Lower crustal granulite xenoliths from the Pannonian Basin, Hungary. Part 1: mineral chemistry, thermobarometry and petrology

2003 ◽  
Vol 144 (6) ◽  
pp. 652-670 ◽  
Author(s):  
Antal Embey-Isztin ◽  
Hilary Downes ◽  
Pamela D. Kempton ◽  
Gábor Dobosi ◽  
Matthew Thirlwall
Keyword(s):  
Pannonian Basin ◽  
Mineral Chemistry ◽  
Lower Crustal ◽  
Granulite Xenoliths

Mafic granulites and clinopyroxenite xenoliths from the Transdanubian Volcanic Region (Hungary): implications for the deep structure of the Pannonian Basin

1990 ◽  
Vol 54 (376) ◽  
pp. 463-483 ◽  
Author(s):  
A. Embey-Isztin ◽  
H. G. Scharbert ◽  
H. Dietrich ◽  
H. Poultidis
Keyword(s):  
Upper Mantle ◽  
Pannonian Basin ◽  
Granulite Facies ◽  
Mantle Xenoliths ◽  
Geochemical Data ◽  
Moderate Pressure ◽  
Spinel Lherzolites ◽  
Volcanic Region ◽  
Lower Crustal ◽  
Granulite Xenoliths

AbstractThe Transdanubian Volcanic Region (TVR) is composed mainly of Pliocene alkali basalts, basanites, olivine basalts and olivine tholeiites, as well as rare nephelinites. The partial melting and genesis of alkali basaltic liquids is a consequence of an upwelling of the upper mantle which also caused thinning of the lithosphere and recent sinking of the Pannonian Basin.Four different types of lower crustal and upper-mantle xenoliths are found within the TVR: garnet-free and garnet-bearing granulites, clinopyroxenites and spinel lherzolites. We present mineralogical and geochemical data on granulite facies and clinopyroxenite xenoliths from three localities in the Hungarian part of the TVR (Bondoróhegy, Szentbékálla and Szigliget). It is concluded that, whilst the protoliths of the granulite facies xenoliths were tholeiitic igneous rocks and could be part of an ancient crust, the clinopyroxenite xenoliths represent recent underplating and may have formed from an alkali basaltic liquid similar to the host lava. Planar contact relations between clinopyroxenites and spinel lherzolites as observed in composite xenoliths, as well as high Al-contents in clinopyroxenes, point to a high-pressure genesis in the upper mantle for these rocks. In contrast, geobarometrical estimates yielded only a moderate pressure range characteristic of lower crustal levels for the garnet-free granulite xenoliths (7–9 kbar). Nevertheless, two-pyroxene geothermometry yielded high temperatures of equilibration (>900°C) for these xenoliths, probably caused by advective heat transfer connected with underplating and in agreement with the high present-day geothermal gradient of this region. In the Central Range localities only garnet-free granulite xenoliths occur, whereas at the border of the TVR both garnet-free and garnet-bearing granulite facies nodules are found. It is possible that the incoming of garnet is retarded by higher temperatures in the lower crust below the Central Range.It is also suggested that the difference in seismically measured crustal thickness between the Central Range and adjacent basin areas may be connected with different thermal conditions below these regions and that the seismically defined Moho and the petrological Moho do not necessarily coincide.

scholarly journals Lower crustal zircons reveal Neogene metamorphism beneath the Pannonian Basin (Hungary)

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Hilary Downes ◽  
Andrew Carter ◽  
Richard Armstrong ◽  
Gabor Dobosi ◽  
Antal Embey-Isztin
Keyword(s):  
Pannonian Basin ◽  
Granulite Facies ◽  
Blocking Temperature ◽  
Late Devonian ◽  
Alkali Basalts ◽  
Volcanic Deposits ◽  
Eruption Age ◽  
Crustal Xenoliths ◽  
Lower Crustal ◽  
Variscan Basement

AbstractNeogene alkaline intraplate volcanic deposits in the Pannonian Basin (Hungary) contain many lower crustal granulite-facies xenoliths. U-Pb ages have been determined for zircons separated from a metasedimentary xenolith, using LA-ICPMS and SHRIMP techniques. The zircons show typical metamorphic characteristics and are not related to the hostmagmatism. The oldest age recorded is late Devonian, probably related to Variscan basement lithologies. Several grains yield Mesozoic dates for their cores, which may correspond to periods of orogenic activity. Most of the zircons show young ages, with some being Palaeocene-Eocene, but the majority being younger than 30Ma. The youngest zircons are Pliocene (5.1-4.2 Ma) and coincide with the age of eruptions of the host alkali basalts. Such young zircons, so close to the eruption age, are unusual in lower crustal xenoliths, and imply that the heat flow in the base of the Pannonian Basin was sufficiently high to keep many of them close to their blocking temperature. This suggests that metamorphism is continuing in the lower crust of the region at the present day.

