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The Main Ethiopian Rift represents a unique insight into process of continental rifting and its comprehensive research can provide partial clarification of open questions such are the causes, mechanisms, and timing of overall tectonic and magmatic evolution. The Main Ethiopian Rift is an intermediary between the Afar triple junction to the north and Kenyan Rift to the south, representing incipient plate boundary between Nubian and Somalian plates. Based on comprehensive geological research of the northern flank of the Southern Main Ethiopian Rift including field geological and structural mapping, petrological and geochemical description of individual lithologies, morphotectonic analysis of Digital Elevation Model, paleostress analysis and gravity pattern assessment including calculation of Linsser indices, some aspects in geodynamic evolution of northern flank of the Southern Main Ethiopian Rift is interpreted. The area recorded typical continental rift-related tectonic and magmatic evolution including "pre-rift" (Eocene to Oligocene) volcanic activity initiated by extensive flood (plateau) alkaline basalt to trachybasalt basalt eruptions due to crustal thinning and mantle plume(s) ascent, followed by fault-dominated "early-rift" (Miocene) bimodal volcanism associated with origin of the rift...

Studies of the Fe, Cu, and Zn isotopic compositions of volcanic rocks and sulfides provide an important tool for understanding magmatic, hydrothermal, and alteration processes, thereby enabling the determination of both transition metal sources and the quantification of the petrologic environmental impacts of hydrothermal activities. In this study, the δ56Fe and δ57Fe values of the mid-ocean ridge basalts (MORBs) are higher than those of the seafloor hydrothermal fluids, while the reverse is true for the δ66Zn and δ68Zn values, suggesting that basalt-fluid interactions preferentially incorporate isotopically light Fe and heavy Zn into the fluids, resulting in the relative enrichment of heavier Fe and lighter Zn isotopes in altered basaltic rocks. Most of the δ56Fe values (−1.96 to +0.11‰) of the sulfide minerals are within the range of the vent fluids, but they are significantly lower than those of the MORBs and back-arc basin basalts (BABBs), suggesting that the Fe in the sulfides was mainly derived from the fluids. However, the majority of the chalcopyrite δ56Fe and δ57Fe values are higher than those of the sphalerite and pyrite. This suggests that high-temperature sulfide minerals are enriched in 56Fe and 57Fe, whereas medium- and low-temperature sulfides are depleted in 56Fe and 57Fe. Moreover, the δ65Cu (−0.88 to −0.16‰) and δ66Zn (−0.39 to −0.03‰) values of the sulfide minerals are significantly lower than those of the MORBs, BABBs, and fluids, suggesting that 63Cu and 64Zn were preferentially removed from the fluids and incorporated into the chalcopyrite and sphalerite, respectively. Consequently, vent fluid injection and deposition can cause the heavier Cu and Zn isotopic compositions of hydrothermal plumes, seawater, and sediments., SCOPUS: ar.j, info:eu-repo/semantics/published

Upper Cretaceous intrusives of limited extent crop out in the Coastal Cordillera near of Valdivia (39º48’ S), 100 km west of the main topographic divide of the Andean Cordillera. Given that plutonic rocks of the same age crop out at the same latitudes in the high Andes the coastal intrusives emplaced in a forearc position in the upper plate of a subduction setting. They correspond to hypabyssal intrusives displaying mainly porphyritic texture and lithological variations with microtonalites (minor), porphyritic microgranodiorites (main) and microgranites. They intrude the Upper Paleozoic-Triassic accretionary complex of the Bahia Mansa Metamorphic Complex. These intrusives, that comprise the Chaihuín Pluton and minor stocks of porphyritic felsic rocks, have calc-alkaline affinities with metaluminous and peraluminous character. They are geochemically similar to the contemporaneous main arc-related plutonic rocks of the Gualletué Plutonic Group. The microgranitoids and dacitic rocks from Los Boldos, the low and Loncoche are peculiar because they show an apparently adakitic affinity in Sr/Y and LaN /YbN discriminant diagrams; nevertheless Sr contents of these rocks (<, SCOPUS: ar.j, info:eu-repo/semantics/published

The Siilinjärvi phosphate deposit (Finland) is hosted by an Archean carbonatite complex. The main body is composed of glimmerite, carbonatite and combinations thereof. It is surrounded by a well-developed fenitization zone. Almost all the rocks pertaining to the glimmerite-carbonatite series are considered for exploitation of phosphate. New petrological and in-situ geochemical as well as spectroscopic data obtained by cathodoluminescence, Raman and laser-induced breakdown spectroscopy make it possible to constrain the genesis and evolution of apatite through time. Apatite in the glimmerite-carbonatite series formed by igneous processes. An increase in rare earth elements (REE) content during apatite deposition can be explained by re-equilibration of early apatite (via sub-solidus diffusion at the magmatic stage) with a fresh carbonatitic magma enriched in these elements. This late carbonatite emplacement has been known as a major contributor to the overall P and REE endowment of the system and is likely connected to fenitization and alkali-rich fluids. These fluids - enriched in REE - would have interacted with apatite in the fenite, resulting in an increase in REE content through coupled dissolution–reprecipitation processes. Finally, a marked decrease in LREE is observed in apatite hosted by fenite. It highlights the alteration of apatite by a REE-poor fluid during a late-magmatic/hydrothermal stage. Regarding the potential for REE exploitation, geochemical data combined with an estimation of the reserves indicate a sub-economic potential of REE to be exploited as by-products of phosphate mining. Spectroscopic analyses further provide helpful data for exploration, by determining the P and REE distribution and the enrichment in carbonatite and within apatite., SCOPUS: ar.j, info:eu-repo/semantics/published

Bogoslof volcano, Alaska, experienced at least 70 explosive eruptions between 12 December 2016 and 31 August 2017. Due to its remote location and limited local monitoring network, this eruption was monitored and characterized primarily using remote geophysical and satellite techniques. SO2 emissions from Bogoslof were persistently detected by the Infrared Atmospheric Sounding Interferometer (IASI) satellite sensors. Of Bogoslof’s 70 explosive events, 50% produced measurable SO2 masses ranging from 0.1 to 21.5 kt, with a median and standard deviation of 0.7 ± 4.0 kt SO2, respectively. Here, we compare IASI-derived SO2 masses from Bogoslof events to complementary geophysical datasets to provide insights into eruption source processes, namely the degree of seawater scrubbing of water-soluble SO2 and variations in magma flux. Correlations with the number of lightning strokes and infrasound energy are expected to indicate magma-flux as a controlling process, while correlations with infrasound frequency index are expected to indicate variations in vent-water content as a controlling factor. These comparisons suggest that the measured SO2 masses are primarily a function of eruption magnitude (degassed magma mass) and that scrubbing of SO2 emissions by vent seawater may have exerted a minor effect on the observed SO2 masses. SO2 masses were combined with petrologic constraints on melt inclusion and matrix glass S concentrations to calculate degassed magma masses and volumes. The cumulative SO2-derived degassed magma mass and estimated volume (dense-rock equivalent) for the full Bogoslof eruption were found to be 2.8 × 1010 kg and 9.3 × 106 m3, respectively. When individual event masses are compared against event masses calculated using an empirical plume-height method, a strong correlation is found (R2 = 0.83), with better than order-of-magnitude agreement in most cases. These estimates of eruption masses provide useful information on the magnitude, behavior, and associated hazards of the 2016–2017 eruption, and potentially future unrest at Bogoslof volcano., SCOPUS: ar.j, info:eu-repo/semantics/published

Selenium is a chalcophile, moderately volatile and redox-sensitive element. The Se isotopic and elemental systematics of mantle-derived rocks and melts may therefore provide new approaches to study the terrestrial volatile origin and evolution as well as secular changes of redox conditions across the surface and mantle reservoirs. Selenium is significantly depleted in mantle samples (at ng/g levels), posing analytical challenges for Se isotopic studies of the igneous system. This study presents an analytical protocol suitable for precise and accurate determination of Se isotope and Se–Te abundances of igneous rocks. The Se–Te elemental systematics provide a petrogenetic context for interpreting Se isotope systematics. The new method was used to analyze a suite of basaltic glasses from the Pacific–Antarctic ridge (PAR) and the Mid-Atlantic ridge (MAR). The magmatic differentiation involving concurrent sulfide segregation results in significant chalcophile element fractionation but no measurable Se isotopic variation. Because of the demonstrated lack of Se isotopic fractionation between sulfides and silicate melt, the Se isotope systematics of MORB reflects a source signature. The southern MAR displays a significant source heterogeneity due to the localized interaction between the ridge and Shona and Discovery mantle plumes that incorporate recycled components.

Determining the extent of mantle mixing during the Hadean-Archean is an integral factor in our understanding of early geodynamic processes as well as the speed and degree of mantle homogenisation. If a dynamic convecting mantle was the predominant regime it would be expected that early formed isotopic anomalies would be quickly homogenised, whilst in a stagnant lid regime these anomalies might last for hundreds of millions of years. Archean terranes are dominated by felsic tonalite, trondhjemite and granodiorite rocks, as such these rocks have been the main rock type studied, even though they are not formed by primary mantle melts. Therefore, in this study, we have focused on mafic rock samples as tracers of primary mantle melting, from the relatively unknown West African craton. The mafic rocks have undergone metamorphism to granulite facies with the majority of samples retrogressed to amphibolite facies. Major element compositions reveal that the protolith was tholeiitic basalt. The majority of trace elements display limited mobility, as primary correlations with Zr are still present. Trace element patterns are typical for Archean mafic rocks, with Nb-Ta and Ti depletions. The meta-basalts yield a 147 Sm- 143 Nd errorchron with an age of 3300 ± 300 Ma, with initial εNd of +4.4. The Nd compositions indicate that the meta-basalts have experienced minimal crustal assimilation and retain primary geochemical attributes. A positive initial εNd for the meta-basalts suggests that the magmatic protolith evolved from an already differentiated source. Nevertheless, 142 Nd compositions are within error of modern day terrestrial, as such, the protolith for these samples either did not experience any early differentiation, or that mantle convection had homogenised any anomalous signal. These results highlight the lack of large (>±8 µ 142 Nd) 142 Nd anomalies detected from outside the North Atlantic and Superior Cratons, suggesting that Archean mantle dynamics was complex, with different processes occurring on different parts of Earth, similar to today., SCOPUS: ar.j, info:eu-repo/semantics/published

On 3 June 2018 Volcán de Fuego (Guatemala) erupted explosively with unusual intensity, producing wide-spread ash dispersal and pyroclastic flows of >11 km length, which destroyed a community on Fuego's flanks, causing hundreds of fatalities. Here, we analyze satellite measurements of the SO 2 plume emitted during the most intense eruptive phase. Key eruption parameters including the injection height and SO 2 flux time-series indicate a degassing intensity at least three orders of magnitude above baseline levels. Our results suggest a steady ~2.5 hour climactic paroxysmal phase of the eruption with a mass eruption rate of ~1.4kg s −1 based on the combination of plume height estimates and an eruption column model, producing 0.03 ± 0.004 km 3 of tephra. We detect at least 130 kt of emitted SO 2 from satellite images, producing a minimum dissolved magmatic sulfur concentration of 500 ppm. Possible source mechanisms are discussed, which may be useful in assessing the risks posed by future large-magnitude eruptions to the large populations that live on Fuego's flanks. This study shows that even under challenging conditions of a tropical atmosphere during the rainy season, vital eruption parameters to constrain source mechanisms of eruptions can be retrieved from satellite remote sensing data., SCOPUS: ar.j, info:eu-repo/semantics/published

Our knowledge of active magmatic hydrothermal system (or magmatic vapors) is largely related to the modeling of geochemical processes including heterogeneous equilibrium calculations with variable bulk composition, temperature or pressure. With the aim to constrain the characteristics of extinct hydrothermal systems it is necessary to look for petrogenic evidence in active ones. The Kudryavy volcano in the Kurile Islands (Russia) provides a unique natural laboratory to study the formation of fumarolic rocks from high temperature fluids (measured temperature for the fumaroles up to 940 °C). By studying the minerals chemistry and assemblages and by computing a thermodynamical modeling, we investigated the mineralogical evidence for such high-temperature. We confirm the documented occurrence of Ca-Fe rich minerals as isolated patches, veins or incrustation in cavities and their formation during the alteration of primary minerals. We describe and documented secondary Na-Al rich minerals (davyne, nepheline, sodalite) and their occurrence together with Ca-Fe minerals in cavities. We also documented the presence of Fe-wollastonite, a relatively rare mineral suggesting high-T formation and we observed assemblages including wollastonite + andradite + magnetite suggesting high-temperature decomposition of andradite. This natural laboratory provides a series of concordant petrologic evidences for high-temperature fumarolic rocks and offers guidelines for the study of ancient high temperature hydrothermal environments on Earth and other planets like Mars., SCOPUS: ar.j, info:eu-repo/semantics/published

