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Papers by Michael Marks Marks

Apatites from the Kaiserstuhl Volcanic Complex, Germany: new constraints on the relationship between carbonatite and associated silicate rocks

European Journal of Mineralogy, 2014

ABSTRACT Apatites from carbonatites, related alkaline silicate rocks, a carbonate-bearing melilit... more ABSTRACT Apatites from carbonatites, related alkaline silicate rocks, a carbonate-bearing melilititic dyke rock (bergalite), and a diatreme breccia (containing both carbonate and silicate fragments) of the Miocene Kaiserstuhl Volcanic Complex, SW Germany, are used to reconstruct the petrogenetic relationship among these rocks. Apatites from carbonatites reach higher Sr and Nb contents but are generally lower in Fe, Mn, Th, U, Si, S, Cl and Br compared to apatites from associated silicate rocks, whilst Na, REE and F contents are overlapping. Apatites from bergalite show a systematic and discontinuous core-rim zonation, with the core being compositionally similar to apatites from silicate rocks and the rim corresponding to carbonatitic apatites. These observations imply that the bergalite apatites nucleated in a silicate melt and continued to crystallize from an evolving CO 2 -enriched melt probably with carbonatitic affinity. Apatites from a diatreme breccia comprise three populations: (1) similar to the apatites from silicate rocks, (2) similar to the carbonatitic apatites, and (3) resembling apatite population (1) partially replaced by apatite (2). We infer that apatite (1) was derived from silicate-rock fragments and apatite (2) crystallized from a later intruding carbonatitic melt, which metasomatized the silicate-rock fragments and caused the replacement textures as observed in apatite population (3). We conclude that apatites from the Kaiserstuhl complex preserve important information on the petrogenetic relationship between carbonatitic and silicate melts. The carbonatitic melts at the Kaiserstuhl complex are probably the products of protracted fractionation of a CO 2 -rich nephelinitic melt.

American Mineralogist, 2001

Two samples from the augite syenite unit of the 1.13 Ga alkaline to peralkaline Ilimaussaq intrus... more Two samples from the augite syenite unit of the 1.13 Ga alkaline to peralkaline Ilimaussaq intrusion in South Greenland contain olivine (Fa 75-85 ) with micrometer-sized exsolution lamellae of intergrown augite and magnetite. The exsolved olivine contains only about 0.6 wt% CaO, whereas the reintegrated magmatic composition contained about 1.4% CaO corresponding to about 3 mol% of a larnite (La) component. The exsolved olivine bears no measurable Na, Al, or Ti, but the reintegrated magmatic olivine contained up to 0.4 wt% Na 2 O, 0.2 wt% Al 2 O 3, and 0.3 wt% TiO 2 . Magmatic baddeleyite in the same samples indicates an extremely low silica activity of below 0.4 during the early stages of magmatic crystallization at > 900 °C and 1 kbar. According to the equilibrium Ca 2 SiO 4 (La in Ol) + SiO 2 = 2 CaSiO 3 (Wo in Cpx), the low silica activity is thought to be responsible for the unusually Ca-rich compositions of the primary olivines, which, in these samples, formed at 875 ± 15 °C and at oxygen fugacities between 1.2 and 2.3 log units below the QFM buffer. The composite exsolution lamellae formed during cooling due to an overstep of the schematic reaction Fa + Kst (Ca-rich component in olivine) + 1/3 O 2 = Hd + 2/3 Mt. Phase equilibria indicate temperatures between 300 and 750 °C and oxygen fugacities close to QFM for this exsolution process. The lamellae only developed in samples where the olivines were both especially high in Ca and presumably rapidly cooled (although not chilled!), as the lamella-bearing samples were collected at the outermost rim of the augite syenite unit and close to the top of the Ilimaussaq intrusion. Schreinemakers analysis shows that Ca-rich olivine of the kirschsteinite-monticellite solid solution series [Ca(Fe,Mg)SiO 4 ] would exsolve from Ca-bearing olivine of the fayalite-forsterite series only at unusually low silica activities, whereas at higher silica activities, the observed exsolutions of clinopyroxene with magnetite are more stable. Hence, both cooling history and evolution of intensive variables during cooling are important for the formation of olivine exsolution textures.

2012 Zaitsev Sadiman volcano Lithos

2013-Turmalines Schwarzwald

Emplacement and geochemical evolution of highly evolved syenites investigated by a combined structural and geochemical field study: The lujavrites of the Ilímaussaq complex, SW Greenland

Lithos, 2015

ABSTRACT

Crystal mat-formation as an igneous layering-forming process: Textural and geochemical evidence from the ‘lower layered’ nepheline syenite sequence of the Ilímaussaq complex, South Greenland

Lithos, 2015

ABSTRACT The lower layered nepheline syenite sequence (kakortokites) of the Mesoproterozoic alkal... more ABSTRACT The lower layered nepheline syenite sequence (kakortokites) of the Mesoproterozoic alkaline to peralkaline Ilímaussaq complex, South Greenland shows spectacular rhythmic meter-scale igneous layering. The 29 exposed units have sharp contacts against each other and each of these units consists of three modally graded layers dominated by arfvedsonitic amphibole, eudialyte-group minerals, and alkali feldspar, respectively.

