Lyell Collection
Geological Society, London, Special Publications
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Giguère, E.
Right arrow Articles by Berclaz, A.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Geological Society, London, Special Publications; 2003; v. 218; p. 369-400;
DOI: 10.1144/GSL.SP.2003.218.01.19
© 2003 Geological Society of London

Hydrothermal and Biogenic Alteration of Oceanic Crust as Recorded in Ophiolites

Hydrothermal circulation and metamorphism in crustal gabbroic rocks of the Bay of Islands ophiolite complex, Newfoundland, Canada: evidence from mineral and oxygen isotope geochemistry

E. Giguère1, R. Hébert1, G. Beaudoin1, J. H. Bédard2 & A. Berclaz3

1 Département de Géologie et de Génie Géologique, Université Laval, Sainte-Foy, Québec, Canada G1K 7P4 hebert{at}ggl.ulaval.ca
2 Commission Géologique du Canada, Centre Géoscientifique de Québec, 880 Chemin Sainte-Foy, bureau 840, Québec, Québec, Canada G1S 2L2
3 Ministère des Ressources naturelles du Québec, 545 boul. Crémazie E, b.1110, Montréal, Québec, Canada H2M 2V1

The gabbroic crust of the Ordovician Bay of Islands ophiolite complex formed in an island-arc setting near the North American continental margin. Detailed structural studies on the North Arm Mountain massif provide us with a scheme of syn-oceanic deformation events recorded in the crust. During a first transtensional stage, which generated gabbroic rocks, sheeted dykes and lavas, the temperature of formation of amphiboles in the gabbroic unit fell with time in three steps from 880–745 °C, to 790–680 °C and to 550–500 °C. The Ti, Na and AlIV contents of amphiboles decreased, whereas the Si activity of the fluid increased with time. The first amphibole to form has typical mid-ocean ridge basalt {delta}18OVSMOW indicating equilibration with a magmatic fluid or evolved seawater at low fluid/rock ratio. Lower {delta}18O values for some amphiboles (0–2.5{per thousand}) indicate the circulation of large volumes of seawater. The lowest {delta}18O values are found in the inner part of the shear zones, which channelled deep infiltration of seawater into the gabbroic unit. During brittle deformation, infiltration of low-temperature seawater produced prehnite, carbonate and quartz veins, and plagioclase with high {delta}18O. This study documents that the hydration of ophiolitic crust in the Bay of Islands ophiolitic complex occurred mainly along pre-obduction oceanic structures in an intraoceanic setting.