We report Ca isotope fractionation among a co-genetic suite of samples from the Mauritanian Guelb el Azib ultramafic-mafic-anorthosite complex (GAC), which represents the fractional crystallization sequence of an igneous magma chamber. We investigate how the composition of an evolving crystallizing liquid and the resultant mineralogy of co-crystallizing assemblages affects inter-phase Ca isotope fractionation. Because the GAC is an Archean metamorphosed complex, we first investigate the resistance of the Ca isotope signature to secondary hydrothermal alteration and to metamorphism. While we cannot conclude here that Ca isotopes are undisturbed at the mineral scale, we show that they are preserved at the bulk rock scale. This is adequate for our study where several samples are almost monomineralic at the bulk scale level. The δ44/40Ca (relative to NIST standard SRM 915a) of GAC layers range from −1.53 to 1.61‰ with the earliest-formed ultramafic cumulate layer being isotopically heaviest and the later, more felsic layers being isotopically lighter. For the first time, we show that plagioclase is much more enriched in light Ca isotopes compared to olivine and (Ca-) pyroxene. Monte Carlo simulations suggest that Ca isotopes are fractionated among co-existing silicate minerals during fractional crystallization, possibly in relation with the residual liquid composition. In qualitative agreement with computational models based on first principles lattice dynamics, we observe that Ca isotope fractionation is mineralogically controlled and importantly, that the degree of fractionation can vary according to the CaO composition of the residual liquid. While previous studies have aimed to understand partial melting as a source of Ca isotope fractionation, our results suggest that fractional crystallization is also a source of Ca isotope variability among co-genetic samples., SCOPUS: ar.j, info:eu-repo/semantics/published

The Upper Ruvubu Alkaline Plutonic Complex (URAPC) in Burundi consists of three separate intrusions, each with a specific emplacement age and petrological composition. Three main units are recognized: an outer unit with silica-saturated plutonic rocks (from gabbro to granite), an inner unit with silica-undersaturated plutonic rocks (feldspathoidal syenite with subordinate feldspathoidal monzonite and ijolite) and a carbonatitic body in the subsoil, known by drilling. The URAPC is quite large in size (∼24 km long and up to 10 km wide). It is considered to have been intruded syntectonically in an overall extensional context, thanks to the kilometric shear zones that accommodated its emplacement. Radiometric ages from literature range from 748 to 705 Ma and point to structurally-controlled magmatic differentiation followed by long-lived circulations of late-stage fluids postdating the emplacement of a part of the undersaturated rocks and the carbonatites. In the north-western part of the outer unit, gabbro likely has been emplaced at a deeper structural level than the granite, which represents a more apical structural level of emplacement. This petrological, geochemical and isotopic (Sr-Nd-Hf) study concentrates on the processes that generated the URAPC: (i) fractional crystallization, evidenced by the chemical evolution trends of the major and trace elements, and by marked P, Ti and Ba anomalies in the trace element patterns; (ii) crustal assimilation/contamination, as shown by the wide range of Nd isotope compositions and the general increase of the Sr isotope ratios with increasing SiO 2 contents, and (iii) late-magmatic/hydrothermal alteration inducing an increase of the Sr isotope composition without changing significantly the Nd isotope composition. The isotopic data are consistent with an asthenospheric mantle source, though less depleted than the Depleted Mantle (DM), contaminated by the Subcontinental Lithospheric Mantle (SCLM). The silicate and carbonate magmatic series are cogenetic. The outer unit is clearly more contaminated than the inner unit, whereas the carbonatitic body could have evolved by liquid immiscibility. The URAPC lies within East Africa's Western Rift Valley, which is marked by 23 alkaline plutonic complexes. Their emplacement has been ascribed to reactivation of Proterozoic lithospheric weakness zones resulting from the breakup of the Neoproterozoic supercontinent Rodinia supercontinent., SCOPUS: ar.j, info:eu-repo/semantics/published

Ultramafic hosted hydrothermal deposits are ubiquitous along slow-spreading ridges such as the Mid-Atlantic Ridge (MAR; e.g. Ashadzé Rainbow, Lost City) where they exert a major control on the cycling of economically important elements (e.g. Zn, Cu, Ni). However, the origin of metal mobility in these environments remains unclear. Here we use Zn (δ66Zn), Cu (δ65Cu) and Fe (δ56Fe) stable isotopes to explore the mobility of metals during (1) the serpentinization of the Rainbow massif basement in a seawater dominated system at low temperature (350 °C) mineralization of serpentinites through seawater-derived fluids that interacted with gabbro prior to interacting with serpentinite near hydrothermal sites (stockworks). The Rainbow samples display among the largest range of isotopic variations ever reported for ultramafic rocks (−0.10‰ ≤ δ66Zn ≤ +0.47‰; −0.93‰ ≤ δ65Cu ≤ +0.24‰; −0.15‰ ≤ δ56Fe ≤ +0.25‰). These variations reflect a two-stage process. (1) Serpentinization of the ultramafic basement is accompanied by a decrease in Zn (26–41 ppm) and Cu (1–13 ppm) concentrations and an increase of δ66Zn (+0.30–+0.47‰) in peridotites relative to primitive mantle (Zn ∼ 55 ppm, Cu ∼ 20 ppm, δ66Zn ∼ +0.16‰). Striking correlations between δ66Zn and indices of serpentinization (LOI and Fe/3+ΣFe) show preferential leaching of isotopically light Zn by fluids during the serpentinization of the massif. This isotopic fractionation is controlled by the dissolution of both mantle sulfides and/or spinels and Zn complexation with chlorine in fluids. At this stage, Fe seems to be immobile as attested by correlations between δ56Fe and indices of peridotite fertility (e.g. Al2O3/SiO2). (2) The mineralization of serpentinites near the Rainbow stockwork is accompanied by an increase in Fe/3+ΣFe (>0.7), FeO (up to 19.8 wt%), Zn (≫50 ppm) and Cu (≫20 ppm) concentrations. The δ66Zn and δ65Cu values progressively decrease with indices of serpentinite mineralization (e.g. Zn, Cu, Fe/3+ΣFe), while several samples display abnormally high δ56Fe (up to 0.25‰) relative to primitive mantle (δ56Fe ∼ 0.025‰), suggesting a high mobility of Zn, Cu and Fe in high temperature hydrothermal fluids. These isotopic fractionations can be explained by the local oxidation of sulfur bearing fluids in contact with seawater. This process enhances metal precipitation as well as the formation of Fe3+-bearing phases, such as magnetite, beneath the stockwork, explaining the presence of magnetic anomalies below the Rainbow hydrothermal field. Our study shows that the mobility of metals in hydrothermal fluids can be enhanced by both peridotite interaction with seawater or with fluid that interacted with deeper mafic bodies and then flowed to the surface. These processes may generate hydrothermal deposits with distinct metal signatures., SCOPUS: ar.j, info:eu-repo/semantics/published

This project is funded by the Natural Environment Research Council grant NE/L013932/1 (RiftVolc). Abstract For many magmatic systems, crystal compositions preserve a complex and protracted history which may be largely decoupled from their carrier melts. The crystal cargo may hold clues to the physical distribution of melt and crystals in a magma reservoir and how magmas are assembled prior to eruptions. Here we present a geochemical study of a suite of samples from three peralkaline volcanoes in the Main Ethiopian Rift. Whilst whole-rock data shows strong fractional crystallisation signatures, the trace element systematics of feldspars, and their relationship to their host glasses, reveals complexity. Alkali feldspars, particularly those erupted during caldera-forming episodes, have variable Ba concentrations, extending to high values that are not in equilibrium with the carrier liquids. Some of the feldspars are antecrysts, which we suggest are scavenged from a crystal-rich mush. The antecrysts crystallised from a Ba-enriched (more primitive) melt, before later entrainment into a Ba-depleted residual liquid. Crystal-melt segregation can occur on fast timescales in these magma reservoirs, owing to the low viscosity nature of peralkaline liquids. The separation of enough residual melt to feed a crystal-poor post-caldera rhyolitic eruption may take as little as months to tens of years (much shorter than typical repose periods of 300-400 years). Our observations are consistent with these magmatic systems spending significant portions of their life cycle dominated by crystalline mushes containing ephemeral, small (

Resolving the possible mantle and crustal sources for shergottite meteorites is crucial for understanding the formation and early differentiation of Mars. Orbiter and rover characterization of the martian surface reveal that the major element composition of most of its surface does not match the shergottites (McSween et al. 2009) leaving the relationship between them poorly understood. The identification of the meteorite NWA 7034 and its pairs as a Mars surface rock (Cartwright et al. 2014) provides access to a representative sample of Mars' crust (Agee et al. 2013; Humayun et al. 2013). Utilizing the short-lived 146Sm–142Nd, and long-lived 147Sm–143Nd and 176Lu–176Hf chronometers, which are sensitive to silicate differentiation, we analyzed three fragments of NWA 7034. The very negative mean isotopic compositions for this breccia, μ142NdJNdi-1=−45±5 (2SD), ε143NdCHUR=−16.7±0.4 (2SD) and ε176HfCHUR=−61±9 (2SD) point to an ancient origin for this martian crust. However, modeling of the data shows that the crust sampled by NWA 7034 possesses a Hf/Nd ratio and coupled ε143Nd–μ142Nd model age that are incompatible with this crustal reservoir being an end-member that generated the shergottite source mixing array. In addition, this crust is not juvenile, despite its rare earth element profile, but has had a multistage formation history. Therefore, early crustal extraction alone was not responsible for the creation of the reservoirs that produced the shergottites. Instead mantle reservoirs formed via other early differentiation processes such as in a Mars magma ocean must be responsible for the trace element and isotopic signatures present in shergottites., SCOPUS: ar.j, info:eu-repo/semantics/published

The iron mine of Tamra (Nefza District, NW Tunisia) is a 50 m thick Upper Mio-Pliocene sedimentary series impregnated by Fe-Mn oxides associated with white clay lenses with high halloysite and kaolinite content. This mineralization results from i) synsedimentary weathering/pedogenesis, and ii) mixing surface water and regional hydrothermal fluids. The oxygen and hydrogen isotope composition of halloysite-kaolinite and goethite-hematite is examined in order to provide new insights into the ore formation. This study concludes that halloysite-kaolinite was not equilibrated only with meteoric fluids: the δ18O values have a range towards high values that are not consistent with weathering conditions for their formation and/or during their subsequent alteration. The δD and δ18O values of goethite lead to the same conclusion. The stable isotope compositions could be related to fluid-rock interaction with the underlying marls (and/or skarns), providing relatively high δ18O values to the fluids responsible for the white clay formation. This model also shows that the Pb-isotope compositions of halloysite-kaolinite are explained by a felsic and a carbonated end-member, similar to other ore deposits (IOCG and Sedex) of the vicinity. Several factors should be considered for the precipitation of halloysite-kaolinite and/or destabilization of primary clays in the Tamra ore, i.e. mixing of deep hot saline fluids, related to a thermally driven circulation, and meteoric waters. This hydrothermal contribution postdates the main synsedimentary weathering/pedogenetic Fe-enrichment and may be related to late Fe, Mn, Pb, Zn and As inputs of the Fe-Mn oxides., SCOPUS: ar.j, info:eu-repo/semantics/published