Compositional variation in apatite from various host rocks: clues with regards to source composition and crystallization conditions

Neues Jahrbuch für Mineralogie - Abhandlungen, 2015

ABSTRACT Electron microprobe (EPMA) and total reflection X-ray fluorescence (TXRF) analyses were ... more ABSTRACT Electron microprobe (EPMA) and total reflection X-ray fluorescence (TXRF) analyses were used to investigate the composition of 17 apatite samples of magmatic to hydrothermal origin, including six carbonatites, two ijolites, and each one phoscorite and pyroxenite (Russia/Kola Peninsula), one apatitite (Brazil/Ipanema), three silico-carbonatic pegmatites (Madagascar/Ampandrandava and Russia/Slyudyanka), one Kiruna-type deposit (Iran/Esfordi), as well as the Otter and Emerald Lake apatites (Canada). Their composition is compared to a compilation of literature data for apatite from carbonatites, gabbros, diorites, biotite (± amphibole) -bearing granitoids, muscovite-bearing granites, felsic pegmatites and the widely known Durango apatite. The results of EPMA in this study reveal that the composition of apatite tends to be distinctive for specific rock-types (e.g. relative high SrO and/or Ce2O3 contents in apatites from carbonatites or high MnO contents in apatites from muscovite-bearing granites). However, source composition, temperature and redox conditions during crystallization or composition of a coexisting fluid can influence the apatite composition, for example, so that a broad overlap of various element contents exists between apatites from different rock-types. In addition, we present TXRF data for barely investigated trace elements in apatite (As, Tl and Br) that appear to be promising elements for future petrological and geochemical investigations.

Rare earth elements in apatite as a monitor of magmatic and metasomatic processes: The Ilímaussaq complex, South Greenland

Lithos, 2015

ABSTRACT Textural and compositional variations of apatite from the plutonic Ilímaussaq complex in... more ABSTRACT Textural and compositional variations of apatite from the plutonic Ilímaussaq complex in South Greenland and its surrounding country rocks track magmatic and metasomatic processes. Detailed back-scattered electron (BSE) imaging reveals various types of apatite textures including (i) growth zonation (concentric, oscillatory as well as sector zonation) formed during magmatic differentiation, (ii) resorption and overgrowth textures due to fluid/melt induced metasomatic overprint of precursor apatite and (iii) replacement textures indicating the destabilization of apatite in favor of monazite.

Lithos, 2015

The concentration of halogens in apatite, biotite and amphibole is investigated for a large varie... more The concentration of halogens in apatite, biotite and amphibole is investigated for a large variety of mantlederived plutonic rocks (gabbros, diorites, monzonites, olivine-and pyroxene-bearing monzonitic to granitic rocks, syenites, carbonatites and a phoscorite). In all rocks studied, apatite occurs as an early magmatic phase, whereas biotite and amphibole may occur either as a late magmatic phase or as late-stage, potentially hydrothermal product replacing precursor olivine, pyroxene and Fe-Ti oxides (ilmenite and magnetite). Based on electron microprobe analyses for F and Cl and detailed textural observations, we test existing models of halogen partitioning between apatite and biotite. Bromine concentration data for apatite, biotite and amphibole are used to further refine our understanding of the geochemical similarities and differences between Cl and Br during magmatic and hydrothermal processes. Our data suggests that F and Cl contents in apatite, biotite and amphibole can indeed be useful monitors of the halogen systematics in magmas, but they may also be subject to post-magmatic changes to variable extents. The relatively small radius and compatible F cation seems to be less prone to post-magmatic alteration and is likely to best reflect the original magmatic halogen abundancesespecially in apatite. However, the larger and probably more incompatible Cl anion, is more easily re-mobilized as reflected by strong redistribution of Cl in biotite and amphibole which have been clearly overprinted by hydrothermal fluids. In certain cases, the ability of halogens to re-distribute themselves after magmatic equilibrium partitioning (as emphasized by our data) suggests that observed partitioning (especially between apatite and biotite) may also be used as a very sensitive indicator for post-magmatic hydrothermal processes.

The compositional variability of eudialyte-group minerals

Mineralogical Magazine, 2011

Eudialyte-group minerals (EGM) represent the most important index minerals of persodic agpaitic s... more Eudialyte-group minerals (EGM) represent the most important index minerals of persodic agpaitic systems. Results are presented here of a combined EPMA, Mössbauer spectroscopy and LA-ICP-MS study and EGM which crystallized in various fractionation stages from different parental melts and mineral assemblages in silica over- and undersaturated systems are compared. Compositional variability is closely related to texture, allowing for reconstruction of locally acting magmatic to hydrothermal processes. Early-magmatic EGM are invariably dominated by Fe whereas hydrothermal EGM can be virtually Fe-free and form pure Mn end-members. Hence the Mn/Fe ratio is the most suitable fractionation indicator, although crystal chemistry effects and co-crystallizing phases play a secondary role in the incorporation of Fe and Mn into EGM. Mössbauer spectroscopy of EGM from three selected occurrences indicates the Fe3+/ΣFe ratio to be governed by the hydration state of EGM rather than by the oxygen fuga...

