Projects

Mafic magmas at subduction settings stagnate at different levels during the ascent through the continental crust and the fractional crystallization, assimilation and mixing processes affect the composition of the magmas. The variation in density of the mafic to intermediate magmas probably cause the layering of the crust because mafic magmas typically stagnate in the lower crust. Sulphide saturation in the mafic magmas probably causes a depletion of chalcophile elements like Cu and Au in the upper continental crust. We suggest to study magmatic rocks and sulphides from two mafic-ultramafic intrusions in the Svecofennian Vammala Ni-Cu Belt of S Finland in order to define the formation of the cumulates from Proterozoic arc magmas and the associated sulphide deposits. The results will provide important insights into fractional crystallization and crustal assimilation processes related to the formation and segregation of sulphides and the fractionation of chalcophile elements. Because the Proterozoic oceans probably were anoxic and sulphidic, subduction-related magmas at that time may have been more reduced than those in the Phanerozoic. We will study the mineral compositions in the Vammala rocks and the potential effects of more reduced arc melts on magma evolution and transport of chalcophile elements by comparing the Vammala rocks to those from intrusions in young arcs. 

The increasing demand of critical and energy critical elements in the high-tech industry requires a secure and steady supply of these rare commodities. Many of these metal(loid)s cannot be substituted due to their very specific application and economic grades in ore deposits exist only in a few countries, which may cause bottlenecks in the supply-chain in the near future. Hence, to secure the future supply of these strategic elements alternative sources must be explored, including those in the deep sea.  

Hydrothermal systems associated with subduction zone volcanism host some of the world’s most important volcanogenic massive sulphide (VMS) deposits. Many of them formed in back-arc rifts, where seafloor massive sulphides (SMS) occur as their modern analogues, some of which are characterized by high metal(loid) grades (e.g., Cu, As, Se, Ag, Sb, Au, Hg, Tl and Pb) exceeding those of deposits currently mined on land. Many of these elements have a strong affinity to volatiles derived from magmas, but it is still poorly understood how magma degassing contributes to the trace metal(loid) budget of SMS and VMS mineralizations. 

This project aims to quantify the geochemical fluxes in submarine back-arc hydrothermal systems from a new 3-dimensional perspective by constraining the effect (1) of magmatic volatile influx, (2) variable host rock compositions and (3) metal(loid) fractionation in the hydrothermal upflow zone on the composition of VMS and SMS mineralizations. In order to address these objectives a continuous sample spectrum from the reaction zone to the seafloor is required, which can only be fulfilled by drill cores, such as those recovered during ODP and IODP expeditions. We have identified suitable cores, which together with samples from the modern seafloor and from ancient VMS-related hydrothermal systems from the Troodos ophiolite provide a unique sample set. This approach is beyond the state of the art and requires an innovative analytical set-up combing (ultra-)trace element with Se and multiple S isotope analyses, which will allow to track the hydrothermal metal(loid) cycle through the oceanic crust, providing a new window into metal(loid) sourcing, fractionation and precipitation. This will ultimately help to develop new fundamental concepts for the economic enrichment of metal(loid)s in submarine back-arc hydrothermal systems.

Immiscible suphide liquids preserved as magmatic sulphide globules in the oceanic crust record the S and chalcophile element evolution of their host magmatic systems. Recent results report systematic variations in the mineralogy and chemistry of magmatic sulphide globules from convergent and divergent plate margins, but the origin of these differences, and the implications for the chalcophile element cycle in the oceanic crust, are unknown. Parameters that control the solubility of S in silicate melts include: (1) temperature, (2) pressure, (3) oxygen fugacity and (4) the degree of fractionation. Although upper mantle melting conditions and magma differentiation in the crust differ between mid-ocean ridges and subduction zones, the effects of these processes on the S saturation limit of a silicate melt and its chalcophile element budget are still poorly understood. Better constraints on the S and chalcophile element evolution of magmatic systems are critical for understanding the chalcophile element cycle in the oceanic lithosphere, the composition of seafloor hydrothermal sulphides, the formation of the continental crust, the composition of volcanic gas and possibly the metal and metalloid budget of some subaerial epithermal-porphyry deposits.

