67 research outputs found
Evaluation of a manufacturing task support system using the Task Technology Fit Model
This paper presents an exploratory study of a Task Support System (TSS) supporting manufacturing task operations. The study investigated the degree to which a TSS, in use in a company, actually supports the task of the shop floor personnel. The approach has been to adopt the Task-Technology Fit (TTF) instrument to measure
the degree of fitness between the TSS and the associated task. The analysis gives an indication of the state of the TSS and the potential improvements that can be made. The study also shows that the instrument can be used as a foundation for the development of a hypermedia TSS and a benchmarking tool for a TSS
Igneous Rock Associations 5. Oceanic Island Volcanism II: Mantle Processes
Oceanic island basalts (OIBs) have been central to understanding evolution o fthe Earth and mantle because their isolated positions in ocean basins limit the potential for magma contamination by continental crust. Melting processes (e.g., percentage melting) affect OIB chemistry but isotopic and trace-element ratios provide information on mantle-source compositions. They indicate that OIB mantle sources represent mixtures between mid-ocean ridge basalt (MORB) mantle and four other mantle components: EM1 (enriched mantle 1), EM2, HIMU (High U/Pb = Hi ”) and FOZO (FOcal ZOne). Mass-balance and noble-gas arguments indicate that most of the mantle is depleted but He and Ne isotopes, and convergence of Sr-Nd-Pb isotopic arrays suggest that FOZO is a somewhat primitive (unmelted) component common to all oceanic basalt sources. The other components contain "materials" such as basaltic ocean floor (HIMU), pelagic sediments (EM1), oceanic plateaus (EM1), subcontinental lithosphere (EM1, EM2), terrigenous sediments or subducted continental crust (EM2), which have been recycled by subduction processes, and mixed back into the depleted mantle. How these components cycle through the mantle is debated but heterogeneities occur on all length-scales. One school argues that oceanic islands develop above mantle plume convection cells that deliver recycled components and FOZO (lower mantle?) for mixing with depleted upper mantle. Others contend that propagating cracks in the lithosphere create oceanic islands, that plumes do not exist, that the upper and lower mantle are isolated and depleted, and that MORB and OIB form from the same upper-mantle reservoir. Small-scale melting allows OIB to sample local, low-melting-point heterogeneities that are averaged-out by the large-scale melting that forms MORB. These radically different views of mantle structure and composition indicate that OIB will continue to be a focal point in studies of Earth's evolution.
SUMMAIRE
L'Ă©tude des basaltes d'Ăźles ocĂ©aniques (BĂOs, ou OIBs en anglais) s'est avĂ©rĂ© essentielle pour la comprĂ©hension de l'Ă©volution de la Terre et de son manteau, et cela, de par l'isolement de ces Ăźles dans les bassins ocĂ©aniques, ce qui limite les possibilitĂ©s de contamination par des matĂ©riaux de la croĂ»te continentale. Les mĂ©canismes de fusion (le pour-centage de fusion par ex.) dĂ©limitent la composition chimique des BĂOs, mais les ratios isotopiques et des Ă©lĂ©ments traces permettent d'obtenir des indications sur la composition des sources mantelliques. Ils indiquent que les sources mantelliques des BĂOs sont des mĂ©langes de basaltes de dorsales ocĂ©aniques (BDOs ou MORBs en anglais) de quatre autres composantes du manteau, soit des EM1 (enriched mantle), EM2, HIMU (ratio Ă©levĂ© de U/Pb= Hi ”), et FOZO (FOcal ZOne). Les Ă©tudes des bilans massiques et des gaz nobles indiquent que la plus grande partie du manteau a subit un appauvrissement, mais les isotopes He et Ne, ainsi que la convergence des ensembles isotopiques Sr-Nd-Pb portent Ă penser que la composante FOZO serait de composition Ă peu prĂšs primitive (n'aurait pas subit de fusion) qui serait commune Ă toutes les sources de basaltes ocĂ©aniques. Les autres composantes renferment