Showing papers in "Chemical Geology in 1998"

TL;DR: This article evaluated subducting sediments on a global basis in order to better define their chemical systematics and to determine both regional and global average compositions, and then used these compositions to assess the importance of sediments to arc volcanism and crust-mantle recycling, and to re-evaluate the chemical composition of the continental crust.

TL;DR: McDougall et al. as mentioned in this paper derived intercalibration factors for McClure Mountain hornblende (MMhb-1), GHC-305 biotite, GA-1550, Taylor Creek sanidine (TCs), relative to Fish Canyon sanidine(ACs), were derived from 797 analyses involving 11 separate irradiations with well-constrained neutronfluence variations.

TL;DR: In this article, the authors show that NMORB and the depleted MORB mantle reservoir are characterised by a similarly limited range in / ratios and suggest that the high / MORB-like basalts may ultimately be related to mantle plumes and represent melts of a depleted component entrained by the plumes.

TL;DR: In this article, the authors explored solutions to the He production-diffusion equation to characterize the response of apatite He ages to thermal histories involving partial He retention, and showed that He ages within the partial retention zone ultimately achieve a balance between He production and loss, yielding a steady state age.

TL;DR: In this paper, the authors calculate conductive geotherms for 41 mW/m 2 surface heat flow to place limits on the heat production of Archean mantle roots and to evaluate the significance of the pressure-temperature (P-T ) array for cratonic mantle xenoliths.

TL;DR: In this article, the effect of volatile fractionation during magma degassing, investigated using new rare gas and CO2 abundances determined simultaneously for a suite of Mid-Ocean Ridge (MOR) basalt glasses, is not the major factor controlling the spread of data, which mainly result from volatile heterogeneity in the mantle source.

TL;DR: The Magdalen Islands are located in the Gulf of St. Lawrence, near the centre of the late Devonian to Carboniferous composite Maritimes Basin, which opened in response to extensional tectonism following continental collision during the Acadian orogeny.

TL;DR: In this paper, the Hf and Nd isotope ratios in ocean island basalts (OIB) are extremely well correlated and it is argued that crustal recycling (by either continental or oceanic sediments) most likely did not cause the variations.

TL;DR: In this paper, the authors present a new kinetic model for the generation of hydrocarbon gas, linking isotopic fractionation and molecular compositions, and show that the evolution trends observed in such a diagram obey a logic depending on both the maturity and the expulsion rate of hydrocarbons.

TL;DR: Apatite dissolution was studied at 25°C in a series of batch experiments carried out within the pH range of 2-7 with or without the presence of aqueous Pb2+ or Cd2+ as discussed by the authors.

TL;DR: In this article, a model is presented that accounts for the development of the oxidation and reduction horizons within the Avicennia -dominated mangrove forest sediment and describes the major controls on metal cycling within the sediment.

TL;DR: In this article, ICP-MS measurements after pyrohydrolysis on a reasonably large series of samples representing about 300 rocks of major units and subunits of the earth's crust, and a few organic materials, are provided for a genetic discussion.

TL;DR: In this paper, the electron microprobe dating technique was used for the analysis of monazites from the central and northern part (Ponmudi Unit) of the Kerala Khondalite Belt (KKB) in southern India.

TL;DR: In this paper, the early ocean was plausibly deuterium-depleted (delta D = -18 +/- 6 parts per thousand) in comparison with the present-day oceans, and a kinetic treatment of the long-term water cycle was used to predict potential variations in the hydrogen stable isotope composition of seawater.

TL;DR: In this article, the authors studied the role of relief and runoff in determining the sediment load of rivers, and concluded that relief and rainfall are the most important factors in determining sediment load.

TL;DR: Oxygen isotope compositions of herbivore tooth enamel from two areas in Kenya were measured using a laser fluorination approach as discussed by the authors, and compositional heterogeneity was found within four sets of teeth in the jaws of different individuals, as well as within individual teeth.

TL;DR: In this article, the diets of proboscideans and associated mammals were reconstructed through isotopic analysis of carbonate in tooth enamel apatite in order to test nutritional hypotheses for late Pleistocene extinction.

TL;DR: Stumm et al. as mentioned in this paper used free-drift rotating disk techniques to determine dissolution rates of calcite crystals, limestones, and compressed calcite powders, and obtained the apparent rate constants and H + diffusion coefficients.

TL;DR: In this article, the authors reviewed the controversy and revises earlier estimates on the 18O-balance within the hydrosphere and concluded that the δ18O of seawater is mainly buffered by hydrothermal and weathering processes at mid-ocean ridges to a value of about 0.

TL;DR: In this paper, the surface chemistry and morphology of poorly crystalline iron sulfides precipitated in a chemically defined growth media for sulfate-reducing bacteria were analyzed by X-ray diffractometry (XRD), Xray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM).

TL;DR: In this article, an evolutionary model was developed to identify and quantify processes which were able to reproduce rare gas and nitrogen isotopic abundances in the main terrestrial reservoirs, which were quite similar to those typical of solar wind-implanted gases.

TL;DR: In this article, nitrogen isotopes were used to study the source of nitrate and its uptake into the food web of a northeastern river in Vermont, USA, and they observed a strong positive correlation between δ15N values of stream water nitrates and percent of agricultural land-use within a given catchment.

TL;DR: In this paper, the C3 vegetation Colospherum mopane and Eucalyptus sp. and the C4 vegetation Cenchris cilliarus, Antephora pubesence and Saccharum officinarum, were burned under controlled conditions in the laboratory in order to better understand how the process of combustion affects the isotopic fractionation of the produced material.

TL;DR: In this paper, the authors present evidence for systematic Nb/Ta variations in an island arc system of the Early Paleozoic Takaka Terrane, New Zealand, using ICPMS.

TL;DR: Fein et al. as discussed by the authors used acid-base titrations to determine the concentrations and deprotonation constants of specific surface functional groups on Bacillus licheniformis, and compared these variations in surface properties to variations in metal affinity in order to predict metal mobilities in complex, natural systems.

TL;DR: In this article, a pre-anthropogenic 129 I / 127 I ratio of 1500×10−15 was measured in 25 sediment samples from five cores taken at geographically distinct coastal areas, and the results indicated that marine iodine is present in two forms, a labile component which is isotopically homogeneous, and a refractory component associated with kerogen (or other fossil organic compounds) whose 129 I/127 I ratio reflects the age of these compounds.

TL;DR: In this paper, a coupled study of the dissolved and suspended loads of the rivers draining the basaltic island of Sao Miguel, in order to determine both chemical and mechanical erosion rates was presented.

TL;DR: Torre Alfina, a Quaternary volcano located in the northernmost part of the Roman Province, is characterized by two main types of mafic ultrapotassic lavas with slightly different chemical, isotopic, and mineralogic characteristics as mentioned in this paper.

TL;DR: In this paper, a high-yield lithium separation technique for rock and aqueous samples has been established together with precise Li isotope analysis by thermal ionization mass spectrometry.

TL;DR: The solubility and weathering reactions of ettringite were used to study the geochemical equilibria of the Ca(OH)2−Al2(SO4)3-H2O system at environmental pH conditions as discussed by the authors.