1,721,573 research outputs found
COEXISTENCE OF PSEUDOTACHYLYTE VEINS AND MYLONITIC ZONES AT THE BASE OF THE DEEP CRUST: AN EXAMPLE FROM THE CALABRIA (SOUTHERN ITALY)
No full textNatural examples indicate that pseudotachylytes cohexist in the same
outcrop with mylonites and ultramylonites. Pseudotachylytes intimately
associated with mylonites and ultramylonites can develop in high strain
zone close to the brittle-ductile transition (e.g. Passchier, 1982) or entirely
within the ductile regime as result of plastic instabilities (e.g. Hobbs et al.,
1986; Handy & Brun, 2004).
This study report microstructural investigations on two pseudotachylyte
veins found within the felsic granulites at the base of the ~20-25 km thick
Variscan crustal section outcropping in the Serre Massif (southern
Calabria). Felsic granulites consist of quartz, plagioclase, K-feldspar,
biotite, garnet, sillimanite and accessory minerals. Stretched minerals and
S-C composite foliations are detected in zones crystal-plastic deformation.
In places, felsic granulites exhibit an alternance of mylonitic and
ultramylonitic bands (a few millimeters thick). Pseudotachylyte fault-veins
develop along planes, which have a parallel orientation to the mylonitic
and/or ultramylonitic foliation. Locally, pseudotachylyte fault-veins occur
along the S-C composite foliations of the felsic granulite. On the other
hand, the pseudotachylyte injection-veins cross cut the mylonitic and/or
ultramylonitic bands.
Microstructural observations indicate that the felsic granulite exhibits a
strong grain-size reduction along the S-C composite foliations and near
the contact with the pseudotachylyte veins. Back scattered electron (BSE)
images, obtained by scanning electron microscopy (SEM) and
Field-Emission Gun SEM, show that in proximity of the contact with the
pseudotachylyte the garnet of the felsic granulite is fractured and shows
rims characterized by a new cristallization of very small euhedral garnet
(3-4 m). On the other hand, the ultramylonitic bands display a very
fine-grained matrix and have a dark appearance. However, the BSE
images reveal a strong penetrative foliation, which is defined by the
alignment of biotite and by the shape preferred orientation of quartz,
plagioclase and garnet. Moreover, the ultramylonitic bands are
characterized by a new crystallization of very small crystals (a few microns
in length) of sillimanite and K-feldspar, aligned along the foliation planes.
Matrix of the pseudotachylytes is microcrystalline and contains abundant
clasts (>50%) made up of quartz, plagioclase, K-feldspar, garnet and rare
biotite. Clasts in the matrix are aligned with a parallel orientation to
oblique foliation of the mylonitic granulite. At the margin of the vein,
garnet of the pseudotachylyte may occur in two habits: 1) garnet
microlites with very small sizes (3-4 m) and an idiomorph habit, which
formed by direct crystallization from the frictional melt, and 2) garnet
clasts (a few ten micrometres in size), with rims characterized by a new
crystallization of very small garnets (<2 m) and with a similar aspect to
the garnet rims of the host rock. In the vein centre, the matrix is mainly
composed of skeletal plagioclase and biotite (a few microns in lenght).
Plagioclase and biotite microlites often nucleated on rounded clasts of
quartz or plagioclase. Garnet microlites are absent in the vein centre.
These data, combined with the indications for the formation depth of the
pseudotachylytes (21-23 km) obtained by Altenberger et al. (2010),
indicate that during propagation of the seismic rupture the shear
deformation was highly heterogeneous and took place through the
development of alternating pseudotachylyte and ultramylonite, as result of
plastic instabilities.
References
Altenberger, U., Prosser, G. & Grande, A. (2010): Workshop
Physico-chemical processes in seismic faults, 11
Handy, M.R. & Brun, J.P. (2004): Earth Planet. Sc. Lett., 223, 427-441
Hobbs, B.E., Ord, A. & Teyssier, C. (1986): Pure Appl. Geophys., 124,
309-336
Passchier, C.W. (1982): J. Struct. Geol., 4, 69-7
Pädagogische Perspektiven für den Schulsport - Orientierungen für einen erziehenden Sportunterricht
No full textKurz D. Pädagogische Perspektiven für den Schulsport - Orientierungen für einen erziehenden Sportunterricht. In: Altenberger H, ed. Mit Sport lernen - mit Sport leben. Augsburg: Ziel; 2001: 173-180
Phänomenale Strukturen beim Bewegungslernen
No full textGröben B. Phänomenale Strukturen beim Bewegungslernen. In: Altenberger H, ed. Im Sport Lernen - mit Sport leben. Augsburg: ZIEL-Verlag; 2001: 259-264
Sprache als Medium - Wirkdimensionen verbaler Instruktionen im Bewegungsunterricht
No full textGröben B. Sprache als Medium - Wirkdimensionen verbaler Instruktionen im Bewegungsunterricht. In: Altenberger H, ed. Medien im Sport - zwischen Phänomen und Virtualität. Schorndorf: Hofmann; 2000: 50-66
The Timpa delle Murge ophiolitic gabbros, southern Apennines: insights from petrology and geochemistry and consequences to the geodynamic setting.
No full textThe Timpa delle Murge ophiolite in the North Calabrian Unit is part of the Liguride Complex (southern Apennines). The study is concentrated on the gabbroic part of the ophiolite of the Pollino area. They preserve the high-grade ocean floor metamorphic and locally developed flaser textures under ocean floor conditions. The primary magmatic assemblages are clinopyroxene, plagioclase, and opaques. Brown hornblende is a late magmatic phase. Green hornblende, actinolite, albite, chlorite and epidote display metamorphic recrystallization under lower amphibolite facies conditions, followed by greenschist facies. The gabbros show subalkaline near to alkaline character with a tendency to a more calkalkaline trend. The normalization to primitive mantle and mid-ocean ridge basalt (N-MORB) compositions indicates a considerable depletion in Nb, P, Zr and Ti and an enrichment in Ba, Rb, K, Sr and Eu. This points to a mantle source, which is not compatible with a "normal" mid-ocean ridge situation. Rather, the gabbros are generated from a N-MORB-like melt with a strong crustal component, which was influenced by subduction related fluids and episodic melting during mid-ocean-ridge processes. Plausible geodynamic settings of the Timpa delle Murge gabbros are oceanic back-arc positions with embryonic MORB-activities. Similar slab contaminated magmatism is also known from the early stage of island arc formation in supra-subduction zone environments like the Izu-Bonin-Mariana island arc
Theoretische Grundlagen des Einsatzes von Lehrmedien beim Erlernen sportlicher Bewegungen
No full textGröben B, Prohl R. Theoretische Grundlagen des Einsatzes von Lehrmedien beim Erlernen sportlicher Bewegungen. In: Altenberger H, ed. Medien im Sport. Schorndorf: Hofmann; 2002: 85-121
Microstructure and petrology of a garnet-bearing pseudotachylyte of Calabria-a link to lower crustal hypocenters
No full textInnensicht und motorisches Lernen: Workshop zur (Re-) Konstruktion der Innensichten
No full textGröben B, et al. Innensicht und motorisches Lernen: Workshop zur (Re-) Konstruktion der Innensichten. In: Altenberger H, ed. Im Sport Lernen - mit Sport leben. Augsburg: ZIEL-Verlag; 2001: 257
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