Tectonic evolution of the northern Verkhoyansk fold-and-thrust belt based on paleostress analysis and U-Pb calcite dating

The formation of the Verkhoyansk fold-and-thrust belt (FTB) is traditionally interpreted as a result of Late Mesozoic subduction and consequent closure of the Oimyakon Ocean, followed by the collision of the Kolyma-Omolon microcontinent with the Siberian Craton. In particular, the northern Verkhoyansk FTB reflects the complex tectonic history and interaction of the Arctic and Verkhoyansk orogens. Although previous studies documented several Cretaceous deformation events, the details of the northern Verkhoyansk evolution are still poorly understood.

A combined structural and geochronological study was carried out to identify the tectonic evolution of the northern Verkhoyansk FTB. Fault and fold geometries and kinematics were used for paleostress reconstruction in the central and western parts of the northern Verkhoyansk FTB. The multiple inverse method was used to separate individual stress fields from heterogeneous fault-slip data and three different stress fields (thrust, normal and strike-slip faulting) were identified. Thrust and normal faulting stress fields were found throughout the study area, whereas a strike-slip faulting stress field was only found in Neoproterozoic rocks in the westernmost part of the northern Verkhoyansk FTB. Furthermore, U-Pb LA-ICP-MS dating of calcite fibers on slickensides was performed to obtain a first-order time constraint on fault activity.

The study reveals the following succession of major deformation events across the northern Verkhoyansk: i) The oldest tectonic event corresponding to the strike-slip faulting stress field with NE-SW-trending compression axis is Early Permian (284±7 Ma) and likely represents a far-field response to the Late Palaeozoic collision of the Kara terrane with the northern margin of the Siberian Craton. ii) A slickenfibrous calcite age of 125±4 Ma is attributed to the most intense Early Cretaceous compression event, when the modern fold and thrust structure developed. Dykes in the eastern part of the northern Verkhoyansk FTB cutting N-S trending folds with 90-85 Ma U-Pb zircon ages mark the end of this event. iii) U-Pb slickenfiber calcite ages of 76-60 Ma estimate the age of a Late Cretaceous–Palaeocene compression event, when thrusts were reactivated. Slickensides related to both (ii) and (iii) compressional tectonic events formed by similar stress fields with W-E trending compression axes. iv) From Palaeocene onwards, extensional tectonics with approximately W-E extension predominated. Within the northern Verkhoyansk FTB, extension settings are supported by the formation of a set of grabens and a clearly recognizable normal faulting stress field.