Late Devonian plume Tsilemsky dyke (Middle Timan): composition and K-Ar age

Abstract

The trachytes of the Tsilemsky Kamen of Middle Timan are rocks of the Shoshonitic series. The rocks have a microporphyry structure with a bostonite groundmass. Trachytes contain two varieties of potassium feldspar. The laths of the groundmass are composed of igneous sanidine, and the small grains along the edges of subisometric late quartz segregations are composed of hydrothermal microcline. Dating of trachytes by the K-Ar method gave an age of 365±8 Ma; the intrusion of the alkaline dike occurred in the Late Devonian. These rocks, along with trap basalts, recorded the occurrence of several pulses of plume magmatism on Timan in Devonian time.