Ronald Bakker - Academia.edu (original) (raw)

Papers by Ronald Bakker

Chemical Geology, 2019

The software AqSo_NaCl (Bakker, 2018) can be used to characterize the properties of phases that m... more The software AqSo_NaCl (Bakker, 2018) can be used to characterize the properties of phases that may exist in the binary H 2 O-NaCl system up to 1000°C and 500 MPa. The model replaces all available correlation equations and other equation of state that are restricted to narrow temperature, pressure, and composition intervals. Liquidvapour, liquid-solid, and vapour-solid immiscibility fields emerge with increasing salinity at relative high temperatures, and already occur at mass fractions of a few μg per gram. The liquid-vapour immiscibility is split in two fractions in solutions between x(NaCl) = 2•10 −5 and 0.00025, at salinities that cannot be detected by microthermometry. Properties such as density, molar volume, composition, and volume fraction of liquid, vapour, and solid phases in fluid inclusions can be calculated in heating and freezing experiments. Isochores can be calculated within the homogeneous fluid field, within immiscibility fields, and along the SLV (solid-liquid-vapour) curve. Iso-T h lines are obtained by modifying the total volume of fluid inclusion with the volumetric properties of quartz. Bulk properties of fluid inclusions can be directly calculated from microthermometric data. 2. Development of the bubble-point, dew-point and sublimation curve up to microthermometry detectable salinities The phase diagram of pure water (e.g. Haar et al., 1984) is occasionally used in fluid inclusion research to characterize density, isochores and trapping conditions. Invariant points such as the triple point and the critical point, are connected with univariant lines and divariant fields in various two dimensional phase diagrams composed by the parameters temperature (T), pressure (p), molar volume (V m) (e.g. Diamond, 2003a). Immiscibility of phases such as liquid, vapour and solid, occurs at the liquid-vapour curve, liquid-solid curve, and solidvapour curve at very limited temperature-pressure conditions that do not usually occur in sediments and rock. The liquid-vapour curve combines the bubble-point curve (i.e. homogenization in to the liquid phase, LV → L) and dew-point curve (i.e. homogenization in to the vapour phase, LV → V) in a single line in a pT diagram.

npj 2D Materials and Applications

Intrinsically magnetic layered materials – especially monolayers – suffer from the lack of ambien... more Intrinsically magnetic layered materials – especially monolayers – suffer from the lack of ambient stability and mostly exhibit magnetic ordering only at cryogenic temperatures. These restrains impose a great challenge for the integration of two-dimensional magnetic materials into future technologies. We propose to overcome this by exploiting phyllosilicates, such as iron-rich talc. Via combined magnetic force microscopy in applied external magnetic fields, superconducting quantum interference device magnetometry, first-principle calculations, and structural analysis, we demonstrate that incorporated iron ions in talc are in a very robust high spin state, resulting in a weak ferromagnetic behavior at room temperature. Iron-rich talc can be thinned down to a monolayer, remaining fully stable under ambient conditions, and retaining magnetic properties even in monolayers. Finally, we propose iron-rich end members of the phyllosilicates as very promising platforms for air-stable magneti...

Computers & Geosciences, 2018

The program AqSo_NaCl has been developed to calculate pressure-molar volume-temperature-compositi... more The program AqSo_NaCl has been developed to calculate pressure-molar volume-temperature-composition (p-V-T-x) properties, enthalpy, and heat capacity of the binary H 2 O-NaCl system. The algorithms are designed in BASIC within the Xojo programming environment, and can be operated as stand-alone project with Macintosh-, Windows-, and Unix-based operating systems. A series of ten self-instructive interfaces (modules) are developed to calculate fluid inclusion properties and pore fluid properties. The modules may be used to calculate properties of pure NaCl, the halite-liquidus, the halite-vapourus, dew-point and bubble-point curves (liquid-vapour), critical point, and SLV solid-liquid-vapour curves at temperatures above 0.1 C (with halite) and below 0.1 C (with ice or hydrohalite). Isochores of homogeneous fluids and unmixed fluids in a closed system can be calculated and exported to a.txt file. Isochores calculated for fluid inclusions can be corrected according to the volumetric properties of quartz. Microthermometric data, i.e. dissolution temperatures and homogenization temperatures, can be used to calculated bulk fluid properties of fluid inclusions. Alternatively, in the absence of total homogenization temperature the volume fraction of the liquid phase in fluid inclusions can be used to obtain bulk properties.

