The structure of the granite massif of Flamanville, Manche, North-West France

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Abstract
Summary: The present structural study of the small granite massif of Flamanville, based on the field technique originated by Hans Cloos, provides critical data from which to reconstruct the tectonic episodes, and the mode of emplacement of the granite. The folding in the region results from two earth-movements. Firstly, the Caledonian (Mesodevonian in the Cotentin) on NE.–SW. axes, and secondly, the Hercynian (Sudeten?) on axes a few degrees south of due west. Superimposed on these tectonic trends are the folds due to the emplacement of the granite. The granite appears to be diapiric in form, and to have risen into place by thrusting aside the country rocks. The primary flow-planes of the minerals in the granite and the foliation in the hornfels of the aureole are due to the same movements. Their form is consistent with the conception of a pluton expanding like a balloon, within its plastic cover. The joint patterns clearly demonstrate the tectonic unity of the granite with its immediate environment, and they cannot be envisaged as resulting from regional movements. It is concluded that, though metamorphism, metasomatism, felspathization, and assimilation of the stoped country rocks have taken place along the contact, these processes were incidental to the emplacement of the magma. This is in contra-distinction to the previous conclusion, that the granite was created in situ by the granitization of the country rocks.

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