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  • 2000-2004  (2)
  • 1995-1999  (10)
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  • 1
    Digitale Medien
    Digitale Medien
    Petrology of phlogopite-sapphirine-bearing Al-Mg granulites from Ihouhaouene, In Ouzzal, Hoggar, Algeria: an example of phlogopite stability at high temperature (1996)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 14 (1996), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Al-Mg granulites, with cordierite, garnet, sapphirine, orthopyroxene, sillimanite, spinel, phlogopite, K-feldspar, plagioclase and variable quartz from Ihouhaouene (In Ouzzal, Algeria), display a range of decompression textures involving the breakdown of orthopyroxene and sillimanite, and of garnet. The succession of parageneses suggests that the P–T–t evolution corresponds to decompression with cooling from peak conditions of about 950°C and 10 kbar. This decompression path is obtained from the paragenetic analysis in the FMAS system. However, according to current KFMASH grids, this P–T–t evolution should take place outside the stability field of phlogopite+quartz; yet this assemblage is probably stable during most of the P-T evolution, notably during peak metamorphism. This discrepancy is interpreted as the effect of the high content of F in phlogopite which should shift its stability limit towards higher temperature. The consequences of this shift on the phase relationships in the KFeMASH system are investigated and it is concluded that a topological inversion could exist in the F-bearing system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1525-1314.1996.00045.x
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  • 2
    Digitale Medien
    Digitale Medien
    How well known are the thermodynamics of Fe–Mg–Ca garnet? Evidence from experimentally determined exchange equilibria (1996)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 14 (1996), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Many thermodynamic calculations relating to metamorphic rocks hinge on the thermodynamic parameters of garnet. Though some models are widely used, it is not clear whether their underlying premise is correct: that a single set of equations can be written for the activities of the end-members of garnet covering the whole compositional range. A voluminous body of data can be used to constrain the thermodynamics of garnet, namely Fe–Mg exchange experimental data involving garnet and another mineral, particularly clinopyroxene, orthopyroxene and olivine. However, examination of these data reveals inconsistencies, apparently stemming from differences between the thermodynamics of low-Ca and high-Ca garnets, with a boundary of about XgCa= 0.15. In the two regions, for the high P–T of the experimental data, the thermodynamics follow the regular model, with values for the interaction parameters in the low Ca region of about wgFeMg= 50R and waFe–wgMgCa=– 1300R, in which R is the gas constant, and in the high Ca region of about wgFeMg= 1100R and wgCaFe–wgMgCa=– 2200R. Using the subregular, rather than the regular, model does not remove the discrepancy. The cause of the discrepancy needs to be identified if reliable calculations on rocks are to be made.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1525-1314.1996.00075.x
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  • 3
    Digitale Medien
    Digitale Medien
    Probable anticlockwise P,–T evolution in extending crust: Hlinsko region, Bohemian Massif (1996)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 14 (1996), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: In the Hlinsko region (Variscan Bohemian Massif, Czech Republic) a major extensional shear zone separates low-grade metasedimentary series (Hlinsko schists) and high-grade rocks of the Moldanubian terrane (Svratka Crystalline Unit). During late-Variscan extension, a tonalite intruded syntectonically into the normal ductile shear zone, and caused contact metamorphism of the overlying schists. Concurrent syntectonic sedimentation of a flysch series took place at the top of the hangingwall schists. In order to decipher the detailed petrological evolution of the Hlinsko unit situated in the hangingwall of this tectonic contact, a phase diagram approach and petrogenetic grids, calculated with the thermocalc computer program, were used.The crystallization/deformation relationships and the paragenetic analysis of the Hlinsko schists define a P–T path with an initial minor increase in pressure followed by cooling. Calculated pseudosections constrain this anticlockwise P-T evolution to the upper part of the andalusite field between 0.36 and 0.40 GPa for temperatures ranging from 570 to 530°C. A low aH2O is required to explain the presence of andalusite-biotite-bearing assemblages, and could be related to the presence of abundant graphite.In contrast, the footwall rocks of the Svratka Crystalline Unit record decompression from around 0.8 GPa at a relatively constant temperature, followed by cooling. Thus, the footwall and the hangingwall units display opposite, but convergent P–T histories. Decompression in the footwall rocks is related to a rapid exhumation. We propose that the inverse, anticlockwise P–T path recorded in the hangingwall pelites is related to the rapid, extension-controlled sedimentation of the overlying flysch series.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1525-1314.1996.t01-1-00049.x
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  • 4
    Digitale Medien
    Digitale Medien
    Gedrite–garnet–sillimanite-bearing granulites from Amessmessa area, south In Ouzzal, Hoggar, Algeria (1996)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 14 (1996), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Some granulites from the Amessmessa area (south In Ouzzal unit, Hoggar) contain the peak assemblage gedrite+garnet+sillimanite+quartz that was used to estimate the P–T conditions of metamorphism. The rocks developed symplectites and corona textures by the breakdown of the primary paragenesis to orthopyroxene, cordierite and spinel. The successive parageneses formed in separate microdomains according to a clockwise P–T path. Geothermometry, geobarometry and phase diagram calculations indicate that the textures formed by decompression and cooling from 7–9 kbar and 850–900°C to 3.5–4.5 kbar and 700–800°C. This P–T evolution is consistent with low to medium aH2O, between 0.4 and 0.7, and is similar to the metamorphic conditions deduced in Al–Mg granulites from the north of In Ouzzal.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1525-1314.1996.00047.x
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  • 5
    Digitale Medien
    Digitale Medien
    Hydration of orthopyroxene–cordierite-bearing assemblages at Laouni, Central Hoggar, Algeria (1996)
    Oxford : Blackwell Science Ltd.