des" matĂ©riaux " issus de plancher ocĂ©anique basaltique (HIMU), de sĂ©diments pĂ©lagiques (EM1), de plateaux ocĂ©aniques (EM1), de lithosphĂšre souscontinentale (EM1 et EM2), de sĂ©diments terrigĂšnes ou de croĂ»tes continentales enfouies (EM2) et qui ont Ă©tĂ© recyclĂ©s par des mĂ©canismes de subduction et rĂ©injectĂ© dans les matĂ©riaux appauvris du manteau. La façon dont ces composantes sont recyclĂ©es dans le manteau fait l'objet de discussions serrĂ©es et on observe la prĂ©sence d'hĂ©tĂ©rogĂ©nĂ©itĂ© Ă toute Ă©chelle. Une des Ă©coles de pensĂ©e soutient que les Ăźles ocĂ©aniques se forment au-dessus de cellules de convection de panaches mantelliques qui apportent des composantes recyclĂ©es et de la FOZO (manteau infĂ©rieur?) et les mĂ©langent avec les couches supĂ©rieures appauvries du manteau. D'autres croient plutĂŽt que ce sont des fissures de la croĂ»te qui permettent la formation des Ăźles ocĂ©aniques, qu'il n'y pas de panaches, que les couches infĂ©rieures et supĂ©rieures du manteau sont isolĂ©es et appauvries et que les BĂO et les BDO sont formĂ©s Ă partir des matĂ©riaux des mĂȘme couches supĂ©rieures. Les BĂO seraient le reflet de fusions d'hĂ©tĂ©rogĂ©nĂ©itĂ©s locales Ă faibles tempĂ©ratures de fusion, alors que les BDO seraient le rĂ©sultat de fusions Ă grande Ă©chelle expliquant une composition correspondant Ă la moyenne de toutes les hĂ©tĂ©rogĂ©nĂ©itĂ©s. L'existence de points de vue si radicalement opposĂ©s sur la structure et la composition du manteau dĂ©montrent que les BĂOs seront encore l'objet d'Ă©tudes sur l'Ă©volution de la Terre
Igneous Rock Associations 18. Transition Metals in Oceanic Island Basalt: Relationships with the Mantle Components
Incompatible elements and isotopic ratios identify three end-member mantle components in oceanic island basalt (OIB); EM1, EM2, and HIMU. We estimate compatible to mildly incompatible transition metal abundance trends (Ni, Co, Fe, Cu, Cr, V, Mn, Sc, and Zn) in âprimitiveâ basalt suites (Mg# = Mg/(Mg + 0.9*Fe) atomic = 0.72) from 12 end-member oceanic islands by regressing metals against Fe/Mg ratios in sample suites, and solving for concentrations at Mg/Fe = 1 (Mg# = 0.72). Using the transition metal estimates, exploratory statistics reveal that islands âgroupâ based on mantle component type even when La/Yb ratios are used to compensate metal concentrations for percentage melting. Higher chalcophile Zn (and Pb, earlier work) in EM1 and EM2 compared to HIMU, and higher Cr (3+) and Sc in HIMU relative to EM1, support views that HIMU represents subduction-processed ocean floor basalt. Incompatible elements, ratios and isotopes indicate that EM1 is Archean, EM2 is Proterozoic or younger, and both are related to sediment subduction. As found with incompatible elements, EM1 and EM2 show similar âcompatibleâ element concentrations, but lower (multi-valence) Cr, Fe and Mn in EM1 could indirectly reflect increasing oxidation of subducted sediment between the Archean and Proterozoic. Alternatively, changes in subduction processes that yielded peak continental formation in the Neoarchean, and craton-suturing in the Paleoproterozoic may account for EM1âEM2 differences. EM1 shows similar or lower Cr, Ni and Co compared to HIMU and EM2 suggesting that economic viability of layered intrusions, which have extreme EM1-like signatures, is unrelated to high metals in EM1 mantle sources, but that high % melting appears important. Because core-concentrated transition metals correlate with mantle component type, lithospheric recycling apparently controls their concentrations in OIB and core-mantle interaction may be unimportant.RĂSUMĂLes Ă©lĂ©ments incompatibles et les rapports isotopiques permettent de dĂ©limiter trois termes extrĂȘmes de composants mantĂ©liques dans des basaltes insulaires ocĂ©aniques (OIB), soit EM1, EM2, et HIMU. Nous estimons les tendances dâabondance de mĂ©taux de transition (Ni, Co, Fe, Cu, Cr, V, Mn, Sc, and Zn) compatibles Ă modĂ©rĂ©ment incompatibles dans des suites de basaltes « primitifs » (Mg# = Mg/(Mg + 0,9*Fe) rayon