O presente trabalho investiga processos de interação e mistura parcial de magmas monzodioríticos e sieníticos s.l. no Plúton Piracaia,(~ 580 Ma), que pertence à Província Granítica Itu, de caráter pós-orogênico. O Plúton Piracaia é uma intrusão alongada com cerca de 30 km2, formada por cinco unidades: Monzodioritos grossos (Mdr); Monzodioritos finos (Mdf); Monzonitos heterogêneos (Mh); Sienitos (Sie); quartzo sienitos e quartzo monzonitos (Qsie). Como base para a caracterização dos processos de interação de magmas, foram estimados os parâmetros físico-químicos dos magmas primários e híbridos identificados no plúton. As temperaturas liquidus foram estimadas a partir da saturação em apatita, e são da ordem de 950-1050°C para os magmas mais primitivos (Mdf) e 850-900°C para os mais diferenciados (quartzo sienitos). As temperaturas solidus, estimadas através das relações de equilíbrio entre hornblenda e plagioclásio, são da ordem de 750°C para Mdf, e 650-700°C para Sienitos e quartzo sienitos (Qsie). A profundidade de alojamento do plúton é estimada em ~13-15 km com base nas pressões estimadas para Mdf com base no conteúdo de Al na hornblenda. A concentração de H2O nos magmas foi estimada com base no teor de An do plagioclásio, conhecida a temperatura de cristalização, que indicou valores da ordem de 2,5-3,3% para Mdf, alcançando até 5% nos quartzo sienitos. Estimativas da fO2 a partir da composição química de cristais de magnetita e ilmenita não puderam ser obtidas, devido a reequilíbrio pós-magmático. Deste modo, foram obtidos valores aproximados com base no conteúdo de ulvoespinélio de cristais de magnetita reconstituídos e no conteúdo da molécula ilmenita dos cristais de ilmenita; em paralelo, foram também utilizadas as razões Fe/(Fe/Mg) de anfibólio e biotita. Os resultados revelaram um importante contraste entre as unidades Mdf e Mdr, caracteristicamente oxidadas, com valores próximos aos do buffer NNO, e as demais unidades, onde quartzo sienitos (Qsie) e especialmente Sie mostram-se mais reduzidas. Os baixos valores de susceptibilidade magnética medidos em campo para as unidade Sie e Mh, que a ela se associa, devem ser reflexos do seu caráter mais reduzido. Ao longo da história de construção da câmara, que foi alimentada intermitentemente por magmas de composição variada, dois eventos principais de interação de magmas foram identificados, com características distintas: (i) interação de magmas monzodioríticos (Mdf) e sieníticos (Sie), gerando a unidade de Monzonitos heterogêneos (Mh), na qual a intensa interdigitação de porções monzodioríticas e sieníticas sugere uma forte atuação mecânica, favorecendo a hipótese de que os magmas tenham se misturado previamente ao alojamento final; e (ii) interação de magmas monzodioríticos (Mdf) e quartzo sieníticos (Qsie), gerando diversas estruturas de coexistência, mistura localizada e possivelmente as rochas quartzo monzoníticas da unidade ( Qsie); neste caso, a interação entre os magmas possivelmente ocorreu na câmara magmática, como sugerido pelas características das estruturas indicativas de coexistência (enclaves e pillows de composição monzodiorítica). / The present study investigates the interaction and partial mixing of monzodiorite and syenite s.l. magmas in the Piracaia Pluton (~580 My), which is part of the post-orogenic Itu Granite Province. The Piracaia Pluton is an elongated intrusion with approximately 30 km², composed by five units: Coarse-grained monzodiorites (Mdr); Fine-grained monzodiorites (Mdf); Heterogeneous monzonites (Mh); Syenites (Sie); quartz syenites and quartz monzonites (Qsie). The physico-chemical crystallization parameters of the primary and hybrid magmas identified in the pluton were determined as references for the characterization of the magma interaction processes. The liquidus temperatures were estimated based on apatite saturation, and are in the range of 950-1050º C for the most primitive magmas (Mdf) and 850-900º C for the more differentiated ones (quartz syenites). The solidus temperatures, estimated on the basis of the equilibrium between hornblende