The Canary islands are formed by a slow moving hotspot, from Fuerteventura 20 Ma to el Hierro 1.2Ma years old and La Palma is in the shield building stage of evolution. La Palma had its last eruption 1971 and has had seven eruptions since 1430, which makes it the most active of the islands in our times. The samples consist of host lavas, basanites, and mafic/ultramafic and felsic xenoliths, alkali gabbros and syenites respectively. Minerals in the lavas and the alkali gabbro xenolith samples are clinopyroxene, olivine, amphibole and plagioclase, the clinopyroxenes are zoned. Forsterite content in the olivines increases at the rim for the xenoliths and decreases for the host lavas. While magnesium number in the clinopyroxenes decreases towards the rim. The Fe-Mg partitioning indicates that there were points of equilibrium between the clinopyroxenes and their host lavas, which was calculated to temperature, pressure and depth indicating 62-74km for the xenoliths and 23-35km for the host lavas. The temperatures and pressures were 1184-1205°C with 6-10 kbar for the host lavas compared to 1316-1341°C and 17-20 kbar for the xenoliths.

A young marine island called Heard Island is located in the southern Kerguelen Plateau in the Indian Ocean, a large igneous province created by the Kerguelen mantle plume. The two major geographic regions on Heard Island have two principal volcano-magmatic suites. Basanites, alkali basalts, and trachybasalts make up one group, the Big Ben Series (BBS), while basanitic to trachytic rocks make up the Laurens Peninsula Series (LPS). The most recent eruption at Big Ben volcano occurred in October 2022. To better understand magma evolution in the underlying plumbing system, clinopyroxene, feldspar, and olivine, mineral chemistry, clinopyroxene thermobarometry, and olivine thermometry were used.      The main phenocrysts from Heard Island are olivine, clinopyroxene, and feldspar. All phenocrysts share the characteristics of sieve textures and fractures. The mineral chemistry of clinopyroxene, zonation, and variation of core and rim of Mg#, Al2O3, TiO2, and Cr2O3, provides insight into the magmatic evolution of magma. Results from clinopyroxene-liquid thermobarometry suggest that clinopyroxene crystallization occurs at depths of 1 to 39 km for the cores and 1 to 47 km for the rims, with corresponding temperatures of 1098 to 1208°C and 1099 to 1254°C respectively. Comparison with olivine thermometry shows concordance in temperature estimates. The Mohorovičić discontinuity, or Moho, which marks the boundary between the Earth's crust and mantle, is believed to lie between 18 and 26 km deep at Heard Island. This study suggests that magma pockets can be found below the Moho between 51 and 18 km, and in the upper and lower crust between 18 and 2 km. Additionally, the density difference between various crustal layers determines where magma storage is located. The evidence from petrology and geochemistry points to common processes of magma mixing, recharge, and fractional crystallization during magma evolution.

