New light on the construction, evolution and correlation of the Langavat Belt (Lewisian Complex), Outer Hebrides, Scotland; field, petrographic and geochronological evidence for an early Proterozoic imbricate zone

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doi: 10.1144/0016-764903-132
Authors:Mason, A. J.; Temperley, S.; Parrish, R. R.
Author Affiliations:Primary:
University of Leicester, Department of Geology, Leicester, United Kingdom
NERC Isotope Geoscience Laboratory, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, Vol.161(Part 5), p.837-848. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:2004
Note:In English. 32 refs.; illus., incl. 1 table, geol. sketch maps
Summary:The South Harris Complex is a domain of largely Palaeoproterozoic rocks within the late Archaean, tonalite-trondhjemite-granodiorite (TTG)-dominated Lewisian gneisses of the Outer Hebrides, NW Scotland. The complex is distinguished by a high proportion of metasedimentary rocks and distinctive meta-igneous units, in part representing the remnants of a continental volcanic arc. The Langavat Belt defines the NE border zone of the South Harris Complex, separating the latter from the Archaean gneisses further NE, and has been repeatedly interpreted as a discrete supracrustal unit. However, detailed mapping and petrographic analysis reveals that up to 60% of the belt may be composed of highly deformed felsic orthogneiss. The metasedimentary rocks that are present have a late Archaean zircon provenance signature, implying that they are younger than, and possibly derived from the TTG gneisses to the NE. Previous work on zircon populations in the Leverburgh metasediments, towards the southern flank of the South Harris Complex, indicates very different provenance and we repudiate correlation of the two sequences. The disposition of units of metasediment, amphibolite and felsic orthogneiss is not a primary, pre-tectonic feature and is very unlikely to be the result of folding. Although direct evidence in the form of early fabrics has been wiped out by later, penetrative ductile shearing and metamorphic annealing, we propose that the Langavat Belt was assembled as a zone of thrust imbrication during early Proterozoic contraction. After imbrication, ductile shearing occurred in two distinct periods, separated by intrusion of granite pegmatites dated at c. 1660 Ma.
Subsections:Igneous petrology; Metamorphism: regional, dynamic
Subjects:Absolute age; Correlation; Dates; Deformation; Diorites; Geochemistry; Igneous rocks; Imbricate tectonics; Intrusions; Island arcs; Isotopes; Lewisian Complex; Metamorphic belts; Metamorphic core complexes; Metamorphic rocks; Metasedimentary rocks; Nesosilicates; Orthosilicates; Paleoenvironment; Paleogeography; Petrography; Plutonic rocks; Precambrian; Proterozoic; Radioactive isotopes; Silicates; Supracrustals; Tectonics; Terranes; Tonalite; U/Pb; Upper Precambrian; Zircon; Zircon group; Europe; Great Britain; Hebrides; Outer Hebrides; Scotland; United Kingdom; Western Europe; Langavat Belt; South Harris Complex
Coordinates:N570000 N580000 W0063000 W0073000
Abstract Numbers:04M/3494
Record ID:2004076609
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from The Geological Society, London, London, United Kingdom
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