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  • Articles  (98)
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  • 1
    Electronic Resource
    Electronic Resource
    Pseudotachylytes from Corsica: fossil earthquakes from a subduction complex (2004)
    Oxford, UK : Blackwell Science Ltd
    Terra nova 16 (2004), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Subduction zones are the most seismically active tectonic environment on Earth. Here we report fault-rock evidence of palaeoearthquakes from a subduction complex. Pseudotachylyte veins formed by shear heating on faults at seismic strain rates contain dendrites, spherulites and acicular minerals characteristic of blueschist facies conditions. The veins have been found in both mantle peridotite and gabbro. Our discovery from Corsica opens a new avenue of research towards understanding mechanisms related to subduction zone earthquakes and the conditions at which these are released.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.2004.00551.x
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  • 2
    Electronic Resource
    Electronic Resource
    Eclogite formation and dynamics of crustal roots under continental collision zones (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 3 (1991), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Field observations on deep parts of the root zone of the Caledonian orogen are combined with the geophysical data available for recent continental collision zones such as the Alps, to provide a model for dynamics of crustal root zones.Rocks descending into the root zone are locally infiltrated by fluids which cause eclogitization along shear zones and fluid pathways. The eclogite facies rocks vary in density from 3.1 to 3.6 g cm-3, reflecting the compositional variation in their protoliths. Where the amount of highly ductile eclogitic material reaches about 40% the descending crustal segment loses its coherence and disintegrates into a breccia where blocks of granulite facies rocks float in a matrix of eclogite material. A density-stratified root zone develops, where light unreacted or partly eclogitized material floats on an ‘ocean’ dominated by eclogite facies rocks, the top of which may correspond to the Moho. Catastrophic decent of this eclogitic layer may (1) transport blocks of light material to depths of 〉 90 km, which upon further disintegration due to eclogitization are released and return by buoyancy forces to the crust; (2) result in extension and uplift of the partly-eclogitized lighter material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1991.tb00184.x
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  • 3
    Electronic Resource
    Electronic Resource
    Accelerated hydration of the Earth's deep crust induced by stress perturbations (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 408 (2000), S. 75-78 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The metamorphic cycle associated with the formation of mountain belts produces a lower crust containing little or no free fluid. The introduction of external fluids to dry and impermeable volumes of the Earth's crust is thus a prerequisite for the retrogressive metamorphism later ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35040537
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  • 4
    Electronic Resource
    Electronic Resource
    Retrograde fluid infiltration in the high-grade Modum Complex South Norway: evidence for age, source and REE mobility (1994)
    Springer
    Contributions to mineralogy and petrology 116 (1994), S. 32-46 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The high-grade metamorphic basement of the Modum Complex, South Norway,exhibits retrogradation and alteration due to late stage fluid infiltration.Extensive alteration zones of albite-and calcite-rich veining occur especiallywithin and around numerous metagabbros. The gabbros, intruded at 1224±15Ma, are now partly altered to amphibolites due to the subsequent high-grade metamorphism.Two generations of albite-rich rocks have been recognized: (1) a fine-grained, foliated type;(2) a coarse-grained, crosscutting type. Both types show a typical greenschist facies mineralassemblage; albite ± actinolite ± chlorite ± talc. The calcite veins/dykesrepresent a younger generation of veins than both albite-rich types. U−Pb data for spheneof type (1) yielded an age of 1080±3 Ma, determining a point on the retrogradeP-T-t path of the Modum Complex. Increasing albitisation of themetagabbros leads to a decrease in(143ND/144Nd)oand an increase in (87Sr/86)o.Albite- and calcite-rich samples show negative ɛNd and positive ɛSr, suggesting that fluids which interacted with the metagabbros originated from a crustal reservoir. The Nd and Sr isotopic data show disequilibrium at the microscale as well as at the macroscale. Negative Sm−Nd model ages of the albite-rich rocks demonstrate that rare-earth elements (REEs) were mobile and fractionated during albitisation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310688
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of fluid and deformation on zoning and inclusion patterns in poly-metamorphic garnets (1993)
    Springer
    Contributions to mineralogy and petrology 115 (1993), S. 204-214 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Within the Bergen Arcs of W Norway, Caledonian eclogite facies assemblages (T≥650°C, P≥15 kbar) have formed from Grenvillian granulites (T= 800–900°C, P≥10 kbar) along shear zones and fluid pathways. Garnets in the granulites (grtI: Pyr56–40 Alm45–25Gro19–14) are unzoned or display a weak (ca. 1 wt% FeO over 1000μm) zoning. The eclogite facies rocks contain garnets inherited from their granulite facies protoliths. These relict garnets have certain areas with compositions identical to the garnets in their nearby granulite, but can be crosscut by bands of a more Almrich composition (grtII: Pyr31–41Alm40–47Gro17–21) formed during the eclogite facies event. These bands, orientated preferentially parallel or perpendicular to the eclogite foliation, may contain mineral filled veins or trails of eclogite-facies minerals (omphacite, amphibole, white mica, kyanite, quartz and dolomite). Steep compositional gradients (up to 9 wt% FeO over 40 μm) separate the two generations of garnets, indicating limited volume diffusion. The bands are interpreted as fluid rich channels where element mobility must have been infinitely greater than it was for the temperature controlled volume diffusion at mineral interfaces in the granulites. The re-equilibration of granulite facies garnets during the eclogite facies event must, therefore, be a function of fracture density (deformation) and fluid availability. The results cast doubts on modern petrological and geochronological methods that assume pure temperature controlled chemical re-equilibration of garnets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00321220
