Maciej Manecki

Kinetics of aqueous pb reaction with apatites

Apatite has been used to remediate Pb contamination; apatite dissolution releases phosphate, which combines with Pb to form highly insoluble Pb-phosphate minerals. This research focused on the effects of aqueous Pb (initial [Pb a ] = 0.185 mM) on the kinetics of apatite dissolution. Synthetic microcrystalline hydroxylapatite (HAP) and natural chlorapatite (CAP) and fluorapatite (FAP) were used in batch experiments at 22°C, with pH within the range of 4.2-7.0, and in the presence of aqueous Cl. In these batch experiments, apatites followed linear (zeroth-order) dissolution kinetics. Dissolution experiments were performed using 1 g apatite/L for all three apatites. When dissolution rate constants (k AP ) are adjusted for particle specific surface area (A s ), k CAP > k FAP > k HAP . In the presence of Pb aq and Cl, all three apatites reacted to form pyromorphite (PY; Pb 10 (PO 4 ) 6 Cl 2 ). Rates of Pb a uptake by the apatites decreased in the same order as the apparent (not normalized for A s ) dissolution rate constants of apatite (k Ap ○): HAP > CAP > FAP, suggesting that Pb aq uptake is controlled by the total amount of dissolved phosphate in the system. While HAP and CAP removed more than 98% of Pb aq during 2 weeks of the experiment, FAP decreased the initial [Pb aq ] by ∼30%. Pb uptake rates calculated on a molar basis correlated with Ca release rates. Concentration of dissolved phosphate during the reaction with Pb aq was below the detection limit of 10 -7 mol/L. Phosphate concentration was probably controlled by solute equilibrium with precipitating PY, which has very low solubility (log K sp = -167). This indicates that the rate-controlling step was apatite dissolution. The presence of Pb aq increased apatite batch dissolution rates, most probably because formation of PY acted as a sink for dissolved phosphate, hence increasing the thermodynamic drive for dissolution. Although PY formed heterogeneously on the surfaces of apatite particles, the PY did not prevent continued apatite dissolution.

Thermochronology of the west Sudetes (Bohemian Massif): Rapid and repeated eduction in the eastern Variscides, Poland and Czech Republic

The Sudete Mountains of northeastern Bohemian Massif were amalgamated during the closure of the Rheic ocean, culminating with Variscan orogenesis, and contain occurrences of high-pressure granulite and small relict ultrahigh-pressure eclogite formed during subduction. We performed 40Ar/39Ar thermochronometry on primarily amphibolite-facies gneisses and schists from two crustal blocks within the Sudetes: Góry Sowie and Orlica-Snieznik massifs. Hornblende and mica plateau ages from the mountainous portion of the Góry Sowie reflect relatively rapid cooling between 382 ± 1 Ma and 373 ± 0.5 Ma, following peak conditions at ca. 400 Ma. Kyanite-sillimanite and cordierite-garnet mineral growth textures denote near isothermal decompression during eduction. Concordant hornblende and biotite cooling ages obtained from the eastern, topographically flat region adjacent to the Niemcza shear zone indicate markedly younger cooling at 337 ± 0.8 Ma. 40Ar/39Ar results from the Snieznik Mountains, 50 km to the south, yield plateau cooling ages for white mica and biotite between 341 ± 1 to 337 ± 0.6 Ma and 342 ± 1 to 334 ± 0.6 Ma, respectively, and are remarkably similar in age to an amphibolite-facies overprinting episode. Mica analyses from the Orlica Mountains also yield cooling ages between 338 ± 0.9 to 335 ± 0.5 Ma. Thermochronometry illustrates temporally disparate cooling histories but similar metamorphic evolutions between the Góry Sowie Block and the Orlica-Snieznik Complex. In both terranes, it took ∼35 m.y. from the time of peak high-pressure conditions to residence in the upper crust, and possibly as little as 10 m.y. between high-pressure and mid-crustal supra-Barrovian events. These results in light of regional geochronology illustrate the rapid, localized and repetitious nature of eduction/exhumation of the Sudetic orogenic root including the eclogite and HP-granulite assemblages during protracted subduction.

Uptake of aqueous Pb by Cl-, F–, and OH– apatites: Mineralogic evidence for nucleation mechanisms

