Gerhard Franz

Gerhard Franz
Technische Universität Berlin | TUB · Institut für Angewandte Geowissenschaften

Prof. Dr.

About

258
Publications
54,022
Reads
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6,558
Citations
Citations since 2016
34 Research Items
2234 Citations
20162017201820192020202120220100200300
20162017201820192020202120220100200300
20162017201820192020202120220100200300
20162017201820192020202120220100200300
Additional affiliations
July 1976 - present
Technische Universität Berlin
Position
  • Prof. of Petrology-Mineralogy

Publications

Publications (258)
Preprint
Full-text available
The Volyn biota, fossilized organisms with a minimum age of 1.5 Ga, were found in cavities in granitic pegmatites from the Korosten pluton, NW Ukrainian shield. Fossilization was due to influx of hydrothermal fluorine-rich waters, which silicified the outermost part of the organisms, thus preserving the 3D morphology. Details of the morphology (inv...
Article
Full-text available
We report on Precambrian microfossils from igneous rocks of the Volyn pegmatite district, associated with the Paleoproterozoic Korosten pluton, northwestern Ukraine. The fossils were recovered from meter-sized miarolitic cavities and show a well-preserved 3D morphology, mostly filamentous but with a large variety of types and also in irregular, fla...
Article
Full-text available
We determined 40Ar/39Ar ages of buddingtonite, occurring together with muscovite, with the laser-ablation method. This is the first attempt to date the NH4-feldspar buddingtonite, which is typical for sedimentary–diagenetic environments of sediments, rich in organic matter, or in hydrothermal environments, associated with volcanic geyser systems. T...
Preprint
Abstract: We report on Precambrian soft-tissue microfossils from igneous rocks of the Volyn pegmatite district, associated with the Paleoproterozoic Korosten Pluton, northwestern Ukraine. The fossils were recovered from m-sized miarolitic cavities and show a well-preserved 3D morphology, mostly fibrous, but with a large variety of fiber types, and...
Article
Full-text available
The chemical composition of metasediments is a valuable source of paleogeographic information about the protolith's sedimentary environment. Here, we compile major-and trace-element whole-rock data, including B contents, and 10/11 B-isotope ratios from the Permo-Triassic metasedimentary cover of the Pfitsch-Mörchner basin, overlying the Variscan ba...
Article
Full-text available
Metabasic rocks of the ophiolitic sequences of the Glockner Nappe and Eclogite Zone in the south-central Tauern Window, Austria, reveal important insights into rifting and spreading of the Alpine Tethys. U–Pb dating of magmatic zircons yields a concordant 157 ± 2 Ma crystallization age for the precursor of a coarse-grained metagabbro from the Glock...
Article
Full-text available
The metastable paragenesis of corundum and quartz is rare in nature but common in laboratory experiments where according to thermodynamic predictions aluminium-silicate polymorphs should form. We demonstrate here that the existence of a hydrous, silicon-bearing, nanometer-thick layer (called “HSNL”) on the corundum surface can explain this metastab...
Article
Ocean oxygenation during the Precambrian-Cambrian transition is thought to be one of the key factors for the rapid diversification of animals, known as the ‘Cambrian Explosion’. Siliceous sponges inhabiting continental slope settings were capable of shifting the respiratory oxygen demand in the water column to depth, resulting in an increase in oxy...
Article
We investigated emerald, the bright-green gem varietal of beryl, from a new locality at Kruta Balka, Ukraine and compare its chemical characteristics with those of emerald from selected occurrences worldwide (Austria, Australia, Colombia, South Africa, Russia) in order to clarify the types and amounts of substitutions as well as the factors control...
Article
Beryl crystals from Minas Gerais (Brazil), Lumäki (Finland), Sichuan (China), and the Himalayas have been investigated by scanning electron microscopy in order to characterize the shape of etch pits on different crystal faces. The objective was to find out whether etch pits on natural crystals can be used as tools to study provenances and the disso...
Conference Paper
