Showing papers in "Chemical Geology in 1995"

TL;DR: In this paper, the authors compared the relative abundances of the refractory elements in carbonaceous, ordinary, and enstatite chondritic meteorites and found that the most consistent composition of the Earth's core is derived from the seismic profile and its interpretation, compared with primitive meteorites, and chemical and petrological models of peridotite-basalt melting relationships.

TL;DR: A mantle value of ∼ 17.5 for Nb/Ta appears well established; less well established are crustal values of ∼ 11-12, although it appears that Nb-Ta for crustal-derived melts is less than mantle Nb /Ta, demonstrating fractionation of these two elements during crustal evolution, and suggesting that the variation may be indicative of a particular chemical process within the crust-mantle system as mentioned in this paper.

TL;DR: In this paper, the authors presented the first quantitative estimates of the upper mantle, sediment and limestone including slab components in CO2 of volcanic and hydrothermal fluids from subduction zones.

TL;DR: In this paper, the relative importance of genetic and post-genetic molecular and isotopic fractionations affecting natural gases was discussed, and it was shown that although the prime order of fractionation in gases is due to genetic phenomena, second-order effects due to postgenetic fractionation (diffusion, oxidation etc.) may be recognized, and must be taken into account to model the geochemical data on a gas field.

TL;DR: In this article, rare-earth elements (REE) and yttrium (Y) were enriched in French Polynesian basaltic sequences, indicating a close relationship to supergene processes.

TL;DR: In this article, a vertical section of shales, siltstones and sandstones from Ordovician to Eocene age in a limited geographic area east of the Wet Mountains and Sangre de Cristo Mountains in Colorado have been analyzed for major elements and a variety of trace-element concentrations, including the REE.

TL;DR: In this paper, an isotopic model was proposed for gas generation from Type II kerogen, which is relatively unaffected by migration or mixing of biogenic gas, so that changes in carbon isotope ratios of the gas components primarily reflect the effect of maturation.

TL;DR: A five-step sequential chemical extraction scheme, originally designed for sediment analysis by flame atomic adsorption spectroscopy (FAAS), has been developed for the multielement analysis of soils by inductively coupled plasma-atomic emission spectrometry (ICP-AES) as discussed by the authors.

TL;DR: A series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350-750°C for 10−1-103 hr (i.e. 4.5 min-∼40 days) as mentioned in this paper.

TL;DR: The Cabal Gerf mafic-ultramafic complex, the largest Neoproterozoic ophiolite in the Arabian-Nubian Shield and located near the Red Sea in the border region between Egypt and the Sudan, was reported in this paper.

TL;DR: In the Athabasca Basin Proterozoic sandstones unconformably overlie Archean and Aphebian rocks as mentioned in this paper, the evolution of Sr isotopic compositions of fluids in the basin and basement rocks, as reflected by the 87 Sr 86 Sr ratios of chlorite, illite and dravite, indicates that mixing of two isotopically-distinct fluids was the process by which uranium was precipitated, similar to that suggested by oxygen and hydrogen isotope systematics in the clays and silicate minerals.

TL;DR: In this paper, the authors analyzed MORB glasses from the mid-Atlantic Ridge (64°N-20°S) and the East Pacific Rise (7-21°N) for chlorine with an electron microprobe and chlorine and bromine by NAA.

TL;DR: In this paper, the effects of hydrothermal alteration and metamorphism on the chemical and isotopic compositions of komatiites were investigated, focusing on multiple layered spinifex-olivine cumulate flows, the argument being that if these flows showed variations in the ratios of elements incompatible with olivine, then these variations were most likely due to chemical mobility during alteration.

TL;DR: In this paper, the authors analyzed the B contents and δ11B of drilled oceanic crust, from DSDP Holes 417A, 417D and 418A and ODP Hole 735B, and Oceanic crust from the Oman and Cyprus ophiolites, were analyzed for B contents, showing that it is a good indicator of the extent of low temperature alteration.

