Abstract:
The energy of interface formation is an important parameter that controls the evolution of magmatic systems. The energy factor plays a critical role during phase transitions at the beginning of crystallization, melting, and retrograde boiling, when numerous nuclei of one phase are formed within another phase. It was shown that the melting style significantly depends on geodynamics. In "static" conditions (oceanic spreading or intraplate activity), magma generation mainly occurs by propagation of melting zones due to decompression in the ascending plume. Newly formed melts migrate upward in intergranular spaces, thus accumulating beneath the upper, cooler zone of the plume to form magma chambers. In dynamic conditions (subduction zones), the bulk periodic and rapid melting is often observed. The composition of volatiles dissolved in the melt plays an important role during retrograde boiling. If CO2 predominates, which is typical of intraplate magmas, the boiling in shallow magma chambers produces foam extruded to form cinder cones. Occasionally, this process is accompanied by small explosions, forming scoria-pyroclastic and pyroclastic cones. Explosive eruptions typical of deep-seated volatile-rich kimberlite and lamproite magmas are related to the abrupt decrease of CO2 solubility in the ascending magmas at 40-50 kbar. Subduction-related water-saturated magmas are characterized by bulk boiling ar shallow depths, which is often accompanied by catastrophic explosions. This is related to the abrupt decrease of H2O solubility in the intermediate-acid melts at 1-1.5 kbar. The contribution of other volatiles (CO2, SO3, etc.) is insignificant in this case.
