Age of New Zealand Pleistocene substages by fission-track dating of glass shards from tephra horizons

Eleven tephras and two pumice-rich horizons interbedded in Pleistocene marine sediments of the Wanganui Basin have been dated using the fission-track method on glass shards. Ages of the lower boundaries of New Zealand Pleistocene marine Substages are 0.45 m.y. (Putikian), 1.06 m.y. (Okehuan), 1.55 m.y. (Marahauan). On the basis of sedimentation rates an estimation of 1.86 m.y. is obtained for the Plio-Pleistocene boundary (Hautawan).     

The reaction kinetics of alanine and glycine under hydrothermal conditions

Experimental data on the hydrothermal reaction kinetics of α-alanine, glycine, and β-alanine were acquired using a custom-built spectrophotometric reaction cell which permits in situ observation under hydrothermal conditions. Quantitative kinetic information, including rate constants, concentration versus time profiles, and calculations of the individual component spectra, was obtained from the data using a self-modeling chemometric approach based on factor analysis which treats the rate expressions simultaneously as a system of differential algebraic equations (DAE) of index 1. Experimental data collected at 120-165 °C and 20 bar indicates that aqueous α-alanine, glycine and β-alanine will preferentially undergo dimerization and subsequent cyclization when heated in an inert reactor. The results presented here lend further support to the roles of temperature, exposed reactive surfaces, and matrix additives in the reaction kinetics of the structurally simple amino acids examined in this study.     

A comment on: ‘TitaniQ under pressure: the effect of pressure and temperature on the solubility of Ti in quartz’, by Jay B. Thomas,E. Bruce Watson,Frank S. Spear,Philip T. Shemella,Saroj K. Nayak and Antonio Lanzirotti

Trace concentrations of Ti in quartz are used to indicate the pressure and temperature conditions of crystallization in the ‘TitaniQ’ geothermobarometer of Thomas et al. (Contrib Miner Petrol 160:743–759, 2010). It utilises the partitioning of Ti into quartz as an indicator of the pressures and/or temperatures of crystal growth. For a given value of TiO₂ activity in the system, if temperatures are inferred to ±20 °C, pressure is constrained to ±1 kbar and vice versa. There are significant contrasts, however, between the conclusions from TitaniQ and those for natural quartz (as well as other mineral phases) in volcanic rocks. Application of the TitaniQ model to quartz from the 27 ka Oruanui and 760 ka Bishop high-silica rhyolites, where the values of T, P and TiO₂ activity are constrained by other means (Fe–Ti oxide equilibria, melt inclusion entrapment pressures in gas-saturated melts, melt and amphibole compositions), yields inconsistent results. If realistic values are given to any two of these three parameters, then the value of the third is wholly unrealistic. The model yields growth temperatures at or below the granite solidus, pressures in the lower crust or upper mantle, or TiO₂ activities inconsistent with the mineralogical and chemical compositions of the magmas. CL imagery and measurements of Ti (and other elements) in quartz are of great value in showing the growth histories and changes in conditions experienced by crystals, but direct linkages to P, T conditions during crystal growth cannot be achieved.     

Constraining provenance,thickness and erosion of nappes using low‐temperature thermochronology: the Northland Allochthon,New Zealand

The Northland Allochthon, an assemblage of Cretaceous–Oligocene sedimentary rocks, was emplaced during the Late Oligocene–earliest Miocene, onto the in situ Mesozoic and early Cenozoic rocks (predominantly Late Eocene–earliest Miocene) in northwestern New Zealand. Using low‐temperature thermochronology, we investigate the sedimentary provenance, burial and erosion histories of the rocks from both the hanging and footwalls of the allochthon. In central Northland (Parua Bay), both the overlying allochthon and underlying Early Miocene autochthon yield detrital zircon and partially reset apatite fission‐track ages that were sourced from the local Jurassic terrane and perhaps Late Cretaceous volcanics; the autochthon contains, additionally, material sourced from Oligocene volcanics. Thermal history modelling indicates that the lower part of the allochthon together with the autochthon was heated to ca. 55–100°C during the Late Oligocene and Early Miocene, most likely due to the burial beneath the overlying nappe sequences. From the Mesozoic basement exposed in eastern Northland, we obtained zircon fission‐track ages tightly bracketed between 153 and 149 Ma; the apatite fission‐track ages on the other hand, generally young towards the northwest, from 129 to 20.9 Ma. Basement thermochronological ages are inverted to simulate the emplacement and later erosion of the Northland Allochthon, using a thermo‐kinematic model coupled with an inversion algorithm. The results suggest that during the Late Oligocene, the nappes in eastern Northland ranged from ca. 4–6‐km thick in the north to zero in the Auckland region (over a distance >200 km). Following the allochthon emplacement, eastern Northland was uplifted and unroofed during the Early Miocene for a period of ca. 1–6 Myr at the rate of 0.1–0.8 km/Myr, leading to rapid erosion of the nappes. Since Middle Miocene, the basement uplift ceased and the erosion of the nappes and the region as a whole slowed down (ca. 0–0.2 km/Myr), implying a decay in the tectonic activity in this region.     

The formation of lead(II) chloride complexes to 300°C: A spectrophotometric study

The spectra of chlorolead(II) complexes in the ultraviolet region have been measured in acid chloride solutions from 0.0012 to 3.223 m and at temperatures from 25 to 300°C. The thermodynamic cumulative and stepwise formation constants as well as the spectra of the individual chlorolead(II) species have been calculated from the spectrophotometric data. At 25°C, the five species PbCl^2?n_n (0 ≤ n ≤ 4) occur, however, at 300°C the predominant species were PbCl⁺, PbCl⁰₂ and PbCl^?₃. Pb²⁺ occurs as a minor species in dilute solutions where total chloride is <0.003 m at 300°C and the presence of PbCl^2?₄ in concentrated solutions was not detected above 150°C. With increasing temperature, chlorolead(II) complex stability is characterised by large endothermic enthalpies and large positive entropies of formation. Lead(II) chloride complexes are important in the transport and deposition of lead by hydrothermal ore solutions of moderate to high salinity.     

