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
Other:
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.
Sections:Petrology
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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072 7 |a 16  |2 georeft 
100 1 |a Cook, C. A.  |e analytic author  |u University of Durham, Department of Geological Sciences, Durham 
245 1 4 |a The tectonic evolution of peridotites in the Lizard ophiolite complex, south-west England 
300 |a p. 182-187 
500 |a In English. 25 refs. 
500 |a Abstract number: 99M/3142 
500 |a Category Section: Petrology 
500 |a Category Subsection: Igneous petrology 
500 |a Affiliation: University of Durham, Department of Geological Sciences; Durham; GBR; United Kingdom 
500 |a Affiliation: British Geological Survey; ; GBR; United Kingdom 
500 |a Key title: Proceedings of the Ussher Society 
500 |a Source note: 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 
500 |a Publication type: conference paper or compendium article 
504 |b 25 refs. 
510 3 |a GeoRef, Copyright 2019 American Geosciences Institute. 
520 |a 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. 
650 7 |a Crust  |2 georeft 
650 7 |a Deformation  |2 georeft 
650 7 |a Diapirs  |2 georeft 
650 7 |a Dikes  |2 georeft 
650 7 |a Faults  |2 georeft 
650 7 |a Foliation  |2 georeft 
650 7 |a Geochemistry  |2 georeft 
650 7 |a Igneous rocks  |2 georeft 
650 7 |a Intrusions  |2 georeft 
650 7 |a Lherzolite  |2 georeft 
650 7 |a Mantle  |2 georeft 
650 7 |a Metamorphic rocks  |2 georeft 
650 7 |a Metasomatism  |2 georeft 
650 7 |a Mineral composition  |2 georeft 
650 7 |a Nappes  |2 georeft 
650 7 |a Obduction  |2 georeft 
650 7 |a Oceanic crust  |2 georeft 
650 7 |a Ophiolite  |2 georeft 
650 7 |a P-T conditions  |2 georeft 
650 7 |a Peridotites  |2 georeft 
650 7 |a Plate tectonics  |2 georeft 
650 7 |a Plutonic rocks  |2 georeft 
650 7 |a Thrust faults  |2 georeft 
650 7 |a Ultramafics  |2 georeft 
651 7 |a England  |2 georeft 
651 7 |a Europe  |2 georeft 
651 7 |a Great Britain  |2 georeft 
651 7 |a South-West England  |2 georeft 
651 7 |a United Kingdom  |2 georeft 
651 7 |a Western Europe  |2 georeft 
653 |a Lizard Complex 
653 |a The Lizard 
700 1 |a Holdsworth, R. E.,  |e analytic author 
700 1 |a Styles, M. T.,  |e analytic author 
711 2 |a Annual conference of the Ussher Society  |d (1998 :  |c Bideford, United Kingdom)  
773 0 |a Williams, Brian J., editor  |t Geoscience in South-west England  |d Bristol : Ussher Society, 1998  |k Proceedings of the Ussher Society  |x 0566-3954  |y PRUSAW  |n 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 type: conference paper or compendium article  |g Vol. 9, Part 3  |h illus., incl. sects., geol. sketch map