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  • 1
    Electronic Resource
    Electronic Resource
    An experimental replication of upper-mantle metasomatism (1995)
    [s.l.] : Nature Publishing Group
    Nature 373 (1995), S. 58-60 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The mantle xenoliths that occur in kimberlites have received much attention (for example, refs 7-10) because they provide the best direct evidence of the nature of the lithospheric mantle. Among the xenolith types that occur in the Group I kimberlites of southern Africa (see Fig. 1 legend for ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/373058a0
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  • 2
    Electronic Resource
    Electronic Resource
    The determination of partial melt compositions of peridotitic systems by melt inclusion synthesis (1997)
    Springer
    Contributions to mineralogy and petrology 129 (1997), S. 209-221 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract An experimental method of melt inclusion synthesis within olivine crystals has been developed to determine the composition of the melt present in a partially molten peridotite assemblage. Trace element doped peridotite was equilibrated with 5 wt% of a C-O-H volatile source at 20 kbar/1175 °C in a piston-cylinder apparatus under buffered oxygen and sulphur fugacity conditions [log(f O2) ∼ IW +1 log unit, log (f S2) ∼ Fe/FeS 〉 +1 log unit]. A single crystal of olivine, which had been cut to a disc shape, was included in the sample capsule. At run conditions the peridotite charge formed olivine, orthopyroxene, clinopyroxene, Fe-Ni sulphide and a volatile-bearing melt. The melt phase is preserved as homogeneous glass inclusions up to 50 μm in size, trapped in situ in the olivine disc. The major element composition of the glass inclusions showed them to be of broadly basaltic character, but with a low Mg/(Mg + ΣFe), which is associated with precipitation of olivine from the melt inclusion onto the walls of the olivine disc during quenching. Thus the equilibrium melt composition has been calculated from the glass inclusion composition by addition of olivine component using the Fe/Mg exchange coefficient of Roeder and Emslie (1970); the desired Mg/(Mg + ΣFe) being determined from the composition of olivine formed at run conditions in the peridotite section of the charge. The melt composition obtained is close to the trend for dry melting established by Falloon and Green (1988), and it is evident that although the reduced volatiles in this case have induced a liquidus depression of some 250 °C, there has been only a small shift in melt composition. Trace element, carbon and hydrogen contents of thirteen melt inclusions have been determined by secondary ion mass spectrometry (SIMS). The trace element signature is consistent with ∼29% melting in equilibrium with a lherzolitic assemblage. The equilibrium melt has a C/H of 0.48 by weight. Carbon solubility in partial melts is thus significant under reducing conditions in the presence of dissolved “water components” and establishes a major melt fluxing role for carbon in the upper mantle. The ubiquitous presence of carbon and hydrogen in basaltic magmas underscores the importance of determining both the position of vapour-present solidi and the composition of melts generated, when developing petrogenetic models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050333
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  • 3
    Electronic Resource
    Electronic Resource
    Natural fracture profiles, fractal dimension and joint roughness coefficients (1994)
    Springer
    Rock mechanics and rock engineering 27 (1994), S. 135-153 
    Details
    ISSN: 1434-453X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Summary Thirteen natural rock profiles (Barton and Choubey, 1977) are analyzed for their fractal properties. Most of the profiles were found to approximate fractal curves but some also showed features of specific wavelengths and amplitudes superimposed on fractal characteristics. The profiles showed fractal dimensions from 1.1 to 1.5 covering a range of selfsimilar and self-affine curves. The analysis results suggest a negative correlation between fractal dimension,D, and amplitude,A. Joint roughness coefficients (JRC) show a positive correlation with amplitude,A, and a negative correlation with fractal dimension,D. A numerical model of fracture closure is used to investigate the effects of different profile characteristics (D, A and sample size) on the nature of dilation and contact area, using the natural profiles and synthetic fractional Brownian motion profiles. Smooth profiles (low JRC, highD, lowA) display many small contact regions whereas rough fractures (high JRC, lowD, highA) display few large contact areas. The agreement with published experimental data supports the suggested correlations between JRC and the fractal parameters,A andD. It is suggested that observed scale effects in JRC and joint dilation can be explained by small differential strain discontinuities across fractures, which originate at the time of fracture formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01020307
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  • 4
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    Properties of fault damage zones in siliclastic rocks: a modelling approach (2007)
    In:  Geological Society Special Publication 249: 43-59.
