Structures and isotopic fractionation factors of complexes AHA-1

1977 ◽  
Vol 99 (15) ◽  
pp. 5207-5209 ◽  
Author(s):  
Maurice M. Kreevoy ◽  
Tai-Ming Liang ◽  
Kwang-Chou Chang
Keyword(s):  
Isotopic Fractionation ◽  
Fractionation Factors

scholarly journals Significant Zr isotope variations in single zircon grains recording magma evolution history

2020 ◽  
Vol 117 (35) ◽  
pp. 21125-21131 ◽  
Author(s):  
Jing-Liang Guo ◽  
Zaicong Wang ◽  
Wen Zhang ◽  
Frédéric Moynier ◽  
Dandan Cui ◽  
...  
Keyword(s):  
Isotopic Fractionation ◽  
Major Type ◽  
Strong Temperature Dependence ◽  
Calc Alkaline ◽  
Southern Tibet ◽  
Rayleigh Distillation ◽  
Single Zircon ◽  
Magmatic History ◽  
Fractionation Factors

Zircons widely occur in magmatic rocks and often display internal zonation finely recording the magmatic history. Here, we presented in situ high-precision (2SD <0.15‰ for δ94Zr) and high–spatial-resolution (20 µm) stable Zr isotope compositions of magmatic zircons in a suite of calc-alkaline plutonic rocks from the juvenile part of the Gangdese arc, southern Tibet. These zircon grains are internally zoned with Zr isotopically light cores and increasingly heavier rims. Our data suggest the preferential incorporation of lighter Zr isotopes in zircon from the melt, which would drive the residual melt to heavier values. The Rayleigh distillation model can well explain the observed internal zoning in single zircon grains, and the best-fit models gave average zircon–melt fractionation factors for each sample ranging from 0.99955 to 0.99988. The average fractionation factors are positively correlated with the median Ti-in-zircon temperatures, indicating a strong temperature dependence of Zr isotopic fractionation. The results demonstrate that in situ Zr isotope analyses would be another powerful contribution to the geochemical toolbox related to zircon. The findings of this study solve the fundamental issue on how zircon fractionates Zr isotopes in calc-alkaline magmas, the major type of magmas that led to forming continental crust over time. The results also show the great potential of stable Zr isotopes in tracing magmatic thermal and chemical evolution and thus possibly continental crustal differentiation.

scholarly journals Dating of Groundwater Recharge in Two Small Adjacent Aquifers in Israel and Their Initial 14C Activities

Radiocarbon ◽  
2011 ◽  
Vol 53 (1) ◽  
pp. 137-149 ◽  
Author(s):  
J Guttman ◽  
J Kronfeld ◽  
I Carmi
Keyword(s):  
Groundwater Recharge ◽  
Unsaturated Zone ◽  
Hydraulic Properties ◽  
Isotopic Fractionation ◽  
Apparent Difference ◽  
Pleistocene Aquifer ◽  
Fractionation Factors

Radiocarbon and tritium determinations were carried out in 2 adjacent small aquifers in Israel. These aquifers have small storage capacities and good hydraulic properties. Darcy calculations suggest that the aquifers contain young waters, ≃50 yr in age. 14C concentrations in the Pleistocene aquifer are between 23–60 pMC, with the lowest activity related to contamination by petroleum-based fertilizers with no 14C. 14C concentrations in the Judea Group aquifer range from 62 to 95 pMC. An apparent difference of ≃1000 yr is indicated for the average recharge age between the 2 aquifers. The tritium data suggests that the water in both aquifers is quite young. The 1000-yr difference is an artifact of initial isotopic fractionation differences through the unsaturated zone as established elsewhere for these 2 aquifers. When these individual fractionation factors (0.54 for the Pleistocene and 0.62 for the Judea Group) are used, it is revealed that both aquifers contain young water, in agreement with the Darcy calculation, which was recharged at the beginning of the period of thermonuclear atmospheric testing in the early 1960s.

