The Tapira alkaline complex is the southernmost of a series of carbonatite-bearing intrusions occurring in the Alto Paranaíba region, western Minas Gerais State, Brazil. Together with kamafugites, lamproites and kimberlites, these complexes form part of the Late-Cretaceous Alto Paranaíba Igneous Province (APIP). The Tapira igneous complex is emplaced into rocks of the Late-Proterozoic Brasilia mobile belt, adjacent to a major cratonic area (the Sāo Francisco craton).The complex is formed by the amalgamation of several intrusions, comprising mainly ultramafic rocks (wehrlites and bebedourites), with subordinate syenite, carbonatite and melilitolite. At least two separate units of ultramafic rocks (B1 and B2) and five episodes of carbonatite intrusion (CI to C5) are recognised. The plutonic rocks are crosscut by fine-grained ultramafic and carbonatite dykes. Two varieties of ultramafic dykes are recognised: phlogopite-picrites are the most primitive rocks in the complex; low-Cr dykes are more evolved, and typically lack olivine. The ultramafic dykes are carbonate-rich, and may contain carbonate ocelli, indicating that immiscibility of carbonatite liquid occurred early in the evolution of the complex. The ultramafic dykes are chemically similar to the APIP kamafugites. The primitive Tapira magmas underwent some differentiation in the crust, before their final emplacement. Crystal fractionation from the phlogopite-picrite magma may have produced olivine and chromite-rich cumulates, but these rocks are under- represented in the complex. Crystal fractionation from low-Cr dykes may have produced the bebedourites. The Tapira complex contains examples of carbonatites that originated by either liquid immiscibility or crystal fractionation. These contrasting petrogenetic mechanisms have produced distinct geochemical and mineralogical signatures, which have been used to pinpoint specific events in the evolution of the complex, and to test the consanguinity of carbonatites and associated silicate rocks.

No description available.

No description available.

This thesis examines organizational use of social media. It focuses on developing an understanding of the ways by which social media are used within formal organizational settings. From the vantage point of this thesis such an understanding can be achieved by looking at tensions and incompatibilities that might potentially exist between social media and organization because of their distinct characteristics. It is argued that the distinct characteristics of social media (e.g. openness, transparency, flexibility, etc.) and organization (e.g., hierarchy, formal relationships, standard procedures, etc.) may engender tensions and incompatibilities that affect the ways of using social media and their potential in organizations. The main premise here is that the possibilities, behaviors, and practices afforded by social media are recognizably different in nature from common and established organizational practices, behaviors, norms, and routines. Through a structurational understanding of organizational use of social media, influenced by Giddens’ theory of structuration and Orlikowski’s practice lens for studying technology use, this thesis offers the perspective of immiscibility to capture tensions and incompatibilities driven by the distinctive characteristics of social media and organization. It basically offers a way of seeing social media use in organizations as a dynamic, in- practice interplay between social media and organization characteristics. One key argument in this thesis is that the immiscible interplay of social media and organization, produces, at least in transition, ‘a bureaucracy of social media’. Social media, it is argued, are used in ways that are essentially bureaucratic, reflecting and also reinforcing established characteristics of formal organizations through the production and reproduction of structures which are driven by the immiscible interplay. The development of such an understanding was achieved through multiple research studies focusing on the use of the wiki technology for knowledge collaboration and sharing in two large, multinational organizations: CCC and IBM. A number of qualitative methods were used in these studies to collect empirical evidence from the two organizations including interviews, field visits, observations, and document analysis. The overarching contribution of this thesis centers on offering a unique way of understanding organizational use of social media by putting forward tensions and incompatibilities between social media and organization and also by providing an understanding of how such tensions and incompatibilities affect the potential for change by social media.

