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Browsing by study line "Berggrundsgeologi och ekonomisk geologi"

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  • Leppälä, Timo (2024)
    Tiivistelmä/Referat – Abstract The Geological Survey of Finland (GTK) conducted extensive bedrock mapping and sampling along the southern border of the Central Finland Granitoid Complex (CFGC) between 2016–2017. The 40000 km2 complex was formed during the early stages of the 1.92–1.77 Ga Svecofennian orogeny and is dominated by felsic plutonic rocks. The main crust-forming phase at 1.91–1.87 Ga generated the felsic syn- and postkinematic suites during active subduction. Jyväskylä suite corresponds to the synkinematic rocks (1.89–1.88 Ga) and Saarijärvi and Rautalampi suites to the postkinematic (1.88–1.87 Ga). Previous studies have divided the postkinematic rocks into Types 1, 2, 3a and 3b, of which Types 1–3a represent the Saarijärvi suite and Type 3b the Rautalampi suite. The postkinematic suites are bimodal because of the local mafic association. Volcanic rocks associated to a continental margin setting are especially found along the southern-southwestern margin of the CFGC. Abundant metasediments with a mainly turbiditic origin surround the complex. The purpose of this thesis is to classify the granitoids and dioritoids of the Jämsä region into either the syn- or postkinematic types, discuss their petrogenesis and compare the data to the adjacent volcanic rocks. New petrographical, geochemical and geochronological data are used to set the plutonic rocks into the regional geological framework. Six distinct types are recognized from the study area: Mettisuo, Akkasuo, Linjamaa, Haavistonmäki, Kalaoja and Hangasjärvi. The first three were found to be synkinematic (Jyväskylä) and the last three postkinematic (Saarijärvi) with respect to the orogenic stages. The synkinematic Mettisuo (1890 ± 4 Ma) and Akkasuo-type (1880 ± 6 Ma) equigranular to inequigranular granitoids are metaluminous to peraluminous with Akkasuo being slightly more mafic. They have higher CaO and Sr and lower K2O and FeOt/MgO than the postkinematic types. The Linjamaa-type inequigranular dioritoids represent the Vaajakoski quartz diorite lithodeme (Jyväskylä suite) owing to their more juvenile character. However, there are discrepancies within the Linjamaa division. Partial melting of biotite- and hornblende-rich high-K calc-alkalic rocks by basaltic underplating produced the synkinematic types, leaving behind a granulitic residue. The Haavistonmäki-type (1876 ± 7 Ma) alkali feldspar-porphyritic granites are postkinematic Type 1 with a sedimentary component from the Pirkanmaa migmatite belt. They are peraluminous with low Na2O and FeOt/MgO and high FeOt and Al2O3. The Kalaoja-type inequigranular to porphyritic granitoids are transitional between postkinematic Types 2 and 3. The lack of fluorite and pyroxenes complicate the classification. They are metaluminous to peraluminous with relatively low FeOt, MgO and CaO and higher FeOt/MgO and K2O. The Hangasjärvi-type (1885 ± 5 Ma) granitoids are silica-rich, resembling postkinematic Type 2. They differ from the Kalaoja rocks by their equigranular to inequigranular character, but the same mineralogical restrictions apply in the classification. A mantle-derived basaltic magma assimilated variable amounts of the lower crust, producing the postkinematic magmas. A depleted granulitic residue likely does not produce sufficient amounts of K2O and LILE contents for the postkinematic magmas. The postkinematic types are bimodal because of the locally associated mafic rocks. The volcanic rocks of the study area belong to the same continental subduction environment, are locally coeval and share a partially similar origin as the Jyväskylä suite and the mafic members of the Saarijärvi suite.
