Lavas and their Congeners—the Rocks of Monte Somma and Vesuvius, and diagram showing the peculiarities of their chemical composition
Abstract
In the present paper the author gives an example of application of his method to the study of the chemistry of rocks by means of diagrams (ref. 1). Here this method is applied to the study of the rocks of Somma and Vesuvius, chiefly according to the data recently published by Rittmann (ref. 6). Fig. 3 in this paper is a diagram of the chemical compositions of these rocks represented by means of vectors. The letter S0 designates trachyte of the Ur-Somma. S1 — products of ancient Somma. S2 — formations of the Young Somma before the historic eruptions. S2′ — products of the historic Young Somma and finally V — products of the activity of Vesuvius. The diagram shows that for every cycle of eruptions the vectors conspicuously change their position corresponding to the considerable change in the chemical composition of eruption products of every cycle. Passing from one cycle to another, we see a displacement of the vectors whose initial points for each cycle are joined together by a dotted line. This displacement goes from left to right, and its direction characterises the type of evolution of the magma in the hearth. Thus in the given example it becomes obvious that there are two directions to distinguish in the position of the vectors: one of them, the more strongly marked, represents differentiation, which takes place in the cycles between paroxysms of the activity of a volcano; the other corresponds to the general change in the chemistry of the magma in the hearth.
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References
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