1. 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

2. 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

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

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

5. 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)

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

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

8. 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)

9. 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

10. 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

11. Thermobarometry I: Ternary feldspar thermometry

12. Thermobarometry II: P-T pseudosections

13. 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= P~16-18 kbar
2. Medium-pressure granulite facies overprint associated with Grt+Sil+Kfs+Pl+Qtz+Bt+Ilm mineral assemblages

14. 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