On the Granite Problem and the Similarity of Salt and Granite Structures

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Abstract
A brief outline of the present knowledge of the formation of granite is given, with evidence favouring a magmatic origin. The deficit of mass which is a distinctive physical feature of a large number of granite structures, has generally been explained by the stoping hypothesis. However, the hypothesis is unsatisfactory in various respects, particularly because no decisive evidence of large-scale stoping as generally conceived has been brought forward. The granite structures share with salt structures their peculiar character of being gravity minima. Other similarities between the two types of structures are shown. Data from a large number of granite structures in Europe, U.S.A. and Africa and salt structures in Germany und U.S.S.R. are included in the study. It is demonstrated that typifying features such as structural overtilting of flanking sequences and rim-synclines are developed in some granite structures as they are in salt structures. In some cases there is evidence of bulk creep of the granite mass in granite diapirs comparable with the creep of salt in salt domes. The relationships between granite diapirs and ring-structures are emphasized, and it is suggested that they are closely related both structurally and genetically. The evidence of granite diapirism suggests that granite masses, whether in the state of a melt, a semi-molten crystal mush or a solid, moved in response to the load of a more dense cover, much the same as diapiric salt masses. It is finally concluded that granite and salt diapirism are of the same general nature.