ПЕТРОГЕНЕЗИС МАГМАТИЧЕСКИХ КАЛИЕВЫХ ПОРОД

Abstract

Drawn up equilibrium diagram of the Si02(#)-KAlSi04(Ap)-Mg2Si04(/o)-CaMgSi04(mo)-U20(aq) system (further q-fo-kp-mo-aq), represented as a F^20-T projection and isobaric sections, reflects, with some simplifying, F\\20-T-X conditions of crystallization from magmas and subsolidus transformations for nearly the whole scope of potassic rocks within the range of water pressure from 0 up to 8 kbar. The above system includes six subsystems, which may be divided in two groups by the type of phase transitions at the low /йгО values. Three subsystems, the least Si02 saturated ones: VHI-mo-norm, VII-£p-norm and Vl-ai-norm, are characterized by eutectic type of the final crystallization stage, and thermal barriers separate them. Three other subsystems haven't dividing thermal barriers and the melt of IV-/c-normative subsystem can freely attain the granite eutectic, when fractionating of precipitating phases or under incomplete, partial course of peritectic reactions. Nevertheless, the wide variety of potassic rocks is caused first of all by variations in composition of magmas, and in addition only - by the crystallization differentiation, partial course of peritectic reactions and subsolidus exchange reactions. Two latter processes and the Phi formation while the decrease of temperature in subsolidus conditions lead to appearance of heteromorphous rocks. The paper contains several examples of the diagram applications to resolve the petrological problems.