Download Výzkumný záměr – 9200

Results in 2007
SUBPROJECT (Code 9200): History of the Bohemian Massif before and after its consolidation
(Co-ordinator V.Cajz, contributions: J. Adamovič, K. Breiter, J. Fiala, J. Filip, M. Chadima, M. Lang,
O. Man, P. Schnabl and M. Svojtka)
Basic research of this project followed several independent ways:
Hydrothermal ferruginization effects were produced in areas of Tertiary alkaline volcanism of the
Bohemian Massif based on the interaction between volcanic rocks and the ambient porous sedimentary
rocks. Spherical goethite-hematite concretions in the Czech sandstones are analogous in many respects to
those found by the Spirit and Opportunity rovers on the surface of Mars. Magnetic properties of the
terrestrial concretions also revealed a minor proportion of magnetite. Field geomagnetic measurements
confirmed their spatial association with basaltic bodies, and XRD and microprobe analyses showed their
layered internal structure with colloform cement rich in phosphorus. The obtained data support the idea of
bacterially-mediated concretion growth within the reach of iron-laden hydrothermal fluids, and contribute
to the discussion on the presence of water and microbial life on Mars.
Volcanic rocks with high content of titanium in the titanomagnetite lattice (up to 18 %) were studied,
using the dependence of magnetic susceptibility (MS) on the field in the inducting coil, to show the relative Ti
content. The samples with titanium rich titanomagnetites have MS in the high field 20% higher than in the low
field. The samples with low amount of titanium in the lattice have high-field MS similar to low-field one. The
dependence of magnetic susceptibility on temperature on these samples had shown variable Curie temperature
– 500 - 580 °C for high-Ti content and 200 – 250 °C for low-Ti content. These results are crucial for
magnetostratigraphic interpretations.
Magnetostratigraphic data obtained in the paleomagnetic laboratory of our institute and those
known from world literature were used to prove the possibility of the identification of sequences of
polarity zones without complementary information. These zones represent the imprint of alternating
polarity of geomagnetic field on the forming sediments. The possibility of their identification will
improve the dating of sections formed by continuous sedimentation in some parts of the last 166 Ma of
the geological history. Following a common trend, we are planning close connection between
magnetostratigraphy and cyclostratigraphy, which is another method of dating young sediments.
The anisotropy of magnetic susceptibility (AMS) has been recognized as a highly sensitive
indicator of rock fabric and widely employed in the field of structural geology. Several methods have
been developed in order to separate paramagnetic and ferrimagnetic sub-fabrics, such as exploiting the
field or temperature dependence of magnetic susceptibility or the measurement of anisotropy of
anhysteretic remanence. The combination of rock magnetic measurements with nonmagnetic analysis
demonstrates that magnetic minerals distribution has an important control on magnetic anisotropy.
U-Pb dating of detrital zircons separated from paragneiss of eastern Crete yielded peaks in
207
Pb/206Pb ages at 0.6, 0.8, 1.0, 2.0, and 2.5 Ga with Mesoproterozoic age gap between 1.1 and 1.6 Ga.
These data are compatible with U-Pb zircon ages of surrounding crystalline complexes of the Cyclades,
the Menderes Massif, Egypt and the Levant. Possible provenances are the Sahara metacraton, the
Arabian-Nubian Shield, and the Kibaran belt of central Africa. The age spectra of the studied EastMediterranean crystalline complexes differ significantly from those of the Cadomian-Avalonian type
terranes. They are, therefore, regarded as a separate collection of peri-Gondwanan terranes referred to as
Minoan terranes. In late Neoproterozoic to ?Cambrian times, the latter underwent Andean-type orogeny at
the northern border of East Gondwana. There is no evidence that the Minoan terranes traveled for a long
distances in Phanerozoic times.
Based on the limited available deglaciated outcrops in the James Ross and Seymour Islands
(Antarctica), the detrital zircons and apatites were dated using fission-track analysis. FT provenance age
of individual zircons and apatites from studied area varies in wide spread of Carboniferous to Early
Paleogene ages (~315 to 60 Ma). It is probable that the FT dating and shortening of individual zircons and
apatites from the samples taken at the northwest James Ross Island and Seymour Island reveal predepositional history of individual rocks before entering into the James Ross Basin.