The volcanic island of Fogo belongs to the Cape Verde archipelago, a two-tiered chain of islands situated 500 km west of the African coast. Fogo is regarded as one of the most active volcanoes in the world with 10 eruptions during the last 250 years. The former shield volcano Monte Amarelo reached 3500 m.a.s.l. before it collapsed into the Atlantic Ocean. The massive landslide event occurred between 124 and 86 ka, forming the Bordeira cliffs and the high plateau Cha das Caldeiras on Fogo. We have collected rock samples from the Bordeira dikes, which intruded into the Bordeira wall prior to collapse. The purpose of the project is to produce a magmatic storage model for Fogo using mineral chemistry and thermobarometric methods. Additionally, I aim to determine the processes prevailing in the magmatic system, the link between the volcanic and plutonic system. Previous studies on the magma storage beneath Fogo have focused on the volcanics, which show crystallization pressures between 0.45 to 0.68 GPa using clinopyroxene-melt thermobarometry on rims. The Bordeira dikes are basanitic to nephelinitic in composition. The mineral assemblage of the 20 dike samples consist of phenocrystic clinopyroxene ± olivine ± plagioclase ± xenocrystic amphibole. Accessory minerals are titanomagnetite, apatite, nepheline, plagioclase and alkali feldspar in a microcrystalline groundmass. Clinopyroxene displays a large compositional variation, ranging from Mg#38 to Mg#85, with a mean of Mg#71±10 2s.d. (n=614). Xenocrystic amphibole varies from Mg#37 to Mg#72, with a mean of Mg#62±15 2s.d. (n=78). Interstitial feldspar forms two groups, one of An#24 to An#79, with a mean of An#66±19 2s.d., (n=125) and a second with Or#19 to 100 with a mean of Or#69±42 2s.d.(n=71). Bulk geochemistry of the 20 samples range from 1.82 to 11.5 MgO wt%. Our clinopyroxene-melt thermobarometry show crystallization pressures ranging from 0.02 to 0.85 GPa, with a mean of 0.47±0.29 2s.d. (n=502) (Putirka et al. 2003). Structural data from the intrusive dikes in the Bordeira contain three preferred orientations, N-S, NW-SE and E-W (n=371). The main process occurring in the magmatic system is fractional crystallization, however there is some evidence for phenocryst accumulation and magma recharge. Our magma storage model show that clinopyroxene crystallization initiates in the lithospheric mantle, between 15 to 28 km depth. Significant clinopyroxene rim and microcryst crystallization occur above Moho, between 9 to 12 km, implying that magma storage levels do exist in the oceanic crust. The intrusive and extrusive rocks present on Fogo show common storage levels, suggesting that they are formed in the same system but the difference being their residence time in the crustal level storage. Our structural data and 3D model suggest that the Monte Amarelo rift zone was composed of three components, being oriented NW-SE, N-NE and E-W. The flank collapse was caused by dike intrusions of N-S orientation which enabled a E-W extension of the shield volcano. / Vulkanön Fogo är en del av ögruppen Kap Verde i Atlanten. Ögruppen bildar en två delad arkipelag positionerad 500 km väster om det afrikanska fastlandet. Ön, tillika vulkanen Fogo har på senare tid varit en av de mest aktiva vulkanerna i världen med 10 utbrott under de senaste 250 åren. Ön byggdes upp av sköldvulkanen Monte Amarelo nådde 3500 m ö h innan delar av den kollapsade ned i Atlanten. Det massiva skredet som skedde mellan 86 och 124 tusen år sedan skapade högplatån Cha das Caldeiras samt den omringande klippsektionen Bordeira. Vi har samlat stenprover från de plutoniska bergarter som har trängt in sig i klippsektionen Bordeira. Målet med vår studie är att skapa en modell för hur magma lagringen fungerar under Fogo. Vi ämnar kartlägga magmalagringsdjupet med hjälp av kemiska variation i mineral som kan användas för att kartlägga kristalliseringstryck och temperatur som i t.ex. klinopyroxen. Vi är samtidigt intresserade av att veta vilka processer som sker i det magmatiska systemet och sambandet mellan vulkanska bergarter t.ex. lava och plutoniska bergarter. Tidigare studier av Fogos magmalagring har använt vulkaniska bergarter, som kristalliserar sig mellan 0.45 till 0.68 GPa när man undersökt kemin på kristallkanter av klinopyroxen. 