georefid:2001-000789georefid:2001-000779SEDIS Publication Catalogue

ana.macario@awi.de

http://sedis.iodp.org/pub-catalogue/informationpointOfContact2011-06-23T00:00:00Zhttp://sedis.iodp.org/pub-catalogue/index.php?id=10.2973/odp.proc.sr.168.006.20002000-01-01publicationgeorefid:2001-000789doi:10.2973/odp.proc.sr.168.006.2000Marescotti, PietroUniversita di Genova, Dipartimento per lo Studio del Territorio a delle sue Risorse, Genoa, ItalyauthorVanko, David A.Geological Survey of Canada, CanadaauthorCabella, RobertoOcean Drilling Program, United StatesauthorTexas A & M University, Ocean Drilling Program, College Station, TX, United StatespublisherdocumentDigitalIn: Fisher, Andrew T., Davis, Earl E., Firth, John V., Andersson, Eva M., Aoike, Kan, Becker, Keir, Brown, Kimberly A., Buatier, Martine D., Constantin, Marc, Elderfield, Henry, Goncalves, Carlos A., Grigel, Jens S., Hunter, Arlene G., Inoue, Atsuyuki, Lawrence, Roisin M., Macdonald, Robert D., Marescotti, Pietro, Martin, Jeffrey T., Monnin, Christophe, Mottl, Michael J., Pribnow, Daniel F. C., Stein, Joshua S., Su, Xin, Sun, Yue-Feng, Underwood, Michael B., Vanko, David A., Wheat, C. Geoffrey, Miller, Christine M. (editor), Peters, Lorri L. (editor), Proceedings of the Ocean Drilling Program, scientific results, hydrothermal circulation in the oceanic crust, eastern flank of the Juan de Fuca Ridge; covering Leg 168 of the cruises of the drilling vessel JOIDES Resolution, San Francisco, California, to Victoria, British Columbia, sites 1023-1032, 20 June-15 August 1996168119-136With this study, we investigate the mineralogical variations associated with the low-temperature (<100 degrees C) alteration of normal tholeiitic pillow basalts varying in age from 0.8 to 3.5 Ma. Their alteration intensity varies systematically and is related to several factors, including (1) the aging of the igneous crust, (2) the increase of temperatures from the younger to the older sites, measured at the sediment/basement interface, (3) the local and regional variations in lithology and primary porosity, and (4) the degree of pillow fracturing. Fractures represent the most important pathways that allow significant penetration of fluids into the rock and are virtually the only factor controlling the alteration of the glassy rim and the early stages of pillow alteration. Three different alteration stages have been recognized: alteration of glassy margin, oxidizing alteration through fluid circulation in fracture systems, and reducing alteration through diffusion. All the observed mineralogical and chemical variations occurring during the early stages of alteration are interpreted as the result of the rock interaction with "normal," alkaline, and oxidizing seawater, along preferential pathways represented by the concentric and radial crack systems. The chemical composition of the fluid progressively evolves while moving into the basalt, leading to a reducing alteration stage, which is initially responsible for the precipitation of Fe-rich saponite and minor sulfides and subsequently for the widespread formation of carbonates. At the same time, the system evolved from being "water dominated" to being "rock dominated." No alteration effects in pillow basalts were observed that must have occurred at temperatures higher than those measured during Leg 168 at the basement/sediment interface (e.g., between 15 degrees and 64 degrees C).completedIgneous and metamorphic petrologyalterationbasaltscrustEast Pacificgeochemistryhydrothermal alterationigneous rocksJuan de Fuca RidgelavaLeg 168low temperaturemetasomatismmineral compositionNorth PacificNortheast PacificOcean Drilling Programoceanic crustoxidationPacific Oceanpillow lavapillow structureporosityreductionsea watersecondary mineralsspectratemperaturetholeiitic basaltvariationsvolcanic rockswater-rock interactionX-ray diffraction dataX-ray fluorescence spectraurn:org.iodp:exp:168urnlargerWorkCitationcampaignEnglishgeoscientificInformation-129.0000-127.300047.450048.0000application/pdfunknownSEDIS Publication Catalogue

ana.macario@awi.de

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