Showing papers in "Chemical Geology in 1991"

TL;DR: In this paper, the Eu 3+ Eu 2+ redox boundary for temperatures up to 600°C and pressures up to 4000 bar has been calculated using the revised HKF model for the prediction of the molal Gibbs free energy of formation at elevated pressures and temperatures.

TL;DR: In this article, high-precision multidynamic analyses for Sr and Nd isotopic standards are reported for a 4-year period on the VG 354 mass spectrometer at Royal Holloway and Bedford New College (RHBNC).

TL;DR: In this article, the authors used published data relevant to the geochemistry of vanadium to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks, including reduction, adsorption, and complexation of dissolved vanadium.

TL;DR: In this paper, a total of 57 surficial sediment samples collected in the Golden Horn Estuary and Izmit Bay (northeastern Marmara Sea) was analyzed for the heavy metals Fe, Mn, Cr, Ni, Co, Zn, Pb, and Cu and the results were compared with various natural and anthropogenic sources.

TL;DR: In this article, the authors show that relatively slight alteration at the earliest stages of weathering can produce drastic changes in the concentrations of rare-earth elements (REE, Y and Ba) and the level of incipient alteration.

TL;DR: Halliday et al. as discussed by the authors modeled the petrogenesis o1 high Rh/Sr silicic magmas and found that the trace-element trend defined by the suite of cogenelic rhyolites is the product of different batches of magma with separate differentiation histories accumulating in the magma chamber roof zone.

TL;DR: In this article, the importance of kinetic control of iron distribution in anoxic sediments using a diagenetic model for dissolved iron(II) was investigated, and a rough estimate of time scales for dissolution and precipitation rates was made by imposing limiting boundary conditions.

TL;DR: In this paper, a film theory model for dissolution and precipitation of calcite from a plane surface in a H2O-CO2-CaCO3 solution under turbulent flow conditions is presented.

TL;DR: Oxygen self-diffusion coefficients (D) were determined in single crystals of Brazilian quartz by measuring 18O concentration profiles with an ion microprobe, and the diffusion rate was also measured in β-quartz from 5- to 350-MPa confining pressure and at 700°C as a function of water, hydrogen and oxygen fugacities as well as for different proton activities as mentioned in this paper.

TL;DR: Olivarez et al. as discussed by the authors investigated the difference between the observed and predicted rare earth element (REE) pattern of seawater and found that the intensity of REE scavenging by hydrothermal precipitates is proportional to the concentration of rare earth elements in the fluid phase.

TL;DR: In this article, a new isotope ratio-gas chromatograph combination in which capillary columns are used for improved resolution has been developed for carbon isotope analysis of oils and source rock bitumens.

TL;DR: The Miocene Misis tectonosedimentary melange was formed during the closing stages of the Neotethys in what is now the Adana basin of southern Turkey as mentioned in this paper.

TL;DR: For example, Valu Fa Ridge (VFR), a back-arc spreading center in Lau Basin, has been found to have high volatile contents, as shown by the abundance and large sizes of vesicles.

TL;DR: In this article, the isotopic data are in agreement with the chemical data in indicating that Sr is almost entirely derived from the host, despite clear evidence of major mass transfer of alkali metals, alkali earths and transition metals, a comparison of the concentrations and ratios of HFSE and REE, and Nd isotopic ratios with those of potential starting protoliths, allows the enclave precursors to be positively discriminated.

TL;DR: In this article, an analysis of samples from a weathering profile on Karoo dolerite allow elements to be divided into three groups depending on their behaviour: immobile, mobile, and reactive elements.

TL;DR: In this article, the authors measured absolute temperatures inside a Rock-Eval crucible in order to determine the true starting and ending temperatures, heating rates, and oven gradient of the Monterey formation samples and other potential oil and gas source rocks.

TL;DR: Risacher et al. as mentioned in this paper studied the evolution of the salar of Uyuni and Coipasa in the central Altiplano of Bolivia and derived the paleochemistry by dissolving the present amounts of all chemical components in the former lake volume, and by simulating the evaporation of the major inflows to the basin.

TL;DR: In this paper, the effect of low molecular weight organic ligands, soil humic acid (HA), and stream water dissolved organic matter (DOM) on the rate of dissolution of kaolinite was examined.

TL;DR: In this article, two examples of felsic-mafic association resulting from a magma mingling mechanism have been studied in Carboniferous calc-alkaline granitoids from Sardinia using mineralogical and geochemical techniques.

TL;DR: In this paper, the authors show that residual granitic liquids from a parent syenitic magma through crystal-liquid fractionation of alkali feldspars, plagioclase, amphibole, Fe-Ti oxides and apatite can be derived from a Rbdepleted and F-enriched granulitic lower crust.

TL;DR: In this paper, trace element and isotopic data are reported for Hercynian granodiorites and tonalites from Capo Vaticano, Calabria, with the aim of clarifying the relationships between acidic and intermediate lithologies in orogenic intrusive suites.

TL;DR: Isotopic compositions in unaltered shell calcites of brachiopods from Genessee County, which was close to the basin depocentre, are heavy for carbon (δ13C, x ¯ = + 5.01 as discussed by the authors, p = 0.0005 ).

TL;DR: In this paper, the laser microprobe (LMP) was used to measure low concentrations of Cl and Ar in natural phlogopite and hydrothermally treated (HT) biotite.

TL;DR: In this article, two consecutive sets of pre and post-monsoon samples of water, suspended solids and sediments were collected from nineteen stations along the intertidal zone of Thane Creek and from eleven stations on the Ulhas River course.

TL;DR: In this paper, a multivariate classification of these geochemical variables in Q-mode (sample space) allows to clearly distinguish major element grouping from those of moderate to highly incompatible elements and the isotope ratios reflecting mantle source heterogeneities present in the region.

TL;DR: In this article, the chemical and isotopic composition of fumarole and geothermal well gases has been studied along a 15 km section of a subaerial spreading center (Hengill area, southwest Iceland).

TL;DR: In this article, equilibrium and kinetic data for Cd sorption on hydroxyapatite were presented for a wide range of Cd2+ concentrations, and experimental conditions were kept close to those found in freshwater environments.

TL;DR: A comparison of the relative abundances of the norhopanes in the soluble organic matter of carbonate sediments and in the hydrocarbon fraction released when the extracted sediments were pyrolysed showed that the 30-nor-17α(H)-hopanes were more abundant in the pyrolysis product as mentioned in this paper.

TL;DR: In this article, a high-precision analytical method for the measurement of 138 Ce 142 Ce ratios was reported using static multicollection mass spectrometry, which reduced the data acquisition time for 2 hours and improved analytical reproducibility to ± 0.002% (n-16) and precision to ±0.002-0.003%.

TL;DR: In this paper, molecular, isotopic and elemental data for a set of 28 Paleogene and 3 Cretaceous oils from the Mackenzie Delta and offshore Canadian Beaufort Sea have been evaluated.