Calcium (Ca) is the fifth most abundant element in the rocky planets. As a lithophile, refractory element, Ca does not partition into planetary cores nor is it volatilized during planetary accretion. These characteristics make Ca ideal for investigating the earliest stages of planetary formation and the subsequent chemical evolution of planetary mantles and crusts. This thesis presents observations of and explores the mechanisms involved in high-temperature mass-dependent Ca isotope fractionation in terrestrial, lunar, and meteoritic material. Chapter 1 reports Ca isotope fractionation among a co-genetic suite of samples from the Guelb el Azib ultramafic-mafic-anorthosite complex, which represents the fractional crystallization sequence of a terrestrial igneous magma chamber. The measurements imply that Ca isotope fractionation in an evolving crystallizing magma is mineralogically controlled and that the degree of fractionation can vary according to the Ca composition of the residual magma. Chapter 2 investigates ureilites, a distinctive group of achondritic meteorites, widely regarded to be mantle remnants of a disrupted asteroidal parent body. To date, it is not clear which of their features were inherited from the original chondritic body and which were created during post-accretionary igneous processes such as partial melting. This chapter presents evidence that partial melting on the ureilite parent body is responsible for two such ambiguous characteristics, Ca isotopic and magnesium number (Mg, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

Upper Cretaceous to Pleistocene volcanic rocks of the Bohemian Massif represent the easternmost part of the Central European Volcanic Province. These alkaline volcanic series include rare melilitic rocks occurring as dykes, sills, scoria cones and flows. They occur in three volcanic periods: (i) the Late Cretaceous to Paleocene period (80–59 Ma) in northern Bohemia including adjacent territories of Saxony and Lusatia, (ii) the Mid Eocene to Late Miocene (32.3–5.9 Ma) period disseminated in the Ohře Rift, the Cheb-Domažlice Graben, Vogtland, and Silesia and (iii) the Early to Late Pleistocene period (1.0-0.26 Ma) in western Bohemia. Melilitic magmas of the Eocene to Miocene and Pleistocene periods show a primitive mantle source [(143Nd/144Nd)t = 0.51280–0.51287; (87Sr/86Sr)t = 0.7034–0.7038)] while those of the Upper Cretaceous to Paleocene period display a broad scatter of Sr-Nd ratios. The (143Nd/144Nd)t ratios (0.51272–0.51282) of the Upper Cretaceous to Paleocene rocks suggest a partly heterogeneous mantle source, and their (87Sr/86Sr)t ratios (0.7033-0.7049) point to an additional late-to post-magmatic hydrothermal contribution. Major rock-forming minerals include forsterite, diopside, melilite, nepheline, sodalite group minerals, phlogopite, Cr-and Ti-bearing spinels. Crystallization pressures and temperatures of clinopyroxene vary widely between ~1 to 2 GPa and between 1000 to 1200 °C, respectively. Nepheline crystallized at about 500 to 770 °C. Geochemical and isotopic similarities of these rocks occurring from the Upper Cretaceous to Pleistocene suggest that they had similar mantle sources and similar processes of magma development by partial melting of a heterogeneous carbonatized mantle source. Svrchnokřídové až pleistocenní melilitické vulkanity Českého masivu jsou nejvýchodnější částí středoevropské provincie alkalických vulkanitů. Tyto vulkanity včetně vzácných melilitických hornin můžeme nalézt v podobě pravých i ložních žil, struskových kuželů a lávových výlevů. Vulkanická aktivita v minulosti probíhala ve třech časových úsecích: (i) od svrchní křídy do paleocénu (80–59 Ma) v severních Čechách a přilehlých oblastech Saska a Lužice, (ii) od středního eocénu do pozdního miocénu (32,3–5,9 Ma) v rámci oháreckého riftu, chebsko-domažlického příkopu, Fojtsku a Slezsku a (iii) od spodního do svrchního pleistocénu (1,0–0,26 Ma) v západních Čechách. Melilitické horniny eocenního až miocenního a pleistocenního stáří vykazují primitivní plášťový zdroj [(143Nd/144Nd)t = 0,51280–0,51287; (87Sr/86Sr)t = 0,7034–0,7038)], zatímco svrchnokřídové až paleocenní melilitoidy vykazují široký rozptyl izotopových poměrů Sr a Nd. Poměry (143Nd/144Nd)t mezi 0,51272 až 0,51282 těchto svrchnokřídových až paleocenních hornin ukazují na částečně heterogenní plášťový zdroj, zatímco poměry (87Sr/86Sr)t mezi 0,7033 až 0,7049 mohou souviset s dodatečným pozdně magmatickým vývojem. Hlavní horninotvorné minerály zahrnují forsterit, diopsid, melilit, nefelín, minerály sodalitové skupiny, flogopit a Cr a Ti spinelidy. Odhad teplotně-tlakových podmínek krystalizace klinopyroxenu kolísá v rozpětí ~1–2 GPa a 1000–1200 °C. Ke krystalizaci nefelínu došlo v rozpětí 500 až 770 °C. Geochemická a izotopická podoba melilitových hornin svrchnokřídového až pleistocenního stáří ukazuje na jejich společný původ vytavením z heterogenního karbonatizovaného plášťového zdroje.

Offshore western Svalbard plumes of gas bubbles rise from the seafloor at the landward limit of the gas hydrate stability zone (LLGHSZ; ∼400 m water depth). It is hypothesized that this methane may, in part, come from dissociation of gas hydrate in the underlying sediments in response to recent warming of ocean bottom waters. To evaluate the potential role of gas hydrate in the supply of methane to the shallow subsurface sediments, and the role of anaerobic oxidation in regulating methane fluxes across the sediment–seawater interface, we have characterised the chemical and isotopic compositions of the gases and sediment pore waters. The molecular and isotopic signatures of gas in the bubble plumes (C1/C2+ = 1 × 104; δ13C-CH4 = −55 to −51‰; δD-CH4 = −187 to −184‰) are similar to gas hydrate recovered from within sediments ∼30 km away from the LLGHSZ. Modelling of pore water sulphate profiles indicates that subsurface methane fluxes are largely at steady state in the vicinity of the LLGHSZ, providing no evidence for any recent change in methane supply due to gas hydrate dissociation. However, at greater water depths, within the GHSZ, there is some evidence that the supply of methane to the shallow sediments has recently increased, which is consistent with downslope retreat of the GHSZ due to bottom water warming although other explanations are possible. We estimate that the upward diffusive methane flux into shallow subsurface sediments close to the LLGHSZ is 30,550 mmol m−2 yr−1, but it is, SCOPUS: ar.j, info:eu-repo/semantics/published

info:eu-repo/semantics/published

Monazite is commonly found in most of geological environments. Monazite can be rich in uranium and thorium, does not incorporate lead, and its isotopic (U-Th-Pb) system is very robust to diffusion in most of crustal conditions, which makes it a very attractive chronometer. In addition, it represents the main source of thorium and a major source of rare earth elements (REE), in the crust. During fluid-monazite interaction, monazite can recrystallize by a coupled dissolution-precipitation process, with a chemical/isotopic composition different from the initial monazite. These recrystallizations involve a redistribution of the elements contained in monazite (REE, Th, U, Pb) and understanding of the mobility of these strategic elements is crucial for their economic (lanthanides resources and actinides) and environmental (storage of radioactive waste) aspects.The aim of this thesis is to investigate the behaviour of monazite during fluid-monazite interactions and its potential as chronometer and geochemical tracer of fluid mineralization, via a multi-disciplinary approach including mineralogy, experimental petrology, geochronology and tectonic. The work presented here is organized in two parts: one on Alpine hydrothermal monazite dating and the other on the results of hydrothermal alteration experiments in laboratory.About forty monazite and ten xenotime crystals were collected in Alpine clefts (hydrothermal veins formed during exhumation) of the external (Argentera, Belledonne, Mont-Blanc) and the internal (Briançonnais Zone) domains. The LA-ICP-MS in-situ U-Th-Pb dating allowed to better constrain the age and duration of hydrothermal circulation during the late deformation stages related to the exhumation of the western Alps. The fluid inclusion analysis of monazite crystals coupled with zircon fission-track dating have brought new constrains on the geothermal gradient induced by fluid circulations in the hydrothermal veins. Systematic analysis of experimental products (monazite and fluid) of 18 experiments confirmed the mobility of elements such as uranium or heavy REE during hydrothermal reactions. The nanoscale study of monazite recrystallized domains showed a new replacement mechanism characterized by the propagation of the reaction front through nano-pores and nano-fractures. This mechanism leads to anisotropic replacement and a mixture of nano-domains of primary and recrystallized monazite. These observations have major implications for the storage of radioactive waste or in geochronology to explain the disturbances of monazite ages that have reacted with fluid in hydrothermal or metamorphic environments., La monazite est présente comme minéral accessoire dans la plupart des environnements géologiques. Elle est souvent riche en U et Th, n’incorpore pas (ou peu) de Pb initial et son système isotopique (U-Th-Pb) est résistant à la diffusion dans la majorité des conditions crustales, ce qui en fait un chronomètre très attractif. De plus, elle constitue la principale source de Th et une des principales sources de terres rares (REE) contenus dans la croûte terrestre. En présence de fluide, la monazite peut recristalliser par un processus de dissolution-précipitation couplée, avec une composition chimique et/ou isotopique différente de la monazite initiale. Ces recristallisations impliquent alors une redistribution des éléments contenus par la monazite (REE, Th, U, Pb) et la compréhension de la mobilité de ces éléments stratégiques est cruciale pour leurs aspects économiques (ressources en lanthanides et actinides) et environnementaux (contexte de stockage des déchets).Cette thèse vise à étudier le comportement de la monazite lors des interactions fluide-monazite et son potentiel comme traceur chronomètre et traceur géochimique des minéralisations hydrothermales. Pour cela une approche pluridisciplinaire a été adoptée, combinant minéralogie, pétrologie expérimentale, géochronologie, et tectonique. Les travaux présentés s’organisent en deux parties: l’une concernant la datation de monazites hydrothermales de fentes alpines, et l’autre des expériences d’altérations hydrothermales en laboratoire.Une quarantaine de cristaux de monazite et une dizaine de cristaux de xénotime ont été collectés dans des fentes alpines (veines hydrothermales se formant durant l’exhumation) des domaines externes (Argentera, Belledonne et Mont-Blanc) et internes (zone Briançonnaise). La datation U-Th-Pb in-situ par LA-ICP-MS a permis de mieux contraindre l’âge et la durée des circulations hydrothermales pendant les épisodes de déformation tardifs liés à l’exhumation des Alpes occidentales. Les analyses d’inclusions fluides dans la monazite couplées à des âges traces de fission sur zircons ont apporté de nouvelles contraintes sur le gradient géothermique induit par les circulations fluides dans les veines hydrothermales. L’analyse systématique des produits expérimentaux (monazite et fluide) de 18 expériences hydrothermales a permis de confirmer la mobilité des éléments comme l’uranium ou les terres rares lourdes lors des réactions hydrothermales. L’étude à l’échelle nanométrique des domaines de monazite recristallisée a mis en évidence un nouveau mécanisme de remplacement caractérisé par la propagation du front de réaction à l’aide de nano-pores et nano-fractures. Ce mécanisme conduit à un remplacement anisotrope et à un mélange de nano-domaines de monazite primaire et recristallisée. Ces observations ont des implications majeures pour le stockage des déchets radioactifs ou en géochronologie pour expliquer les perturbations des âges monazites ayant réagi avec un fluide dans les milieux hydrothermaux ou métamorphiques.

