Structural Setting and Geochemistry of Devonian Dikes in the Kola Peninsula

摘要

The structural setting and geochemistry of the Devonian dikes in the Kola Peninsula are considered. The alkaline dikes are controlled by rift- and drift-related structural elements. The first type of structures is exemplified by the Khibiny-Kontozero Fault Zone, which is regarded as a propagation zone of the East Barents Rift. The second type comprises Early Precambrian structural elements reactivated during Devonian drift of the East European Plate. Alkaline dikes occur in the ring structures at the ends of rifts and in the accommodation zones where the polarity of the main fault plane changes. These are the sites of accumulation and abrupt relaxation of tectonic stresses. Despite the significant differences in the petrography and chemistry of alkaline dikes, all of them are enriched in REE, apparently due to the elevated concentrations of these elements in the fluids. The dolerite dikes at the Murmansk Coast are located in the outer zone of the vast, concentrically zoned plateau basalt province with the East Barents Trough as its center. According to geophysical data, basaltic flows are suggested within this trough. The dolerite dikes increase in number in the inland propagation zone of the East Barents Trough extending in the Baltic Shield. The alkaline igneous rocks of the Kola Peninsula were formed under local compression at the periphery of the plateau basalt province.