Abstract Isobaric (200 MPa) experiments have been performed to investigate the effects of H2O alone or in combination with P, S, F or Cl on the phase relations and elemental and oxygen isotopic partitioning between immiscible silicate melts in the systems Fe2SiO4-Fe3O4-KAlSi2O6-SiO2, Fe3O4-KAlSi2O6-SiO2 and Fe3O4-Fe2O3-KAlSi2O6-SiO2 +/- plagioclase (An50). Experiments were heated in a newly-designed rapid-quench internally-heated pressure vessel at 1075, 1150 or 1200 oC for 2 hours. Water alone or in combination with P, S, or F significantly increases the temperature and composition range of two-liquid fields at fO2= NNO and MH buffers. Water-induced suppression of liquidus temperatures, considered with the effects of pressure on two-liquid fields stability in silicate melts, suggests that liquid phase separation may occur in some volatile-rich silicate magmas at pressures up to 2GPa. Two-liquid partition coefficients for Fe, Si, P and S correlate well with the degree of polymerization of the SiO2-rich conjugate melts and the data can be applied to assess the involvement of liquid-phase separation in the genesis of coexisting volatile-rich magmas. The partitioning of trace concentrations of selected HFSE, REE and transition elements between immiscible experimental volatile-rich melts at 1200 oC, 200 MPa has been determined at QFM, NNO and MH oxygen buffers. Water generally increases the partitioning of HFSE, REE and transition elements into the Fe-rich melt. Water alone, or combined with P or S, produces nearly parallel partitioning trends for HFSE and REE. Absolute partitioning values of transition elements are strongly dependent on the network-modifier composition of the melt. 18O in experimental immiscible melts with H2O or H2O and P or S partitions preferentially into the felsic conjugate melt (δ18O felsic melt- δ18O mafic melt values range from 0.4 to 0.8 permil) consistent with observations in anhydrous immiscible silicate melts. The expansion of the P-T-X-fO2 stability ranges of two- or three-liquid fields observed in the experimental melts demonstrates that liquid-immiscibility may be an important process in the evolution of some volatile-rich natural magmas. The results support an immiscible petrogenetic origin for some iron-oxide dominated, Kiruna-type, ore-deposits. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2012-04-10 15:06:35.797

This thesis examines organizational use of social media. It focuses on developing an understanding of the ways by which social media are used within formal organizational settings. From the vantage point of this thesis such an understanding can be achieved by looking at tensions and incompatibilities that might potentially exist between social media and organization because of their distinct characteristics. It is argued that the distinct characteristics of social media (e.g. openness, transparency, flexibility, etc.) and organization (e.g., hierarchy, formal relationships, standard procedures, etc.) may engender tensions and incompatibilities that affect the ways of using social media and their potential in organizations. The main premise here is that the possibilities, behaviors and practices afforded by social media are recognizably different in nature from common and established organizational practices, behaviors, norms and routines. Through a structurational understanding of organizational use of social media, influenced by Giddens’ theory of structuration and Orlikowski’s practice lens for studying technology use, this thesis offers the perspective of immiscibility to capture tensions and incompatibilities driven by the distinctive characteristics of social media and organization. It basically offers a way of seeing social media use in organizations as a dynamic, in-practice interplay between social media and organization characteristics. One key argument in this thesis is that the immiscible interplay of social media and organization, produces, at least in transition, ‘a bureaucracy of social media’. Social media, it is argued, are used in ways that are essentially bureaucratic, reflecting and also reinforcing established characteristics of formal organizations through the production and reproduction of structures which are driven by the immiscible interplay. The development of such an understanding was achieved through multiple research studies focusing on the use of the wiki technology for knowledge collaboration and sharing practices in two large multinational organizations: CCC and IBM. A number of qualitative methods were used in these studies to collect empirical evidence from the two organizations including interviews, field visits, observations and document analysis. The overarching contribution of this thesis centers on offering a unique way of understanding organizational use of social media by putting forward tensions and incompatibilities between social media and organization and also by providing an understanding of how such tensions and incompatibilities affect the potential for change by social media.