Asteroids Vesta and Ceres motivated the space mission Dawn because they represent two different planetary embryos that remained relatively intact since their formation. Vesta is broadly considered as the parent body of the HED meteorites suite that are witnesses of a magmatic activity probably due to the presence of the radioactive isotope 26 Al which was present in significant amount to cause internal melting of primitive rocky bodies. The composition of a planetary surface can be quantified through the analysis of the gamma rays it produces. This is made possible for the Dawn spacecraft by the instrument GRaND and the scintillation of a BGO crystal. This thesis presents the analysis of gamma ray spectra from Vesta by two blind source separation methods: the independent component analysis and the non negative matrix factorization. These methods are also applied to an equivalent lunar dataset already well interpreted. Lunar synthetic spectra are used to test ICA and NMF. The separation of elementary spectra is delicate although K, Th and Fe can be discriminated due to the more favorable statistical properties of their source signals. The sensitivity of separation to the chemical variability is assessed based on artificial lunar spectra, which allows to explain the lack of separation of a clear elemental signal in the case of Vesta. Despite the observations of Dawn and the important collection of HED data, there is no consensus on the conditions of the vestan magmatism. A global magma ocean is often put forward, whereas the migration of the heat source, contained in the easiest mineral to melt, plagioclase, does not allow it. A model of melt migration is implemented, based on two-phase flow equations. This model is combined with the olivine-anorthite-quartz equilibrium phase diagram. This allows to predict the mineralogy as a function of depth and time. Results obtained show that eucrites and diogenites may be a common feature of large bodies accreted early in solar system history.; Les astéroïdes Cérès et Vesta ont motivé la mission spatiale Dawn parce qu’ils représentent deux embryons planétaires différents restés relativement intacts depuis leur formation. Vesta est large- ment considéré comme le corps parent des météorites HED témoins d’une activité magmatique probablement due à la présence de l’isotope radioactif 26Al qui était suffisamment abondant pour permettre la fusion interne des corps rocheux primitifs. La composition d’une surface planétaire peut être mesurée grâce à l’analyse des rayons gammas qu’elle produit. Pour la sonde Dawn cela est rendu possible par l’instrument GRaND et la scintillation d’un cristal de BGO. Cette thèse présente l’analyse des spectres gammas de Vesta par deux outils de séparation aveugle de source: l’analyse en composantes indépendantes (ICA) et la factorisation en matrice non-négative (NMF). Ces méthodes sont aussi appliquées à un jeu de données lunaire comparable et déjà bien interprété. Des spectres synthétiques lunaires permettent de tester ICA et NMF. La séparation de spectres élémentaires s’avère délicate même si on peut distinguer les éléments K, Th et Fe en raison des propriétés statistiques de leur signaux sources plus favorables. On mesure la sensibilité d’ICA-NMF à la variabilité chimique de la surface pour des Lunes artificielles, ce qui permet d’expliquer l’absence de séparation d’un signal élémentaire clair dans le cas de Vesta. Malgré les observations de la sonde Dawn et le nombre important d’informations fournies par les HED, il n’y a pas de consensus sur la formation des HED. On met souvent en avant l’existence d’un océan magmatique global sur Vesta, alors que la migration de la principale source chaleur, contenue dans le premier minéral fondu, le plagioclase, ne permet pas la fusion totale. On met en oeuvre un modèle de migration des magmas, basé sur les équations de la compaction. On adapte ce modèle en utilisant un diagramme d’équilibre de phase olivine-anorthite-quartz. Cela permet de calculer l’évolution de la minéralogie en fonction du temps et de la profondeur. Les résultats montrent que les eucrites et les diogénites pourraient être une caractéristique commune des gros corps accrétés tôt dans l’histoire du système solaire.

Asteroids Vesta and Ceres motivated the space mission Dawn because they represent two different planetary embryos that remained relatively intact since their formation. Vesta is broadly considered as the parent body of the HED meteorites suite that are witnesses of a magmatic activity probably due to the presence of the radioactive isotope 26 Al which was present in significant amount to cause internal melting of primitive rocky bodies. The composition of a planetary surface can be quantified through the analysis of the gamma rays it produces. This is made possible for the Dawn spacecraft by the instrument GRaND and the scintillation of a BGO crystal. This thesis presents the analysis of gamma ray spectra from Vesta by two blind source separation methods: the independent component analysis and the non negative matrix factorization. These methods are also applied to an equivalent lunar dataset already well interpreted. Lunar synthetic spectra are used to test ICA and NMF. The separation of elementary spectra is delicate although K, Th and Fe can be discriminated due to the more favorable statistical properties of their source signals. The sensitivity of separation to the chemical variability is assessed based on artificial lunar spectra, which allows to explain the lack of separation of a clear elemental signal in the case of Vesta. Despite the observations of Dawn and the important collection of HED data, there is no consensus on the conditions of the vestan magmatism. A global magma ocean is often put forward, whereas the migration of the heat source, contained in the easiest mineral to melt, plagioclase, does not allow it. A model of melt migration is implemented, based on two-phase flow equations. This model is combined with the olivine-anorthite-quartz equilibrium phase diagram. This allows to predict the mineralogy as a function of depth and time. Results obtained show that eucrites and diogenites may be a common feature of large bodies accreted early in solar system history.; Les astéroïdes Cérès et Vesta ont motivé la mission spatiale Dawn parce qu’ils représentent deux embryons planétaires différents restés relativement intacts depuis leur formation. Vesta est large- ment considéré comme le corps parent des météorites HED témoins d’une activité magmatique probablement due à la présence de l’isotope radioactif 26Al qui était suffisamment abondant pour permettre la fusion interne des corps rocheux primitifs. La composition d’une surface planétaire peut être mesurée grâce à l’analyse des rayons gammas qu’elle produit. Pour la sonde Dawn cela est rendu possible par l’instrument GRaND et la scintillation d’un cristal de BGO. Cette thèse présente l’analyse des spectres gammas de Vesta par deux outils de séparation aveugle de source: l’analyse en composantes indépendantes (ICA) et la factorisation en matrice non-négative (NMF). Ces méthodes sont aussi appliquées à un jeu de données lunaire comparable et déjà bien interprété. Des spectres synthétiques lunaires permettent de tester ICA et NMF. La séparation de spectres élémentaires s’avère délicate même si on peut distinguer les éléments K, Th et Fe en raison des propriétés statistiques de leur signaux sources plus favorables. On mesure la sensibilité d’ICA-NMF à la variabilité chimique de la surface pour des Lunes artificielles, ce qui permet d’expliquer l’absence de séparation d’un signal élémentaire clair dans le cas de Vesta. Malgré les observations de la sonde Dawn et le nombre important d’informations fournies par les HED, il n’y a pas de consensus sur la formation des HED. On met souvent en avant l’existence d’un océan magmatique global sur Vesta, alors que la migration de la principale source chaleur, contenue dans le premier minéral fondu, le plagioclase, ne permet pas la fusion totale. On met en oeuvre un modèle de migration des magmas, basé sur les équations de la compaction. On adapte ce modèle en utilisant un diagramme d’équilibre de phase olivine-anorthite-quartz. Cela permet de calculer l’évolution de la minéralogie en fonction du temps et de la profondeur. Les résultats montrent que les eucrites et les diogénites pourraient être une caractéristique commune des gros corps accrétés tôt dans l’histoire du système solaire.

This thesis revealed the petrological and geochemical characterization of post-collisional Quaternary basalts of Central Anatolia (Erciyes and Hasandağ stratovolcanoes, and dispersed volcanisms of Obruk-Zengen and Karapınar), focusing on the spatiotemporal evolution of the magmatism in Cappadocia (Turkey).K-Ar geochronology indicated the coexistence of alkaline and calc-alkaline basalts from the same location and age. Moreover, the results also show that these basalts may be very young (a few thousand years). The mineralogy of Quaternary basalts from the Cappadocia is as follows: plagioclase, olivine, clinopyroxene, orthopyroxene and oxides (magnetite, ilmenite). Orthopyroxene is observed only in basalts of Erciyes, while it is lacking in Hasandağ and dispersed volcanisms of Obruk-Zengen and Karapınar. The plagioclase phenocrysts often exhibit disequilibrium features attributed to magma mixing process: complex zoning (normal, inverse, oscillatory), concentric zones rich in melt inclusions, resorption features.However, the observed mineralogy is consistent with a dominant fractional crystallization process. The estimated geobarometer show that the origin of magmas of Erciyes is shallower than the other settings.The results in geochemistry confirm not only the mineralogical duality between Erciyes and the other settings but also the coexistence of alkaline (normative nepheline) and calc-alkaline characters of contemporary basalts. All studied basalts are enriched in LREE (Light Rare Earth Elements) and LILE (Large Ion Lithophile Elements). The isotopic data (Sr, Nd, Pb, O) indicate the importance of enriched lithospheric source. All geochemical data also display the signature of other sources and processes such as contamination by the continental crust and heritage of a former subduction., Cette thèse est consacrée à la caractérisation pétrologique et géochimique des basaltes quaternaires post-collisionnels d’Anatolie centrale (strato-volcans Erciyes et Hasandağ et volcanisme dispersé d'Obruk-Zengen et de Karapınar), en se focalisant sur l’évolution spatio-temporelle de ce magmatisme de la Cappadoce (Turquie). Par la géochronologie K-Ar, la coexistence de basaltes alcalins et calco-alcalins a été démontrée, parfois dans un même lieu et à la même époque. Par ailleurs, nos résultats montrent aussi que ces basaltes peuvent être très jeunes (quelques milliers d’années seulement).La minéralogie des basaltes quaternaires de la Cappadoce est la suivante : plagioclase, olivine, clinopyroxène, orthopyroxène et oxydes (magnétite, ilménite). Pourtant, seuls les basaltes de l’Erciyes contiennent de l’orthopyroxène, alors que ceux du Hasandağ et du volcanisme dispersé d’Obruk-Zengen et de Karapınar en sont dépourvus. Les phénocristaux de plagioclases présentent souvent des figures de déséquilibre, attribuées au processus de mélange magmatique : zonages complexes (normaux, inverses, oscillatoires), richesse en inclusions vitreuses, figures de résorption. Toutefois, la minéralogie observée est compatible avec un processus de cristallisation fractionnée dominant. Les géobaromètres utilisés montrent que l’origine des magmas de l’Erciyes est plus superficielle que celle des autres sites. Les résultats en géochimie confirment la dualité minéralogique observée entre l’Erciyes et les autres secteurs, ainsi que les caractères alcalins (néphéline normative) et calco-alcalins de basaltes parfois contemporains. Tous les basaltes étudiés sont enrichis en LREE et LILE. Les données isotopiques (Sr, Nd, Pb, O) montrent l’importance de la source lithosphérique enrichie. L’ensemble des données géochimiques montre aussi la signature d’autres sources et processus comme la contamination par la croûte continentale et l’héritage d’une ancienne subduction.