TL;DR: A review of selected data sets from the Mesozoic and Tertiary CFB confirms significant differences in their major and trace-element compositions compared with those of basalts erupted through oceanic lithosphere as discussed by the authors.

TL;DR: In this paper, a new experimental campaign aimed at obtaining reliable values of DMmets/sil melt for selected HSE's indirectly, by measuring the solubilities of the pure metals (or simple HSE alloys) in haplobasaltic melts as a function of oxygen fugacity.

TL;DR: Isotopic and incompatible-element ratios of the plateau lavas are distinct from those of Indian mid-ocean ridge basalts; their Nd, Sr, 207Pb 204Pb and 208Pb204Pb isotopic ratios overlap with but cover a much wider range than measured for more recent oceanic products of the Kerguelen hotspot (including the Ninetyeast Ridge) or, indeed, oceanic lavas from any other hotspot in the world as discussed by the authors.

TL;DR: In this article, the authors analyzed sediment samples from the Gulf of Gdansk and the southern Baltic Sea and found that up to 45% of the total Cu was extracted from the sediments by 0.1 M NaOH and appears to be associated with the humic acid fraction.

TL;DR: In this paper, the authors investigated sedimentary organic matter, in particular coals, as a potential source of molecular nitrogen in the subsurface and concluded that the amounts of gas encountered in nitrogen-rich gas accumulations represent only a small fraction (possibly < 1 %) of the total gas generation potential of this area while the bulk of the generated gas has escaped to the atmosphere.

TL;DR: In this article, microbodies containing DNA were identified within altered parts of the glass rims of pillow lavas in the upper oceanic crust, 237 m below the top of the volcanic basement of ODP Hole 896A at the Costa Rica Rift.

TL;DR: In this paper, an experiment was performed in which basaltic glass samples were immersed in growth media at room temperature for up to 394 days, inoculated with bacteria derived from a naturally altered pyroclastic deposit (Surtsey tuff).

TL;DR: The authors showed that the geochemistry of komatiites can be explained by hot Archean plumes that experienced melting in the transition zone and the top of the lower mantle of the Earth.

TL;DR: The global rate of organic carbon burial was probably fairly constant during deposition of the Bangemall Group, and perhaps generally during the Mesoproterozoic, as was the redox state of the atmosphere and hydrosphere.

TL;DR: In this article, the authors demonstrate that subduction can deliver, to various parts of the mantle, fluids, melts, and residual mineral reservoirs strongly fractionated isotopically and chemically relative to initial compositions of the subducted rocks.

TL;DR: In this article, the Raman spectra were collected for barium silicate, strontium silicates and calcium silicate melts at temperatures ranging from the glass transition region to temperatures as high as 1600°C.

TL;DR: In this article, the authors have carried out experimental simulations of coal and kerogen degradation in open and closed pyrolysis systems to determine both the gas and oil potential of Type II and Type III organic matter.

TL;DR: In this paper, an algae-rich kerogen and a xylite were subjected to an open-system pyrolysis that allows a simulation of primary cracking (temperatures: 20 to 810°C, heating rate: 5°C/min, helium flow: 21 ml/min) within the (measured) maturity range 0.3 to 5.4% vitrinite reflectance.

TL;DR: In this article, the authors proposed that excess argon, probably conveyed by a fluid phase and trapped in defects within the structure of the phengite grains at the time of their isotopic closure, is the best explanation for the observed spread in apparent ages on a regional to single grain scale, in spite of a nearly universal existence of homogeneous age maps.

TL;DR: A suite of rocks from the Rajmahal-Bengal-Sylhet Traps of northeastern India has been analyzed to ascertain the timing and duration of volcanism and elucidate their petrogenesis.

TL;DR: In this article, a lake column profile was collected in 24 m of water from Colour Lake, Axel Heiberg Island, Northwest Territories, Canada, in early June of 1991 beneath 1.8 m of lake-ice.