and plagioclase, are about 750º C for Mdf, and 650-700º C for and quartz syenites (Qsie). The depth of emplacement is estimated at 13-15 km, as indicated by pressure estimates for Mdf, based on the Al-in-hornblende content. The H2O concentration of the magmas was estimated based on the An content of plagioclase, with results are in the range of 2.5-3.3% for Mdf, reaching up to 5% in quartz syenites. fO2 estimates based on the composition of coexisting magnetite and ilmenite could not be performed, due to post-magmatic re-equilibration. However, approximate values were obtained based on the ulvospinel content of reconstructed titanomagnetite crystals, and on the content of ilmenite molecule in ilmenite crystals; in parallel, the Fe/(Fe/Mg) ratios of amphibole and biotite were also used. The results show an important difference between the Mdf and Mdr units, which are distinctively oxidized, with values near the NNO buffer, and the other units which have lower ?O2, the quartz syenites and especially the syenites being the more reduced units. The lower magnetic susceptibility values measured in the field for the Sie and Mh units must reflect their more reduced nature. During the construction of the magma chamber, which was intermittently recharged by magmas of varied composition, two main events of magma interaction with distinct characteristics were identified: (i) the interaction of monzodiorites (Mdf) and syenites (Sie), generating the Heterogeneous monzonite unit, in which the interfingering of monzodiorite and syenite portions suggest a strong mechanical interaction, favoring the hypothesis that the magmas were already mixing previously to the final emplacement; (ii) interaction of monzodiorite (Mdf) and quartz syenite (Qsie), generating diverse mingling structures, local hybridization and possibly the quartz monzonite rocks of the unit Qsie; in this case, the magma interaction must have occurred at the magma chamber, as suggested by the type of structures indicative of coexistence (enclaves and monzodiorite pillows).

O presente trabalho investiga processos de interação e mistura parcial de magmas monzodioríticos e sieníticos s.l. no Plúton Piracaia,(~ 580 Ma), que pertence à Província Granítica Itu, de caráter pós-orogênico. O Plúton Piracaia é uma intrusão alongada com cerca de 30 km2, formada por cinco unidades: Monzodioritos grossos (Mdr); Monzodioritos finos (Mdf); Monzonitos heterogêneos (Mh); Sienitos (Sie); quartzo sienitos e quartzo monzonitos (Qsie). Como base para a caracterização dos processos de interação de magmas, foram estimados os parâmetros físico-químicos dos magmas primários e híbridos identificados no plúton. As temperaturas liquidus foram estimadas a partir da saturação em apatita, e são da ordem de 950-1050°C para os magmas mais primitivos (Mdf) e 850-900°C para os mais diferenciados (quartzo sienitos). As temperaturas solidus, estimadas através das relações de equilíbrio entre hornblenda e plagioclásio, são da ordem de 750°C para Mdf, e 650-700°C para Sienitos e quartzo sienitos (Qsie). A profundidade de alojamento do plúton é estimada em ~13-15 km com base nas pressões estimadas para Mdf com base no conteúdo de Al na hornblenda. A concentração de H2O nos magmas foi estimada com base no teor de An do plagioclásio, conhecida a temperatura de cristalização, que indicou valores da ordem de 2,5-3,3% para Mdf, alcançando até 5% nos quartzo sienitos. Estimativas da fO2 a partir da composição química de cristais de magnetita e ilmenita não puderam ser obtidas, devido a reequilíbrio pós-magmático. Deste modo, foram obtidos valores aproximados com base no conteúdo de ulvoespinélio de cristais de magnetita reconstituídos e no conteúdo da molécula ilmenita dos cristais de ilmenita; em paralelo, foram também utilizadas as razões Fe/(Fe/Mg) de anfibólio e biotita. Os resultados revelaram um importante contraste entre as unidades Mdf e Mdr, caracteristicamente oxidadas, com valores próximos aos do buffer NNO, e as demais unidades, onde quartzo sienitos (Qsie) e especialmente Sie mostram-se mais reduzidas. Os baixos valores