Isotopic and chemical constraints on the building of the deep Scottish lithosphere

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doi: 10.1144/sjg21040465
Authors:Halliday, A. N.; Stephens, W. E.; Hunter, R. H.; Menzies, M. A.; Dickin, A. P.; Hamilton, P. J.
Author Affiliations:Primary:
Scott. Univ., Res. and React. Cent., Glasgow, United Kingdom
St. Andrews Univ., Dep. Geol., United Kingdom
Open Univ., Dep. Earth Sci., United Kingdom
Volume Title:Scottish Journal of Geology
Source:Scottish Journal of Geology, 21(4), p.465-491. Publisher: Scottish Academic Press, Edinburgh, United Kingdom. ISSN: 0036-9276
Publication Date:1985
Note:In English. 100 refs.; illus. incl. sketch maps
Summary:The Scottish late Caledonian granites define a chemical province characterized by high Na, Ba and Sr abundances, particularly towards the north and west where they also have higher REE, Zn, and La/Y and lower Rb and Th. Comparison with data for inclusions found in younger volcanic rocks and hypabyssal intrusions, and thought to have been excavated from the mantle and lower crust, indicates that the source of some of the chemical variation in the granitic magmas lies in the lithospheric mantle. The asthenosphere or postulated subducted slab from the Iapetus ocean floor cannot have directly contributed significant amounts of these elements. Isotopic data indicate that materials derived from the lower crust are essential components of the more evolved granites, implying that considerable melting took place near the Moho. The Mid-Grampian line may represent the rifted continental edge during Dalradian deposition. There is no isotopic evidence for primary crust of Grenville age under Scotland; rather the lower crust appears to be a complex mixture including some very young components (?Lower Palaeozoic) under the Midland Valley. The only location where clearly enriched mantle has been identified is under the Lewisian of the Outer Hebrides. The lower crust in this region is also Lewisian, apparently metasomatized. It is suggested that the chemical variations in the lithosphere north of the Mid-Grampian line may be due to a volatile-flushing mechanism. [R.A.H.]
Subjects:Absolute age; Alkaline earth metals; Caledonian Orogeny; Crust; Dalradian; Dates; Geochemistry; Granites; Grenvillian Orogeny; Iapetus; Igneous rocks; Isotopes; Lead; Lewisian; Lithosphere; Magmas; Mantle; Metals; Mohorovicic discontinuity; O-18/O-16; Oxygen; Paleozoic; Pb-206/Pb-204; Plutonic rocks; Precambrian; Proterozoic; Radioactive isotopes; Rb/Sr; Slabs; Sr-87/Sr-86; Stable isotopes; Strontium; Upper Precambrian; Europe; Great Britain; Hebrides; Outer Hebrides; Scotland; United Kingdom; Western Europe; Mid Grampian Line
Abstract Numbers:86M/4638
Record ID:1987000935
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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