Pre-emplacement structural history recorded by mantle peridotites; an example from the Lizard Complex, SW England

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doi: 10.1144/jgs.157.5.1049
Authors:Cook, C. A.; Holdsworth, R. E.; Styles, M. T.; Pearce, J. A.
Author Affiliations:Primary:
University of Durham, Department of Geological Sciences, Durham, United Kingdom
British Geological Survey, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, Vol.157(Part 5), p.1049-1064. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:2000
Note:In English. 75 refs.; illus., incl. 1 table, geol. sketch maps
Summary:The Lizard Complex of SW England includes thrusted units of peridotites that were initially exhumed from upper mantle (c. 52 km) to lower crustal (c. 24 km) depths during a period of Early Devonian rifting and break-up. This basin closed during the Late Devonian, when the Lizard Complex was thrust towards the NNW along a major low-angle detachment and became incorporated within a series of Variscan thrust nappes. In the peridotites, a primary high-T and high-P spinel lherzolite mineral assemblage (c. 1119°C and c. 15.7 kbar) was progressively exhumed and re-equilibrated to conditions of lower T and P (c. 991-1010°C and c. 7.5 kbar) during the development of kilometre-scale mylonitic plagioclase- and amphibole-bearing mantle shear zones. These fabrics demonstrably pre-date emplacement related structures. The new structural and geochemical evidence from the peridotites also strongly suggests that the Lizard Complex formed in a rifted, non-volcanic continental margin setting, possibly in a pull-apart basin, rather than at a mid-ocean ridge. The P-T and textural evolution of the Lizard peridotites supports growing evidence that shear zones in the lithospheric upper mantle may to some extent accommodate large-scale displacements associated with crustal extension and continental breakup.
Subsections:Igneous petrology
Subjects:Crust; Deformation; Devonian; Emplacement; Fabric; Igneous rocks; Lower crust; Lower Devonian; Mantle; Orogeny; P-T conditions; Paleozoic; Peridotites; Plate tectonics; Plutonic rocks; Rifting; Structural analysis; Tectonics; Ultramafics; Upper mantle; Variscan Orogeny; Cornwall England; England; Europe; Great Britain; United Kingdom; Western Europe; Lizard Complex; Southwestern England
Coordinates:N500000 N505000 W0041500 W0063000
Abstract Numbers:01M/808
Record ID:2001001979
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from The Geological Society, London, London, United Kingdom
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