Insights into shallow magmatic processes in large silicic magma bodies: the trace element record in the Fish Canyon magma body, Colorado

Highly evolved rhyolite glass plus near-solidus mineral assemblages in voluminous, dacitic, crystal-rich ignimbrites provide an opportunity to evaluate the late magmatic evolution of granodiorite batholiths. This study reports laser-ablation ICP-MS analyses of trace element concentrations in feldspars, hornblende, biotite, titanite, zircon, magnetite, and interstitial glass of the crystal-rich Fish Canyon Tuff. The high-silica rhyolite glass is characterized by relatively high concentrations of feldspar-compatible elements (e.g., 100ppm Sr and 500ppm Ba) and low concentrations of Y (40) compared to many well-studied high-silica rhyolite glasses and whole-rock compositions. Most minerals record some trace element heterogeneities, with, in particular, one large hornblende phenocryst showing four- to six-fold core-to-rim increases in Sr and Ba coupled with a decrease in Sc. The depletions of Y and HREE in the Fish Canyon glass relative to the whole-rock composition (concentrations in glass ~30% of those in whole rocks) reflect late crystallization of phases wherein these elements were compatible. As garnet is not stable at the low-P conditions at which the Fish Canyon magma crystallized, we show that a combination of modally abundant hornblende (~4%) + titanite (~0.5-1%) and the highly polymerized nature of the rhyolitic liquid led to Y and HREE depletions in melt. Relatively high Sr and Ba contents in glass and rimward Sr and Ba increases in euhedral, concentrically zoned hornblende suggest partial feldspar dissolution and a late release of these elements to the melt as hornblende was crystallizing, in agreement with textural evidence for feldspar (and quartz) resorption. Both observations are consistent with thermal rejuvenation of the magma body prior to eruption, during which the proportion of melt increased via feldspar and quartz dissolution, even as hydrous and accessory phases were crystallizing. Sr/Y in Fish Canyon glass (13-18) is lower than the typical "adakitic” value (>40), confirming that high Sr/Y is a reliable indicator of high-pressure magma generation and/or differentiation wherein garnet is implicate

Mont Blanc and Aiguilles Rouges geology of their polymetamorphic basement (external massifs, Westerns Alps, France-Switzerland)

Les massifs du Mont Blanc et des Aiguilles Rouges appartiennent aux massifs dits cristallins externes de la chaîne alpine occidentale. Ils sont constitués de roches pré-mésozoïques et dessinent des nappes de socle dans le bâti alpin. Ces massifs ont enregistré une longue histoire géologique comprenant le dépôt de sédiments néoprotérozoïques à cambriens, la mise en place de roches magmatiques basiques et ultrabasiques au paléozoïque inférieur, ainsi que l’intrusion de granitoïdes ordoviciens en contexte de marge active. Ces roches sont considérées appartenir à un ensemble de blocs continentaux originaires de la marge septentrionale du Gondwana et accrétés à la marge sud-européenne après leur détachement du Gondwana et leur dérive vers le nord consécutif à l’ouverture de la Paléotéthys. Cet épisode d’accrétion correspond à l’orogenèse varisque (hercynienne), bien documentée dans les massifs du Mont Blanc et des Aiguilles Rouges, par une évolution tectono-métamorphique polyphasée essentiellement carbonifère avec formation de migmatites et intrusion de granitoïdes de types variés. Une érosion active, liée à une forte exhumation, est enregistrée au carbonifère supérieur dans les dépôts détritiques continentaux de bassins d’effondrement de type graben. Ce mémoire présente des cartes géologiques inédites et des suggestions d’excursions dans ces secteurs nouvellement cartographiés. Les lithologies sont abondamment illustrées et décrites en détail du point de vue structural, pétrologique et géochimique. Les analyses chimiques sont fournies en annexe.The Aiguilles Rouges and Mont Blanc external massifs belong to the pre-Mesozoic basement areas of the external domain of the Alps. Before their involvement into the Alpine building (basement nappes) they registered a multiple geological evolution comprising the deposition of Neoproterozoic to Cambrian sediments and emplacement of granitoid and metabasic to ultramafic magmatic rocks of Early Palaeozoic age at the Gondwanan border. After rifting and drifting (formation of Palaeotethys) all rocks underwent polyphase metamorphic and structural transformations during the Variscan orogeny, and were intruded by late Variscan granitoids. The resulting polymetamorphic basement was eroded during formation of Upper Carboniferous sedimentary troughs. New geological maps are presented in this volume, together with structural, petrological and geochemical characteristics of all lithologies. The geochemical data are presented in annexes

