Barnes Butte, Phoenix Arizona

[Admin]

South Mountain Landslides?

South Mountain Geology map

South Mountain Geology

Yes, I'll buy it! The rocks didn't travel far.

[Admin]

Jul 31, 2018 12:40:28 GMT -7 @edmost said:

I can concur with the analysis that
South Mountain Metamorphic Kinematic Complex
is the bedrock that the buttes sit upon.

Mr S J Reynolds alludes to that in this fine statement

The 20- and 9- m.y.a range cooling area on the plutonic rocks
Probably reflect uplift caused by tectonic denudation during detachment faulting. – Reynolds pa 50

I cannot abide though- that the pediment the buttes sit upon
were formed by some detachment of a South Mountain rock slide.

That is not where the redbeds, breccias and clastic come from.

So the question becomes:

Were the buttes established and, some underground plutonic event,
(associated with the South Mountain Metamorphic Kinematics Complex),
uplift those buttes?

Or

Was the bedrock already established,
and some other event as yet undetermined,

-terrestrial or extra terrestrial-

deposit the breccia & clastic that build up those buttes?

mostly

[Admin]

That is what I'm trying to establish now @edmost.

I believe the buttes themselves are ancient granite with two layers of landslide coatings.

The southwest half of south Mountain is ~1.5 billion year old granite that was metamorphosed to gneiss.
The northeastern half is 25 million year old granite. in the middle is 22 million year old granite that caused the northeast corner to brecciate. Something later caused the outer layer to brecciate again making two layers, the outer layer finer than the inner.

That would provide the two slides.

The first slide was MOSTLY rhyolite.
The second slide was MOSTLY granite.

So far I haven't found of there being any rhyolite on South Mountain. Perhaps most of it was removed with the first slide, and the rest with the second?

Now, does the granite in the Barnes Butte Breccia match the granite from South Mountain?

Earthquakes?

www.tucsonnewsnow.com/story/17203031/history-of-earthquakes-in-arizona