Browsing by master's degree program "Geologian ja geofysiikan maisteriohjelma"
Now showing items 41-60 of 89
-
(2023)Cobalt is a strategic metal whose production is dominated by a handful of countries and mines. The Terrafame (formerly known as Talvivaara) black-shale hosted Ni-Cu-Zn-Co deposit in North-Eastern Finland is a globally significant deposit for cobalt containing 1 453 Mt of ore averaging 0.02% Co. The enrichment of cobalt has likely taken place during multiple phases throughout the geological history of the deposit with both the depositional phase and the orogeny phase having a key effect on concentrating cobalt. Scanning electron microscope based automated mineralogy (SEM-AM) and electron probe microanalyses (EPMA) were applied to study the mineralogy of 15 thin sections from Kuusilampi ore body. The results from SEM-AM were further enhanced by applying a python programming language-based data processing procedure that was created specifically for this study. The main Co-containing sulfide minerals at Terrafame are pyrite, pyrrhotite and pentlandite. The Co concentration in pyrite is controlled by the grain type, with pyrites that exsolved from the monosulfide solid solution having the highest average Co concentration. The Co concentration in pentlandite appears to be controlled by the host rock with Mn-rich calc-silicate rocks having an average of 2.77 wt.% Co and black shales 0.47 wt.% Co in pentlandite. Co-rich, with up to 27 wt.% Co sulfarsenide group minerals also occur in the deposit, but their abundances were calculated to be too low to be considered a major contributor to the bulk cobalt concentration at the Terrafame deposit.
-
(2021)The Paleoproterozoic (1.87 Ga, ɛNd -3.7) Suvasvesi granitoid intrusion in southeastern Finland is considered to be a part of the Heinävesi intrusive suite. Inner parts of the lithologically zoned Suvasvesi intrusion are variably alkali feldspar porphyritic biotite granitoid rock and the margins are composed of a more biotite-rich equigranular granitoid rock variety. The Paleoproterozoic metasedimentary rocks of the Viinijärvi suite adjacent to the Suvasvesi intrusion are intruded by leucocratic pegmatite dikes. Potential sources and possible contamination of the granitoid melt are considered with the help of structural and textural observations, petrography, whole-rock geochemistry, mineral chemistry, and petrophysical data. The data were acquired from 34 rock samples collected during a bedrock mapping campaign and combined with the pre-existing mapping, petrographic, and geochemical data from the Suvasvesi and surrounding areas. The Suvasvesi granitoid intrusion is compared to other members of the Heinävesi suite to verify the hypothesis of their petrogenetic connection. The compositions of both Suvasvesi intrusion and Heinävesi suite are also compared to the potential proximal sources, the adjacent Paleoproterozoic metasedimentary rocks and Archean units in the area. In addition, the compositions of the Suvasvesi intrusion and Heinävesi suite rocks are compared to other granitoids from Eastern and Northern Finland with suggested Archean sources, and to regional granitoids of same age. Based on the similarity of major and trace element compositions, it is suggested that the Suvasvesi granitoid is part of the Heinävesi suite. The granites and granodiorites of the Suvasvesi granitoid and the Heinävesi suite are ferroan, calc-alkalic, and peraluminous with average ASI value of 1.08 (n = 73). Although the Heinävesi suite is postkinematic, it shows very few similarities to other rocks of same age. The εNd values of the Heinävesi suite and the paragneiss enclaves within the Suvasvesi intrusion indicate metasedimentary source component or assimilation. Conversely, the I-type mineralogy and geochemistry suggest igneous/meta-igneous source component for the Heinävesi suite. Potential infracrustal sources for the granitoid magma are the Archean TTGs and amphibolites. The conclusion for the magma source is ambiguous. For further studying additional isotope analyses and thermodynamic modelling of the Suvasvesi and Heinävesi magmas are suggested.
