Ridge axis deformation and coeval melt migration within layer 3 gabbros: evidence from the Lizard Complex,U.K. |
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| Authors: | L Hopkinson S Roberts |
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| Institution: | (1) Department of Geology, Southampton University, Southampton, SO17 1BJ, UK, GB |
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| Abstract: | Ridge-parallel extensional shear zones within the layer 3 gabbros of the Lizard ophiolite have recorded varied and numerous
chemical and mineralogical changes under a variety of P-T conditions. These changes accompany tectonic exhumation of lower crustal levels by a listric fault mechanism during amagmatic
extension at a slow-spreading centre. Deformation within the mid-crustal level of layer three resulted in the migration and
impregnation of an evolved iron-titanium-rich silica-poor melt along the shear zones. This syntectonic infiltration occurred
along the lowermost portions of listric faults which rooted in a partially molten zone beneath the ridge axis. Residual melt
was tapped from this underlying zone and tectonically redistributed about deforming gabbros situated immediately above the
partially molten zone. The occurrence of sub-solidus synkinematic assemblages within the shear zones, which were generated
at various temperatures and water : rock ratios, is explained in terms of their simultaneous development on listric fault
planes in the presence of a hydrothermal fluid phase. The sequential overprinting of pre-existing assemblages arises from
repeated block rotation during amagmatic episodes of extension within an oceanic slow-spreading environment.
Received: 8 February 1994/Accepted: 4 April 1995 |
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