The project aims to address these questions by investigating the magmatic trace metal and metalloid flux (e.g., Co, Ni, Cu, Se, Ag, Te, PGE, Au, Bi) through the oceanic lithosphere at mid-ocean ridges and at oceanic subduction zones. State-of-the-art analytical techniques will be used to present the first global trace element data set of magmatic sulphide globules from all sections of the oceanic lithosphere, with respect to the plate-tectonic setting and the temporal evolution of the magmatic system. Samples reflecting the initiation of ocean spreading during continental break-up and recent on-axis volcanic activity at mid-ocean ridges together with a full succession of the lava pile from the youngest at the seafloor to the oldest at the lava/dyke transition record the evolution of the magmatic chalcophile trace element cycle at high temporal resolution. In order to address these objectives, a continuous sample spectrum from the upper lithospheric mantle to the uppermost crust is required, which can only be provided by drill cores, such as those recovered during DSDP, ODP and IODP expeditions. We have identified suitable cores, which together with samples from the modern seafloor and from ancient oceanic lithosphere (e.g., Troodos ophiolite) provide a comprehensive sample set including upper mantle peridotites, lower crustal gabbros, sheeted dykes and lavas from basaltic to rhyolitic composition. Magmatic sulphide globules have already been identified in many of these samples. The proposed project will allow us to develop the first models of the magmatic chalcophile trace element cycle through the entire oceanic lithosphere at both convergent and divergent plate margins.

Supplying critical and energy critical elements for the green transition is a growing challenge. Many of these metals and metalloids have a strong by-product dependency and their supply therefore depends on the primary target commodities. The strong impact of these elements on the energy and economy sector of the European Union gives them a strategic importance. Thus, the dependency on mining countries like China must be reduced to secure the future supply of raw materials, since their import from these countries may be at risk because of political tensions leading to bottlenecks in the supply-chain. In this respect, the European continent needs to be re-explored to constrain economic zones enriched in critical and energy critical elements. 

The deposits of Thrace, NE Greece, represent such an example, where zones with high metal and metalloid concentrations (e.g., Cu, Ga, Ge, Se, Mo, Sb, Te, Re, Au and Bi) occur at variable crustal depth in a mineralized continental arc setting in Europe. This includes the porphyry environment in the direct vicinity of a magma chamber, as well as shallower epithermal systems with some that may even preserve a surface expression. Regional variations in deposit mineralogy have been observed, but the ore-forming processes of the porphyry-epithermal deposits are still poorly constrained from a trace element perspective. The magmatic and hydrothermal prerequisites that lead to the formation of such a mineralised arc system are also still controversial, but essential to discover positive anomalies of critical and energy critical elements in the continental crust. 

The trace metal and metalloid composition of associated plutonic and volcanic/sub-volcanic rocks will provide new results on the magmatic processes in the deeper crust and the potential loss of these elements during magma ascent towards the surface; into regions where they may feed an overlying porphyry-epithermal system. This allows to investigate the effect of magma degassing, as well as sulphide saturation and segregation to form a pre-concentrate in the mid- to lower crust, as possible magmatic prerequisites for arc mineralisation. Pyrite and magnetite occur in most metal-bearing veins in the overlying hydrothermal system. High-resolution trace element analyses on these minerals will provide insights into the processes of ore-formation from a 3D perspective, i.e. in a stratigraphic and regional context. The (in situ) S isotope composition of hydrothermal pyrite will help to better understand the interaction processes between the magmatic and hydrothermal system. Hence, the combined investigation of magmatic and hydrothermal processes makes this approach unique and will help to develop new fundamental concepts with respect to S and metal sourcing, fractionation and precipitation, which ultimately defines the magmatic and hydrothermal prerequisites for continental volcanic arc mineralisation and energy critical element enrichment in Europe.

Tellurium (Te) is classified by the European Union as an energy critical element of high importance due to its application in the rapidly growing sector of green energy technologies. Currently, most Te is recovered as a by-product from non-ferrous metal mining, principally by refining of Cu providing little opportunity to increase the Te supply based on current extraction methods.  Hence, a shortage in Te is likely to be reached in the near future due to its increasing demand. 

Tellurium in hydrothermal pyrite reaches 8,000 ppm and is typically enriched together with other trace elements, such as As and Au (up to 4.8 wt. % and 11,000 ppm). Pyrite is stable under a wide range of fluid conditions including low and high temperatures, variable fO2and pH conditions. Thus, the trace element chemistry of pyrite can be used to define the key ore-forming processes of Te, which are poorly constrained to date. Due to its ubiquity and ability to concentrate trace elements, pyrite may be considered as an economically important host for Te. Hence, the future supply of Te may be resolved by the processing of minerals including pyrite. However, the behaviour of Te during the ore-processing is not well understood and if not recovered and sent to tailings it may have an eco-toxicological impact. 

