scispace - formally typeset

JournalISSN: 0016-7037

Geochimica et Cosmochimica Acta 

About: Geochimica et Cosmochimica Acta is an academic journal. The journal publishes majorly in the area(s): Chondrite & Meteorite. It has an ISSN identifier of 0016-7037. Over the lifetime, 20844 publication(s) have been published receiving 1515154 citation(s). The journal is also known as: Geoch. Cosm. Act. & Geochim. Cosmochim. Acta.
More filters

Journal ArticleDOI
Edward Anders1, Nicolas Grevesse2Institutions (2)
Abstract: New abundance tables have been compiled for C1 chondrites and the solar photosphere and corona, based on a critical review of the literature to mid-1988. The meteorite data are generally accurate to + or - 5-10 percent. Significant discrepancies between the sun and meteorites occur only for Fe, Mn, Ge, Pb, and W; other well-determined elements agree to + or - 9 percent on the average. There is no evidence for group fractionations in C1 chondrites of cosmochemically similar elements (refractories, siderophiles, volatiles, etc.), but a selective fractionation of Fe cannot be ruled out. Abundances of odd-A nuclides between A = 65 and 209 show a generally smooth trend, with elemental abundances conforming to the slope defined by isotopic abundances. Significant irregularities occur in the Nd-Sm-Eu region, however, suggesting that the abundance curve is dependably smooth only down to about 20 percent level.

9,935 citations

Journal ArticleDOI
Michael J. DeNiro1, Samuel Epstein1Institutions (1)
Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

5,190 citations

Journal ArticleDOI
Abstract: A new calculation of the crustal composition is based on the proportions of upper crust (UC) to felsic lower crust (FLC) to mafic lower crust (MLC) of about 1:0.6:0.4. These proportions are derived from a 3000 km long refraction seismic profile through western Europe (EGT) comprising 60% old shield and 40% younger fold belt area with about 40 km average Moho depth. A granodioritic bulk composition of the UC in major elements and thirty-two minor and trace elements was calculated from the Canadian Shield data (Shaw et al., 1967, 1976). The computed abundance of thirty-three additional trace elements in the UC is based on the following proportions of major rock units derived from mapping: 14% sedimentary rocks, 25% granites, 20% granodiorites, 5% tonalites, 6% gabbros, and 30% gneisses and mica schists. The composition of FLC and MLC in major and thirty-six minor and trace elements is calculated from data on felsic granulite terrains and mafic xenoliths, respectively, compiled by Rudnick and Presper (1990). More than thirty additional trace element abundances in FLC and MLC were computed or estimated from literature data. The bulk continental crust has a tonalitic and not a dioritic composition with distinctly higher concentrations of incompatible elements including the heat producing isotopes in our calculation. A dioritic bulk crust was suggested by Taylor and McLennan (1985). The amount of tonalite in the crust requires partial melting of mafic rocks with about 100 km thickness (compared with about 7 km in the present MLC) and water supply from dehydrated slabs and mafic intrusions. At the relatively low temperatures of old crustal segments MLC was partly converted into eclogite which could be recycled into the upper mantle under favourable tectonic conditions. The chemical fractionation of UC against FLC + MLC was caused by granitoidal partial melts and by mantle degassing which has controlled weathering and accumulation of volatile compounds close to the Earth's surface.

4,815 citations

Journal ArticleDOI
Harmon Craig1Institutions (1)
Abstract: Seventy-four mass spectrometric analyses have been made on eight isotopic standards for carbon and oxygen. The standards reported on are the National Bureau of Standards limestone, water, and graphite reference samples, the Solenhofen standard used by Niee for absolute measurements, and the carbonate standards used by the Stockholm, Basel, Wellington and Chicago laboratories. The basic measurements are reported as δ values relative to the Chicago PDB standard and as absolute isotope ratios. The absolute ratios are based on new figures for Nier's standard, derived from a reevaluation of his data and new measurements on atmospheric oxygen. The correction factors for instrumental effects and for the nature of the mass spectra have been studied. Simple but precise equations for the mass spectra effects have been derived, which give the correction factors as functions of the measured differences between sample and standard. The oxygen isotopic composition of carbon dioxide produced by combustion of carbon has been studied and the derived correction factors for carbon measurements were checked experimentally by varying the oxygen-18 content of carbon dioxide.

3,955 citations

Network Information
Related Journals (5)
Chemical Geology

10.6K papers, 571.6K citations

96% related
Earth and Planetary Science Letters

18.3K papers, 1.2M citations

92% related
American Mineralogist

13.2K papers, 437.8K citations

89% related
Contributions to Mineralogy and Petrology

6.3K papers, 433.1K citations

89% related

12.6K papers, 793.8K citations

88% related
No. of papers from the Journal in previous years