Papers by Michael Marks Marks
Geochmica et Cosmochimica Acta
cspg.org
Summary We present details of a field-based study on the evolution of alkaline to peralkaline roc... more Summary We present details of a field-based study on the evolution of alkaline to peralkaline rocks from the Mont Saint-Hiliaire complex, Quebec, Canada. The progressive magmatic evolution of the complex is represented by three melt batches:(1) primitive ...
Neues Jahrbuch für Mineralogie - Abhandlungen, 2010
ABSTRACT Eudialyte-group minerals (EGM) are typical constituents of agpaitic varieties of peralka... more ABSTRACT Eudialyte-group minerals (EGM) are typical constituents of agpaitic varieties of peralkaline rocks. In their complex structure (N15-16M(1)6M(2)3Z3M(3)M(4)Si24O66-73(OH)0-9X2), many cations (e.g. Na+, Ca2+, Fe2+, Mn2+, REE3+, Zr4+, and Si4+) as well as different hydrogen-bearing species (H2O, OH-, H3O+) may occupy different structural sites. Also, two potentially vacancy bearing positions are present. Thus, various methods of calculation of mineral formulae for EGM in the literature are inconsistent and in some cases not charge-balanced. We present an extended and improved scheme for site assignment using IMA-approved end-members and taking into account the different structural units of EGM. This method is based on electron microprobe analyses alone not considering different valence states of Fe and Mn and undetermined H2O-contents. However, comparison with structural refinement data from the literature reveals major agreement and significant improvement compared to earlier proposed methods. The instruction given here can easily be transferred to a table calculation spread sheet (e.g. EXCEL©), which is available from the corresponding author on request.
Journal of Petrology, 2010
American Mineralogist, 2014
More than 150 samples of pyromorphite, mimetite, vanadinite, and minerals of the hedyphane-group ... more More than 150 samples of pyromorphite, mimetite, vanadinite, and minerals of the hedyphane-group (which collectively are summarized here under the term PyGM for pyromorphite-group minerals) from the Schwarzwald mining district, southwest Germany, have been analyzed by electron microprobe and compositions and the amount of solid solution between the various end-members were investigated. In addition, we report the colors of the many analyzed mineral compositions. Here is a list of the most important results. appears to asymmetrical with up to about 3 mol% of vanadinite component in pyromorphite and up to constrained, but we report vanadinite analyses with up to 12 mol% mimetite and 8 mol% pyromorphite component. and hedyphane. mimetites, and vanadinites are Cl-or OH-dominated. ing to mimetite. metals like REE, Cr, Sb, Bi, or U up to a factor of 10 6 in the primary ore deposit very reliably. of the REE during PyGM growth. In the absence of conclusive data, the former possibility appears the more likely one. ity of ore deposits.
Eur J Mineral, 2001
The layered peralkaline igenous Ilimaussaq complex (Gardar failed-rift province in southwest Gree... more The layered peralkaline igenous Ilimaussaq complex (Gardar failed-rift province in southwest Greenland) has attracted exploration activities in past and present. The intrusion was emplaced in three magmatic phases, evolving in an essentially closed-system. The composition of the rocks covers a broad range of alkaline rocks, ranging from alkaline to peralkaline granites and syenites to highly evolved nepheline syenites. The latest magmatic rocks are among the most differentiated, known on earth [1]. During late-stage magmatic ...