Abstract Apatites provide a mechanism for in-situ remediation of Pb-contaminated sites, by supplying phosphate which combines with dissolved Pb to form highly insoluble pyromorphite. This study expanded upon previous research using hydroxylapatite (HAP), to focus on how the surface properties of natural chlorapatite (CAP) and fluorapatite (FAP) affect pyromorphite nucleation and growth, when aqueous Pb2+ ([Pb] < 50 mg/L as PbCl2) is reacted with apatite at pH = 4.2, 22 °C. A combination of atomic force microscopy (AFM), scanning electron microscopy (SEM), optical microscopy, energy dispersive X-ray fluorescence spectroscopy (EDS), infrared spectroscopy (FTIR), and X-ray diffraction (XRD) was used for in-situ and ex-situ examination of the interface and the reaction products. A variety of experiments were performed, and pyromorphite [PY = Pb10(PO4)6Cl2] was the only identified reaction product. PY nucleated both homogeneously (directly from solution) and heterogeneously on CAP and FAP; relationship between PY and HAP could not be determined definitively. The nucleation mechanism was sensitive to initial experimental conditions, which suggests that care should be taken to consider initial conditions in designing sorption and nucleation experiments. Heterogenous nucleation on FAP and CAP showed strong evidence for epitaxy. Epitaxial crystals of PY on CAP and FAP grew away from the substrate surface, which was the only source of phosphate available for crystal growth. Epitaxial crystals showed distinctly different morphologies from homogeneously nucleated crystals, and appeared to grow by a spiral growth mechanism.

Exhumation and metamorphism of an ultrahigh-grade terrane: geochronometric investigations of the Sudete Mountains (Bohemia), Poland and Czech Republic

The Sudete Mountains, NE Bohemian Massif (Czech Republic and Poland), preserve abundant eclogitic and granulitic centimetre- to decimetre-scale boudins enveloped in a predominantly migmatitic matrix. Published geochronometry and thermobarometry from the UHP and UHT rocks broadly constrain the crystallization and initial stage 1 exhumation history for these units; however, the timing of stage 2 metamorphism and associated unroofing is less well constrained. New in situ ion microprobe Th–Pb monazite results, together with complementary U–Pb zircon and electron microprobe analyser total-Pb monazite results, on 11 amphibolite-facies gneissic to migmatitic samples, place important temporal constraints on the second stage of UHP and UHT metamorphism–exhumation. The Orlica–Snieznik Dome records UHP metamorphism occurring at 375 Ma and subsequent exhumation to midcrustal levels in supra-Barrovian conditions at c. 345–330 Ma. In contrast, the western Góry Sowie Block preserves evidence of HP-granulite conditions at c. 400 Ma, and exhumation to mid-crustal levels at 380–370 Ma, revealing a c. 30 million years difference in exhumation events between the neighbouring terranes. The eastern Góry Sowie Block preserves ages similar to the Orlica–Sneiznik Dome, suggesting that different preserved metamorphic–cooling histories are juxtaposed across the Sudetic Marginal fault. The bounding Niemcza shear zone yields preliminary Th–Pb dates that range from 380 ± 8 Ma to 283 ± 2 Ma, preserving a protracted metamorphic record that spans the exhumation history of the region. The distinct collapsed geochronologies of both terranes probably reflect rapid vertical transport of low-viscosity crust under supra-Barrovian conditions near the mid-crustal high-strength lid during oblique (transpressional) convergence.

Late Neoproterozoic amphibolite-facies metamorphism of a pre-Caledonian basement block in southwest Wedel Jarlsberg Land, Spitsbergen: new evidence from U-Th-Pb dating of monazite

Abstract – Southwest Spitsbergen, Wedel Jarlsberg Land, consists of two Proterozoic crustalblocks with differing metamorphic histories. Both blocks experienced Caledonian greenschist-faciesmetamorphism, but only the southern block records an earlier pervasive M1 amphibolite-faciesmetamorphism and strong deformational fabri c. In situ EMPA total-Pb monazite geochronologyfrom both matrix and porphyroblast inclusion results indicate that the older M1 metamorphismoccurred at 643 ±9 Ma, consistent with published cooling ages of c . 620 Ma (hornblende) and580 Ma (mica) obtained from these same rocks. This region thus contains a lithostratigraphic profileand metamorphic history which are unique within the Svalbard Archipelago. Documentation of apervasive late Neoproterozoic Barrovian metamorphism is difficult to reconcile with a quiescent non-tectonic regime typically inferred for this region, based on the occurrence of rift-drift sequences onthe Baltic and Laurentian passive margins. Instead, our new metamorphic age implies an exotic originof the pre-Devonian basement exposed in SW Spitsbergen and supports models of terrane assemblypostulated for the Svalbard Archipelago.Keywords: Svalbard, Caledonides, terranes, geochronology, tectonics.

A strike-slip terrane boundary in Wedel Jarlsberg Land, Svalbard, and its bearing on correlations of SW Spitsbergen with the Pearya terrane and Timanide belt

Abstract: Southwest Spitsbergen, Wedel Jarlsberg Land, consists of two Proterozoic terranes with differing structural and metamorphic histories. The northern terrane experienced two Early Palaeozoic deformation events both accompanied by greenschist-facies metamorphism of similar grade. The southern terrane records a Neoproterozoic pervasive amphibolite-facies metamorphism and strong deformational fabric only locally retrogressed during a Caledonian greenschist-grade event. These terranes are separated by an important sinistral ductile shear zone defined as the Vimsodden–Kosibapasset zone, which comprises wrench- and contraction-dominated domains characteristic of strain partitioning in transpression zones; in this case apparently controlled by contrasting rheologies of the juxtaposed crustal domains. The northern terrane of Wedel Jarlsberg Land shares affinities with Pearya in northern Ellesmere Island of Arctic Canada whereas the southern one resembles the Timanide belt of NE Europe. A quantitative approach facilitated by a numerical plate model demonstrates that correlation with Pearya is feasible if sinistral displacement of c. 600 km occurred during the Caledonian orogeny. The correlation with the Timanides is valid if the southern terrane represents an outlier of the Timanide belt separated from Baltica by the opening of the Iapetus Ocean.

