Slow oxygen diffusion rates in igneous zircons from metamorphic rocks
-
William H. Peck
,
John W. Valley
Abstract
Empirical tests of oxygen exchange rate in zircon crystals from amphibolite- and granulite-facies metamorphic rocks of the Grenville Province demonstrate preservation of igneous δ18O through protracted igneous and metamorphic histories, forming the basis of quantitative estimates of diffusion rate. Granitic orthogneisses, which cooled slowly after granulite-facies metamorphism, show no consistent relationship between zircon size and δ18O, indicating slow oxygen diffusion. Detrital zircon crystals from granulite-facies quartzites are out of equilibrium with their host rocks, and no consistent correlation is seen between δ18O and grain size in high-precision analyses by laser fluorination of multiple grains, sieved for size. In a single sample, individual detrital zircon crystals preserve grain-to-grain variability in δ18O (determined by ion microprobe), ranging from 5.0 to 9.5‰. The inherited cores of some zircon crystals are up to 5.6‰ lower than igneous overgrowths, showing that gradients of 5.6‰ can be preserved over 50 mm even at magmatic conditions. All of these lines of evidence show that oxygen diffusion in zircon in these rocks was slow both during metamorphism and during slow cooling of 1-3 °/m.y. Calculations based on the measurements indicate that the oxygen diffusion rate in zircon (D) must be ≥ 10-22 cm2/s at 600 °C to explain δ18O(zircon) values measured from Grenville quartzite and orthogneiss. This value is consistent with the experimentally determined value of D = 2 × 10-27 cm2/s for dry diffusion experiments extrapolated to 600 °C (Watson and Cherniak 1997). These results indicate that oxygen-isotope analysis of zircon may be used to see through granulite-facies metamorphism and anatexis, and to unravel crustal recycling processes in igneous rocks.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Bonding preferences of non-bridging O atoms: Evidence from 17O MAS and 3QMAS NMR on calcium aluminate and low-silica Ca-aluminosilicate glasses
- BNa–BLi solid-solution in A-site-vacant amphiboles: synthesis and cation ordering along the ferri-clinoferroholmquistite–riebeckite join
- A new uranyl carbonate sheet in the crystal structure of fontanite, Ca[(UO2)3(CO3)2O2](H2O)6
- XANES calibrations for the oxidation state of iron in a silicate glass
- Dissolution of strontianite at high P-T conditions: An in-situ synchrotron X-ray fluorescence study
- Intergrown niobian rutile phases with Sc- and W-rich ferrocolumbite: An electron-microprobe and Rietveld study
- Bulk moduli and high-pressure crystal structures of minium, Pb3O4, determined by X-ray powder diffraction
- Slow oxygen diffusion rates in igneous zircons from metamorphic rocks
- Chemistry of grain boundaries in mantle rocks
- Heats of mixing of silicate liquid in the systems diopside-anorthite-akermanite, diopside-anorthite-forsterite, and diopside-silica
- High-pressure crystal structure of kosmochlor, NaCrSi2O6, and systematics of anisotropic compression in pyroxenes
- Monte Carlo simulations of ordering of Al, Fe, and Mg cations in the octahedral sheet of smectites and illites
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- Hydrogen-bonded water in laumontite II: Experimental determination of site-specific thermodynamic properties of hydration of the W1 and W5 sites
- High P-T phase relations and stability of a (21)-hydrous clinopyribole in the system K2ONa2O- CaO-MgO-Al2O3-SiO2-H2O: An experimental study to 18 GPa
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- Partitioning of Sr, Ba, Rb, Y, and LREE between plagioclase and peraluminous silicic magma
- Infrared and TEM characterization of amphiboles synthesized near the tremolite-pargasite join in the ternary system tremolite-pargasite-cummingtonite
- Coupling between non-convergent ordering and transition temperature in the C2/c ↔ P21/c phase transition in pigeonite
- 57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part I. Paramagnetic spectra of magnesian hedenbergite
- 57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part II. Magnetic spectra of magnesian hedenbergite
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