eocene metamorphic ages (Liati, 1986; Liati & Kreuzer, 1990). However, neither the Ar– nor the Rb–Sr isotopic systems can date the peak (U)HP-HT conditions. Because these chronometers are considered to have low closure temperatures and be sensitive to retrogression, they only record age information for late stages of the P–T–t path. Moreover, K–Ar and Ar–Ar dating of white micas and hornblendes affected by HP metamorphism may yield erroneously high ages, due to contamination by excess Ar (e.g., Kelley, 2002).

Sm–Nd dating has been applied in few cases in rocks of the Rhodope. The possibility of disequilibrium within and amongst the analyzed minerals and their inclusions, which may be responsible for yielding erroneous results needs to be taken into consideration when interpreting such data (e.g., Scherer et al., 2000 and references therein).

Monazite U–Th–Pb dating has been applied in some cases either by using electron microprobe (Reischmann & Kostopoulos, 2002) or single-grain isotope dilution and TIMS analyses (Jones et al., 1994). The most obvious problem with the electron microprobe method is that it does not allow the measurement of isotope ratios. As a consequence, (a) concordance has to be assumed, (b) no correction for common Pb can be made, (c) the sensitivity is relatively low, (d) monazite can be strongly zoned, and (e) isotopic disequilibrium may occur. The latter two problems apply also to the isotope dilution method and SIMS.

Furthermore, as already mentioned in the beginning of this chapter, a notorious problem with all mineral chronometers is the common interpretation of the dates as cooling ages. It should be taken into account that closure temperatures are not fixed numbers (see earlier). The role of fluids in disturbing the isotopic clock at temperatures significantly lower than the theoretical “closure temperatures” is usually underestimated, especially by non-geochronologists. Such possible misinterpretations may lead to incorrect ideas and erroneous linking of “ages” to large-scale geodynamic processes.

Therefore, in the following evaluation interpretation of the time of metamorphism(s) and of protolith formation is mainly based on U–Pb zircon SHRIMP data.

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Alexander N. Konilov, ... Suzanne Y. O’Reilly, in Boots Lace up Brown Fashionable Kiomi p7nxtA, 2011 Kyanite–Garnet Felsic Vein

Rare Ky–Grt-bearing felsic veins with trondjemitic bulk compositions are locally observed. These are light-colored and 1–40 cm thick and are laterally continuous on a scale of a few meters (Figure 19.2A). The veins fill isolated tension gashes within the eclogite and are structurally unrelated to the surrounding TTG gneisses. Where the veins are in contact with eclogite, the eclogite shows strong retrogression to a garnet-bearing amphibolite. The veins are largely composed of quartz, blue kyanite, garnet, and plagioclase. A weak foliation in the veins is defined by the alignment of minor biotite. Most of the garnet crystals tend to be concentrated along the vein contacts. Further accessories are rutile, zircon, chalcopyrite, and pentlandite.

In thin sections a reaction relationship between kyanite, garnet, and quartz can be observed (Figure 19.17), characterized by plagioclase rimming kyanite. This is most easily explained as a down-pressure reaction modelled in simplified form by the well-calibrated GASP endmember reaction grossular+2 kyanite+quartz=3 anorthite (Kurt nbsp;leather Heeled Geiger Black Lining Mules Berner Koziol & Newton, 1988). According to this reaction, a clear retrograde zoning was observed in garnet rims. The cores yield CaO contents of 9–10 wt%, whereas this decreases to 4–5 wt% at the rims close to coronitic plagioclase. The plagioclase rim domain also commonly contains biotite (Figure 19.17B). Mineral compositions in local equilibria are given in Table 19.4.

