GEOSCAN, résultats de la recherche


TitreThe effect of diagenesis and fluid migration on rare earth element distribution in pore fluids of the northern Cascadia accretionary margin
AuteurKim, J -H; Torres, M E; Haley, B A; Kastner, M; Pohlman, J W; Riedel, M; Lee, Y -J
SourceChemical Geology vol. 291, 2012 p. 152-165, (Accès ouvert)
Séries alt.Secteur des sciences de la Terre, Contribution externe 20110042
ÉditeurElsevier BV
Documentpublication en série
Mediapapier; en ligne; numérique
ProvinceRégion extracotière de l'ouest
Lat/Long OENS-128.0000 -123.0000 50.2500 48.0000
Sujetsmarges continentales; migration des fluides; migration des hydrocarbures; capacité de production d'hydrocarbures; terres rares; échantillons d'eau interstitielle; fluides des pores; combustibles fossiles; géologie marine
Illustrationslocation maps; tables; plots; cross-sections
ProgrammeHydrates de gaz, Caractérisation des Hydrates de gaz
Résumé(disponible en anglais seulement)
Analytical challenges in obtaining high quality measurements of rare earth elements (REEs) from small pore fluid volumes have limited the application of REEs as deep fluid geochemical tracers. Using a recently developed analytical technique, we analyzed REEs from pore fluids collected from Sites U1325 and U1329, drilled on the northern Cascadia margin during the Integrated Ocean Drilling Program (IODP) Expedition 311, to investigate the REE behavior during diagenesis and their utility as tracers of deep fluid migration. These sites were selected because they represent contrasting settings on an accretionary margin: a ponded basin at the toe of the margin, and the landward Tofino Basin near the shelf's edge. REE concentrations of pore fluid in the methanogenic zone at Sites U1325 and U1329 correlate positively with concentrations of dissolved organic carbon (DOC) and alkalinity. Fractionations across the REE series are driven by preferential complexation of the heavy REEs. Simultaneous enrichment of diagenetic indicators (DOC and alkalinity) and of REEs (in particular the heavy elements Ho to Lu), suggests that the heavy REEs are released during particulate organic carbon (POC) degradation and are subsequently chelated by DOC. REE concentrations are greater at Site U1325, a site where shorter residence times of POC in sulfate-bearing redox zones may enhance REE burial efficiency within sulfidic and methanogenic sediment zones where REE release ensues.
Cross-plots of La concentrations versus Cl, Li and Sr delineate a distinct field for the deep fluids (z > 75 mbsf) at Site U1329, and indicate the presence of a fluid not observed at the other sites drilled on the Cascadia margin. Changes in REE patterns, the presence of a positive Eu anomaly, and other available geochemical data for this site suggest a complex hydrology and possible interaction with the igneous Crescent Terrane, located east of the drilled transect.