de susceptibilidade magnética medidos em campo para as unidade Sie e Mh, que a ela se associa, devem ser reflexos do seu caráter mais reduzido. Ao longo da história de construção da câmara, que foi alimentada intermitentemente por magmas de composição variada, dois eventos principais de interação de magmas foram identificados, com características distintas: (i) interação de magmas monzodioríticos (Mdf) e sieníticos (Sie), gerando a unidade de Monzonitos heterogêneos (Mh), na qual a intensa interdigitação de porções monzodioríticas e sieníticas sugere uma forte atuação mecânica, favorecendo a hipótese de que os magmas tenham se misturado previamente ao alojamento final; e (ii) interação de magmas monzodioríticos (Mdf) e quartzo sieníticos (Qsie), gerando diversas estruturas de coexistência, mistura localizada e possivelmente as rochas quartzo monzoníticas da unidade ( Qsie); neste caso, a interação entre os magmas possivelmente ocorreu na câmara magmática, como sugerido pelas características das estruturas indicativas de coexistência (enclaves e pillows de composição monzodiorítica). / The present study investigates the interaction and partial mixing of monzodiorite and syenite s.l. magmas in the Piracaia Pluton (~580 My), which is part of the post-orogenic Itu Granite Province. The Piracaia Pluton is an elongated intrusion with approximately 30 km², composed by five units: Coarse-grained monzodiorites (Mdr); Fine-grained monzodiorites (Mdf); Heterogeneous monzonites (Mh); Syenites (Sie); quartz syenites and quartz monzonites (Qsie). The physico-chemical crystallization parameters of the primary and hybrid magmas identified in the pluton were determined as references for the characterization of the magma interaction processes. The liquidus temperatures were estimated based on apatite saturation, and are in the range of 950-1050º C for the most primitive magmas (Mdf) and 850-900º C for the more differentiated ones (quartz syenites). The solidus temperatures, estimated on the basis of the equilibrium between hornblende and plagioclase, are about 750º C for Mdf, and 650-700º C for and quartz syenites (Qsie). The depth of emplacement is estimated at 13-15 km, as indicated by pressure estimates for Mdf, based on the Al-in-hornblende content. The H2O concentration of the magmas was estimated based on the An content of plagioclase, with results are in the range of 2.5-3.3% for Mdf, reaching up to 5% in quartz syenites. fO2 estimates based on the composition of coexisting magnetite and ilmenite could not be performed, due to post-magmatic re-equilibration. However, approximate values were obtained based on the ulvospinel content of reconstructed titanomagnetite crystals, and on the content of ilmenite molecule in ilmenite crystals; in parallel, the Fe/(Fe/Mg) ratios of amphibole and biotite were also used. The results show an important difference between the Mdf and Mdr units, which are distinctively oxidized, with values near the NNO buffer, and the other units which have lower ?O2, the quartz syenites and especially the syenites being the more reduced units. The lower magnetic susceptibility values measured in the field for the Sie and Mh units must reflect their more reduced nature. During the construction of the magma chamber, which was intermittently recharged by magmas of varied composition, two main events of magma interaction with distinct characteristics were identified: (i) the interaction of monzodiorites (Mdf) and syenites (Sie), generating the Heterogeneous monzonite unit, in which the interfingering of monzodiorite and syenite portions suggest a strong mechanical interaction, favoring the hypothesis that the magmas were already mixing previously to the final emplacement; (ii) interaction of monzodiorite (Mdf) and quartz syenite (Qsie), generating diverse mingling structures, local hybridization and possibly the quartz monzonite rocks of the unit Qsie; in this case, the magma interaction must have occurred at the magma chamber, as suggested by the type of structures indicative of coexistence (enclaves and monzodiorite pillows).