Chemical Geology, 2007
Li contents [Li] and isotopic composition (δ 7 Li) of mafic minerals (mainly amphibole and clinop... more Li contents [Li] and isotopic composition (δ 7 Li) of mafic minerals (mainly amphibole and clinopyroxene) from the alkaline to peralkaline Ilímaussaq plutonic complex, South Greenland, track the behavior of Li and its isotopes during magmatic differentiation and final cooling of an alkaline igneous system. [Li] in amphibole increase from b 10 ppm in Caamphiboles of the least differentiated unit to N 3000 ppm in Na-amphiboles of the highly evolved units. In contrast, [Li] in clinopyroxene are comparatively low (b 85 ppm) and do not vary systematically with differentiation. The distribution of Li between amphibole and pyroxene is controlled by the major element composition of the minerals (Ca-rich and Na-rich, respectively) and changes in oxygen fugacity (due to Li incorporation via coupled substitution with ferric iron) during magmatic differentiation. δ 7 Li values of all minerals span a wide range from +17 to -8‰, with the different intrusive units of the complex having distinct Li isotopic systematics. Amphiboles, which dominate the Li budget of whole-rocks from the inner part of the complex, have constant δ 7 Li of + 1.8 ± 2.2‰ (2σ, n = 15). This value reflects a homogeneous melt reservoir and is consistent with their mantle derivation, in agreement with published O and Nd isotopic data. Clinopyroxenes of these samples are consistently lighter, with Δ 7 Li amph-cpx as large as 8‰ and are thus not in Li isotope equilibrium. These low values probably reflect late-stage diffusion of Li into clinopyroxene during final cooling of the rocks, thus enriching the clinopyroxene in 6 Li. At the margin of the complex δ 7 Li in the syenites increases systematically, from + 2 to high values of + 14‰. This, coupled with the observed Li isotope systematics of the granitic country rocks, reflects post-magmatic open-system processes occurring during final cooling of the intrusion. Although the shape and magnitude of the Li isotope and elemental profiles through syenite and country rock are suggestive of diffusion-driven isotope fractionation, they cannot be modeled by one-dimensional diffusive transport and point to circulation of a fluid having a high δ 7 Li value (possibly seawater) along the chilled contact. In all, this study
Lithos, 2004
The mid-Proterozoic Isortoq dike swarm in the Gardar Province, South Greenland, comprises a varie... more The mid-Proterozoic Isortoq dike swarm in the Gardar Province, South Greenland, comprises a variety of alkaline rocks ranging from gabbroic to syenitic in composition. Major magmatic mineral phases are olivine, clinopyroxene, Fe -Ti oxides, amphibole, plagioclase and alkali feldspar. Quartz occurs in some samples as a late magmatic phase. Liquidus temperatures of olivine-bearing samples range between 1120 and 1145 jC and solidus temperatures are 850 -930 jC. Calculated silica activities are highly variable between 0.53 and unity. Oxygen fugacities vary from À 3 to + 1 log units relative to the fayalite -magnetite -quartz buffer.
Lithos, 2012
ABSTRACT Sadiman volcano is located in the Crater Highlands area of northern Tanzania, which lies... more ABSTRACT Sadiman volcano is located in the Crater Highlands area of northern Tanzania, which lies next to the western escarpment of the Gregory rift—a part of the eastern branch of the East African Rift system. It consists of inter-layered phonolitic tuffs, tuff breccias (with blocks of nephelinites) and nephelinitic lava flows. Rare xenoliths of phonolite lava and ijolite were observed within the nephelinite lavas with ijolite blocks occurring in pho-nolitic tuffs. No evidence for the presence of melilite-bearing and/or carbonatitic rocks was found during this study. On the basis of petrography, mineralogy and geochemistry the nephelinites are divided into highly porphyritic nephelinite, wollastonite nephelinite and phonolitic nephelinite, the latter of which is the dominant variety at Sadiman. Nepheline + clinopyroxene + titanite ± perovskite ± andradite–schorlomite ± wollastonite ± sanidine ± sodalite are the principle pheno-and microphenocryst phases. The nephelinites are highly evolved (Mg# = 0.17–0.26) alkaline to peralkaline (AI = 0.88–1.21) rocks enriched in incompati-ble elements such as Rb, Ba, Th, U, Nb, Pb, Ta, Sr and light REEs, and strongly depleted in P and Ti. This sug-gests derivation from an enriched mantle source and fractionation of apatite and Ti-rich mineral(s). Primary melt inclusions in nepheline phenocrysts (T homogenization = 860–1100 °C) indicate enrichment of volatile components in the melts, particularly of fluorine (up to 1.8 wt.% in silicate glass) resulting in the formation of daughter fluorite in partly and complete crystallized inclusions. The Sadiman nephelinites crystallized under relatively oxidizing conditions (above the FMQ buffer), which differ from the reducing conditions reported for trachytic and pantelleritic rocks from other parts of the Gregory rift. Similar rock types and rel-atively oxidizing conditions are known from Oldoinyo Lengai and other localities, all of which are closely associated with carbonatites. By analogy, we conclude that andradite–schorlomite-rich nephelinites may in-dicate a pre-stage on the evolutionary path towards carbonatitic magmatism.
