Petrochemical Features of Volcanism in Relation to the Types of the Earth'S Crust
- Gordon A. Macdonald and
- Hisashi Kuno
Published Online: 21 MAR 2013
Copyright 1962 by the American Geophysical Union.
The Crust of the Pacific Basin
How to Cite
Gorshkov, G. S. (1962) Petrochemical Features of Volcanism in Relation to the Types of the Earth'S Crust, in The Crust of the Pacific Basin (eds G. A. Macdonald and H. Kuno), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM006p0110
- Published Online: 21 MAR 2013
- Published Print: 1 JAN 1962
Book Series Editors:
- Waldo E. Smith
Print ISBN: 9780875900063
Online ISBN: 9781118669310
- Earth's Crust;
- Niggli method;
- Oceanic crust;
- Petrochemical and geological data;
- Petrochemical features of rocks;
- Sagging geosyncline;
The author has made a large number of petrochemical calculations from analyses of volcanic rocks from the Pacific Ocean and adjacent continents. The calculations were made by the Zavaritsky method, which permits the comparison of many analyses expressed by vectors on a plane graph, the variation curves reflecting the process of magmatic differentiation. It was found that calc-alkalic lavas of island arcs and alkalic rocks of intracontinental volcanoes form a single class, all the members of which are connected by gradual transitions. The direction of oceanic variation curves is distinctly different from the continental ones; alkalic rocks of intracontinental and intraoceanic volcanoes are products of clearly different differentiation series.
The petrochemical features of separate types belonging to the continental class are independent of the precise local geological and tectonic situation. These features are determined only by the distance from an island are. This fact is of fundamental importance, and leads to the following conclusions: (1) The feeding sources of volcanoes are situated beyond the limits of the crust, in the upper mantle, where geological and tectonic peculiarities no longer affect the chemical composition. At the same time it is possible to consider that the chemical composition of the upper mantle is slightly different under the crust of continental and oceanic types. The two classes of rocks reflect this difference. (2) Assimilation of crustal material is very limited as a rule, and the whole variety of rocks is caused by the initial magma itself. The principal process consists of relatively rapid and distinct differentiation in the volcanic chimneys.
The oceanic magma is considered ancestral. The clear change of an oceanic-type magma to a continental one in island arcs is caused by the rise of new portions of substance from the deeper mantle. Thus the Earth's crust should not be considered as a source of the volcanism, and the composition of the crust is not one of the leading factors in the chemistry of magmas. On the contrary, volcanism is one of the main factors in the formation of the Earth's crust.