A two‐layer lithospheric compressional model for the tertiary uplift of the southern United Kingdom

Abstract

Reflection seismic records show that many of the Mesozoic sedimentary basins of the southern United Kingdom were compressed and uplifted (inverted) during the Late Cretaceous‐Tertiary. Recent quantitative studies based on apatite fission track analysis and Chalk porosity data show that uplift and erosion, although concentrated in the inverted basins, was regional, and not limited to the recognized areas of crustal shortening (inversion). A two‐layer, or heterogeneous model of lithospheric compression, similar to two‐layer models of lithospheric extension, may account for this pattern of uplift. Upper‐lithospheric shortening is accommodated by reverse movement on major, reactivated, extensional detachments, causing inversion of pre‐existing basins. Pure shear shortening of the lower lithosphere is decoupled, and may be laterally displaced, from that in the upper lithosphere. Lower lithospheric shortening and thickening displaced from that in the upper lithosphere causes initial subsidence due to the submersion of cold, dense lithosphere into the surrounding asthenosphere. Subsequent thermal re‐equilibration of the lower lithosphere may have generated the uplift without attendant crustal shortening witnessed by apatite fission track and Chalk porosity data.