Chemical Geology, 2016

Experiments have been performed to elucidate post-entrapment modifications of natural fluid inclu... more Experiments have been performed to elucidate post-entrapment modifications of natural fluid inclusions. Synthetic H 2 O and H 2 O-NaCl fluid inclusions in quartz were re-equilibrated at 599.7-600.7°C and 332.6-338.3 MPa in hydrothermal autoclaves, and subjected to H 2 O fugacity gradients at similar temperature and hydrostatic pressure conditions to those of the original syntheses. Individual inclusions in specific assemblages were analyzed in detail, i.e. size, shape, depth, homogenization and ice-dissolution temperatures, before and after the re-equilibration experiments. Accurate loading and unloading of the samples along isochoric T-p paths require monitoring the temperature at the sample within the autoclaves. Multiple loading and unloading of the samples along these paths do not affect the properties of fluid inclusions. Synthetic H 2 O fluid inclusions are not modified after re-equilibration in a pure H 2 O fluid, but reveal significantly higher homogenization temperatures after re-equilibration in 20 mass% NaCl solution. Synthetic NaCl-H 2 O fluid inclusions with 10, 16.3 and 19.8 mass% NaCl reveal higher salinities after re-equilibration in a pure H 2 O fluid, and highly variable homogenization temperatures: positive as well as negative modifications. The magnitude of modifications indicates that two processes must have operated simultaneously to obtain the observed homogenization and dissolution temperatures in individual inclusions: (1) preferential H 2 O loss via diffusion; and (2) total volume loss by diffusion of quartz into the former inclusion volume. These processes are inconsistent with the expected H 2 O diffusion into inclusions according to the applied fugacity gradients in the experimental setup. These simultaneously operating processes are suggested to be the main modification method of natural fluid inclusions in a variety of experimental settings and in geological environments.

Bulletin of the Geological Survey of Finland

Minerals, Sep 1, 2016

The Cedrolina chromitite body (Goiás-Brazil) is concordantly emplaced within talc-chlorite schist... more The Cedrolina chromitite body (Goiás-Brazil) is concordantly emplaced within talc-chlorite schists that correspond to the poly-metamorphic product of ultramafic rocks inserted in the Pilar de Goiás Greenstone Belt (Central Brazil). The chromite ore displays a nodular structure consisting of rounded and ellipsoidal orbs (up to 1.5 cm in size), often strongly deformed and fractured, immersed in a matrix of silicates (mainly chlorite and talc). Chromite is characterized by high Cr# (0.80-0.86), high Fe 2+ # (0.70-0.94), and low TiO 2 (av. = 0.18 wt %) consistent with variation trends of spinels from metamorphic rocks. The chromitite contains a large suite of accessory phases, but only irarsite and laurite are believed to be relicts of the original igneous assemblage, whereas most accessory minerals are thought to be related to hydrothermal fluids that emanated from a nearby felsic intrusion, metamorphism and weathering. Rutile is one of the most abundant accessory minerals described, showing an unusually high Cr 2 O 3 content (up to 39,200 ppm of Cr) and commonly forming large anhedral grains (>100 µm) that fill fractures (within chromite nodules and in the matrix) or contain micro-inclusions of chromite. Using a trace element geothermometer, the rutile crystallization temperature is estimated at 550-600 • C (at 0.4-0.6 GPa), which is in agreement with P and T conditions proposed for the regional greenschist to low amphibolite facies metamorphic peak of the area. Textural, morphological, and compositional evidence confirm that rutile did not crystallize at high temperatures simultaneously with the host chromitite, but as a secondary metamorphic mineral. Rutile may have been formed as a metamorphic overgrowth product following deformation and regional metamorphic events, filling fractures and incorporating chromite fragments. High Cr contents in rutile very likely are due to Cr remobilization from Cr-spinel during metamorphism and suggest that Ti was remobilized to form rutile. This would imply that the magmatic composition of chromite had originally higher Ti content, pointing to a stratiform origin. Another possible interpretation is that the Ti-enrichment was caused by external metasomatic fluids which lead to crystallization of rutile. If this was the case, the Cedrolina chromitites could be classified as podiform, possibly representing a sliver of tectonically dismembered Paleoproterozoic upper mantle. However, the strong metamorphic overprint that affected the studied chromitites makes it extremely difficult to establish which of the above processes were active, if not both (and to what extent), and, therefore, the chromitite's original geodynamic setting.

Journal of Geochemical Exploration, May 1, 2003

The Cantabrian Zone (CZ) in NW Spain represents the foreland belt of the Variscan Iberian Massif.... more The Cantabrian Zone (CZ) in NW Spain represents the foreland belt of the Variscan Iberian Massif. It consists of a Precambrian basement covered by Palaeozoic sediments. These underwent intense thinskinned tectonics, diagenetic to epizonal thermal events, and several episodes of fluid flow causing large-scale hydrothermal dolomitization. Aim of this research is to trace the carbonate diagenesis in the Carboniferous Barcaliente and Valdeteja Formations in the Bodón Unit, and to define type and origin of the dolomitizing fluids. Employed methods include petrography, cathodoluminescence (CL), XRD, stable isotopes and fluid inclusion (FI) microthermometry/Raman spectrometry. The dolomitizing fluid was possibly hot (100 to 150 jC), saline, Mg-rich modified seawater, operating in a burial environment. It is assumed that the dolomitization occurred during late-to post-Variscan extensional phases. Main pathways for the fluids were the Variscan thrust and fault planes, as well as stratification/lamination joints of the host limestones. One of the main tectonic lineaments, the Leon Line, played an effective role for fluid circulation, as reflected by the highest temperatures and often almost complete dolomitization close to this fault. Extensional tectonics may have promoted a gravity driven flow of fluids, which circulated deeply down, underwent heating and depletion in 18 O and dolomitized the primary carbonates.