The opportunity was taken in 2010 to carry out a full scientific and technical examination of the brass head from Ife, popularly known as the Olokun head, first published in 1912 by Leo Frobenius, together with a selection of other Ife heads that came to London for exhibition at the British Museum. This was especially appropriate as on its last visit some 60 years previously, the Olokun head had been examined and condemned as a sand cast copy. The present study has established beyond doubt that the Olokun head is a hollow cire perdue or lost wax casting, very similar in technique and composition to the other heads. The balance of evidence suggests that this is the head unearthed at Ife in 1910. En 2010, une exposition de têtes Ife au British Museum à Londres a fourni l’opportunité de procéder à un examen scientifique et technique détaillé d’une tête en laiton, plus connue sous le nom de tête d’Olokun, et publiée par Léo Frobenius en 1912 ; une sélection d’autres têtes Ife exposées ont fait également l’objet d’analyses. La tête d’Olokun avait été étudiée et reléguée, soixante ans auparavant, au statut de simple copie obtenue par fonte au sable. Cette nouvelle approche, particulièrement bienvenue, établit sans aucun doute que la tête d’Olokun est une fonte à cire perdue, très similaire aux autres têtes en termes de technique et de composition. Par ailleurs, tout un faisceau d’éléments suggère qu’il s’agit bien de la tête mise au jour à Ife en 1910.Cet article livre les résultats du ré-examen technique et scientifique de la célèbre tête en laiton d’Olokun, originaire d’Ife (Nigéria), considérée en 1949 par William Fagg et Léon Underwood comme une copie réalisée par moulage de la tête originale découverte en 1910 par Leo Frobenius.La discussion s’articule autour de trois grandes parties. La première examine les nombreux arguments utilisés par W. Fagg et L. Underwood pour reléguer la tête au statut de simple copie. La seconde décrit la façon dont on pense actuellement que la tête a été coulée. Enfin, la troisième dévoile l’examen scientifique établissant son ancienneté probable, sa production en Afrique de l’Ouest, et sa ressemblance frappante avec d’autres têtes d’Ife.Parmi les nombreux points retenus par W. Fagg et L. Underwood, trois revêtent une certaine importance. Dans l’ensemble ils dénoncent la nature diffuse de la surface du métal et le manque de détails précis (les points a, b, f et g de Fagg et Underwood), alors attribués à la méthode de fonte au sable. En réalité, l’examen attentif a très vite démontré que l’origine de cette différence d’aspect résidait dans le fait que, contrairement aux autres têtes d’Ife présentes au British Museum de nombreux mois avant l’exposition – pour examen et nettoyage –, la tête d’Olokun n’était arrivée en Grande-Bretagne que la veille de son ouverture et n’avait, par conséquent, reçu qu’un traitement très superficiel. Sous la couche de cire appliquée à la hâte, la corrosion, la terre et même des restes du matériau de moulage d’origine ont subsisté, remplissant les interstices et brouillant les détails de la fonte (fig. 8).Une objection plus sérieuse (g) résidait dans le fait, qu’en certains endroits de la tête, des accrétions de matière de surface paraissaient être en métal, comme si on avait là la traduction dans le métal du moulage de résidus, de poussières et de traces de corrosion, ce qui aurait pu effectivement être un argument en faveur d’une copie moulée sur l’original. Cependant, l’examen approfondi des zones concernées a montré que la plupart de ces « moulages de poussière » sont en fait constitués de vraies poussières et de résidus de fonte (fig. 9). À la base du cimier, on distingue quelques gerces de métal et le décor du cimier lui-même est ­recouvert de métal (fig. 10), mais cela pourrait s’expliquer par le simple fait que l’argile utilisée pour le moulage n’était pas assez fine pour pénétrer profondément dans cet interstice, ou encore que la surface du moule avait été endommagée pendant la cuisson et la coulée.Leur point h nécessite également une explication. Ainsi W. Fagg et L. Underwood décrivent deux zones sur le front qu’ils attribuent à une ­tentative d’introduction de broches en fer dans un possible moule en plâtre. Cette interprétation est entièrement erronée. Pour que cela soit interprété comme la preuve que cette tête était une copie d’un original, le métal aurait dû être coulé par les canaux intérieurs dans l’original et ce que l’on voit dans le métal de la présente tête correspondrait alors au moulage des canaux de coulée de la tête originale. Toutefois ces canaux de coulée coupés contenaient encore les extrémités de broches de renforcement et par conséquent il s’agit bien, non de moulages de canaux, mais de vrais canaux qui pour une raison quelconque n’ont pas été utilisés. En outre l’examen indique que c’est la cire que l’on a coupée à cet endroit, et non le métal. L’explication la plus probable est que le moule a été assemblé, prêt à être chauffé, mais qu’il a subi un accident qui l’a endommagé avant le début de la coulée. Les canaux de cire originaux ont alors probablement dû être coupés et remplacés par deux autres à l’intérieur de la tête (fig. 2).Dans l’ensemble il est à noter que, dans leur discussion, W. Fagg et L. Underwood ne mentionnent aucune des principales caractéristiques qui permettent de distinguer les fontes au sable ou les fontes postérieures, telle une réduction de taille de la copie qui aurait pu être constatée. De même, la présence de traits tout aussi distinctifs de la fonte à cire perdue qui peuvent être observés sur la tête ne sont pas évoqués.L’examen scientifique a établi que le métal est sérieusement corrodé, avec une corrosion intergranulaire très importante, témoignant fortement d’un enfouissement prolongé (fig. 16 et 18). Les produits de corrosion sont les minéraux auxquels on peut s’attendre sur une véritable antiquité. Il y a aussi une contamination très superficielle de pigments synthétiques. Ces derniers sont identiques à ceux trouvés sur les moulages en plâtre des têtes réalisés au British Museum, lors de la présence de la tête d’Olokun en 1948.La composition élémentaire et isotopique du métal de la tête d’Olokun est similaire à celle des autres têtes d’Ife, ce qui suggère fortement qu’elle a été fabriquée à partir du même stock de métal. L’examen du noyau de la tête indique une composition similaire à celle de l’une des autres têtes échantillonnée pour comparaison (Willett & Sayre 2006). Plus significatif encore, une partie de la matière végétale utilisée comme remplissage du noyau de la tête d’Olokun provenait de plantes qui poussent uniquement en Afrique de l’Ouest, signe évident que la tête a été coulée dans cette région.Ainsi, dans l’ensemble, le réexamen jette un doute considérable sur le rapport de 1949. Il établit que la tête est certainement une fonte creuse à la cire perdue, probablement réalisée en fonte directe – bien qu’une fonte indirecte ne puisse pas être totalement exclue –, très similaire à celle mise en œuvre pour réaliser les autres têtes. L’ensemble de ces arguments suggère qu’il s’agit bien de la tête exhumée par L. Frobenius en 1910.

Because there remains a lack of knowledge about the spatially explicit distribution of chemical weathering rates at the global scale, a model that considers prominent first-order factors is compiled step by step and the implied spatial variability in weathering is explored. The goal is to fuel the discussion about the development of an "Earth System" weathering function. We use as a starting point an established model of the dependence of chemical weathering on lithology and runoff, calibrated for an island arc setting, which features very high chemical weathering rates and a strong dependence on lithology and runoff. The model is enhanced stepwise with further factors accounting for soil shielding and temperature, and the observed variation of fluxes is discussed in context of observed data from large rivers globally.Results suggest that the global soil shielding reduces chemical weathering (CW) fluxes by about 44%, compared to an Earth surface with no deeply weathered soils but relatively young rock surfaces (e.g. as in volcanic arc and other tectonically active areas). About 70% of the weathering fluxes globally derive from 10% of the land area, with Southeast Asia being a primary "hot spot" of chemical weathering. In contrast, only 50% of runoff is attributed to 10% of the land area; thus the global chemical weathering curve is to some extent disconnected from the global runoff curve due to the spatially heterogeneous climate as well as rock and soil properties. The analysis of carbonate dissolution reveals that about half of the flux is not delivered from labeled carbonate sedimentary rocks, but from trace carbonates in igneous rocks as well as from siliciclastic sediment areas containing matrix carbonate.In addition to total chemical weathering fluxes, the release of P, a nutrient that controls biological productivity at large spatial scales, is affected by the spatial correlation between runoff, lithology, temperature and soil properties. The areal abundance of deeply weathered soils in Earth's past may have influenced weathering fluxes and P-fuelled biological productivity significantly, specifically in the case of larger climate shifts when high runoff fields shift to areas with thinner soils or areas with more weatherable rocks and relatively increased P-content. This observation may be particularly important for spatially resolved Earth system models targeting geological time scales. The model is discussed against current process knowledge and geodata with focus on improving future global chemical weathering model attempts.Identified key processes and geodata demanding further research are a) the representation of flowpaths to distinguish surface runoff, interflow and baseflow contributions to CW-fluxes, b) freeze-thaw effects on chemical weathering, specifically for the northern latitudes, c) a more detailed analysis to identify to what extent the spatially heterogeneous distribution of Earth surface properties causes a decoupling of the Earth system rating functions between CW-fluxes and global runoff, as well as d) an improved understanding of where and to what extent trace or matrix carbonates in silicate-dominated rocks and sediments contribute to carbonate weathering. The latter demands e) an improved representation of carbonate content in lithological classes in the lithological representation of the Earth surface. Further improvement of the lithological database is needed for f) the age of rocks and g) the geochemistry of sediments with focus on unconsolidated sediments in the large basins. And clearly h) an improved global soil database is needed for future improvements with reliable soil depth, mineralogical composition as well as physical properties. © 2013 The Authors., SCOPUS: ar.j, info:eu-repo/semantics/published

The dissertation at hand comprises three independent chapters The first chapter contains for the first time a comprehensive data set from the enigmatic Marie Byrd Seamount province including morphological, geochronological, and geochemical data, combined with additional data for the De Gerlache and Peter I Island volcanic complexes. The centerpiece of this study is the 40Ar/39Ar dating of 9 samples including the Marie Byrd Seamounts and the submarine base of Peter I Island. The second chapter is focused on a geochronological and geochemical study presenting new 40Ar/39Ar age and XRF, ICPMS element concentration data, from recovered plutonic and dyke rocks of the Pine Island Bay region, Marie Byrd Land. The third chapter encompasses a major and trace element study on diffuse intraplate volcanism of the Christmas Island Seamount Province (CHRISP), situated in the northeastern Indian Ocean.

The Ph.D. study is aimed at characterising the composition of pyroxenite xenoliths brought to the surface by Cenozoic intraplate volcanism in the Azrou Timahdite district of Middle Atlas (Morocco) to unravel their origin and significance in the frame of the geodynamic evolution of the North Africa lithospheric mantle. The interpretations are based on a petrological approach and on reliable geochemical information at both bulk rock and mineral scale. The data are used to address a largely debated and crucial issue, namely whether pyroxenites do represent ancient magmatic events or section of subducted crust recycled into the lithospheric mantle. The geochemical data revealed that the Middle Atlas pyroxenites formed through different processes: 1 – recycling of older oceanic crust in the lithospheric mantle; 2 – reactions between mantle melt and older mafic layers; 3 – magmatic crystallization from enriched melts at mantle depth. In an overall geodynamic scenario, the origin and age of the pyroxenites interpreted as fragments of recycled oceanic crust and as products of melt-Rock interaction processes are not completely understood. By analogy with Ronda and Beni Bousera these pyroxenites could represent old mafic rocks that have been isolated in the subcontinental lithospheric mantle for very long time spans. The fragments of oceanic material and the crustal components recorded by pyroxenites may be tentatively related to subduction processes occurred during Pan-African times. If so, these pyroxenites maintained for long time their pristine geochemical signatures without marked changes.; Cette étude vise à caractériser la composition chimique d’enclaves de pyroxénites échantillonnées par le volcanisme cénozoïque intraplaque de la province volcanique de Azrou Timahdite dans le Moyen Atlas marocain afin de préciser leur origine et leur signification dans le cadre de l’évolution géodynamique du manteau sous l’Afrique du Nord. Les interprétations sont basées sur une étude pétrologique et sur des données géochimiques à l’échelle de la roche totale et du minéral. Les données sont utilisées dans le cadre du débat récurrent pour savoir si les pyroxénites représentent d’anciens événements magmatiques ou sont des fragments de croûte océanique recyclés dans le manteau lithosphérique. Les données géochimiques montrent que les pyroxénites du Moyen Atlas ont été formées par différents processus : 1 - recyclage de croûte océanique dans le manteau lithosphérique; 2 – réactions entre un magma et des roches basiques anciennes ; 3 – cristallisation dans le manteau à partir d’un magma enrichi. L’origine et l’âge des pyroxénites formées par recyclage de la croûte océanique ou par réaction entre un magma et des roches plus anciennes sont difficile à interpréter dans le cadre de l’évolution géodynamique de cette région. Par analogie avec les massifs de Ronda et de Beni Bousera, ces pyroxénites pourraient représenter d’anciennes roches basiques isolées depuis très longtemps dans le manteau lithosphérique sous-Continental. Ces fragments de croûte océanique et certaines signatures crustales peuvent être reliés à des processus de subduction pan-Africains. Dans ce cas, ces pyroxénites ont gardé leur signature géochimique intacte, sans modification significative au cours du temps.