Low-pressure, water-assisted anatexis of basic dykes in a contact metamorphic aureole, Fuerteventura (Canary Islands): oxygen isotope evidence for a meteoric fluid origin

Migmatites produced by low-pressure anatexis of basic dykes are found in a contact metamorphic aureole around a pyroxenite-gabbro intrusion (PX2), on Fuerteventura. Dykes outside and inside the aureole record interaction with meteoric water, with low or negative δ18O whole-rock values (+0.2 to −3.4‰), decreasing towards the contact. Recrystallised plagioclase, diopside, biotite and oxides, from within the aureole, show a similar evolution with lowest δ18O values (−2.8, −4.2, −4.4 and −7.6‰, respectively) in the migmatite zone, close to the intrusion. Relict clinopyroxene phenocrysts preserved in all dykes, retain typically magmatic δ18O values up to the anatectic zone, where the values are lower and more heterogeneous. Low δ18O values, decreasing towards the intrusion, can be ascribed to the advection of meteoric water during magma emplacement, with increasing fluid/rock ratios (higher dyke intensities towards the intrusion acting as fluid-pathways) and higher temperatures promoting increasing exchange during recrystallisatio

Tourism Events and the Nature of Stakeholder Power

This exploratory case study examines the power relations among the stakeholders of a tourism event in Borneo. It examines the sources of stakeholder power and the pattern of interdependence of various stakeholders, primarily based on interviews with event managers and stakeholders, as well as field visits. An analysis of the different types and amount of resource control, dependency, and network centrality resulted in four different categories of stakeholder power patterns—executive, asset based, referral, and diffuse stakeholders. The study also found that resource-based power was the primary source of power, whereas network-based power was a secondary and supplementary source. The case study revealed that the salience of event stakeholders based on their power was highly variable due to the different types of power that they had. This article contributes to the literature of event tourism, a typology of the event stakeholder powers in a predominately government-owned music festival, and offered practical suggestions to event management. It also advances the stakeholder power concept within event tourism studies

Igneous Layering, Fractional Crystallization and Growth of Granitic Plutons: the Dolbel Batholith in SW Niger