Tourmaline, a common accessory mineral in the metasedimentary units of the Pfitsch Formation in the Western Tauern Window, Eastern Alps, records the variation in fluid composition and B mobilization during Alpine metamorphism. These post-Variscan metasediments are part of the Subpenninic nappes, the former European distal margin, and experienced pe...
Article
The Münchberg Massif in northeastern Bavaria, Germany is an allochthonous metamorphic nappe complex within the Saxothuringian Zone of the Variscan orogen. From top to bottom it consists of four major units: Hangend-Serie, Liegend-Serie, Randamphibolit-Serie and Prasinit-Phyllit-Serie, which show an inverted metamorphic gradient of eclogite- to amph...
Article
Full-text available
The Volyn pegmatites from Volodarsk-Volynskyi in the Zhytomyr Oblast, NW Ukraine, are associated with granites genetically related to the Paleoproterozoic Korosten pluton. Their late-stage evolution is characterized by the formation of opal-cemented breccia. A polymineralic pseudomorph after beryl within the breccia includes bertrandite (±euclase)...
Article
Metaigneous mafic and ultramafic rocks from the juvenile Neoproterozoic Arabian Nubian Shield (ANS) and the Proterozoic, reworked Saharan Metacraton (SMC) have been analysed for major- and trace elements and Sr, Nd, and Pb isotopes. Most of the rocks are amphibolites metamorphosed at amphibolite facies, some with relicts of granulite facies. The ot...
Article
Many studies dealing with the synthesis of tourmaline report a sharp intragranular chemical gradient such as extensive porosity in the tourmaline root zones both of which still lack a reliable explanation. Using the example of olenitic tourmaline, we show that these features are likely explained by the occurrence of a precursor phase during tourmal...
Article
Tourmaline is a common accessory mineral in the metasedimentary Pfitsch Formation located in the Pfitscher Joch (Passo de Vizze) area in the Tauern Window of the Eastern Alps. These post-Variscan metasedimentary units experienced peak metamorphic conditions of ~ 550 °C, 1.0 GPa during the Alpine orogeny. Tourmaline is most abundant in a ~ 25 m thic...
Article
Subduction zones are the sites where crustal materials are recycled into the mantle. In response to increasing pressures and temperatures during this process, hydrated minerals break down and release solute-bearing fluids, and, above ~750˚C, form hydrous melts. Magmas generated by interaction of these melts and fluids with the mantle have a charact...
Conference Paper
Tourmaline (Tur) is a common accessory mineral in the metasedimentary Pfitsch Formation located in the Pfitscher Joch area in the W Tauern Window of the Eastern Alps. These post-Variscan metasedimentary units experienced peak metamorphic conditions of ~550°C, 1.0 GPa during the Alpine orogeny (Selverstone et al. 1984). Tur is most abundant in a ~25...
Article
Full-text available
It has been established that important changes in the marine environment and the biosphere occurred during the Cambrian. However the relationships between the so-called “ Cambrian Explosion” and the concomitant environmental changes are not yet fully understood. This study presents new geochemical data from the black shale successions from differen...
Article
Full-text available
Ca-Na partitioning between tourmaline and a coexisting fluid is investigated in the system CaO-Na2O-B2O3-Al2O3-MgO-SiO2-H2O-Cl between 0.2 – 4.0 GPa and 500 – 700 °C. The synthesis experiments produced a mineral assemblage of tourmaline, coesite/quartz, and in some cases additional phases, typically comprising <1 wt.% of the solid product. The synt...
Article
Olenitic tourmaline with high amounts of tetrahedral B (up to 2.53 [4]B pfu) has been synthesized in a piston-cylinder press at 4.0 GPa, 700 °C, and a run duration of 9 days. Crystals are large enough (up to 30 × 150 μm) to allow for reliable and spatially resolved quantification of B by electron microprobe analysis (EMPA), single-crystal X-ray dif...
Poster
Full-text available
A reinterpretation of the metasediments of the Pfitsch-Mörchner Basin in the Western Tauern Window (E-Alps), based on the geodynamic context at the time of deposition. Our findings highlight the value of analysing rock units in context rather than isolated.
Article
Full-text available
We present an example where xenotime-(Y) together with metamorphic zircon replaces detrital zircon in a phosphatic sandstone from the Mesoproterozoic Espinhaço fold belt, Brazil, in a dissolution–precipitation reaction: zircon1relict + P-bearing fluid = zircon2metamorphic + xenotime. During the Brasiliano orogeny at 634 ± 19 Ma, the rocks experienc...