Field evidence from exposed plutonic rocks indicates that mafic-felsic magma interaction is an important process during the construction and evolution of magma chambers. The exhumed, ~140 Ma, Halfmoon Pluton of Stewart Island, New Zealand is characterized by a sequence of mingled mafic sheets and enclaves preserved within an intermediate-felsic host, and provides a unique opportunity to directly investigate the physico-chemical processes that operate within an arc setting. Interpretation of mingling structures and textures in the field, in combination with extensive petrographic, geochemical and geochronological data, allow for conclusions to be reached regarding the nature of the mafic-felsic magma interactions, and the physical, chemical and thermal processes responsible for the generation and evolution of the calc-alkaline magmas. Detailed documentation and interpretation of mafic-felsic magma mingling structures and textures reveal that the Halfmoon Pluton formed incrementally as the result of episodic replenishments of mafic magma emplaced onto the floor of an aggrading intermediate-felsic magma chamber. Physico-chemical processes identified include fractional crystallization and accumulation of a plagioclase – hornblende – apatite – zircon mineral assemblage, episodic replenishment by hot, wet basaltic magmas, magmatic flow and compaction. Early amphibole and apatite crystallization played an important role in the compositional diversity within the Halfmoon Pluton. Variations in the style of magma mingling preserved within the magmatic “stratigraphy” indicate that processes operating within the chamber varied in space and time. Variations in mineral zoning and composition within hornblende indicate that the Halfmoon Pluton crystallized within a magma in which melt composition fluctuated in response to repeated mafic magma replenishments, fractionation, crystal settling and convection. Mineral assemblages, chemical characteristics, isotopic data and geochronological evidence indicate that the amphibole-rich calc-alkaline Halfmoon Pluton was emplaced into a juvenile arc setting, most probably an island-arc. Data are consistent with a model whereby ‘wet’ amphibole-rich basaltic magmas pond at the crust-mantle interface and episodically rise, inject and mingle with an overlying intermediate-felsic magma chamber that itself represents the fractionated product of the mantle melts.

Field evidence from exposed plutonic rocks indicates that mafic-felsic magma interaction is an important process during the construction and evolution of magma chambers. The exhumed, ~140 Ma, Halfmoon Pluton of Stewart Island, New Zealand is characterized by a sequence of mingled mafic sheets and enclaves preserved within an intermediate-felsic host, and provides a unique opportunity to directly investigate the physico-chemical processes that operate within an arc setting. Interpretation of mingling structures and textures in the field, in combination with extensive petrographic, geochemical and geochronological data, allow for conclusions to be reached regarding the nature of the mafic-felsic magma interactions, and the physical, chemical and thermal processes responsible for the generation and evolution of the calc-alkaline magmas. Detailed documentation and interpretation of mafic-felsic magma mingling structures and textures reveal that the Halfmoon Pluton formed incrementally as the result of episodic replenishments of mafic magma emplaced onto the floor of an aggrading intermediate-felsic magma chamber. Physico-chemical processes identified include fractional crystallization and accumulation of a plagioclase – hornblende – apatite – zircon mineral assemblage, episodic replenishment by hot, wet basaltic magmas, magmatic flow and compaction. Early amphibole and apatite crystallization played an important role in the compositional diversity within the Halfmoon Pluton. Variations in the style of magma mingling preserved within the magmatic “stratigraphy” indicate that processes operating within the chamber varied in space and time. Variations in mineral zoning and composition within hornblende indicate that the Halfmoon Pluton crystallized within a magma in which melt composition fluctuated in response to repeated mafic magma replenishments, fractionation, crystal settling and convection. Mineral assemblages, chemical characteristics, isotopic data and geochronological evidence indicate that the amphibole-rich calc-alkaline Halfmoon Pluton was emplaced into a juvenile arc setting, most probably an island-arc. Data are consistent with a model whereby ‘wet’ amphibole-rich basaltic magmas pond at the crust-mantle interface and episodically rise, inject and mingle with an overlying intermediate-felsic magma chamber that itself represents the fractionated product of the mantle melts.

