Oxygen isotopic and chemical compositions of rocks of the Sudbury Basin, Ontario

1984 ◽  
Vol 21 (3) ◽  
pp. 305-318 ◽  
Author(s):  
T. P. Ding ◽  
H. P. Schwarcz
Keyword(s):  
Chemical Composition ◽  
Isotopic Composition ◽  
Oxygen Isotopic Composition ◽  
Chemical Compositions ◽  
The South ◽  
Microscopic Appearance ◽  
The North ◽  
Rock Types ◽  
Oxygen Isotopic ◽  
Oceanic Basalts

The whole-rock oxygen isotopic composition of the main units of the Sudbury Irruptive and surrounding rocks has been studied, using samples from two traverses of the North Range and one of the South Range. Norite has an average δ18O of 6.7‰, about 1‰ greater than that of fresh oceanic basalts, and similar to that of some continental basalts. Granophyre is slightly richer in 18O (δ18O = 7.3‰). In neither unit is there significant correlation between δ18O and SiO2 content or degree of alteration as estimated by water content or microscopic appearance. The pervasive hydrous alteration of norite and granophyre apparently occurred in the presence of a small volume of water whose isotopic composition was buffered by the igneous rocks. Inclusion-free devitrified glass ("melt rock") and matrix from the Onaping Formation have δ18O values in the range 6.2 – 12.1‰. Its average δ18O is 8.2‰, comparable to that of Archean gneiss [Formula: see text], as required by the model for the origin of the formation as a fallback breccia from a meteoritic impact. However, the chemical composition of the Onaping rocks requires an admixture of rocks much more mafic than typical Archean gneiss (e.g., greywackes or gabbros of the Southern Province). Norites of the South Range are 1‰ heavier than those of the North Range, possibly due to assimilation of 18O-rich rocks of the McKim Formation. It has been suggested that the granophyre was produced through assimilation of Onaping rocks by the norite; this is consistent with the oxygen isotopic composition of the three rock types but not with their chemical compositions, which show the granophyre to be more depleted in MgO than the Onaping Formation. The granophyre's chemical composition is consistent with an origin by differentiation from a magma with a composition equivalent to that of the transition (oxide-rich) gabbro.

Paleoclimatic implications of the spatial patterns of modern and LGM European land-snail shell δ18O

2010 ◽  
Vol 74 (1) ◽  
pp. 166-176 ◽  
Author(s):  
Natalie M. Kehrwald ◽  
William D. McCoy ◽  
Jeanne Thibeault ◽  
Stephen J. Burns ◽  
Eric A. Oches
Keyword(s):  
Isotopic Composition ◽  
Source Region ◽  
Warm Season ◽  
Land Snail ◽  
Oxygen Isotopic Composition ◽  
Preferential Sampling ◽  
The North ◽  
Westerly Jet ◽  
Single Location ◽  
Oxygen Isotopic

AbstractThe oxygen isotopic composition of land-snail shells may provide insight into the source region and trajectory of precipitation. Last glacial maximum (LGM) gastropod shells were sampled from loess from Belgium to Serbia and modern land-snail shells both record δ18O values between 0‰ and − 5‰. There are significant differences in mean fossil shell δ18O between sites but not among genera at a single location. Therefore, we group δ18O values from different genera together to map the spatial distribution of δ18O in shell carbonate. Shell δ18O values reflect the spatial variation in the isotopic composition of precipitation and incorporate the snails' preferential sampling of precipitation during the warm season. Modern shell δ18O decreases in Europe along a N–S gradient from the North Sea inland toward the Alps. Modern observed data of isotopes in precipitation (GNIP) demonstrate a similar trend for low-altitude sites. LGM shell δ18O data show a different gradient with δ18O declining toward the ENE, implying a mid-Atlantic source due to increased sea ice and a possible southern displacement of the westerly jet stream. Balkan LGM samples show the influence of a Mediterranean source, with δ18O values decreasing northward.

