The role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism

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doi: 10.1007/s004100050426
Authors:Wada, Hideki; Ando, Takamaru; Suzuki, Masayuki
Author Affiliations:Primary:
Shizuoka University, Department of Biology and Geosciences, Shizuoka, Japan
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 132(4), p.309-320. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1998
Note:In English. 66 refs.; illus., incl. 2 tables, geol. sketch map
Summary:Carbon and O isotopic profiles, around a low-P metasomatic wollastonite reaction front in a calcite marble of the Hida metamorphic terrain, central Japan, display typical metamorphic fluid-enhanced isotopic zoning, probably resulting from diffusion-enhanced isotopic exchange. Behaviour of C and O isotopes in grain boundaries is remarkably different, the commonly occurring O isotopic troughs (18O depleted rims) around calcite grain boundaries demonstrating that diffusion of O in grain boundaries dominates over lattice diffusion in calcite. Conversely, there are no differences between C isotopic profiles obtained from grain cores and rims, and hence the grain boundary has no specific role in the diffusion of carbonic species in the metamorphic fluid during transportation, species such as CO2 and CO3 ions migrating mainly through lattice diffusion. The C and O isotope profiles may be modelled by diffusion into a semi-infinite medium. Empirically, lattice diffusion of O isotopes is ∼ six times faster than for C isotopes, and O grain boundary diffusion is ten times faster than O lattice diffusion. O isotope values from around the wollastonite vein indicate that migration of metamorphic fluid into calcite marble was small, and parallel to the aquifer. The stability of wollastonite, and attainment of O isotopic equilibrium, suggest that diffusion of O occurred through an aqueous fluid phase. Using the experimentally-determined diffusion constant, the calculated time for formation of the O isotope profile around the wollastonite vein is ∼ 0.76 × 106 y. [J.F.]
Sections:Geochemistry
Subsections:Metamorphic rocks
Subjects:C-14; Calcite; Carbon; Carbonates; Chain silicates; Chemical reactions; Contact metamorphism; Diffusion; Equilibrium; Geochemistry; Grain boundaries; Isotopes; Lattice parameters; Marbles; Metamorphic rocks; Metamorphism; Metasomatism; O-18; Oxygen; Radioactive isotopes; Silicates; Stable isotopes; Wollastonite; Wollastonite group; Asia; Far East; Hida metamorphic belt; Honshu; Japan
Coordinates:N361000 N365000 E1374500 E1371000
Abstract Numbers:99M/1802
Record ID:1999057584
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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