    Details
    Publication Date: 2007-10-08
    Description: Major faults are surrounded by damage zones of minor faults that, in siliclastic rocks, can form barriers to flow in their own right. Reservoir flow simulation -- now a routine part of reservoir management -- requires equivalent hydraulic parameters on the scale of the whole fault, while reservoir geological models, from which flow simulator grids are generated, require information on the 3D characteristics of fault populations. Here, a stochastic model of fault damage zone architecture is generated and used to explore the impact of damage zone architecture on extrapolation from 1D (fault throw) and 2D (fault length) to 3D fault population characteristics. Sampling of the simulated damage zone models shows that clustering of faults causes deviations from simple laws relating particularly 1D samples to 3D population power-law exponents, with differences between expected and observed values of up to 0.25. The stochastic model is used to generate input for a 2D discrete fracture flow model for the case where minor (isotropic) fault permeability is four orders of magnitude lower than that of the host rock and, thus, forms partial barriers to flow. The flow model is used to explore the impact of fault damage zones on bulk fault permeability. The damage zone is shown to be around 50% efficient, i.e. a simple estimate of bulk permeability can be made using the harmonic average of fault rock and host-rock permeability weighted by thickness in 1D traverses (e.g. core, well logs), where only half the observed thickness of fault rock in the fault damage zone is assumed. Considering the contributions of the damage zone and the major slip zone, the fault damage zone is likely to make a significant contribution to the bulk permeability of the fault as a whole when the permeability of minor faults in the damage zone is similar to, or at most, one order of magnitude greater than that of the slip zone fault rocks.
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  • 5
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    Petrophysical characterization of the Sherwood Sandstone from East Yorkshire, UK (2007)
    In:  Geological Society Special Publication 263: 103-118.
    Details
    Publication Date: 2007-10-08
    Description: Petrophysical tests were conducted on core samples from the unsaturated zone of the Sherwood Sandstone Group in East Yorkshire. Tests were conducted to determine which physical parameters most influenced its hydraulic conductivity values. The main parameters analysed were grain-size distribution, pore-throat size distribution, clay content, mineralogy and porosity. A constant flow rate permeameter was used to measure saturated hydraulic conductivity values in the vertical direction (perpendicular to lamination), Kv, and horizontal direction (parallel to lamination), Kh. Hydraulic conductivity values in the vertical direction, Kv, ranged from 0.004 to 0.12 m day-1 while values in the horizontal direction, Kh, ranged from 0.01 to 0.17 m day-1. Hydraulic conductivity anisotropy, Kh/Kv, varied from 0.6 to 35. Scanning electron microscope analysis showed this anisotropy to be caused mainly by millimetre-scale laminations. Representative bulk hydraulic conductivity values were estimated from the core data; bulk horizontal hydraulic conductivity, Khb, was estimated as 0.1 m day-1, and bulk vertical hydraulic conductivity, Kvb, as 0.01 m day-1. Principal components analysis and multiple regression analysis were used to determine parameters that affect hydraulic conductivity most. Grain sorting is established to be the most important parameter to influence Kv values; samples with fine laminations have relatively low Kv.
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  • 6
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    Rapid karstic bypass flow in the unsaturated zone of the Yorkshire chalk aquifer and implications for contaminant transport (2007)
    In:  Geological Society Special Publication 279: 111-122.
    Details
    Publication Date: 2007-10-08
    Description: Tracer tests have been performed on the unsaturated zone of the East Yorkshire chalk aquifer, UK. Rapid tracer travel times through significant thicknesses of unsaturated chalk (15-38 m) indicate that bypass flow must occur through fractures. Transport processes in the unsaturated zone of the chalk aquifer thus have similarities to those in the vadose zone of more typically karstic limestone aquifers. Modelling of tracer breakthrough curves indicates that bypass flow is sufficiently rapid to significantly inhibit diffusional loss of tracer into the porous matrix of the chalk. The presence of rapid karstic bypass flow in the unsaturated zone of the chalk will limit the potential for attenuation of groundwater contaminants in this zone.
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  • 7
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    Models of tracer breakthrough and permeability in simple fractured porous media (2007)
    In:  Geological Society Special Publication 249: 91-102.