  • Karampelas, Nikolaos (2022)
    Archean cratons hold information of the early crustal development of the Earth, in conditions much different than the ones that exist today. Archean cratons consist of felsic plutonic rocks and greenstone belts. These belts are a useful tool for the understanding of the development of the early geological processes that shaped the Earth. There has been a variety of suggestions regarding the origin and geodynamic conditions that formed the Archean greenstone belts and there are several possible geotectonic scenarios that could form them. This thesis focuses on the Takanen greenstone belt found in the Karelia province in the Fennoscandian shield. The main objective of this study is to constrain the age of the greenstone belt, as well as to classify and group the formations found in it and compare it with its neighbouring, and much larger, Suomussalmi-Kuhmo-Tipasjärvi greenstone belt system - the biggest complex of its kind in the Karelian craton. A diamond drilling profile across the Takanen belt has been sampled. The various rocks found in the belt are divided into 5 groups based on their thin-section petrography and major and trace element geochemistry, outlining the general stratigraphy of the belt. There are also whole rock analyses that help to obtain major and trace element geochemical data for multiple samples from different locations throughout the belt. There are 3 calc-alkaline units (CALC1, CALC2, CALC3, named after their predominantly calc-alkaline nature) that include felsic, to intermediate volcanic/volcanosedimentary rocks and 2 units that consist of channelized komatiitic lavas and tholeiitic basalts (KOMBAS, named after the komatiites and basalts of the unit), olivine/olivine-pyroxene cumulates and high-Mg to tholeiitic basalts (OLIAD, named after the abundance of olivine adcumulates). The CALC1 unit is found lowest in the stratigraphy of the area and bares the oldest age of 2.95 Ga, while CALC3, which is the youngest formation of the belt, gives an age of 2.7 Ga. There is a direct correlation with the lowest CALC1 unit and the Luoma group in the Suomussalmi greenstone belt in terms of petrography, geochemistry and age, indicating that Takanen is the continuation of the Suomussalmi-Kuhmo-Tipasjärvi system to the north. Based on the initial Lu-Hf isotope composition of the dated samples, and the stratigraphic layering of Takanen, the oldest units in the belt originate from a process of continental rifting, while the youngest ones were most likely formed by a combination of continental rifting and some interaction of the continental crust with oceanic lithosphere. The Takanen greenstone belt lies on top of a large positive gravimetric and magnetic anomaly in the Koillismaa area called the ‘‘hidden dyke’’, composed of mafic-ultramafic cumulates and hypothesized to be related to the Paleoproterozoic Koillismaa-Näränkävaara Layered Intrusion Complex. The dyke and Takanen may not be genetically related, yet their overlapping existence points to a large crustal structure that served as a magma pathway throughout the Archean and the Paleoproterozoic. The potential of an economic orthomagmatic nickel deposit related to Takanen should not be completely overlooked, as there are some favorable indications in the geochemistry of the komatiitic units, as well as their possible interaction of these units with older sulphur rich units of the belt.
  • Markkanen, Minna (2021)
    The orbicular quartz monzonite from Kuohenmaa, Southwest Finland, is one of the most beautiful and well-known orbicular rocks in the world. The cores of the orbicules are peraluminous in composition, most likely of xenolithic metasedimentary origin. The cores are surrounded by orbicule mantles, which consist of several alternating biotite- and plagioclase-rich shells. There are three types of orbicules in Kuohenmaa orbicular rock: proto-, small-, and large-orbicular types. Proto-orbicules have only a few shells, small orbicules ~ 50 shells in average, and large orbicules over 250 distinct shells. In addition to shells, one sample was observed to be associated with comb layering in the contact of proto-orbicular and large orbicular types. Structures and textures of the comb layer resembles those of the outer shells of large orbicules. The orbicules are embedded in interstitial coarse-grained groundmass that forms locally almost pegmatitic patches. The petrographic observations were acquired from eight samples or sample photographs gathered from different collections. A mineral chemistry dataset was measured from a single large orbicule from the University of Helsinki collections. The main minerals of the Kuohenmaa orbicular rock are plagioclase, biotite, microcline, muscovite, and chlorite. The shell textures vary from branching plagioclase-rich shells to fine-grained plagioclase- or biotite-rich shells. Branching shells are mainly oligoclase, but a few granular andesine crystals were detected in the core. Peculiar interstitial fibrous allanite masses were found in the inner branching plagioclase-rich shells. The plagioclase compositions generally follow a regular fractional crystallization trend from core to groundmass, but some changes towards more primary compositions are observed in the orbicule mantle. Plagioclase crystals display only minor compositional zoning, suggesting rather quick crystallization. Biotite is very aluminous (Al2O3 17.63–18.53) in composition, and the compositional changes seem to have somewhat positive correlation with plagioclase compositions, suggesting changes in their crystallization conditions. Injections of primary melt from a deeper source most likely caused the observed changes to more primitive composition in plagioclase and biotite composition. Through the detailed petrographic and geochemical studies, a model of undercooling caused by decompression driven fluid saturation is proposed as a mechanism for orbicule formation in the Kuohenmaa orbicular rock. Branching plagioclase with interstitial fibrous allanite masses and several fluid inclusions in plagioclase indicates separate aqueous REE-enriched melt and rapid crystallization. Further studies of fluid inclusions and REE-enriched phases could provide information of the fluid origin and crystallization conditions.
