Eruptivity and mountain building
The following paper presents the concept that the terrestrial globe has hot spots where melting follows upon gradual heating by radioactive energy, and that in connection with such spots orogenic disturbances may develop: it is suggested that the growth of a molten body produces uplift; uplift results in unbalanced load; unbalanced load tends to cause lateral creep; heat from the molten body initiates expansion in the cover and also reduces strength of rock; creep becomes plastic flow by intimate, low-angle shearing; when shearing progresses to displacements on structure planes of crystal lattices atoms are forced out of balanced positions and jump into new ones; crystals are thus elongated and the crystalline rock mass is expanded accordingly; a very powerful thrust is thus set up and the opposing rock mass is sheared on a level at or near the top of the molten body; the magma transmits hydrostatically the pressure exerted upon it by the wall at the deep level of its bottom; that relatively great pressure causes it to intrude the major shear at the base of the expanding segment and to lubricate it; the dynamic elongation of the cover and the lifting power of the magma combine to thrust the segment forward and upward and it appears at the surface as a mountain uplift, characterized by sheared and folded rocks in association with intrusives. Emphasis is laid upon the fact that the rate of heat generation is extremely slow and the cycle of an orogeny should comprise the stages of initiation, gestation, upthrust, and decadence, i.e. , the time lapse of millions of years from peneplain to peneplain, but not the succeeding period of stability.