Journal of Petrology, 2011

Chemical Geology, 2014

The halogen contents of granitoid rocks and their distribution between apatite, biotite, muscovit... more The halogen contents of granitoid rocks and their distribution between apatite, biotite, muscovite and amphibole from two different localities (German part of the Bohemian Massif and Central Aegean, Greece) are investigated in detail. Whole rock F and Cl contents and F/Cl mass ratios vary systematically with the magmatic halogenbearing mineral assemblage in which biotite and apatite are present in all rock samples: muscovite-bearing granites are F-rich (mostly 1100-2000 μg/g, but up to 3100 μg/g) and are relatively Cl-poor (50-130 μg/g). In contrast, amphibole-bearing rocks reach high Cl contents (50-900 μg/g) and are relatively F-poor (500-1400 μg/g). Only biotite-and apatite-bearing granites show intermediate F (750-1100 μg/g) and Cl (120-350 μg/g) contents. Bromine contents of all rock samples are below the detection limit of about 0.6 μg/g. In general, F and Cl are preferentially incorporated in apatite over biotite and biotite usually contains higher amounts of F and Cl than muscovite. Similarly, biotite prefers F over amphibole, but the distribution of Cl between biotite and amphibole varies between different rock samples. Bromine contents in muscovite are below the detection limit of 0.4 μg/g, but can reach up to 0.8 μg/g in biotite and up to 2.5 μg/g in apatite and amphibole. Near-solidus effects such as fluid exsolution, diffusive re-equilibration and hydrothermal overprint may change the initial halogen distribution in the rock. Importantly, significant amounts of the whole rock's F (up to 60%) and Cl (up to 90%) may be accommodated in post-magmatic alteration phases (fluorite and Na-K-Ca-bearing sheet silicates) and fluid inclusions. Therefore, great care has to be taken when interpreting halogen contents of whole rocks and the influence of post-magmatic halogen-carriers needs to be taken into account.

Halogens (F, Cl and Br) at Oldoinyo Lengai volcano (Tanzania): Effects of magmatic differentiation, silicate–natrocarbonatite melt separation and surface alteration of natrocarbonatite

Chemical Geology, 2014

ABSTRACT Halogen abundances of natrocarbonatites and their alteration products from Oldoinyo Leng... more ABSTRACT Halogen abundances of natrocarbonatites and their alteration products from Oldoinyo Lengai (Tanzania) are compared to those of associated silicate rocks and to various calcite carbonatites from eleven occurrences worldwide. Fresh natrocarbonatites are extremely enriched in F (up to 3.6 wt.%), Cl (up to 5.9 wt.%) and Br (up to 100 μg/g). During meteoric alteration, however, the major Cl- and Br-bearing minerals (mainly sylvite and gregoryite) are easily dissolved, leaving behind residual materials with relatively low Cl (≤ 1000 μg/g) and Br (≤ 15 μg/g) contents. The comparatively low Cl/Br ratios suggest preferential leaching of Cl relative to Br during alteration. At the same time, F is passively enriched as fluorite remains relatively stable during alteration. In the associated silicate rocks at Oldoinyo Lengai concentrations of all three halogens increase from primitive olivine melilitite to evolved combeite–wollastonite nephelinite, demonstrating their incompatible behavior during magmatic differentiation. Relatively constant Cl/Br ratios, but strongly decreasing F/Cl ratios, in these samples are explained by moderately incompatible behavior for F compared to pronounced and very similar incompatibilities for Cl and Br. Our data further imply that during silicate–natrocarbonatite melt separation all three halogens show a strong affinity for the natrocarbonatite. F and Cl are equally enriched in the natrocarbonatite while Cl and Br are slightly fractionated from each other with a preferential partitioning of Cl relative to Br into the natrocabonatite melt.

Chemical Geology, 2014

We use thallium (Tl) concentrations, K/Rb, K/Tl and Rb/Tl ratios and Tl isotopes in minerals from... more We use thallium (Tl) concentrations, K/Rb, K/Tl and Rb/Tl ratios and Tl isotopes in minerals from the alkaline to peralkaline Ilimaussaq complex (South Greenland) to trace magmatic differentiation, crustal assimilation, magmatic degassing, ore precipitation and hydrothermal metasomatism. Closed-system magmatic differentiation is marked by a coherent decrease of K/Tl-and K/Rb-ratios, whereas crustal assimilation results in a strong Tlenrichment, causing low K/Tl-ratios compared to K/Rb-ratios. Thallium isotopes show only slight changes during orthomagmatic differentiation and the assimilation of crustal material cannot be traced, since the isotopic composition of the average crust is within the range of the mantle and mantle-derived rocks. Magmatic degassing, however, increases Rb/Tl-ratios and changes the isotopic composition of Tl. The released fluids are enriched in Tl, characterized by high 205 Tl/ 203 Tl ratios and can precipitate Tl-rich sulfide and silicate minerals as indicated by some late-magmatic hydrothermal veins, which contain a conspicuous assemblage of Tl-Fe-Cu-sulfides (thalcusite, djerfisherite, chalcothallite). The oxidative alteration of these assemblages at high pH results in small-scale redistribution of Tl. Thallium released by this process is entrained into late-stage Tl-enriched astrophyllite.