This study reassesses the development of compositional layering during the growth of granitic plutons, with emphasis on fractional crystallization and its interaction with both injection and inflation-related deformation. The Dolbel batholith (SW Niger) consists of 14, kilometre-sized plutons emplaced by pulsed magma inputs. Each pluton has a coarse-grained core and a peripheral layered series. Rocks consist of albite (An≤11), K-feldspar (Or96-99, Ab1-4), quartz, edenite (XMg = 0·37-0·55), augite (XMg = 0·65-0·72) and accessories (apatite, titanite and Fe-Ti-oxides). Whole-rock compositions are metaluminous, sodic (K2O/Na2O = 0·49-0·62) and iron-rich [FeOtot/(FeOtot + MgO) = 0·65-0·82]. The layering is present as size-graded and modally graded, sub-vertical, rhythmic units. Each unit is composed of three layers, which are, towards the interior: edenite ± plagioclase (Ca/p), edenite + plagioclase + augite + quartz (Cq), and edenite + plagioclase + augite + quartz + K-feldspar (Ck). All phases except quartz show zoned microstructures consisting of external intercumulus overgrowths, a central section showing oscillatory zoning and, in the case of amphibole and titanite, complexly zoned cores. Ba and Sr contents of feldspars decrease towards the rims. Plagioclase crystal size distributions are similar in all units, suggesting that each unit experienced a similar thermal history. Edenite, characteristic of the basal Ca/p layer, is the earliest phase to crystallize. Microtextures and phase diagrams suggest that edenite cores may have been brought up with magma batches at the site of emplacement and mechanically segregated along the crystallized wall, whereas outer zones of the same crystals formed in situ. The subsequent Cq layers correspond to cotectic compositions in the Qz-Ab-Or phase diagram at PH2O = 5 kbar. Each rhythmic unit may therefore correspond to a magma batch and their repetition to crystallization of recurrent magma recharges. Microtextures and chemical variations in major phases allow four main crystallization stages to be distinguished: (1) open-system crystallization in a stirred magma during magma emplacement, involving dissolution and overgrowth (core of edenite and titanite crystals); (2) in situ fractional crystallization in boundary layers (Ca/p and Cq layers); (3) equilibrium ‘en masse' eutectic crystallization (Ck layers); (4) compaction and crystallization of the interstitial liquid in a highly crystallized mush (e.g. feldspar intercumulus overgrowths). It is concluded that the formation of the layered series in the Dolbel plutons corresponds principally to in situ differentiation of successive magma batches. The variable thickness of the Ck layers and the microtextures show that crystallization of a rhythmic unit stops and it is compacted when a new magma batch is injected into the chamber. Therefore, assembly of pulsed magma injections and fractional crystallization are independent, but complementary, processes during pluton constructio

Organization of pre-Variscan basement areas at the north-Gondwanan margin

Pre-Variscan basement elements of Central Europe appear in polymetamorphic domains juxtaposed through Variscan and/or Alpine tectonic events. Consequently, nomenclatures and zonations applied to Variscan and Alpine structures, respectively, cannot be valid for pre-Variscan structures. Comparing pre-Variscan relics hidden in the Variscan basement areas of Central Europe, the Alps included, large parallels between the evolution of basement areas of future Avalonia and its former peri-Gondwanan eastern prolongations (e.g. Cadomia, Intra-Alpine Terrane) become evident. Their plate-tectonic evolution from the Late Proterozoic to the Late Ordovician is interpreted as a continuous Gondwana-directed evolution. Cadomian basement, late Cadomian granitoids, late Proterozoic detrital sediments and active margin settings characterize the pre-Cambrian evolution of most of the Gondwana-derived microcontinental pieces. Also the Rheic ocean, separating Avalonia from Gondwana, should have had, at its early stages, a lateral continuation in the former eastern prolongation of peri-Gondwanan microcontinents (e.g. Cadomia, Intra-Alpine Terrane). Subduction of oceanic ridge (Proto-Tethys) triggered the break-off of Avalonia, whereas in the eastern prolongation, the presence of the ridge may have triggered the amalgamation of volcanic arcs and continental ribbons with Gondwana (Ordovician orogenic event). Renewed Gondwana-directed subduction led to the opening of Palaeo-Tethy

Igneous Layering, Fractional Crystallization and Growth of Granitic Plutons: the Dolbel Batholith in SW Niger

