Tuesday, February 15, 2011

It's our fault

Sabino Canyon fault, photo by Carol Tornow
Text by Peggy 'cool as dirt' Wenrick: This photo shows an exposure of the Sabino Canyon Fault.  The canyon itself has eroded along this fault since it has been exposed at earth’s surface.  The reddish material in the lower portion is fault breccia (bre cha), formed as rock is broken and/or crushed by forces along the fault.  The reddish color is caused by groundwater circulating in the fault zone, rusting (or oxidizing) iron minerals and cementing the broken rock particles.  The rocks [brownish-black] above the fault were plastically deformed rather than broken and show sinuous bending with little oxidation.

Both samples from the site above
Both sample photos from Peggy Wenrick
Peggy: The samples illustrate the crushing and cementing that occurs. Anne says: Do take a look at the Wiki site on breccia. It's very readable. Thanks, Peggy, for sharing your expertise.

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