Timescales and mechanisms of fluid infiltration in a marble; an ion microprobe study

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doi: 10.1007/s004100050430
Authors:Graham, Colin M.; Valley, John W.; Eiler, John M.; Wada, Hideki
Author Affiliations:Primary:
University of Edinburgh, Department of Geology and Geophysics, Edinburgh, United Kingdom
Other:
University of Wisconsin, United States
California Institute of Technology, United States
Shizuoka University, Japan
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 132(4), p.371-389. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1998
Note:In English. 59 refs.; 3 tables, geol. sketch map
Summary:To constrain scales of O isotope equilibrium, timescales and mechanisms of metamorphic fluid infiltration, and fluid sources and pathways, a detailed O isotope map of calcite grain in a coarse-grained marble was constructed. The marble, from the high-T-low-P Hida metamorphic belt, underwent granulite-facies then amphibolite-facies metamorphic events, the latter associated with regional granite intrusion. CL imaging indicates two types of calcite: yellow- (YLC) and purple-luminescing (PLC). The YLC, which occupies grain boundaries, fractures, replacement patches, and most of the abundant deformation twin lamellae, post-dates the dominant PLC, and maps out fluid pathways, is enriched in Mn and Fe, depleted in 18O and Sr compared with PLC, and is more 18O-depleted than is indicated from conventional analyses. Results indicate infiltration of 18O-depleted (metamorphic or magmatic) fluid (initial δ 18O = 9-10.50/00) along grain boundaries, fractures and deformation twin lamellae, depleting calcite grains in Sr and enriching them in Mn and Fe. Areas of PLC unaffected by 'short-circuiting' fluid pathways, contain O diffusion profiles of ∼ 10 0/00/200 µm in grain boundary regions or adjacent to fractures or patches. Correcting for estimated grain boundary/fracture and profile orientation in 3-D, produces profiles which when modelled give consistent estimates of Dt of 0.8 × 10-8 m2, from which times of ∼ 103-104 y. are obtained for fluid transport along grain boundaries; implying much higher rock permeabilities during fluid flow than those calculated from time-integrated fluid fluxes or predicted from laboratory measurements. It is likely that preservation of 18O/16O profiles requires loss of grain boundary fluid during a period of dry cooling following fluid passage. δ 18O-trace-element correlations are also consistent with volume diffusion-controlled transport in the PLC. Fluid transport and element exchange occurred by two interrelated mechanisms over short timescales, and different lengthscales-long-distance flow along cracks, grain boundaries and twin lamellae, and ∼ 200 µm-scale volume diffusion of O. [J.F.]
Sections:Geochemistry
Subsections:Metamorphic rocks
Subjects:Amphibolites; Calcite; Carbonates; Cathodoluminescence; Coarse-grained materials; Facies; Fluid phase; Granulites; Imagery; Infiltration; Ion probe data; Isotope ratios; Isotopes; Marbles; Mass spectra; Mechanism; Metamorphic rocks; O-18/O-16; Oxygen; Permeability; Spectra; Stable isotopes; Time scales; Trace elements; Asia; Far East; Hida metamorphic belt; Honshu; Japan
Coordinates:N354500 N374500 E1380000 E1354500
Abstract Numbers:99M/1803
Record ID:1999057588
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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