Abstract
The Gramscatho flysch sequence of south Cornwall, including the mélanges of the Meneage Formation, and the Lizard ophiolite are described in relation to the development of the Gramscatho basin. The timing and geotectonic evolution of this feature are considered in its regional context within the Rhenohercynian zone of Northwest Europe. This zone is interpreted as an intracontinental dextral transform system that developed during the Devonian closure of the so-called Massif Central Ocean. A basin and rise topography is attributed to extension and compression at offsets on major faults. E–W extension of the Gramscatho pull-apart basin in Middle and Upper Devonian times is believed to have caused rifting and the development of ocean crust from which the Lizard ophiolite was assembled in an oceanic setting at a ridge-transform junction. The Meneage Formation was generated as a result of intrabasinal uplift on transcurrent faults. A major change of plate motions took place when the Massif Central Ocean finally closed at the end of the Devonian and the weak Rhenohercynian zone became a site of crustal convergence from which thrust nappes were transported northwards. Foreland basins were sequentially developed and deformed by thin-skinned tectonics as the system advanced northwards during the Carboniferous.