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Lower Palaeozoic and Precambrian igneous rocks from eastern England, and their bearing on late Ordovician closure of the Tornquist Sea: constraints from U-Pb and Nd isotopes

Published online by Cambridge University Press:  01 May 2009

S. R. Noble ,
R. D. Tucker  and
T. C. Pharaoh
S. R. Noble
Affiliation:
NERC Isotope Geosciences Laboratory, Keyworth, Nottingham NG12 5GG, U.K.
R. D. Tucker
Affiliation:
Department of Earth and Planetary Sciences, Washington University, Campus Box 1169, St Louis, MO, 63130-4899, U.S.A.
T. C. Pharaoh
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.
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Abstract

The U-Pb isotope ages and Nd isotope characteristics of asuite of igneous rocks from the basement of eastern England show that Ordovician calc-alkaline igneous rocks are tectonically interleaved with late Precambrian volcanic rocks distinct from Precambrian rocks exposed in southern Britain. New U-Pb ages for the North Creake tuff (zircon, 449±13 Ma), Moorby Microgranite (zircon, 457 ± 20 Ma), and the Nuneaton lamprophyre (zircon and baddeleyite, 442 ± 3 Ma) confirm the presence ofan Ordovician magmatic arc. Tectonically interleaved Precambrian volcanic rocks within this arc are verified by new U-Pb zircon ages for tuffs at Glinton (612 ± 21 Ma) and Orton (616 ± 6 Ma). Initial εNd values for these basement rocks range from +4 to - 6, consistent with generation of both c. 615 Ma and c. 450 Ma groups of rocksin continental arc settings. The U-Pb and Sm-Nd isotope data support arguments for an Ordovician fold/thrust belt extending from England to Belgium, and that the Ordovician calc-alkaline rocks formed in response to subductionof Tornquist Sea oceanic crust beneath Avalonia.

Type
Articles
Information
Geological Magazine , Volume 130 , Issue 6 , November 1993 , pp. 835 - 846
Copyright
Copyright © Cambridge University Press 1993

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