Petro-geological Investigation of Basaltic Rocks

Abstract

In this paper, the writer summarized some petro-geological investigation of basaltic rocks that seems to have been overlooked by most petrologists.Though the general tectonic sequence and magmatic cycle in the diastrophism is not yet fully realized, we find some intimate association of certain types of tectonism or tectonic stages and certain types of magmatism represented by some characteristic types of basaltic rocks.For these phenomena the writer presents some tentative interpretation, based on many geological facts and petrological data from various basaltic fields in our country and over-seas, in view of the general theory of tectonism compatible with the recent geophysical knowledge concerning to the crust and depths of the earth.In connection with these magma-tectonic investigations, the writer made some inquiries on the varieties and composition of basaltic rocks erupted in older and newer geological periods. For the general tendency that distinctly femic or salic types of basalts and alkaline basaltic rocks are more abundant in newer than older geological periods, and that the range of composition extends, generally, as geological age becomes younger, the writer is of opinion that it is attributable mainly to the effect of denudation subsequent to the eruption of basaltic rocks characteristic in areas of positive tectonism, by which a greater part of them is removed, instead of being preserved within the sedimentary formation as in the case of basaltic rocks in negative tectonic areas that are relatively simple in their types and compositions.