American Mineralogist, 2010

American Mineralogist, 2012

In this work, we present an improved method for the semi-quantitative determination of sulfur spe... more In this work, we present an improved method for the semi-quantitative determination of sulfur species in S-bearing minerals by electron microprobe analysis. For calibration, we analyzed several sulfate and sulfide standard minerals such as baryte, celestine, chalcopyrite, and pyrite, and correlated the results with theoretical calculations retrieved from density functional theory (DFT). We applied this method to natural sodalite-group minerals from various localities. In addition, we applied the more common Raman spectroscopy to some samples and show that this method cannot be applied to sodalite-group minerals to determine their sulfur speciation. We show that even though sodalite-group minerals have a complex crystal structure and are sensitive to the electron beam, electron microprobe analysis is a reliable tool for the analysis of their sulfur speciation. The natural sodalite-group minerals show systematic variations in sulfur speciation. These variations can be correlated with the independently determined oxidation state of the parental magmas thus making S-bearing sodalitegroup minerals good redox proxies, although we show that the electron microprobe analysis of the sulfur speciation is matrix-dependent, and the sulfur speciation itself depends on crystal chemistry and structure, and not only on f O 2 .

American Mineralogist, 2014

The supergene alteration of cobalt arsenides produces various characteristic mineral assemblages ... more The supergene alteration of cobalt arsenides produces various characteristic mineral assemblages including erythrite, pharmacolite, and other Ca±Mg±Co-bearing arsenates, which upon precipitation remove Co and As from natural waters. Their paragenetic relationships and stability conditions have not been investigated in detail. We present a detailed study on these assemblages, their successions and coexisting fluid compositions from the mining area of Wittichen, southwest Germany, where primary skutterudite and safflorite in granite-hosted barite-calcite veins are undergoing oxidation. Water analyses from the old mines, a semi-quantitative stability diagram and quantitative reaction path modeling are used to constrain their conditions of formation. Cobalt-and arsenate-bearing solutions invariably precipitate erythrite first and hence buffer Co concentrations to very low values. Both during skutterudite or safflorite dissolution and erythrite precipitation, the fluid's Co/As ratio decreases rapidly. Therefore, spherocobaltite (Co carbonate) is unstable in the presence of arsenate ions under most conditions. The formation of various mineral assemblages precipitating after or simultaneously with erythrite strongly depends on Ca 2+ and Mg 2+ activities and pH. Small changes in one of these parameters lead to different mineral assemblages. These small changes are partly governed by fluid-host rock or fluid-vein mineral reactions and partly by the precipitation of the secondary arsenate minerals themselves. This complex interdependence produces the rich variety of mineral assemblages observed, which effectively serves as a very sensitive monitor of fluid compositions. Furthermore, the assemblages themselves are able to buffer the Ca-Mg-Co-As concentrations in the fluid to some extent and effectively immobilize both As and Co in close proximity to the ore deposit.

Bowen Lecture: Tracing Crust-Mantle Recycling With Lithium Isotopes

AGU Fall Meeting Abstracts, Dec 1, 2006

Li isotopes are thought to hold great potential for tracing crustal recycling, due to the very la... more Li isotopes are thought to hold great potential for tracing crustal recycling, due to the very large isotopic fractionations (over 700/00) documented at the Earth's surface. If highly fractionated crustal Li makes it past the subduction environment, it should be sampled by mantle rocks, provided it is not efficiently re-homogenized within the mantle by diffusion or stirring. However, data for arc lavas show that, contrary to initial expectations, Li generally does not track with other fluid-mobile elements and most arc lavas have isotopic ...

Chemical and physical evolution of the ‘lower layered sequence’ from the nepheline syenitic Ilímaussaq intrusion, South Greenland: Implications for the origin of magmatic layering in peralkaline felsic liquids

Lithos, 2008

ABSTRACT The Mid-Proterozoic composite Ilímaussaq complex, South Greenland, is a classic locality... more ABSTRACT The Mid-Proterozoic composite Ilímaussaq complex, South Greenland, is a classic locality to study magmatic layering in evolved peralkaline magmas. Most of the rock units show magmatic layering to differing extents, but ‘kakortokites’ – generally medium-grained agpaitic nepheline syenites – show a spectacular recurrence of black, red and white layers, which is due to regular changes in the modal contents of arfvedsonitic amphibole, eudialyte (sensu lato), alkali feldspar and nepheline, respectively. These three-layer units are found in the lower part of the intrusion and recur 29 times before grading into the overlying lujavrites (melanocratic agpaitic nepheline syenites), which are generally fine-grained and fissile with less-developed layering.The compositional trends observed in amphibole and eudialyte throughout the stratigraphic sequence reflect various processes including the chemical evolution of the melt by crystal fractionation, changes in the crystallising mineral assemblage and sub-solidus alteration. Eudialyte is the first mineral to crystallise in the investigated sequence and is therefore appropriate for recording evolution trends within the melt. Amphibole, on the other hand, always crystallises later and is therefore affected by other crystallising minerals. A detailed microprobe study of both minerals through the whole kakortokite stratigraphy displays surprisingly little change in mineral compositions within the kakortokites, but strong fractionation trends in the overlying lujavrites.Although various models have been proposed to explain the recurrence of the 29 rhythmic units, the origin of this prominent magmatic layering in the kakortokites and the lack of mineralogical and strong mineral chemical changes has not been quantitatively explained. We propose, that in the kakortokites, minerals were probably separated from each other as a result of their different densities. The interior cooled, resulting in crystallization but only a very small proportion of crystals (0.1–0.3% for each of the four minerals) could remain suspended in the melt before gravity forced them to settle down in a stagnant layer of reduced convection. A combination of volatile pressure variations caused by eruptive activity and repeated replenishment can explain the oscillating liquidus temperature, the small changes in mineral compositions and such a process would produce enough crystals to form the 29 layers.