atomique = 0,72) sur 12 termes extrĂȘmes de matĂ©riaux insulaires ocĂ©aniques, par rĂ©gression des concentrations des mĂ©taux sur les rapports Fe/Mg dans des Ă©chantillons des suites, la dĂ©termination Ă©tant dĂ©finie au rapport Mg/Fe = 1 (Mg# = 0,72). Lâutilisation dâune approche statistique exploratoire sur les estimations de mĂ©taux de transition montre que la composition des Ăźles se « regroupent » en fonction du type de composition du manteau, cela mĂȘme lorsque les ratios La/Yb sont utilisĂ©s pour compenser les concentrations de mĂ©taux pour dĂ©terminer le pourcentuel de fusion. Le caractĂšre plus chalcophile du Zn (et Pb, travail antĂ©rieur) dans EM1 et EM2 comparĂ© Ă HIMU, et la plus grande teneur en Cr (3+) et Sc dans HIMU par rapport Ă EM1, accrĂ©ditent lâidĂ©e que HIMU reprĂ©sente le basalte de subduction des fonds ocĂ©aniques. Les Ă©lĂ©ments incompatibles, les ratios et les isotopes montrent que EM1 est archĂ©en, que EM2 est protĂ©rozoĂŻque ou plus jeune, et que les deux sont liĂ©s Ă la subduction sĂ©dimentaire. Comme constatĂ© pour les Ă©lĂ©ments incompatibles, EMI et EM2 affichent une compatibilitĂ© similaire des concentrations en Ă©lĂ©ments « compatibles », toutefois une concentration infĂ©rieure en Cr (multivalent), Fe et Mn dans EM1 pourrait reflĂ©ter indirectement une oxydation croissante des sĂ©diments subduits entre lâArchĂ©en et le ProtĂ©rozoĂŻque. Par ailleurs, les changements dans les mĂ©canismes de subduction qui ont menĂ© Ă un maximum de formation continentale au NĂ©oarchĂ©en et Ă des Ă©pisodes de sutures cratoniques au PalĂ©oprotĂ©rozoĂŻque, peuvent expliquer les diffĂ©rences entre EM1 et EM2. La teneur similaire ou infĂ©rieure en Cr, Ni et Co de EM1 par rapport Ă HIMU et EM2 permet de croire que la viabilitĂ© Ă©conomique des intrusions stratifiĂ©es â lesquelles montrent des signatures extrĂȘmes EM1 â est sans rapport avec les sources mantĂ©liques Ă fortes teneurs en mĂ©taux, mais que le fort pourcentuel de fusion qui importerait. Parce que la concentration du noyau en mĂ©taux de transition correspond avec le type de composant du manteau, câest le recyclage lithosphĂ©rique qui contrĂŽle apparemment leurs concentrations dans l'OIB, et l'interaction noyau-manteau pourrait ĂȘtre sans importance
Igneous Rock Associations 12. A Geologistâs Look at Archaeological Ceramics and Glass
Ceramics and glass represent synthetic metamorphic rocks and obsidian, respectively. Consequently, it is not surprising that many archaeologists have collaborated with geologists on projects dealing not only with lithic artifacts, but with ceramic and glass objects as well. This paper presents an overview of these latter two materials from a geological perspective, considering in turn how they are characterized and classified, their ages constrained, provenance and in some instances use determined, and how they were made. SOMMAIRELa céramique et le verre représentent respectivement des roches métamorphiques et l'obsidien synthétiques. En conséquence, il n'est pas étonnant que beaucoup d'archéologues aient collaboré avec des géologues sur des projets traitant non seulement des objets façonnés lithiques, mais également des objets en céramique et en verre. Ce document présente un aperçu de ces derniers deux matériaux d'une perspective géologique, considérant comment ils sont caractérisés et classifiés, leurs ùges, provenances et emploies parfois déterminés, et comment elles ont été faites
A petrochemical study of basaltic layering at Henley Harbour, Labrador, using multidimensional scaling