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  • 6
    Electronic Resource
    Electronic Resource
    Fluid controlled eclogitization of granulites in deep crustal shear zones, Bergen arcs, Western Norway (1990)
    Springer
    Contributions to mineralogy and petrology 104 (1990), S. 184-193 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract During the Caledonian orogeny large parts of the western margin of the Baltic shield were disrupted, sliced and stacked. Caledonian deformation resulted in a massif thickening of the continental crust. Mafic granulites and granulite facies meta-anorthosites build up a large portion of the Bergen Arcs terrane in southwestern Norway. The rocks represent typical Precambrian continental lower crust. These rocks experienced extensive eclogitization in response to stacking and crustal thickening during the Caledonian orogenic cycle. Eclogite formation resulted from shear deformation and associated infiltration of H2O-rich fluids (X H2O≥0.75). During an early stage, eclogite facies mineralogy formed in extension fractures (veins). The veins are probably related to hydraulic fracture systems which transported the inferred fluid phase. During the main stage, eclogitization occurred along shear zones ranging from centimeters to tens of meters in thickness. Eclogite forming reactions are shown to consume H2O, alkalies and to release SiO2. Much of the SiO2 released by the eclogitization process can be found in late quartz vein systems. The eclogitization took place at a temperature of about 700°C and a pressure between 18 and 21 kbar. Fluid infiltration was supported by a decrease in rock volume during reaction (ΔV solids〈0). The negative volume change of reaction occurs despite that the process of eclogitization involves hydration reactions. The formation of eclogite from granulite produces approximately 15 KJ heat per 100 cm3 original granulite. Numerical modeling of the regional temperature effects associated with partial hydration of the lower crust suggests that these processes may not cause large perturbations on the geotherm. Both, transport of heat and matter by advection of the fluid phase is negligible on a regional scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00306442
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  • 7
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    Sustainable densification of the deep crust (2020)
    Geological Society of America
    Details
    Publication Date: 2020-04-27
    Description: The densification of the lower crust in collision and subduction zones plays a key role in shaping the Earth by modifying the buoyancy forces acting at convergent boundaries. It takes place through mineralogical reactions, which are kinetically favored by the presence of fluids. Earthquakes may generate faults serving as fluid pathways, but the influence of reactions on the generation of seismicity at depth is still poorly constrained. Here we present new petrological data and numerical models to show that in the presence of fluids, densification reactions can occur very fast, on the order of weeks, and consume fluids injected during an earthquake, which leads to porosity formation and fluid pressure drop by several hundreds of megapascals. This generates a mechanically highly unstable system subject to collapse and further seismic-wave emission during aftershocks. This mechanism creates new pathways for subsequently arriving fluids, and thus provides a route for self-sustained densification of the lower crust.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America
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  • 8
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    Formation of magnesium silicate hydrate cement in nature (2017)
    Geological Society of London
    Details
    Publication Date: 2017-11-01
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 9
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    Dynamic Metasomatism: Stable Isotopes, Fluid Evolution, and Deformation of Albitite and Scapolite Metagabbro (Bamble Lithotectonic Domain, South Norway) (2018)
    Hindawi
    Details
    Publication Date: 2018-01-01
    Print ISSN: 1468-8115
    Electronic ISSN: 1468-8123
    Topics: Geosciences
    Published by Hindawi
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  • 10
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    Microstructural Records of Earthquakes in the Lower Crust and Associated Fluid-Driven Metamorphism in Plagioclase-Rich Granulites (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-05-01
    Description: Coseismic damage associated with earthquakes in the lower continental crust is accompanied by postseismic annealing and fluid-mediated metamorphism that influence the physical and chemical development of the continental crust on regional scales. A transition from brittle deformation to crystal-plastic recrystallization is a recurring characteristic of rocks affected by lower crustal earthquakes and is observed in plagioclase adjacent to pseudotachylytes in granulite facies anorthosites from the Bergen Arcs, western Norway. The microstructural and petrological records of this transition were investigated using electron microscopy, electron microprobe analysis, and electron backscatter diffraction analysis. Microfractures associated with mechanical twins are abundant within plagioclase and contain fine-grained aggregates that formed by fragmentation with minor shear deformation. The presence of feather features, which are described for the first time in feldspar, suggests that fractures propagate at near the shear wave velocity into the wall rock of earthquake slip planes. Grain size insensitive recrystallization took place within the time frame of pseudotachylyte formation, forming high-angle grain boundaries required for shear zone initiation. Fluid infiltration synfracture to postfracture facilitated the epitactic replacement of plagioclase by alkali feldspar and the nucleation of clinozoisite, kyanite, and quartz. The grain size reduction and crystallization associated with the microfractures create rheologically weak areas that have the potential to localize strain within the plagioclase-rich lower crust. ©2018. American Geophysical Union. All Rights Reserved.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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