Geochmica et Cosmochimica Acta

Apatites from the Kaiserstuhl Volcanic Complex, Germany: new constraints on the relationship between carbonatite and associated silicate rocks

European Journal of Mineralogy, 2014

ABSTRACT Apatites from carbonatites, related alkaline silicate rocks, a carbonate-bearing melilit... more ABSTRACT Apatites from carbonatites, related alkaline silicate rocks, a carbonate-bearing melilititic dyke rock (bergalite), and a diatreme breccia (containing both carbonate and silicate fragments) of the Miocene Kaiserstuhl Volcanic Complex, SW Germany, are used to reconstruct the petrogenetic relationship among these rocks. Apatites from carbonatites reach higher Sr and Nb contents but are generally lower in Fe, Mn, Th, U, Si, S, Cl and Br compared to apatites from associated silicate rocks, whilst Na, REE and F contents are overlapping. Apatites from bergalite show a systematic and discontinuous core-rim zonation, with the core being compositionally similar to apatites from silicate rocks and the rim corresponding to carbonatitic apatites. These observations imply that the bergalite apatites nucleated in a silicate melt and continued to crystallize from an evolving CO 2 -enriched melt probably with carbonatitic affinity. Apatites from a diatreme breccia comprise three populations: (1) similar to the apatites from silicate rocks, (2) similar to the carbonatitic apatites, and (3) resembling apatite population (1) partially replaced by apatite (2). We infer that apatite (1) was derived from silicate-rock fragments and apatite (2) crystallized from a later intruding carbonatitic melt, which metasomatized the silicate-rock fragments and caused the replacement textures as observed in apatite population (3). We conclude that apatites from the Kaiserstuhl complex preserve important information on the petrogenetic relationship between carbonatitic and silicate melts. The carbonatitic melts at the Kaiserstuhl complex are probably the products of protracted fractionation of a CO 2 -rich nephelinitic melt.

American Mineralogist, 2001

Two samples from the augite syenite unit of the 1.13 Ga alkaline to peralkaline Ilimaussaq intrus... more Two samples from the augite syenite unit of the 1.13 Ga alkaline to peralkaline Ilimaussaq intrusion in South Greenland contain olivine (Fa 75-85 ) with micrometer-sized exsolution lamellae of intergrown augite and magnetite. The exsolved olivine contains only about 0.6 wt% CaO, whereas the reintegrated magmatic composition contained about 1.4% CaO corresponding to about 3 mol% of a larnite (La) component. The exsolved olivine bears no measurable Na, Al, or Ti, but the reintegrated magmatic olivine contained up to 0.4 wt% Na 2 O, 0.2 wt% Al 2 O 3, and 0.3 wt% TiO 2 . Magmatic baddeleyite in the same samples indicates an extremely low silica activity of below 0.4 during the early stages of magmatic crystallization at > 900 °C and 1 kbar. According to the equilibrium Ca 2 SiO 4 (La in Ol) + SiO 2 = 2 CaSiO 3 (Wo in Cpx), the low silica activity is thought to be responsible for the unusually Ca-rich compositions of the primary olivines, which, in these samples, formed at 875 ± 15 °C and at oxygen fugacities between 1.2 and 2.3 log units below the QFM buffer. The composite exsolution lamellae formed during cooling due to an overstep of the schematic reaction Fa + Kst (Ca-rich component in olivine) + 1/3 O 2 = Hd + 2/3 Mt. Phase equilibria indicate temperatures between 300 and 750 °C and oxygen fugacities close to QFM for this exsolution process. The lamellae only developed in samples where the olivines were both especially high in Ca and presumably rapidly cooled (although not chilled!), as the lamella-bearing samples were collected at the outermost rim of the augite syenite unit and close to the top of the Ilimaussaq intrusion. Schreinemakers analysis shows that Ca-rich olivine of the kirschsteinite-monticellite solid solution series [Ca(Fe,Mg)SiO 4 ] would exsolve from Ca-bearing olivine of the fayalite-forsterite series only at unusually low silica activities, whereas at higher silica activities, the observed exsolutions of clinopyroxene with magnetite are more stable. Hence, both cooling history and evolution of intensive variables during cooling are important for the formation of olivine exsolution textures.

2012 Zaitsev Sadiman volcano Lithos

2013-Turmalines Schwarzwald

Emplacement and geochemical evolution of highly evolved syenites investigated by a combined structural and geochemical field study: The lujavrites of the Ilímaussaq complex, SW Greenland

Lithos, 2015

ABSTRACT

Crystal mat-formation as an igneous layering-forming process: Textural and geochemical evidence from the ‘lower layered’ nepheline syenite sequence of the Ilímaussaq complex, South Greenland

Lithos, 2015

ABSTRACT The lower layered nepheline syenite sequence (kakortokites) of the Mesoproterozoic alkal... more ABSTRACT The lower layered nepheline syenite sequence (kakortokites) of the Mesoproterozoic alkaline to peralkaline Ilímaussaq complex, South Greenland shows spectacular rhythmic meter-scale igneous layering. The 29 exposed units have sharp contacts against each other and each of these units consists of three modally graded layers dominated by arfvedsonitic amphibole, eudialyte-group minerals, and alkali feldspar, respectively.