-
Mineral supply in Viiankiaapa mire during the Holocene : evidenced by geochemistry and ash content (2021)In 2011 Anglo American published a promising multi metal ore deposit in Sodankylä, Northern Finland. The ore is named Sakatti, after a small pond in the vicinity of the discovering place. The ore is under the Viiankiaapa mire, which is part of national mire protecting program and Natura 2000 program. Viinkiaapa is at the eastern side of river Kitinen, which is known to have flooded, bringing mineral material to the mire. To prevent the possibly environment effects in the future, it is essential to know present conditions of the mire. The study area is at the southern part of the Viiankiaapa mire and consist of eight sampling sites for peat. The basal sediment of the study area was determined with ground penetrating radar profiles that pass the sampling sites. To study the mineral supply of the mire, nine elements (Na, Mg, Al, S, P, K, Ca, Mn, and Fe) were chosen for geochemical analyses and the ash content of the peat profiles was determined. The basal sediment is highly affected by the vicinity of the river Kitinen. Fluvial channels have eroded till, which was deposited during the last glacial period. At the eastern side of the study area possibly aeolian sand is detected. Depressions eroded by fluvial channels are filled by gyttja, typically below 179 m a.s.l. The geochemistry of the peat indicates that the early phase of the mire was characterized with higher mineral supply. At the eastern part of Viiankiaapa the mineral supply has decreased after the early phase of the mire. The mineral supply has been higher at the middle parts of the mire throughout the Holocene. The floods of the river Kitinen are the main source of the mineral supply. The decrease in the mineral supply indicates that the flooding events have reduced, and the normal floods inundate smaller area than the early floods.
-
(2020)High amounts of H2 have been observed worldwide in deep bedrock aquifers. Sources and interaction processes of H2 within bedrock are poorly known so far, but recognizing those are important on order to identify risks related to various deep bedrock utilizing projects, such as repository of the nuclear waste. Aim of this study was to investigate if there is a correlation between H2 or fractionation factor α (H2O–H2) and the lithology of the host rock. In addition, several proposed low temperature H2 producing processes were reviewed via literature in order to investigate if α (H2O–H2) might help to identify the source of H2. In this study, H2 isotope data collected in previous studies in Finland from Pori, Pyhäsalmi, Juuka and Outokumpu deep bore holes representing various lithologies were used. In addition to α (H2O–H2), other parameters such as relative gas volumes, isotopic composition of water, temperature data, water pH, H2/He ratio of gasses were summarized. As part of the study, in the summer of 2019 new sampling was conducted in the Pinomäki borehole, in Pori by using tube sampling method and also field measurements were applied. Samples were later analyzed with ion chromatographic and spectrometric methods. In the results, isotope geochemical analyses were applied by using H2O–H2 system as a geothermometer. Results of the water analysis from Pori borehole were consistent with previous studies thus confirming two distinct water layers. Volume of H2 (0,4 %) differed considerably when compared with the previous study (28 %). Results of the isotopic composition of the hydrogen gas revealed extremely low values from -816 to -848 ‰ relative VSMOW which are among the most depleted δ2H-H2 values ever measured in the world. According to isotope analysis, in most of the boreholes in the study, except Outokumpu, H2 is not in equilibrium with groundwater when compared to in situ temperatures. α (H2O–H2) values were partially in similar range as fractionation related to some specific hydrogen forming processes, but there wasn’t a clear connection and values from different processes were overlapping each other. H2O–H2 system re-equilibrates relatively fast in a geologic timescale, which means that the possible isotopic fingerprint of H2 origin is lost. On the other hand, since H2 was clearly in a disequilibrium state, it might indicate the presence of possible active H2 forming processes. There wasn’t any clear correlation with host rock lithology and H2 concentration nor α (H2O–H2) either, except in Juuka, where lithology, α (H2O–H2), pH, and H2/He ratio summoned with high H2 volume (12,8 %) strongly indicates serpentinization as origin of H2. There are many challenges in the sampling of deep and narrow bore holes, especially related to the intention of preserving original conditions and also preventing gas contamination. In addition to further H2 sampling, recommendations for further studies include studying H2 producing reactors to investigate the effect of different H2 forming process to the isotope fractionation of H2.
