Lizard Complex - Structure

Structure

The current outcrop pattern of the various units of the Lizard Complex is mainly controlled by Carboniferous age normal faulting. The earliest structures seen in the ophiolitic rocks are steeply-dipping foliations thought to represent deformation in lithosphere scale shear zones, associated with continental break-up in the early Devonian. Locally thrust contacts can be seen showing evidence of northwestward movement between parts of the ophiolite and between the ophiolitic rocks and the metamorphic basement. It has been suggested that the Kennack Gneiss (a mixture of basic and acidic igneous rocks) was formed by partial melting during the obduction of the ophiolite onto the continental crust. Although an earlier stage of 'hot' emplacement is not ruled out, it is now generally accepted that in the final stage of emplacement, during the Variscan orogeny, the ophiolite was relatively 'cold'.

The northward dip of thrusts at the base of, and within, the ophiolitic rocks is interpreted to be caused by rotation of initially south-dipping thrust planes due to the dominantly south-dipping post-Variscan extensional faults.