Chemical Geology, 2014
Keywords: Natrocarbonatite Halogen fractionation Bromine TXRF Oldoinyo Lengai Leaching Halogen ab... more Keywords: Natrocarbonatite Halogen fractionation Bromine TXRF Oldoinyo Lengai Leaching 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.
Journal of Petrology, 2008
The EoceneTamazeght complex, High Atlas Mountains, Morocco is a multiphase alkaline to peralkalin... more The EoceneTamazeght complex, High Atlas Mountains, Morocco is a multiphase alkaline to peralkaline intrusive complex. A large variety of rock types (including pyroxenites, glimmerites, gabbroic to monzonitic rocks, feldspathoidal syenites, carbonatites and various dyke rocks) documents a progression from ultramafic to felsic magmatism. This study focuses on the silicate plutonic members and the genetic relationships between the various lithologies. Based on detailed petrographic and mineral chemical data we show that the various units crystallized under markedly different oxygen fugacity and silica activity conditions and demonstrate how these parameters influence both the phase assemblage and the detailed chemical evolution of the fractionating phases. Nepheline, olivine^clinopyroxene and hornblende^plagioclase thermometry indicate equilibration temperatures !8008C for all major rock types. Highly oxidized conditions (close to the hematite^magnetite buffer) are characteristic of the garnet-rich pyroxenites, ultrapotassic glimmerites and associated olivine-shonkinites. The parental magmas to these rocks evolved from low initial a SiO2 values of 0Á1 to values of 0Á5^0Á8 during nepheline and alkali feldspar saturation. In contrast, the monzonitic rocks evolved from initially high a SiO2 values (up to 0Á75) down to about 0Á1 at intermediate values of oxygen fugacity (ÁFMQ ¼ þ2^5 to À1, where FMQ is the fayalite^magnetiteq uartz buffer). For nepheline syenites and malignites, more reduced conditions (ÁFMQ ¼ À2) and intermediate a SiO2 values (between 0Á25 and 0Á5) dominate. We conclude that fractional crystallization is not a likely mechanism to explain the large variety of lithologies present in theTamazeght complex. It is more probable that successive melting of a compositionally heterogeneous mantle source region gave rise to several melt batches with distinct chemical and physicochemical characteristics. Low-degree melts from a K-phase-bearing mantle domain resulted in the formation of ultrapotassic glimmerites, whereas garnet-rich pyroxenites and olivine-shonkinites may have originated from hybrid melts and partly from a pyroxene-dominated source. Less alkaline lithologies such as monzonites potentially reflect larger degrees of melting and the increased importance of a basaltic component, whereas nepheline syenites and malignites may be explained by lower degrees of melting and a more alkaline character for the parental melt of these rocks.
