SULFUR ISOTOPIC COMPOSITION OF THE TRIASSIC IGNEOUS ROCKS OF EASTERN UNITED STATES
Mass spectrometric measurements were made of the isotopic composition of sulfur in troilite from meteorites and in sulfides from igneous rocks and genetically associated mineral deposits of the Triassic Newark group, in eastern United States. Some of the intrusives sampled are strongly differentiated. The igneous rocks are tholeiitic, and presumably originated in the upper mantle. Considering the probable isotopic inhomogeneity of sulfur in the nnany rock types underlying the Newark basins, the observed isotopic uniformity of sulfides in normal diabase from intrusives suggests little contamination with crustal sulfur. The following delta S/sup 34/ per mil values were obtained: meteoritic troilite-- -- average 10.2 plus or minus 0.1; normal diabases from intrusives---average 10.1 plus or minus 0.4; late stage facies from differentiated intrusives---- mostly +3 to +8, maximum +11, with purite enriched in S/sup 34/ relative to coexisting chalcopyrite; specimens from the Cornwall, French Creek, and Dillsburg deposits, formed from emanations from adjacent diabase intrusives, --- range from -0.2 to +17, averaging about +7; extrusives--- range from -12 to +0.7, averaging about -5. The standard deviation analytical error is plus or minus 0.2. Data are calculated relative to Canon Diablo troilite with an assumed S/sup 32//S/sup 34/ ratio of 22.220. From these data, it was concluded that: beneath the Newark basins, during late Triassic time, upper mantle sulfur was isotopically similar to meteoritic sulfur; isotopic fractionation can occur during crystallization of tholeiitic magma, resulting in a slight enrichment of S/sup 34/ in late stage sulfides; fractionation may continue into hydrothermal stages, causing an enrichment of S/sup 34/ in magnetic hydrothermal sulfides; and by some mechanism of isotopic fractionation associated with crystallization at the earth's surface, sulfides in Newark extrusives are slightly enriched in S/sup 32/ relative to the magma source. (auth)
- Research Organization:
- Memorial Univ. of Newfoundland, St. John's, Can.
- NSA Number:
- NSA-18-010266
- OSTI ID:
- 4083965
- Journal Information:
- Geochimica et Cosmochimica Acta (England), Journal Name: Geochimica et Cosmochimica Acta (England) Vol. Vol: 27; ISSN GCACA
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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