Isotopic-geochemical data on dikes and diatremes that intrude the Khybina Massif and its host rocks are reported. The dike rocks are subdivided into three series: alkaline-ultramafic (alkaline picrites and olivine melanephelinites), phonolite (phonolites and tinguaites), and alkaline gabbroid (essexites and theralites). The alkaline gabbroids are demonstrated to affiliate with a regionally spread series of Paleozoic dolerites, whose composition was modified via the assimilation of an alkaline-ultramafic melt by a basaltic magma. The Ar-Ar, Rb-Sr, and Sm-Nd isotopic ages of the dike rocks indicate that magmatic activity terminated in the Khibina caldera at approximately 362 Ma. Thus, the Khibina Massif was formed over the time span of 410-362 Ma, starting with the development of a collapse caldera, the first manifestations of volcanic activity in it, and ending with the origin of a dike complex. Sr-Nd isotopic data on the dike and plutonic rocks of the Khibina Massif show variations corresponding to a trend (common to the whole Kola province), characterized by an increase in the proportion of enriched mantle source in the products of the early, main, and final stages of alkaline magmatism, perhaps, because of the progressively increased addition of plume material enriched in incompatible elements to the depleted Precambrian mantle that underwent partial melting.
|Number of pages||22|
|State||Published - 1 May 2005|
Scopus subject areas
- Geochemistry and Petrology