Lack of internal textural evidence for flow tops and small chemical variability among late Proterozoic basalt samples suggest the presence of a single flow at Henley Harbour, Labrador, Canada, despite spectacular, m-scale layering in outcrop. Total chemical variation just slightly exceeds analytical uncertainty for many elements. Multidimensional scaling (MDS) enhances "effective" analytical precision by allowing all data (elements and samples) to be compared simultaneously. Scaling of elements reveals element associations/patterns consistent with igneous controls on distribution, even for alteration-sensitive (Na, K, Sr) elements. MDS also shows that the m-scale layering has a chemical fingerprint. However, to explain chemical variability between layers using mass balance calculations and averaged whole-rock data requires unreasonable (low temperature) phenocryst compositions. Textural features of the m-scale layering record changes in cooling regime between the bottom and center of the flow but chemical variation may reflect changing magma compositions during formation of an inflated flow. However, mass balance calculations suggest that large-scale chemical variation reflects the migration of residual liquid, perhaps as vesicle plumes, within an initially chemically homogeneous flow. Low in the flow (layer 1), metres-long but cm-scale raised and eroded subhorizontal "bands" superficially resemble segregation veins but lack coarse-grained textures. MDS confirms that raised and eroded samples are chemically distinct. Mass balance indicates that banding is not related to phenocryst percentages but may reflect the abundance of a residual liquid resembling the liquid explaining compositional variation between large-scale layers. Alignment of microlites and variations in the quantity of altered residual-liquid glass suggest that banding is related to magma movement during extrusion. It is possible that banding of this type has not been recognized before.
RESUMĂ
L'absence d'attestation texturale interne des sommets d'Ă©coulement et la faible variabilitĂ© chimique entre les Ă©chantillons de basalte du ProtĂ©rozoĂŻque tardif laissent supposer la prĂ©sence d'un Ă©coulement unique Ă Henley Harbour, Labrador, Canada, malgrĂ© la stratification spectaculaire Ă moyenne Ă©chelle de l'affleurement. La variation totale des compositions chimiques dĂ©passe tout juste lĂ©gĂšrement l'incertitude analytique de nombreux Ă©lĂ©ments. L'analyse multidimensionnelle (AMD) amĂ©liore la prĂ©cision analytique « effective » en permettant une comparaison simultanĂ©e de toutes les donnĂ©es (Ă©lĂ©ments et Ă©chantillons). L'analyse des Ă©lĂ©ments rĂ©vĂšle des associations/dispositions d'Ă©lĂ©ments correspondant Ă des contrĂŽles ignĂ©s de la rĂ©partition, mĂȘme dans le cas des Ă©lĂ©ments sensibles Ă l'altĂ©ration (Na, K, Sr). L'AMD rĂ©vĂšle par ailleurs que la stratification Ă moyenne Ă©chelle prĂ©sente une empreinte chimique. L'explication de la variabilitĂ© chimique entre les couches au moyen de calculs du bilan pondĂ©ral et de moyennes des donnĂ©es sur la roche totale nĂ©cessite cependant des compositions de phĂ©nocristaux excessives (basse tempĂ©rature). Les caractĂ©ristiques texturales du fil de stratification Ă moyenne Ă©chelle changent en rĂ©gime de refroidissement entre le fond et le centre de l'Ă©coulement, mais la variation des compositions chimiques peut correspondre Ă des compositions magmatiques changeantes pendant la formation d'un Ă©coulement gonflĂ©. Les calculs du bilan pondĂ©ral laissent toutefois supposer que la variation des compositions chimiques Ă grande Ă©chelle tĂ©moigne de la migration de liquides rĂ©siduels, peut-ĂȘtre sous forme de panaches de vacuoles Ă l'intĂ©rieur d'un Ă©coulement initialement homogĂšne du point de vue chimique. Au bas de l'Ă©coulement (premiĂšre strate), des « bandes » subhorizontales de plusieurs mĂštres de longueur mais Ă©rodĂ©es et soulevĂ©es de quelques centimĂštres ressemblent superficiellement Ă des filons d'exsudation mais sont dĂ©pourvues de textures Ă grain grossier. L'AMD confirme que les Ă©chantillons soulevĂ©s et erodes sont chimiquement distincts. Le bilan pondĂ©ral rĂ©vĂšle que le rubanement n'est pas liĂ© au pourcentage de phĂ©nocristaux, mais qu'il tĂ©moigne de l'abondance d'un liquide rĂ©siduel ressemblant au liquide expliquant la variation des compositions entre les strates Ă grande Ă©chelle. L'alignement des microlites et les variations de la quantitĂ© de verre soluble rĂ©siduel altĂ©rĂ© laissent supposer que le rubanement est apparentĂ© Ă un dĂ©placement magmatique survenu pendant l'extrusion. Il est possible qu'on n'ait pas dĂ©celĂ© un rubanement de ce genre auparavant
