Revealing upper plate dynamics by looking at fission tracks from the lower plate sediments – an approach for the Southern Chile Trench

Bianca Heberer (Univ. Freiburg, Germany), supervised by Jan Behrmann (GEOMAR Kiel, Germany) and Meinert Rahn (HSK, Switzerland)

An apatite fission track study is carried out on marine gravity core samples taken along the Chilean trench axis from 31 to 47 deg S in order to address the spatial variation of denudation and hinterland dynamics. The study area comprises the Chile triple junction in the South, where the currently spreading Chile Rise is being subducted underneath the South American Plate causing an enhanced uplift of the forearc. The current plate tectonic setting produces an increase of ocean floor ages of the lower subducting Nazca Plate north of the triple junction, thus a different thermal and mechanical behavior, which is expected to be visible in the uplift of the upper plate. Gravity cores were taken from the trench fans at the bottom of submarine canyons, which are fed by turbidity currents. Within those fans along-trench sediment mixing processes are believed to be of minor importance. Assumptions about the denudation of the upper plate are limited to those areas where the amount of volcanic detritus is low, which is the case for the North and South of the study area. For areas with recent volcanic activity within the drainage system, our data will give evidence about the current erosion patterns. The question of the sediment origin is further addressed by modal analysis on the trench samples. In addition to the marine sediment analysis, samples from major river estuaries and prominent hinterland lithologies are currently being analysed for comparison with the trench ages. By correlating the ages with corresponding age distributions from the trench fans, the concept of a negligible transport time, which is commonly applied in detrital thermochronology, shall be tested.

Kate Dobson - SAGES Post-doctoral Research Fellow University of Glasgow Geographical & Earth Sciences G12 8QQ UK email: This e-mail address is being protected from spambots. You need JavaScript enabled to view it Tel: +44 (0) 141 330 5442