The Ph.D. study is aimed at characterising the composition of pyroxenite xenoliths brought to the surface by Cenozoic intraplate volcanism in the Azrou Timahdite district of Middle Atlas (Morocco) to unravel their origin and significance in the frame of the geodynamic evolution of the North Africa lithospheric mantle. The interpretations are based on a petrological approach and on reliable geochemical information at both bulk rock and mineral scale. The data are used to address a largely debated and crucial issue, namely whether pyroxenites do represent ancient magmatic events or section of subducted crust recycled into the lithospheric mantle. The geochemical data revealed that the Middle Atlas pyroxenites formed through different processes: 1 – recycling of older oceanic crust in the lithospheric mantle; 2 – reactions between mantle melt and older mafic layers; 3 – magmatic crystallization from enriched melts at mantle depth. In an overall geodynamic scenario, the origin and age of the pyroxenites interpreted as fragments of recycled oceanic crust and as products of melt-Rock interaction processes are not completely understood. By analogy with Ronda and Beni Bousera these pyroxenites could represent old mafic rocks that have been isolated in the subcontinental lithospheric mantle for very long time spans. The fragments of oceanic material and the crustal components recorded by pyroxenites may be tentatively related to subduction processes occurred during Pan-African times. If so, these pyroxenites maintained for long time their pristine geochemical signatures without marked changes.; Cette étude vise à caractériser la composition chimique d’enclaves de pyroxénites échantillonnées par le volcanisme cénozoïque intraplaque de la province volcanique de Azrou Timahdite dans le Moyen Atlas marocain afin de préciser leur origine et leur signification dans le cadre de l’évolution géodynamique du manteau sous l’Afrique du Nord. Les interprétations sont basées sur une étude pétrologique et sur des données géochimiques à l’échelle de la roche totale et du minéral. Les données sont utilisées dans le cadre du débat récurrent pour savoir si les pyroxénites représentent d’anciens événements magmatiques ou sont des fragments de croûte océanique recyclés dans le manteau lithosphérique. Les données géochimiques montrent que les pyroxénites du Moyen Atlas ont été formées par différents processus : 1 - recyclage de croûte océanique dans le manteau lithosphérique; 2 – réactions entre un magma et des roches basiques anciennes ; 3 – cristallisation dans le manteau à partir d’un magma enrichi. L’origine et l’âge des pyroxénites formées par recyclage de la croûte océanique ou par réaction entre un magma et des roches plus anciennes sont difficile à interpréter dans le cadre de l’évolution géodynamique de cette région. Par analogie avec les massifs de Ronda et de Beni Bousera, ces pyroxénites pourraient représenter d’anciennes roches basiques isolées depuis très longtemps dans le manteau lithosphérique sous-Continental. Ces fragments de croûte océanique et certaines signatures crustales peuvent être reliés à des processus de subduction pan-Africains. Dans ce cas, ces pyroxénites ont gardé leur signature géochimique intacte, sans modification significative au cours du temps.

The Pontides orogenic belt (Ketin, 1966), is the central portion of an extensive belt running from western Bulgaria (Rhodope Mountains) through northern Turkey to the Caucasus. Three tectono-stratigraphically different sectors can be distinguished: the Western Pontides (Istanbul zone), the Central Pontides and the Eastern Pontides (Sakarya zone). The Central Pontides, located between the Izmir-Ankara suture to the south and the Black Sea to the north is the geographical term for the arched central part of the Pontides orogenic belt (Fig. 1.1). The Central Pontides is one of the well preserved areas where the late Early Cretaceous juxtaposition of the Western Pontides (Istanbul Zone) and the Eastern Pontides (Sakarya Zone) (Okay and Tüysüz, 1999; Tüysüz, 1999) can be observed (Sengör and Yilmaz, 1981). Four main units are comprised in the Central Pontides: two major tectonic units, the Devrekani metamorphic unit (Eurasian-derived basement) and the Çangaldag arc complex separated by two oceanic basins, the Küre and the Domuzdag-Saraycikadag complexes. The study area is marked by the Çangaldag arc complex, and numerous granitoids and associated volcanics collectively called the Kastamonu granitoid belt (KGB) (Yilmaz and Boztug, 1986), that pierced the imbricated Palaeotethyan continental and oceanic basement assemblage. The Kastamonu belt documents large scale, multi-episodic magmatism, formed in response to subduction of the Palaeotethys and the subsequent late orogenic tectonics. The occurrence of these plutons and ophiolites in the Central Pontides has attracted geologists for several decades, because of their importance in understanding Palaeotethyan evolution, and the Tethysides-Variscides connection. However, data necessary to identify the type and origin of all the intrusions are not available. On the basis of stratigraphic correlation and a few K-Ar data earlier workers assigned Middle Jurassic emplacement time to all the plutons of the KGB. In an attempt to elucidate the petrogenetic and magmatic evolution of this belt, zircons from Deliktas, Sivrikaya and Devrekani granitoids and their basement have been analyzed by means of Pb-Pb evaporation and U-Pb isotope dilution combined with isotope and geochemical data. Geochemical compositions, isotopic data and geochronological constraints are presented and interpreted for the evolution of the Palaeotethys in the Central Pontides. The Late Carboniferous Sivrikaya granitoid (SG) comprises biotite-hornblende granodiorite, tonalites and minor two-mica granites. Sivrikaya rocks are slightly metaluminous to peraluminous, and transitional to S-type (ASI= 0.9 to > 1.1). The rocks are characterized by variably low initial 87Sr/86Sr ratios [Sr(i)= 0.705 - 0.708], moderate eNd(t) values (-1 to -3.8) and young Nd-model ages (TDM= 0.75 - 1.05 Ga), suggesting variable degrees of mixing between mantle and crustal components. Chondrite-normalized (cn) rare earth element (REE) patterns are characterized by fractionation between the light (LREE, [La/Yb]cn= 9 - 49) and heavy REEs (HREE, [Gd/Yb]cn= 0.79 - 2.37) and no to strong Eu depletion (Eu/Eu*= 1.19 - 0.18). All these characteristics, combined with moderate d18O(whole-rock) values (10 - 11.6 per mil) point to dehydration melting of heterogeneous amphibolites-metagreywackes-type sources with variable mantle contribution. The Early Permian Deliktas leucogranite (DLG) is host to muscovite-bearing monzogranites. Deliktas rocks are strongly peraluminous S-type granites (ASI >1.1), as reflected in the mineralogy that includes highly aluminous phases such as muscovite and cordierite. DLG samples exhibit strongly fractionated REE patterns ([La/Yb]cn= 3.6 - 35), rather flat HREE ([Gd/Yb]cn= 0.59 - 0.78) and small positive to distinct negative Eu- anomalies (Eu/Eu*= 1.15 - 0.42) suggesting melting of metapelitic-type source with residual plagioclase and/or high degree fractional crystallization. Rocks from this intrusion have high Sr(i) ratios (0.7103 - 0.7123) and low eNd(t) values (-2.2 to -5.0), indicating an arc underlain by a mature continental crust. Nearly constant d18O(whole-rock) values (~11.5 per mil) and old Nd-model ages (TDM= 1.2 - 2.2 Ga) of the rocks, in conjunction with the geochemical characteristics further support material contribution from mature continental crust in their genesis. The Middle Jurassic Devrekani pluton (DG) consists of metaluminous I-type (ASI= 0.55 - 0.88) hornblende-biotite diorites and tonalites. The samples have low Sr(i) ratios (0.705 - 0.706) and very low negative eNd(t) values (-0.8 to -2.2). These features together with the low d18O(whole-rock) values (7 - 9 per mil), very high Mg# values, young model TDM ages (1.04 - 1.6 Ga) and high CaO/Al2O3 ratios suggests dehydration melting of mafic lower crustal rocks, and/or derivation from amphibolite-type source with significant upper mantle-derived material input. DG rocks are further characterized by moderately fractionated REE patterns ([La/Yb]cn= 2 - 11), flat HREE patterns (Gd/Yb)cn= 1.35 - 1.68) indicating garnet and zircon accumulation. The high Sr/Y ratios (10-37), no to distinct positive Eu-anomalies (Eu/Eu*= 0.72 - 0.95), and Sr-spikes, indicate plagioclase accumulation. These geochemical characteristics indicate magmas derivation from an enriched mantle and/or metasomatized mantle sources with minor crustal contamination. It is suggested that, after the Cimmeridgian continent collided with the south Eurasian margin subsequent slab break-off and flip in subduction polarity, resulted in asthenospheric upwelling and the production of the near primary melts of the Devrekani pluton. The melts en route to higher levels interacted or not with mantle- and crustal-derived magmas. It can be concluded that the Middle Mesozoic magmatism was initiated by the brief southward subduction of the Küre marginal basin (e.g. Ustaömer and Robertson, 1997) beneath the newly formed Late Carboniferous orogen (e.g. Okay et al. 2006). The mineralogy and geochemistry of the rocks distinct from those closer to the Black sea coast, and their location in the far south of the Küre ophiolite, the similar WSW-ENE orientation of the Devrekani pluton and the major thrust system that resulted from the gravitational collapse, indicate a juvenile stage of a subduction system (Nzegge et al. in review). Because the intrusion is late syn-tectonic with respect to the shear fabric it is reasonable to assume that its generation in some way is related to the extension-collapse events. According to Dewey (1988) large volumes of mantle partial melts are injected into the lower crust during gravitational collapse of mountain chains by detachment faulting. I speculate that during this collapse event the geotherm crossed the garnet-lherzolite solidus and mafic melts were produced. The melt had little interaction with the felsic upper crust, accumulated plagioclase, and intruded in the shear zones, giving rise to the Devrekani I-type pluton. Geochronologic analyses yielded ages ranging from 295-270 Ma for DLG, and 303-300 Ma for SG and in the south of the belt DG 190-165 Ma. Zircon xenocryst ages as old as ~2.7 Ga provide evidence for Proterozoic protolith, and highlights the association of the Central Ponitdes with Laurasia and Gondwana. The 360-340-320 Ma episodes of Pb loss in zircons are indicative of Variscan metamorphism. These new geochemical and age data from the Sivrikaya, Deliktas and Devrekani granitoids indicate the evolution of the Kastamonu magmatism from tholeiitic to calc-alkaline to tholeiitic compositions with time. Furthermore, the presence of Late Palaeozoic pre- to post-collisional, transitional to peraluminous granites and Middle Mesozoic juvenile arc (post-collisioinal) rocks challenges previous evolution models for the Kastamonu granitoid belt and the Central Pontides. The data presented herein underlines the complex thermo-tectonic history of the Central Pontides, and the magmatism associated with a “long-lasting” northward and a “short-lived” southward subduction of the Palaeotethys respectively during the Palaeozoic and Mesozoic times (proposed model), and the subsequent crustal growth processes (collision-accretion of Gondwanan-derived continental fragments with Laurasia). The Precambrian-Palaeozoic Eurasian-derived basement (Devrekani metamorphic unit) of the Central Pontides is exposed between the Küre and Çangaldag complexes. Evidence of the Precambrian basement in the Central Pontides comes from a Büyükçay sample (BÜ-20, ortho-amphigneiss, ~502 Ma), from inherited zircons (U-Pb upper intercept ages) and Nd isotope data. Probably the BÜ-20 zircons crystallized in the Late Cambrian-Early Ordovician magmatic event as part of the wide-spread subduction-related magmatism in the Gondwana-derived terranes (e.g. Linnemann et al. 2000 and the references therein). Die Pontiden (Ketin, 1966), sind der zentrale Teil eines ausgedehnten Gebirgsgürtels der sich von West-Bulgarien (Rhodope Berge) über die Nord-Türkei bis in den Kaukasus erstreckt. Sie lassen sich in drei tektono-stratigrafische Abschnitte gliedern: die West-Pontiden (Istanbul Zone), die Zentral-Pontiden und die Ost-Pontiden (Sakarya Zone). Die Zentral-Pontiden, zwischen der Izmir-Ankara-Sutur im Süden und dem Schwarzen Meer im Norden gelegen, sind geographisch gesehen der gebogene, zentrale Teil des Pontidengürtels (Fig. 1.1). Die Zentral-Pontiden sind eines der am besten erhaltenen Gebiete wo die frühkretazische Nebeneinanderstellung der West- und Ost-Pontiden (Okay and Tüysüz, 1999; Tüysüz, 1999) beobachtet werden kann (Sengör and Yilmaz, 1981). Die Zentral-Pontiden umfassen vier Hauptabschnitte: Zwei tektonische Großeinheiten, die metamorphe Eurasische Devrekani- und die Çangaldag-Einheit, die durch zwei ozeanische Becken, den Küre- und den Domuzdag-Saraycikadag-Komplex getrennt sind. Der metamorphe präkambrisch-paläozoische Devrekani Abschnitt ist ein Störungsgebundenes tektonisches Fenster, das zwischen der Küre- und der Çangaldag-Einheit liegt, und die zusammen das Grundgebirge der zentralen Pontiden bilden. Im Untersuchungsgebiet liegen der Çangaldag-Inselbogen-Komplex und zahlreiche Granitoide und mit ihnen verbunden Vulkanite, die als Kastamonu-Granitoid-Gürtel (KGB) bezeichnet werden. Die Magmen durchdrangen die Vergesellschaftung der paläotethischen Kontinental- und Ozeanboden-Einheiten. Der KGB dokumentiert großmaßstäblichen, vielphasigen Magmatismus, der im Zusammenhang mit der Subduktion der Paläotethys und spätorogener Kollisions-Tektonik der Pontiden gebildet wurde. Für das Verständnis des Tethys-Varisziden-Übergangs hat das Auftreten dieser Granitoide und Ophiolite in den zentralen Pontiden große Bedeutung. Wie auch immer, Daten über Typ und Ursprung der Intrusionskörper sind nicht vorhanden. Auf Grundlage stratigrafischer Korrelationen und wenigen K-Ar-Daten haben frühere Geologen mitteljurassische Alter für die gesamten Kastamonu-Plutone angenommen. Um über Petrogenese und Magmenentwicklung die Bildung des Gebirgsgürtels zu klären, wurden Zirkone von den Deliktas-, Sivrikaya- and Devrekani-Granitoiden mit der Pb-Pb-Evaporationsmethode und der U-Pb-Isotopenverdünnungsmethode untersucht und mit geochemischen Daten kombiniert. Die spätkarbonische Sivrikaya Granitoide (SG) besteht aus Biotit-Hornblende-Granodioriten, Tonaliten und wenigen Zweiglimmer-Graniten. Sivrikaya Gesteine sind schwach metaluminöse bis peraluminöse, und in Richtung S-Typ entwickelt (ASI = 0.9 to > 1.1). Die Gesteine zeichnen sich durch niedrige initiale Sr-Verhältnisse [Sri= 0.705 - 0.708], moderate initiale eNd(t)-Werte (-1 to -3.8) und junge Nd-Modellalter (TDM= 0.75 - 1.05 Ga) aus, die auf unterschiedliche Mischungsverhältnisse zwischen Mantel- und Krustenkomponenten hinweisen. Chondritnormierte (cn) Seltene Erden-Elementmuster zeigen Fraktionierung zwischen leichten ( [La/Yb]cn= 9 - 49) und schweren Seltenen Erden ([Gd/Yb]cn= 0.79 - 2.37), sowie keine zu starke Eu-Abreicherung (Eu/Eu* = 1.19-0.18) an. Diese Charakteristika kombiniert mit moderaten d18O-Werte (10 - 11.6 Promille) weisen auf Dehydrationsschmelzen von heterogenen Amphibolit-Metagrauwacken-Typen mit variabler Mantelmaterialbeteiligung hin (Nzegge et al. 2006). Der frühpermische Deliktas-Leukogranit (DLG) enthält muskovitführende Monzogranite. Deliktas Gesteine sind stark peraluminöse S-Typ Granite (ASI >1.1), was die Mineralogie mit hochaluminösen Phasen wie Muskovit und Cordierit zeigt. DLG Proben zeigen stark fraktionierte Seltene Erden- ([La/Yb]cn= 3.6 - 35), eher flache schwere Seltene Erden-Elementmuster ([Gd/Yb]cn= 0.59 - 0.78) und kleine, positive bis deutlich negative Eu-Anomalien (Eu/Eu*= 1.15 - 0.42), die auf Schmelzen von metapeltischen Gesteinen mit Rest-plagioklas und/oder hochgradige Kristallisationsfraktionierung hinweisen. Gesteine dieser Intrusion haben hohe Sr(i)-Verhältnisse (0.7103 - 0.7123) und niedrige eNd(t)-Werte (-2.2 bis -5.0), die einen Inselbogen mit unterlagernder, entwickelter kontinentalen Kruste nahelegen. Nahezu konstante d18O-Werte (~11.5 Promille) und alte Nd-Modelalter (TDM= 1.2 - 2.2 Ga) der Gesteine, in Verbindung mit geochemischen Charakteristika unterstützen weiter die Beteiligung von entwickelter kontinentaler Kruste in ihrer Genese. Der mitteljurassische Devrekani pluton (DG) besteht hauptsächlich aus metaluminösen I-Typ (ASI = 0.55 - 0.88) Hornblende-Biotit Dioriten und wenigen Tonaliten. Die Proben haben niedrige Sr(i)-Verhältnisse (0.705 - 0.706), sehr niedrige negative eNd(t)-Werte (-0.8 bis -2.2). Diese Merkmale zusammen mit den niedrigen d18O-Werten (7 - 9 Promille), sehr hohen Mg# Werten, jungen Nd-Modellaltern (TDM = 1.04 - 1.6 Ga) und hohen CaO/Al2O3-Verhältnissen legen Dehydrationsschmelzen von mafischen Unterkrusten-Gesteinen und/oder die Abstammung von amphibolithischen Quellen mit einem signifikantem Beitrag von Material aus dem oberen Mantel nahe. DG Gesteine sind weiterhin durch moderat fraktionierte leichte Seltene Erden- ([La/Yb]cn= 2 - 11), flache schwere Seltene Erden-Elementmuster ([Gd/Yb]cn= 1.35 - 1.68), welche Granat- und Zirkon-Anreicherung anzeigen, charakterisiert. Die hohen Sr/Y-Verhältnisse (10 - 37), keine bis deutlich positive Eu-Anomalien (Eu/Eu* = 0.72 - 0.95), und Sr-spikes, zeigen Plagioklas-Anreicherung an. Diese chemischen Charakteristika zeigen Magmenabstammung von einer angereicherten und/oder metasomatischen Mantelquelle mit geringer krustaler Kontamination an. Es liegt nahe, dass nachdem der kimmeridgische Kontinent mit dem Südrand Eurasiens kollidierte, Platten-Abbruch und Subduktion eintraten, was in einer Asthenospärenaufwölbung und der Produktion von nahezu primären Schmelzen des Devrekani-Plutons führte. Die aufsteigenden Schmelzen interagierten mit vom Mantel und der Kruste abstammenden Magmen. Es kann gefolgert werden, dass der mittelmesozoische Magmatismus durch die kurze südwärts gerichtete Subduktion des Küre-Randbeckens (Ustaömer and Robertson, 1997) unter das neu gebildete spätkarbonische Orogen (Okay et al. 2006) ausgelöst wurde. Die WSW-ENE-Orientierung des Devrekani-Plutons und der Scherzone, die mit dem gravitativen Kollaps verbunden sind, die Mineralogie und Chemie der Gesteine Verschieden von der, die näher an der Schwarzmeerküste liegen, und der DG Lage weit im Süden des Küre-Ophioliths zeigt ein Subduktionssystem in jungem Stadium (Nzegge et al. in review). Da die Intrusion bezogen auf die Schergefüge spät syn-tektonisch ist, kann angenommen werden, dass ihre Bildung mit dem Dehnungs-Kollaps-Ereignis zusammenhängt. Nach Dewey (1988) spritzen, verursacht durch Trennungsbruch während Gravitations-Kollaps eines Gebirges große Volumina von Mantelpartiellschmelzen in die untere Kruste. Es ist vorgeschlagen, dass während dieser Einstürzung die Geotherme den Granat-Lherzolith-Solidus überschritten hat und mafischen Schmelzen erzeugt wurden. Die Schmelze wurde kaum von der felsischen Oberkruste beeinflusst, reicherte Plagioklas an, und drang in die Scherzonen ein, den Devrekani metaluminöse I-Typ Pluton bildend. Geochronologische Analysen lieferten Alter, die für Deliktas zwischen 295-270 Ma, für Sivrikaya zwischen 303-300 Ma und für den Devrekani Granitoid im Süden des Gürtels bei 190-165 Ma liegen. Zirkonxenokristall-Alter von ~2,7 Ga liefern den Nachweis für proterozoischen Protolith, und unterstreichen die Verbindung der zentralen Pontiden mit Laurasia und Gondwana. Die 360-340-320 Ma Phasen von Bleiverlust in Zirkonen sind für variskischen Metamorphismus bezeichnend. Diese neuen geochemischen Daten, und Altersdaten der Sivrikaya-, Deliktas- und Devrekani- Granitoide zeigen die Entwicklung des Kastanmonu Magmatismus mit tholeiitischer bis kalk-alkaliner zu tholeiitischer Zusammensetzung in Abhängigkeit der Zeit an. Weiterhin stellt das Vorkommen von spätpaläozoischen prä- bis postkollisionalen Graniten, Übergangsgraniten und peraluminösen Graniten, sowie mittelmesozoische junge Inselbögen bisherige Enwicklungsmodelle für den Kastamonu-Granitgürtel und die zentralen Pontiden in Frage. Die hier präsentierten Daten unterstreichen die komplexe thermo-tektonische Geschichte der Zentralen Pontiden, den damit verbundenen Magmatismus mit einer “long-lasting” nordwärtigen und einer “short-lived” südwärtigen Subduktionsphase der Paläotethys (beziehungsweise während des Paläozoikums und Mesozoikums??) (vorgeschlagenes Modell), und der folgende Krustenwachstumsprozess (Kollison-Akkretion von Gondwana Kontinent Fragmenten mit Laurasia). Das präkambrisch-paläozoisch von Eurasien stammende Basement (Devrekani Metamorphe Einheit) der Zentralen Pontiden liegt zwischen den Küre und Çangaldag-Komplexen. Der Nachweis des präkambrischen Basements in den Zentralen Pontiden kommt von einer Büyükçay-Probe (BÜ-20, Ortho-Amphigneis, ~502 Ma), von ererbten Zirkone und Nd Isotopen Daten. Wahrscheinlich kristallierten die BÜ-20 Zirkone in einem spätkambrischen-frühordovizischen magmatischen Ereignis als Teil des weit verbreiteten subduktionsgebundenen Magmatismus Nördliche von Gondwana (e.g. Linnemann et al. 2000).

