Behrmann, Jan

Leiss, Bernd

Schumann, Kai

Stipp, Michael

English

OceanRep

Geophysical Research AbstractsVol. 15, EGU2013-8472, 2013EGU General Assembly 2013© Author(s) 2013. CC Attribution 3.0 License.Synchrotron texture analysis of clay-rich sediments from the Nankaitrench and accretionary prismKai Schumann (1), Michael Stipp (1), Bernd Leiss (2), and Jan-Hinrich Behrmann (1)(1) GEOMAR, Helmholtz-Zentrum fu¨r Ozeanforschung, Kiel, Germany (kaschumann@geomar.de, mstipp@geomar.de,jbehrmann@geomar.de), (2) Geowissenschaftliches Zentrum, Universität Göttingen, Göttingen, Germany (bleiss1@gwdg.de)Synchrotron diffraction is the most suitable tool for fast multi-mineral phase texture analysis of water-containingclay rich sediment samples due to short wavelengths (in the range of 0.12 Å), high energy radiation and a resultingmm- to cm-scale sample penetration. We carried out synchrotron texture analysis on a sample set from the Nankaitrench and accretionary prism offshore Japan. Samples were encountered by IODP Expeditions 315, 316 and 333of the NanTroSEIZE project from a depth range between 25 mbsf (meters below seafloor) and 522 mbsf. Theaccretionary prism sediments have a relatively uniform composition of approximately 40% clay minerals, 25%quartz, 25% feldspar, and up to 10% calcite. A first sample set analyzed was taken as recovered from drilling; asecond sample set was additionally experimentally deformed in a triaxial deformation apparatus up to axial strainsof 60%.Measurements were carried out at DESY (German Electron Synchrotron source) in Hamburg. In order to measurecomplete pole figures sample cylinders of 2 cm in diameter and 2 cm in length were measured in a phi angle-rangefrom -90 to +90˚ in 5˚ steps. Rietveld refinement results using the MAUD program package show that the com-position of the IODP Expedition 333 samples from the incoming plate differs slightly from the relatively uniformIODP Expedition 315 and 316 samples of the accretionary prism. They contain∼35% clay minerals,∼30% quartzand ∼35% feldspar. For IODP Expedition 315 and 316 samples the Rietveld refinement results correspond to thestandard XRD data. The synchrotron texture results of the recovered samples without experimental deformationshow an increasingly strong preferred orientation of the clay minerals with increasing sediment depth for the in-coming plate. Interestingly, also feldspar shows a significant texture, which is likely due to a shape fabric of thegrains. The sediment texture can be explained by compaction and porosity reduction with increasing depth. Alsothe original samples from the accretionary prism show a bedding-related texture, but the relation to sediment depthis not so clear. This is probably related to the intense reworking of the accretionary prism sediments by slumpingand/or by tectonic deformation, especially in the zone between the frontal thrust and the megasplay fault. Theexperimentally deformed samples show an increasingly strong texture of the clay minerals with increasing axialstrain. While the low strain samples show relict bedding, which rotates towards an orientation perpendicular to theaxial shortening direction, no such relict bedding orientation can be observed in the very high strain experimentsup to 60% axial shortening.

Synchrotron texture analysis of clay-rich sediments from the Nankai trench and accretionary prism

Abstract

Similar works

Full text

Available Versions

OceanRep