20 prover har analyserats från Bordeiraklipporna och de innehåller låga kiselhalter, mellan 37 till 47% samt höga mängder alkaliska oxider så som kalium och natrium. Provernas mineralinnehåll består främst av större kristaller av silikatmineralen klinopyroxen ± olivin± fältspat ± främmande amfibolkristaller. De större kristallerna är omringande av en mikrokristallin grundmassa bestående av järn-titanoxider, apatit och fältspatoider. Klinopyroxen har en relativt stor kemisk variation, med Mg#37 till Mg#85, med ett medelvärde på Mg#71. Vi har även två olika sorter av fältspat, en grupp med ett kalciumrik rikt innehåll klassificeras som anortit, och en annan med ett kaliumrikt innehåll, som ortoklas. Vår analys av klinopyroxen-smälta har gett oss kristalliseringstryck som sträcker sig mellan 0.02 till 0.85 GPa med ett medelvärde på 0.47 GPa. Detta innebär att den dominerande processen i magmalagringssystemet är fraktionerad kristallisering då vi kan se ett linjärt avtagande för många ämnen när de jämförs mot magnesiumhalten. Vår magmalagringsmodell för vulkanen Fogo visar att klinopyroxenkrystallisering påbörjas i den litosfäriska manteln, mellan 15 och 28 km djup. Kristallisering av kanter på klinopyroxenkristaller samt mindre kristaller i grundmassan sker ytligare och visar på att det finns en eller flera magmalagringsnivåer i den oceaniska jordskorpan, mellan 9 till 12 km djup. Vulkaniska och plutoniska bergarter vittnar om ett delat magmasystem, vilket indikerar att skillnaden mellan de två bergarterna främst är tiden de befinner sig på respektive lagringsnivå. Vår strukturgeologiska data samt 3D modell visar att den intrusiva aktiviteten var primärt orienterad NV-SO, N-NO och O-Vriktning. Monte Amarelo-vulkanens skred och kollaps orsakades av intruderande gångar med en generell N-S orientering vilket ledde till ett skred på östsidan.

The southern part of Iceland incorporates two parallel volcanic zones, the Eastern Volcanic Zone and the Western Volcanic Zone. These two branches are connected by an E-W transform. Hekla is located close to intersection between the two plate boundaries. Hekla is one of Iceland's most active and explosive volcanoes. Unique to Hekla is that it is one of the few volcanoes on Iceland that produces explosive silica rich magma. Hekla gives no clear warning of its eruptions and sends out seismic signals with very short notice. It is therefore of interest to try to understand Hekla's magma system and magmatic processes in order to gain an increased knowledge of its volcanic processes. The study is based on calculating crystallization conditions for the minerals plagioclase, clinopyroxene and orthoproxene. Calculations is based on the assumption that minerals, which are in equilibrium with the associated melt are directly associated with the thermodynamics of crystallization. The result of the study shows that Hekla's magma chamber is located at a depth of 8-12 km. The samples from Hekla are poor in minerals, which can be explained by separation due to fractional crystallization that forms a crystal mush. Fast ascending primitive magma along with degassing will eventually lead to an eruption. The absence of crystal zoning indicates a limited chance of magma mixing or crustal contamination. Oxides related to the eruption tend to comprise a low titanium content, which is related with an increased pressure condition. Geospeedometry suggested that recharge occurred up to 10 days before eruption. Erupted oxides shows up to 30 years residence which suggest long-term crystal mush. / Hekla är en av Islands mest aktiva och explosiva vulkan. Dess vulkaniska beteende grundar sig i det underliggande magma systemet samt kompositionen av magman. Unikt för Hekla är att det är en av få vulkaner på Island som producerar explosiv kiselrik magma. Hekla sänder dessutom inte ut tydliga varnings signaler innan utbrott. Det är därför av intresse att försöka förstå Heklas magma system och magmatiska processer för att kunna få en ökad uppfattning om dess vulkaniska processer.Undersökningen grundar sig i att beräkna kristalliseringsförhållanden för mineralerna plagioklas, klinopyroxen samt ortopyroxen. Resultatet av studien påvisar att Heklas magmaförvar är belägget på ett djup av 8-12 km. Proverna från Hekla har varit fattiga i mineraler vilket kan förklaras genom att mineraler har separerats från magman genom kristallisering. Magmas komposition kommer därför att ändras i och med att mineraler som kristalliserats tar bort element från den. Mineralkristallerna bildar sedan en egen zon som innefattar en liten del magma. Utbrotten triggas sedan när varm mafisk magma från ett större djup infiltrerar den grunda magma kammaren samt frisläppandet av gaser som sker vid kristallisering av mineraler.Beräkningar av tiden det tar för oxider att svalna tyder på att ny magma har infiltrerat magma kammaren upp till 10 dagar innan utbrottet. Den nya magman hinner inte blanda sig med den mer utvecklade magman. Detta event skulle leda till att kluster av mineral skulle följa med i utbrottssekvensen. Ett antal oxider visar även på att det börjat svalna upp till 30 år sedan, vilket kan förklaras av en zon bestående av kristaller.

