The Petrogenesis of a Spilitic Rock Series from New Zealand

Abstract

Well-preserved examples of spilites show marked affinities with certain tholeiites in texture, chemistry, differentiation trend, and in some aspects of their mineralogy. The presence in them of albite and apparently primary chlorite, in association with unaltered augite, is ascribed to the influence of water as a component of the magma, and the high content of alkali in the basic members to retention of volatile oxides present in tholeiitic magma. Evidence is lacking of large-scale metasomatism by external agencies and the postulate of a special primary magma seems unwarranted. A series may be traced, in rocks of different environments, from “dry tholeiite” to “wet tholeiite” to spilite.Four new rock analyses and one of chlorite are given.