Petrography and mineralogy of the Late Devonian dolerites of the central and south-eastern Kanin Peninsula

Petrographic characteristics and new data on mineralogical characteristics of rocks of the Kanin- Timan dolerite complex (βD3kt) in the central and southeastern part of the Kanin Peninsula are presented. Pyroxenes of dolerites correspond in chemical composition: in the center of grains – to augite, and at the edges – to ferroavgite. Difference between pyroxenes of dolerites from different regions of the peninsula is in the presence of exsolution in the pyroxenes of dolerites from the center of the Kanin Peninsula. Using the Lindsley diagram for determining the crystallization temperature for all studied clinopyroxenes, it was found that the central part of the crystals crystallized at a temperature from 1300 to 1000 °C, in the marginal part the crystallization temperature varied from 1100 to 900 °C. According to the Nekvasil diagram, the central compositions of the clinopyroxene grains fall into the pressure field from 4.3 to 14.3 kbar. The compositions of the edge parts of clinopyroxenes correspond to pressure fields of 1 atm. Thus, from the grain centers to the edges, a regularity of pressure decrease during the crystallization of clinopyroxenes and, accordingly, dolerites is observed. The beginning of crystallization of dolerites in the central part of the Kanin Peninsula occurred in deeper conditions compared to the same rocks in the southeastern part of the peninsula. As a result of studies of the mineral composition of the rocks of the complex under study, it was found that the dolerites in the center and southeast of the peninsula differ in the depth of rock crystallization and the rate of melt cooling.