This study reassesses the development of compositional layering during the growth of granitic plutons, with emphasis on fractional crystallization and its interaction with both injection and inflation-related deformation. The Dolbel batholith (SW Niger) consists of 14, kilometre-sized plutons emplaced by pulsed magma inputs. Each pluton has a coarse-grained core and a peripheral layered series. Rocks consist of albite (An≤11), K-feldspar (Or96-99, Ab1-4), quartz, edenite (XMg = 0·37-0·55), augite (XMg = 0·65-0·72) and accessories (apatite, titanite and Fe-Ti-oxides). Whole-rock compositions are metaluminous, sodic (K2O/Na2O = 0·49-0·62) and iron-rich [FeOtot/(FeOtot + MgO) = 0·65-0·82]. The layering is present as size-graded and modally graded, sub-vertical, rhythmic units. Each unit is composed of three layers, which are, towards the interior: edenite ± plagioclase (Ca/p), edenite + plagioclase + augite + quartz (Cq), and edenite + plagioclase + augite + quartz + K-feldspar (Ck). All phases except quartz show zoned microstructures consisting of external intercumulus overgrowths, a central section showing oscillatory zoning and, in the case of amphibole and titanite, complexly zoned cores. Ba and Sr contents of feldspars decrease towards the rims. Plagioclase crystal size distributions are similar in all units, suggesting that each unit experienced a similar thermal history. Edenite, characteristic of the basal Ca/p layer, is the earliest phase to crystallize. Microtextures and phase diagrams suggest that edenite cores may have been brought up with magma batches at the site of emplacement and mechanically segregated along the crystallized wall, whereas outer zones of the same crystals formed in situ. The subsequent Cq layers correspond to cotectic compositions in the Qz-Ab-Or phase diagram at PH2O = 5 kbar. Each rhythmic unit may therefore correspond to a magma batch and their repetition to crystallization of recurrent magma recharges. Microtextures and chemical variations in major phases allow four main crystallization stages to be distinguished: (1) open-system crystallization in a stirred magma during magma emplacement, involving dissolution and overgrowth (core of edenite and titanite crystals); (2) in situ fractional crystallization in boundary layers (Ca/p and Cq layers); (3) equilibrium ‘en masse' eutectic crystallization (Ck layers); (4) compaction and crystallization of the interstitial liquid in a highly crystallized mush (e.g. feldspar intercumulus overgrowths). It is concluded that the formation of the layered series in the Dolbel plutons corresponds principally to in situ differentiation of successive magma batches. The variable thickness of the Ck layers and the microtextures show that crystallization of a rhythmic unit stops and it is compacted when a new magma batch is injected into the chamber. Therefore, assembly of pulsed magma injections and fractional crystallization are independent, but complementary, processes during pluton constructio

Organization of pre-Variscan basement areas at the north-Gondwanan margin

Pre-Variscan basement elements of Central Europe appear in polymetamorphic domains juxtaposed through Variscan and/or Alpine tectonic events. Consequently, nomenclatures and zonations applied to Variscan and Alpine structures, respectively, cannot be valid for pre-Variscan structures. Comparing pre-Variscan relics hidden in the Variscan basement areas of Central Europe, the Alps included, large parallels between the evolution of basement areas of future Avalonia and its former peri- Gondwanan eastern prolongations (e.g. Cadomia, Intra-Alpine Terrane) become evident. Their plate-tectonic evolution from the Late Proterozoic to the Late Ordovician is interpreted as a continuous Gondwana-directed evolution. Cadomian basement, late Cadomian granitoids, late Proterozoic detrital sediments and active margin settings characterize the pre-Cambrian evolution of most of the Gondwana-derived microcontinental pieces. Also the Rheic ocean, separating Avalonia from Gondwana, should have had, at its early stages, a lateral continuation in the former eastern prolongation of peri-Gondwanan microcontinents (e.g. Cadomia, Intra-Alpine Terrane). Subduction of oceanic ridge (Proto-Tethys) triggered the break-off of Avalonia, whereas in the eastern prolongation, the presence of the ridge may have triggered the amalgamation of volcanic arcs and continental ribbons with Gondwana (Ordovician orogenic event). Renewed Gondwana-directed subduction led to the opening of Palaeo-Tethys

Optical evidence for the proximity to a spin-density-wave metallic state in Na0.7_{0.7}CoO2_2

We present the optical properties of \na single crystals, measured over a broad spectral range as a function of temperature ($T$). The capability to cover the energy range from the far-infrared up to the ultraviolet allows us to perform reliable Kramers-Kronig transformation, in order to obtain the absorption spectrum (i.e., the complex optical conductivity). To the complex optical conductivity we apply the generalized Drude model, extracting the frequency dependence of the scattering rate ($\Gamma$) and effective mass ($m^*$) of the itinerant charge carriers. We find that $\Gamma(\omega)\sim \omega$ at low temperatures and for $\omega > T$. This suggests that \na is at the verge of a spin-density-wave metallic phase