  • Hakala, Heini (2021)
    A NW–SE trending dike swarm cuts Miocene volcanic rocks in the Ibex Hills and Precambrian to Cambrian cratonic rocks and sedimentary strata in the Saddlepeak Hills and Salt Spring Hills in southern Death Valley, California. These dikes are aligned with Jurassic and Cretaceous dike swarms of eastern California that are linked to the Mesozoic North American Cordilleran magmatism. The Ibex Hills dikes have been previously dated and yield K-Ar date of 12.7 Ma and are coeval with the early stage of the Miocene Basin and Range crustal extension in Death Valley. This Master’s thesis examines in detail the geology, petrography and geochemistry of the previously unstudied dikes of Ibex Hills, Saddlepeak Hills and Salt Spring Hills of southern Death Valley and a ~90 Ma dike of Mojave Desert to discuss (1) their petrogenetic link to each other and (2) their geologic significance. The samples and field observations were obtained in 2019. The Ibex Hills samples are relatively fresh compared to the dikes of Saddlepeak Hills and Salt Spring Hills which are pervasively altered by secondary minerals and have been subject to low-grade metamorphism. The sub-solidus processes that have modified the mineral assemblages of the metamorphic dikes are also reflected in various degrees of major element mobility and LOI. The whole-rock geochemical composition of the Ibex Hills and Mojave Desert samples is trachyandesite to trachyte, the Saddlepeak Hills and Salt Spring Hills samples are andesites. One Saddlepeak Hills sample is basaltic and, based on mineralogy, texture and composition, represents a 1.1 Ga diabase intrusion. All studied samples are enriched in LREEs and LILEs and have negative Ta-Nb anomaly, representing magmas with typical subduction zone characteristics with enriched lithospheric mantle component in source. EPMA and in situ LA-MC-ICP-MS analysis of plagioclase phenocrysts of two Miocene samples of Ibex Hills shows variation in anorthite content and 87Sr/86Sr ratios across phenocryst profiles indicating open-system magma chamber evolution with episodes of recharge, hybridization and assimilation during the crystallization. Variation in anorthite content and 87Sr/86Sr ratios between samples suggest heterogeneities in the source magmas. The studied dikes represent multiple episodes of dike emplacements in southern Death Valley. The Miocene dikes of Ibex Hills, coeval with the Basin and Range crustal extension, indicate an early period of southwest directed extension in the southern Death Valley. The metamorphosed dikes of Saddlepeak Hills and Salt Spring Hills represent one or more episodes of older dike emplacement and could be coeval with the Mesozoic magmatism of North American Cordilleran orogeny and the Cretaceous dike of Mojave Desert. However, geochronological analysis is needed to verify the exact ages of these dikes.
  • Tolonen, Miika (2023)
    The island of Suur-Pellinki is located near the town of Porvoo in the southern Finland. The bedrock in the area consists of different rock types such as plutonic rocks and rock types that are rare in the southern Finland, for example agglomerate and different kinds of metavolcanites. The bedrock has undergone several tectonic events, of which Svecofennian orogenesis (1.9-1.8 Ga) has been the most notable. The orogenesis caused compression, extension and shearing of the bedrock, and signs of these stresses can be seen as fractures, folds, foliations and faults. The development of unmanned aerial vehicles, such as drones, has been significant in recent years. Thus, usage of them has increased in different fields of science, of which geosciences are not an exception as drones are used in data collecting. In this study, a drone was used to study outcrops of Suur-Pellinki. Four outcrops were photographed by a drone, and photographs were used to build three-dimensional models. The models were built in Pix4D and Metashape software using Structure-from-Motion photogrammetry. In addition, the models were exported to GeoVis3D software, in which orientation of fractures was studied. The aim was to study the bedrock with traditional fieldwork methods and technology that has not been used in the area. It was studied if three dimensional modelling can provide any significant additional benefits over traditional fieldwork methods. Moreover, the aim was to find ways to operate a drone efficiently and build three-dimensional models straightforwardly. The bedrock was found to be undergone extensional and differently oriented compressional events during the orogeny, and the maximum principal stress (σ1) orientations had been firstly NW-SE and later NE-SW. These stress orientations formed the main structures of the bedrock such as fractures, folds, and foliation, which is prevalent in metavolcanites of the area. In addition, some strike-slip faults were seen in the area, which have not been studied significantly in the previous studies. The three-dimensional models turned out to be useful in order to study the bedrock. Critically, building of the models was not fast and straightforward. The final resolution of the models is under three centimetres, which let to study even the smallest structures of the bedrock.