Chemical Geology, 2012
Keywords: Apatite Halogens Bromine SIMS TXRF Apatite is ubiquitous in a wide range of magmatic ro... more Keywords: Apatite Halogens Bromine SIMS TXRF Apatite is ubiquitous in a wide range of magmatic rocks and its F-Cl-Br-S systematics can be used to decipher e.g., mixing processes within a magmatic complex and may give insights into fluid un-mixing and degassing processes during the emplacement and cooling of plutonic rocks. In this study, we analyzed a F-apatite (Durango, Mexico), a Cl-apatite (Ødegården, Norway) and apatites from five plutonic samples from the alkaline Mt. Saint Hilaire Complex (Canada) by means of Electron Microprobe Analysis (EPMA), Laser Ablation ICP-MS (LA-ICP-MS), Secondary Ion Mass Spectrometry (SIMS), pyrohydrolysis combined with ion chromatography, Fourier Transformed Infrared Spectroscopy (FTIR), Instrumental Neutron Activation Analysis (INAA) and Total Reflection X-ray Fluorescence Analysis (TXRF). The special focus of our study is Br, since the analytical possibilities for this element are especially in the lowto sub-μg/g range restricted and thus, reliable concentration data for Br in rock-forming minerals are scarce. We demonstrate here that TXRF, which is barely used in geosciences so far, is suitable for analyzing the bulk content of Br and Cl as well as of a range of important trace metals (e.g., Sr, Ce, Fe, Mn, As) in apatite simultaneously. The TXRF method combines the advantages of low to very low detection limits (μg/g-to sub-μg/g range), small sample amounts needed (mg range) and a relatively fast and inexpensive analytical procedure. Depending on the As content of apatite, reliable concentration data for Br can be produced with detection limits as low as 0.2 μg/g. Using the Durango apatite as an internal reference material, SIMS analyses give consistent results with EPMA, INAA and TXRF and allow for detailed insights into the F-Cl-Br-S systematics of apatites. The presented data set reveals significant heterogeneities within and between different apatite grains from a single sample.
The Cretaceous Mont Saint-Hilaire complex (Quebec, Canada) comprises three major rock units that ... more The Cretaceous Mont Saint-Hilaire complex (Quebec, Canada) comprises three major rock units that were emplaced in the following sequence: (I) gabbros; (II) diorites; (III) diverse partly agpaitic foid syenites. The major element compositions of the rock-forming minerals, age-corrected Nd and oxygen isotope data for mineral separates and trace element data of Fe^Mg silicates from the various lithologies imply a common source for all units. The distribution of the rare earth elements in clinopyroxene from the gabbros indicates an ocean island basalt type composition for the parental magma. Gabbros record temperatures of 1200 to 8008C, variable silica activities between 0·7 and 0·3, and f O2 values between À0·5 and þ0·7 (log ÁFMQ, where FMQ is fayalite^magnetite^quartz).The diorites crystallized under uniform a SiO2 (a SiO2 ¼ 0·4^0·5) and more reduced f O2 conditions (log ÁFMQ $ À1) between $1100 and $8008C. Phase equilibria in various foid syenites indicate that silica activities decrease from 0·6^0·3 at $10008C to 50·3 at $5508C. Release of an aqueous fluid during the transition to the hydrothermal stage caused a SiO2 to drop to very low values, which results from reduced SiO 2 solubilities in aqueous fluids compared with silicate melts. During the hydrothermal stage, high water activities stabilized zeolite-group minerals. Fluid inclusions record a complex post-magmatic history, which includes trapping of an aqueous fluid that unmixed from the restitic foid syenitic magma. Cogenetic aqueous and carbonic fluid inclusions reflect heterogeneous trapping of coexisting immiscible external fluids in the latest evolutionary stage. The O and C isotope characteristics of fluid-inclusion hosted CO 2 and late-stage carbonates imply that the surrounding limestones were the source of the external fluids. The mineral-rich syenitic rocks at Mont Saint-Hilaire evolved as follows: first, alkalis, high field strength and large ion lithophile elements were pre-enriched in the (late) magmatic and subsequent hydrothermal stages; second, percolation of external fluids in equilibrium with the carbonate host-rocks and mixing processes with internal fluids as well as fluid^rock interaction governed dissolution of pre-existing
Eudialyte-group minerals (EGM) are typical constituents of agpaitic varieties of peralkaline rock... more Eudialyte-group minerals (EGM) are typical constituents of agpaitic varieties of peralkaline rocks. In their complex structure (N 15-16 M(1) 6 M(2) 3 Z 3 M(3)M(4)Si 24 O 66-73 (OH) 0-9 X 2 ), many cations (e.g. Na + , Ca 2+ , Fe 2+ , Mn 2+ , REE 3+ , Zr 4+ , and Si 4+ ) as well as different hydrogen-bearing species (H 2 O, OH -, H 3 O + ) may occupy different structural sites. Also, two potentially vacancy bearing positions are present. Thus, various methods of calculation of mineral formulae for EGM in the literature are inconsistent and in some cases not charge-balanced.