-
(2020)The Southern Andes is an important region to study strain partitioning behavior due to the variable nature of its subduction geometry and continental mechanical properties. Along the plate margin between the Nazca plate and the South American plate, the strain partitioning behavior varies from north to south, while the plate convergence vector shows little change. The study area, the LOFZ region, lies between 38⁰S to 46⁰S in the Southern Andes at around 100 km east of the trench. It has been characterized as an area bounded by margin-parallel strike-slip faults that creates a forearc sliver, the Chiloe block. It is also located on top of an active volcanic zone, the Southern Volcanic Zone (SVZ). This area is notably different from the Pampean flat-slab segment directly to the north of it (between latitude 28⁰ S and 33⁰ S), where volcanic activity is absent, and slip seems to be accommodated completely by oblique subduction. Seismicity in central LOFZ is spatially correlated with NE trending margin-oblique faults that are similar to the structure of SC-like kinematics described by Hippertt (1999). The margin-oblique faults and rhomb-shaped domains that accommodate strain have also been captured in analog experiments by Eisermann et al. (2018) and Eisermann relates the change in GPS velocity at the northern end of LOFZ to a decrease in crustal strength southward possibly caused by the change in dip angle. This project uses DOUAR (Braun et al. 2008), a numerical modelling software, to explore the formation of the complex fault system in the LOFZ in relation to strain partitioning in the Southern Andes. We implement the numerical versions of the analog models from Eisermann et al. (2018), called the MultiBox and NatureBox models to test the possibility to reproduce analog modelling results with numerical models. We also create simplified models of the LOFZ, the Natural System models, to compare the model displacement field with deformation pattern in the area. Our numerical model results in general replicate the findings from MultiBox experiment of Eisermann et al. (2018). We observe the formation of NW trending margin-oblique faulting in the central deformation zone, which creates rhombshaped blocks together with the margin-parallel faults. More strain is accommodated in the stronger part of the model, where the strain is more distributed across the area or prefers to settle on a few larger bounding faults, whereas in the weaker part of the model, the strain tends to localize on more smaller faults. The margin-oblique faults and rhomb-shaped domains accommodating strain is not present in the Natural System models with and without a strength difference along strike. This brings the question about the formation of the complex fault system in both the analog models and our numerical versions of them and hypothesis other than a strength gradient could be tested in the future.
-
(2022)Continental flood basalts (CFBs) in the Karoo large igneous province were formed 189–178 Ma ago during the breakup of the Gondwana supercontinent. The flood basalts are found in the southern part of Africa, in Antarctica, and in the Falkland. The Karoo province can be divided into the North Karoo and South Karoo subprovinces on the basis of the geochemical compositions of the CFBs. The source of the South Karoo lavas has been interpreted to consist of pyroxenitic mantle and depleted upper mantle. The North Karoo lavas have been less well studied. The source of the North Karoo lavas at Luenha River, Mozambique, has been interpreted to be in a primitive part of the African LLSVP (Large Low Shear Velocity Province) in deep mantle. It is also believed that they have surfaced as part of a mantle plume. The results on the mantle source of the North Karoo CFBs have not been conclusive, however. In this study I analyze olivine crystals from the Luenha River picrites and utilize their mineral composition to address the mantle source of the North Karoo lavas. Four of the samples from Luenha River contain fresh olivine. They were analyzed using EPMA. All the analyzed olivine crystals are within Fo77–89. The compositional variation within the samples is relatively small and there is no evidence of multiple olivine populations. The olivine compositions support the proposed primitive peridotitic mantle source of the Luenha picrites. They are very similar to the olivines of the Etendeka CFBs that have been interpreted to be from peridotitic mantle source. The olivines from the Luenha picrites have high Mn/Fe ratios and low Ni, Ca, and Zn concentrations, which indicates a peridotitic source. The portions of pyroxenite and recycled oceanic crust were calculated to be less than 10 weight percent. In two samples, the crystallization temperatures were determined to be 1207–1368°C using an Al-in-olivine thermometer. Combined use of the Al-in olivine and the melt-olivine Mg-Fe equilibrium thermometers enabled the estimation of the temperatures of the primary melts (Fo92). The temperatures of the primary melts were 1300–1472°C, which supports the theory of Luenha picrites being derived from a mantle plume.
