Deformation and emplacement of the Lizard Ophiolite Complex, SW England, based on evidence from the Basal Unit

Abstract

The Basal Unit of the Lizard Ophiolite Complex preserves evidence of a protracted deformation and accretion history. The earliest recognizable events record the construction of ocean crust and the generation of the Lizard Ophiolite Complex in a slow-spreading ridge-axis environment. The initial stages of deformation involved the development of a sub-horizontal crustal-scale shear zone and its progressive deformation by ductile thrusting and folding. Subsequent deformation progressed with the out-of-sequence stacking of ocean lithosphere in which detachment, initiated at mid-crustal levels, culminated in mantle decoupling as thrust slices were derived from progressively deeper crustal levels. The progressive emplacement of a coherent slice of ocean lithosphere over previously accreted units and the generation of a dynamothermal aureole are consistent with models suggesting rapid overthrusting of young ocean lithosphere. Evidence from the dynamothermal aureole indicates that syn-emplacement extensional collapse of the complex occurred in response to thrust loading. Foreland-directed offsliding and lateral thrusting mark the final stages in the collapse of the complex.