This project aims to close these knowledge gaps by providing a detailed understanding about Te ore formation in epithermal and Carlin-type systems; two distinct mineralisation-styles suggested to reach economic Te concentrations. State-of-the-art analytical techniques will be used for a full structural and chemical characterisation of Te in pyrite down to the micro- and nano-scale. This allows to develop a solid tool to define the incorporation mechanisms of Te in pyrite either as a structurally bound element or as micro- to nano-sized inclusions. Phase quantification will be combined with mineral and bulk ore Te chemistry to quantitively demonstrate that pyrite is one of the major Te hosts in these deposits. Trace element mapping will be performed to investigate possible intra-crystalline Te variations (i.e. zoning) in pyrite, which will be used to define key ore-forming processes to finally present a new micro-analytical exploration tool for Te. Hydrothermal experiments under controlled laboratory conditions will help to define fluid parameters (e.g., temperature, pH, fO2) controlling the distribution of Te in pyrite. The composition of experimental pyrite synthesized from a fluid of known Te composition allows to define the first Te Nernst partition coefficients (KD) in the pyrite-fluid system. Consequently, the combined use of natural and synthetic systems will allow, for the first time, to provide a quantitative understanding about the precipitation and incorporation mechanisms of Te in pyrite; a ubiquitous mineral hosting an element of growing economic interest.

Vulkanische Gesteine, die im Rahmen der INDEX 2019 Ausfahrt unter der Leitung der Bundesanstalt für Geowissenschaften und Rohstoffe gewonnen werden, sollen in dem Projekt am GeoZentrum Nordbayern (GZN) geochemisch analysiert werden. Die Daten werden von Wissenschaftlern des GZN interpretiert und die vulkanischen Prozesse im Zusammenhang mit den hydrothermalen Austritten am Zentralindischen Rücken und am SE Indischen Rücken bestimmt.

We request ship time with RV Maria S. Merian to conduct detailed ROV-based geological and biological investigations of the Vesteris Seamount in the Central Greenland Sea. High-resolution bathymetry mapping with modern multibeam echosounders and comprehenisve sampling of the volcanic substrate are one focus of the cruise. These samples will be investigated geochemically and geochronologically to unravel the petrological/volcanological evolution of the seamount. Hydrographic surveys will be conducted to look for hydrothermal venting. Another emphasis is on geobiological investigations, including an assessment of the colonization of the volcanic substrate by fungi, fungal diversity and activity as well as relations to seawater-rock interactions during weathering. We will also do a detailed appraisal of the sponge communities that densely colonize the seamount and will conduct comprehensive molecular-ecological studies to understand the functioning of the holobiont. Furthermore, we propose to map and sample a prominent seamount south of our main work area as well as several volcanic centers northeast of it. These materials and data will allow us to shed new light on the magmatic- tectonic evolution of the northernmost Atlantic.

The volcanic flux at the Hawaiian hotspot generally increased over the last 30-80 Ma, with second-order variations over 10~15 Ma. This significant increase remains unexplained by classic plume theory, which predicts that a plume-head stage with massive volcanic activity is followed by a plume-tail stage with ever decreasing activity. In particular, 25-30 Ma ago there was a sharp increase in the Hawaiian volcanic flux by a factor ~4 that appears to be associated with an increase in Pacific plate motion from ~60 km/Ma to ~100 km/Ma.At about the same time there was a surge across the South Pacific of young low-volume hotspot tracks. It is unclear from our understanding of the poorly sampled Hawaiian track if these volcanic flux variations are related to speed up of the Pacific plate or to pulsations of the Hawaiian plume. In order to explain the coupled observations of faster plate speed and increased volcanic flux we aim to explore three young, relatively low-volume Pacific hotspot tracks. High–precision geochronological data for multiple hotspot tracks is the only way of extracting fundamental new information from the intraplate record about the poorly-sampled young end of the Hawaiian hotspot track. We propose to determine high-precision ages using the next generation of multi-collector mass spectrometer for 111 samples from the Foundation, Easter and Pukapuka-Rano Rahi volcanic tracks. We will use these new data to (1) pinpoint the timing of Pacific plate-speed increases and variations in hotspot volcanic flux, and (2) understand the underlying mechanisms controlling volcanic flux variations at Pacific hotspots.

