Djajadihardja, Y

Engels, M.

Flueh, Ernst R.

Kopp, Heidrun

Lüschen, E.

Müller, C.

Planert, Lars

Shulgin, Alexey

English

OceanRep

Planert, L., Kopp, H., Shulgin, A. (Kiel, IFM-GEOMAR), Lüschen, E., Müller,C. (Hannover, BGR), Flüh, E. (Kiel, IFM-GEOMAR), Engels, M. (Hannover,BGR), Djajadihardja, Y. (Jakarta, BPPT)Crustal structure of the Sunda-Banda arc transition: linking lower platevariability and forearc deformationE-Mail: lplanert@ifm-geomar.deThe Sunda-Banda arc transition, the easternmost portion of the Indonesianconvergent margin, presents a probably unique natural laboratory to study lowerplate variability and related upper plate deformation in the so-called “subductionfactory” for a deeper understanding of forearc evolution. In neighboring marginsegments, we can observe strong changes of the incoming plate (transition froman oceanic to a continental lower plate, presence/absence of an oceanic plateau,variability in plate roughness) as well as a wide range of corresponding forearcstructures, including large sedimentary basins and an accretionary prism/outer archigh of variable size and shape. During RV Sonne cruise SO190 in 2006, we ac-quired a combination of seismic wide-angle OBH/OBS refraction, multichannelstreamer and gravity data along a number of trench normal corridors located be-tween 113°E and 121°E. Additionally, a number of trench parallel profiles wereconducted which mainly focus on the internal structure of the large sedimentarybasins and which were also intended for further clarifying the type of underlyingforearc crust and mantle, respectively.To obtain seismic velocity models we used a tomographic approach for refractedand reflected phases. The results show the seismic velocity structure of the incom-ing plate, starting 100 km seaward of the trench, and the adjoining forearc downto depths of 20-28 km, i.e. well into the upper mantle, and at the same time fit thegravity data very well, using simple velocity-density relations.In the Argo abyssal plain, the models show 8.0-8.5 km thick oceanic crust. Thevelocities in the crust and uppermost mantle are reduced within distances of 50km seaward of the trench, which coincides with the onset of normal faulting on theincoming oceanic plate. Anomalously low mantle velocities of 7.5 km/s directlybeneath the Moho are possibly due to the intrusion of seawater and subsequentserpentinisationof mantle peridotite. Landward of the trench in the outer arc high,velocities do not exceed 5.5 km/s down to the top of the subducting slab, whichcan be traced over 70 km length beneath the forearc down to 13 km depth. Theplate boundary is of irregular shape, obviously imprinted by the complex defor-mation of the oceanic basement prior to subduction. Offshore Lombok island,our models reveal the geometry of the Lombok basin as well as the forearc Mohoin 16 km depth. Reduced upper mantle velocities suggest a hydrated shallow1mantle wedge for this corridor. Further east offshore Sumba island, we find noevidence for a shallow mantle wedge beneath the forerarc. Crustal-type velocitiesare found down to depths of 20 km, which would point towards a different forearcregime, most likely related to the collision with the Sumba block. Our results givea detailed view into the complex deformation in both the deeper and shallowerportions of this convergent margin.2Contact personName: Lars PlanertAddress: IFM-GEOMARWischhofstr. 1-3 24148 KielTelephone:Telefax:email: lplanert@ifm-geomar.deContributionTitle: Crustal structure of the Sunda-Banda arc transition: lin-king lower plate variability and forearc deformationPresentation type: OralSession MG Marine GeophysicsKeywords: subduction zone, forearc, oceanic crust, refraction seis-micsKey Topic(s): S 3 Continental MarginsInfo WWW:Info email: lplanert@ifm-geomar.deSpecial devices:3

Crustal structure of the Sunda-Banda arc transition: linking lower plate variability and forearc deformation

Crustal structure of the Sunda-Banda arc transition: linking lower plate variability and forearc deformation

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