Silicate-oxide equilibria (abbreviated as QUIlF) have proven to be very powerful tools for recons... more Silicate-oxide equilibria (abbreviated as QUIlF) have proven to be very powerful tools for reconstructing the temperature and oxygen fugacity evolution of magmatic systems containing magnetite and ilmenite with olivine, quartz, or pyroxenes. In this paper, we extend these QUIlF equilibria to include rocks where silica activity is controlled by equilibria between feldspars and feldspathoids.
We experimentally investigated the phase relations of a peralkaline phonolitic dyke rock associat... more We experimentally investigated the phase relations of a peralkaline phonolitic dyke rock associated with the Ilímaussaq plutonic complex (South Greenland). The extremely evolved and iron-rich composition (magnesium number = 2, alkalinity index = 1.44, FeO* = 12 wt%) may represent the parental magma of the Ilímaussaq complex. This dyke rock is therefore perfectly suited for performing phase-equilibrium experiments, since in contrast to the plutonic rocks of the complex, no major cumulate formation processes complicate defining a reasonable starting composition. Experiments were carried out in hydrothermal rapid-quench cold-seal pressure vessels at P = 100 MPa and T = 950-750°C. H 2 O contents ranging from anhydrous to H 2 O saturated (*5 wt% H 2 O) and varying fO 2 (*DlogFMQ -3 to ?1; where FMQ represents the fayalite-magnetite-quartz oxygen buffer) were applied. Reduced and dry conditions lead to substantial crystallization of alkali feldspar, nepheline, hedenbergite-rich clinopyroxene, fayalite-rich olivine and minor amounts of ulvøspinel-rich magnetite, which represent the phenocryst assemblage of the natural dyke rock. Oxidized and H 2 O-rich conditions, however, suppress the crystallization of olivine in favor of magnetite and clinopyroxene with less or no alkali feldspar and nepheline formation. Accordingly, combined low fO 2 and aH 2 O force the evolution of the residual melt toward decreasing SiO 2 , increasing FeO* and alkalinity index (up to 3.55). On the contrary, high fO 2 and aH 2 O produce residual melts with relatively low FeO*, high SiO 2 and a relatively constant alkalinity index. We show that variations of aH 2 O and fO 2 lead to contrasting trends regarding the liquid lines of descent of iron-rich silicaundersaturated peralkaline compositions. Moreover, the increase in FeO* and alkalinity index (reduced and dry conditions) in the residual melt is an important prerequisite to stabilize late-magmatic minerals of the dyke rock, for example, aenigmatite (Na 2 Fe 5 TiSi 6 O 20 ), coexisting with the most evolved melts at 750°C. Contrary to what might be expected, experiments with high aH 2 O and interlinked high fO 2 exhibit higher liquidus T's compared with experiments performed at low aH 2 O and fO 2 for experiments where magnetite is liquidus phase. This is because ulvøspinel-poor magnetite crystallizes at higher fO 2 and has a higher melting point than ulvøspinel-rich magnetite, which is favored at lower fO 2 .