To understand the complex structure of magmatic plumbing systems beneath volcanoes, one needs to study the different textures shown in the igneous rocks produced by the volcano in question. By doing this, one can get a clue of the processes that resulted in the final rock. One of the most important methods to use for studying rock samples is the Crystal Size Distribution (CSD), which can reveal a great amount of information about the history of the rock and give an insight in the journey of the crystals during their time in the magma. An extinct volcano named Chachahuén, located in Argentina, South America, was chosen for this study. Samples of rock were collected from one of its laccoliths named Cerro Bayo and was identified as hornblende-bearing dacite. The difference in crystal size was very significant in these samples, with both larger and smaller crystals embedded in the same matrix. This is interesting considering the fact that large crystals form by slow cooling of the magma while smaller crystals form as the magma cools rapidly. By studying the CSD and interpreting other textures found in samples of igneous rock, one may interpret different processes which affected the crystals, indicating what the structure of the magma chamber once looked like. / För att kunna förstå den komplexa strukturen hos magmatiska system under vulkaner måste man studera olika texturer som påträffas i de magmatiska bergarter producerade av vulkanen i fråga. Genom att göra detta kan man få en inblick i de processer som resulterade i den slutgiltiga bergarten. En av de viktigaste metoderna att använda sig av för att studera stenprov är kristallstorleksfördelningen (CSD), som kan avslöja en mängd viktig information om bergarten och kristallernas historia under sin färd i magman. En slocknad vulkan vid namn Chachahuén belägen i Argentina, Sydamerika, valdes ut för denna studie. Stenprover samlades från en av dess lakkoliter med namnet Cerro Bayo, och identifierades som hornblände-bärande dacit. Skillnaden i kristallstorleken var mycket markant, med både större och mindre kristaller inbäddade i samma matrix. Detta är intressant med tanke på att stora kristaller bildas under en långsam nedkylning av magma medan mindre kristaller bildas när magma kyls ner snabbt. Genom att studera CSD och tolka andra texturer som finns hos magmatiska stenprover kan man tolka olika processer som har påverkat kristallerna, vilket i sin tur indikerar hur strukturen av magmakammaren en gång såg ut.

Understanding U-series isotopic disequilibria of partially melted crust is integral for determining the effect that crustal assimilation has on the U-series signature of magmas. In this work, U, Th and Ba (as a proxy for Ra) elemental abundances were gathered on the quenched glass in partially melted crustal xenoliths of granitic composition using microbeam techniques. The crustal xenoliths, which are found in basaltic lava, from Mirador Volcano in Chile, are old, and can be assumed to be at secular equilibrium, whereas melting occurred during eruption of Mirador in 1979. A comparison of the ratios Ba/Th and U/Th in the partial melts with those of the whole rock reveal how much fractionation has occurred during partial melting. Different ratios of U, Th and Ba compared to the whole rock substantiate fractionation via partial melting. Thus, assimilation of partial melts of crust can play a role in U-series isotopic disequilibria.

Student Number : 0201438A - PhD thesis - School of Geosciences - Faculty of Science / This project focuses on the Upper Critical and Lower Main Zones in the eastern Bushveld Complex, South Africa. Lithological and stratigraphic information show that there are distinct differences at this level between the eastern and western limbs of the complex. Geochemical studies are centred on the Merensky and Bastard Cyclic Units in which the platiniferous Merensky Reef occurs. A major geochemical hiatus occurs in the Bushveld Complex at the level of the platiniferous Merensky Reef, close to the Critical/Main Zone boundary. The origin of this hiatus and its relation to mineralisation has not been fully resolved. Geochemical parameters are investigated that allow minerals in the Merensky and Bastard Cyclic Units to be classified as originating from either Critical or Main Zone magmas. Modelling of element ratios (Ni/Y, Cr/Ni, Cr/Co, Y/Co, Cr/V, Co/V and Cr/MgO) demonstrates the varying reliability of using ratios as geochemcial tools to constrain magma influxes within a chamber. However, it is shown that the Cr/MgO ratio is effective in determining real differences across the Critical/Main Zone boundary that are independent of lithology. In addition, initial Sr isotope ratios for plagioclase are significantly different in Critical and Main Zone rocks. Geochemical data through the Merensky and Bastard Cyclic Units indicate that orthopyroxene that originated from magma with composition like that of the Critical Zone magma sometimes occurs together with plagioclase that originated from Main Zone magma. In detail, in the pyroxenite