Rock magnetic study on the Yetti–Eglab Intrusions, Sahara: contribution to the West African Craton geology

Abstract

AbstractNew palaeopoles have been calculated for the West African Craton (WAC) using palaeomagnetic data obtained on 178 cores of the Yetti–Eglab intrusions and stromatolite-bearing formation. One, two or three components of magnetization on 172 (14 sites) and 37 (6 sites) oriented specimens or cores were isolated mainly on doleritic dykes. High and low unblocking temperature components were evidenced in the dykes but also at four sites of the well-dated Hank stromatolite-bearing formation (875–890 Ma). Rock magnetic analyses show stable remanent magnetizations mainly carried by magnetite (or titanomagnetite) but may also reveal the presence of hematite, pyrrhotite and goethite. Regarding the recently constructed apparent polar wander path of the WAC until 500 Ma, these newly computed remanent components seem to be mainly older, some of which could be remagnetizations at different periods. However, according to geological dating and literature, the Yetti and Eglab terranes belonging to the WAC were amalgamated around 1.9 Ga and involved in the formation of the Columbia Supercontinent. The palaeopole computed for the stromatolite-bearing formation corresponds with the location of Rodinia Supercontinent at its early stages of amalgamation. The geodynamic evolution of the WAC with respect to both supercontinents suggests that the Eglab and Yetti could be separated by oceanic crust before 1.9 Ga. A volcanic arc developed during the subduction of this ocean followed by crustal thickening that generated an intrusive suite (Aftout granites) when it was at low northern latitudes. Baltica and Rio de la Plata cratons were close to the WAC after 1.7 Ga, following a nearly similar path between 1.7 and 0.9 Ga. In Africa, the collapse of the Birimian orogen was probably contemporaneous with the fragmentation of Columbia. At 0.9 Ga, Baltica was probably not attached to the WAC since the latter was not affected by the later Grenvillian orogen.