Composition of volatile components in endogenous spherules.
1Yatsenko I.G., 1Yatsenko G.M., 2Naumko I.M., 1Bekesha S.N., 2Sahno B.E.
1 - Geology Department, Lviv National Ivan Franko University, Lviv, Ukraine; Yatsenko1941@list.ru
2 - Institute of Geology and Geochemistry of Combustible Minerals of NASU, Lviv, Ukraine; firstname.lastname@example.org
The results of the mass-spectrometric study of volatile components in glass and magnetic spherules are represented. The different types of spherules (SPH), hyaloclastes (HC) as well as number of oxygen-free minerals moissanite, qusongite, cohenite, fersilicite, hapkeite, native metals (Fe, Cr, Cu, Zn, Sn, Pb ets.) and their intermetallic alloys have occurred in explosive structures of the Ukrainian shield (USh) and in Yakutian kimberlite pipes.
In various volcaniclastic rocks, in explosive formations (kimberlite, lamproite etc.) specific spherical (SPH) and scoriaceous (HC) mineral particles, composed mainly of ore minerals and glass have been found (Lukin, 2007; Bekesha, Yatsenko, 2010). Their presence is usually accompanied by association of deep minerals and accidental lithic clasts that are typical for ultrabasic, alkaline-ultrabasic and alkaline rocks.
The volatile composition of SPH are poorly studied in comparison with the volcanic rocks and minerals. The available data demonstrate the specific high-reduced composition of gas, characterized by the domination of nitrogen and hydrogen (CO2 and CH4 are present in lesser amounts). In ñommon volcanic rocks main volatile component is CO2, and minerals of kimberlites occupy an intermediate position (Bratus et al.,1987, Yatsenko et al., 2012).
Ten samples of SPH consisting of transparent Ca-rich (CaO up to 40 wt.%) glass (C-SPH), opaque dark Ti,Mn,Fe-rich glass (TMF-SPH), magnetite-iron (MI-SPH) and several HC irregular shape have been investigated. For the comparison the samples of the host rocks - kimberlite (pipe “Mir”) and of alkaline-ultramafic explosive breccia from Kirovogradsky block of Ukrainian shield (USh) have been analyzed as well. The weight of one sample is 50-100 mg, gas composition was analyzed by a mass spectrometer MCX-3A, adapted for the determination of the composition of micro-volume quantities of gases (Bratus et al., 1987).
The investigation revealed the dominant part of nitrogen in the gas component of spherules and hyaloclastes. In four samples, it amounts to almost 100 % vol. The samples are :
- TMF-SPH and HC from lamproite “Mriya” pipes (western Azovian block of US);
- HC composed of Ca-rich glass with wustite (Nagolny ridge, village Malaya Tarasovka)
- HC composed of K-rich silicate glass (K2O-20 wt.%) from alkaline-ultramafic explosive breccia (Zakharovsky site of USh, Cherkasky district);
- C-SPH calcium-rich silicate spherules (CaO-40 wt.%) from the Neogene-Quaternary explosive volcaniclastic deposits (village Putrintsy, Zhitomirsky district, Ukraine).
The high content of nitrogen was observed in the composition of gases from the next samples:
- kimberlite from the “Mir” pipe - N2 - 75,4 vol. %, CH4 - 24,6 vol. %;
- TMF-SPH from the clastogenic sediments of the Malaya Kuonamka river (Yakutia) - N2 - 54,9 vol. %, CO2 - 45, 1 vol. %.
Four samples revealed the predominance of carbon dioxide gas (CO2). The samples are:
- MI-SPH from the Pliocene tuffaceous red clay (Gayvoronsky district, Kirovogradsky block of USh ) - CO2 - 84,5vol. %, N2 - 15,5 vol. %;
- MI-SPH (two samples) from the alluvial deposits (the middle reaches of Dniester the River) - CO2 - 80,2-87,4 vol. %, N2 - 12,6-19,8 vol. %;
- explosive alkaline-ultramafic breccias (Kirovogradsky block of USh) - CO2 - 89,9 vol. %, N2 - 18,3 vol. %.
Only one sample MI-SPH from explosive alkaline-ultramafic breccia (Kirovogradsky block of USh) showed the high hydrogen content: H2 - 64,4 vol. %, CO2 - 17,3 vol. %, N2 -18,3 vol. %. It should also be noted that only in two samples represented by rocks (kimberlite from “Mir” pipe and explosive breccias from Kirovogradsky block of USh) water has been fixed.
Analysis of the results of the study reveals that SPH are characterized by the very constant composition of volatile components which is not related to one of the host rocks. Deep minerals, particularly diamonds and minerals-satellites (Bartoshinsky et al.,1987, 1989) are characterized by wide range of volatile components. Such exotic high-reduced composition of volatile components of SPH can indicate that the formation of primary melt of the spherules is associated with the very deep levels of the Earth, deeper than the level of the kimberlite magma generating. This assumption is confirmed by a number of previous studies of SPH. In this context it is worth noting the genetic relations between SPH and a group of oxygen-free mantle minerals: moissanite, qusongite, cohenite, native metals (Cu, Zn, Sn, Pb etc.) and their intermetallic alloys (Lukin, 2007).
It is quite interesting is the fact that the main volatile component of SPH is nitrogen. The possibility of penetration of atmospheric nitrogen into them seems very problematic. On the other hand it is a promising to study the behavior of nitrogen in overpressured conditions of the Earth's core and mantle.
Nitrogen is rather inert element, but under certain conditions can form chemical combination with metals, hydrogen and other elements (nitrides, asides, chloride, iodide). Thus in the deep overpressured conditions nitrogen must be important element of fluidodynamics, it can be an important agent in the chemical reaction and in the processes of matter migration. It is noteworthy that most of the nitrogen compounds are unstable and often highly explosive. So hypothetically we assume the possibility of initiation of explosive processes caused by the decomposition of nitrogen compounds in the lower parts of the lithosphere and the mantle. The permanent presence of SPH in explosive formations enables to use them as an indicator in the search and prospecting of various types of deposits. It is currently known that the explosive process leads not only to forming o diamond deposits, but also can form ore deposits: gold, PGE, TR, etc. (Yatsenko, 2012).
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