The geological and geodynamic evolution of the Northumberland Trough Region: insights from numerical modelling

Abstract

The geological and geodynamic processes that have controlled the evolution of the Northumberland Trough Region in Northern England have been investigated to expand understanding of the evolution of continental extensional basins. The region has experienced a number of extensional, compressional and wrench tectonic events throughout Late Palaeozoic, Mesozoic and Cenozoic times. These events have led to a complex subsidence and uplift history.

A kinematic model has been developed in two-dimensions to simulate the structural deformation caused by extension by faulting and pure shear, thermal processes and the flexural isostatic due to tectonic loading. The stratigraphy varies across the region between the block and basins, which has been addressed within the modelling by the development of algorithms to simulate palaeobathymetry, compaction and erosion.

Extension within the crust was taken up on multiple faults generating an average total heave of approximately 10-15km. Model results indicate there was non-uniform extension of the lithosphere with greater extension below the fault detachment depth where ductile deformation is the principal deformation mechanism. Results generated using a modelling approach that utilises multiple tectonic events generate stratigraphic patterns of syn-rift and post-rift deposition that support extension at multiple time stages within the Northumberland Trough Region during the early-Carboniferous period.

Models that reconcile the observed amount of fault-controlled deformation with the magnitude of overall thinning of the crust generate comparable amounts of subsidence to that observed in the basin structures. In contrast, these models over-estimated the amount of subsidence on the block structures. It has been hypothesised that this mismatch was due to the North Pennines Batholith, which acts as a negative load upon the lithosphere.

Development of an algorithm to model the isostatic response of the lithosphere to the North Pennines Batholith has provided insights into the influence of igneous intrusions on the post-emplacement structural development of the area. Model results incorporating the batholith indicate the generation of a significant amount of uplift coincident with the presence of the batholith, and show a realistic geometry and upliftsubsidence pattern across the Alston Block and adjacent basins.