Changes of Ionic and Oxygen Isotopic Composition of the Snowpack at the Glacier Austre Okstindbreen, Norway, 1995

1998 ◽  
Vol 29 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Peter Raben ◽  
Wilfred H. Theakstone
Keyword(s):  
Isotopic Composition ◽  
Sea Level ◽  
Oxygen Isotopes ◽  
Oxygen Isotopic Composition ◽  
Isotopic Ratios ◽  
Vertical Variations ◽  
Oxygen Isotopic ◽  
The Difference ◽  
Liquid Precipitation ◽  
Different Altitudes

Marked vertical variations of ions and oxygen isotopes were present in the snowpack at the glacier Austre Okstindbreen during the pre-melting phase in 1995 at sites between 825 m and 1,470 m above sea level. As the first meltwater percolated from the top of the pack, ions were moved to a greater depth, but the isotopic composition remained relatively unchanged. Ions continued to move downwards through the pack during the melting phase, even when there was little surface melting and no addition of liquid precipitation. The at-a-depth correlation between ionic concentrations and isotopic ratios, strong in the pre-melting phase, weakened during melting. In August, concentrations of Na+ and Mg2+ ions in the residual pack were low and vertical variations were slight; 18O enrichment had occurred. The difference of the time at which melting of the snowpack starts at different altitudes influences the input of ions and isotopes to the underlying glacier.

scholarly journals δ2Hn-alkane and δ18Osugar biomarker proxies from leaves and topsoils of the Bale Mountains, Ethiopia, and implications for paleoclimate reconstructions

2021 ◽  
Author(s):  
Bruk Lemma ◽  
Lucas Bittner ◽  
Bruno Glaser ◽  
Seifu Kebede ◽  
Sileshi Nemomissa ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Leaf Growth ◽  
Thermal Conversion ◽  
Oxygen Isotopic Composition ◽  
Leaf Water ◽  
Isotope Ratio Mass Spectrometer ◽  
Oxygen Isotopic ◽  
Calibration Study ◽  
Microclimatic Conditions ◽  
Paleoclimate Reconstructions

AbstractThe hydrogen isotopic composition of leaf wax–derived n-alkane (δ2Hn-alkane) and oxygen isotopic composition of hemicellulose–derived sugar (δ18Osugar) biomarkers are valuable proxies for paleoclimate reconstructions. Here, we present a calibration study along the Bale Mountains in Ethiopia to evaluate how accurately and precisely the isotopic composition of precipitation is imprinted in these biomarkers. n-Alkanes and sugars were extracted from the leaf and topsoil samples and compound–specific δ2Hn-alkane and δ18Osugar values were measured using a gas chromatograph–thermal conversion–isotope ratio mass spectrometer (GC–TC–IRMS). The weighted mean δ2Hn-alkane and δ18Osugar values range from − 186 to − 89‰ and from + 27 to + 46‰, respectively. Degradation and root inputs did not appear to alter the isotopic composition of the biomarkers in the soil samples analyzed. Yet, the δ2Hn-alkane values show a statistically significant species dependence and δ18Osugar yielded the same species–dependent trends. The reconstructed leaf water of Erica arborea and Erica trimera is 2H– and 18O–enriched by + 55 ± 5 and + 9 ± 1‰, respectively, compared to precipitation. By contrast, Festuca abyssinica reveals the most negative δ2Hn-alkane and least positive δ18Osugar values. This can be attributed to “signal–dampening” caused by basal grass leaf growth. The intermediate values for Alchemilla haumannii and Helichrysum splendidum can be likely explained with plant physiological differences or microclimatic conditions affecting relative humidity (RH) and thus RH–dependent leaf water isotope enrichment. While the actual RH values range from 69 to 82% (x̄ = 80 ± 3.4%), the reconstructed RH values based on a recently suggested coupled δ2Hn-alkane –δ18Osugar (paleo–) hygrometer approach yielded a mean of 78 ± 21%. Our findings corroborate (i) that vegetation changes, particularly in terms of grass versus non–grassy vegetation, need to be considered in paleoclimate studies based on δ2Hn-alkane and δ18Osugar records and (ii) that the coupled δ2Hn-alkane –δ18Osugar (paleo–) hygrometer approach holds great potential for deriving additional paleoclimatic information compared to single isotope approaches.

Oxygen isotopic composition as an indicator of ruby and sapphire origin: A review of Russian occurrences

2015 ◽  
Vol 68 ◽  
pp. 164-170 ◽  
Author(s):  
S.V. Vysotskiy ◽  
V.P. Nechaev ◽  
A.Yu. Kissin ◽  
V.V. Yakovenko ◽  
A.V. Ignat'ev ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Oxygen Isotopic Composition ◽  
Oxygen Isotopic
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