georefid:2007-087743georefid:2007-087742SEDIS 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.209.001.20072007-01-01publicationgeorefid:2007-087743doi:10.2973/odp.proc.sr.209.001.2007Kelemen, Peter B.Woods Hole Oceanographic Institution, Woods Hole, MA, United StatesauthorKikawa, EiichiWoods Hole Oceanographic Institution, United StatesauthorMiller, D. JayOcean Drilling Program, United StatesauthorAbe, NatsueUniversity of Houston, United StatesauthorBach, WolfgangBritish Geological Survey, United KingdomauthorCarlson, Richard L.University of Wyoming, United StatesauthorCasey, John F.Lamont-Doherty Earth Observatory, United StatesauthorChambers, Lynne M.Australian National University, AustraliaauthorCheadle, MichaelUniversitat de Barcelona, SpainauthorCipriani, AnnaUniversidad de Granada, SpainauthorDick, Henry J. B.Scripps Institution of Oceanography, United StatesauthorFaul, UlrichUniversite de Montpellier II, FranceauthorGarces, MiguelOregon State University, United StatesauthorGarrido, Carlos J.U. S. Geological Survey, United StatesauthorGee, Jeffrey S.Open University, United KingdomauthorGodard, Marguerite M.Universitaet Bonn, Federal Republic of GermanyauthorGraham, David W.GeoForschungsZentrum Potsdam, Federal Republic of GermanyauthorGriffin, Dale W.Institut de Physique du Globe de Paris, FranceauthorHarvey, JasonNiigata University, JapanauthorIldefonse, BenoitJapan Marine Science and Technology Center, JapanauthorIturrino, Gerardo J.Ocean Drilling Program, United StatesauthorJosef, Jennifer A.University of Houston, United StatesauthorMeurer, William P.British Geological Survey, United KingdomauthorPaulick, HolgerUniversity of Wyoming, United StatesauthorRosner, MartinAustralian National University, AustraliaauthorSchroeder, TimothyUniversitat de Barcelona, SpainauthorSeyler, MoniqueUniversidad de Granada, SpainauthorTakazawa, EiichiScripps Institution of Oceanography, United StatesauthorTexas A&M University, Ocean Drilling Program, College Station, TX, United StatespublisherdocumentDigitalIn: Kikawa, Eiichi, Kelemen, Peter B., Miller, D. Jay, Abe, Natsue, Bach, Wolfgang, Carlson, Richard L., Casey, John F., Chambers, Lynne M., Cheadle, Michael, Cipriani, Anna, Dick, Henry J. B., Faul, Ulrich, Garces, Miguel, Garrido, Carlos J., Gee, Jeffrey S., Godard, Marguerite M., Graham, David W., Griffin, Dale W., Harvey, Jason, Ildefonse, Benoit, Iturrino, Gerardo J., Josef, Jennifer A., Meurer, William P., Paulick, Holger, Rosner, Martin, Schroeder, Timothy, Seyler, Monique, Takazawa, Eiichi, Proceedings of the Ocean Drilling Program; scientific results; drilling mantle peridotite along the Mid-Atlantic Ridge from 14 degrees to 16 degrees N; covering Leg 209 of the cruises of the drilling vessel JOIDES Resolution; Rio de Janeiro, Brazil, to St. George, Bermuda; Sites 1268-1275; 6 May-6 July 2003209This paper provides a summary of postcruise scientific results from Ocean Drilling Program (ODP) Leg 209 available to date, building upon shipboard observations and syntheses summarized in the Leg 209 Initial Results volume. During Leg 209, 19 holes were drilled at 8 sites along the Mid-Atlantic Ridge from 14 degrees 43' to 15 degrees 44'N, mainly in residual mantle peridotite intruded by gabbroic rocks, in order to understand the tectonic and structural processes responsible for formation of oceanic lithosphere with abundant residual peridotite exposed on the seafloor coupled with a relatively low proportion of volcanic rocks. Based on proportions of recovered lithologies, the entire area may be underlain by mantle peridotite with approximately 20%-40% gabbroic intrusions and impregnations. Impregnated peridotites with olivine + two pyroxenes + plagioclase + spinel that apparently formed in equilibrium probably record crystallization from primitive mid-ocean-ridge basalt at pressures of 0.5-0.6 GPa. Metamorphic equilibria record isobaric cooling to approximately 1100 degrees C at this pressure. Thus, the conductively cooled thermal boundary layer beneath the Mid-Atlantic Ridge in this region is >15 km thick. Combined crystallization and reaction with residual peridotite formed a series of impregnated peridotites recording increasing Na content at nearly constant Mg#; this process could explain some of the variation in fractionation-corrected Na (e.g., Na = 8.0) observed in mid-ocean-ridge basalts. Clinopyroxene textures and compositions record such impregnation processes, and they are particularly well documented for Site 1274. Other Leg 209 gabbroic rocks formed from extensive crystallization of highly evolved melts, indicating that a substantial proportion of melt entering the thermal boundary