    Journal of metamorphic geology 14 (1996), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: In the Laouni region (Central Hoggar, Algeria), retrogression of high-grade orthopyroxene–cordierite-bearing rocks led to the crystallization of orthoamphibole and garnet, and at a later stage of chlorite, from the original paragenesis. Calculated phase diagrams show that this retrogression occurred at about 3 kbar with the simplest model involving hydration at 650–700° C and at around 500° C, with the rocks experiencing aH2O less than 1, except possibly in the last stages of chlorite crystallization. As the other rock types occurring in the same area as the orthopyroxene–cordierite rocks display similar features, it is concluded that regional hydration occurred, presumably related to the release of fluids during the crystallization of the Pan-African granitic and mafic magmas that are widespread in the Laouni area.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1525-1314.1996.06016.x
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  • 6
    Digitale Medien
    Digitale Medien
    Special issue on the In Ouzzal Granulite Unit, Hoggar, Algeria: Introduction (1996)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 14 (1996), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1525-1314.1996.00001.x
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  • 7
    Digitale Medien
    Digitale Medien
    Corundum–quartz-bearing assemblage in the Ihouhaouene area (In Ouzzal, Algeria) (1996)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 14 (1996), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Granulite facies quartzites from the Ihouhaouene region, in the northern part of In Ouzzal, contain the assemblage corundum+quartz+magnetite together with hercynitic spinel+quartz+magnetite, sillimanite+quartz+magnetite and almandine-rich garnet+quartz+magnetite. Two types of corundum have been recognized: the first is primary and is found with quartz and magnetite only; the second type is found together with magnetite and chlorite rimming spinel as a fine-grained corona. The textures show that spinel-rich magnetite probably exsolved primary corundum, sillimanite, spinel and garnet during the cooling history. The secondary corundum formed later from the spinel already exsolved from magnetite. The secondary corundum is certainly metastable with respect to quartz. This may also apply for the primary corundum. However, given the high-temperature setting of this rock, it cannot be excluded that the stable contacts observed between primary corundum and quartz indicate equilibrium between the two phases. Taking into account the uncertainties in the thermodynamic data, the stability of this assemblage would imply that this part of In Ouzzal has recorded very high P–T conditions, above 1100°C at 12 kbar.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1525-1314.1996.00046.x
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  • 8
    Digitale Medien
    Digitale Medien
    H2O in metamorphism and unexpected behaviour in the preservation of metamorphic mineral assemblages (2001)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 19 (2001), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The preservation of mineral assemblages that were fluid-present during their prograde history is primarily related to the consumption of the fluid by growth of more hydrous minerals as the retrograde history begins. The range of behaviour relating to the preservation of mineral assemblages is examined using calculated phase diagrams for fluid-saturated conditions, contoured for the H2O content of the mineral assemblage. At equilibrium, as a mineral assemblage crosses contours of decreasing H2O content along a pressure–temperature path, it dehydrates, the fluid being lost from the rock. If the assemblage crosses contours of increasing H2O content, the mineral assemblage starts to rehydrate using any fluid on its grain boundaries. When the rock has consumed its fluid, the resulting mineral assemblage is that preserved in the rock. Conditions relating to the preservation of mineral assemblages are discussed, and examples of the consequences of different pressure–temperature paths on preservation in a metapelitic and a metabasic rock composition are considered on phase diagrams calculated with thermocalc.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.0263-4929.2001.00320.x
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  • 9
    Digitale Medien
    Digitale Medien
    Calculating the long-term displacement rates of a normal fault from the high-resolution stratigraphic record (early Tethyan rifting, French Alps) (2003)
    Oxford, UK : Blackwell Science Ltd
    Terra nova 15 (2003), S. 0 
    Details
    ISSN: 1365-3121
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Displacement rates of normal faults deduced from stratigraphic data are often unreliable. Here we calculate the velocity of motion on a normal fault from the variations in accommodation potential on both sides of the fault within a high-resolution time-frame established by biostratigraphy and physical stratigraphy. Our example is the Ornon normal fault bounding the Early Jurassic Bourg-d'Oisans Basin formed during Tethyan rifting. We show that motion on the fault was discontinuous when examined at high resolution and over a long time interval. During a first interval (Hettangian to Sinemurian Arietites bucklandi zone) a low rate of displacement (=202–423 m Myr−1) coeval with diffused extensional deformation throughout the sedimentary basin is observed. A second interval of localized deformation (Early Sinemurian Caenisites turneri zone) is characterized by higher rates of displacement on the fault (1846 m Myr−1). Our results concur with recent numerical models identifying the main stages of extensional deformation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-3121.2003.00508.x
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  • 10
    Digitale Medien
    Digitale Medien
    Early Cretaceous deltaic sedimentary environment of the Côte d’Ivoire–Ghana transform margin as deduced from deep dive data (1997)
    Springer
    Geo-marine letters 17 (1997), S. 79-86 
    Details
    ISSN: 1432-1157
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract  During the Equanaute cruise (June 1992), 14 submersible deep dives were conducted along the steep southern slope of the Côte d’Ivoire–Ghana marginal ridge. In situ diving observations and sample analysis were done to specify the clastic lithology of a sedimentary sequence about 2200 m thick. Most of the rocks collected consist of dark shales, greenish lenticular- to wavy-bedded siltstones and large-scale trough cross-bedded sandstones. Lithofacies analysis favors a deltaic origin for this sedimentary synrift succession, which is probably of Early Cretaceous age.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003670050011
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