Journal of Petrology, 2003
The Puklen complex of the Mid-Proterozoic Gardar Province, South Greenland, consists of various s... more The Puklen complex of the Mid-Proterozoic Gardar Province, South Greenland, consists of various silica-saturated to quartzbearing syenites, which are intruded by a peralkaline granite. The primary mafic minerals in the syenites are augite AE olivine Fe±Ti oxide amphibole. Ternary feldspar thermometry and phase equilibria among mafic silicates yield T 950±750 C, a SiO 2 0Á7À1 and an f O 2 of 1±3 log units below the fayalite± magnetite±quartz (FMQ) buffer at 1 kbar. In the granites, the primary mafic minerals are ilmenite and Libearing arfvedsonite, which crystallized at temperatures below 750 C and at f O 2 values around the FMQ buffer. In both rock types, a secondary post-magmatic assemblage overprints the primary magmatic phases. In syenites, primary Ca-bearing minerals are replaced by Na-rich minerals such as aegirine± augite and albite, resulting in the release of Ca. Accordingly, secondary minerals include ferro-actinolite, (calcite±siderite) ss , titanite and andradite in equilibrium with the Na-rich minerals. Phase equilibria indicate that formation of these minerals took place over a long temperature interval from near-magmatic temperatures down to $300 C. In the course of this cooling, oxygen fugacity rose in most samples. For example, late-stage aegirine in granites formed at the expense of arfvedsonite at temperatures below 300 C and at an oxygen fugacity above the haematite±magnetite (HM) buffer. The calculated d 18 O melt value for the syenites (5Á9 to 6Á3 %) implies a mantle origin, whereas the inferred d 18 O melt value of 55Á1% for the granitic melts is significantly lower. Thus, the granites require an additional low-d 18 O contaminant, which was not involved in the genesis of the syenites. Rb/Sr data for minerals of both rock types indicate open-system behaviour for Rb and Sr during post-magmatic metasomatism. Neodymium isotope compositions (eNd 1170 Ma À3Á8 to À6Á4) of primary minerals in syenites are highly variable, and suggest that assimilation of crustal rocks occurred to variable extents. Homogeneous e Nd values of À5Á9 and À6Á0 for magmatic amphibole in the granites lie within the range of the syenites. Because of the very similar neodymium isotopic compositions of magmatic and late-to post-magmatic minerals from the same syenite samples a principally closed-system behaviour during cooling is implied. In contrast, for the granites an externally derived fluid phase is required to explain the extremely low e Nd values of about À10 and low d 18 O between 2Á0 and 0Á5 % for late-stage aegirine, indicating an open system in the late-stage history. In this study we show that the combination of phase equilibria constraints with stable and radiogenic isotope data on mineral separates can provide much better constraints on magma evolution during emplacement and crystallization than conventional whole-rock studies.
Lithos, 2012
ABSTRACT Sadiman volcano is located in the Crater Highlands area of northern Tanzania, which lies... more ABSTRACT Sadiman volcano is located in the Crater Highlands area of northern Tanzania, which lies next to the western escarpment of the Gregory rift—a part of the eastern branch of the East African Rift system. It consists of inter-layered phonolitic tuffs, tuff breccias (with blocks of nephelinites) and nephelinitic lava flows. Rare xenoliths of phonolite lava and ijolite were observed within the nephelinite lavas with ijolite blocks occurring in pho-nolitic tuffs. No evidence for the presence of melilite-bearing and/or carbonatitic rocks was found during this study. On the basis of petrography, mineralogy and geochemistry the nephelinites are divided into highly porphyritic nephelinite, wollastonite nephelinite and phonolitic nephelinite, the latter of which is the dominant variety at Sadiman. Nepheline + clinopyroxene + titanite ± perovskite ± andradite–schorlomite ± wollastonite ± sanidine ± sodalite are the principle pheno-and microphenocryst phases. The nephelinites are highly evolved (Mg# = 0.17–0.26) alkaline to peralkaline (AI = 0.88–1.21) rocks enriched in incompati-ble elements such as Rb, Ba, Th, U, Nb, Pb, Ta, Sr and light REEs, and strongly depleted in P and Ti. This sug-gests derivation from an enriched mantle source and fractionation of apatite and Ti-rich mineral(s). Primary melt inclusions in nepheline phenocrysts (T homogenization = 860–1100 °C) indicate enrichment of volatile components in the melts, particularly of fluorine (up to 1.8 wt.% in silicate glass) resulting in the formation of daughter fluorite in partly and complete crystallized inclusions. The Sadiman nephelinites crystallized under relatively oxidizing conditions (above the FMQ buffer), which differ from the reducing conditions reported for trachytic and pantelleritic rocks from other parts of the Gregory rift. Similar rock types and rel-atively oxidizing conditions are known from Oldoinyo Lengai and other localities, all of which are closely associated with carbonatites. By analogy, we conclude that andradite–schorlomite-rich nephelinites may in-dicate a pre-stage on the evolutionary path towards carbonatitic magmatism.
