Physicochemical conditions and timing of rodingite formation: evidence from rodingite-hosted fluid inclusions in the JM Asbestos mine, Asbestos, Québec

Charles Normand¹ and Anthony E Williams-Jones²

¹Département des Sciences de la Terre et de l'Atmosphère, Université du Québec à Montréal, Case postale 8888, Succursale Centre-ville, Montréal (Québec) H3C 3P8 Canada

²Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal (Québec) H3A 2A7 Canada

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Geochemical Transactions 2007, 8:11doi:10.1186/1467-4866-8-11


Published:	25 October 2007

Abstract

Fluid inclusions and geological relationships indicate that rodingite formation in the Asbestos ophiolite, Québec, occurred in two, or possibly three, separate episodes during thrusting of the ophiolite onto the Laurentian margin, and that it involved three fluids. The first episode of rodingitization, which affected diorite, occurred at temperatures of between 290 and 360°C and pressures of 2.5 to 4.5 kbar, and the second episode, which affected granite and slate, occurred at temperatures of between 325 and 400°C and pressures less than 3 kbar. The fluids responsible for these episodes of alteration were moderately to strongly saline (~1.5 to 6.3 m eq. NaCl), rich in divalent cations and contained appreciable methane. A possible third episode of alteration is suggested by primary fluid inclusions in vesuvianite-rich bodies and secondary inclusions in other types of rodingite, with significantly lower trapping temperatures, salinity and methane content. The association of the aqueous fluids with hydrocarbon-rich fluids containing CH₄and higher order alkanes, but no CO₂, suggests strongly that the former originated from the serpentinites. The similarities in the composition of the fluids in all rock types indicate that the ophiolite had already been thrust onto the slates when rodingitization occurred.