No description available.

abstract: Primitive arc magmas provide a critical glimpse into the geochemical evolution of subduction zone magmas, as they represent the most unadulterated mantle-derived magmas observed in nature in these tectonic environments and are the precursors of the more abundant andesites and dacites typical in arcs. To date, the study of primitive arc magmas has largely focused on their origins at depth, while significantly less is known about pre-eruptive crustal storage and ascent history. This study examines the crustal storage and ascent history of the Mt. Shasta primitive magnesian andesite (PMA), the demonstrated dominant parent magma for the abundant mixed andesites erupted at Mt. Shasta. Petrographic and geochemical observations of the PMA identify a mid-crustal magma mixing event with a less evolved relative of the PMA recorded in multiple populations of reversely zoned clinopyroxene and orthopyroxene phenocrysts. Prior phase equilibrium experiments and thermobarometric calculations as part of this study suggest the PMA experienced storage, mixing with a less evolved version of itself, and subsequent crystallization at 5kbar and 975°C. Modeling of Fe-Mg interdiffusion between the rims and cores of the reversely-zoned clinopyroxene and orthopyroxenes suggest this mixing, crystallization and subsequent ascent occurred within 10 years, or ~2.9 (+6.5 / -2.5) years, prior to eruption. Ascent from 5kbar or ~15 km, with no meaningful shallower storage, suggests minimum crustal transit rates of ~5 km/year. This rate is comparable to only a couple of other similar types of crustal transit rates (and slower than the much faster, syn-eruptive ascent rates measured through methods like olivine-hosted melt embayment volatile gradients and U-series isotope measurements on other arc magmas). The results of this study help to constrain the pre-eruptive history and ascent rates of hydrous primitive arc magmas, illuminating their magmatic processes during ascent. When combined with geophysical signals of magma movement, mixing to eruption timescales such as this have the power to inform volcanic hazard models for monogenetic, cinder cone eruptions in the Southern Cascades. / Dissertation/Thesis / Masters Thesis Geological Sciences 2019

Volcanoes with alkaline differentiated magma belong to the more explosive and destructive types, but knowledge about these systems is often limited. Unravelling the position and conditions in the source magma chamber systems that feed volcanism at the surface is vital to understand these systems better. Due to deep erosion and barren grounds the oceanic island of Gran Canaria, Spain, provides a natural laboratory to study unique chemical and structural volcanic features of alkaline volcanism. The centre of Gran Canaria is made up of the Miocene Tejeda intrusive complex including a cone-sheet swarm and shallow alkaline differentiated plutonic rocks that form the closing phase of the Miocene activity pulse on Gran Canaria. Cone-sheets and other high-level plutonic rocks can give important insights into the interior of a volcano, such as depth and geometry of the magma supply reservoir, and thus provide vital data for the interpretation of active volcanoes in the Canary Islands and beyond. This work uses the clinopyroxene-melt thermobarometric methodology by Putirka (2008) and Masotta et al. (2013), the latter being a re-calibration of the first making it specific to alkaline differentiated magmas, to further constrain the depth of mineral. Geochemical analysis was preformed with electron microprobe (EMPA) at Uppsala University to determine mineral compositions and to extend the dataset, chemical data from the extensive work by Schirnick (1996) was also utilised. When the calculated