Article
Tourmaline was synthesized in the system MgO–Al2O3–B2O3–SiO2–KCl–NaCl–H2O from an oxide mixture and excess fluid at 500–700 °C and 0.2–4.0 GPa to investigate the effect of pressure, temperature, and fluid composition on the relative incorporation of Na and K in dravitic tourmaline. Incorporation of K at the X-site increases with pressure, temperatu...
Article
Full-text available
The occurrence of a trioctahedral analog of illite, the dioctahedral interlayer-deficient K-mica, has long been debated. Due to the inherent difficulties of determining structure and chemical composition of the extremely fine-grained material, earlier descriptions based on separated material are equivocal. Here we describe low-temperature (diagenet...
Article
The N-S running Espinhaço fold belt, situated in the São Francisco craton in central-eastern Brazil, separates this craton in a western and an eastern part along the Paramirim Corridor, a Brasiliano-Panafrican (∼650–500 Ma) deformation zone. The (meta)sediments of the Espinhaço basin consist of several synthems with dominantly siliciclastic deposit...
Conference Paper
Metamorphic rocks are the most important indicators for deciphering the evolution of an orogeny by determination of P-T conditions, time constraints and deformation conditions. However, the type of protolith may also contribute to a better understanding of the complete orogenic cycle. For meta-igneous rocks, this is well established, but for metase...
Article
In situ Fe(0) permeable reactive barriers are suitable for the passive treatment of various hazardous substances in groundwater. Unavoidable secondary minerals on cast iron granules (Fe(0)) in permeable reactive barriers cause passivation and reduction of pore volume. Precipitate agglomeration on mixing components might reduce the passivating layer...
Conference Paper
Full-text available
Hydrothermally formed quartz-kyanite rocks from the WSW-ENE-striking Greiner shear zone (Pfitscher Joch, Italy) on the south-western border of Tauern window were investigated in order to reconstruct conditions and processes of kyanite formation from metamorphic fluids. It is known from experiments that kyanite does not precipitate spontaneously fro...
Article
Full-text available
The Ca-Sr fractionation between zoisite and, respectively, lawsonite and an aqueous fluid has been determined by synthesis experiments in the presence of a 1 M (Ca,Sr)Cl2 aqueous fluid at 2.0 GPa/550, 600, and 700°C and 4.0 GPa/800°C for zoisite and 2.0 GPa/400°C and 4.0 GPa/600°C for lawsonite. Solid run products were characterized by EMP, SEM, an...
Article
Full-text available
We performed hydration experiments of pure and Nb-, Cr-, and V-doped synthetic dry (H2O < 3 ppm) single rutile crystals. They were equilibrated with pure H2O in hydrothermal experiments at constant conditions of 600 °C, 400 MPa, and fO2 near the Ni-NiO buffer, run time between ∼25 min and 14 days. Slabs cut parallel to (110) of the reacted single c...
Article
Full-text available
Chemical and Sr, Nd and Pb isotopic compositions of Late Cenozoic to Quaternary small-volume phonolite, trachyte and related mafic rocks from the Darfur volcanic province/NW-Sudan have been investigated. Isotope signatures indicate variable but minor crustal contributions. Some phonolitic and trachytic rocks show the same isotopic composition as th...
Article
In the central-eastern Bayuda Desert (Sudan), a border area between the Saharan Metacraton and juvenile Pan-African crust of the Nubian Shield, the Rahaba-Absol and the Abu Harik-Kurmut Terranes were amalgamated along suture and shear zones. U–Pb zircon ages by laser-ablation dating of metamorphosed granitoid rocks reveals ages interpreted as magma...
Article
Trace element distribution in titanite overgrowths on rutile has been investigated experimentally at 600 °C, 400 MPa and fO2 near NiNiO buffer. Compositionally homogenous Cr- or Nb-doped synthetic rutile single crystals or Nb-containing natural rutile crystals were the source of Cr, Nb and Ti to synthesize titanite using the double-capsule techniqu...
Article
Full-text available
Phosphatized globular microfossils from the Edi-acaran and lower Cambrian of South China represent an im-pressive record of early animal evolution and development. However, their phylogenetic affinity is strongly debated. Un-derstanding key processes and conditions that cause excep-tional egg and embryo preservation and fossilization are cru-cial f...