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Lehrstuhl für Geodynamik und Geomaterial- forschung
Arbeitskreis Archäometrie und Denkmalpflege der DMG
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Variscan Basement in Northeast Bavaria and West Bohemia, including KTB Pan-African Basement of the Wilson Terrane, northern Victoria Land and Oates Coast, Antarctica Eocene-Oligocene Impact structures in Spain
Variscan Basement in Northeast Bavaria and West Bohemia, including KTB
Petrology, geochemistry and K-Ar/Ar-Ar age determinations on metabasic rocks in the KTB target area and adjacent regions In the course of the KTB pre-investigations, metabasic rocks of all tectonometamorphic units in the surrounding of the KTB target area in Northeast Bavaria and the neighbouring West Bohemia have been investigated concerning The investigations include the Zone of Erbendorf-Vohenstrauss, the Zone of Tirschenreuth-Mähring, the Fichtelgebirge, the Zone of Tepla-Domazlice and the adjacent Moldanubian. Metabasites of the Münchberg Gneiss Complex were analysed by a cooperating working group (Seidel et al.). Results in:
Petrology of very high-pressure calc-silicate rocks of the Münchberg gneiss complex Calc-silicate band and boudins are interlayered with eclogites and high-pressure gneisses within the Weissenstein drill core and contain the mineral assemblage grossulare-rich garnet + diopside + quartz + zoisite + clinozoisite + calcite + rutile + titanite. Reactions between these minerals have been modelled in the CaO - Al2O3 - SiO2 - CO2 - H2O system with an internally consistent thermodynamic data base (Klemd). High pressure metamorphism has been estimated at a minimum pressure of 31 kbar at a temperature of 360°C with XH2O >0.03. Results in:
Interlayers of ultramafic rocks in the KTB drill core Ultramafic intelayers in the KTB drill core are similar to rocks which have been detected in surface outcrops of the KTB target area. In their composition these rocks are talc-chlorite-amphibole felses, also called “hösbachites”. From their educt, they are interpreted to represent basic cumulates of basaltic sills. Intergrowth of various amphiboles have been observed by optical microscope, electron microprobe, but in a nm-scale also by TEM. Results in:
Age and geological position of the Cu-Zn ore deposit Kupferberg-Wirsberg at the margin of the Münchberg gneiss complex In the area of Kupferberg, the stratiform deposit is bound to a pile of dark and in part sapropelitic, but also tuffite sediments and small basaltic intercalations which was formerly assumed to have Odovician age. However, the detection of a rich occurrence of microfossils (Schüssler) and their classification as Lower Ems acritarchs (Hammann) and spores (Heunisch) clearly showed the Lower Devonian age of these sediments and therefore the maximum age of the ore deposit. In the area of Wirsberg, a similar deposit occurs within a sequence of phyllites and prasinites, which was formerly interpreted as a low-grade metamorphic equivalent of the Kupferberg sediments. The Vendian age of the phyllites, the different chemical composition of the prasinites and the tectonic position of the prasinite-phyllite-series as a separate nappe unit, however, do not support this view. Therefore, the deposit of Kupferberg and the deposit of Wirsberg genetically have to be seen as two separate ore deposites despite of their spacial, lithological and petrological similarities. Results in:
Pan-African Basement of the Wilson Terrane, northern Victoria Land and Oates Coast, Antarctica Since 1988, the expeditions GANOVEX V and VII of the Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover (Germany) and the joint GANOVEX VIII - ITALIANTARTIDE XVIII expedition have visited Oates Coast (sometimes also called “Oates Land”) west of northern Victoria Land at the Pacific end of the Transantarctic Mountains. During these expeditions, a systematic geological mapping and sampling was carried out for the first time in the Oates Coast area. The high-grade basement of the northwestern Wilson Terrane at Oates Coast is subdivided into three roughly north-south trending zones on the basis of tectonic thrusting (Flöttmann, Kleinschmidt) and differences in metamorphic petrology (Schüssler). Results of detailed petrological investigations show that metamorphic rocks of the central zone were formed in course of one single, clockwise directed P-T evolution including a medium-pressure and high-temperature granulite-facies stage at about 8 kbar and >800°C, a subsequent isothermal decompression and a final stage with retrograde formation of biotite + muscovite gneisses. In the eastern and western zone the majority of metamorphic rocks experienced clockwise oriented metamorphism at somewhat lower P-T conditions of about 4-5.5 kbar and 700–800°C. While few rocks in both zones even hardly reached the upper stability limit of muscovite + quartz, granulite-facies rocks have now been detected in parts of the western zone which were formed under P-T conditions similar to those of the central zone. U-Pb (Bröcker) and SHRIMP data (Henjes-Kunst) support an age for the metamorphic peak of 499-500 Ma. 40Ar-39Ar dating (Henjes-Kunst) of amphiboles and micas indicate a general trend to younger ages from the west to the east of the basement complex, i.e. from 488–486 Ma to 472–469 Ma for amphiboles and from 484–482 Ma to 466 Ma for micas. This is explained by temporal differences in the retrograde metamorphic evolution of the three zones in the course of the late-Ross-orogenic thrust-related uplift of the basement complex. Results in: Geological Maps:
