Petrochemistry of the volcanic rocks of the Island of Principe,Gulf of Guinea |
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| Authors: | J G Fitton D J Hughes |
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| Institution: | 1. Grant Institute of Geology, University of Edinburgh, UK
2. Department of Geology, Portsmouth Polytechnic, UK
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| Abstract: | Principe is one of the volcanic centres comprising the Cameroun line in West Africa. The volcanic rocks can be divided into two stratigraphic units: - Younger lava series — basanite and nephelinite overlying.
- Older lava series — transitional to mildly alkaline basalt and hawaiite.
These units lie on a basement of palagonite breccias of tholeiitic affinities. The basic lavas are intruded by plugs ranging in composition from tristanite to phonolite and are overlain by phonolite lavas. These rocks form two chemically and mineralogically distinct suites: - Phonolites which evolved by low pressure crystal fractionation of the younger lava series basanitic magma, and
- Tristanite — trachyte — trachyphonolite suite which may have evolved by high pressure crystal fractionation of the older lava series magma.
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