Pyroxenite and granulite xenoliths from beneath the Scottish Northern Highlands Terrane; evidence for lower-crust/upper-mantle relationships

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Authors:Upton, B. G. J.; Aspen, P.; Hinton, R. W.
Author Affiliations:Primary:
University of Edinburgh, Department of Geology and Geophysics, Edinburgh, United Kingdom
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 142(2), p.178-197. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:2001
Note:In English. 59 refs.; illus., incl. 11 tables, sketch map
Summary:Xenoliths from Permian host rocks in Orkney and NE Scotland (Duncansby Ness) are described, and compared to others from the N Highlands terrain. Tingwall Dyke (Orkney) samples comprise ultramafic (wehrlites, clinopyroxenites, websterites, hornblendites) and mafic-felsic rocks (gabbroic, noritic and dioritic granulites, tonalites, trondhjemites). Duncansby samples are mainly olivine-poor ultramafic rocks (clinopyroxenites, pargasite pyroxenites, biotite pyroxenites) and gabbroic-tonalitic-trondhjemitic meta-igneous lower crustal (5-10 kbar) granulites. Pyroxenes (and biotites) in ultramafic xenoliths have higher mg than those in granulites, implying higher formation T. The pyroxene-rich ultramafic rocks form a substantial zone at or around Moho level, separating the granulites and underlying peridotites, forming a density trap at which K-, Fe-, Ti- and OH-rich melts interact with the ultramafic cumulates. Since similar xenolith assemblages also occur in Mull (SW N Highland terrain), such metasomatized olivine- and orthopyroxene-deficient ultramafic rocks may be common in the shallowest part of the mantle beneath the terrain. Xenolith bimodalism (ultramafic or mafic-felsic) implies a very sharp boundary to the petrological Moho in this region. [J.F.]
Sections:Petrology
Subsections:Igneous petrology
Subjects:Chemical composition; Crust; Granulites; Igneous rocks; Inclusions; Lower crust; Mantle; Metamorphic rocks; Mineral composition; Petrography; Plutonic rocks; Pyroxenite; Ultramafics; Upper mantle; Xenoliths; Europe; Great Britain; Scotland; Scottish Highlands; Scottish Northern Highlands; United Kingdom; Western Europe
Coordinates:N563000 N584000 W0030000 W0062000
Abstract Numbers:02M/2072
Record ID:2003043052
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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