The Himalayas and the Tibetan Plateau are considered as the classical case of continental collision. In the meantime, some fundamental questions concerning the structure, rheology and physical processes influencing the evolution of the region's lithosphere are still pending.The Hi-CLIMB seismology experiment deployed a large number (255) of broadband stations during three years on an 800 km profile along 85°E, across the Himalayas and the southern half of the Tibetan Plateau. The close station spacing (~4-9 km), the large amount of data (1.5 terabyte), the high-frequency receiver functions and the use of multiply converted waves result in a detailed image of lithospheric structures at all scales. These images allow to follow: (1) faults at shallow (~3-4 km) depth; (2) the Main Himalayan Thrust from its shallow part to its deep and ductile continuation; (3) shallow and localized low-velocity layers (previously referred to as "bright spots") in Tibet in correlation with grabens; and (4) underplating of the Indian lower crust beneath Lhasa block. Furthermore, our results show (5) that the Indian lower lithosphere advances northward to about the centre of the Tibetan Plateau, where it is opposed to the Eurasian lithospheric mantle; (6) that the main sutures at the surface have no pronounced signature at depth; and (7) that the upper mantle discontinuities at 410 and 670 km do not seem to be affected by the ongoing orogeny. The obtained information on geometries are then used in two applications.Based on the improved knowledge on flexural geometry beneath the foreland basin, the rheology of the India plate is re-assessed. Thermomechanical modelling results reveal that the effective elastic thickness decreases from south to north due to decoupling, caused by flexural and thermal weakening. To explain the support of the Tibetan Plateau's topography as well as regional isostasy in the Himalayas, a strong upper mantle is required.Combining the geometry of underplating with Bouguer anomaly data, localized densification of the Indian lower crust is shown to occur where it reaches its maximal depth. This effect is associated to eclogitization. Investigations of the thermal field and pressure--temperature--density relations assuming different hydration levels are performed using thermo-kinematic and petrological models, respectively. The results suggest that the Indian lower crust is partially hydrated, and that eclogitization is kinetically hindered compared to phase equilibria. Overstepping is explained by the absence of free water in the system, and subsists until dehydration reactions occur at higher P-T conditions.In conclusion, constraints on geometry and internal properties, as well as evaluation of the importance of physical processes are necessary in order to better understand the build-up of the observed lithospheric structures and the evolution of their deformation., RésuméL'Himalaya et le Plateau Tibétain sont considérés comme l'exemple classique de collision continentale. Cependant, de nombreuses questions fondamentales sur la structure, la rhéologie et les processus physiques liés à l'évolution de la lithosphère de cette région restent ouvertes.Dans le cadre de l'expérience sismologique Hi-CLIMB, un grand nombre de stations large-bande (255) a été déployé pendant trois ans sur un profil de 800 km, à travers l'Himalaya et la moitié sud du Plateau Tibétain. L'espacement serré des stations (~4-9 km), la quantité importante des données (1.5 téraoctets), et l'utilisation de méthodes comme les fonctions récepteurs haute-fréquence ainsi que les conversions multiples ont permis d'obtenir une image détaillée des structures lithosphériques à toute échelle. Ces images permettent un suivi: (1) des failles à faible profondeur (~3-4 km); (2) du chevauchement majeur (MHT) de sa partie superficielle jusqu'à sa continuité profonde et ductile; (3) des zones à vitesses lentes localisées et peu profondes ("bright spots") sous le Tibet en corrélation avec des grabens; (4) de la croûte inférieure indienne sous-plaquée au bloc Lhasa. De plus, nos résultats suggèrent que (5) la lithosphère inférieure indienne avance vers le nord jusqu'au centre du Plateau Tibétain, où elle est opposée au manteau lithosphérique de l'Eurasie; que (6) les sutures en surface n'ont pas de signature marquée en profondeur; et que (7) les discontinuités du manteau supérieur à 410 et 670 km ne sont pas affectées par l'orogenèse. Les informations obtenues sur les géométries sont ensuite utilisées dans deux applications.La rhéologie de la plaque Inde est réévaluée en utilisant l'image améliorée de sa flexure sous le bassin avant-arc. Les résultats des modélisations thermomécaniques montrent que l'épaisseur élastique équivalente diminue du sud au nord dû au découplage lié à l'affaiblissement flexural et thermique. Le support de la topographie du Plateau Tibétain ainsi que l'isostasie régionale en Himalaya nécessitent un manteau résistant.En combinant la géométrie du sous-plaquage avec des anomalies de Bouguer, une densification localisée de la croûte inférieure indienne est mise en évidence à l'endroit où elle atteint sa profondeur maximale. Cette densification est associée à l'éclogitisation. Des analyses du champ thermique et les relations pression--température--densité en supposant différents niveaux d'hydratation sont effectuées par des modélisations thermo-cinématiques et pétrologiques. Les résultats suggèrent que la croûte inférieure indienne est partiellement hydratée, et que l'éclogitisation subit un retard. Ce dernier effet est expliqué par l'absence d'eau libre dans le système, l'éclogitisation n'ayant pas lieu jusqu'à l'occurrence des réactions de déshydratation à des P-T plus élevées que les conditions d'équilibre.En conclusion, cette thèse apporte de nouvelles contraintes sur la géométrie et les propriétés internes de la lithosphère, éléments clés pour mieux évaluer l'importance des différents processus physiques impliqués dans la mise en place des structures et l'évolution de la déformation en Himalaya-Tibet.

