Behrmann, Jan Hinrich

Heberer, B.

Kopf, Achim

Rahn, M.

Roeser, G.

English

OceanRep

Young sediments from the Southern Chile Trench: arecord of active margin magmatism, tectonics, andpaleoseismicityJ.H. Behrmann(1), B. Heberer(2,5), G. Roeser(2,6), M. Rahn(3), A. Kopf (4)(1) SFB 574, IFM-GEOMAR, Kiel, Germany, (jbehrmann@ifm-geomar.de / Fax:+49-431-6002922)(2) Geologisches Institut, Universität Freiburg, Freiburg, Germany(3) Swiss Federal Nuclear Safety Inspectorate, Villigen-HSK, Switzerland(4) RCOM, Universität Bremen, Bremen, Germany(5) Present Address: Dept. Geography and Geology, Universitaet Salzburg, Salzburg, Austria(6) Present Address: Schlumberger D&M, Campo Anadrill, Ciudad Ojeda, VenezuelaSedimentology, petrography and the provenance of sediments from the Southern ChileTrench (36˚S to 47˚S) that are about to be subducted into the seismogenic zone be-neath the South American Plate, were investigated in an integrated approach combin-ing description of a collection of gravity cores, measurement of physical properties,quantitative X-ray petrography and modal analysis. Inferences made from the regionalinformation on sedimentation rates suggest that the cored sediments are of Holoceneage. The sediments studied were trench hemipelagics, trench fan deposits, and moredistal hemipelagics deposited on the Nazca Plate north of the Chile Triple Junction.The trench is fed from multiple point sources via submarine canyons, extending fromthe shelf break across the slope, and building submarine fans at the bottom. In thetrench, hemipelagic sediment becomes finer northward, reflecting the profound influ-ence of trench architecture on grain size distribution. Modal analyses of turbiditesshow a southward increase in sediment maturity. While volcanic lithics and plagio-clase represent the most dominant fraction in the north, quartz content strongly in-creases in the southern part of the study area. This reflects the source lithologies, andis also mirrored in the southward decreasing magnetic susceptibility. Further north,active volcanoes in the Main Cordillera almost cause singularities in the provenancesignal due to an overwhelming contribution of highly erodible volcanics. Recurrencerates of sandy and silty turbidites in the trench fan sediments indicate a close connec-tion to the paleoseismic record on land. Our study documents the potential usefulnessof proximal turbidites to reconstruct paleoseismicity, even at a scale of individual seg-ments of the plate boundary. However, more high-resolution dating of the cores isneeded to confirm our conclusions.

Young sediments from the Southern Chile Trench: a record of active margin magmatism, tectonics, and paleoseismicity

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