Compositional variation in apatite from various host rocks: clues with regards to source composition and crystallization conditions

Neues Jahrbuch für Mineralogie - Abhandlungen, 2015

ABSTRACT Electron microprobe (EPMA) and total reflection X-ray fluorescence (TXRF) analyses were ... more ABSTRACT Electron microprobe (EPMA) and total reflection X-ray fluorescence (TXRF) analyses were used to investigate the composition of 17 apatite samples of magmatic to hydrothermal origin, including six carbonatites, two ijolites, and each one phoscorite and pyroxenite (Russia/Kola Peninsula), one apatitite (Brazil/Ipanema), three silico-carbonatic pegmatites (Madagascar/Ampandrandava and Russia/Slyudyanka), one Kiruna-type deposit (Iran/Esfordi), as well as the Otter and Emerald Lake apatites (Canada). Their composition is compared to a compilation of literature data for apatite from carbonatites, gabbros, diorites, biotite (± amphibole) -bearing granitoids, muscovite-bearing granites, felsic pegmatites and the widely known Durango apatite. The results of EPMA in this study reveal that the composition of apatite tends to be distinctive for specific rock-types (e.g. relative high SrO and/or Ce2O3 contents in apatites from carbonatites or high MnO contents in apatites from muscovite-bearing granites). However, source composition, temperature and redox conditions during crystallization or composition of a coexisting fluid can influence the apatite composition, for example, so that a broad overlap of various element contents exists between apatites from different rock-types. In addition, we present TXRF data for barely investigated trace elements in apatite (As, Tl and Br) that appear to be promising elements for future petrological and geochemical investigations.

Rare earth elements in apatite as a monitor of magmatic and metasomatic processes: The Ilímaussaq complex, South Greenland

Lithos, 2015

ABSTRACT Textural and compositional variations of apatite from the plutonic Ilímaussaq complex in... more ABSTRACT Textural and compositional variations of apatite from the plutonic Ilímaussaq complex in South Greenland and its surrounding country rocks track magmatic and metasomatic processes. Detailed back-scattered electron (BSE) imaging reveals various types of apatite textures including (i) growth zonation (concentric, oscillatory as well as sector zonation) formed during magmatic differentiation, (ii) resorption and overgrowth textures due to fluid/melt induced metasomatic overprint of precursor apatite and (iii) replacement textures indicating the destabilization of apatite in favor of monazite.

Lithos, 2015

The concentration of halogens in apatite, biotite and amphibole is investigated for a large varie... more The concentration of halogens in apatite, biotite and amphibole is investigated for a large variety of mantlederived plutonic rocks (gabbros, diorites, monzonites, olivine-and pyroxene-bearing monzonitic to granitic rocks, syenites, carbonatites and a phoscorite). In all rocks studied, apatite occurs as an early magmatic phase, whereas biotite and amphibole may occur either as a late magmatic phase or as late-stage, potentially hydrothermal product replacing precursor olivine, pyroxene and Fe-Ti oxides (ilmenite and magnetite). Based on electron microprobe analyses for F and Cl and detailed textural observations, we test existing models of halogen partitioning between apatite and biotite. Bromine concentration data for apatite, biotite and amphibole are used to further refine our understanding of the geochemical similarities and differences between Cl and Br during magmatic and hydrothermal processes. Our data suggests that F and Cl contents in apatite, biotite and amphibole can indeed be useful monitors of the halogen systematics in magmas, but they may also be subject to post-magmatic changes to variable extents. The relatively small radius and compatible F cation seems to be less prone to post-magmatic alteration and is likely to best reflect the original magmatic halogen abundancesespecially in apatite. However, the larger and probably more incompatible Cl anion, is more easily re-mobilized as reflected by strong redistribution of Cl in biotite and amphibole which have been clearly overprinted by hydrothermal fluids. In certain cases, the ability of halogens to re-distribute themselves after magmatic equilibrium partitioning (as emphasized by our data) suggests that observed partitioning (especially between apatite and biotite) may also be used as a very sensitive indicator for post-magmatic hydrothermal processes.

The compositional variability of eudialyte-group minerals

Mineralogical Magazine, 2011

Eudialyte-group minerals (EGM) represent the most important index minerals of persodic agpaitic s... more Eudialyte-group minerals (EGM) represent the most important index minerals of persodic agpaitic systems. Results are presented here of a combined EPMA, Mössbauer spectroscopy and LA-ICP-MS study and EGM which crystallized in various fractionation stages from different parental melts and mineral assemblages in silica over- and undersaturated systems are compared. Compositional variability is closely related to texture, allowing for reconstruction of locally acting magmatic to hydrothermal processes. Early-magmatic EGM are invariably dominated by Fe whereas hydrothermal EGM can be virtually Fe-free and form pure Mn end-members. Hence the Mn/Fe ratio is the most suitable fractionation indicator, although crystal chemistry effects and co-crystallizing phases play a secondary role in the incorporation of Fe and Mn into EGM. Mössbauer spectroscopy of EGM from three selected occurrences indicates the Fe3+/ΣFe ratio to be governed by the hydration state of EGM rather than by the oxygen fuga...

