Natrocarbonatitic Melts of the Bol'shaya Tagna Massif, the Eastern Sayan Region

摘要

The calcite-fluorite and fluorite rocks together with cognate carbonatites are commonly associated with alkaline ultrabasic complexes. The magmatic or meta-somatic (postmagmatic) origin of carbonatites has been actively discussed for almost half a century. Nevertheless, no certain view on this subject has been settled to date, especially concerning the usual carbonatites and fluorite rocks formed at the late stage of the evolution of the alkaline ultramafic complexes. Many petrologists refer to these rocks as products of metasomatic or hydrothermal processes. The findings of melt inclusions in minerals from the aforementioned rocks served as conclusive evidence for their magmatic origin. However, an attempt to estimate the composition of the respective melts in quantitative terms was made only in [1, 3]. These data remain insufficient, and it is necessary to furnish additional data on the state and composition of mineral-forming medium of such objects as a basis for understanding the genesis of car-bonatitic complexes.