pressure from the method of Masotta et al. (2013), was converted to the depth, the results from syenite samples show that crystallization of clinopyroxene occurred at depths of ~ 4 km (100 MPa) to ~ 15 km (400 MPa), with the highest concentration between ~ 7 km (200 MPa) and ~ 11 km (300 MPa). The results indicates that crystallization took place through the pressure range equivalent to crustal levels and possibly reaching as far down as MOHO depth, with temperature estimates calculated to about 860 to 960 °C. After combining the thermobarometric results with other evidence of magmatic processes, from this work and previous publications, the magma system expresses characteristics of fractional crystallization trends and simultaneously evidence of magma mixing, small-scale convection, and magma contamination. To explain these contradictory features, this work promotes a network of interconnected magma chambers that allows for magma stagnation and evolution at different levels. The results have thus contributed to further constrain the depth of which the cone-sheet swarm originated from on Gran Canaria, Spain. / Vulkaniska system av den typ studerade i detta arbete tillhör de mer explosiva och destruktiva typer avsystem på jorden, men kunskapen om dem är begränsad. En viktig komponent som krävs för att bättreförstå dessa system är att utröna tryck och temperaturförhållanden i magmakammarna som livnärvulkanismen vid ytan. På grund av djup erosion och karg mark så fungerar ön Gran Canaria(Kanarieöarna, Spanien) som ett naturligt laboratorium för att studera både kemiska och strukturellaegenskaper. Den centrala delen av Gran Canaria består till stor del av det så kallade Tejeda intrusivakomplexet, vilket inkluderar en inverterad kon-intrusionssvärm samt djupbergarten syenit somtillsammans representerar den avslutande fasen av magmatisk aktivitet under epoken Miocen på ön.Inverterade kon-intrusioner kan ge viktiga insikter i det inre av en vulkan, såsom magmakammarensdjup, och därmed ge viktig data för tolkningen av aktiva vulkaner på Kanarieöarna och liknandeplatser.I detta arbete beräknades tryck och temperaturförhållanden utifrån kemin hos mineraletklinopyroxen och dess ursprungliga smälta. Detta gjordes med en metodik av Putirka (2008) samt enav Masotta et al. (2013) för att ytterligare begränsa djupet av mineraltillväxt. Geokemiskanalysutfördes vid Uppsala universitet med elektronmikrosond (EMPA) av insamlade stenprover för attbestämma de kemiska sammansättningarna som sedan användes i beräkningarna. Även kemiska datafrån omfattande arbete av Schirnick (1996) användes för att komplettera datasetet som anskaffadesunder detta arbete.När beräknat tryck från metoden av Masotta et al. (2013) omvandlats till djup, visar resultaten påatt kristallisation av klinopyroxen skedde på ca. 4 km (100 MPa) till ca. 15 km (400 MPa) djup, ochmed högst koncentration mellan ~ 7 km (200 MPa) och ~ 11 km (300 MPa) djup. Resultaten indikeraratt kristallisation skedde i tryckområdet motsvarande jordskorpans nivåer och möjligen nådde så långtner som till manteln, med temperaturer mellan ca 860 till 960 °C. Efter att ha kombinerat dessaresultat med andra bevis för aktiva magmatiska processer, från detta arbete och tidigare publikationer,uttrycker det magma systemet egenskaper som fraktionerad kristallisations trender och samtidigttecken på magma blandning, småskalig konvektion, och förorening av magma från jordskorpan. Föratt förklara dessa motstridiga egenskaper, främjar detta arbete ett nätverk av flera sammankopplademagmakammare som möjliggör magmatisk stagnation och utveckling på olika nivåer. Resultaten harsåledes bidragit till att ytterligare begränsa från vilket djup de inverterade kon-intrusionernahärstammar från Gran Canaria, Spanien.