Dramatic Rise in Plasma Viremia after CD8+ T Cell Depletion in Simian Immunodeficiency Virusâinfected Macaques
To determine the role of CD8+ T cells in controlling simian immunodeficiency virus (SIV) replication in vivo, we examined the effect of depleting this cell population using an anti-CD8 monoclonal antibody, OKT8F. There was on average a 99.9% reduction of CD8 cells in peripheral blood in six infected Macaca mulatta treated with OKT8F. The apparent CD8 depletion started 1 h after antibody administration, and low CD8 levels were maintained until day 8. An increase in plasma viremia of one to three orders of magnitude was observed in five of the six macaques. The injection of a control antibody to an infected macaque did not induce a sustained viral load increase, nor did it significantly reduce the number of CD8+ T cells. These results demonstrate that CD8 cells play a crucial role in suppressing SIV replication in vivo
Effect of concrete slats, three mat types and out-wintering pads on performance and welfare of finishing beef steers
peer-reviewedBackground
The objective was to investigate the effect of placing mats on concrete slatted floors on performance, behaviour, hoof condition, dirt scores, physiological and immunological variables of beef steers, and to compare responses with animals on out-wintering pads. Continental crossbred beef steers [n = 360; mean (±SD) initial live weight 539 kg (42.2)] were blocked by breed and live weight and randomly assigned to one of five treatments; (1) Concrete slats alone, (2) Mat 1 (Natural Rubber structure) (Durapak Rubber Products), (3) Mat 2 (Natural rubber structure) (EasyFix), (4) Mat 3 (modified ethylene vinyl acetate (EVA) foam structure) and (5) Out-wintering pads (OWPâs).
Results
Animals on the OWPs had a greater (PÂ Â 0.05) as the other treatments. Animals on the OWPs had reduced lying percentage time compared with all the other treatments. Dry matter (DM) intake was greater for animals on the OWPs compared with all the other treatments. Carcass weight, kill out proportion, carcass fat score, carcass composition score, FCR and physiological responses were similar (PÂ >Â 0.05) among treatments. No incidence of laminitis was observed among treatments. The number of hoof lesions was greater on all mat types (PÂ <Â 0.05) compared with concrete slats and OWP treatments. Dirt scores were greater (PÂ <Â 0.05) for animals on OWPs when measured on days 42, 84, 105, 126 and 150 compared with animals on slats.
Conclusions
Under the conditions adopted for the present study, there was no evidence to suggest that animals housed on bare concrete slats were disadvantaged in respect of animal welfare compared with animals housed on other floor types. It is concluded that the welfare of steers was not adversely affected by slats compared with different mat types or OWPs
Dramatic Rise in Plasma Viremia after CD8+ T Cell Depletion in Simian Immunodeficiency Virusâinfected Macaques
Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world
Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic.
Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality.
Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States.
Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis.
Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection
Igneous Rock Associations 4. Oceanic Island Volcanism I Mineralogy and Petrology
Oceanic islands tend to occur at the young ends of hotspot trails because they record the passage of oceanic plates over rising convection cells (plumes) in the mantle, or the propagation of cracks in the lithosphere. Basaltic volcanism on oceanic islands is generally unexplosive and, although potentially destructive, poses less threat to human life than volcanism in other tectonic environments. However, the possibility of giant tsunamis from the catastrophic gravitational collapse of islands is of real concern for major cities surrounding the ocean basins.