Eocene-Oligocene Impact structures in Spain Within the Iberian Chains west of Zaragoza, the new impact structure of Rubielos de la Cérida was recently detected several tens of kms beside the well established Azuara impact structure. Both impact structures were formed about 30 million years ago and therefore are assumed to represent a double impact. The geology of the target area is strongly dominated by sedimentary rocks which behave completely different from crystalline target rocks. As components in various impact breccia of the Rubielos de la Cérida structure, different melt rocks were found. Silicate melt rocks occur as dm-wide inclusions in the breccia and consist of loosely welded sphaeroidal or irregularly formed glass particles. Other samples show amoebae-like carbonate droplets swimming within a phosphate matrix which in part is glassy and in part recrystallized apatite. The carbonate droplets are interpreted as quench products of a former carbonate melt, immiscible with a coexisting phosphate melt. Melt rocks with similar texture are also described from the Nördlinger Ries and the Haughton crater. Very fine-grained glassy particles are dispersed in components of a suevite-like impact rock, as shown by x-ray diffraction analysis. At least, very hard and slag-like particles of amorphous carbon (+oxygen) were found, which most probably result from a reduction process of carbonate target rocks in the course of the impact. In den iberischen Ketten westlich von Zaragoza wurde neben dem seit längerem bekannten Azuara Impaktkrater vor kurzem ein weiterer Impakt bei Rubielos de la Cérida entdeckt. Da beide Strukturen etwa zeitgleich vor etwa 30 Millionen Jahren entstanden, kann man von einem Doppelimpakt ausgehen. Die Gesteine des Zielgebietes sind zum allergrößten Teil Sedimentgesteine, die auf Impakt z.T. völlig anders reagieren als Kristallingesteine. Innerhalb verschiedener Impaktbrekkzien der Rubielos de la Cérida Struktur wurden verschiedenartige Schmelzen entdeckt. Silikatische Schmelzen treten in dm-großen Stücken auf und bestehen aus lose aneinandergeschweißten kugeligen oder fetzenartigen Glaspartikeln. Einige sehr eigenartige Proben zeigen amöbenförmige Karbonatpartikel, die in einer phosphatischen Matrix schwimmen, letztere z.T. verglast, z.T. zu Apatit rekristallisiert. Die Kabonate werden als Quenchprodukte einer ehemaligen Karbonatschmelze interpretiert, die auf Grund einer Nichtmischbarkeit mit der phosphatischen Schmelze in letzterer schwimmen. Schmelzen mit ähnlicher Stuktur sind auch aus dem Nördlinger Ries und dem Haughton-Krater beschrieben. Feindispers verteilte Schmelze wurde mittels Diffraktometrie in Partikeln eines Suevit-ähnlichen Gesteins nachgewiesen. Schließlich wurden noch sehr harte, schlackenartige Partikel aus röntgenamorphem Kohlenstoff (+Sauerstoff) gefunden, die höchstwahrscheinlich durch Reduktion aus Karbonat in Folge des Impakts entstanden sind. Results in: Poster-presentation of our working group at the 6th ESF-Impact Workshop “Impact markers in the stratigraphic record”, Granada, 19.-25.5.2001 (abstracts here)
West-central pan-African mobile belt in Nigeria and Cameroon The West-Central African mobile belt is situated between the West African Craton to the west and the Congo Craton to the south and experienced its most recent penetrative deformation, metamorphism and related plutonic activity during the pan-African orogeny. Within the Ilesha schist belt of Nigeria, the metamorphosed mafic-ultamafic complex of Mokuro in southwestern Nigeria was investigated. The most common mafic rocks are layered amphibolites, massive amphibolites and apatite-rich amphibolites. Among the massive ultramafic rocks, nearly monomineralic amphibole rocks predominate, while chlorite-amphibole, talc-chlorite-amphibole and talc-olivine-chlorite-amphibole rocks occur in subordinate amounts. The complex is interpreted to derive from a thick, structurally differentiated basaltic sill with formation of ultramafic cumulates. The metamorphic peak conditions of 1.5 - 3 kbar and 550 - 620°C were estimated by thermodynamic calculations in the CMFASH-system (Schmädicke). Results in: Subject of a recently finished DAAD doctorate project of Merline Laure Djouka Fonkwe is the Central African mobile belt in the area of Bafoussam in West Cameroon. The predominant rock units are various pan-African granitoid intrusions which, after detailled fieldwork including geological mapping, are investigated petrographically, geochemically and by their isotope composition. Aim is to learn about the differences and relationships between the various granitoid types, at least for a comparison with granitoids of neighbouring regions and the continuation of the mobile belt in Brazil. Part of the granitoids was deformed in the course of tectonic activity along the Adamaoua shear-zone. The project was carried out in cooperation with Dr. Jean-Pierre Tchouankoué, University of Yaoundé I, Cameroon. A new investigation carried out by Bernhard Schulz includes age determination of monazite in the granites by use of chemical electron microprobe analyses. These will soon be published together with results of Rb-Sr and Sm-Nd analyses and further results of Djouka Fonkwe (2005). Results in:
Ore petrology - various projects Results in:
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