TECTONITE
“Tectonite” is a term used by structural geologists to
refer to any rock that has been subjected to solid-state flow. Tectonites
show pervasive foliation and/or lineation (crystals are lined up more or less
parallel). Most tectonites are "LS-tectonites" (rocks that show
both foliation and lineation). The rock shown below is an L-tectonite,
a less common form of tectonite. L-tectonites have lineation, but
not foliation. The sketch below shows the fabric geometry of such
rocks. The crystals are lined up parallel when viewed in two different dimensions,
but not in the third dimension. L-tectonites form by significant stretching
(extension).
L-Tectonite - sketch of the 3-D geometry of L-tectonite fabrics. From Davis
(1984) - Structural Geology of Rocks and Regions.
L-tectonite gneiss (7.1 cm across) -
surface equivalent to "A" in sketch above.
Locality:
railroad ballast along Norfolk Southern line at Cook Road, Columbus, Ohio, USA.
L-tectonite gneiss (2.8 cm across at base) - surface showing lineation,
equivalent to "B" in sketch above.
L-tectonite gneiss (6.6 cm across) - surface showing lineation,
equivalent to "C" in sketch above.