Basites of Vilyui-Markhinsky dike belt (Vilyui paleorift)
 and their relations with Nakyn field kimberlites

Abstract

The Vilyui-Markhinsky dike belt (VMDB), which
 was formed as a result of Devonian rifting on the eastern
 margin of the Siberian Platform, is the marginal
 part (area of scattered rifting) of the Vilyui paleorift
 structure. The Nakyn field is located in the central part
 of the belt, but is controlled by an independent system of
 NNE-trending tectonic faults. The belt dyke intrudes the
 Nyurbinskaya kimberlite pipe. On their contact, specific
 breccias were formed resulting from the interaction between
 degassing products of basic magma with kimberlites.
 The typical zonality of the dyke endocontact indicates
 a later dyke introduction. Dolerite dikes thermally
 metamorphosed breccias in which high-temperature
 neoplasms of andradite, Al-lizardite, and clinochrysotile
 were generated. VMDB basites represent a single association,
 in which two series of rocks are distinguished:
 moderate-titanium (TiO2 ~ 2.5 wt. %) with normal alkalinity
 and low P2O5 content, and high-titanium (TiO2
 ~ 4.4 wt. %), occasionally with moderate alkalinity. The
 differences in the dike composition are insignificant and
 are the result of natural variations in the composition
 of individual bodies. 40Ar/39Ar dating of the VMDB basites,
 the method characterized by the best results convergence,
 shows that they formed in a narrow timeframe
 corresponding to the Upper Frasnian – Famenian stage
 of the Upper Devonian (368.5 to 376.3 Ma). The location
 of the Nakyn field basites and kimberlites is controlled
 by faults of various types, orientation and age. Kimberlites
 formed first, and VMDB intrusions followed.