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Composite Ordovician lamprophyre (spessartite) intrusions around the Midlands Microcraton in central Britain

Published online by Cambridge University Press:  01 May 2009

R. S. Thorpe ,
J. W. Gaskarth  and
P. J. Henney
R. S. Thorpe
Affiliation:
Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, U.K.
J. W. Gaskarth
Affiliation:
School of Earth Sciences, Birmingham University, P.O. Box 363, Birmingham B15 2TT, U.K.
P. J. Henney
Affiliation:
Mineral & Geochemical Surveys, British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.
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Abstract

Lamprophyre sills and dykes of Ordovician age were emplaced within Cambrian–Lower Ordovician sedimentary rocks around the northern margins of the Midlands Microcraton. The intrusions show internal mineralogical and chemical variations indicating emplacement as multiple intrusions of co-magmatic pulses. The chemical characteristics of the lamprophyre magmas indicate formation by small-degree volatile-rich partial melting of lithospheric mantle enriched and modified by Lower Palaeozoic subduction (Th/Ta 5.3–11.6, La/Ta 29–82.3), together with a contribution from within-plate mantle source (Zr/Yc. 6) and/or mineralogically heterogeneous lithosphere, followed by varying degrees of fractional crystallization during uprise.

Type
Articles
Information
Geological Magazine , Volume 130 , Issue 5 , September 1993 , pp. 657 - 663
Copyright
Copyright © Cambridge University Press 1993

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