New Ar-Ar geochronology of the Catanda carbonatitic magmatism (Angola) and implications on its origin

The Catanda Complex is one of the few examples of extrusive carbonatitic volcanoes in the world, and the only one known in Angola. It occurs along the Lucapa corridor that runs SW-NE across Angola. Kimberlitic, alkaline (mostly syenitic to ijolitic terms) and carbonatitic intrusions mark this corridor out that runs SW-NE across Angola. This magmatism was previously related to the Mesozoic continental rifting and the opening of the South Atlantic Ocean. However, recent geochronology from the carbonatitic volcanics of the Catanda Complex indicates that these volcanic rocks are much younger (0.56-0.78 Ma), and related to the Pleistocene reactivation of Mesozoic structures coeval with the formation of the East African rift. Newly acquired Ar39-Ar40 geochronology during the PLANAGEO project illustrates the complexities of dating these carbonatitic melts. The whole-rock Ar-Ar spectra shows a U-shape pattern indicative of excess-Ar with a series of well-defined steps at 471 ± 28 Ma and 210 ± 6 Ma, confirmed by the intercepts of their separate Ar-isochrons. The geological significance of these dates is questionable, but this Ar-spectra could indicate the presence of older Ar reservoirs. A phlogopite separate from the same sample does provide a reliable spectra with an Ar-Ar plateau age of 3.01 ± 0.53 Ma and a concordant Ar-isochron age of 2.83 ± 0.66 Ma. This age is slightly older than the previously reported ages suggesting the existence of several carbonatitic magmatic pulses in the Catanda area during the Pliocene-Pleistocene.