Boletín de la Sociedad Geológica Mexicana, 2010

Forty-seven grains of platinum group minerals (PGM) associated with small chromitite bodies of th... more Forty-seven grains of platinum group minerals (PGM) associated with small chromitite bodies of the Santa Elena ultramafic Nappe (Costa Rica) were mineralogically investigated with electron microscope, electron microprobe and Raman spectroscopy. The mineralogical assemblage includes sulfides of the laurite-erlichmanite series (RuS 2-OsS 2), irarsite (IrAsS), osmium, Ir-Rh sulfides containing relevant amounts of Ni, Fe and Cu, and a Ru-AsS compound, possibly ruarsite (RuAsS). Most platinum group element (PGE) sulfides and sulfarsenides represent primary magmatic phases entrapped in chromite at high temperatures, whereas native osmium is probably formed by subsolidus exsolution. The lack of primary PGE alloys suggests relatively high S-fugacity in the chromite forming system. This investigation emphasizes the efficiency of Raman spectroscopy in the identification of PGM of extremely small size, and shows how this technique can be used in revealing distinctive compositional differences among PGM of the laurite-erlichmanite series and irarsite.

Journal of Petrology, Jun 1, 2020

High-grade metamorphic rocks underlying the intrusive layered dunite-pyroxenite-gabbronorite East... more High-grade metamorphic rocks underlying the intrusive layered dunite-pyroxenite-gabbronorite East-Khabarny Complex (EKC) are integrated in the complex Khabarny mafic-ultramafic Massif in the Sakmara Allochthon zone in the Southern Urals. These rocks are associated with hightemperature shear zones. Garnetites from the upper part of the metamorphic unit close to the contact with EKC gabbronorite are chemically and texturally analysed to estimate their formation conditions and fluid regime. Fluids provide crucial information of formation conditions and evolution of these garnetites during high-grade metamorphism, and are preserved in channel positions within Si 6 O 12À 18 rings of cordierite, and in fluid inclusions in quartz and garnet. Minerals and fluid inclusions of the garnetites are studied with X-ray fluorescence spectrometry, electron microprobe analyses, Raman spectroscopy, and microthermometry. The garnetites mainly consist of garnet (up to 80 vol. %), cordierite and quartz. Accessory minerals are rutile, ilmenite, graphite, magnetite and cristobalite. Granulite-facies metamorphic conditions of the garnetites are estimated with the garnet-cordierite-sillimanite-quartz geothermobarometer: temperatures of 740 to 830˚C and pressures of 770-845 MPa. The average garnet composition in end-member concentrations is 48Á5 mole % almandine (63Á9), 34Á7 mole % pyrope (63Á3), 10Á3 mole % spessartine (61Á1), 1Á8 mole % grossular (61Á5), and 1Á5 mole % andradite (61Á5). The cordierite electron microprobe analyses reveal an average Mg 2þ fraction of 0Á79 6 0Á01 in the octahedral site. Relicts of a strong positive temperature anomaly (up to 1000˚C) are evidenced by the preservation of cristobalite crystals in garnet and the high titanium content of quartz (0Á031 6 0Á008 mass % TiO 2) and garnet (0Á31 6 0Á16 mole % endmember Schorlomite-Al). The fluid components H 2 O, CO 2 , N 2 and H 2 S are detected in cordierite, which correspond to a relatively oxidized fluid environment that is common in granulites. In contrast, a highly reduced fluid environment is preserved in fluid inclusions in quartz nodules, which are mono-fluid phase at room temperature and composed of CH 4 (>96 mole %) with locally minor amounts of C 2 H 6 , N 2 , H 2 S and graphite. The fluid inclusions occur in homogeneous assemblages with a density of 0Á349 to 0Á367 gÁcm-3. The CH 4-rich fluid may represent peak-temperature metamorphic conditions, and is consistent with temperature estimation ($1000˚C) from Ti-in-garnet and Ti-in-quartz geothermometry. Tiny CH 4-rich fluid inclusions (diameter 0Á5 to 2 mm) are also detected by careful optical analyses in garnet and at the surface of quartz crystals that are included in garnet grains. Graphite in fluid inclusions precipitated at retrograde metamorphic conditions around 300-310 6 27˚C. Aragonite was trapped simultaneously with CH 4-rich fluids and is assumed to have crystallized at metastable conditions. The initial granulite facies conditions that led to the formation of a cordierite and garnet mineral assemblage must have occurred in a relative