Granulite boulders from pleistocene conglomerate Csaba Vígh Geologist student V. Department of Petrology and Geochemistry Eötvös Loránd University Advisors: Sándor Józsa and Péter Horváth Meeting of Young Geoscientist 26-27 March 2010 Mátrafüred

Introduction Pleistocene gravel terrace of Danube has been mined by gravel pits SE from Budapest and Little Hungarian Plain This boulder-bearing gravel is very polymict, contains several exotic rock types with unclear origin (granulites, eclogites, migmatite, amphibolites, granites) Zsemle et al. (2001) first described granulites from this formation however many open questions remained about P-T evolution and source area New samples have been found Our aims: 1.describe the petrography of granulites, 2.calculate P-T conditions, 3. Identify the possible source area

Geological setting: gravel pits from 2 investigated area Web-based version of the Geological Map of Hungary in scale 1:100 000

Field investigations and sampling Öttevény (2009) Dunavarsány (2008)

Analytical methods Macroscopic examination Microscopic textural examination In situ chemical analysis by EPMA Whole-rock analysis by XRF Feldspar thermometer (Furhman&Lindsley 1998) with Solvcalc softwarwe( Wen&Nekvasil 1994) Phase diagram modelling with Perplex software package (Conolly 1990)

Macroscopic features I. Foliated structure with blue coloured visible kyanite grains Granofelsic (non-foliated) structure with red garnets and quartz-feldspatic matrix

Macroscopical features II. Felsic granulite with sillimanite- boundles Banded felsic granulite with light bands and biotite-rich dark bands Gneissose structure with biotite bands

Petrography I. Mosaics of minerals that are interpreted to have once in equilibrium rather than equilibrium mineral assemblages Type1: Garnet-Kyanite granulites Garnet+kyanite+perthitic feldspar+quartz+rutile (±biotite)‏ According to textural features: Porhpyroclastic texture: >1 mm garnet, perthitic feldspar and quartz in a recrystallized two-feldspars+quartz matrix. Garnet porphyroblasts in a finegrained quartz+two-feldspar matrix. Inclusions of garnets give information for early mineral assemblages. Well-developed foliation and lineation: platy quartz and quartz ribbons, oriented kyanite grains (Mp=mesoperthite, Grt=garnet, Qtz=quartz, Rt=rutile Ky=kyanite, Kfs=K-feldspar, Pl=plagioclase Bt=biotite, Spl=spinel)

Petrography II. Type2: Garnet-sillimanite granulites: The boarder of the biotite-rich and biotite-free part of the banded granulite Type2: Garnet-sillimanite granulites: Garnet+sillimanite(Ky)+K- feldspar+plagioclase+quartz+ biotite mineral assemblages Kyanite is commonly replaced by sillimanite: occur as elongate aggregates or prisms Kyanite can be exist as a metastable phase, surronded by plagioclase corona Secondary biotite bands

Mineral chemistry garnet composition and zoning profile Ca-poor almandine-pyrope-rich composition:Alm57-72 Prp25-39 Grs2-12 Sps1-4 And0-1 Zoning compositional profile: Ca-content decreses from core to rim. -> Ca-exchange with plagioclase (matrix and inclusions) XFe and XMg is influenced by formation of retrograde biotite Homogenous garnets, flat compositional profile

Thermobarometry I: Ternary feldspar thermometry

Thermobarometry II: P-T pseudosections

A possible source area: Bohemian massif Variscan orogen zone: granulites associated with high-grade gneisses, eclogites and amphibolites 1. High-pressure granulite facies event with peak mineral assemblages: Grt+Ky+Mp+Qt+Rt T=800-850 P~16-18 kbar 2. Medium-pressure granulite facies overprint associated with Grt+Sil+Kfs+Pl+Qtz+Bt+Ilm mineral assemblages

Summary Two types of granulites were identified: 1. Garnet-kyanite granulites: Grt-Ky-Mp-Qtz-Rt 2. Garnet-sillimanite granulites: Grt-Sil-Kfs-Pl-Qtz-Bt- Ilm Pseudosection modeling show a high-pressure and high- temperature peak metamorphism ( 900 °C, ~18 kbar) that was followed a decompression and cooling. The nearest occurrences of similar felsic granulites are on the Moldanubian part of the Bohemian massif- >regarded as a possible source region of the investigated granulite samples