  • McDonald, Isabel (2020)
    Talc is a problematic alteration mineral at the Kevitsa Ni-Cu-(PGE) mine in Sodankylä, Finland, and its distribution and control were assessed in this thesis. Kevitsa is a polymetallic mine hosted in an ultramafic intrusion, extracting Ni, Cu, Co, Au, Pt and Pd, which are of increasing importance in green energy technologies. Talc – a common alteration product in ultramafic rocks – detrimentally interferes with the recovery of copper in the flotation stage of ore processing when concentrations exceed 5 wt. %, thus affecting the economics of mine operations. It was found different talc concentrations had different spatial associations and controls, with three dominant styles identified, and a multi-stage genesis of talc alteration is proposed. The talc styles identified in the study are as follows: (style 1) pervasive talc-chlorite alteration, (style 2) talc-dolomite alteration haloes proximal to dolomite veins and (style 3) talc on brittle structures, associated with magnetite. Low values of talc between 0.2-0.5 wt.% (style 1) were found to have no preferential spatial distribution, occurring as background alteration throughout the intrusion. Intermediate values (between 1-5 wt. %) were associated with late brittle fractures and structures (style 3), with a notable association with the NE-flt-rv1 fault zone. Style (2) was found to have a dominant structural control, specifically being associated with north-south trending structures. Dominant structures with this association identified are NS-flt1_flt-002 and NS-flt-2_flt-009. Highest values (commonly exceeding >10 wt. %) manifest themselves as alteration haloes proximal to veins, where talc-carbonate replaces the intercumulus mineral phases. Here it is proposed that ‘low talc’ alteration, style (1), was the first talc association to occur, generated by late magmatic fluids or regional metamorphism accompanying amphibole and serpentine alteration. The association observed as style (2) was likely generated by the infilling of north-south trending structures by carbonate-talc veins through metasomatism by a CO2 rich metamorphic fluid, perhaps delivered by a deep-seated structure, often generating talc values in excess of 10 wt.%. The third stage is proposed to be talc enrichment via meteoric fluid percolation, after exhumation. This generated talc along brittle structures associated with magnetite style (3), and talc-carbonate concentrations may also be upgraded at this stage. Further enrichment of talc is observed at the surface, attributed to freeze thaw-cycles of permafrost upgrading talc values. The identification of these processes and controls on talc will not only have implications for the economics of Kevitsa as high talc zones can be avoided, but findings may have useful applications for mining of similar deposits in the Central Lapland Greenstone belt such as the nearby Sakatti Cu-Ni-(PGE) project, when it enters production.
  • Maunu, Liisa (2023)
    Macquarie Island is a subaerial fraction of oceanic crust where lithology from mantle peridotites to crustal gabbro, dolerite, and extrusive rocks are present, thus providing a unique opportunity to study geochemistry and petrology of the oceanic crust. Macquarie Island represents a mid-ocean crust ophiolite in which the potential geochemical modification of continental crust and effects of subduction initiation are absent. A genetic link between plutonic and extrusive rocks and processes leading to formation of the ophiolite sequence were studied in this thesis. A set of samples representing different rock types of the oceanic crust were studied petrographically as well as for whole-rock major and trace element geochemistry. Selected samples were studied for chromian spinel, silicates, and apatite major and minor component geochemistry. Harzburgites of Macquarie Island are depleted in trace element composition and are not a straightforward residue for the source of the crustal section of the island. Melt infiltration of basaltic melt into potentially former lherzolitic mantle source has been dominating process leading to formation of Macquarie Island oceanic crust. As a consequence to melt infiltration plagioclase-bearing wehrlites recrystallized and these rocks probably acted as a more enriched source for crustal rocks.Major and trace element data show that fractional crystallization has not been significant process forming the island. Extrusive basalts are more primitive in MgO and SiO2 contents and more enriched in REE contents compared to gabbroic rocks of the island. This could be explained by porous fluids migrating through oceanic crust modifying both major and trace element compositions of the samples or extrusive and gabbroic rocks forming from different mantle sources. This study shows that formation of oceanic crust is much more complex than often assumed simple model of fractional crystallization from mantle melt leading to formation of the oceanic crust, or a hypothesized gabbro-dolerite-basalt plumbing system forming the genetically linked crustal rocks.