-
(2024)Seismic modelling was conducted to investigate the extent to which seismic methods, and vertical seismic profiling (VSP) in particular, can be used to image steeply dipping faults and fractures in a crystalline bedrock environment typical of southern Finland. Modelling is based on the geology and subsurface geometry found in Kopparnäs, Inkoo, where a steeply dipping fault zone is intersected by a borehole. The goal of modelling was to design the optimal survey for seismic data acquisition to image the fault zone. Borehole geophysical data analysis and computing of 1D synthetic seismograms gave a first insight into the expected response of the subsurface structures. Simple travel-time modelling was used to define the time-window for direct and reflected waves as well as gaining some understanding of useful source positions, based on the separation of direct and reflected waves. To assess the compatibility of distributed acoustic sensing (DAS) in this setting, a modelling software for comparing the response of geophones with that of a fiber optic cable / DAS was used. For more accurate modelling of the propagating wavefield, a finite-difference based full waveform modelling scheme was used to create shot gathers for both acoustic and elastic wave propagation through a 2D model. The raw shot gathers were first briefly analysed before further processing. Using a common VSP processing sequence resulted in migrated and stacked shot gathers to determine the optimal source positions. High frequencies are needed for imaging the subsurface structures in Kopparnäs, largely due to the high velocities of the crystalline bedrock and the shallow geometry of the fault. It was found that a high-resolution image of the upper part of the fault can be obtained using only four shot points located on the south side of the borehole collar, away from the fault. Shear wave reflections provided the best image of the fault, even with noise added to the shot record. The feasibility of using DAS for data acquisition was evaluated, and due to the imaging ability comparable to geophones, this method can be suggested for data acquisition in Kopparnäs. Further modelling can be conducted if desired, but good imaging results should be obtained if the suggested survey geometry is used. The practical and financial benefits of using DAS technology for data acquisition could enable some testing in the field, reducing the need for additional modelling.
-
(2019)Kaapelinkulma is an orogenic gold deposit located in the Paleoproterozoic Vammala Migmatite Belt (1.91 – 1.79 Ma) in Valkeakoski municipality in Southwestern Finland, and it is considered to have been formed in microcontinent collision during Svecofennian orogeny and has been classified as an orogenic gold deposit. Kaapelinkulma comprises a set of sub-parallel lodes in a tight array hosted within a sheared quartz-diorite unit inside a tonalitic intrusion. Gold occurrence is hosted by an en echelon type sheared quartz-dioritic dyke which forms a large xenolith inside synorogenic tonalite intrusion, surrounded by mica gneiss. It is estimated that Kaapelinkulma gold deposit contains at least, 168 Kt of ore containing 3.8 g/t Au. Textural setting, mineralogical association form and assemblage of gold, sulphides and telluride grains in Kaapelinkulma were studied with field-emission scanning electron microscopy, with electron probe microanalyzer and scanning electron microscopy. Ore minerals observed in Kaapelinkulma are: arsenopyrite, löllingite, pyrrhotite, pyrite and chalcopyrite. Other ore minerals identified are native bismuth, gold, scheelite, bismuth-tellurides and maldonite, which were all found in abundant amounts. Ore minerals occur as dissemination in intergranular spaces between silicate matrix, as polycrystal aggregates in quartz-veins and quartz clusters; and within shear zones. Gold in Kaapelinkulma is present as two generations: as single free native gold grains and as polycrystalline gold aggregates. Polycrystalline gold aggregates are grains formed from several mineral association and their combinations. Most common polycrystalline gold aggregates are formed from combination of: maldonite-native Au, Au-Bi alloys, Au-Ag grains and Au-hedleyite. Single free native gold grains are pure gold or gold-silver alloys. Free native gold grains can be found as intergranular, single grains in silicate matrix and adjacent or as a part of disseminated ore together with polycrystalline gold aggregates, bismuth and bismuth tellurides. Polycrystalline gold aggregates are found in disseminated ore, which are in close contact with quartz-veins and sulphide aggregates, or as inclusions in arsenopyrite-löllingite contact zones- or in other sulphides. Concentration of Au varies in native-gold grain from 76.83 to 97.87 wt% according to EPMA analyzes and from 50.03 to 100 wt% according to FE-SEM analyzes. Minor to moderate amounts of silver and copper were identified within the grains. Grain sizes of gold varies significantly from 7µm2 to 5mm2. Ore mineral paragenesis were observed to start when arsenopyrite and löllingite crystallized first, followed, partly simultaneously by pyrrhotite, pyrite and chalcopyrite. This was followed by crystallization of maldonite, first occurrence of native gold and bismuth, bismuth-tellurides, hedleyite and finally tellurides and main occurrence of gold. General ore forming process in Kaapelinkulma has been open space filling.
