Possible thermal states of the granite crust. Apart from transient thermal regiments, the thermal state of the granite crust is solely determined by the flow from the upper mantle and the distribution of radiogenic sources (Birch et alii, 1968). In wiew of this premiss, a study was made of four actual thermal situations to determine both the development of radiogenic heat and that ascribable to the flow from the upper mantle. It was found that: a) the temperature increases caused by radiogenic sources was never more than 350 °C, which means that melting phenomena, if any solely determined by this factor can be ruled out; b) the sum of the two factors gives temperatures of more than 800 °C at depht of $15 \div 16$ km. It may realistically be supposed, therefore, that a temperature of this nature, which is higher the melting of granite, must by attributable to pockets of molten material in the middle and upper layers of the crust.
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Con il contributo del Ministero per i Beni e le Attività Culturali