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This edited work contains the most recent advances related to the study of layered intrusions and cumulate rocks formation. The first part of this book presents reviews and new views of processes producing the textural, mineralogical and geochemical characteristics of layered igneous rocks. The second part summarizes progress in the study of selected layered intrusions and their ore deposits from different parts of the world including Canada, Southwest China, Greenland and South Africa. Thirty experts have contributed to this update on recent research on Layered Intrusions. This highly informative book will provide insight for researchers with an interest in geology, igneous petrology, geochemistry and mineral resources.

Earth Sciences. --- Mineralogy. --- Geochemistry. --- Mineral Resources. --- Geography. --- Mines and mineral resources. --- Géographie --- Géochimie --- Mines et ressources minières --- Minéralogie --- Intrusions (Geology). --- Igneous rocks Inclusions. --- Geology --- Earth & Environmental Sciences --- Mineralogy --- Intrusions (Geology) --- Intrusive bodies --- Pluton --- Earth sciences. --- Mineral resources. --- Geology, Structural --- Physical geology --- Crystallography --- Minerals --- Deposits, Mineral --- Mineral deposits --- Mineral resources --- Mines and mining --- Mining --- Natural resources --- Geology, Economic --- Chemical composition of the earth --- Chemical geology --- Geological chemistry --- Geology, Chemical --- Chemistry --- Earth sciences

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In this work, diffusion of Fe-Mg and Mn is used to model the relative timescale of pre-eruptive processes of olivine crystals. The applied method of diffusion chronometry is based on the new, more complex concept of a magmatic system and the process of disequilibrium between crystal and melt. The first conceptual model of a magmatic system involved a large melt-dominated magma body, which was recharged by a feeder system from a deeper source. This interpretation has changed to a more open system with smaller, stacked sills, vertically connected with each other. In such a system, magma can be altered by magma replenishment, resulting in magma mixing and crystal transport, as well as by crustal assimilation. This thesis is based on the concept of magma mixing and crystal transport with the assumption that crystallization happened deep in the crust, in a primitive magma. A primitive magma is a magma directly derived from the mantle and has not changed in composition since formation. Olivine crystals that crystallize in such magma have a high magnesium concentration. After this crystallization, the crystals are carried through vertical connections towards a more shallow magma reservoir with a more evolved magma. An evolved magma has changed in composition by increasing silica and decreasing magnesium concentration. The transport of primitive magma, comprising the crystals towards the shallow magma chamber leads to magma mixing and disequilibrium between the crystals and the newly formed melt. The crystals react by diffusion of mobile elements, where elements flow in the direction of the lowest concentration. Therefore, diffusion induces a chemical concentration gradient between core and rim, which is expressed in rim zonation in olivine. This concentration gradient can be modeled with the diffusion coefficients of certain elements. The obtained model provides constraints on how long the crystals resided in different sections in the complex volcanic plumbing system up until eruption. Diffusion chronometry studies the timescale of crystals, this method is increasingly applied in the last decade, because of the accurate determination of diffusion coefficients for mobile elements in crystals. In this thesis, the focus lies on modeling the diffusion of Fe-Mg, as forsterite, and Mn in olivine. The studied olivine crystals originate from Nyamuragira volcano, situated in the Democratic Republic of Congo. Nyamuragira is a shield volcano, which is characterized by a broad domed volcano with gently sloping flanks. The volcano is located on the Western Branch of the East African Rift System and is the most western volcano of the Virunga Volcanic Province. Nyamuragira is one of the most active volcanoes on earth with an average eruption frequency of three years. The lava is classified as basanite to tephritic phonolite. The first step in this thesis was to petrographically describe the volcanic rocks to select the samples with the best examples of zoned olivine crystals. Next, the chemical bulk composition is determined with X-Ray fluorescence, in order to classify our samples. Then, the main objective of establishing the diffusion time is accomplished through best-fit diffusion modeling with the use of the MATLAB software. With our model, we obtained timescales ranging between 1 and 70 days for olivine crystals from Nyamuragira. The average diffusion time is 20 days, therefore, we can conclude that the pre-eruptive processes in the plumbing system

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Temperature exerts a major control on magmatic processes in the mantle. Spatial and temporal variations in mantle temperature are thought to drive deep planetary processes such as the mantle convection. Strong temperature anomalies near the core-mantle boundary may give rise to mantle plumes that are considerably hotter than the ambient mantle. Methods to investigate the mantle temperature at which a melt formed are needed to confirm whether such hot magmas are truly present within the mantle. Geothermometers based on olivine equilibria are a good proxy to assert the minimal melting temperature of a magma since olivine is one of the first phases to crystallise. Early olivine-based geothermometers focussed on cation equilibria between olivine and the melt, but the necessity to estimate liquid composition has proven to give rise to uncertainties. Hence, Wan et al. (2008) proposed the Al-in-olivine geothermometer which is no longer dependent on mineral-melt equilibria, but only on mineral-mineral equilibria. The Al-in-olivine geothermometer uses the partitioning of Al between forsterite-rich olivine and Cr-rich spinel as proxy for the liquidus of a melt, which is dependent on temperature and spinel Cr#. The limited calibration range concerning pressure, temperature, oxygen fugacity (fO2) and compositional conditions gives rise to uncertainties when research is conducted on mantle plumes. The goal of this thesis was to gain further insight in the Al partitioning by investigating higher fO2 and temperature conditions for a wider range of chemical compositions. Obtaining spinel minerals from the melt has proven difficult, but doping with Cr2O3 was partially successful in generating higher spinel Cr# [=Cr/(Cr+Al)]. Secondary fluorescence during microprobe analysis gave rise to anomalous high Al2O3 concentrations in olivine. Analytical uncertainties made it difficult to properly assess the Al equilibrium. Moderate trends suggest that – other than for temperature and spinel Cr# – the Al equilibrium seems to be dependent on glass SiO2, olivine Cr# and forsterite content, spinel P2O5 and Fe3+, and fO2. Further research is needed to fully understand the influence of these factors. Recalibration of the Al-in-olivine geothermometer and application to natural samples have shown that – although a wider calibration range can be reached with the experimental results of this thesis – the original geothermometer is still more accurate. Application to natural rocks of high Cr# suggests that the original geothermometer remains realistic. More accurate results are needed to properly investigate the Al-equilibrium and recalibrate the geothermometer. Measurements with a nano-SIMS are suggested to avoid secondary fluorescence on trace elements.