Pseudotachylytes
© All photographs on this webpage may be downloaded and used for teaching purposes only. The photographs may not be reproduced in any publications - commercial or scientific - without permission by Ralf Hetzel.
Picture 1: Pseudotachylite vein
Download full size image (1,2 MB)
Black pseudotachylite vein in red foliated gneiss. Pseudotachylites are frictional melts that form during seismic events. Note the extremely sharp contacts between the pseudotachylite fault vein and its host rock. Red gneiss clasts were incorporated in the pseudotachylite melt (fault zone in Mozambique Belt basement, Kenya).
Related Publications:
Hetzel R., Altenberger U., Strecker M.R. (1996). Structural and chemical evolution of pseudotachylytes during seismic events. Mineralogy and Petrology 58, 33-50.
Hetzel R., Strecker M.R. (1994). Late Mozambique Belt structures in western Kenya and their influence on the evolution of the Cenozoic Kenya Rift. Journal of Structural Geology 16, 189-201.
Picture 2: Pseudotachylite biotite melting
Download full size image (972 KB)
Thin section photograph (plane-polarized light) of contact between pseudotachylite vein (above) and host rock gneiss (below). Biotite in the host rock is preferentially molten, mainly because it has a lower melting point than quartz and feldspar in the host rock. Width of photo is about 2 mm.
Related Publications:
Sherlock S.C. and Hetzel R. (2001). A laser-probe 40Ar/39Ar study of pseudotachylite from the Tambach Fault Zone, Kenya: direct isotopic dating of brittle faults. Journal of Structural Geology 23, 33-44.
Hetzel R., Altenberger U., Strecker M.R. (1996). Structural and chemical evolution of pseudotachylytes during seismic events. Mineralogy and Petrology 58, 33-50.
Picture 3a: Pseudotachylite with marginal cataclasite
Download full size image (1,3 MB)
Back-scatter electron image of marginal cataclasite zone in pseudotachylite vein. Such intensely fragmented cataclasite zones occur typically between the once molten part of pseudotachylite veins (see picture 3b) and the adjacent host rock. Grain size of the fine-grained cataclasite matrix is about 1 µm. Scale bar is 20 µm long.
Related Publications:
Hetzel R., Altenberger U., Strecker M.R. (1996). Structural and chemical evolution of pseudotachylytes during seismic events. Mineralogy and Petrology 58, 33-50.
Hetzel R., Strecker M.R. (1994). Late Mozambique Belt structures in western Kenya and their influence on the evolution of the Cenozoic Kenya Rift. Journal of Structural Geology 16, 189-201.
Picture 3b: Pseudotachylite with microlites
Download full size image (1,4 MB)
Back-scatter electron image of pseudotachylite vein with abundant plagioclase microlites. The plagioclase microlites crystallized from the rapidly cooling mafic pseudotachylite melt. The large grey clast on the left is a plagioclase porphyroclast, on which the microlites were able to nucleate. The three dark quartz porphyroclasts could not be used for nucleation. Scale bar is 20 µm long.
Related Publications:
Hetzel R., Altenberger U., Strecker M.R. (1996). Structural and chemical evolution of pseudotachylytes during seismic events. Mineralogy and Petrology 58, 33-50.
Hetzel R., Strecker M.R. (1994). Late Mozambique Belt structures in western Kenya and their influence on the evolution of the Cenozoic Kenya Rift. Journal of Structural Geology 16, 189-201.
Picture 3c: Contact between microlites and marginal cataclasite in pseudotachylite
Download full size image (1,1 MB)
Back-scatter electron image of pseudotachylite vein showing the contact between the two zones made up of microlites (above) and cataclasite (below), respectively (see also Pictures 3a and 3b). Scale bar is 20 µm long.
Related Publications:
Hetzel R., Altenberger U., Strecker M.R. (1996). Structural and chemical evolution of pseudotachylytes during seismic events. Mineralogy and Petrology 58, 33-50.
Hetzel R., Strecker M.R. (1994). Late Mozambique Belt structures in western Kenya and their influence on the evolution of the Cenozoic Kenya Rift. Journal of Structural Geology 16, 189-201.
