The evolution of alkali basaltic magma based on the study of silicate melt inclusions from Hegyestű and Haláp, Balaton Highland

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1 The evolution of alkali basaltic magma based on the study of silicate melt inclusions from Hegyestű and Haláp, Balaton Highland Klára Kóthay Summary of PhD dissertation PhD Program for Geology and Geophysics at the PhD School of Earth Sciences Eötvös Loránd University Budapest Chair of the PhD School of Earth Sciences Prof Dr Gyula Gábris, DSc (Department of Geography, Eötvös Loránd University, Budapest) Chair of the PhD Program for Geology and Geophysics Prof Dr Miklós Monostori, DSc (Department of Paleontology, Eötvös Loránd University, Budapest) Advisor Dr Csaba Szabó, PhD, Associate Professor (Department of Petrology and Geochemistry, Eötvös Loránd University, Budapest) Tutors Dr Kálmán Török, CSc (ELGI, Budapest) Dr Victor V. Sharygin (SB RAS, UIGGM, Novosibirsk) 2009 Eötvös Loránd University Budapest 1

2 Table of contents Introduction 2 Analitical techniques 3 Results 4 Acknowledgements 4 Papers and abstracts connected to the PhD dissertation 6 2

3 Introduction The petrologic and geochemical study of the alkali basalts enrich our knowledge on the earth mantle and its processes (such as partial melting, metasomatism, melt differentiation). On the other hand, the study of silicate melt inclusions, i.e. magma droplets risen to the surface in a closed system, gives more information on the physical and chemical circumstances characteristic of the upper mantle and of partial melting, the processes of the magma during uprising and the behavior of the melts, than the bulk analysis of the host basalt. Moreover, it also makes possible the quantitative and compositional study of the volatiles, one of the most significant components of the melts. The volatiles present and migrating in the earth mantle have a major role in its processes (such as partial melting, metasomatism, or deformation). As a result of our recent investigations on the alkali basalts of the Carpathian-Pannonian Region together with their peridotite xenoliths originating from the upper mantle, the upper mantle beneath the Carpathian-Pannonian Region became one of the best studied and known part of the Earth. However, before the beginning of the present study, in international petrologic investigations, only Szabó et al. (1996) used information resulting from analyses of silicate melt inclusions. Since then, the use of such data have became widespread and several studies have been published, which used results of melt inclusion analyses when studying the rocks of the Carpathian-Pannonian Region. On the other hand, very few studies deal with the silicate melt inclusions trapped and preserved in the phenocrysts of primer mafic magmas formed during the partial melt of the mantle. Since the study of melt inclusions has not been a common method in Hungary, we have started our work in a volcanic field of the Carpathian-Pannonian Region, in the case of which we have data provided by geochemical methods and interpreted petrologically in details. Our results thus can be reliably compared with other data. The studied territory is the Bakony- Balaton Volcanic Field in the centre of the Carpathian-Pannonian Region. We selected for the study two such volcanoes that, on the basis of previous analyses of the basalts, are considerably different. Hegyestű is one the oldest and more unsaturated alkali basalt in the Bakony-Balaton Highland Volcanic Fields, while Haláp is one of the youngest volcano, which is formed from less unsaturated. The silicate melt inclusions and the primary fluid inclusions embedded in the olivine phenocrysts of the two selected volcanoes were studied in order to get more detailed knowledge on some physical and chemical characteristics of the 3

4 primary basic melt forming the basalt, such as chemical composition, temperature, oxygen fugacity, pressure. We also intended to get information on the early phase of the crystallization of the rock. My further aim was to compare the crystallization processes in the host basalt and to follow the evolution of the magma. Analytical techniques The thin-sections and separated olivine grains from the carefully selected samples were analyzed by different methods in order to determine the bulk composition of the silicate melt inclusions. The study of the major element composition of the solid phases have been carried out in three laboratories (Budapest, Vienna and Novosibirsk) by electron microprobe. The determination of the trace elements was done by secondary ion mass spectroscopy (SIMS) at Yaroslave. For the investigation of the fluid phases we used Raman spectroscopy and two types of heating stages (Fluid Inc. USGS, Linkam THMS600). For the homogenization of the silicate melt inclusions I used Linkam TS1500, Vernatsky stage, and furnace technique (method of Petrushin). Results 1/ The core of the olivine phenocrysts of the alkali basalts from Hegyestű and Haláp contain primary silicate melt inclusions, Cr-rich spinel inclusions and CO 2 -rich fluid inclusions. 2/ The bulk chemical composition of carefully selected silicate melt inclusions, based on mass balance calculations, provides the major element compositions of the primary magmas forming the basalts, which, at both localities, show similarities with the chemistry of melts determined by homogenization experiments and harmonize well with the bulk rock compositions. 3/ The primary magmas from Hegyestű could be highly mafic melts, less saturated in Si (SiO 2 ~41 m/m%), while rich in Mg and alkali (MgO~8 m/m%, Na 2O+K 2O~6 m/m%), as well as in CO 2 (min. 1,5 m/m%). With their lesser SiO 2 and greater TiO 2, Al 2 O 3 and CaO contents, they considerably differ from the average composition of the alkali basalts forming the Haláp rocks. The primer melts from Haláp contain considerable (~10m/m% ) FeO and MgO, while they show more variable and more acidic composition. Both melts 4

