Coarse-Grained rocks from Ascension Island

Harris, Chris; Bell, J. D.; Atkins, F. B.

http://hdl.handle.net/10400.3/4896

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Authors

Harris, Chris

Bell, J. D.

Atkins, F. B.

Abstract(s)

The lavas and pyroclastic rocks of Ascension Island contain a suite of coarse-grained igneous blocks which range in composition from dunite to granite paralleling, but extending beyond, the compositional range of the volcanic. The mineralogy, texture and chemistry of these blocks discussed, together with their modes of occurrence. More specific features observed include partial melting seen in one suite which suggests that granitic liquids may be formed from blocks of intermediate composition; the occurrence of the rare minerals dalyite (K₂Zr Si₆O₁₅) and vlasovite (Na₂ZrSi₄O₁₁); and the crystallization ‘in situ’ of a rock type considered to reproduce several of the features displayed by the blocks. The implications of this for the origin of the coarse-grained suite as a whole are considered.