    Details
    Publication Date: 2007-10-08
    Description: Tailing and bimodal behaviour of tracer breakthrough curves from tracer tests conducted in fractured porous media are commonly presented as deviations' from the Fickian model for homogeneous porous media. Tailing is mainly attributed to: (1) tracer storage brought about by diffusion between mobile and static regions of fluid; (2) a concentration of flow towards the wider (aperture) and, thus, more permeable fracture zones; and (3) the high variance in fracture conductivity and consequent mixing of tracer. Bi- (or multi-) modality has been attributed to solute following a few highly permeable flow paths. Systematic numerical simulations of flow and transport in geometrically simple fractured porous media were conducted using a 2D finite difference flow code and a particle tracking transport model. As a simplification only advective dispersion was considered. The modelling study produced a large variety of tracer breakthrough curves, including two patterns commonly seen in field data -- the backward tailed uni-modal type and the Gaussian type. The study demonstrates that different types of breakthrough might be characteristic of particular sets of conceptual models for heterogeneities and, as such, may provide a useful pointer in the application and interpretation of tracer tests.
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  • 8
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    Kungnat, revisited. A review of five decades of research into an alkaline complex in South Greenland, with new trace-element and Nd isotopic data (2013)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2013-06-19
    Description: The Kûngnât Complex (1275±1.8 Ma) in the Gardar Alkaline Province, South Greenland, cuts Archaean gneisses and comprises two intersecting syenitic stocks and a gabbroic ring-dyke. The magmas, with increasingly more primitive compositions, were emplaced successively by ring-faulting and roof stoping. The syenites are orthocumulates (cumulus alkali feldspar, olivine, pyroxene, titanomagnetite and apatite; intercumulus phases include alkali amphibole, biotite, quartz and calcite). In the well dissected earlier stock, a 2.2 km-thick layered sequence displays graded modal layering, feldspar lamination and cryptic layering. Modal layering in both stocks is directed mainly inwards at 35°–50°. Heterogeneous nucleation of the cumulus assemblage, close to steep thermal boundary layers, is inferred. The modal layering is ascribed primarily to gravitational sorting aided by the large density differential between a) feldspar and b) Fe-rich silicates and oxides. Episodic collapse of cumulus + melt slurries contributed to inward-dipping crystal pediments on the chamber floors. The Ring-Dyke (up to 100 m wide) is nearly continuous through 360°. Kûngnât exhibits a compositional near-continuum from olivine gabbro through syenite intermediaries to alkali granite, ascribed to protracted assimilation/fractional crystallization processes. The most radiogenic Nd isotope data from Kûngnât (Nd i values between –3.3 and –1.0) point to a lithospheric mantle source, whereas the most unradiogenic values imply enrichment in LREE by crustal contamination of the magmas.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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  • 9
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    The origin of Earths first continents and the onset of plate tectonics (2016)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2016-10-08
    Description: The growth and recycling of continental crust has resulted in the chemical and thermal modification of Earth’s mantle, hydrosphere, atmosphere, and biosphere for ~4.0 b.y. However, knowledge of the protolith that gave rise to the first continents and whether the environment of formation was a subduction zone still remains unknown. Here, tonalite melts are formed in high P - T experiments in which primitive oceanic plateau starting material is used as an analogue for Eoarchean (3.6–4.0 Ga) oceanic crust generated at early spreading centers. The tonalites are produced at 1.6–2.2 GPa and 900–950 °C and are mixed with slab-derived aqueous fluids to generate melts that have compositions identical to that of Eoarchean continental crust. Our data support the idea that the first continents formed at ca. 4 Ga and subsequently, through the subduction and partial melting of ~30–45-km-thick Eoarchean oceanic crust, modified Earth’s mantle and Eoarchean environments and ecosystems.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 10
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    The origin of Earths first continents and the onset of plate tectonics (2016)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2016-10-14
    Description: The growth and recycling of continental crust has resulted in the chemical and thermal modification of Earth’s mantle, hydrosphere, atmosphere, and biosphere for ~4.0 b.y. However, knowledge of the protolith that gave rise to the first continents and whether the environment of formation was a subduction zone still remains unknown. Here, tonalite melts are formed in high P - T experiments in which primitive oceanic plateau starting material is used as an analogue for Eoarchean (3.6–4.0 Ga) oceanic crust generated at early spreading centers. The tonalites are produced at 1.6–2.2 GPa and 900–950 °C and are mixed with slab-derived aqueous fluids to generate melts that have compositions identical to that of Eoarchean continental crust. Our data support the idea that the first continents formed at ca. 4 Ga and subsequently, through the subduction and partial melting of ~30–45-km-thick Eoarchean oceanic crust, modified Earth’s mantle and Eoarchean environments and ecosystems.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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