  • Barron, Pelayo (2020)
    Sakatti is one of the most significant magmatic Ni-Cu-PGE deposits discovered in the last decade. With a reported 44.4 Mt resource, is a polymetallic deposit with grades of: 1.90 % Cu, 0.96 % Ni, 1.40 g/t PGE; Anglo American ltd. report (2019). Sakatti is located within the Early Proterozoic Central Lapland Greenstone Belt (CLGB), Finland. The deposit is hosted by three ultramafic magma–derived olivine cumulate bodies: Main body, North-East body and South-West body. Very distinctive ore types can be recognized according to several academic studies: A) Massive ore containing an average 3.04 % Ni and 7 % Cu and showing a wide range in Ni/Cu (average of 1.42) and Pt/Pd of 0.98 (Ahvenjärvi 2015); B) Stockwork ore that is extremely copper-rich containing an average 0.68 % Ni and 26.17 % Cu, with Ni/Cu of 0.03 and Pt/Pd of 0.85 (Fröhlich 2016); C) Disseminated ore, where sulfides form a wide halo around the massive and stockwork ores, again being highly copper-dominated containing an average 0.07 % Ni and 0.61 % Cu. Ni/Cu and Pt/Pd values for disseminated ore are 0.13 and 1.83 respectively. The aim of this study is to shed some light on the genesis of the Sakatti´s disseminated ore and the massive sulfides from the NE and SW bodies. The disseminated mineralization was studied more in depth. Moreover, a comparison with other major Ni-Cu-(PGE) magmatic deposits in the world was done. Overall the disseminated ore seems to be dominated by a patchy texture with low connectivity but high wettability. Chalcopyrite is the predominant sulfide mineral and forms intergrowths with the texturally earlier pyrrhotite and pentlandite. These primary phases are widely altered to secondary phases like marcasite, millerite, violarite, pyrite, bornite, covellite and magnetite. Only a few platinum-group minerals (PGM) were found. They all are tellurides or bismuth-tellurides of which the merenskyite-moncheite-melonite series minerals are the most abundant. The chemical composition of the disseminated ore revealed compositional and fractionation similarities with both the massive and stockwork ores. When recalculated to 100 % sulfides and normalized to mantle values, the disseminated ore showed a moderate content in Ni, Co, IPGE and Rh close to the massive mineralization, and a higher enrichment in PPGE, Au and Cu with similar evolution patterns as the stockwork vein sulfides. This led to a fractionation path of the disseminated sulfide phase that seemed to be a mixture of the other two main ore types. Thus, it is suggested that the disseminated ore is formed by a combination of monosulfide solid solution (MSS) and intermediate solid solution (ISS), which originated from a sulfide melt genetically linked to the one that gave rise to the massive and stockwork ores. The massive sulfides from the NE and SW bodies show compositional similarities with the massive ore from the Main body that suggest a share origin and genesis. The Oktabr'sky, Noril'sk-Talnakh, disseminated ore, when normalized to mantle values, shows similar Ni, Co, PGE, Au and Cu distribution as the Sakatti´s disseminated sulfides. Moreover, the Oktabr'sky deposit seems to have similar S/Se vs Pt+Pd evolution trend to the one from Sakatti deposit.
  • Malinen, Lauri (2024)
    The Early Cretaceous igneous rocks in the circum-Arctic, collectively referred to as the High Arctic Large Igneous Province, are predominantly manifested on Svalbard as dolerite intrusions, classified as the Diabasodden Suite. The well-exposed intrusions in the Grønsteinfjellet- Botneheia study area, Svalbard, provide a window to a magmatic plumbing system, which has not been previously thoroughly studied. Samples collected in 2022 and 2023 were analysed for whole-rock major and trace element geochemistry. Additionally, two thin sections were studied petrographically and analysed for mineral chemistry. Geochemical data were used to model fractional crystallization, calculate primary melt composition and depth of crystallization for clinopyroxene. Stratigraphical maps and available elevation data were used to estimate the final emplacement depths of the intrusions. The geochemistry of the intrusions represents well-evolved tholeiitic basalts. The primary melt composition, with a minimum MgO content of 13.8 wt.%, suggests 45 mol% fractional crystallization before reaching a composition similar to the most primitive sample. Whole-rock major and trace element data, supported by the modelled fractional crystallization, indicate that fractional crystallization has been the primary magmatic differentiation process, while complex zoning and mineral chemistry suggest additional differentiation processes, such as magma mixing. Over-enrichment of K, Rb and Ba, implies crustal contamination. The presence of amygdales and depletion of mobile elements K and Rb indicate hydrothermal alteration. Thermobarometric calculations suggest multi-stage crystallization at depths from 2.8 to 11.2 km. The final emplacement depths were estimated to range from 230 to 560 m, based on elevation differences with the coeval Helvetiafjellet Formation. These findings propose that the Grønsteinfjellet-Botneheia intrusions underwent various and extensive differentiation processes before being emplaced in a shallow environment.
