Rift-related explosive volcanism on the eve of the Cambrian ‘explosion’ on the Olenek Uplift (northeastern margin of Siberian Craton)

Abstract

Igneous occurrences comprising stratiform volcanic breccia, diatremes, basalt flows and feeders, and dolerite sills exhibit structural relationships with the Ediacaran–Cambrian boundary strata on the Olenek Uplift (northeastern Siberian Craton). A U-Pb date of 543.9 ± 0.24 Ma for zircons from the volcaniclastics (Bowring et al., 1993) had been considered as the age of the magmatic complex and used to constraint the Ediacaran-Cambrian boundary. We conducted a multifaceted study of this complex shedding additional light on its classification, petrology, tectonics and emplacement regime. We distinguish between basic and high-potassic rock varieties and attribute this diversity to a syn-emplacement overprint by K⁺-bearing sedimentary brines. All the rocks are co-magmatic, originated from a mantle-derived alkali-basaltic melt, and constitute a single event herein formally described as the Tas-Yuryakh complex. Its parental melt supposedly originated via 15–20 % melting of a garnet lherzolite at 65–70 km depth due to reaction of a plume with moderately enriched lithospheric mantle at the passive continental margin. These data combined with the geological evidence corroborate an earlier conclusion that the Tas-Yuryakh complex together with the adjacent Kharaulakh occurrence mark a rift structure that existed at ∼ 540 Ma in an ocean basin between Siberia and Baltica. The volcanic events took place over > 600 km² in shallow-depth coastal settings over a drowned carstified carbonate platform. The reaction of the hot magma with seawater and underground brines could have released a substantial mass of halogen- and boron-bearing compounds into the water and atmosphere affecting local environment and biota.