-
(2023)Global warming and anthropogenic activity will change the environmental conditions in the northern regions. For example, precipitation and river flow are expected to increase, the amount of organic matter ending up in the sea from land will increase, and its quality will change. The impact of changes in organic matter on northern coastal ecosystems and the carbon cycle is poorly known and these impacts need to be studied. In this study, the amount, quality and variations of organic matter accumulated in the surface sediments of the Bothnian Bay coastal areas in the northern part of the Baltic Sea and in the Liminka Bay over the past 100 years are studied by analyzing the concentrations of organic carbon and nitrogen (TOC and TN), C/N ratio, and the stable isotope ratios δ13C and δ15N, thus assessing environmental change in the coastal area of the Bothnian Sea. The accumulation of organic matter along the coast of Bothnian Bay is affected by both the proximity of the rivers and the land cover and land use of the river basin. More organic matter accumulates on the coasts (average 3.5 wt%) than further into the open sea (average 1.9 wt%). Contrary to presuppositions, there is no clear variation in the quality of organic matter between the coast and the open sea, but the observed change is north-south: in the northern areas, organic matter is more terrestrial and autochthonous, and in the southern areas it is more aquatic and allochthonous. The northern regions are characterized by large rivers with large amounts of forests and peatlands in the catchment areas. Further south, the rivers are smaller and carry less organic matter in quantity. Further north in the coastal ecosystem, the amount of primary production is lower and nitrogen does not limit primary production, as opposed to more southern areas. Primary production of ice may also have affected the organic matter deposited in the Bothnian Sea sediments. The amount of organic matter deposited in Liminka Bay has been on the rise over the past century, probably due to global warming, increased river flow and the impact of human activity. Based on the C/N ratio, the material has been more terrestrial in the 1930s to 1970s, after which the material has become more aquatic. In addition, aquatic primary production has increased in the Liminka Bay and nitrogen has begun to restrict primary production more. The study shows that climate and environmental change and human activities affect the amount and quality of organic matter in northern coastal areas, but further research is needed to determine more accurate ecosystem impacts.
-
(2020)Pedogenic ferromanganese nodules and concretions are prevalent redoximorphic features in tropical and sub-tropical soils. The nodules are typically highly enriched in Fe and Mn that are present as oxides, hydroxides and oxyhydroxides. The formation of nodules happens via precipitation and translocation of metals as the soil redox state undergoes cyclical changes between reductive and oxidizing settings. As the nodule elemental distribution and structure is primarily and expression of the prevailing soil redox conditions, Fe-Mn nodules have the potential to be a useful tool of paleoclimatological analysis. The Chinese Loess Plateau (CLP) is a terrestrial archive for study of changes in the monsoon climate system. During Late Miocene, the intensification of the Asian Monsoon system caused an increase in warmth and humidity in inland Eastern Asia during a global trend of increased aridity and decreasing temperatures. Fe-Mn nodules from three different soil horizons, formed 8.07, 7.7 and 3.7 Ma ago in Lantian, southern CLP, were studied to compare nodules from varying sedimentary settings formed under different moisture regimes. Using electron microscopy methods, the structure and elemental distribution of nodules were described to compare their redoximorphic features. Large Fe-Mn nodules from floodplain sediments (8.07 Ma) show a well-developed structure, high metal enrichment and signs of variations in rate of formation and dominant redox states. The soil redox conditions are likely primarily controlled by the river flooding. Nodules from two eolian deposits (7.7 Ma and 3.7 Ma) were, on average smaller and showed less metal enrichment, less elemental differentiation and less variance in the dominant redox conditions. Only small, poorly developed nodules were found from older eolian sediments whereas younger soil horizon contained larger nodules with evidence of higher hydromorphism. While potential for using the nodules from eolian sediments to assess changes in precipitation exists, the lack of paleoclimatological information in smaller nodules, the small sample count, limitations of the methods and variance in depositional settings increase the uncertainty of the interpretation.
