The migration of subduction-related triple junctions affects sediment distribution across plate boundaries through uplift and subsidence along plate margins and the sequential migration of sedimentary sources, including magmatic provinces. The uplifted/deformed zones in the forearc region may include trench fill, accretionary prism and forearc basin sediments, accreted terranes, and near-trench volcanic rocks in the case of ridge subduction. Erosion of these uplifted regions supplies sediment deposited as submarine fan or apron complexes within adjacent forearc basins, or out onto adjacent oceanic crust. The effects of sediment recycling, basement exposure and uplift, and anomalous magmatism can be detected in marine clastic sequences associated with triple junctions. Petrological data for sand and sandstone cored at circum-Pacific Deep Sea Drilling Project and Ocean Drilling Program sites associated with subduction-related triple junctions indicates that they differ compositionally from "normal" forearc sedimentary sequences. For example, on a QtFL ternary diagram, their mean detrital modes tend to plot in the Transitional Arc field of Dickinson et al. (1983). Thus sand/sandstone detrital modes may provide fingerprints of triple junction migration in the rock record.