Le lien entre les éléments volatils CO₂-H₂O et la fusion mantellique a depuis maintenant longtemps été illuminé par l’expérimentation. Une large base de données expérimentales existe et souligne l’effet primordial de ces éléments sur l’abaissement des températures de fusion de la péridotite ainsi que sur la composition des liquides magmatiques produits comme une fonction des conditions P – T – fo₂ – composition du système. Néanmoins, la diversité et la complexité de cette base de données peuvent compliquer sa compréhension globale. Dans cette étude, une analyse détaillée de la composition des liquides magmatiques riches en CO₂ et H₂O est réalisée, soulignant notamment une transition non-linéaire et plus ou moins abrupte entre des liquides carbonatitiques et des liquides silicatés. Un modèle thermodynamique est élaboré afin de calculer l’activité de SiO₂ dans les liquides magmatiques riches en CO₂-H₂O (aSiO₂(l)) et coexistant avec un assemblage péridotitique, depuis des termes carbonatitiques jusqu’à des termes basaltiques. L’application de ce modèle dans des conditions de ride océanique prédit la stabilisation des liquides carbonatitiques au démarrage de la fusion redox (liée à la transition graphite/diamant- carbonates) jusqu’à environ 100 km de profondeur, avant d’évoluer plus ou moins abruptement vers des liquides silicatés riche en CO₂. Au niveau des cratons, les kimberlites de Groupe I sont stabilisés en base de lithosphère (~250 km de profondeur), et peuvent être formés à partir d’un plume mantellique. L’épaisseur de cette lithosphère empêche la remontée du plume et la formation des OIB. Afin de décrire plus pleinement les propriétés thermodynamiques du liquide magmatique, un modèle plus complexe (système CMAS-CO₂) est en construction, dont la méthodologie est modifiée par rapport au précédent modèle calculant aSiO₂(l) ; un effort tout particulier est ici mené afin de mieux considérer les incertitudes expérimentales et thermodynamiques. / The link between volatiles (CO₂-H₂O) and mantle melting has so far been illuminated by experiments. A large experimental database exists and emphasizes the importance of volatiles on lowering solidus temperatures of peridotite and modifying the melt composition as a function of P – T – fo₂ – bulk composition. Nevertheless, the diversity and the complexity of this experimental database may complicate its global understanding. In this study, an analysis of CO₂-H₂O-rich melt composition is done, emphasizing the non-linear and more or less abrupt character of the transition between carbonate-rich melts and silicate-rich melts. A thermodynamic model is accomplished to calculate the silica activity in CO₂-H₂O-rich melts coexisting with peridotite assemblage and covering carbonatitic to basaltic terms. Along an oceanic ridge adiabat, the model predicts that carbonatitic melts can be stabilized at the onset of “redox melting” (transition between graphite/diamond-carbonates) to about 100 km depth, before abruptly evolving towards carbonated silicate melts. In cratons, Group I kimberlites are stabilized at the base of the lithosphere (about 250 km depth), and can originate from a mantle plume. The thickness of the lithosphere prevents the plume ascent and the production of OIB. In the aim of describing the melt thermodynamic properties more precisely, a more complex model (system CMAS-CO₂) is under construction, with a modified methodology relative to the previous model of silica activity; a specific effort is here conducted in order to better consider experimental and thermodynamic uncertainties.

This thesis examines organizational use of social media. It focuses on developing an understanding of the ways by which social media are used within formal organizational settings. From the vantage point of this thesis such an understanding can be achieved by looking at tensions and incompatibilities that might potentially exist between social media and organization because of their distinct characteristics. It is argued that the distinct characteristics of social media (e.g. openness, transparency, flexibility, etc.) and organization (e.g., hierarchy, formal relationships, standard procedures, etc.) may engender tensions and incompatibilities that affect the ways of using social media and their potential in organizations. The main premise here is that the possibilities, behaviors and practices afforded by social media are recognizably different in nature from common and established organizational practices, behaviors, norms and routines. Through a structurational understanding of organizational use of social media, influenced by Giddens’ theory of structuration and Orlikowski’s practice lens for studying technology use, this thesis offers the perspective of immiscibility to capture tensions and incompatibilities driven by the distinctive characteristics of social media and organization. It basically offers a way of seeing social media use in organizations as a dynamic, in-practice interplay between social media and organization characteristics. One key argument in this thesis is that the immiscible interplay of social media and organization, produces, at least in transition, ‘a bureaucracy of social media’. Social media, it is argued, are used in ways that are essentially bureaucratic, reflecting and also reinforcing established characteristics of formal organizations through the production and reproduction of structures which are driven by the immiscible interplay. The development of such an understanding was achieved through multiple research studies focusing on the use of the wiki technology for knowledge collaboration and sharing practices in two large multinational organizations: CCC and IBM. A number of qualitative methods were used in these studies to collect empirical evidence from the two organizations including interviews, field visits, observations and document analysis. The overarching contribution of this thesis centers on offering a unique way of understanding organizational use of social media by putting forward tensions and incompatibilities between social media and organization and also by providing an understanding of how such tensions and incompatibilities affect the potential for change by social media.