-
(2023)The Bjurböle meteorite, which fell near Porvoo in 1899, is categorised as a fall. The Bjurböle meteorite is classified as an L/LL4 ordinary chondrite. Chondrites are undifferentiated meteorites that contain notable amounts of non-volatile elements of the early solar system. Chondrites usually contain small spherical igneous chondrules and they are classified into three groups: carbonaceous (C), enstatite (E) and ordinary chondrites (O). Ordinary chondrites are further classified into groups H, L and LL according to their metallic iron content. Chondrites are classified into petrologic types 1 – 6 based on their metamorphic grade so that Type 3 is the least metamorphosed and Type 6 is the most strongly metamorphosed, whereas Type 1 and Type 2, on the other hand correspond to meteorites that are, respectively, strongly and mildly affected by low-temperature aqueous alteration processes. The chemical equilibration of chondrites is controlled by the degree of metamorphism they go through. The more equilibrated a chondrite is, the more simplified its mineral assemble is and the more homogenised compositions the minerals have. Chondrules contain mostly olivine, pyroxene and interchondrule matrix. They are classified into Type I and Type II by the compositions of their olivine and pyroxene. Chondrule types can be further divided into A, B and AB by their olivine content. In addition, chondrules can be classified according to their texture into porphyritic, barred, radial, granular, cryptocrystalline, and metallic chondrules. The aim of this thesis is to inspect the variation in olivine composition in Bjurböle meteorite chondrules, to document the petrography of the Bjurböle meteorite and to find connections between petrographic discoveries and olivine composition. Furthermore, in this study I will discuss about the classification of the Bjurböle meteorite and the formation of chondrules in the Bjurböle meteorite. For this study, I examined 11 thin sections and three epoxy buttons that have 34 chondrules in total. Thin sections were inspected by microscope and six of the uncoated thin sections were also inspected under cold-cathode luminescence. The epoxy buttons were inspected with a scanning electron microscope, scanning electron microscope cathodoluminescence and scanning electron microscope energy-dispersive X-ray spectroscopy. Most of the inspected chondrules in the Bjurböle meteorite samples have very uniform olivine composition, as reported in earlier studies. Most of the olivines are Fo75–78, but there is also a bimodal peak at Fo89–92. The E1 chondrules (small) have very uniform olivine compositions of approximately Fo76–77. The E2 chondrules (medium) have also olivines of approximately Fo76–77, but some of the olivines reach Fo80–83. The E3 chondrules (large) have the broadest olivine composition variation at Fo74–93. However, most of the E3 olivines are Fo76–79. The E3-2 chondrule, in particular, has a broad olivine composition variation and its Fo-value increases up to 93 in the core of the chondrule. All chondrules with broader olivine variation have barred texture and are relatively large. Cathodoluminescence did not provide substantial data for the study. Other links between olivine compositions and petrography were not observed and, for example, proximity to metallic phases did not seem to have any effect on the olivine composition, and the exceptionally Mg-rich (Fo90) olivines may represent primary compositions. E3-6 and E3-7 chondrules are abundant in sulphide and metallic phases. The E3-7 chondrule resembles something that might be called micropallasite. Based on porosity, magnetic susceptibility, metamorphic signs, and the Fe variation in olivine and mineral assemblages, the Bjurböle meteorite fits the classification of an L/LL4 ordinary chondrite. Chondrules of the Bjurböle meteorite also have diverse forming histories.
-
(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.
-
(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.
-
(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.
-
(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.
-
(2023)Ongoing climate change alters Northern marine ecosystems, where annual sea-ice cover has a significant role. Changes caused by climate change, such as sea surface temperature and sea-ice season, affect the composition of the community of primary producers. Primary producers have an important role in the ecosystems and biological and geological cycle, and a slight change in their community can have a significant impact on the marine system. Past environments provide important information on the effects of future changes in the environment and climate as well as tools to control them. Diatoms are commonly used in micropaleontology and paleoecology as an indicator for past environmental conditions and are therefore important proxies for paleoenvironments and climates. To better understand the past and future changes in the environment and climate, it is important to study not only microfossils in the sediments but also the relationship of modern diatoms to environmental factors. In the Baltic Sea, seasons strongly regulate the environmental conditions, which are reflected in the diatom community. Different seasons are represented by diatoms adapted to different conditions, which could lead to misrepresentation of environmental conditions if seasonal patterns are not recognized. In this master’s thesis, modern diatom seasonal succession is studied, as well as the role of environmental factors on diatom species over one year period. A sediment trap was used to monitor seasonal diatom succession and sediment vertical flux in Tvärminne Storfjärden, Gulf of Finland between 2012–2013. New information was discovered on the ecology and succession of common diatom species in the Baltic Sea. Data shows a clear succession according to the season as diatom community evolved to represent winter and early spring community, late spring community and autumn community. In winter the diatom community consists mainly of sea-ice species such as Pauliella taeniata and cold-water species Thalassiosira levanderi. The role of Pauliella taeniata was smaller than expected, possibly due to long-term decreasing trend associated with changing environment. Other central species were sea-ice related Stauroneis radissonii and a species belonging to Chaetoceros group. Sea-ice species formed a bloom around sea-ice melt and again during the spring bloom. In contrast to sea-ice species Thalassiosira levanderi formed a bloom only in the early spring, although it was present throughout the year. The bloom was probably initiated by optimal environmental conditions and lack of competition. Dominant species during spring bloom were common spring species in the Baltic Sea Skeletonema marinoi and Diatoma moniliformis. The latter occurs in benthic and planktic environments that were discovered blooming in planktic on spring blooms in May of 2013. In summer diatoms were relatively scarce, but a group of small centric species (including Cyclotella Choctawhatcheeana, Cyclotella atomus, Minidiscus proschkinae) formed massive autumn blooms as turbidity and nutrient concentrations increased in September and August.
