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Journal of the Geological Society; 2006; v. 163; issue.5; p. 827-836;
DOI: 10.1144/0016-76492005-075
© 2006 Geological Society of London

Original Article

Stable isotope transfer in open and closed system across chemically contrasted boundaries: metacarbonate–granitoid contacts in the Quérigut magmatic complex (Eastern Pyrenees, France)

Cyril DurandD1, Philippe Boulvais2, Didier Marquer1 & Michel Rossy1

1 1Département de Géosciences, EA 2642, Université de Franche-Comté, 16 Route de Gray, 25030 Besançon, France (e-mail: cyril.durand@univ-fcomte.fr)
2 2Géosciences, UMR 6118, Université Rennes 1, Campus de Beaulieu, 35042 Rennes cedex, France

The processes of stable isotope transfer between chemically contrasted boundaries are examined for two metacarbonate–granitoid contacts in the Quérigut complex, Pyrénées, France. External contacts, between the sedimentary basement and granitic intrusions, behaved like a fluid-dominated open system whereas septa contacts, between carbonate septa and the host granitoids, behaved like a closed system with respect to external fluids. Along external contacts, skarns of several decimetres to several metres were developed. {delta}18O values of calcite, buffered at 13.5–14{per thousand}, suggest an advection of metamorphic aqueous fluid with a minor contribution of low {delta}13C CO2 during skarn formation. Internal contacts are characterized by a thin centimetre-sized skarn layer. {delta}13C and {delta}18O values of calcite follow an evolution explained by decarbonation processes alone. {delta}18O exchange profiles across the contact show a typical diffusion profile with their inflection points slightly displaced towards the metacarbonate side, interpreted as a limited influx of magmatic fluids. Moreover, the shape of septa profiles varies according to the thermal energy budget induced by the intrusive rock: more isotopic alteration appears where the intrusion size is larger.