Petrology of Teschenites and alkaline picrites associated with them

In Carpathians and Caucasian regions

 

Mamedov M.N., Babayeva G.J., Kerimov V.M.

Geology Institute of ANAS, Baku, Azerbaijan.

 

Teschenites and genetically connected with them volcanogenic-alkaline picrites, tephrites, basanites, analcimites and others are of restricted development among alkaline basic and ultrabasic rocks. According to data available (Wilkinson, 1956; Grobovski et al., 2003; Jan Spicak et al., 2004; Skhirtladze N.I., 1943; Borsuk A.M., 1979 et al.) this volcanoplutonic association is mainly Late Cretaceous, Eocene and sometimes is Oligocene.

Cretaceous teschenites and associated with them alkaline picrites, tephrites, basanites are mainly developed in northwest and west provinces of Carpathian region (Spisak, Hovorka, 2004; Wladyka, Karwonski, 2006; Grabovski, 2003) and in north and south slopes of the Greater Caucasus (Borsuk, 1979; Skhirtladze, 1943; Dudauri, 1989, 2003) and the Lesser Caucasus (Mamedov, 1999).

Above-mentioned association of rocks is localized among Jurassic and Cretaceous tuffogenic sedimentary and volcanogenic formations. According to data of absolute geochronology they refer to the Late Cretaceous (Dudauri, 1989; Borsuk, 1979).

Teschenite intrusives form small bed-like, sil, laccolith-like outcrops among jurassic and Cretaceous geological complexes.

Macroscopic rocks of intrusives of lying flank are dark-grey, sometimes dark fully.

From lying flank to hanging one dark and dark grey colours become grey and light grey. Microscopic research showed that these colours changes in rocks of studied intrusives are caused by quantitative variation of femic and salic rockforming minerals. In this from lying flank to hanging one quantity of olivine elinopyroxene, titanomagnetite and sometimes Kaersutite gradually reduces and quantity of plagioclase, potassium feldspars, analcime increases.

Chrysolite-hyalosiderite olivine, salite-fassaite clinopyroxene, labradorite-bytownite plagioclase, kaersulite-barkevikite amphibole, ulvospinel titanomagnetite and analcime participate in melanocratic teschenites composition confined to lying flank of intrusives. Small amount of apatite, granate, and biotite and other minerals is available as well.

Content of melanocratic minerals reduces from melanocratic teschenite to normal one. In this direction content of plagioclase increases which is gradually enriched by albite molecule. In final differentiate of teschenite intrusives which consists of teschenite sienite and sienite, salite and fassaite clinopyxenes alternate by ferrosalite and hedenbergite and the basic plagioclase by oligoclase andesine. In some cases this paragenesis takes tabular, leistolike grains of nepheline. In mesostasis of these rocks content of xenomorph analcime and potassium feldspar (50-60%) increases noticeably.

Volcanic facies of teschenite intrusives is represented by volcanic breccia and lavobreccia, flows of tephrites, basanites, melanocratic analcimites, alkaline picrites, analcime trachybasalts and trachydolerites.

Golden-brown megacrystal of phlogopite, size 3x5 sm, is found in lavobreccia of tephrites. Here the crystallization process occurring in relatively deeper intermediate focus is connected also with formation of large accumulative megacrystal of phlogopite. The next stage of crystallization of alkaline picritic melting probably occured in less deep intermediate focus where porphyric paragenesis of minerals were forming. They consist of hyalosiderite olivine, salite clinopyroxene and aluminous titanomagnetite. Final stage of crystallization of alkaline picritic melt is represented by formation interstitial analcime with potassium feldspar. The latter is confined to analcime as the needles.

So, volcanoplutonic associations of rocks in Caucasus and Carpathians regions are comagmatic between each other. Volcanic facies of teschenite melt formed at earlier stage of Late Cretaceous evolution stage of Caucasus-Carpathians regions. Probably instrusive magmatism formed a bit later.

Evolution of teschenite melt was controlled by crystallized differentiation in intrusive chamber and intermediate focuses. Availability of water (analcime) and hydroxyl (biotite, kaersutite, barkevikite) minerals in rocks composition of teschenite melt prove the oxidizing conditions of crystallization. In these cases crystallization of aluminous titanomagnetite exceeds crystallization salite clinopyroxene and frequently is confined to latter as inclusion.

Along with mentioned the other larger cations such as potassium, rubidium, barium of intrusive chamber and intermediate focuses accumulate in residual melting anmd isomorphically include into content of potassium feldspar.

Due to duration of crystallization processes in intrusive chamber titanomagnetite is more enriched by ulvospinel molecule. In this case alumina more concentrates in composition of bytownite plagioclase.

Unlike intrusive chamber in intermediate focus mineral parageneses of intratelluric stage of alkaline picritic melt crystallization were probably controlled by water fluids. Here impregnations of high aluminous titanomaagnetite were crystallized before porphyric emissions of salite clinopyroxene and were enriched by proper spinel minal (MgAl2O4= 8-12%).

 

Reference:

Borsuk A.M. Mesozoic and Cenozoic magmatic formations of the Greater Caucasus. Moscow: Nauka, 1979, p.299 (in Russian).

Dudauri O.Z., Togonidze M.G., Bortnitsky Y.N. Potassium argon age of teschenites in West Georgia // Reports of AS of GSSR, 1989, 134, N1, p.137-140 (in Russian).

Dudauri O.Z. Petrology of Mesozoic intrusive complexes of Georgia. Dissertation for doing Doctor Degree (geology and Mineralogy), Tbilisi, 2003, p.192-261.

Gugushvili V.I. Cretaceous volcanism of Georgian Block //Proceedings of Research Institute of as a GSSR, 1989, 134, 1, p.137-140 (in Russian)

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Skhirtladze N.I., Teschenite formation of West Georgia //Proceedings of AS of GSSR, series Mineralogy and Petrography, v II, 1943,p.102 (in Russian)

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Grabowski I et al. Geochronology of teschenitic intrusion in the outer Western Carpatian of Poland constrains from 40K40Ar ages and biostratigraphy // Geologica Carpathica, 54, 2003, p. 385-393 (in English).


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