Le craton archéen de l’In Ouzzal représente une succession d'événements intrusifs et métamorphiques depuis l’Eburnéen qui en font un marqueur important des processus géodynamiques à travers les temps géologiques. La région d’Ihouhaouene située au N-W du terrane de l’In Ouzzal en Algérie est unique de par la présence d’intrusions protérozoïques de carbonatites associées à des roches alcalines saturées. Ces carbonatites intracontinentales comptent parmi les plus anciennes et inhabituelles de par leurs diversités et la présence de minéraux à terres rares. Les carbonatites sont pegmatitiques ou bréchiques avec des fragments de syénite. Elles sont des calciocarbonatites composées de calcite (>50 vol.%), apatite, clinopyroxène et wollastonite et sont associées à des syénites rouges ou blanches présentes sous forme massive. Les syénites sont composées d’alternance de niveaux clairs de feldspaths alcalins rouges ou de wollastonites associées aux feldspaths blancs et de niveaux sombres d’apatites et de clinopyroxènes. Les carbonatites et syénites forment une suite cogénétique caractérisée par une augmentation en SiO2 et une diminution en CaO et CO2. Les carbonatites ont des compositions en silice comprises entre 5 et 35 pds.%, 28 et 53 pds.% CaO et 11 à 36 pds.% CO2. Les syénites montrent une forte teneur en K2O (12 pds.%) et des teneurs très faibles en Na2O (1 pds.%). Les carbonatites et syénites sont riches en éléments incompatibles avec des teneurs en REE supérieures à 7000 fois les chondrites et 1000 fois les chondrites dans les syénites, respectivement, et de fortes teneurs en U, Sr et Th. Les éléments en trace dans les minéraux magmatiques (apatite et pyroxène) mettent en évidence des processus complexes à l’origine de ces roches impliquant plusieurs étapes de cristallisation fractionnée et d’immiscibilité à partir d’un magma mélilititique riche en CO2. Les minéraux des carbonatites riches en silice et des syénites blanches ont des signatures géochimiques similaires et se caractérisent par des rapports élevés en Nb/Ta typiques de magmas riches en carbonate par immiscibilité. Les syénites rouges ont des caractéristiques de liquides silicatés évolués par différentiation. Les minéraux des carbonatites pauvres en silice ont des rapports Nb/Ta très variables, sub-chondritiques (<10), indiquant une cristallisation à partir de liquides très évolués et la présence de magmas carbonatitiques tardifs. Les apatites, en particuliers, enregistrent divers épisodes magmatiques et également supergènes. Elles présentent dans certaines roches une redistribution et un enrichissement en terres rares variables qui se caractérisent par des exsolutions de britholite dans les carbonatites riches en silice et monazite dans les carbonatites pauvres en silice. Ces exsolutions traduisent des rééquilibrations locales sub-solidus avec des fluides tardi-magmatiques de composition riche en Cl-Th-REE pour l’exsolution de la britholite et S-Ca-P-CO2 pour les inclusions de monazite. L’apatite et le zircon présents dans ces roches alcalines et carbonatites, ont permis de déterminer l’âge de mise en place du complexe magmatique de Ihouahouene à 2100 Ma syn-métamorphique et de confirmer l’âge panafricain de son exhumation. L’étude pétrologique, géochimique et géochronologique des carbonatites et syénites d’Ihouhaouene a permis de mettre en évidence l’origine magmatique de ces roches et de définir les interactions fluides-roches supergènes à l’origine des enrichissements en REE. Les carbonatites et syénites d’Ihouahouene proviennent d’un faible taux de fusion partielle d’un manteau Précambrien riche en CO2. Plusieurs étapes de cristallisation fractionnée et d'immiscibilité ont permis