Dissimilarity of Continental and Oceanic Rock Types1

Recent papers cite the similarity of rocks, particularly andesites,in continental and oceanic regions, but the similarity is primarilyone of name. The oceanic ‘andesites’ belong to thealkaline suite, whereas the typical continental andesites arecalc alkaline and hyperstheneor hornblende-bearing. To avoidfurther confusion it is suggested that the name ‘andesite’for the oceanic rocks be replaced by the names hawaiite andmugearite. Whatever name is used, it is essential to emphasizethe difference between the oceanic ‘andesites’ andthe andesites of continental orogenic regions. All members of the oceanic suite are present also in continentalregions, but the calc alkaline rocks characteristic of orogenicregions on the continents are absent within the true ocean basins,except in island arcs near the continents that were formerlyregarded as the continental border.