Résumé
The Hoggar massif (SE Algeria) is located above an E-W trending belt of anomalously high heat flow [1]. The maximum heat flow (100-120 mW.m-²) has been recorded at the Northern margin of the Hoggar swell, near In’Teria district. The volcanic In’Teria district is composed of melilite pipe, which contains xenoliths of spinel and garnet peridotite, pyroxenite, and mega-crystals of pyroxene and amphibole. Spinel peridotites record two metasomatism events before their entrainment by melilitic magmas: (1) injection of alkalisilicated magmas (basaltic or kimberlitic); (2) carbonatitic metasomatism possibly related to the partial melting of a volatile enriched garnet bearing peridotite. Nd and Pb isotope analyses were performed on all lithologies. The Pb isotopic ratios range from 18.4 to 19.9, 15.60 to 15.68, and 38.2 to 39.5 for 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb, respectively. In the 207Pb/204Pb- 206Pb/204Pb space the samples report into two distinct domains. A first one carried by spinel peridotites and pyroxenites shows a clear himu affinity, signature which seems to be characteristic of the rejuvenated North African lithosphere [2]. This composition is also expressed in the melilitites from In’Teria and from recent alkaly magmatism [3]. The Garnet bearing peridotites (±spinel peridotites) show high 207Pb/204Pb (15.6) for a given 206Pb/204Pb (18.5) and form a second domain close to the EM1 pole.The data suggest (1) an isotopic stratification of the Lithosphere, (2) an evolution through time of the source of magmatism and (3) intricate interaction between those reservoirs via melting and metasomatism reactions. The In’Teria peridotites sample thus a more complex possibly more ancient (or preserved) lithosphere than in the central Hoggar. This is suggested by the “persistence” of EM1signature not registered in the Central Hoggar.