Abstract
IF the sima magma, when still in its original position under the heavy pressure of the superincumbent sial, remained at too high a temperature for crystallisation to take place, the magma and the rocks differentiated from it would be of the normal types. The temperature- gradient, however, in the great masses of sial (the continental shields of some authors) shows a relatively slow increase in depth; consequently, a comparatively low temperature may be found at their under surface, temperature sufficiently low for some crystallisation to take place.
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References
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EVANS, J. Regions of Tension and Continental Drift1. Nature 116, 212–215 (1925). https://doi.org/10.1038/116212a0
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DOI: https://doi.org/10.1038/116212a0