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Subduction-related magmatism of late Ordovician age in eastern England

Published online by Cambridge University Press:  01 May 2009

T. C. Pharaoh
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.
T. S. Brewer
Affiliation:
Department of Mineral Resources Engineering, Nottingham University, University Park, Nottingham NG7 2RD, U.K.
P. C. Webb
Affiliation:
Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, U.K.

Abstract

Deep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the Caledonian basement in eastern England. The isotopic compositions of these rocks reveal that many of them are of late Ordovician age (440–460 Ma), and their geochemical compositions suggest calc–alkaline affinities. The intermediate (diorite-tonalite) plutonic rocks are associated with a prominent northwest–southeast trending belt of aeromagnetic anomalies extending from Derby to St Ives, Hunts., which is interpreted to work the plutonic core of a calc-alkaline magmatic arc. It is inferred that this arc was generated by the subduction of oceanic lithosphere, possibly from the Tornquist Sea, in a south or southwest direction beneath the Midlands Microcraton in late Ordovician times. The age and geochemical composition of concealed Ordovician volcanic rocks in eastern England, and hypabyssal intrusions of the Midlands Minor Intrusive Suite in central England, is compatible with such a hypothesis.

Type
Articles
Copyright
Copyright © Cambridge University Press 1993

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