The Halogen budget of Bolivian mafic shoshonites

The halogen budget of the shoshonitic series of the Bolivian Altiplano has been assessed, and found that they have contents similar to other enriched basalts worldwide. We observe F (range between 0.02 and 0.24 wt%) behaviour as similar to that of crustal derived elements in this environment, while Cl (range between 0.01 and 0.26 wt%) is more complex and probably is controlled by heterogenous source regions. F and Cl both decrease in abundance towards the more evolved end of the series that, despite large distances (~300 km) between the furthest samples, bear a striking similarity in numerous geochemical indices. It follows that the lack of F in Bolivian Sn-systems is due to petrogenetic process rather than parental material. A model involving amphibole fractionation promoted by the anomalously thick crust is proposed to account for these observations.