-
Pinta- ja pohjavesien vuorovaikutus Vesioronkankaan pohjavesialueella Imatralla, Kaakkois-Suomessa (2022)The aim of this study was to research surface water-groundwater interactions and groundwater flow directions with stable isotopes of water, dissolved silica, d-excess, electrical conductivity, pH and temperature in the Vesioronkangas groundwater area in the city of Imatra, South-Carelia. Elevations of groundwater pipe heads existing in year 2015 were measured and connected to N2000-elevation system, and their coordinates were checked. Groundwater levels were measured, and pipe coordinates checked in the summer of 2015. Water samples were collected in the late winter of 2016 and temperature, pH and electrical conductivity of the samples were determined on site with YSI multiparameter probe. The samples were analyzed in the University of Helsinki laboratory during the spring and summer of 2016. Stable isotopes δ18O and δD were analyzed with Picarro L1115-i device and dissolved silica with Agilent 4100 device. Electrical conductivity was measured again in the laboratory after heating the samples. In the cluster analysis, the water samples formed three groups that were already detectable on the basis of the stable isotope composition of the water and other physical and chemical variables: surface waters, groundwater-influenced surface waters/mixed waters and groundwaters. Maps and flow and structural modellings of the groundwater area were created with QGIS and TopoDrive programs and it seems that there is no hydraulic connection between Lake Saimaa and Lake Immalanjärvi even if there is a bedrock fracture zone. Groundwater flows to many directions in the area, almost all compass points.
-
(2021)The study area is Hyrylä groundwater area, located in southern Finland, in the city center of Tuusula. Hyrylä groundwater area is class 1 groundwater area, and it is classified as a chemical risk area. The Koskenmäki water pumping plant, owned by Keski-Uudenmaan Vesi Kuntayhtymä, is in the groundwater area, where on average 1000 m3 of water is pumped daily for domestic use. The groundwater area is situated in a southwest to northeast orientated esker which is a part of a bigger esker series starting from I-Salpausselkä in Hyvinkää. There is a big southwest to northeast orientated shear zone in the bedrock under the groundwater area where Lake Tuusulanjärvi and Tuusula-river follow the shear zone. The aim of this study was to research the interactions between river water and groundwater in the Hyrylä groundwater area and to get a better understanding of the geology of the area. Additionally, the movements of the groundwater were studied. Based on earlier studies the groundwater is discharging to the Tuusula-river near the Koskenmäki water pumping plant and the river water has been recharging to the groundwater. There are contaminated areas surrounding the old gas station in Hyrylä, where the soil and groundwater are contaminated with oil hydrocarbons, hence it was important to study where the water to Koskenmäki water pumping plant is coming from. Effects of the shear zone to the movements of the groundwater and to the amount of water available for pumping were also examined. The groundwater-river water interactions were studied with thermal methods and seepage meters. Isotopic and chemical tracers were analyzed from the water samples, which were collected from the groundwater observation wells, groundwater discharging to Tuusula-river and from the river water itself. A 3D geological structure model of the groundwater area was made based on earlier gravimetric measurements and drillhole data. The water table measurements from the observation wells were taken at the same time when the water samples were collected. Based on the 3D structure model a groundwater flow model was made to explain the movements of groundwater in Hyrylä. The geology of the groundwater area was examined with ground-penetrating radar, but the measurements were not successful and did not give any useful data for making the 3D model. The results of this study show that the groundwater is discharging to the Tuusula-river near the Koskenmäki water pumping plant. Based on the water analyses done, there was only one water sample with surface water mixed in it. 3D modeling gave a clear picture of the bedrock surface and cross-sections of the soil structure. According to the groundwater flow model, groundwater is flowing to the Koskenmäki water pumping plant from southeast. To the shear zone groundwater flows mostly from east and southeast. From the northwest part of the groundwater area the groundwater is flowing via northeast to the northern parts of the shear zone. The contaminated areas are not in the flow path to Koskenmäki water pumping plant. Based on the water analyses, groundwater discharging to the western parts of Tuusula-river is from a different source than the water discharging to the eastern parts of the river. In the shear zone the groundwater flow direction is to the south and the groundwater discharges to the river southwest of the Koskenmäki water pumping plant.
