Late- to post-Variscan extensional tectonics in south Cornwall

Abstract

Faults which post-date Variscan contractional deformation are ubiquitous in south Cornwall. Three broad geometric/kinematic types can be defined. The first type comprises low angle (dip <45°) extensional faults which exhibit listric or ramp and flat geometries and may display complex arrangements of secondary faults and folds in their hangingwalls. In some instances they host elvans and "mainstage" magmatic-hydrothermal lodes (more rarely lamprophyres). The second type are moderate to high angle (dip >45°) extensional faults which generally offset earlier low-angle faults; they frequently host elvans and "mainstage" magmatichydrothermal lodes. The third type are high-angle faults which usually exhibit dominant strike-slip displacement, offset all previous faults and are often associated with base metal mineralization. Collectively these structures exerted a strong control on granite emplacement, mineralization and the development of offshore sedimentary basins. The approximately coeval association of potassic volcanicity, granite magmatism, extensional faulting and sedimentary basin development was probably a consequence of late Carboniferous to early Permian collapse of previously thickened lithosphere.