Palladium(II) chloride complexation: Spectrophotometric investigation in aqueous solutions from 5 to 125°C and theoretical insight into Pd-Cl and Pd-OH2 interactions

Monomeric palladium(II) chloro aqua complexes of the form PdCl_r(H₂O)_4-r^2-r (r = [0,4]) were studied both experimentally and theoretically to gain insight on both the stabilities and the nature of palladium-chloride interactions.The thermodynamic stabilities of these complexes were studied in aqueous solutions from 5 to 125°C with UV-vis spectrophotometry using a quartz flow-through cell. Tentative measurements up to 200°C were also carried out in pressurised titanium and gold-lined optical cells but revealed important losses in soluble palladium. The strong ligand-to-metal charge transfer bands of the palladium complexes below 350 nm were used to constrain the stepwise thermodynamic formation constants at each temperature, using results of singular value decompositions of the spectra over a broad range of palladium:chloride ratios and wavelengths. The temperature-dependent constants were used to obtain changes in enthalpy and in entropy for each reaction. The thermodynamic stabilities of PdCl(H₂O)₃⁺, PdCl₂(H₂O)₂⁰, and PdCl₃(H₂O)^- are larger at higher temperatures, whilst the one of PdCl₄^2- is smaller. All changes in entropies are positive for the former three species, but negative for the latter, presumably due to a larger solvent reorganisation around the doubly charged PdCl₄^2- species. The room temperature thermodynamic values derived from this study are also in agreement with previously published calorimetric data.Theoretical calculations on the intramolecular distributions of electrons in the different palladium(II) chloro aqua complexes, using the methods of atoms in molecules and of the electron localisation function, showed Pd-Cl and Pd-OH₂ interactions to be of largely closed-shell/ionic nature. These interactions induce an important distortion of the outer core shell electrons of Pd, as well as stable accumulations of electrons between adjacent Pd-Cl and Pd-OH₂ bonds known as ligand opposed core charge concentrations.     

Gold(I) complexing in aqueous sulphide solutions to 500°C at 500 bar

The solubility of gold has been measured in aqueous sulphide solutions from 100 to 500°C at 500 bar in order to determine the stability and stoichiometry of sulphide complexes of gold(I) in hydrothermal solutions. The experiments were carried out in a flow-through system. The solubilities, measured as total dissolved gold, were in the range 3.6 × 10⁻⁸ to 6.65 × 10⁻⁴ mol kg⁻¹ (0.007-131 mg kg⁻¹), in solutions of total reduced sulphur between 0.0164 and 0.133 mol kg⁻¹, total chloride between 0.000 and 0.240 mol kg⁻¹, total sodium between 0.000 and 0.200 mol kg⁻¹, total dissolved hydrogen between 1.63 × 10⁻⁵ and 5.43 × 10⁻⁴ mol kg⁻¹ and a corresponding pH_{T, p} of 1.5 to 9.8. A non-linear least squares treatment of the data demonstrates that the solubility of gold in aqueous sulphide solutions is accurately described by the reactions

Au(s)+H₂S(aq)=AuHS(aq)+0.5H₂(g) K_s,100     

Analysis of lignin-derived phenols in standard reference materials and ocean dissolved organic matter by gas chromatography/tandem mass spectrometry

A series of reference materials are proposed for intercomparison and quality control purposes during the quantification of lignin oxidation products (LOP) from diverse environmental matrices. These materials are all easily accessible and certified for diverse organic constituents (NIST and IHSS). They represent a suite of natural environmental matrices (from solids to aqueous) and are characterized by a wide range of organic carbon and lignin concentrations with abundant proportions of all major LOP. The variability of LOP concentrations and signatures for all these materials averages 3–5% and does not exceed 10%. Using these standards, a new quantification method was developed and validated for the determination of low-level CuO oxidation products using capillary gas chromatography–tandem mass spectrometry (GC/MS–MS). Tandem mass spectrometry provides both the high sensitivity and selectivity required for the identification and quantification of trace levels of dissolved lignin. The method is particularly useful for removing interference from co-eluting isotopes generated from the DOM matrix and during glucose amendment procedures of low-carbon samples. Such glucose amendment is not necessary, however, when the CuO to organic carbon weight-to-weight ratio can be kept at a value < 200–300.     

Stability of chloridogold(I) complexes in aqueous solutions from 300 to 600°C and from 500 to 1800 bar

The solubility of gold has been measured in the system H₂O+H₂+HCl+NaCl+NaOH at temperatures from 300 to 600°C and pressures from 500 to 1800 bar in order to determine the stability and stoichiometry of chloride complexes of gold(I) in hydrothermal solutions. The experiments were carried out in a flow-through autoclave system. This approach permitted the independent determination of the concentrations of all critical aqueous components in solution for the determination of the stability and stoichiometry of gold(I) complexes. The solubilities (i.e. total dissolved gold) were in the range 9.9 × 10⁻⁹ to 3.26 × 10⁻⁵ mol kg⁻¹ (0.002-6.42 mg kg⁻¹) in solutions of total dissolved chloride between 0.150 and 1.720 mol kg⁻¹, total dissolved sodium between 0.000 and 0.975 mol kg⁻¹ and total dissolved hydrogen between 4.34 × 10⁻⁶ and 7.87 × 10⁻⁴ mol kg⁻¹. A nonlinear least squares treatment of the data demonstrates that the solubility of gold in chloride solutions is accurately described by the reactions,