-
(2022)The construction of the Savio railway tunnel caused an unexpectedly large decrease in the groundwater heads in part of the observation points in the vicinity of the railway tunnel after the completion of the tunnel construction work. The study aimed to investigate the ability of the groundwater model to forecast such groundwater drawdown caused by a railway tunnel in the urban areas of East Hakkila, Kaskela and Hakunila. The uncertainty of the groundwater model and its sensitivity to certain parameters were studied and analyzed. The groundwater model was built using the GMS (Groundwater Modeling System) numerical groundwater modeling program. For the groundwater flow model, the bedrock mesh was built in Leapfrog Geo - program based on gravimetric measurements and rotary drilling. The groundwater model was calibrated manually and automatically to correspond to the groundwater heads measured in the area. The circumstances after the construction of the railway tunnel were then simulated. The model-calculated groundwater heads were compared to the observed groundwater heads and the observed tunnel leakage. Sensitivity analysis was performed for the horizontal conductivity parameters and recharge parameters of the model. The groundwater model before the construction of the tunnel mimicked the measured groundwater heads and flow directions in the study area. The simulation of the time after the construction of the tunnel caused groundwater drawdown of 0-16 meters at 0-730 meters from the railway tunnel. In the simulation of the time after tunnel construction, the groundwater heads calculated by the model differed by 0,01-24 meters from measured groundwater heads. According to the results of the sensitivity analysis, the model was most sensitive to changes in the horizontal conductivity of the upper bedrock layer and granite. The recharge parameters and soil layer had a marginal impact on the groundwater model. The uncertainty of the model was affected by the few measurement points in relation to the size of the area and the absence of field measurements of the hydraulic conductivity of the parameters. To reduce the uncertainty, the model should be calibrated based on the measured conductivity values of the bedrock. Despite the uncertainty, computational models give indications of the direction of change and are important tools in questions related to nature and the built environment.
-
(2022)The construction of the Savio railway tunnel caused an unexpectedly large decrease in the groundwater heads in part of the observation points in the vicinity of the railway tunnel after the completion of the tunnel construction work. The study aimed to investigate the ability of the groundwater model to forecast such groundwater drawdown caused by a railway tunnel in the urban areas of East Hakkila, Kaskela and Hakunila. The uncertainty of the groundwater model and its sensitivity to certain parameters were studied and analyzed. The groundwater model was built using the GMS (Groundwater Modeling System) numerical groundwater modeling program. For the groundwater flow model, the bedrock mesh was built in Leapfrog Geo - program based on gravimetric measurements and rotary drilling. The groundwater model was calibrated manually and automatically to correspond to the groundwater heads measured in the area. The circumstances after the construction of the railway tunnel were then simulated. The model-calculated groundwater heads were compared to the observed groundwater heads and the observed tunnel leakage. Sensitivity analysis was performed for the horizontal conductivity parameters and recharge parameters of the model. The groundwater model before the construction of the tunnel mimicked the measured groundwater heads and flow directions in the study area. The simulation of the time after the construction of the tunnel caused groundwater drawdown of 0-16 meters at 0-730 meters from the railway tunnel. In the simulation of the time after tunnel construction, the groundwater heads calculated by the model differed by 0,01-24 meters from measured groundwater heads. According to the results of the sensitivity analysis, the model was most sensitive to changes in the horizontal conductivity of the upper bedrock layer and granite. The recharge parameters and soil layer had a marginal impact on the groundwater model. The uncertainty of the model was affected by the few measurement points in relation to the size of the area and the absence of field measurements of the hydraulic conductivity of the parameters. To reduce the uncertainty, the model should be calibrated based on the measured conductivity values of the bedrock. Despite the uncertainty, computational models give indications of the direction of change and are important tools in questions related to nature and the built environment.
Now showing items 41-60 of 89