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Folded and refolded rhyolite, Chiricahua Mountains, Arizona


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Age & Formation: 
Miocene rhyodacitic volcanic rock, ~27 Ma.
Geohistory: 
We know that rhyolitic flows are much stiffer than basaltic flows, and this is evident in the flow structure displayed by this rock. The clarity of the delicate flow laminae is quite nice, and it is obvious that the fricitional flow of the stiff lava locally created tight folding. A particularly striking example in this rock is the tight isoclinal fold residing between flow layers. Moreover, because of progressive deformation during flow, early formed patterns can be refolded, and this rock contains a perfect example of this: the obvious broad fold has refolded the earlier formed isoclinal fold.
Whereabouts: 
I collected this rock in 1973 just outside of Chiricahua National Monument in southeastern Arizona, at a time in which I was directing geology field camp at The University of Arizona. I like this specimen for it underscores the stiff nature of rhyolitic lava, and it is my very best example of refolded folds.