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Foliations and Lineations |
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These pictures illustrate an example of strong linear fabrics. The outcrop on the top right picture shows a deformed rhyolite (felsic volcanic rock equivalent to granite) of the Wyman formation (ca. 3.3 Ga) in the East Pilbara (WA). This outcrop shows a very strong steeply dipping linear fabrics and a rather weak to very weak flattening plane. The pictures below show the linear fabric on 3 perpendicular planes. The bottom left picture shows the lineation within the foliation plane (ie the pen lies on top of the foliation). The middle picture shows a plane perpendicular to the foliation and parallel to the lineation. The last picture (bottom right) shows a plane perpendicular to the lineation. In this last picture, the flattening plane is barely visible. Such a strong linear fabric is referred to as a constrictional fabric. In the field, the attitude of a lineation is fully characterized by its plunge (angle from an horizontal surface down to the lineation) and plunge direction (azimuth of the imaginary vertical plane carrying the lineation).
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