| Abstract: | By the aid of a new petrochemical diagram, introduced by V.Gottini, it is shown that the high-alumina basalts have no relation to other basalt types. That they are intimately linked to true andesites in orogenic regions and are better said to be mela-andesites. Their probable origin is discussed with the conclusion that the high-alumina basaltic and andesitic magmas are due to anatexis of the lower parts of the sialic earth crust. A systematics is proposed which reflects the bimodality of vulcanism supposed to be due to the contrast between upper mantle and crustal material. |
