Search USGSSearch

USGS · 70013811

Normalization of oxygen and hydrogen isotope data

Abstract

To resolve confusion due to expression of isotopic data from different laboratories on non-corresponding scales, oxygen isotope analyses of all substances can be expressed relative to VSMOW or VPDB (Vienna Peedee belemnite) on scales normalized such that the δ 18 O of SLAP is −55.5% relative to VSMOW. H 3 + contribution in hydrogen isotope ratio analysis can be easily determined using two gaseous reference samples that differ greatly in deuterium content.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

T.B. Coplen. 1988. Normalization of oxygen and hydrogen isotope data. https://doi.org/10.1016/0168-9622(88)90042-5

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

Resetting of RbSr ages of volcanic rocks by low-grade burial metamorphism

We report a nine-point RbSr whole-rock isochron age of 70±3 Ma (MSWD 3.97) for Mid-Jurassic volcanic rocks. The same rocks have also been dated by the UThPb method on zircon, giving a crystallization age of 166 ± 11 Ma, over twice as old as the RbSr age. The data demonstrate that whole-rock RbSr ages of volcanic rocks, even lava flows with SiO 2 content as low as 57 wt.%, are susceptible to complete resetting. The rocks range in composition from rhyodacite tuffs to andesite lavas. The complete breakdown of all major minerals that contain Rb and Sr resulted in an alteration mineral assemblage consisting of phengite, albite, secondary quartz, and minor amounts of chlorite and epidote. Phengite is the K-bearing product of the breakdown of biotite and K-feldspar. Pressure during low-grade metamorphism of the volcanic rocks, estimated from phengite composition to have been in the range of 4 to 6 kbar, points to thrust-related burial as the main cause of resetting. Consequently, such reset isochrons may date large-scale events such as regional thrusting and metamorphism. The coherent resetting of the RbSr isochron suggests large-scale pervasive fluid movement during thrust-related burial metamorphism.

Chemical Geology: Isotope Geoscience Section

Caution on the use of Viton® or FETFE® O-rings in carbon dioxide sample containers for δ 18 0 analysis

After 10 days, 3-&mu;mol CO 2 samples in containers having glass stopcocks with Viton &reg; or FETFE O-rings were enriched in 18 O by 1.5% as a result of absorption by the elastomer; this amount of enrichment is &sim;20 times greater than the precision of &delta; 18 O measurements of most laboratories. No change in 13 C content was observed. Increasing the sample size to 100 &mu;mol resulted in an 18 O enrichment of 0.2% and did not affect the 13 C content. Caution needs to be exercised in selecting sample containers for CO 2 isotope-ratio samples of < 200 &mu;mol. If stopcocks are used in construction of containers for such samples, the use of all-glass stopcocks with Apiezon N &reg; hydrocarbon-based grease will eliminate the fractionation of oxygen isotopes.

Chemical Geology: Isotope Geoscience Section

UPb ages of zircon rims: A new analytical method using the air-abrasion technique

We present a new technique for directly dating, by conventional techniques, the rims of zircons. Several circumstances, such as a xenocrystic or inherited component in igneous zircon and metamorphic overgrowths on igneous cores, can result in grains with physically distinct age components. Pneumatic abrasion has been previously shown by Krogh to remove overgrowths and damaged areas of zircon, leaving more resistant and isotopically less disturbed parts available for analysis. A new abrader design, which is capable of very gently grinding only tips and interfacial edges of even needle-like grains, permits easy collection of abraded material for dating. Five examples demonstrate the utility of the “dust-collecting” technique, including two studies that compare conventional, ion microprobe and abrader data. Common Pb may be strongly concentrated in the outermost zones of many zircons and this Pb is not easily removed by leaching (even in weak HF). Thus, the benefit of removing only the outermost zones (and avoiding mixing of age components) is somewhat compromised by the much higher common Pb contents which result in less precise age determinations. A very brief abrasion to remove the high common Pb zones prior to collection of material for dating is selected.

Chemical Geology: Isotope Geoscience Section