The Rio Grande Rise (RGR) is a massive plateau and seamount province in the SW Atlantic that has been assumed to represent a large igneous province formed by voluminous magmatic activity of the Tristan-Gough mantle plume on the South American plate. But new evidence showing that the RGR might be a sliver of continental crust that was captured, and possibly rifted, at the time of continental breakup, is throwing considerable doubt on a hotspot origin. We propose a combined seismic, geochemical, geo- and thermochronological study of the nature of the deep and shallow RGR basement to test our hypothesis that the RGR is a microcontinent that has been modified by a complex tectonic and magmatic history, including 1000 km long rifts, associated with buoyant plume upwelling and formation of the Jean Charcot Seamount Chain. These data will determine the relative amounts of continental and oceanic crust, age and origin of the volcanic rocks, and chemical changes with time. The results will have important implications for the understanding of continental rifting and opening of ocean basins and the role of microcontinents in the formation of hotspot trails.

Oceanic island arcs probably evolve through different tectonic stages that are marked by the formation and eruption of different magmatic rocks. Boninites have a peculiar geochemical composition reflecting partial melting of highly depleted mantle and are believed to be typical for the early stages of island arc evolution. The main objectives of the proposed project are sampling of shallow crustal profiles at the NE Tonga Ridge and Lau backarc basin where boninitic lavas appear to be very abundant in order to establish the stratigraphic situation of these boninites. Lavas from the N Tonga volcanic islands have unique compositions reflecting very strong depletion of the mantle wedge and re-enrichment by fluids from subducted seamount lavas, whereas some backarc lavas indicate influence of mantle plume material, possibly from Samoa. The Niuatahi volcano is surrounded by young lava flows and volcanic ridges that reach to the NE Lau spreading centre and the abundant on- and off-axis lavas allow studying the magma generation and mixing processes from the arc front to the backarc. We propose to study the composition of the NE Tonga volcanoes to better define the different sources and the implications for mantle and melting dynamics in a subduction zone. The recently active volcanoes in the NE Lau backarc and NE Tonga arc show highly variable hydrothermal venting and thus offer a natural laboratory for the study of the effects of magma degassing on hydrothermal fluid and precipitate composition. We suggest sampling of different vents related to different magmatic structures in order to test models of the effects of varying magmatic volatile input and water depth on the fluids.

Andesite magmas at active continental margins may form due to assimilation-fractional crystallization processes from basaltic mantle melts or due to direct partial melting of unusual mantle rocks resulting, for example, from mixing of sediment melts with peridotite. Magmas of the Aegean Arc indicate a reaction of the melts with the crust during the ascent as well as a strong input of sediment into the melting zone of the mantle wedge. These different mixing processes are difficult to define in most rocks and require detailed studies of melt (glass) and mineral compositions. Thus, submarine lavas are best suited for a study of andesite formation because melts are quenched and their composition including volatile contents can be determined. The volcanoes of the western Aegean mainly erupted effusive lavas in domes and flows rather than showing explosive activity. We propose a cruise to the westernmost submarine volcano Paphsanias of the Aegean Arc that has not been studied petrologically and geochemically. We suggest studying and sampling this volcano using an ROV that will give us stratigraphic control of the samples. The ROV dives will allow determining the relative abundance of lavas and volcaniclastic rocks and yield insights into the apparently different magma ascent and eruption processes in the western volcanoes. Given the young age of the Paphsanias volcano the crater may also show hydrothermal activity that we will be able to observe and sample using the ROV.Andesite magmas at active continental margins may form due to assimilation-fractional crystallization processes from basaltic mantle melts or due to direct partial melting of unusual mantle rocks resulting, for example, from mixing of sediment melts with peridotite. Magmas of the Aegean Arc indicate a reaction of the melts with the crust during the ascent as well as a strong input of sediment into the melting zone of the mantle wedge. These different mixing processes are difficult to define in most rocks and require detailed studies of melt (glass) and mineral compositions. Thus, submarine lavas are best suited for a study of andesite formation because melts are quenched and their composition including volatile contents can be determined. The volcanoes of the western Aegean mainly erupted effusive lavas in domes and flows rather than showing explosive activity. We propose a cruise to the westernmost submarine volcano Paphsanias of the Aegean Arc that has not been studied petrologically and geochemically. We suggest studying and sampling this volcano using an ROV that will give us stratigraphic control of the samples. The ROV dives will allow determining the relative abundance of lavas and volcaniclastic rocks and yield insights into the apparently different magma ascent and eruption processes in the western volcanoes. Given the young age of the Paphsanias volcano the crater may also show hydrothermal activity that we will be able to observe and sample using the ROV.