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An unusual and noteworthy assemblage consists of a transparent isotropic or cryptocrystalline material typical of a glassy phase (Figure 19.18Sons amp; Hoody Csbl black Downtown White Cayler Hoodie 6pw5qI44)—the noncrystalline state was confirmed using Raman microprobe. Its chemical composition is listed in Table 19.5, from which it is obvious that the glassy phase is extremely enriched in copper (CuO=2.9–9.0 wt%) and volatile components, although sulfur and chlorine contents are below the detection limits. The volatile-free recalculated compositions from the microprobe analyses show high alumina (∼25–29 wt%) mostly tonalitic chemistry. The textural position of the glassy phase rimmed by plagioclase (Figure 19.18) suggests that this may represent a quenched silicate melt rather than an aqueous fluid or a supercritical phase. It is unclear whether this glassy phase could represent a parental melt for the TTG suite or a residual liquid that remained after some degree of crystallization.

A Belowground Perspective on Dutch Agroecosystems: How Soil Organisms Interact to Support Ecosystem Services

Christian Mulder, ... Michiel Rutgers, in Advances in Ecological Research, 2011

G Conserving Ecosystem Services

Biodiversity and agricultural pressure are closely and negatively related, and a comprehensive survey of all the consequences of increasing farming pressure (resulting in changes in ET) for soil biodiversity and ecological services remains an important goal, particularly in Europe's heavily modified landscape. Although there seems to be a remarkable regularity over a size range of 15 orders of magnitude (from bacteria to earthworms), subtle changes in allometric scaling relationships show clear faunal responses to nutrient availability and strong effects of the soil biota on ecosystem services are emerging. The application of food web modeling can contribute, in an analogous way to the use of size spectra in commercial fisheries (Black Mules Geiger Kurt Heeled Lining Berner nbsp;leather Jennings, 2005; Petchey and Belgrano, 2010), to prevent ecosystem degradation or retrogression and to predict the rate of changes in soil processes and associated ecosystem services: this would effectively create a new way of applying theoretical ecology to address real-world problems.

Box 1

Is ecology a set of contingent case studies or do universal laws apply?

A paucity of data is increasingly claimed. However, we have never had such a plethora of information available as now. Borne (2008) states that “The more we know, the more we are driven to tweak or to revolutionize our models, thereby advancing our scientific understandingLining Mules Heeled Black Berner nbsp;leather Kurt Geiger .Mahootian and Eastman (2009) described this historical shift in the conceptual process of investigation, from their theory-driven hypothetico-deductive framework, with all its logical implications like the classical “je pense donc je suis”, later Ego cogito, ergo sum (Descartes, 1637, 1644, respectively), up to the hypothetico-inductive (balancing theory and empirical data at different levels) and observational-inductive frameworks. Internet access, intellectual networking, international research programmes and the vast amount of data have converged in the latter framework. Essentially, the traditional modes of empirical fieldwork and laboratory research and related descriptive assessment within the hypothetico-inductive framework were forced to change by surges in data increased volume, computing power and availability into an observational-inductive framework more closely focused on understanding causal relationships in the real world (). These frameworks reflect the strong dichotomy that arose between perception and calculation, even to the extent that mathematicians started to declare every argumentation not submitted to calculation as being potentially inaccurate or even invalid. Ecology progresses by testing fundamental conceptualizations of patterns and trends, which although they vary in complexity (), are essentially rooted within this Observational-Inductive framework. Although we may argue as to what the most appropriate kind of data-organisation might be, data-sharing always allows (and demands) greater insights. Databases published as supplementary files in the online section of peer-reviewed journals, in fact, are faced with another—still unmentioned—problem: the “publication bias” (Begg and Mazumdar, 1994; Rosenthal, 1979), also known as “file drawer effect” (Rosenthal, 1979). This tendency to report the results that are positive (i.e. “significant”) differently from the results that are negative is widespread in pharmacological and biomedical worlds () and seems to occur in fundamental and applied sciences as well. Despite trait-based researches became very popular through studies on body-mass development (life-history experiments) in laboratory and in space and time (even as investigations at geological scales), debates regarding allometric scaling and biodiversity–ecosystem functioning possibly resemble this kind of bias. But we are also seeing, especially within the large-scale collaborative research programmes that span several European countries, a greater willingness and ability to exchange data openly, and this may continue to accelerate the rate of theoretical development within applied ecology in the near future.