Exotic lamproites or normal ultrapotassic rocks? The Late Miocene volcanic rocks from Kef Hahouner, NE Algeria, in the frame of the circum-Mediterranean lamproites

The late Miocene (11-9 Ma) volcanic rocks of Kef Hahouner, similar to 40 km NE of Constantine (NE Algeria), are commonly classified as lamproites in literature. However, these rocks are characterized by an anhydrous paragenesis with plagioclase and Mg-rich olivine phenocrysts, set in a groundmass made up of feldspars, pyroxenes and opaque minerals. Thus, we classify the Kef Hahouner rocks as ultrapotassic shoshonites and latites, having K2O > 3 wt.%, K2O/Na2O > 2.5, MgO > 3-4 wt.%, SiO2 < 55-57 wt.% and SiO2/K2O < 15.All the investigated samples show primitive mantle-normalized multi-element patterns typical of orogenic (arc type) magmas, i.e. enriched in LILE (e.g. Cs, Rb and Ba) and LREE (e.g. La/Yb = 37-59) with respect to the HFSE, peaks at Pb and troughs at Nb and Ta. Initial isotopic ratios are in the range of Sr-87/Sr-86 = 0.70874-0.70961, 143Nd/144Nd = 0.51222-0.51223, (206)pb/(204)pb 18.54-18.60, Pb-207/Pb-204 = 15.62-15.70 and Pb-208/Pb-204 = 38.88-39.16.