The tectonic evolution of peridotites in the Lizard ophiolite complex, south-west England

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Authors:Cook, C. A.; Holdsworth, R. E.; Styles, M. T.
Author Affiliations:Primary:
University of Durham, Department of Geological Sciences, Durham, United Kingdom
British Geological Survey, United Kingdom
Volume Title:Geoscience in South-west England
Volume Authors:Williams, Brian J., editor
Source:Proceedings of the Ussher Society, Vol.9(Part 3), p.182-187; Annual conference of the Ussher Society, Bideford, United Kingdom, Jan. 1998, edited by Brian J. Williams. Publisher: Ussher Society, Bristol, United Kingdom. ISSN: 0566-3954
Publication Date:1998
Note:In English. 25 refs.; illus., incl. sects., geol. sketch map
Summary:The mantle peridotites of the Lizard Complex, south-west England, preserve direct and indirect evidence for several deformation episodes: 1) Extensional uplift of mantle prior to the formation of oceanic crust in an incipient ocean basin; 2) Their subsequent emplacement by thrusting in an intra-oceanic setting at the onset of obduction; 3) Extensional reactivation of the intra-oceanic thrust contacts in response to late stage collapse of a nappe pile (Jones, 1997). An early fabric is characterised by a sub-vertical foliation and a steeply plunging mineral lineation. This fabric pre-dates the formation of oceanic crust as it is cross-cut by MORB-type gabbro intrusions and dykes. Among the least deformed peridotites are spinel- and plagioclase-lherzolites with a coarse to medium-grained porphyroclastic texture. With increasing deformation, these pass transitionally into mylonitic plagioclase-bearing peridotites and mylonitic amphibole-bearing peridotites which have a medium to fine-grained porphyroclastic textures. The presence of "fertile" spinel lherzolite and the orientation of the peridotite fabric is not typical of emplacement of peridotites at an oceanic spreading centre. Alternatively it is proposed that systematic changes in microstructure, mineral chemistry and geothermometry of the different peridotite types are related to changing conditions of P and T during tectonically controlled uplift of mantle. Changes in the whole-rock compositions of the deformed peridotites are thought to be related to syntectonic metasomatism by hydrous melts. The subsolidus trajectory of the peridotites suggests deformation in the footwall of an extensional shear zone or in the margins of a upwelling mantle diapir.
Subsections:Igneous petrology
Subjects:Crust; Deformation; Diapirs; Dikes; Faults; Foliation; Geochemistry; Igneous rocks; Intrusions; Lherzolite; Mantle; Metamorphic rocks; Metasomatism; Mineral composition; Nappes; Obduction; Oceanic crust; Ophiolite; P-T conditions; Peridotites; Plate tectonics; Plutonic rocks; Thrust faults; Ultramafics; England; Europe; Great Britain; South-West England; United Kingdom; Western Europe; Lizard Complex; The Lizard
Coordinates:N495800 N495800 W0051200 W0051200
Abstract Numbers:99M/3142
Record ID:1999047752
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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