⭐Hi Rockstars! Being able to recognize little geological hints in the field is an important skill for all Rockstars. Slickenlines are one great example of a feature that the observant Rockstar can take note of and glean valuable information from! 😁 Slickenlines are features found on the surface of a fault. That’s right, they’re found on the slip surface of a fault! There are actually two very similar features, known as slickensides and slickenlines. A slickenside is a very fine-grained, polished surface along a fault plane, polished by the actual movement of the rocks against each other. A slickenline is a lineation on the feature, which can tell us the orientation of movement of one side of the fault relative to the other! The lineation can be caused by a few things, such as a simple asperity that gouges the surface of the fault, abrasion of larger grains into pulverized rock, or precipitation of mineral fibers (Twiss & Moores, 2007). Combined with a marker layer which can suggest which side of the fault moved up or down, a slickenline gives us a powerful indicator of the potential movement of the fault, as much as a 2D feature can. 🤓 Keep in mind though, that they are not good indicators of the amount of displacement of the fault! They are of most use when at some angle to the observable fault surface, giving additional vector information in conjunction with marker layers in other axes. For example, observing a fault in an outcrop, a Rockstar might suggest a simple normal fault due to the displacement of an obvious marker rock down on the hanging wall. On closer inspection, the fault surface reveals slickenlines pointing outwards from the outcrop! This would then prompt our astute Rockstar to investigate the possible movement of the fault not only in the normal regime, but also the strike-slip! 😍
Until next time, Rockstars – enjoy our photos of slickensides and slickenlines from core samples!! 😘 ------------ Sources: Twiss, R. J. & Moores, E. M., (2007). Structural Geology. 2nd Ed.
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