28 research outputs found
Von der Idee zur Umsetzung: BodenBildungsKonzept Sandkaute Gundernhausen: Konzeption eines bodenkundlichen, auĂerschulischen Lernorts mit Studierenden im Messeler HĂŒgelland (Hessen)
Im Messeler HĂŒgelland östlich von Darmstadt (Hessen) wird in der Sandkaute Gundernhausen an einem auĂerschulischen Lernort gearbeitet. Seit mehreren Jahren findet im Rahmen des Masterstudienganges Physische Geographie an der Goethe-UniversitĂ€t Frankfurt am Main eine landschaftsökologische Lehrveranstaltung statt. Ein zentraler Inhalt ist dabei die Sandkaute Gundernhausen. Studierende sollen hier Konzepte fĂŒr einen auĂerschulischen Lernort entwickeln, in dem bodengeographische und bodenkundliche Inhalte, didaktisch reduziert, fĂŒr unterschiedliche Klas-senstufen erarbeitet werden. Diese Konzepte sollen nun passgenau an den Lernplan fĂŒr die Klassen 5 und 11 (gymnasialer Bildungsgang) angepasst werden. Eine nahegelegene Schule und das Institut fĂŒr Physische Geographie kooperieren in der Konzeptentwicklung mit dem Landkreis Darmstadt/Dieburg, Hessen Forst sowie der Gemeinde RoĂdorf
Numerical simulations of an ocean/continent convergent system: influence of subduction geometry and mantle wedge hydration on crustal recycling
The effects of the hydration mechanism on continental crust recycling are
analyzed through a 2D finite element thermo-mechanical model. Oceanic slab
dehydration and consequent mantle wedge hydration are implemented using a
dynamic method. Hydration is accomplished by lawsonite and serpentine
breakdown; topography is treated as a free surface. Subduction rates of 1, 3,
5, 7.5 and 10 cm/y, slab angles of 30o, 45o and 60o and a mantle rheology
represented by dry dunite and dry olivine flow laws, have been taken into
account during successive numerical experiments. Model predictions pointed out
that a direct relationship exists between mantle rheology and the amount of
recycled crustal material: the larger the viscosity contrast between hydrated
and dry mantle, the larger the percentage of recycled material into the mantle
wedge. Slab dip variation has a moderate impact on the recycling. Metamorphic
evolution of recycled material is influenced by subduction style. TPmax,
generally representative of eclogite facies conditions, is sensitive to changes
in slab dip. A direct relationship between subduction rate and exhumation rate
results for different slab dips that does not depend on the used mantle flow
law. Thermal regimes predicted by different numerical models are compared to PT
paths followed by continental crustal slices involved in ancient and recent
subduction zones, making ablative subduction a suitable pre-collisional
mechanism for burial and exhumation of continental crust.Comment: 10 figures, 3 table
Integration of natural data within a numerical model of ablative subduction: A possible interpretation for the Alpine dynamics of the Austroalpine crust
A numerical modelling approach is used to validate the physical and ge-
ological reliability of the ablative subduction mechanism during Alpine con-
vergence in order to interpret the tectonic and metamorphic evolution of an
inner portion of the Alpine belt: the Austroalpine Domain. The model pre-
dictions and the natural data for the Austroalpine of the Western Alps agree
very well in terms of P-T peak conditions, relative chronology of peak and
exhumation events, P-T-t paths, thermal gradients and the tectonic evolu- tion
of the continental rocks. These findings suggest that a pre-collisional
evolution of this domain, with the burial of the continental rocks (induced by
ablative subduction of the overriding Adria plate) and their exhumation (driven
by an upwelling flow generated in a hydrated mantle wedge) could be a valid
mechanism that reproduces the actual tectono-metamorphic config- uration of
this part of the Alps. There is less agreement between the model predictions
and the natural data for the Austroalpine of the Central-Eastern Alps. Based on
the natural data available in the literature, a critical discus- sion of the
other proposed mechanisms is presented, and additional geological factors that
should be considered within the numerical model are suggested to improve the
fitting to the numerical results; these factors include varia- tions in the
continental and/or oceanic thickness, variation of the subduction rate and/or
slab dip, the initial thermal state of the passive margin, the oc- currence of
continental collision and an oblique convergence.Comment: 11 Figures and 3 Tabe
Permian high-temperature metamorphism in the Western Alps (NW Italy)
During the late Palaeozoic, lithospheric thinning in part of the Alpine realm caused high-temperature low-to-medium pressure metamorphism and partial melting in the lower crust. Permian metamorphism and magmatism has extensively been recorded and dated in the Central, Eastern, and Southern Alps. However, Permian metamorphic ages in the Western Alps so far are constrained by very few and sparsely distributed data. The present study fills this gap. We present U/Pb ages of metamorphic zircon from several Adria-derived continental units now situated in the Western Alps, defining a range between 286 and 266 Ma. Trace element thermometry yields temperatures of 580-890°C from Ti-in-zircon and 630-850°C from Zr-in-rutile for Permian metamorphic rims. These temperature estimates, together with preserved mineral assemblages (garnet-prismatic sillimanite-biotite-plagioclase-quartz-K-feldspar-rutile), define pervasive upper-amphibolite to granulite facies conditions for Permian metamorphism. U/Pb ages from this study are similar to Permian ages reported for the Ivrea Zone in the Southern Alps and Austroalpine units in the Central and Eastern Alps. Regional comparison across the former Adriatic and European margin reveals a complex pattern of ages reported from late Palaeozoic magmatic and metamorphic rocks (and relics thereof): two late Variscan age groups (~330 and ~300 Ma) are followed seamlessly by a broad range of Permian ages (300-250 Ma). The former are associated with late-orogenic collapse; in samples from this study these are weakly represented. Clearly, dominant is the Permian group, which is related to crustal thinning, hinting to a possible initiation of continental rifting along a passive margin
Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria-Europe plate boundary (Western Alps, Calabria, Corsica)
Since the first discovery of ultrahigh pressure (UHP) rocks 30 years ago in the Western Alps, the mechanisms for exhumation of (U)HP terranes worldwide are still debated. In the western Mediterranean, the presently accepted model of synconvergent exhumation (e.g., the channel-flow model) is in conflict with parts of the geologic record. We synthesize regional geologic data and present alternative exhumation mechanisms that consider the role of divergence within subduction zones. These mechanisms, i.e., (i) the motion of the upper plate away from the trench and (ii) the rollback of the lower plate, are discussed in detail with particular reference to the Cenozoic Adria-Europe plate boundary, and along three different transects (Western Alps, Calabria-Sardinia, and Corsica-Northern Apennines). In the Western Alps, (U)HP rocks were exhumed from the greatest depth at the rear of the accretionary wedge during motion of the upper plate away from the trench. Exhumation was extremely fast, and associated with very low geothermal gradients. In Calabria, HP rocks were exhumed from shallower depths and at lower rates during rollback of the Adriatic plate, with repeated exhumation pulses progressively younging toward the foreland. Both mechanisms were active to create boundary divergence along the Corsica-Northern Apennines transect, where European southeastward subduction was progressively replaced along strike by Adriatic northwestward subduction. The tectonic scenario depicted for the Western Alps trench during Eocene exhumation of (U)HP rocks correlates well with present-day eastern Papua New Guinea, which is presented as a modern analog of the Paleogene Adria-Europe plate boundary
A multi-component model for granular activated carbon filters combining biofilm and adsorption kinetics
Phase equilibrium constraints on a deep crustal metamorphic field gradient: metapelitic rocks from the Ivrea Zone (NW Italy)
The metamorphic rocks of the Ivrea Zone in NW Italy preserve a deep crustal metamorphic field gradient. Application of quantitative phase equilibria methods to metapelitic rocks provides new constraints on the PâT conditions recorded in Val Strona di Omegna, Val Sesia and Val Strona di Postua. In Val Strona di Omegna, the metapelitic rocks show a structural and mineralogical change from micaâschists with the common assemblage biâmuâsillâplâqâilmâ±âliq at the lowest grades, through metatexitic migmatites (gâsillâbiâkspâplâqâilmâliq) at intermediate grades, to complex diatexitic migmatites (gâsillâruâbiâkspâplâqâilmâliq) at the highest grades. Partial melting in the metapelitic rocks is consistent with melting via the breakdown of first muscovite then biotite. The metamorphic field gradient in Val Strona di Omegna is constrained to range from conditions of âŒ3.5â6.5âkbar at â650â°C to âŒ10â12âkbar at >900â°C. The peak PâT estimates, particularly for granulite facies conditions, are significantly higher than those of most earlier studies. In Val Sesia and Val Strona di Postua, cordieriteâbearing rocks record the effects of contact metamorphism associated with the intrusion of a large mafic body (the Mafic Complex). The contact metamorphism occurred at lower pressures than the regional metamorphic peak and overprints the regional metamorphic assemblages. These relationships are consistent with the intrusion of the Mafic Complex having post dated the regional metamorphism and are inconsistent with a model of magmatic underplating as the cause of granulite facies metamorphism in the region
Formation and exhumation of ultra-high-pressure rocks during continental collision: role of detachment in the subduction channel
UHP rocks commonly form and exhume during the transition from oceanic subduction to continental collision. Their exhumation in subduction channels depends on the balance between down-channel shear traction and up-channel buoyancy. Thermal-mechanical upper-mantle-scale numerical models are used to investigate how variations in material properties of the subducting continental margin affect this balance. Changes in shear traction leading to crustal decoupling/detachment are investigated by varying the onset of strain weakening, thermal parameters, and convergence velocity. Variations in buoyancy force are investigated by modifying subducted material density and volume. The model results are interpreted in terms of the exhumation number E, which expresses the role of the pressure gradient, channel thickness, effective viscosity, and subduction velocity. Peak metamorphic conditions, exhumation velocity, and timing of exhumation are temporally and spatially variable and are sensitive to the evolution of E. The models reproduce natural PTt constraints and indicate that neither slab breakoff nor surface erosion is required for UHP exhumation
Deep subduction and rapid exhumation: role of crustal strength and strain weakening in continental subduction and ultrahigh-pressure rock exhumation
The exhumation of crustal ultra-high-pressure (UHP) material depends on temporal and spatial variations in its detachment within the subduction channel. This dependence is investigated using numerical models with variable initial crustal strengths, representing a range of initial crustal compositions, and parameterized strain weakening, representing a range of processes that reduce effective crustal viscosity during deformation. Competition between down-channel shear traction, favoring subduction, and up-channel buoyancy, favoring exhumation, is expressed as the exhumation number, E, which can vary with time and position along the channel. Exhumed lower strength crust, which resists subduction owing to weak down-channel traction, records peak conditions â1. Higher strength crust is efficiently subducted to UHP depths (E 38 kbar. Given sufficient strain weakening, exhumation proceeds at >60 km Maâ1, indicating that buoyancy (E » 1) drives exhumation in these models. In all models, exhuming UHP material forms a deforming ductile plume, with a range of possible structural relationships predicted between exhumed UHP and HP materials