Boninitic variolites of the Buribay volcanic complex the Southern Urals: mineralogy, geochemistry and formation conditions

Литосфера

Sergei A. Svetov¹  Svetlana Yu. Chazhengina¹  Aleksandr M. Kosarev²  Gul’nara T. Shafigullina² 

[1] Institute of Geology, Karelian Science Centre of RAS;Institute of Geology, Ufa Science Centre of RAS;

关键词: вариолиты;    ликвация;    бониниты;    южный урал;    variolites;    immiscibility;    boninites;    southern urals;   

DOI  :  10.24930/1681-9004-2018-18-2-246-279

来源: DOAJ

【 摘 要 】

The object of this research are the boninites variolites of Lower Devonian Baymak-Buribay Formation in the Southern Urals, which many researchers are interpreted as the products of immiscibility. The role of processes of immiscibility in the formation of the contrasting composition of igneous rocks is discussed, starting from first quarter of former century to the present time. We used the petrological-geochemical, geological and petrographic materials of former regional studies and extensive new data obtained at the Institute of Geology KarSC RAS (Petrozavodsk) on SEM VEGA II LSH (Tescan) with an energy dispersive microprobe INCA Energy 350 (Oxford instruments). The chemical composition of variola and matrix was determined by microprobe areal scanning. The study of the content of the impurity components in variolitic formations were held by method local laser sampling (LA-ICP-MS) using the consoles Laser Ablation UP-266 Macro. Results of a research allow discussing serial accessory of volcanites of a Buribay complex, a petrogenesis the boninite variolites and value of immiscibility in formation of silicate rocks. It is established that the leucocratic globule is enriched Si, Na, K, Rb, Ba, Sr that is connected with significantly feldspath compositions of globules. In comparison with matrix the globules are poor by the petrogenic elements composing dark-colored minerals (Mg, Fe, Ca), high-charging (Hf, Zr, Nb), radioactive (U, Th), sulfur-bearing (Cu, Zn). Insignificant impoverishment of globules is found in concentration of REE (La, Ce, Eu, Yb), Pb, Cr. It is possible to assume that in the globules there was more oxidizing situation and in a matrix - reduction one. Process of a immiscibility is integrated with crystallization differentiation and was stimulated with pressure drop and sharp “dumping” of a fluid phase, in case of gradual reduction of temperature of fusion when cooling. The chemical composition of variola has a high total alkalinity then most effusive and subvolcanic rocks of Buribay complex. Most likely, the immiscibility took a prominent part in petrogenesis only part of the acidic rocks related to moderately alkaline petrochemical series.

【 授权许可】

Unknown