The U, Th and Pb elemental and isotope compositions of mantle clinopyroxenes and their grain boundary contamination derived from leaching and digestion experiments

摘要: Minerals from peridotites are known to be affected by trace element contamination on their grain boundaries. In this contribution we investigate the extent and origin of exogenous associated with mantle clinopyroxenes various localities (Middle Atlas, Beni Bousera [Morocco], Pyrenean Massif, Massif Central [France]) test efficacy different leaching methodologies used remove contamination. doing so present new U–Th–Pb (double-spike) isotope elemental data leachates spinel-facies sub-continental lithospheric (SCLM, n = 18). Sequential dissolution one clinopyroxene separate shows that multiple short attacks dilute HCl at moderate temperatures (e.g., 120 °C) interspersed rigorous ultra-pure water washes do not induce fractionation sufficient grain-boundary Short very mixtures HF induced strong parent/daughter significant loss prior digestion HF/HNO3. Such is suitable for studies investigating or ratios clinopyroxenes. Fluoride co-precipitates formed in presence moderately HF, during typical HF/HNO3 digestions, an important sink all elements studied here lock up least 60% considered. A suite clinopyroxene–leachate pairs Moroccan confirm extreme show 65% U, 82% Th 91% Pb, respectively, origin. Pb isotopes considered nearly reconstructed unleached have highly positive Δ7/4 207Pb/204Pb–206Pb/204Pb systematics reminiscent enriched (particularly EM II), whereas corresponding extensively leached (verified replicate digestions). Furthermore, often marked remarkably high 232Th/238U (leachate much greater-than bulk silicate Earth) addition 238U/204Pb 232Th/204Pb seemingly consistent depleted (DM) (HIMU) mixing. After leaching, may elevated distinct DM- HIMU mantle, bear resemblance anthropogenic recovered rainwater, snow aerosols. In light great potential compiled literature peridotites. These seem suggest SCLM devoid signatures but ostensibly represents repository signatures. However, dominance verified when 87Sr/86Sr 208Pb/204Pb same database considered. We highlight scarcity HIMU-like alleged continental roots reconciled if current contains samples were insufficiently thus contaminated Pb. stress importance adequate leachate analysis verify any given (-derived) sample.