Experimental calibration of silicon and oxygen isotope fractionations between quartz and water at 250°C by in situ microanalysis of experimental products and application to zoned low δ<sup>30</sup>Si quartz overgrowths [electronic resource].
- Washington, D.C. : United States. Dept. of Energy. Office of Basic Energy Sciences, 2015.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy
- Physical Description:
- pages 127-142 : digital, PDF file
- Additional Creators:
- Los Alamos National Laboratory
United States. Department of Energy. Office of Basic Energy Sciences
United States. Department of Energy. Office of Scientific and Technical Information
- The interpretation of silicon isotope data for quartz is hampered by the lack of experimentally determined fractionation factors between quartz and fluid. Further, there is a large spread in published oxygen isotope fractionation factors at low temperatures, primarily due to extrapolation from experimental calibrations at high temperature. We report the first measurements of silicon isotope ratios from experimentally precipitated quartz and estimate the equilibrium fractionation vs. dissolved silica using a novel in situ analysis technique applying secondary ion mass spectrometry to directly analyze experimental products. These experiments also yield a new value for oxygen isotope fractionation. Quartz overgrowths up to 235 μm thick were precipitated in silica–H<sub>2</sub>O–NaOH–NaCl fluids, at pH 12–13 and 250 °C. At this temperature, 1000lnα<sup>30</sup>Si(Qtz–fluid) = 0.55 ± 0.10‰ and 1000lnα<sup>18</sup>O(Qtz–fluid) = 10.62 ± 0.13‰, yielding the relations 1000lnα<sup>30</sup>Si(Qtz–fluid) = (0.15 ± 0.03) * 10<sup>6</sup>/T<sup>2</sup> and 1000lnα<sup>18</sup>O(Qtz–fluid) = (2.91 ± 0.04) * 10<sup>6</sup>/T<sup>2</sup> when extended to zero fractionation at infinite temperature. Values of δ<sup>30</sup>Si(Qtz) from diagenetic cement in sandstones from the basal Cambrian Mt. Simon Formation in central North America range from 0 to −5.4‰. Paired δ<sup>18</sup>O and δ<sup>30</sup>Si values from individual overgrowths preserve a record of Precambrian weathering and fluid transport. In conclusion, the application of the experimental quartz growth results to observations from natural sandstone samples suggests that precipitation of quartz at low temperatures in nature is dominated by kinetic, rather than equilibrium, processes.
- Published through SciTech Connect.
Chemical Geology 421 C ISSN 0009-2541 AM
Anthony D. Pollington; Reinhard Kozdon; Lawrence M. Anovitz; R. Bastian Georg; Michael J. Spicuzza; John W. Valley.
- Funding Information:
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