layer crystallizes entirely beneath the seafloor, with no volcanic equivalent. Alteration of peridotites occurred over a range of temperatures and is the result of three distinct processes: rock-dominated serpentinization with formation of brucite in olivine-rich lithologies, fluid-dominated serpentinization with formation of magnetite and no brucite, and fluid-dominated talc alteration with addition of SiO (super 2) as well as H (super 2) O and oxygen. The latter two processes also exhibit detectable trace element metasomatism that is distinct in its character from the igneous impregnation described in the previous paragraph. Microstructures show that most residual peridotites were not ductilely deformed at temperatures less than approximately 1200 degrees C. Structural and paleomagnetic data require tectonic rotations of relatively undeformed blocks; some rotations probably exceeded 60 degrees around nearly horizontal axes parallel to the rift axis. Rotations occurred along several generations of high-temperature mylonitic shear zones extending deeper than 15 km depth and numerous faults at lower temperature. Early formed shear zones and faults were passively rotated around later features; such a process could have produced low-angle fault surfaces without slip on low-angle faults. This region provides end-member examples of processes that are common at many or most slow-spreading ridges. Osmium isotope ratios indicate an ancient history of depletion for residual peridotites from the 14 degrees -16 degrees N region along the Mid-Atlantic Ridge. Though depleted Os isotope ratios in peridotite have been reported elsewhere along the global ridge system, the values from this region are among the most depleted. In general, Os isotope ratios from mid-ocean-ridge basalts are systematically more radiogenic than Os isotope ratios from ridge peridotite samples, suggesting a polygenetic heterogeneous source for mid-ocean-ridge basalts. Geochemical studies of zircons from Leg 209 gabbroic rocks and impregnated peridotites, together with other ridge and arc-related zircons, indicate that ridge zircons have systematically lower fractionation-corrected U and Th concentrations compared to arc zircons. This observation provides a tool for interpreting the tectonic provenance of ancient detrital zircons and indicates an arclike provenance for Hadean detrital zircons. Geobiological studies and aerobiological studies were also undertaken during Leg 209. The geobiological work found no measurable microbial enhancement of olivine dissolution rate, possibly because the samples from Leg 209 were sterile. The aerobiological study determined that dust from North Africa, collected from the derrick of the JOIDES Resolution during Leg 209, contains a variety of abundant microorganisms.completedIgneous and metamorphic petrologyIsotope geochemistryAtlantic Oceanboreholesboundary layerchemical ratiosconcentrationcorescrustgabbrosgeochemistrygeologic barometrygeologic thermometryhydrothermal alterationigneous rocksisotope ratiosisotopesleadLeg 209lithospheremantlemetalsmetamorphismmetasomatismMid-Atlantic Ridgemineral compositionnesosilicatesNorth AtlanticOcean Drilling Programoceanic crustODP Site 1268ODP Site 1269ODP Site 1270ODP Site 1271ODP Site 1272ODP Site 1273ODP Site 1274ODP Site 1275orthosilicatesOs-188/Os-187osmiumpaleomagnetismPb-206/Pb-204Pb-207/Pb-204peridotitespetrofabricspetrographypetrologyplatinum groupplutonic rockspreferred orientationradioactive isotopesrare earthssilicatesstable isotopesstructural analysistrace elementsultramaficszirconzircon groupurn:org.iodp:exp:209urnlargerWorkCitationcampaignurn:org.iodp:exp:209:site:1268urnlargerWorkCitationstudyurn:org.iodp:exp:209urnlargerWorkCitationcampaignurn:org.iodp:exp:209:site:1269urnlargerWorkCitationstudyurn:org.iodp:exp:209urnlargerWorkCitationcampaignurn:org.iodp:exp:209:site:1270urnlargerWorkCitationstudyurn:org.iodp:exp:209urnlargerWorkCitationcampaignurn:org.iodp:exp:209:site:1271urnlargerWorkCitationstudyurn:org.iodp:exp:209urnlargerWorkCitationcampaignurn:org.iodp:exp:209:site:1272urnlargerWorkCitationstudyurn:org.iodp:exp:209urnlargerWorkCitationcampaignurn:org.iodp:exp:209:site:1273urnlargerWorkCitationstudyurn:org.iodp:exp:209urnlargerWorkCitationcampaignurn:org.iodp:exp:209:site:1274urnlargerWorkCitationstudyurn:org.iodp:exp:209urnlargerWorkCitationcampaignurn:org.iodp:exp:209:site:1275urnlargerWorkCitationstudyurn:org.iodp:exp:209urnlargerWorkCitationcampaignEnglishgeoscientificInformation-47.0000-44.300014.400015.4500application/pdfunknownSEDIS Publication Catalogue

ana.macario@awi.de

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