at the base of the Merensky Unit, both plagioclase and orthopyroxene display Critical Zone signatures, but in the overlying part of the Merensky Cyclic Unit, plagioclase increasingly shows a Main Zone signature, whereas orthopyroxene continues to display a Critical Zone signature. Similarly, in the Bastard pyroxenite, Sr isotopes and absolute Sr in plagioclase display a range of values from Main Zone to Critical Zone, but orthopyroxene consistently displays Critical Zone affinity. These observations of mineral disequilibrium clearly show that the two major minerals in the Merensky and Bastard Cyclic Units were formed from two different, but coexisting, magmas. A model that accounts for this disequilibrium is proposed here. It invokes the influx of Main Zone magma at the level of the base of the Merensky unit that dispalced the Critical Zone magma upward, but the two magmas did not mix. The latter continued to crystallise orthopyroxene which sank through the Main Zone influx, due to its density contrast. These crystals collected on the crystal pile to form the Merensky pyroxenite. The Main Zone magma, into which the cumulus Critical Zone orthopyroxene accumulated, crystallised interstitial plagioclase that had a Main Zone Sr isotopic ratio. Whole-rock, major element geochemical data show that a variable proportion of the plagioclase in both the Merensky and Bastard pyroxenites is cumulus. It is inferred to have accumulated with orthopyroxene and has a Critical Zone initial Sr isotope ratio. Thus the two pyroxenites now yield a mixed Sr isotopic signature of Critical Zone cumulus and Main Zone intercumulus and possibly cumulus plagioclase that varies along strike. Above the two pyroxenites, the Sr signature of the norites and anorthosites of both cyclic units is dominated by cumulus plagioclase from the Main Zone magma. It is concluded that the variations in initial Sr isotope ratios do not result from mixing of magmas, but result from accumulation of orthopyroxene and plagioclase from a higher, isotopically distinct layer of magma into an underlying layer. The Merensky and Bastard Cyclic Units therefore display features of Critical or Main Zone magma characteristics depending upon which chemical parameter is considered. These cycles are therefore classified as a Transitional Unit.

Structures and deformation mechanisms of magmatic rocks are controlled by rheology. An increase in melt fraction can weaken a rock body and localises significant amount of strain. This interplay between rheology, melting and deformation in a magma reservoir, however, is not always clearly documented in literature. Therefore, this thesis illustrates the Syn-Magmatic Deformation Features (SMDFs) discovered in the Slaufrudalur pluton in Iceland. The goal of this thesis is to test whether these features formed during the emplacement of the Slaufrudalur pluton. Field mapping, microscopy, geochemistry analysis, electron microprobe analysis (EMPA) and Raman spectroscopy were employed to document and investigate the formation of these features and their relationships with the pluton. The SMDFs bear sharp contacts with the host granite and are divided into two types according to their morphology: 1) Type I SMDFs resemble shear zone with internal deformation fabric. 2) Type II SMDFs resemble magmatic dykes. The Type I SMDFs are interpreted as melt-assisted shearing structures while Type II SMDFs are interpreted as magmatic dykelets. Previous studies postulated that amalgamation of magma batches was responsible for the emplacement of the large plutons. Frequent injection of magma batches built up internal pressure and increased internal temperature of the emplacing pluton, which allowed the pluton to stay partially molten and mechanically weak. This allowed the mixing and mingling of different magma batches, resulting in the occurrence of various structures within the pluton. Solidified magma batches could also be re-mobilised to form mush or magma. The difference in formation mechanisms hints different rheology heterogeneity within the Slaufrudalur pluton. Hence, the occurrence of SMDFs is directly linked to the Slaufrudalur pluton during its emplacement. / Linking Magma Batch Intrusion to the Construction of Geothermal Systems and Mineral Deposits

Cone-sheet swarms are magmatic sheet intrusions and part of volcanic plumbing systems and are pathways for magma to the Earth’s surface, where they feed volcanic eruptions. The analysis of cone-sheets provides information on the geometry of the magmatic plumbing system of a volcano and allows to understand processes and dynamics of magma transport. This is important to interpret information during a volcanic crisis and to help reduce risks to humans and infrastructure. In order to create a realistic model, the structure and shape of cone-sheet complexes can be reconstructed in three-dimensional space. Most cone-sheet swarms are not sufficiently exposed to allow such a reconstruction. The Tejeda cone-sheet swarm on Gran Canaria (Canary Islands, Spain), however, is an excellent