Fractionation of an Aquatic Fulvic Acid upon Adsorption to the Bacterium, Bacillus subtilis

This study investigated the adsorption of an aquatic XAD-8 isolate (primarily fulvic acid, FA with some humic acid, HA; herein after referred to as FA) to the aerobic, gram-positive bacterial species Bacillus subtilis, at pH 2 to 7. Adsorption increased with decreasing pH and was strongest when both the bacterial surface and the bulk of the FA were uncharged, suggesting that hydrophobic interactions exerted an important control on adsorption. Analysis of FA molecular weight distributions by high-pressure size exclusion chromatography (HPSEC) indicated preferential adsorption of higher molecular weight FA components, especially at high pH and low surface coverage. Adsorption kinetics were fast, approaching steady state in terms of total FA adsorbed and molecular weight distribution within 30 min. Unlike FA adsorption to mineral surfaces, we did not observe initial adsorption of low molecular weight components, followed by replacement by higher molecular weight components. Rather, relatively high-molecular weight components (∼ 1500–8000 Da) adsorbed first, and were gradually joined by the highest molecular weight fraction (> ∼ 8000 Da). Considering that higher molecular weight components tend to be more hydrophobic, this fractionation phenomenon is consistent with a hydrophobic control of adsorption.

Microdiamond discovered in the Seve Nappe (Scandinavian Caledonides) and its exhumation by the “vacuum-cleaner” mechanism

When a continent collides with an island arc or other continent, continental crust of the subducted continent may be buried to depths exceeding 100 km, and exposed to pressures that can cause formation of coesite and diamond. This process leads to substantial density increase in SiO2-rich rocks and, in turn, to a reduction of the buoyancy of the subducted material, which should inhibit exhumation. Nevertheless, coesite- and diamond-bearing continental crustal rocks are known from several occurrences worldwide. We report on the discovery of microdiamond in kyanite-garnet gneiss from allochthonous metasediments of the Seve Nappe Complex in the Scandinavian Caledonides. Our discovery calls for general reconsideration of existing exhumation models of deeply subducted continental crust. We propose that the diamond-bearing rocks were subducted in an arc-continent collision setting, and their exhumation was facilitated by local pressure reduction resulting from extraction of the forearc lithospheric block.

Thermochronological evidence for late Proterozoic (Vendian) cooling in southwest Wedel Jarlsberg Land, Spitsbergen

Two Proterozoic terranes with different metamorphic histories are distinguished from geological mapping in southwestern Wedel Jarlsberg Land: a northern greenschist facies terrane and a southern amphibolite facies terrane which has been overprinted by greenschist facies metamorphism. To better characterize the tectonothermal history of these terranes we have obtained new 40 Ar/ 39 Ar mineral dates from this area. A muscovite separate from the northern terrane yielded a Caledonian plateau age of 432±7 Ma. The southern terrane yielded significantly older 40 Ar/ 39 Ar ages with three muscovite plateau dates of 584±14 Ma, 575±15 Ma, and 459±9 Ma, a 484±5 Ma biotite plateau date, and a 616±17 Ma hornblende plateau date. The oldest thermochronological dates are over 300 Ma younger than the age of amphibolite facies metamorphism and therefore probably do not represent uplift-related cooling. Instead, the Vendian dates correlate well with a regionally widespread magmatic and metamorphic/thermal resetting event recognized within Caledonian complexes of northwestern Spitsbergen and Nordaustlandet. The apparent Ordovician dates are interpreted to represent partial resetting, suggesting that late Caledonian greenschist facies overprinting of the southern terrane was of variable intensity.

Synchrotron-based X-ray diffraction of the lead apatite series Pb10(PO4)6Cl2–Pb10(AsO4)6Cl2

A number of compounds of the pyromorphite-mimetite solid solution series were synthesized at room temperature and analyzed with infrared spectroscopy and powder X-ray diffraction. High-resolution high-quality powder diffraction data were obtained by means of the state-of-the-art instrument at the 11-BM beamline of the Advanced Photon Source at Argonne National Laboratory, Argonne, IL, USA. The unit-cell dimensions, atomic position and atomic displacement parameters, as well as site occupancy for analyzed phases, were refined by the Rietveld method and reported herein for the first time. The results of this study indicate that the pyromorphite-mimetite series is continuous in near-Earth-surface environments. Detailed structural changes caused by P(5+)-As(5+) substitutions in minerals from the pyromorphite-mimetite solid solution series are reported.