A variety of xenoliths from the lower crust to mantle transition occur in Quaternary mafic intraplate lavas of the Bayuda volcanic field of northern Sudan. The lower-crust xenoliths include plagioclase- and garnet-bearing mafic granulite. Ultra-mafic garnet-bearing pyroxenite, websterite, hornblendite, and distinct peridotite xenoliths are from the upper lithospheric mantle. Sr, Nd, and Pb isotope signatures distinguish between ultramafic and granulite xenoliths. The latter show a strong compositional affinity to juvenile Neoproterozoic crust. The Pb isotope composition of the ultramafic xenoliths resembles the distinct high-μ signature ( 206 Pb/ 204 Pb >19.5) of their host basanite. These xenoliths may represent cumulates of late Mesozoic to Quaternary mafic intraplate magmatism. The felsic upper crust in a schematic lithospheric profile of the Bayuda area includes predominantly granitoids, migmatites, and metasedimentary rocks that represent reworked old cratonic or juvenile Neoproterozoic rocks. The deep lower crust is represented by mafic granulite, likely cumulate rocks from Neoproterozoic juvenile magmatism. The crust-mantle transition is characterized by ultramafic cumulate rocks possibly from the late Mesozoic to Quaternary magmatism. The peridotites of the same xenolith suites represent typical lithospheric mantle with variable degrees of depletion by melt extraction.

Abstract The subduction orogeny of the Central Andes, which created the Cenozoic Altiplano-Puna high plateau, shares many geological features with the early Palaeozoic Orogen at the western margin of South America. The presently available datasets for both orogens are compared. The similarities are a large-scale high temperature metamorphism, which was active in the Palaeozoic Orogen over a geological long period of time in the order of 100 Ma and which is active now in the crust of the Cenozoic plateau. It produced abundant granitoid melts from the crust during the Palaeozoic as well as during the Andean Orogen. The main contribution to granitoid magmatism is recycling of felsic crustal material with only minor additions from the mantle. Transport of deep parts of the crust into the erosion level did not occur in both orogens and, in both orogens, large-scale nappe tectonics typical for collision orogens are absent. Based on the similarities of the two orogens it is argued that the early Palaeozoic Orogen is a non-collisional orogen. Indications for terrane accretion are absent in the development of the high-grade metamorphic and igneous basement. The early Palaeozoic Orogen is an analogue for the presently active continental margin and, thus, allows the extrapolation of features which cannot be observed in the Andean Orogen.