On the participation of natural salts in alkaline magmatism. Article 2. Standard objects and geological aspects of the model
Research subject. The author suggests a new geologic and genetic model for alkaline magmatism. This model considers the saline complexes that are located along the paths of ascending deep magmas as additional sources of alkaline and volatile components. An analysis of the geological and genetic probability of the participation of salts in alkaline magmatism is based on the study of the space-time relationships of natural salts and alkaline magmatic complexes performed using global and regional data. This problem is investigated in a series of three articles. The first article was devoted to characterization of geological prerequisites and their tectonic types. This article sets out to describe the geological aspects of salt-magmatic interactions in greater detail. To this end, the standard alkaline-salt associations of three tectonic types - Italian (cover-fold type), Upper-Rhine (rift type) and North-West-African (passive-margin type) - were characterized. Methods. The most significant tectonic, lithological and petrological features of all the aforementioned types were described, along with the evolution of space-time relationships of alkaline magmatic complexes. The features confirming the participation of saline complexes in alkaline magmatism were generalized . Results. It is found that the presence of salt-bearing strata in deep zones of the Earth's crust along the ascending routes of mantle magmas is a geological phenomenon. The places of their intersection are favourable for the injection of hot magmas and the formation of interstitial chambers, which form centres for interaction between these magmas and the components of saline (salt-carbonate) complexes. The assimilation of the alkaline and volatile components localized in these complexes can contribute to the formation of highly enriched (supersaturated) melt mixtures and a subsequent alkaline specialization of the magmas. Conclusion. On the basis of the data obtained, a geological model of salt-magmatic interactions has been developed. The author's next article will discuss the genetic aspects of the proposed model along with a possible role of various alkaline and volatile halophilic components in the formation of alkaline magmas. In addition, a comparative analysis of various geological and genetic models of alkaline petrogenesis will be provided.