location to study a cone-sheet complex in great detail, as it is exposed over 15 kmhorizontally and 1000 m vertically. This allows to determine its geometry in 3D space. The felsic deposits of the Miocene Tejeda caldera were intruded by cone-sheets between 11.7 and 7.3 Ma. Schirnick et al. (1999) assumed straight cone-sheets, based on 2D projections, and suggested that the Tejeda cone-sheet swarm is formed by a stack of uniformly dipping, parallel intrusive sheets that converge towards a common, static, laccolith-like source, forming a concentric structure around acentral axis that has the geometry of a truncated cone. This hypothesis was tested in this study, using structural data from Schirnick (1996) as well as additional data collected in the field. Using the software Move™, the extensive data set was visualized and projected in three dimensional space. The underlying magmatic source of the cone-sheets was reconstructed using two different approaches, with the first one based on sets of cross-sections to select intersection points, following an approach prognosed by Burchardt et al. (2013a). To improve the quality of the reconstruction of the magma chamber, a second method was developed using geometric calculations in MATLAB. The results indicate that individual cone-sheets are straight with parallel to slightly fanning dips, which can be steeper in the central part of the cone-sheet complex. They converge towards a common centre, creating a sub-spherical geometry of the source of the cone-sheet complex. Comparison of the two approaches used for the magma chamber reconstruction indicate that the second approach (geometric calculations) produces less uncertainties in data interpretation. The modelling results lead to the proposition of a dynamic model for the emplacement of the Tejeda cone-sheet complex. Cone-sheets would start to intrude from a reservoir situated at about 4500m below sea level that became successively shallower with time. / Inverterade koniska intrusionssvärmar är en del av det underjordiska vulkaniska systemet som möjliggör vägar för magma till jordens yta, där de livnär vulkaniska utbrott. Genom analys av inverterade koniska intrusioner kan information om geometrin hos magmatiska system erhållas vilket gör det möjligt att förstå magmans processer och transportdynamik. Detta är viktigt då det hjälper att tolka information under vulkaniska kriser och kan bidra till att minska risker för människor och infrastruktur. För att skapa en realistisk modell, kan strukturer och former av komplexa inverterade koniska intrusionssvärmar rekonstrueras i ett tredimensionellt utrymme. De flesta inverterade koniska intrusionssvärmar är inte tillräckligt blottade på jordens yta för att möjliggöra en sådan rekonstruktion.Tejedas inverterade koniska intrusionssvärm på Gran Canaria (Kanarieöarna, Spanien) är dock utmärktbelägen för att studera ett inverterat koniskt intrusionskomplex i detalj, detta då den är blottad i över 15 km horisontell och 1000 m i vertikal utsträckning. Detta gör det möjligt att bestämma dess geometrii tre dimensioner. De felsiska avlagringarna av den Miocena Tejeda kalderan blev intruderade av inverterade koniskaintrusioner mellan 11,7 och 7,3 Ma. Schirnick et al. (1999) antog att dessa intrusioner var raka, baseratpå 2D-projektioner, och föreslog att Tejedas inverterade koniska intrusionssvärm bildades som enlikformigt stupande stapel av parallella intruderande plan som konvergerar mot en gemensam, statiskoch lakkolitisk källa, vilken i sin tur bildar en koncentrisk struktur runt en central axel med samma geometri som en inverterad stympad kon. Denna hypotes undersöktes i detta arbete, med hjälp avstrukturell data från Schirnick (1996) samt ytterligare data insamlat från fält. Den omfattande datamängden visualiserades och projicerades i tre dimensioner med hjälp av mjukvaran Move™. Denunderliggande magmatiska källan till det inverterade koniska intrusionskomplexet rekonstruerades medhjälp av två olika metoder, den första är baserad på tvärsnitt där planens skärningspunkter kan studeras, följt av ett tillvägagångssätt framställt av Burchardt et al. (2013a). För att förbättra kvalitén pårekonstruktionen av magmakammaren utvecklades en andra metod med hjälp av geometriskaberäkningar i MATLAB. Resultaten tyder på att enskilda inverterade koniska intrusioner är raka med parallellt till svagt flacktstupning, vilka kan vara brantare mot den centrala delen av komplexet. De konvergerar mot ettgemensamt centrum, vilket skapar en sub-sfärisk geometri hos källan till det inverterade koniskaintrusionskomplexet. Jämförelse av de två metoderna som används för magmakammarens rekonstruktion tyder på att denandra metoden (geometriska beräkningar) ger färre osäkerheter i tolkningen. Modelleringsresultatettyder på en dynamisk modell för bildningen av Tejedas inverterade koniska intrusionskomplex. Enligtdessa resultat skulle de inverterade koniska intrusionerna till en början ha utgått från en reservoarungefär 4500 m under havsytan som med tiden förflyttade sig mot grundare nivåer.

