On the Petrogeny of the Leucite-bearing Rocks of the Roman and Birunga Volcanic Regions

The petrogeny of the leucite-bearing rocks occurring in theRoman and Birunga volcanic regions is reappraised using previouslypublished data. It is shown by means of Principal Latent VectorVariation Diagrams (Le Maitre, 1968) that the chemical analysesof rocks from the two provinces form complementary suites withina well defined trend, which can be interpreted in terms of low-pressurecrystal differentiation. The potential role of the basic compositionsof the trend as parent material is examined in the light ofrecent experimental evidence and a possible evolutionary modelis proposed involving polybaric crystallization.