Symplectite formation during decompression induced garnet breakdown in lower crustal mafic granulite xenoliths: mechanisms and rates

2009 ◽  
Vol 159 (3) ◽  
pp. 293-314 ◽  
Author(s):  
Júlia Dégi ◽  
Rainer Abart ◽  
Kálmán Török ◽  
Enikő Bali ◽  
Richard Wirth ◽  
...  
Keyword(s):  
Mafic Granulite ◽  
Lower Crustal ◽  
Granulite Xenoliths

Lower crustal contamination of Deccan Traps magmas: evidence from tholeiitic dykes and granulite xenoliths from western India

2008 ◽  
Vol 93 (3-4) ◽  
pp. 243-272 ◽  
Author(s):  
A. G. Dessai ◽  
H. Downes ◽  
F.-J. López-Moro ◽  
M. López-Plaza
Keyword(s):  
Crustal Contamination ◽  
Deccan Traps ◽  
Western India ◽  
Lower Crustal ◽  
Granulite Xenoliths

Almandine garnet phenocrysts in a ~1 Ga rhyolitic tuff from central India

2008 ◽  
Vol 146 (1) ◽  
pp. 133-143 ◽  
Author(s):  
SARBANI PATRANABIS-DEB ◽  
JUERGEN SCHIEBER ◽  
ABHIJIT BASU
Keyword(s):  
Central India ◽  
Mineral Chemistry ◽  
Triple Junctions ◽  
Fine Grained ◽  
Mineral Inclusions ◽  
Major Oxide ◽  
Shale Formation ◽  
Igneous Zircon ◽  
Compositional Variability ◽  
Lower Crustal

AbstractWe report on the newly discovered almandine garnet phenocrysts in rhyolitic ignimbrites (Sukhda Tuff) in the Precambrian Churtela Shale Formation of the Chhattisgarh Supergroup in central India. SHRIMP ages of igneous zircon from the ignimbrites range from 990 Ma to 1020 Ma. These ignimbrites exhibit characteristic eutaxitic texture with compacted curvilinear glass shards with triple junctions. Quartz (commonly embayed; bluish cathodoluminescence) and albite (altered but retaining ghosts of twinning) are common phenocrysts; others are apatite, ilmenite, rutile, magnetite, zircon, monazite and garnet. There are no metamorphic or granitic xenoliths in the ignimbrites. Garnet grains occur as isolated broken isotropic crystals with sharp or corroded boundaries in a very fine-grained groundmass of volcanic ash that consists principally of albite, quartz, magnetite and glass. They do not have any systematically distributed inclusions. A few have penetratively intergrown phenocrysts of apatite, ilmenite, rutile and zircon, which we interpret as subophitic texture. Extensive SEM-BSE imaging of more than 100 grains and electron microprobe traverses across about 30 grains showed no zoning or systematic compositional variability. Common (metamorphic) garnets are usually zoned with respect to Fe–Mg–Mn and typically have mineral inclusions. We infer, therefore, that these observed garnets are not metamorphic xenocrysts. The average major oxide composition of analysed garnets from five different horizons within the Sukhda Tuff, spanning approximately 300 m of the stratigraphic section, have very small standard deviation for each element, which is suggestive of a single magmatic source. Phenocrysts of quartz, including those in contact with coexisting garnets, show blue scanning electron CL, indicating rapid cooling from high temperature; this suggests that adjacent coexisting garnets are not slowly cooled restites. We conclude, on the basis of texture, mineral chemistry and absence of any indicative xenoliths or xenocrysts, that these almandine garnets (Al78.7Py12.3Gr7.4Sp1.6) are phenocrysts within the Sukhda Tuff. Almandine of such composition is stable under high pressure. We infer that almandine crystallized at lower crustal depths in a magma that ascended very rapidly and may have erupted explosively.

Metamorphism, isotopic ages and composition of lower crustal granulite xenoliths from the Cretaceous Salta Rift, Argentina

1999 ◽  
Vol 134 (4) ◽  
pp. 325-341 ◽  
Author(s):  
Friedrich Lucassen ◽  
Sven Lewerenz ◽  
Gerhard Franz ◽  
José Viramonte ◽  
Klaus Mezger
Keyword(s):  
Lower Crustal ◽  
Granulite Xenoliths
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