5 are volatile-rich, the CO 2 content of the Hegyestű melt is 2 m/m%, that of Haláp is ~1.5 m/m%. 4/ Except for small differences, the distribution of the trace elements of the silicate melt inclusions from both localities is similar to that of the host rock. The silicate melt inclusions in the olivine phenocrysts of the Hegyestű basalts are more rich in all trace elements compared to the host rock, while the Sr-content and the less incompatible heavy rare earth element content (Dy Yb) of the Haláp silicate melts are poorer than that of the basalt. The compositions of the silicate melt inclusions from both localities are more useful to show the geochemical differences of the melts than the bulk rock analyses. 5/ Upon cooling of the magma, the evolution of the magma droplets entrapped in olivine phenocrysts can be characterized at both localities by sulfide-silicate immiscibility in deep magma chambers and by partial crystallization of the silicate daughter minerals. This crystallization in the Hegyestű inclusions is follows a definite trend: sulfide bleb Alspinel rhönite Ti-augite apatite±rutile±ilmenite±ca-sulfate. In contrast, the Haláp silicate melt inclusions show more variable chemical composition, implying a more heterogeneous system. During their solidification, despite the uncertainties, they may have formed the following crystallization sequence: Al-rich spinel + sulfide and silicate melt immiscibility rhönite + amphibole + clinopyroxene apatite + ilmenite. The noncrystallized, highly acid melt quenched as glass with high Na and/or K content, while the considerable CO 2 content of both magmas were immicibled as bubbles in the early phase of the crystallization of the daughter minerals. 6/ From the crystal phases in silicate melt inclusions, rhönite and Al-spinel appear in alkali basalts as primer constituents. However, they are common phases in the closed system Hegyestű and Haláp inclusion melts. The presence of the Al-spinel is due to the fact that following its crystallization it did not react to the melt to form olivine and plagioclase, but remained a stable phase. This is only possible in Si-poor melts that crystallize only at high temperature (>7 kbar). Contrary to earlier hypotheses, rhönite can be a typical phase in such high pressure systems, following Al-spinel during crystallization when it uses the majority of the Ti-, Al- and Ca-content of the melt, and prevents the formation of plagioclase. 5

6 7/ Silicate melt inclusion in Hegyestű have been entrapped in olivine phenocrysts at a relatively narrow temperature interval of C in high oxygen fugacity and OIBlike environment. Papers written in the framework of the PhD dissertation Kovács I., Bali, E., Kóthay, K., Szabó, Cs. & Nédli, Zs. (2003), Bazaltos kőzetekben előforduló kvarc és földpát xenokristályok petrogenetikai jelentősége (with English summary: Petrogenetic significance of quartz and feldspar xenocrysts in basaltic rocks ). Földtani Közlöny, 133/3, Kóthay, K., Szabó, Cs., Török, K. & Sharygin, V. (2005), Egy csepp a magmából: Szilikátolvadék-zárványok a hegyestűi bazalt olivin fenokristályaiban (with English summary: A droplet of the magma: Silicate melt inclusions in olivine phenocrysts from alkali basalt of Hegyestű ). Földtani Közlöny, 135/1, Schubert, F., Kóthay, K., Dégi, J., M. Tóth, T., Bali, E., Szabó, Cs., Benkó, Zs., Zajacz, Z. (2007), A szakirodalomban használt fluidum- és olvadékzárványokkal kapcsolatos kifejezések és szimbólumok szótára (with English summary: Terms and symbols used in English and Hungarian fluid and melt inclusion literature ). Földtani Közlöny 137/1, Sharygin, V.V., Szabó, CS.,Kóthay, K., Timina, T.JU., Pető, M., Török, K., Vapnik, YE., Kuzmin, D.V. (2007), Rhönite in silica-undersaturated alkali basalts: inferences on silicate melt inclusions in olivine phenocrysts. in Alkaline magmatism, its sources and plumes, Ed.: Vladykin, N.V., Vinogradov Institute of Geochemistry, Irkutsk-Napoli, (UDK ), Conference abstracts Kóthay, K. (1999) Szilikátolvadék-zárványok kőzettani vizsgálata a hegyestűi bazalt olivin fenokristályaiban (Balaton-felvidék). Ifjú Szakemberek Ankétja, Siófok, March, Program és absztrakt füzet, 14. (conference talk) Kóthay, K. (1999) Egy csepp a magmából: Szilikátolvadék-zárványok vizsgálata a hegyestűi bazalt olivin fenokristályaiban (Balaton-felvidék). XXIV. Országos Tudományos Diákköri Konferencia, Debrecen, 31 March 2 April 1999, 115. (conference talk) Kóthay, K & Szabó, Cs. (1999) Silicate melt inclusion study on olivine phenocrysts from the Hegyestű basalt, Balaton Highland, Hungary. Terra Nostra, 99/6, ECROFI XV, Potsdam, June, 1999, (poster) Kóthay, K. (1999) Petrologic study of silicate melt inclusions in olivine phenocrysts of the Hegyestű basalt (Balaton Highland, Hungary). Berichte der Deutschen Mineralogischen Gesellschaft, Beihefte 6