Southeast Iceland exhibits a granophyre pluton called Reyðarártindur, which has never been described in detail before. The Reyðarártindur magma chamber formed 7.30 ± 0.06 Ma ago (Padilla, 2015). Glacial and coastal erosion expose the pluton, and a river cuts through the pluton roof and walls, revealing interaction between different blob-like structures of magma. The formation of magma chambers can take a very long time, it is therefore likely for several different magmas to interact. Incremental formation of different magma batches give rise to mixing and mingling in magma chambers. To understand when the magma mixing was initiated and the mechanisms controlling it, descriptive analysis were made to obtain textural properties of collected rock samples from the field. The purpose for this thesis study was to examine if there is a frequency size and shape distribution of the magma blobs and if the different magma blobs are systematically distributed across the river. Previous studies have inferred conduit locations and magma mixing processes through similar methods. Extensive field studies have provided all samples for this thesis. Five distinct, magma types were described and found to be interacting. There was one ‘host magma’ which the other four different magma types are exposed as ‘blobs’ within. The statistical analysis involved mapping the blob-like structures from photos taken with an Unmanned Aerial System (URA; drone), using the software Inkscape. The data and measurements for the blobs was collected and summarized in ImageJ. The data was then statistically analyzed in Excel, illustrating the frequency of the magma blob’s size and shape distribution in selected parts of the river. The results of the statistical analysis of the magma blobs showed that ~80 % of the blobs existed in a size interval between 0 – 0.1 m2 . This thesis provides a discussion about the implications of the blob distributions for magma chamber recharge and processes within this section of the magma chamber. The shape distribution analysis showed an indication for all the blobs to be more rounded and equant. This suggest that the magma mixing event probably happened at the same time, during a liquid phase. / På sydöstra Island återfinns en granofyrisk pluton kallad Reyðarártindur. Det är en magmakammare som aldrig tidigare blivit beskriven i detalj. Magmakammaren bildades för 7,30 ± 0,06 Ma sedan (Padilla, 2015). Plutonen har blivit exponerad genom glacial- och fluvial erosion samt att en flod skär igenom plutonens tak och väggar. Den eroderande floden exponerar olika fläckliknande strukturer av magmainteraktioner. Ett gradvist bildande av olika magmasatser har över lång tid gett upphov till en blandning i magmakammaren. För att förstå när magmablandningen initierades och mekanismerna bakom fenomenet, har en beskrivande analys gjorts för att ta reda på texturella egenskaper av insamlade bergartsprover från fält. Syftet med denna studie var att undersöka om det fanns en storleks- och formdistribuering av magmafläckarna samt om de olika magmafläckarna är systematiskt distribuerade i flodbädden. Tidigare studier har antytt var undersökta magmakanalsystemen kan finnas samt hur blandningsprocesser för magma går till med hjälp av liknande metoder. Redan genomförda fältstudier har samlat in allt råmaterial som ligger till grund för denna studie. Fem olika magmatyper har beskrivits och påvisades interagera. Det fanns en ”värdmagma” som de andra fyra magmatyperna var exponerade som fläckar i. De statistiska analyserna inkluderade kartering av de fläckliknande magmaformerna baserat på foton tagna med hjälp av en drönare. Tre olika mjukvaror användes för att samla in, mäta och analysera data; Inkscape, Image J och Excel. Resultaten från den statistiska analysen visade att ungefär 80 % av alla fläckar existerade inom ett areaintervall mellan 0 – 0,1 m2 . Denna studie innehåller en diskussion om implikationerna av magmafläckarnas distribution med avseende på magmaomladdning och -processer inuti denna sektion av magmakammaren. Den generella formdistributionen visade en indikation för att alla fläckar tenderar att vara mer rundade och kvadratiska. Detta antyder att magmans blandningsförlopp troligtvis inträffade vid ungefär samma tidpunkt, under en flytande fas.