Rifting of arc crust may host large hydrothermal systems with the potential of forming large mineral deposits of economic relevance. The highly variable structural and magmatic conditions across arcs into the backarc environment provide a unique opportunity to investigate a large diversity of magmatic and hydrothermal systems (e.g., Hannington et al., 2005). Here, we aim at quantifying both the changes in the melting regime (physical conditions, melting and mantle sources) in the transition from arc front into backarc and the impact on metal potential. A direct contribution of magmatic volatiles to (ore-forming) hydrothermal fluids is known from island arc volcanoes but the general links between oxidation state, sulphur saturation and magmatic degassing on metal behaviour in silicate melts are still a matter of active debate. Jenner et al. (2010, 2015) pointed at the importance of the onset of magnetite crystallization for sulphur saturation and thus chalcophile element behaviour. However, their magnetite crisis may be restricted to specific physicochemical circumstances (such as closed system behaviour, oxidation state and melt composition etc.) and needs to be investigated in different magmatic systems (e.g., arc to backarc transition) and spatial resolution. Here, we are aiming at disentangling the influence of mantle sources and melting on the metal enrichment in melts and volatiles and the geological framework of pathways for melts and volatiles at a scale that is relevant to resource exploration. This project consists of two sub-projects, one with an emphasis on mantle sources, melting conditions and magmatic differentiation providing the basic framework and the other focused on seafloor geology (ascent paths and geodynamics) and the distinct behaviour of metals (especially Cu, Au and the so-called critical metals) and volatiles (H2O, CO2, Cl, S) in the melts. However, these two projects are closely linked (especially through the aspect of magma evolution), requiring close collaboration and frequent exchange. The focus of this study will be on the Tonga-Kermadec subduction system, where extensive sample material is readily available and two additional research cruises have been recently approved (ARCHIMEDES I and TongaRIFT). 

Ophiolites are often used to infer the internal structure of the oceanic crust and the processes by which it is formed, but most ophiolites were not formed in typical mid-ocean ridge settings. Instead, they appear to have formed close to former subduction zones, but the exact tectonic setting in which they were formed is debated. If ophiolites represent fore-arc crust formed during subduction initiation events, then they provide insights into the initiation of subduction zones, an outstanding unresolved question in plate tectonics. If ophiolites were formed in back-arc or plate edge settings they may represent useful analogues for the internal structure of oceanic crust. If they were formed at a ridge-trench-trench or ridge-trench-transform triple junction then they could be used to infer mantle wedge structure and processes. These tectonic models predict different geochemical variations in ophiolite lavas with space and time. We will map out the 3D gechemical structure of the Troodos Ophiolite of Cyprus, one of the best preserved an exposed ophiolites. We will use major and trace element microanaysis of fresh volcanic glass in order to avoid the effects of alteration. Detailed high resolution sampling of sections through the Troodos volcanic section on both the northern and southern margins of the ophiolite will be used to determine the chemical evolution of magmatism and test hypotheses for the tectonic origin of this ophiolite.

Combined with local and regional anthropogenic factors, current human-induced climate warming is thought to be a major threat to biodiversity. The ecological imprint of climate change is already visible on land and in the oceans. The imprint is largely manifested in demographic/abundance changes and phenological and distribution shifts, whereas only local extinctions are yet attributable to climate change with some confidence. This is expected to change in the near future owing to direct heat stress, shortage of food, mismatches in the timing of seasonal activities, geographic barriers to migration, and new biological interactions. Additional stressors are associated with climate warming in marine systems, namely acidification and deoxygenation. Ocean acidification is caused by the ocean's absorption of CO2 and deoxygenation is a result of warmer water, increased ocean stratification and upwelling of hypoxic waters. The combination of warming, acidification and deoxygenation is known as the "deadly trio". Temperature is the most pervasive environmental factor shaping the functional characteristics and limits to life and is also central to the generation and biological effects of hypoxic waters and to modulating the effects of ocean acidification, with and without concomitant hypoxia. Due to the key role of temperature in the interaction of the three drivers we termed these temperature-related stressors (TRS).