7 Kóthay, K. & Szabó, Cs. (2000) Rhönite in silicate melt inclusions of olivine phenocrysts from the alkali basalt of Hegyestû, Balaton highland, Hungary. Acta Mineral.-Petrogr., XLI, Suppl., Minerals of the Carpathians International Conference, Miskolc, március 9-10., absztrakt, p. 63. (poszter) Kóthay, K. (2001) Szilikátolvadék-zárványok és fluid zárványok a hegyestűi basalt olivin és klinopiroxén fenokristályaiban. Ifjú Szakemberek Ankétja, Győr, március , Program és absztrakt füzet, p. 26. (előadás) Kóthay, K., Szabó, Cs., Sharygin, V. & Török K. (2001) Silicate melt inclusion study on olivine phenocrysts and clinipyroxene microphenocryst in the Hegyestű basalt, Bakony- Balaton Highland, Hungary. Faculdade de Ciências do Porto, Departemento de Geologia, Memória nº7, 16th ECROFI XVI, Porto, Portugália, május 2-4., absztrakt, pp (poszter) Kóthay, K., Szabó, Cs., Sharygin, V. & Török K. (2001) Silicate melt inclusions in olivine and clinopyroxene microphenocryst from the Hegyestű basalt, Bakony-Balaton Highland, Hungary. PANCARDI 2001 Conference, Sopron, szeptember , Abstracts, PO- 12. (előadás) Kóthay, K. & Szabó, Cs. (2001) Silicate melt inclusions in olivine phenocrysts in the Hegyestű basalt, Bakony-Balaton Highland. MinPet 2001, Bécs, Ausztria, 2001 szeptember 24-26,. Mitt. Österr. Miner.Ges, 146, absztrakt, p. S 151. (poszter) Kóthay, K., (2003) One drop from the magma: silicate melt inclusions in the olivine phenocrysts of alkali basalts. (In Hungarian) Mining, Metallurgy and Geology Conference, Zilău, Románia, április , absztrakt, p. 70. (előadás) Kóthay, K., Pető, M., Szabó, Cs., Török, K., Sharygin, V.V., Timina, T. Ju. & Ntaflos, T. (2003) A comprehensive silicate melt inclusion study of olivine phenocrysts from Hegyestű (Bakony-Balaton Highland) and Pécskő (Nógrád-Gömör) alkali basalts, Pannonian Basin, Hungary. ECROFI XVII Conference, Budapest, június 5-7., Acta Mineralogica- Petrographica, Abstract Series 2, pp (előadás) Kóthay, K.; Pető, M.; Sharygin, V.; Török, K.; Szabó, Cs.(2003) Silicate melt inclusions in olivine phenocrysts from Hegyestu (Bakony-Balaton Highland) and Pecsko alkaline basalts (Nógrád-Gömör), Hungary. EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6-11 April 2003, abstract #748 Sharygin, V.V., Kóthay, K., Pető, M., Török, K., Timina, T. Ju., Vapnik, Y., Kuzmin, D. & Szabó, Cs (2003) Rhönite in alkali basalts: studies of silicate melt inclusions in olivine phenocrysts. ECROFI XVII Conference, Budapest, június 5-7., Acta Mineralogica- Petrographica, Abstract Series 2, pp (előadás) Kóthay, K. (2004) Similarities and differences between primary alkali basaltic magmas from the Bakony-Balaton Highland Volcanic Field, Hungary: evidence from silicate melt inclusions. Mineralogy and Museums 5, Párizs, Franciaország, szeptember 5-8., Bulletin de liaisonde la Société Francaise de Minéralogie et Cristallographie, Vol. 16. No. 2. (poszter) 7

8 Weiszburg, T.G. & Kóthay, K. (2004) Moving the 230 year old Historical Mineral and Rock Collection of the Eötvös Loránd University, Budapest, Hungary to a modern university campus. Mineralogy and Museums 5, Párizs, Franciaország, szeptember 5-8., Bulletin de liaisonde la Société Francaise de Minéralogie et Cristallographie, Vol. 16. No. 2. (poszter) Kóthay, K., Szabó, Cs., Török, K., Sharygin, V. & Ntaflos, T. (2005) Comprehensive study on silicate melt inclusions of olivine phenocrysts from different alkali basalt volcanoes (Hegyestű and Haláp) from the Bakony-Balaton Highland Volcanic Field, Central Pannonian Basin, Hungary. ECROFI XVIII Conference, Siena, Olaszország, július 6-9., Abstracts e-book, p. 03_K_thay.pdf. (előadás) Kóthay, K., Sharygin, V.V., Török, K., Ntaflos, Th. & Szabó, Cs.: New results in study of silicate melt inclusions in Bakony-Balaton Highland Volcanic Field, Pannonian Basin, Western Hungary. European Current Research on Fluid Inclusions (ECROFI-XIX) University of Bern, Switzerland, July, Abstract Volume, p (poszter) 8