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 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.