la genèse de ces roches hybrides, piégées le long de grandes zones de cisaillement durant la période de transition Archéen /Eburnéen dans un régime extensif à l’In Ouzzal caractérisé par un environnement granulitique d’ultra-haute-température. / The In Ouzzal Archaean craton represents a succession of intrusive and metamorphic events since Eburnean, and an important marker of geodynamic processes through geological time. The Ihouhaouene area located in the N-W of In Ouzzal terrane in Algeria is unique by the presence of Proterozoic carbonatite intrusions associated with silica-saturated alkaline rocks. These intracontinental carbonatites are among the oldest and exceptional because of their diversity and the presence of unusual rare earth minerals. Carbonatites are pegmatitic or brecciated with fragments of syenite. They are calciocarbonatites with calcite (> 50 vol.%), apatite, clinopyroxene and wollastonite and are associated with red or white syenites in massive outcrops. Syenites are composed of alternating light levels of red alkaline feldspar or wollastonite associated with white feldspar and dark levels of apatite and clinopyroxene. Carbonatites and syenites form a cogenetic suite characterized by an increase in silica and decrease in calcium and CO2 content. The carbonatites have silica content ranging from 5 to 35 wt.%, 28 to 53 wt.% CaO, and 11 to 36 wt.% CO2. Syenites have high K2O (12 wt.%) and low Na2O content (1 wt.%). Carbonatites and syenites have high incompatible element concentrations with high REE content (7000*chondrites and 1000*chondrites, respectively) and high U, Pb, Sr and Th content. Trace elements (eg. Rare Earths, Nb-Ta, Zr-Hf) in magmatic minerals (apatite-pyroxene) of carbonatites and syenites reveal complex magmatic processes at the origin of these rocks involving several stages of fractional crystallization and immiscibility from a CO2-rich melilititic magma. Silica-rich carbonatites and white syenites are characterized by high Nb/Ta, Y/Zr and Rb/Sr ratios, typical of carbonate-rich magmas by immiscibility. The red syenites have characteristics of immiscible differentiated silicate melt. Silica-poor carbonatite minerals have variable subchondritic Nb/Ta (<10) indicating crystallization from highly evolved liquids and the presence of late carbonatitic magmas. Apatites, in particular, record various magmatic and supergene processes. They present, in some rocks, redistribution and enrichment in rare earth elements, which are characterized by exsolutions of britholite in silica-rich carbonatites and monazite-quartz-calcite inclusions in silica-poor carbonatites. These minerals reflect local sub-solidus re-equilibration with late-magmatic fluids rich in Cl-Th-REE for the exsolution of britholite and S-Ca-P-CO2 for monazite inclusions. The apatite and zircon present in these alkaline and carbonatite rocks, allow determination of the syn-metamorphic crystallization age of the Ihouahouene magmatic complex at 2100 Ma and confirm the pan-African age of its exhumation. The petrological, geochemical and geochronological study of Ihouhaouene carbonatites and syenites highlights the magmatic origin of these rocks and constrains the fluid-rock interactions at sub-solidus conditions leading to REE-enrichment. The carbonatites and syenites result from a low partial melting rate of a CO2-rich Precambrian mantle. Several fractional crystallization and immiscibility stages allowed the genesis of these hybrid magmas, trapped along large shear-zones during the Archean/Eburnean transition period in the In Ouzzal terrane, characterized by extensive deformation in ultra-high-temperature granulitic environment.

No description available.