Stable isotopic evidence for large-scale seawater infiltration in a regional metamorphic terrane; the Trois Seigneurs Massif, Pyrenees, France

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Authors:Wickham, S. M.; Taylor, H. P.
Author Affiliations:Primary:
Calif. Inst. Technol., Div. Geol. Planet. Sci., Pasadena, CA 91125, United States
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 91(2), p.122-137. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1985
Note:In English. 57 refs.; illus. incl. 1 table, geol. sketch maps, sect.
Summary:Oxygen isotope analyses of 95 metamorphic and igneous rocks and minerals from a Hercynian metamorphic sequence in the massif indicate that all lithologies at higher metamorphic grades than the 'andalusite-in' isograd have relatively homogeneous delta 18O values. The extent of homogenization is shown by the similarity of delta 18O values in metacarbonates, metapelites and granitic rocks, and by the narrow range of oxygen isotope composition shown by quartz from these lithologies. These values contrast with the delta 18O values of metapelites of lower metamorphic grade. Homogenization was caused by a pervasive influx of hydrous fluid, probably high-level ground-waters or connate formation water. Hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at delta D = -25 to -30, suggesting a sea-water origin. Petrological evidence suggests that metamorphism and anatexis of pelitic metasediment occurred at depths of 6-12 km in the presence of this water-rich fluid, the composition of which was externally buffered. Deep penetration of surface waters in such environments may be a key factor in promoting major anatexis of continental crust at shallow depth. Three types of granitic rock are exposed in the area: leucogranites and biotite granite-quartz diorite were both derived from fusion of local Palaeozoic pelitic metasediment, whereas post-metamorphic biotite granodiorite was probably derived from a deeper level in the crust. Rare mafic xenoliths within the deeper parts of the biotite granite-quartz diorite possibly represent input of mantle-derived magma, which may have provided heat for the metamorphism. [P.Br.]
Subjects:D/H; Deuterium; Geochemistry; Glacial geology; Hydrogen; Igneous rocks; Infiltration; Isotopes; Mass balance; Metamorphic rocks; Mica group; Muscovite; O-18/O-16; Oxygen; Petrology; Sea water; Sheet silicates; Silicates; Stable isotopes; Surveys; Ariege France; Europe; France; French Pyrenees; Pyrenees; Western Europe; Metamorphic terranes
Abstract Numbers:86M/3351
Record ID:1987017662
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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