Spilites, keratophyres, and the igneous spectrum

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Abstract
Summary: Although the structures and textures of spilites and keratophyres are comparable to those of fresh lavas, recent work has established that they did not acquire their present mineralogy at the time of extrusion. Furthermore, the compositions of many analyzed samples of spilites and keratophyres are shown to lie outside a ‘spectrum’ of compositions of all comparable fresh igneous rocks. A later metamorphism has therefore been responsible for their formation and has commonly been accompanied by metasomatism. This possibility of later metasomatism must be appreciated before conclusions are drawn that are based upon analysis of rocks of a spilitic or keratophyric mineralogy. This applies to age-dating and to analytically based petrographic and petrogenetic conclusions.