FENITES ASSOCIATED WITH CARBONATITES

A review of occurrences of potassic and sodic fenitization around carbonatites is presented, including several new examples and oceanic ones. Taken in conjunction with the many examples quoted in the literature, conclusions are drawn that the K and Na contents of carbonatitic melts that induce fenitization are primary constituent parts of both calciocarbonatitic and magnesio-carbonatitic melts, which have a source in the mantle, and that the K and Na are not derived from the crust during passage by these melts. Potassic fenitization can lead to the production of pseudotrachytes with up to 16 wt% K2O; these are genetically unrelated to common magmatic trachytes, which have only 5–10 wt% K2O.