Petrological-mineralogical evolutional transformation of Cretaceous teschenite-tephrite, syenite-trachyte, and essexite-trachybasalt primary meltings (Carpathian, Caucasian and North TransBaikal regions)

Abstract


 
 
 This article discusses spatial and time distribution of Cretaceous teschenite-tephrite and essexite-trachybasalt complexes of the Carpathian, Caucasian, North TransBaikal regions. The main aim of the article is a comparative analysis of petrological-mineralogical features of similar complexes located in the Carpathians, North Caucasus and Transbaikal, Georgia in the Khojavand depression in the southeast of the Lesser Caucasus. Rocks of teschenite-tephrite, essexite-trachybasalt complexes were formed in the Cretaceous, early Eocene and Miocene. The differentiates of the considered complexes are localized in graben-like structures. The initial stage of graben formation is associated with the formation of rocks of the essexite-trachybasalt complex. The next stage of this process is associated with the formation of the teschenite-tephrite complex. According to stages of bedding and develop- ment of riftogenic graben structures, the essexite-trachybasalt complex formed first, at a mature stage – teschenite-tephrite one. At the initial stage high titanian olivine subalkaline basaltic melting occurred from the garnet-phlogopite lherzolite substratum. At the second stage – subalkaline picrite melting occurred from this substratum, which is primary for teschenite-tephrite and syenite-trachyte com- plexes. The metasomatized high-titanium phlogopite lherzolite substrate was subjected to melting twice. An earlier stage of melting of the substrate did not exceed 0.1%, from which a high-titanium olivine trachybasalt melt was separated. The second stage of melting of the substrate reached 10-12%. In this case, a subalkaline olivine picrite melt was formed. Evolution of primary meltings occurred in different-depth intermediate foci and intrusive chambers. The main factor in evolution along with controlling geodynamic regime was gravitational-crystallized differentiation. The identified mineral parageneses, starting from the early stage of the evolution of the subalkaline picrite melt to the late one, actually characterize the stages of crystallization of the noted melt in the intrusive chamber and intermediate chambers. The Eocene and Miocene teschenite-tephrite and essexite-trachybasalt complexes are characterized by a smaller areal distribution and petrographic diversity. Obviously, during this period, the intense activation of transverse magma-feeding faults contributed to the rapid uplift of the subalkaline picrite melt into the upper horizons of the earth’s crust.