Journal of Petrology, 2011

Chemical Geology, 2014

The halogen contents of granitoid rocks and their distribution between apatite, biotite, muscovit... more The halogen contents of granitoid rocks and their distribution between apatite, biotite, muscovite and amphibole from two different localities (German part of the Bohemian Massif and Central Aegean, Greece) are investigated in detail. Whole rock F and Cl contents and F/Cl mass ratios vary systematically with the magmatic halogenbearing mineral assemblage in which biotite and apatite are present in all rock samples: muscovite-bearing granites are F-rich (mostly 1100-2000 μg/g, but up to 3100 μg/g) and are relatively Cl-poor (50-130 μg/g). In contrast, amphibole-bearing rocks reach high Cl contents (50-900 μg/g) and are relatively F-poor (500-1400 μg/g). Only biotite-and apatite-bearing granites show intermediate F (750-1100 μg/g) and Cl (120-350 μg/g) contents. Bromine contents of all rock samples are below the detection limit of about 0.6 μg/g. In general, F and Cl are preferentially incorporated in apatite over biotite and biotite usually contains higher amounts of F and Cl than muscovite. Similarly, biotite prefers F over amphibole, but the distribution of Cl between biotite and amphibole varies between different rock samples. Bromine contents in muscovite are below the detection limit of 0.4 μg/g, but can reach up to 0.8 μg/g in biotite and up to 2.5 μg/g in apatite and amphibole. Near-solidus effects such as fluid exsolution, diffusive re-equilibration and hydrothermal overprint may change the initial halogen distribution in the rock. Importantly, significant amounts of the whole rock's F (up to 60%) and Cl (up to 90%) may be accommodated in post-magmatic alteration phases (fluorite and Na-K-Ca-bearing sheet silicates) and fluid inclusions. Therefore, great care has to be taken when interpreting halogen contents of whole rocks and the influence of post-magmatic halogen-carriers needs to be taken into account.

Halogens (F, Cl and Br) at Oldoinyo Lengai volcano (Tanzania): Effects of magmatic differentiation, silicate–natrocarbonatite melt separation and surface alteration of natrocarbonatite

Chemical Geology, 2014

ABSTRACT Halogen abundances of natrocarbonatites and their alteration products from Oldoinyo Leng... more ABSTRACT Halogen abundances of natrocarbonatites and their alteration products from Oldoinyo Lengai (Tanzania) are compared to those of associated silicate rocks and to various calcite carbonatites from eleven occurrences worldwide. Fresh natrocarbonatites are extremely enriched in F (up to 3.6 wt.%), Cl (up to 5.9 wt.%) and Br (up to 100 μg/g). During meteoric alteration, however, the major Cl- and Br-bearing minerals (mainly sylvite and gregoryite) are easily dissolved, leaving behind residual materials with relatively low Cl (≤ 1000 μg/g) and Br (≤ 15 μg/g) contents. The comparatively low Cl/Br ratios suggest preferential leaching of Cl relative to Br during alteration. At the same time, F is passively enriched as fluorite remains relatively stable during alteration. In the associated silicate rocks at Oldoinyo Lengai concentrations of all three halogens increase from primitive olivine melilitite to evolved combeite–wollastonite nephelinite, demonstrating their incompatible behavior during magmatic differentiation. Relatively constant Cl/Br ratios, but strongly decreasing F/Cl ratios, in these samples are explained by moderately incompatible behavior for F compared to pronounced and very similar incompatibilities for Cl and Br. Our data further imply that during silicate–natrocarbonatite melt separation all three halogens show a strong affinity for the natrocarbonatite. F and Cl are equally enriched in the natrocarbonatite while Cl and Br are slightly fractionated from each other with a preferential partitioning of Cl relative to Br into the natrocabonatite melt.

Chemical Geology, 2014

We use thallium (Tl) concentrations, K/Rb, K/Tl and Rb/Tl ratios and Tl isotopes in minerals from... more We use thallium (Tl) concentrations, K/Rb, K/Tl and Rb/Tl ratios and Tl isotopes in minerals from the alkaline to peralkaline Ilimaussaq complex (South Greenland) to trace magmatic differentiation, crustal assimilation, magmatic degassing, ore precipitation and hydrothermal metasomatism. Closed-system magmatic differentiation is marked by a coherent decrease of K/Tl-and K/Rb-ratios, whereas crustal assimilation results in a strong Tlenrichment, causing low K/Tl-ratios compared to K/Rb-ratios. Thallium isotopes show only slight changes during orthomagmatic differentiation and the assimilation of crustal material cannot be traced, since the isotopic composition of the average crust is within the range of the mantle and mantle-derived rocks. Magmatic degassing, however, increases Rb/Tl-ratios and changes the isotopic composition of Tl. The released fluids are enriched in Tl, characterized by high 205 Tl/ 203 Tl ratios and can precipitate Tl-rich sulfide and silicate minerals as indicated by some late-magmatic hydrothermal veins, which contain a conspicuous assemblage of Tl-Fe-Cu-sulfides (thalcusite, djerfisherite, chalcothallite). The oxidative alteration of these assemblages at high pH results in small-scale redistribution of Tl. Thallium released by this process is entrained into late-stage Tl-enriched astrophyllite.

