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Geological Society, London, Special Publications; 1993; v. 76; p. 245-256;
DOI: 10.1144/GSL.SP.1993.076.01.11
© 1993 Geological Society of London

Ophiolites and Oceanic Crust

The interaction and geometries of diapiric uprise centres along mid-ocean ridges — evidence from mantle fabric studies of ophiolite complexes

I. D. Bartholomew

Oryx UK Energy Company, Charter Place, Vine Street, Uxbridge, Middlesex UB8 1EZ, UK

Detailed structural mapping and thin-section fabric studies of oceanic upper mantle sections exposed within 3 ophiolite complexes have shown that in all of the ophiolites studied two co-existing high-temperature mantle fabric orientations can be identified. The fabrics are related both in time and space in that one fabric is ductile shear-folded by a later one to varying degrees. Olivine and orthopyroxene crystal slip-system and fabric orientation studies show that all the fabrics identified are high-temperature ‘primary’ asthenospheric flow fabrics and that simple shearing is the main flow process. The fabrics observed are at varying angles to the orientation of the Moho plane, with the slip directions varying both along strike with the Moho as well as vertically down from the Moho plane.

The identified flow fabrics are considered to be indicative of mantle flow directions ‘frozen’ into the mantle as it cooled from being ductile asthenosphere to lithosphere. Each fabric is interpreted as originating from a different localized mantle diapiric uprise centre. The centres interact with each other both in space and time, the observable ‘frozen’ fabrics indicating the closeness and ‘strength’ of individual diapirs relative to the position of the data measurement point.