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ABSTRACT Detrital fission-track studies on sedimentary basins surrounding eroding mountain belts provide a powerful tool to reconstruct exhumation histories of the source area. However, examples from active arc-trench systems are sparse. In this study, we report detrital apatite fission-track (AFT) data from Holocene and Pleistocene turbiditic trench and modern river sediments at the Chilean margin (36°S-47°S). Sediment petrography and detrital AFT data point to different major sediment sources, underlining the need for multidisciplinary studies: whereas sediment petrography indicates the erosion of large volumes of volcanic detritus, no such volcanic signal is seen in the detrital age pattern. Areally subordinate plutonic units are identified as the main, often unique sources. This result has important implications for studies of fossil systems, where the feeder areas are eroded, and where the youngest age population is often interpreted to indicate active volcanism. For the southernmost part of the study area in the Patagonian Andes, where the source area is mainly composed of granitoids, the sediment is derived from only small portions along the main divide, pointing to focused glacial erosion there. Our detrital AFT data show no exhumational signal that could be related to the subduction of the actively spreading Chile Ridge at c. 47°S and to the opening of a slab window beneath the South American Plate. [ABSTRACT FROM AUTHOR]