Chemical Geology
Apatite is ubiquitous in a wide range of magmatic rocks and its F–Cl–Br–S systematics can be used... more Apatite is ubiquitous in a wide range of magmatic rocks and its F–Cl–Br–S systematics can be used to decipher e.g., mixing processes within a magmatic complex and may give insights into fluid un-mixing and degassing processes during the emplacement and cooling of plutonic rocks.In this study, we analyzed a F-apatite (Durango, Mexico), a Cl-apatite (Ødegården, Norway) and apatites from five plutonic samples from the alkaline Mt. Saint Hilaire Complex (Canada) by means of Electron Microprobe Analysis (EPMA), Laser Ablation ICP-MS (LA-ICP-MS), Secondary Ion Mass Spectrometry (SIMS), pyrohydrolysis combined with ion chromatography, Fourier Transformed Infrared Spectroscopy (FTIR), Instrumental Neutron Activation Analysis (INAA) and Total Reflection X-ray Fluorescence Analysis (TXRF).The special focus of our study is Br, since the analytical possibilities for this element are especially in the low- to sub-μg/g range restricted and thus, reliable concentration data for Br in rock-forming minerals are scarce. We demonstrate here that TXRF, which is barely used in geosciences so far, is suitable for analyzing the bulk content of Br and Cl as well as of a range of important trace metals (e.g., Sr, Ce, Fe, Mn, As) in apatite simultaneously. The TXRF method combines the advantages of low to very low detection limits (μg/g- to sub-μg/g range), small sample amounts needed (mg range) and a relatively fast and inexpensive analytical procedure. Depending on the As content of apatite, reliable concentration data for Br can be produced with detection limits as low as 0.2 μg/g.Using the Durango apatite as an internal reference material, SIMS analyses give consistent results with EPMA, INAA and TXRF and allow for detailed insights into the F–Cl–Br–S systematics of apatites. The presented data set reveals significant heterogeneities within and between different apatite grains from a single sample.► Br concentrations for magmatic minerals are scarce. ► TXRF can be used to analyze the bulk Br content in apatite. ► A Br concentration of around 0.1 μg/g for the Durango apatite is proposed.
Lithos, 2004
The mid-Proterozoic Isortoq dike swarm in the Gardar Province, South Greenland, comprises a varie... more The mid-Proterozoic Isortoq dike swarm in the Gardar Province, South Greenland, comprises a variety of alkaline rocks ranging from gabbroic to syenitic in composition. Major magmatic mineral phases are olivine, clinopyroxene, Fe -Ti oxides, amphibole, plagioclase and alkali feldspar. Quartz occurs in some samples as a late magmatic phase. Liquidus temperatures of olivine-bearing samples range between 1120 and 1145 jC and solidus temperatures are 850 -930 jC. Calculated silica activities are highly variable between 0.53 and unity. Oxygen fugacities vary from À 3 to + 1 log units relative to the fayalite -magnetite -quartz buffer.
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Papers by Michael Marks Marks