The concentrations of atmospheric noble gases dissolved in groundwater mostly exceed their respective atmospheric equilibrium concentrations. In groundwater hydrology, this well-known phenomenon is usually referred to as the "excessair" phenomenon. The presence of excess air crucially affects the quantitative interpretation of environmental tracer concentrations in terms of paleo-environmental conditions and groundwater residence time, because a reliable determination of the atmospheric equilibrium component is required in such cases. In addition, excess air itself is potentially a tracer for paleo-rechargeconditions. This represents an opportunity in the field of environmental tracer hydrology which has not yet been fully exploited. The formation of excess air as a result of the dissolution of entrapped air within the quasi-saturated zone is still not thoroughly understood. Although knowledge of the physical processes governing the formation of excess air has been greatly enhanced during recent years, verification of the underlying conceptual ideas in natural systems is still lacking. In the work described here, both laboratory and field experiments were conducted in conjunction with numerical simulations, with the aim of obtaining a better understanding of the role of kinetic effects and flow direction in the dissolution of entrapped air. In addition, the conceptual ideas developed within the context of laboratory experiments and numerical investigations were upscaled and verified by field experiments. A sand-column experiment, in combination with numerical simulations, indicates that kinetic effects on the dissolution of entrapped air in quasi-saturated porous media are negligible for the small water flow velocities usually found in natural systems. Only for large flow velocities are kinetic effects of significant importance. The assumption of local equilibrium between the water and entrapped gas phases is not valid in such a case. However, the flow direction (horizontal, vertically downward or vertically upward) crucially affects the bubble-mediated gas transfer, because the hydrostatic pressure gradient in the direction of the flow depends on flow direction. Furthermore, laboratory experiments showed that apparently unfractionated excess air can be produced in the presence of a progressively dissolving entrapped gas phase. This finding contradicts the original conceptual idea of the formation of unfractionated excess air as being the result of complete bubble dissolution,and opens up new vistas for the interpretation of the presence of such apparently unfractionated excess air. Field experiments confirmed that excess air results from the dissolution of entrapped air during infiltration. However,the experiments also suggest a strong dependence on soil properties, such as grain-size and pore-size distributions and hydraulic conductivity. Infiltration into a fine-grained sediment produced significant amounts of excess air in the seepage water, whereas infiltration into very coarse and highly conductive gravels did not. Moreover, the depth profile of the noble gas temperature - i.e., the temperature calculated from the noble gas concentrations in the seepage water - was identicalto that of the soil temperature. This indicates that the infiltrating water was in equilibrium with the ambient soil air under atmospheric pressure, and that noble gas temperatures do indeed record the soil temperature during infiltration, an assumption which is implicitly made when noble gases are used as a proxy for paleotemperature at the time of recharge. Based on these results, explanations were found for a noble gas data set from an aquifer in Michigan in which the noble gas temperatures are consistently lower than the mean annual soil temperature. Because noble gases record the temperature at the time of recharge, the noble gas temperature can indeed be lower than the mean annual soil temperature if the unsaturated zone is shallow and recharge occurs predominantly during the cold season. Both of these seem to be the case in Michigan. Since the amount and fractionation of excess air refiect the environmental conditions prevailing during groundwater recharge, they can, in principal, be used as a proxy for paleo-recharge conditions. Excess air amounts and their fractionation in Pleistocene groundwater from a deep aquifer in Wisconsin indicate the oecurrence of changes in recharge conditions shortly before and at the beginning of the last glacial period, leading to an increase in the amount of excess air during this time period. To summarize, the results presented in this thesis yield new insights into gas exchange in quasi-saturated porous media on very different scales. Based on the findings from well-controlled, small-scale laboratory experiments and numerical investigations, the conceptual model of the formation of excess air could be transferred to field experiments which confirmed the validity of this conceptual model in natural systems. Moreover, excess air in (paleo-)groundwater proved to be a promising tracer for past hydrological conditions, thus opening up an interesting field for future work. Die Konzentrationen gelöster atmosphärischer Gase im Grundwasser übertreffen meistens die entsprechenden atmosphärischen Gleichgewichtskonzentrationen. Diese Luftüberschüsse werden in der Grundwasserhydrologie als "Excess Air" bezeichnet. Die Luftüberschüsse erschweren die quantitative Interpretation von Umwelttracerdaten hinsichtlich der Paläo-Umweltbedingungen und der Aufenthaltszeit des Grundwassers, da diese Anwendungen die zuverlässige Bestimmung der atmosphärischen Gleichgewichtskomponente an der Gesamtkonzentration der Gase voraussetzen. Ausserdem stellen die Luftüberschüsse selbst einen potenziellen Tracer für die Bedingungen während der Grundwasserneubildung dar - eine Möglichkeit,die in der Tracerhydrologie bis heute erst wenig Anwendung fand. Die Entstehung der Luftüberschüsse als Folge der Auflösung von eingeschlossenen Luftblasen in der quasigesättigten Zone ist bis heute noch nicht vollständig verstanden. Obwohl das Verständnis der physikalischen Prozesse, die die Bildung der Luftüberschüsse kontrollieren,in den letzten Jahren deutlich erweitert werden konnte, fehlt die Übertragung der Konzepte auf natürliche Systeme. In der vorliegenden Arbeit wurden sowohl Labor- und Feldexperimente, als auch numerische Simulationen mit dem Ziel durchgeführt, die Relevanz kinetischer Effekte und den Einfluss der Fliessrichtung auf die Auflösung eingeschlossener Gasblasen zu untersuchen. Ausserdem wurden die konzeptuellen Modelle, die im Zusammenhang mit Laborexperimenten entwickelt wurden, in Feldexperimenten überprüft und verifiziert. Ein Sandsäulenexperiment hat in Kombination mit numerischen Simulationen gezeigt, dass kinetische Effekte bei der Auflösung eingeschlossener Gasblasen in der quasigesättigten Zone bei kleinen Strömungsgeschwindigkeiten,die typisch sind für natürliche Systeme, vernachlässigbar sind. Nur für sehr hohe Strömungsgeschwindigkeiten sind kinetische Effekte von signifikanter Bedeutung und die Annahme von lokalem Lösungsgleichgewicht ist in solchen Fällen nicht zulässig. Hingegen beeinflusst die Richtung der Strömung, d.h. horizontal, vertikal abwärts oder vertikal aufwärts, die Gasblasenauflösung deutlich, weil der Gradient des hydrostatischen Druckes unterschiedlich ist für verschiedene Strömungsrichtungen. Darüberhinaus zeigten die Laborexperimente, dass scheinbar unfraktionierte Luftüberschüsse trotz Anwesenheit einer sich auflösenden Gasphase gebildet werden. Diese Beobachtung widerspricht der ursprünglichen Erklärung für die Entstehung von unfraktionierten Luftüberschüssen durch die vollständige Auflösung eingeschlossener fraktionierter Luftüberschüsse. Die Ergebnisse der durchgeführten Feldexperimente bestätigen das konzeptuelle Modell zur Entstehung der Luftüberschüsse durch die Auflösung von eingeschlossenen Luftblasen während der Infiltration. Die Experimente zeigen eine starke Abhängigkeit der Bildung der Luftüberschüsse von Bodeneigenschaften, wie der Korn und Porengrössenverteilung und der Durchlässigkeit. Während die Infiltration in einen feinkörnigen Boden zur Produktion von Luftüberschüssen im Wasser führte, wurden bei der Infiltration in grobkörnige, gut durchlässige Sedimente keine Luftüberschüsse gebildet. Das Tiefenprofil der Edelgastemperatur, d.h. der Temperatur, die aus den im Sickerwasser gemessenen Edelgaskonzentrationen berechnet wurde, stimmt sehr gut mit dem Profil der Bodentemperatur überein. Das deutet darauf hin, dass das Wasser im Lösungsgleichgewicht mit der umgebenden Bodenluft unter Atmosphärendruck war und die Edelgastemperatur tatsächlich die Bodentemperatur während der Infiltration wiedergibt - eine Annahme, die bei der Verwendung von Edelgasen als Indikator für Paläotemperaturen implizit gemacht wird. Basierend auf diesen Ergebnissen konnten neue Erklärungen für einen Edelgasdatensatz aus einem Grundwasserleiter in Michigan gefunden werden, in dem die Edelgastemperaturen durchweg niedriger sind, als die mittlere Jahresbodentemperatur. Da Edelgase die Bodentemperatur zum Zeitpunkt der Neubildung repräsentieren, kann die Edelgastemperatur tatsächlich niedriger sein als die mittlere Jahresbodentemperatur, falls die ungesättigte Zone geringmächtig ist und die Grundwasserneubildung vorwiegend während der kalten Jahreszeit stattfindet. Beide Voraussetzungen scheinen in Michigan erfüllt zu sein. Da die Bildung der Luftüberschüsse von den Umweltbedingungen während der Infiltration abhängt, können sie im Prinzip selbst als Proxy für die Bedingungen während der Grundwasserneubildung verwendet werden. Luftüberschüsse in pleistozänem Grundwasser aus einem tiefen Grundwässerleiter in Wisconsin zeigen Änderungen in der Grundwasserneubildung, die zu einem Anstieg der Luftüberschüsse kurz vor und zu Beginn der letzten Vereisungsphase führten. Die Resultate der vorliegenden Arbeit gewähren neue Einblicke in den Gasaustausch in quasigesättigten porösen Medien auf sehr unterschiedlichen Grössenskalen. Aufbauend auf den Erkenntnissen aus Laborversuchen, durchgeführt unter gut kontrollierbaren Bedingungen, und numerischen Untersuchungen liefern die Feldexperimente Informationen über die Entstehung von Luftüberschüssen in natürlichen Systemen. Weiterhin stellte sich der Luftüberschuss als viel versprechender Tracer für paläohydrologische Verhältnisse heraus und es eröffnet sich somit ein interessantes Feld für künftige Arbeiten.