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A 2 m-thick spheroidal weathering profile, developed on a quartz diorite in the Rio Icacos watershed (Luquillo Mountains, eastern Puerto Rico), was analyzed for major and trace element concentrations, Sr and Nd isotopic ratios and U-series nuclides (238U-234U-230Th-226Ra). In this profile a 40 cm thick soil horizon is overlying a 150 cm thick saprolite which is separated from the basal corestone by a ∼40 cm thick rindlet zone. The Sr and Nd isotopic variations along the whole profile imply that, in addition to geochemical fractionations associated to water-rock interactions, the geochemical budget of the profile is influenced by a significant accretion of atmospheric dusts. The mineralogical and geochemical variations along the profile also confirm that the weathering front does not progress continuously from the top to the base of the profile. The upper part of the profile is probably associated with a different weathering system (lateral weathering of upper corestones) than the lower part, which consists of the basal corestone, the associated rindlet system and the saprolite in contact with these rindlets. Consequently, the determination of weathering rates from 238U-234U-230Th-226Ra disequilibrium in a series of samples collected along a vertical depth profile can only be attempted for samples collected in the lower part of the profile, i.e. the rindlet zone and the lower saprolite. Similar propagation rates were derived for the rindlet system and the saprolite by using classical models involving loss and gain processes for all nuclides to interpret the variation of U-series nuclides in the rindlet-saprolite subsystem. The consistency of these weathering rates with average weathering and erosion rates derived via other methods for the whole watershed provides a new and independent argument that, in the Rio Icacos watershed, the weathering system has reached a geomorphologic steady-state. Our study also indicates that even in environments with differential weathering, such as observed for the Puerto Rico site, the radioactive disequilibrium between the nuclides of a single radioactive series (here 238U-234U-230Th-226Ra) can still be interpreted in terms of a simplified scenario of congruent weathering. Incidentally, the U-Th-Ra disequilibrium in the corestone samples confirms that the outermost part of the corestone is already weathered.

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15Regoliths encompass different materials from the fresh bedrock to the top of the organic 16 horizons. The occurrence and evolution of these materials are determined by deposition, 17 erosion and weathering processes that are specific for each region. The origin and interaction 18 of the regolith layers are still important issues in the study of critical zone functioning. 19Studies that attempt to understand the processes responsible for the structure and the 20 evolution of regoliths often focus either on the soil or on the bedrock compartment, and often 21 from a narrowly focused approach using just a single tool such as major element patterns or 22 mineralogy. This limits the understanding of the complete regolith composition and evolution. 23The present study proposes the combination of mineralogy, major and trace element 24 concentrations, and Sr-Nd-Pb-U isotopes as an extremely useful procedure for tracking the 25 Pleistocene Periglacial Slope Deposits (PPSD). The data allowed the differentiation of three 29 compartments within the regolith: 1) the organic compartment, where low 206 Pb/ 207 Pb and 30 87 Sr/ 86 Sr isotopic ratios reflected the impact of atmosphere-derived components; 2) the PPSD 31 compartment, whose upper horizons were characterised by the presence of atmosphere-32 derived particles rich in Cd, Sn, Sb, Hg and Pb and by relatively low 206 Pb/ 207 Pb and 87 Sr/ 86 Sr 33 ratios, whereas the lower horizons showed Nb enrichments in their matrix and a mineralogical 34 composition pointing to ancient volcanic events; and 3) the weathered slate compartment, 35 whose weathering progression and genetic relationship with the PPSD were particularly well 36 tracked with 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotope ratios, ( 234 U /238 U) activity ratios and positive 37Ce anomalies. The results prove the efficiency of radiogenic isotopes measurements 38 combined with the analysis of major and trace elements to complete regolith studies. 39Moreover, these isotopes and elements are shown to be potential geochemical tracers of 40 exchange processes at the water-mineral interface. This approach allows for the first time the 41 description of an evolution scheme of a complete slate regolith, which covers a large part of 42 the Rhenish Massif. 43 44