Berndt, Christian

Brückmann, Warner

Hensen, Christian

Klaeschen, Dirk

Planert, Lars

English

OceanRep

Planert, L., Kläschen, D., Berndt, C., Brückmann, W., Hensen, C. (Kiel, IFM-GEOMAR)Drilling into dewatering sites along the Costa Rica margin (IODP pro-posal 633): first results from pre-site survey seismic data evaluationE-Mail: lplanert@ifm-geomar.deIODP drilling proposal 633 (Costa Rica Mud Mounds) aims to enhance thegeneral understanding of complex forearc dewatering processes of the erosive sub-duction system off Costa Rica. Major sites of dewatering planned for drilling aremounds, related to mud diapirism/volcanism and precipitation of authigenic car-bonates, and large-scale slides related tothe subduction of seamounts.New pre-site survey seismic data was collected during a cruise of R/V MarcusLangseth in 2008 at the proposed sites of Mound Culebra and Mounds 11 and12. The new seismic profiles were acquired using a 36-gun, four-string linear gunarray up to 240 Hz, and a 240 channel streamer with 3000 m of active length.The new data are of exceptionally high quality and allow a detailed analysis of theprocesses that control fluid migration in the Costa Rican margin. We will presentfirst results obtained from prestack depth migration focusing on structures abovethe acoustic basement.The selected mound sites at Mound Culebra andMound 11 are both clearly relatedto deep-reaching fault systems, corroborating preliminary estimates of the sourcedepth of fluids and extruded material. In addition, the new seismic data show dif-ferences in terms of the mounds’ activity and stage of development. A continuousbottom simulating reflector (BSR), i.e. the base of the gas hydrate stability zone,is visible in the vicinity of themounds, but seems to vanish directly beneath theirsurface expression. The selected drill sites are chosen to penetrate deeper thanBSR depth in order to record changes in fluid geochemistry and microbiologyalong the flow path where it transgresses into the hydrate stability field.At Jaco Scar, which is the target site selected for studying seamount subduction,there is evidence for fluid flow as detected by geochemical anomalies in scarsediments and prominent methane plumes in the water column. Drilling of theseamount site at Jaco Scar will test the hypothesis that seamount subduction cre-ates deep-reaching conduits between the upper plate sediments and the continentalbasement wedge.1Contact personName: Lars PlanertAddress: IFM-GEOMARWischhofstr. 1-3 24148 KielTelephone:Telefax:email: lplanert@ifm-geomar.deContributionTitle: Drilling into dewatering sites along the Costa Rica mar-gin (IODP proposal 633): first results from pre-site sur-vey seismic data evaluationPresentation type: PosterSession MG Marine GeophysicsKeywords: Costa Rica, mud mounds, IODPKey Topic(s): S 3 Continental MarginsInfo WWW:Info email: lplanert@ifm-geomar.deSpecial devices:2

Drilling into dewatering sites along the Costa Rica margin (IODP proposal 633): first results from pre-site survey seismic data evaluation

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