Junges Rifting (< 3 Ma) im südlichen Neue Hebriden Inselbogen erzeugte drei vulkanische und hydrothermal aktive Becken im Coriolis Becken, in denen z.T. alkaline Magmen mit Anreicherungen an Nb und Ta auftreten. Weiterhin zeigt der Vanuatu Inselbogen eine starke Dynamik mit einem Umspringen der vulkanischen Aktivität weiter nach Osten. Durch das Rifting wurden tiefe Bereiche des Inselbogens freigelegt, die offenbar bis 7 Ma alt sind. Eine detaillierte stratigraphische Beprobung dieser Riftflanken und der jungen Vulkane im südlichen Inselbogen und im Backarc ermöglichen daher einmalige Möglichkeiten zur Entwicklung der Magmen, ihres Aufstiegs und ihrer Quellen in den letzten 7 Ma. Drei Vorkommen von hydrothermalen Quellen bzw. Präzipitaten wurden in den Coriolis Troughs bisher beschrieben aber nicht detailliert untersucht. Mit einem ROV sollen die zeitliche und chemische Variabilität zwischen Magmengenese, Vulka­nismus und Hydrothermalismus im Gebiet der Coriolis Becken untersucht werden. Von Bedeutung sind Fragen der lithologischen Kontrolle durch volatilreiche, alkaline Magmen und Einflüsse vulkanischer Entwicklung auf metallogenetische Prozesse sowie der Fluiddynamik und –entwicklung. Die Auswirkung unterschiedlicher Wassertiefen auf die Entgasungs­prozesse und Zusammensetzung hydrothermaler Fluide steht dabei im Vordergrund. Ein weiterer Schwer­punkt liegt in der Untersuchung der kleinräumigen Variabilität magmatischer Differenziation  im Inselbogen und deren Rückkopplung auf Metallfraktionierung und hydrothermale Aktivität. Von biologischer Seite steht das Verständnis der Kontrolle der Habitate sowie der Faunenverteilung und -zusammensetzung an hydrothermalen Austritten im Vordergrund. 

Lavas from the Azores islands show some of the most extreme variation in trace element and isotope compositions known from oceanic intraplate volcanoes. This extreme variation has partly been explained by the presence of recycled crustal rocks in the mantle sources. Stable isotopes provide the prospect to increase our understanding of the generation of such mantle sources. While the 18O/16O of upper mantle olivines shows a small variability (~δ18O of 5.0-5.2 ‰) the incorporation of sedimentary and continental material into the mantle will significantly increase the δ18O. Contrastingly, the high temperature alteration of the oceanic crust will result in lower δ18O. The Azores archipelago displays an ideal site to study the O isotope variation of highly variable mantle sources on a small scale in order to determine their origin. We propose a systematic study of olivine and clinopyroxene phenocrysts from primitive lavas and plagioclase phenocrysts from evolved lavas as well as glass analyses from all lavas of the Azores volcanoes both east and west of the Mid-Atlantic Ridge in order to better understand the variability of mantle sources and their origin. Chlorine and F concentrations in glasses from different islands will help to define crustal assimilation of the Azores magmas and can also be used to define recycled crustal material in pristine mafic rocks. This study will complement the large geochemical data set on the Azores magmas and provide important new insight into the origin of mantle sources.

The buoyant continental mantle root plays an important role in stabilizing of the lithosphere but its composition and age as well as its relationship to the crust are poorly understood. The crust is believed to be largely generated in subduction zones while several other geodynamic settings have been proposed to facilitate lithospheric mantle generation. In this project we suggest to study the lower crust and subcontinental lithospheric mantle along the Eger Rift with highly precise and accurate trace element and isotope methodologies. The Eger region is particularly interesting because it transverses the boundary of two major lithospheric blocks (the Saxothuringian and the Moldanubian) and has been amalgamated during the Variscan orogeny. We propose to study the geochemical and isotopic composition of crustal and mantle xenoliths in order to compare the petrogenesis of the different parts of the lithosphere and define possible relationships. The lithosphere beneath the Eger Rift is also believed to contribute to the alkaline magmatism and thus another part of the project is concerned with the better definition of magma sources and their regional variation.

