Mantle dynamics of the Central Atlantic Magmatic Province (CAMP): Constraints from platinum group, gold and lithophile elements in flood basalts of Morocco

Abstract

Mantle melting dynamics of the Central Atlantic Magmatic Province (CAMP) are constrained from new platinum group element (PGE), rare earth element (REE), and high field strength element (HFSE) data and geochemical modelling of flood basalts in Morocco. The PGE are enriched similarly to flood basalts of other large igneous provinces. The magmas did not experience sulphide saturation during fractionation and were therefore fertile. The CAMP province is thus prospective for PGE and Gold mineralisation. The Pt/Pd ratio of the Moroccan lavas indicates that they originated by partial melting of the asthenospheric mantle, not the subcontinental lithospheric mantle. Mantle melting modelling of PGE, REE and HFSE suggests: (1) that the mantle source for all the lavas was dominated by primitive mantle and invariably included a small proportion of recycled continental crust (<8%); (2) the mantle potential temperature was moderately elevated (c. 1430\u2009°C) relative to ambient mantle; (3) intra-lava unit compositional variations are likely a combined result of variable amounts of crust in the mantle source (heterogeneous source) and fractional crystallisation; (4) mantle melting initially took place at depths between c. 110\u2009km and c. 55\u2009km and became shallower with time (c. 110\u2009km to c. 32\u2009km depth); and (5) the melting region appears to have changed from triangular to columnar with time. These results are best explained by melting of asthenospheric mantle that was mixed with continental sediments during the assembly of Pangaea, then heated and further mixed by convection while insulated under the Pangaea supercontinent, and subsequently melted in multiple continental rift systems associated with the breakup of Pangaea. Most likely the CAMP volcanism was triggered by the arrival of a mantle plume, although plume material apparently was not contributing directly (chemically) to the magmas in Morocco, nor to many other areas of CAMP.