Tectonic evolution of the Northumberland Basin; the effects of renewed extension upon an inverted extensional basin

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Abstract
The Northumberland sedimentary basin has a history of repeated extensional and contractional tectonic phases and a study of the deformation interference pattern and sedimentary record allows the identification of the tectonic state through time. Initial rifting is represented by a thick Dinantian sedimentary fill, but Carboniferous extension is thought to have ceased by the early Namurian. In order to explain the development of certain facies patterns during the Westphalian thermal subsidence phase of the evolution of the Northumberland Basin, some syn-depositional extensional fault movements are required. At other times in the Westphalian, compaction-induced subsidence was the dominant control on facies distribution. A single phase of E–W to SE–NW Variscan compression commenced during or after late Westphalian times and ceased prior to the intrusion of the Whin sills and dykes. Subsequent Permo-Mesozoic extension, with a right-lateral shear component, re-activated pre-existing normal fault lines. These later structures may be interpreted as being listric in form, shallowing onto decollement surfaces within the Carboniferous basin fill and overlie the buried faulted margin at the southern side of the basin.