Experimental determinations of isotopic fractionation factors associated with N2O production and reduction during denitrification in soils

2014 ◽  
Vol 134 ◽  
pp. 55-73 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Reinhard Well ◽  
Jan Reent Köster ◽  
Roland Fuß ◽  
Mehmet Senbayram ◽  
...  
Keyword(s):  
Isotopic Fractionation ◽  
N2o Production ◽  
Factors Associated ◽  
Fractionation Factors

scholarly journals Hydrogen isotope fractionation in the photolysis of formaldehyde

2008 ◽  
Vol 8 (5) ◽  
pp. 1353-1366 ◽  
Author(s):  
T. S. Rhee ◽  
C. A. M. Brenninkmeijer ◽  
T. Röckmann
Keyword(s):  
Isotope Ratio ◽  
Isotope Fractionation ◽  
Isotopic Fractionation ◽  
Photochemical Oxidation ◽  
Atmospheric Conditions ◽  
Isotopic Enrichment ◽  
Fractionation Factor ◽  
Removal Processes ◽  
Molecular Channel ◽  
Fractionation Factors

Abstract. Experiments investigating the isotopic fractionation in the formation of H2 by the photolysis of CH2O under tropospheric conditions are reported and discussed. The deuterium (D) depletion in the H2 produced is 500(±20)‰ with respect to the parent CH2O. We also observed that complete photolysis of CH2O under atmospheric conditions produces H2 that has virtually the same isotope ratio as that of the parent CH2O. These findings imply that there must be a very strong concomitant isotopic enrichment in the radical channel (CH2O+hν → CHO+H) as compared to the molecular channel (CH2O+hν → H2+CO) of the photolysis of CH2O in order to balance the relatively small isotopic fractionation in the competing reaction of CH2O with OH. Using a 1-box photochemistry model we calculated the isotopic fractionation factor for the radical channel to be 0.22(±0.08), which is equivalent to a 780(±80)‰ enrichment in D of the remaining CH2O. When CH2O is in photochemical steady state, the isotope ratio of the H2 produced is determined not only by the isotopic fractionation occurring during the photolytical production of H2 (αm) but also by overall fractionation for the removal processes of CH2O (αf), and is represented by the ratio of αm/αf. Applying the isotopic fractionation factors relevant to CH2O photolysis obtained in the present study to the troposphere, the ratio of αm/αf varies from ~0.8 to ~1.2 depending on the fraction of CH2O that reacts with OH and that produces H2. This range of αm/αf can render the H2 produced from the photochemical oxidation of CH4 to be enriched in D (with respect to the original CH4) by the factor of 1.2–1.3 as anticipated in the literature.

Sulfur Isotope Partitioning in Metallic Sulfide Systems

1971 ◽  
Vol 8 (11) ◽  
pp. 1397-1408 ◽  
Author(s):  
Y. Kajiwara ◽  
H. R. Krouse
Keyword(s):  
Sulfur Isotope ◽  
Equilibrium Constants ◽  
Isotopic Fractionation ◽  
Exchange Constant ◽  
Equilibrium Exchange ◽  
Direct Measurements ◽  
Theoretical Predictions ◽  
Mineral Pair ◽  
Isotope Partitioning ◽  
Fractionation Factors

Sulfur isotopic fractionation factors involving pairs of pyrite, pyrrhotite, sphalerite, chalcopyrite, and galena have been determined experimentally over the temperature range 250 °C to 600 °C.Since chalcopyrite and pyrrhotite are not stable at higher PS2 conditions, buffer assemblages were necessary to control PS2 in experiments with these minerals. Since low PS2 values and low temperatures are unfavorable to rapid isotope exchange, techniques were devised whereby equilibrium constants could be estimated indirectly in systems where direct measurements are not possible because of the time factor.Current data place the sulfide minerals in the following order of 34S enrichment under equilibrium exchange conditions: pyrite > (pyrrhotite [Formula: see text]sphalerite) > chalcopyrite > galena in agreement with theoretical predictions. In agreement with theory the equilibrium exchange constant K for a given mineral pair depends upon temperature as follows: 1000 ln [Formula: see text], where A denotes a constant. The A values for various mineral pairs have been determined with ± 10% uncertainties as follows: 11.0 × 105 (py–gn), 8.0 × 105 (sp–gn), 6.5 × 105 (cp–gn), 4.5 × 105 (py–cp), 3.0 × 105 (py–sp, py–po), 1.5 × 105 (sp–cp, po–cp), and [Formula: see text] 0 (sp–po).

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