  • Ioannou, Christos (2020)
    The Siivikko-Kellojärvi area forms the southern part of the Kuhmo greenstone belt. The rocks in the area are mainly tholeiitic and komatiitic lavas. In some occasions primary textures can still be observed in the rocks, including spinifex and pillow lavas in mafic and ultramafic volcanic rocks, evident of marine environment. The purpose of this M.Sc. thesis is to investigate the possible hydrothermal alteration processes involved in the formation of the Siivikkovaara Ni-Cu-Zn-Pb mineralized sulfide body. The goal of the M.Sc. thesis is to examine the Siivikkovaara Ni-Cu-Zn-Pb mineralized body using mineralogy, whole-rock geochemistry, mineral chemistry and sulfur isotope geochemistry (δ34S values). Komatiites in the present study have a Cr content of 0.28-0.62 wt.% and show a positive correlation between MgO and Cr, following a cotectic olivine-chromite cumulate trend. Analyses of the studied samples show an average Pd + Pt value of 300 ppb. Given the results, the mineralization represents an enriched body in Pd + Pt, relative to the majority of deposits in Finland. Samples presented in the current study are mildly depleted in (La/Sm)N and generally LREE, relative to chondrite values. The analysed minerals show an average δ34S value of 0.45‰. The source of sulfur is magmatic and cannot be related with any other geological setting. Enrichment in some elements may be attributed to later post-magmatic modification of the mineralization and remobilization of the elements. Komatiitic rocks of the studied samples were derived from Cr-saturated magmas. Cr depletion in tremolite rock may be related with alteration processes or post-magmatic modification. REE data suggest a rather primitive and uncontaminated magma for the studied samples. The studied komatiites are principally of Aluminum-Undepleted komatiite-type. Owing to the poor exposure and extensive post-magmatic modification, any solid conclusions on the origin of the mineralized body are rather difficult. Therefore, more work can be done in the studied samples to further examine the assumption of a possible black-smoker setting.
  • Ambroziak-Murzyn, Karolina (2024)
    Pyroxene in komatiites, ultramafic volcanic rocks that originated in the Archean and are characterized by their high MgO content, is usually represented by a clinopyroxene subgroup member – most commonly augite. In some rare cases, orthopyroxene may also be present – sometimes even as a major phase. Primary orthopyroxene is unusually ubiquitous in atypical South African silica-rich komatiites. The stability and crystallization behavior of orthopyroxene in komatiitic-picritic melts is investigated utilizing the Magma Chamber Simulator (MCS) by modeling three distinct komatiitic compositions: Al-depleted Barberton, Al-undepleted Alexo and Si-rich Commondale, under 1, 500, 1000, 2000, 3000, 4000, 5000, 6000, 8000 and 10000 bar pressures and varying H2O contents up to 0.5 wt.%. The results indicate that higher pressures enhance the stability of orthopyroxene across all compositions. Anhydrous conditions favor orthopyroxene crystallization whereas the presence of 0.5 wt.% of H2O reduces orthopyroxene stability, especially at lower pressures. Increased silica activity from felsic TTG wall rock assimilation does not enhance orthopyroxene stability contrary to expectations, indicating that other factors may control the elevated SiO2 levels in orthopyroxene-rich komatiites like Commondale. Clinopyroxene, most abundant in Barberton and Alexo komatiites, appears after orthopyroxene and typically precipitates below the MgO content threshold for komatiitic-picritic melts, which does not reflect the natural komatiite mineral compositions. The modeling relies on theoretical and experimental data, which may not fully capture the complexities of natural magmatic systems. Limited experimental data on orthopyroxene in komatiitic liquids constrain the validation of modeling results. Further experimental studies are needed to refine the understanding of FeO and Fe2O3 ratios and their impact on orthopyroxene stability.