In dem beantragten Projekt soll eine kombinierte geochemische und experimentell petrologische Untersuchung der Bildung von SiO2-reichen Magmen in der ozeanischen Kruste durchgeführt werden. Diese Studie soll das Verständnis 1) der Fraktionierungsprozesse, die zur Bildung von felsischen Magmen führen, 2) der Magmendynamik während des Aufstiegs in der ozeanischen Kruste und 3) die Interaktion von Shcmelzen mit der alterierten ozeanischen Kruste verbessern. Hauptbestandteil des vorgeschlagenen Projektes soll die Untersuchung von Gesteinen des Oman Ophiolits darstellen, wobei einerseits die felsischen Gesteine und andererseits die damit auftretenden mafischen und hydrothermal alterierten Nebengesteinen untersucht werden sollen. Damit soll festgestellt werden, durch welche Prozesse (Assimilation, partielle Aufschmelzung oder fraktionierende Kristallisation) die felsischen Magemn entstanden. Ausserdem sollen basaltische, andesitische und dazitische Laven des Pazifisch-Antarktischen Rückens untersucht werden, da an dieser schnell-spreizenden Achse felsische Laven verbreitet sind, aber noch keine detaillierte Studie ihrer Entstehung durchgeführt wurde. Wir planen im Rahmen einer Dissertation geochemische und isotopengeochemische Untersuchungen an Gesamtgesteinen, vulkanischen Gläsern, Phäno- und Xenokristallen zur Entwicklung eines umfassenden Verständnisses der Transformation von mafischem zu felsischem Material. Gleichzeitig sollen in einer anderen Dissertation die Mineral-Schmelzgleichgewichte, Verteilungskoeffizienten von Spurenelementen und mögliche Aufschmelz oder Kristallisationsprozesse mit experimentellen Methoden an den gleichen Proben untersucht werden. 

Die Azoren liegen auf einem ozeanischen Plateau mit etwa 10-12 km mächtiger Kruste basaltischer Zusammensetzung. Das Plateau mit der verdickten Kruste entwickelte sich offenbar durch verstärkten Vulkanismus vor etwa 6-4 Ma. Seit 4 Ma entsteht am Mittelatlantischen Rücken dünnere Kruste, da die Schmelzanomalie abgeschwächt ist und so das Azoren Plateau geteilt wird. Der magmatische Puls vor 6-4 Ma wurde möglicherweise durch einen Mantelplume-Kopf ausgelöst, der zur Bildung des Plateaus aus ozeanischen (Flut)basalten führte. Die Insel Santa Maria am östlichen Rande des Plateaus reflektiert eine Schlüsselrolle in der Bildung des Plateaus. Das Projekt hat drei Ziele: (1) die zeitliche und chemische Entwicklung des Vulkanismus auf dem Plateau zu klären (z.B. der Übergang von tholeiitischen Flutbasalten zu alkalinen Magmen der Inseln), (2) die Wechselwirkung zwischen der Azoren Schmelzanomalie und dem Mittelatlantischen Rücken zu bestimmen, (3) den Magmentransport und die Eruptionsmechanismen in der frühen Plateaubildungsphase zu bestimmen und (4) den zeitlichen Rahmen und biogeographischen Kontext sowie Diagenesepfade der eingeschalteten Karbonate zu bestimmen.

Oxygen isotopes are an important tool to study reactions between ascending mantle-derived magmas and material in the oceanic lithosphere that has been altered by surface processes like for example, sediments or hydrothermally altered rocks. Furthermore, crystal fractionation processes can also affect the O isotope composition especially of evolved magmas because different mineral phases fractionate O isotopes. Both assimilation and crystal fractionation thus impede the study of O isotope compositions of the magma sources in the mantle which could give important insights into recycling processes at subduction zones and in deep mantle plume-derived intraplate magmas. Here we suggest a study of the O isotope variation of five well-characterized lava series from different oceanic magmatic settings (mid-ocean ridge, oceanic intraplate, back-arc, and island arc settings) in order to define the variations between basaltic and silicic lavas and the processes affecting the O isotope ratios. Based on the understanding of lithospheric processes we will be able to distinguish the O isotope composition of the mantle sources of the magmas and draw conclusions on crustal recycling into the deep mantle and into the mantle wedge beneath subduction zones.