Weld kinematics of synrift salt during basement-involved extension and subsequent inversion: Results from analog models

Abstract

Scaled analog models based on extensional basins with synrift salt show how basement topography exerts a control factor on weld kinematics during the extension and inversion phases. In the case of basement-involved extension, syn-rift salt thickness differences may lead to variable degrees of extensional decoupling between basement topography and overburden, which in turn have a strong impact on the development of salt structures. With ongoing extension and after welding, the basin kinematics evolves toward a coupled deformation style. The basin architecture of our experimental results record the halokinetic activity related to growing diapirs and the timing of weld formation during extension. Moreover, the structures that result from any subsequent inversion of these basins strongly depends on the inherited welds and salt structures. While those basins are uplifted, the main contractional deformation during inversion is absorbed by the pre-existing salt structures, whose are squeezed developing secondary welds that often evolve into thrust welds. The analysis of our analog models shows that shortening of diapirs is favored by: 1) basement topography changes that induce reactivation of primary welds as thrust welds; 2) reactivation of the salt unit as a contractional detachment; and 3) synkinematic sedimentation during basin inversion. Finally in this article we also compare two natural examples from the southern North Sea that highlight deformation patterns very similar to those observed in our analog models.