Abstract Amphibole and garnet are among the most widespread heavy minerals in orogenic sediments. Their chemical composition and optical properties vary markedly and systematically with temperature and pressure conditions during growth, and thus provide important information on the metamorphic evolution of source areas that is crucial in palaeotectonic and palaeogeodynamic reconstructions. This study investigates the chemical composition of detrital amphiboles and garnets derived from parent rocks of progressively increasing metamorphic grade through a well-studied composite section across the Central and Southern Alps, including the granulite-facies core of the Late Palaeozoic orogen exposed in the Ivrea–Verbano Zone and the amphibolite-facies core of the Cenozoic orogen exposed in the Lepontine Dome. We specifically focus on metamorphic grade because it represents the best proxy for tectono-stratigraphic crustal level, and hence degree of unroofing of source areas. In river sands collected between metamorphic isograds corresponding to crystallization temperatures ranging from c. 500 °C to c. 850 °C, TiO 2 gradually increases in detrital amphibole while its colour progressively changes from blue-green in the lower amphibolite-facies where actinolite, hornblende and tschermakite are most abundant, to brown in the granulite facies where pargasite is dominant. Detrital garnets display moderate gradual changes across the amphibolite-facies Lepontine Dome, where low-Mg ‘type B’ garnets predominate. Almandine-spessartine is spatially associated with abundance of pegmatites while entering the zone of anatexis (Southern Steep Belt), where grossular or grossular-andradite-spessartine are occasionally found. A sharp change occurs while reaching granulite-facies in the Ivrea–Verbano Zone, where high-Mn garnets disappear and ‘type A’ almandine-pyrope (from ‘stronalite’ metasediments) and ‘type C’ almandine-pyrope-grossular (from metagabbros of the Mafic Complex) predominate. Also redefined in this article are a series of numerical indices based on amphibole colour and relative abundances of diverse key minerals (chloritoid, staurolite, andalusite, kyanite, fibrolitic and prismatic sillimanite), useful to accurately assess the average metamorphic grade of meta-igneous and metasedimentary source rocks. Supplementary material: Chemical composition of detrital amphiboles and garnets and full information on the location and mineralogical composition of studied samples is available at http://www.geolsoc.org.uk/SUP18618 .

Abstract Raman spectroscopy is an innovative tool with tremendous potential, serving as a fundamental complement to a variety of provenance methods including heavy-mineral analysis and detrital geochronology. Because of its accuracy, efficiency and versatility, the results of the Raman technique are indispensable for fully reliable identification of heavy minerals in grain mounts or thin sections. Thorny long-standing problems that cannot be solved confidently with a polarizing microscope alone, such as the determination of opaque and altered heavy minerals, of detrital grains as small as a few microns, or of colourless crystals with uncertain orientation and rounded morphology, can finally be addressed. Although the method can be highly automatized, the full ability and experience of the operator is required to combine Raman data with the optical information obtained under the microscope on the same grains, which is essential for the efficient application of the method in provenance studies. This article provides exemplary Raman spectra useful for the comparison and determination of over 70 different opaque and transparent heavy-mineral species commonly found in sediments, conveying specific information on the genesis of their source rocks, and thus is particularly useful in provenance diagnoses and palaeotectonic reconstructions. Supplementary material: Detailed information on the lasers used and the origin of the analysed minerals is available at http://www.geolsoc.org.uk/SUP18615 .

Abstract Fission-track dating on detrital apatites from modern sands of the Po Delta is used for a provenance study of sediments in the Po River basin. Analysed samples show a fission-track grain-age distribution characterized by two prominent peaks at 7.7 Ma and 17 Ma. The youngest peak accounts for 46% of the total population of dated grains. This young component in the grain-age distribution is consistent with bedrock cooling ages observed in the Western Alps between the External Massifs and the Houiller unit, as well as in the Lepontine dome of the Central Alps and in the Miocene foredeep units of the Apennines, that overall represent only 12% of the orogenic source area. Results suggest that most of the sediment load in the last 10 2 –10 5 years was supplied by focused erosion of relatively small areas that experienced short-term erosion rates one order of magnitude higher than in the rest of the belt.