Kručné hory / Erzgebirge Mts. granite samples from the Nejdek pluton and adjacent small
intrusions were investigated using apatite fission-track (AFTA) dating method. The samples raised from
total annealing zone during time interval from 140 Ma to 245 Ma. Preliminary interpretation revealed that
the unit situated at south of the Sokolov basin was uplifted significantly earlier (approx. 245 Ma) than the
Krušné hory Mts. unit (from 140 Ma to 185 Ma). Preliminary results demonstrate similarly earlier uplift
of Saxothuringicum in comparison with results published for Bavaricum (from 44 Ma to 69 Ma) till now.
Geochemical and mineralogical study of small granite body near Hory sv. Kateřiny (same area)
reveal its subvolcanic origin and strong enrichment F, Rb, Sn, Nb, W, Th, Zr, HREE, and Be. Fast
decrease of temperature and pressure during intrusion resulted in crystallisation of quartz layers in form
of unidirectional solidification textures. Contents of trace elements in quartz were analysed using LAICP MS. The most important result is, that Al-entry in quartz lattice is not correlated with Al-activity in
melt, but with concentration of water and fluorine. Monazite, xenotime, thorite and zircon are common
accessories in studied granite. These minerals generally are not able to form mixtures among each other.
But, in condition of water- and fluorine-rich granite melt, we found unlimited miscibility among slightly
hydrated varieties of xenotime, thorite and zircon.
Analyses of the rock-forming minerals of phonolite, xenoliths of phonolite and trachyte were
processed by MINPET 2 program to crystalochemical formulas of pyroxene, amphibole, apatite, sphene,
glimmers, feldspars and nepheline. The bulk of crystalochemical data was processed graphically in
classification diagrams.
Fig. 1. A schematic profile across a hematite-goethite concretion from the Slunecna site near Česká Lípa, Bohemian
Cretaceous Basin. Zones: P-rich colloform goethite (1) passing to crystalline goethite (2), zone with acicular hematite crystals
(3), cloudy hematite aggregates (4) and large hematite crystals intergrown in tile-like pattern (5); the outermost massive
goethite±hematite (6).
seznam našich impaktů jen doplňkově:
Adachi T., Kletetschka G., Chan M., Mikula V., Adamovic J., Pruner P., Schnabl P. and Wasilewski P.
(2007): High field remagnetization of hematite concretions from Utah, USA and Czech Republic.
Abstracts 38th Lunar and Planetary Science Conference, March 12-16, 2007, League City, Texas.
Adachi T., Kletetschka G., Mikula V., Chan M., Adamovic J., Herrero-Bervera E. and Fuller M. (2007):
Testing the origin of Martian "blueberries": Magnetic measurements may be key to the answer. Abstracts
59th Annual Meeting, GSA, Rocky Mountain Section, 7-9 May 2007, St. George, Utah.
Cifelli F., Mattei M., Chadima M., Lenser S. and Hirt A.M. (2007) : The importance of the AMS analysis
for reconstructing the tectonic history in weakly deformed sediments. – IUGG XXIV General Assembly,
July 2-13, 2007, Perugia, Italia. (CD only)
Kletetschka G., Adachi T., Adamovic J., Mikula V. and Chan M. (2007): Utah and Czech Mars analog
concretions; Aquatic hematite and goethite characterization. Goldschmidt Conference Abstracts 2007. –
Geochim. Cosmochim. Acta, 71, 15: A 493. Suppl. S.
Man O. (2007): The (un)ambiguity of identification of magnetostratigraphic polarity zones. Poster,
Magnetic Interactions UK 2007, organized by Department of Earth Sciences, University of Cambridge,
January 9-10, 2007.
Murakami M. and Svojtka M. (2007): Zircon fission-track technique: a laboratory procedure adopted at
the Institute of Geology, Academy of Sciences of the Czech Republic, v.v.i. Fission Track News Letter, 20,
13-19.
Radoň, M., Langrová, A., Ulrych J. and Skála R. (2007): Draselný živec z čediče významné
mineralogické lokality na vrchu Kočka u Žitenic v Českém středohoří. [K-feldspar from basalt of the
prominent mineralogical site at Kočka hill near Žitenice, České středohoří Mts.]. – Bull. mineral.petrolog. Odd. Nár. Muz. (Praha), 15, 20 pp.
Zulauf G., Romano S. S. Dörr W. and Fiala J. (2007): Crete and the Minoan Terranes: Age constraints
from U-Pb dating of detrital zircons. In: Linnemann U., Nance R. D., Kraft P., Zulauf G. (eds.): The
evolution of the Rheic Ocean: From Avalonian-Cadomian active margin to Alleghenian-Variscan
Collision. - Geological Society of America, Special Paper 423: 401-411.