Weathering and abrasion of Fe-Ti oxides during rock degradation and fluvial transport: implications for sedimentary provenance studies

Physical and chemical degradation of individual grains of titanomagnetite a nd ilmenite during rock weathering and fluvial transport processes in the R iver Eden catchment, Eastern Scotland, have been traced using backscattered electron images and electron probe microanalysis. Magnetic characteristics have been used to detect differences in magnetic mineralogy concentration, paragenesis and grain size between rock samples showing different stages o f weathering, and between different sources and sediment samples. Results h ave shown higher physical and chemical durability of ilmenite during this s egment of the geological cycle than titanomagnetite, which is rapidly alter ed. During progressive subaerial weathering of a dolerite, the increasingly intensive and extensive oxidation and development of internal fractures in titanomagnetite are observed. However, under subaqueous conditions, titano magnetite was found to be progressively replaced by titanite and Ti-impover ished magnetite due to hydrocirculation. Neither the total physical nor the total compositional degradation of titanomagnetite is achieved under rock weathering and fluvial transport processes. Thus, the importance of titanom agnetite as a provenance indicator remains despite its degradation during t he geological processes studied in the River Eden catchment.