No description available.

A travers deux champs d'étude, nous nous intéressons au couplage mécanique entre le magma et l'encaissant, utilisant des méthodes numériques. Tout d'abord, nous étudions l'influence de perturbations de contraintes sur les réservoirs magmatiques, avec comme exemple deux volcans sous-glaciaires (Islande). Au volcan Grímsvötn, notre modèle montre que les vidanges, du lac sous-glaciaire (jökulhlaup) présent dans la caldera, peuvent déclencher une éruption comme ce fut le cas en 2004, en favorisant la rupture du réservoir magmatique. L'effet est cependant faible, ce qui implique que le système magmatique doit déjà être proche des conditions de rupture avant que le jökulhlaup se produise. Au volcan Katla, notre modèle indique que les conditions de rupture sont favorisées en été durant la fonte du glacier Mýrdalsjökull. Les changements de contrainte de Coulomb montrent aussi une plus forte probabilité de séismes durant la même période, résultats en accord avec la sismicité enregistrée sous le Mýrdalsjökull. Il existe une modulation à la fois de l'activité volcanique et sismique au Katla, en relation avec la variation saisonnière de la charge glaciaire. Dans un second temps, nous travaillons sur les écoulements de magma dans les conduits andésitiques. Améliorer nos connaissances sur la dynamique du magma durant son ascension est nécessaire, car les processus dans le conduit volcanique semblent gouverner l'évolution de l'activité éruptive de ces volcans. Des précédents modèles ont montré que la viscosité du magma augmente dans la partie supérieure du conduit lors de l'écoulement, ce qui cause la formation d'un plug visqueux. Mais la relation entre la mise en place du plug et les signaux précurseurs, telles que la déformation ou la sismicité, n'est pas totalement établie. A partir de nos modèles de plug, nous trouvons que les déplacements de surface sont contrôlés par la géométrie du conduit et du plug ainsi que le contraste de viscosité entre le plug et la colonne de magma. Nous montrons que l'évolution de la taille du plug est une hypothèse possible pour expliquer les rapides transitions inflation/subsidence observées à la surface des volcans andésitiques. / Through two different applications, we focus on the mechanical coupling between magma and host rocks, using numerical method. First, we study the influence of stress perturbations on shallow magma chambers, with the exemple of two subglacial volcanoes (Iceland). A variation in the stress field acts to modify the magma pressure within the reservoir as well as the failure conditions to initiate an intrusion at the reservoir wall. At Grímsvötn volcano, subglacial lake discharges (so-called "jökulhlaup") often occur in relation to eruptions. Our models show that jökulhlaup promote the failure of the magma reservoir and thus trigger eruptions, as observed for 2004 eruption. The triggering effect is small, so magmatic system must be already pressurized and close to failure before the discharge of the lake occurs. At Katla volcano, our models indicate that reservoir failure is highest in summer period when the ice load at Mýrdalsjökull icecap is reduced. Coulomb stress calculation predicts also an increase of earthquake occurrence at the caldera rim at the same time. A seasonal modulation of volcanic and seismic activity at Katla related to the loading/unloading of the icecap can exist. Secondly, we focus on magma conduit flow for andesitic volcanoes. Improving our knowledge of magma dynamic during ascent is a challenge, because processes occurring in the conduit seem to govern the temporal evolution of eruptive activity. Previous models showed that magma viscosity increases during flow in the upper part of the conduit, which causes the emplacement of a viscous plug. But the relationship between the plug emplacement and precursors signals, such as ground deformation or seismicity, is not yet fully described. From our plug flow model, we find that surface deformation is mainly controlled by the geometry of the conduit, the ratio between the plug length and the total conduit length and the viscosity contrast between the plug and the magma column. We show that the evolution of the plug size is a possible explanation for rapid transition between ground inflation and ground subsidence observed on andesitic volcanoes before extrusion.