Two series of magmas are recognized in oceanic islands. Tholeiites form at lower pressures than alkali basalts, from higher percentages of decompression melting. The former contain a low-Ca pyroxene and the latter can crystallize nepheline. Furthermore, minerals common to both series (chromite, olivine, augite, plagioclase, magnetite and ilmenite) are compositionally distinct reflecting fundamental chemical differences between the two magma series.
Mineral compositions vary as magmas evolve in sub-volcanic, lithospheric magma chambers by assimilation and differentiation. Magmas assimilate wall rocks in these chambers. Time-scales for differentiation (mostly crystal fractionation) are generally less than a few thousand years. Early olivine, pyroxene, chromite and immiscible sulfide formation cause compatible elements(e.g., Ni, Co, Cr) to decline rapidly as differentiation proceeds. Plagioclase dramatically removes Sr at intermediate stages and alkali feldspars sequester Ba and Rb as late-stage trachytes and phonolites form in alkaline magmas. The high-field-strength elements are generally incompatible but locally decline reflecting apatite (P) and Fe-Ti oxide (Ti, Nb, Ta) removal. Studies of layering in individual lava flows suggest that rising volatiles may effect mass transfer of complexed ions during differentiation in magma chambers.
SOMMAIRE
Les Ăźles ocĂ©aniques se trouvent gĂ©nĂ©ralement Ă l'extrĂ©mitĂ© la plus jeune des traĂźnĂ©es de points chauds parce qu'elles sont la marque du passage de plaques ocĂ©aniques au-dessus de cellules de convection ascendantes (panaches) dans le manteau ou de la propagation de fissures de la lithosphĂšre. En gĂ©nĂ©ral, le volcanisme basaltique des Ăźles ocĂ©aniques n'est pas explosif, et bien qu'il puisse ĂȘtre destructeur, il prĂ©sente moins de danger pour les humains que le volcanisme d'autres environnements tectoniques. Cependant, la formation possible de tsunamis gĂ©ants provoquĂ©s par l'effondrement d'Ăźles constitue un danger rĂ©el pour les grandes agglomĂ©rations situĂ©es au pourtour des basins ocĂ©aniques.
On distingue deux séries magmatiques dans les matériaux constitutifs des ßles océaniques. Les tholéiites qui se forment à des pressions plus faibles que les basaltes alcalins, et plus souvent sous des conditions de fusion par décompression, et les basaltes alcalins. Les premiÚres contiennent un pyroxÚne à faible teneur en calcium et l'autre permet la cristallisation de la néphéline. De plus, les minéraux communs à ces deux séries (chromite, olivine, augite, plagioclase, magnétite et ilménite) ont des compositions distinctes qui reflÚtent les différences de composition chimique intrinsÚques de ces deux séries magmatiques.
Les compositions minérales varient puisque les magmas changent de composition dans les chambres magmatiques lithosphériques pré-volcaniques par assimilation et différentiation. Les magmas absorbent les roches des murs d'enceinte dans ces chambres. Les échelles de temps de ces différentiations (principalement de fractionnement cristallin) s'étalent généralement sur quelques milliers d'années. D'abord, la formation d'olivine, de pyroxÚne, de chromite et de sulfures immiscibles entraßne un appauvrissement rapide du magma en éléments compatibles (Ni,Co, Cr par ex.). Puis, aux stades intermediaires, la formation de plagioclases réduit considérablement la teneur en Sr et, aux stades finaux, la formation de feldspaths alcalins en extrait le Ba et le Rb alors que se forment les trachytes et les phonolites à partir de magmas alcalins. Les éléments les plus fortement polarisés sont généralement incompatibles mais, localement, leur teneur décline, reflétant ainsi la formation d'apatite (P) et d'oxydes de Fe-Ti (Ti, Nb, Ta). Les résultats d'études sur la formation en couche de coulées de laves indiquent que l'ascension gravitation-nelle des volatils pourrait avoir un effet sur le transfert de masse d'ions complexes durant la différenciation dans les chambres magmatiques
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