American Mineralogist, 2010

American Mineralogist, 2012

In this work, we present an improved method for the semi-quantitative determination of sulfur spe... more In this work, we present an improved method for the semi-quantitative determination of sulfur species in S-bearing minerals by electron microprobe analysis. For calibration, we analyzed several sulfate and sulfide standard minerals such as baryte, celestine, chalcopyrite, and pyrite, and correlated the results with theoretical calculations retrieved from density functional theory (DFT). We applied this method to natural sodalite-group minerals from various localities. In addition, we applied the more common Raman spectroscopy to some samples and show that this method cannot be applied to sodalite-group minerals to determine their sulfur speciation. We show that even though sodalite-group minerals have a complex crystal structure and are sensitive to the electron beam, electron microprobe analysis is a reliable tool for the analysis of their sulfur speciation. The natural sodalite-group minerals show systematic variations in sulfur speciation. These variations can be correlated with the independently determined oxidation state of the parental magmas thus making S-bearing sodalitegroup minerals good redox proxies, although we show that the electron microprobe analysis of the sulfur speciation is matrix-dependent, and the sulfur speciation itself depends on crystal chemistry and structure, and not only on f O 2 .

American Mineralogist, 2014

The supergene alteration of cobalt arsenides produces various characteristic mineral assemblages ... more The supergene alteration of cobalt arsenides produces various characteristic mineral assemblages including erythrite, pharmacolite, and other Ca±Mg±Co-bearing arsenates, which upon precipitation remove Co and As from natural waters. Their paragenetic relationships and stability conditions have not been investigated in detail. We present a detailed study on these assemblages, their successions and coexisting fluid compositions from the mining area of Wittichen, southwest Germany, where primary skutterudite and safflorite in granite-hosted barite-calcite veins are undergoing oxidation. Water analyses from the old mines, a semi-quantitative stability diagram and quantitative reaction path modeling are used to constrain their conditions of formation. Cobalt-and arsenate-bearing solutions invariably precipitate erythrite first and hence buffer Co concentrations to very low values. Both during skutterudite or safflorite dissolution and erythrite precipitation, the fluid's Co/As ratio decreases rapidly. Therefore, spherocobaltite (Co carbonate) is unstable in the presence of arsenate ions under most conditions. The formation of various mineral assemblages precipitating after or simultaneously with erythrite strongly depends on Ca 2+ and Mg 2+ activities and pH. Small changes in one of these parameters lead to different mineral assemblages. These small changes are partly governed by fluid-host rock or fluid-vein mineral reactions and partly by the precipitation of the secondary arsenate minerals themselves. This complex interdependence produces the rich variety of mineral assemblages observed, which effectively serves as a very sensitive monitor of fluid compositions. Furthermore, the assemblages themselves are able to buffer the Ca-Mg-Co-As concentrations in the fluid to some extent and effectively immobilize both As and Co in close proximity to the ore deposit.

Bowen Lecture: Tracing Crust-Mantle Recycling With Lithium Isotopes

AGU Fall Meeting Abstracts, Dec 1, 2006

Li isotopes are thought to hold great potential for tracing crustal recycling, due to the very la... more Li isotopes are thought to hold great potential for tracing crustal recycling, due to the very large isotopic fractionations (over 700/00) documented at the Earth's surface. If highly fractionated crustal Li makes it past the subduction environment, it should be sampled by mantle rocks, provided it is not efficiently re-homogenized within the mantle by diffusion or stirring. However, data for arc lavas show that, contrary to initial expectations, Li generally does not track with other fluid-mobile elements and most arc lavas have isotopic ...

Chemical and physical evolution of the ‘lower layered sequence’ from the nepheline syenitic Ilímaussaq intrusion, South Greenland: Implications for the origin of magmatic layering in peralkaline felsic liquids

Lithos, 2008

ABSTRACT The Mid-Proterozoic composite Ilímaussaq complex, South Greenland, is a classic locality... more ABSTRACT The Mid-Proterozoic composite Ilímaussaq complex, South Greenland, is a classic locality to study magmatic layering in evolved peralkaline magmas. Most of the rock units show magmatic layering to differing extents, but ‘kakortokites’ – generally medium-grained agpaitic nepheline syenites – show a spectacular recurrence of black, red and white layers, which is due to regular changes in the modal contents of arfvedsonitic amphibole, eudialyte (sensu lato), alkali feldspar and nepheline, respectively. These three-layer units are found in the lower part of the intrusion and recur 29 times before grading into the overlying lujavrites (melanocratic agpaitic nepheline syenites), which are generally fine-grained and fissile with less-developed layering.The compositional trends observed in amphibole and eudialyte throughout the stratigraphic sequence reflect various processes including the chemical evolution of the melt by crystal fractionation, changes in the crystallising mineral assemblage and sub-solidus alteration. Eudialyte is the first mineral to crystallise in the investigated sequence and is therefore appropriate for recording evolution trends within the melt. Amphibole, on the other hand, always crystallises later and is therefore affected by other crystallising minerals. A detailed microprobe study of both minerals through the whole kakortokite stratigraphy displays surprisingly little change in mineral compositions within the kakortokites, but strong fractionation trends in the overlying lujavrites.Although various models have been proposed to explain the recurrence of the 29 rhythmic units, the origin of this prominent magmatic layering in the kakortokites and the lack of mineralogical and strong mineral chemical changes has not been quantitatively explained. We propose, that in the kakortokites, minerals were probably separated from each other as a result of their different densities. The interior cooled, resulting in crystallization but only a very small proportion of crystals (0.1–0.3% for each of the four minerals) could remain suspended in the melt before gravity forced them to settle down in a stagnant layer of reduced convection. A combination of volatile pressure variations caused by eruptive activity and repeated replenishment can explain the oscillating liquidus temperature, the small changes in mineral compositions and such a process would produce enough crystals to form the 29 layers.

Geochmica et Cosmochimica Acta