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Levy
Big Wall climber
So Cal
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Topic Author's Original Post - Feb 19, 2011 - 07:40pm PT
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While researching the geology of the Coso mountains I came across the term "Dike Swarm". It is a funny name for an area that features hundreds or more intrusions into the surrounding strata.
There is a famous one near Independence, CA. http://www.geolab.unc.edu/Petunia/IDS_Web_Site/IDS.html
Batrock or Minerals - What's the deal with these? Was the surrounding strata already fractured by faulting or did some other force cause this?
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cintune
climber
the Moon and Antarctica
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Feb 19, 2011 - 08:00pm PT
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The intrusion causes the quakes that fracture the host rock and the magma just fills them in. Source of a lot of great East Coast diabase outcrops.
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jfailing
Trad climber
A trailer park in the Sierras
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Feb 19, 2011 - 08:47pm PT
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Diabase. It's all over the place.
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cintune
climber
the Moon and Antarctica
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Feb 19, 2011 - 09:35pm PT
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Makes for some of the best boulders in Pa., anyway.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Feb 19, 2011 - 10:43pm PT
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If you go to this website and select the Mount Pinchot geologic map you will see that the Independence dike swarm (Kdk)is Cretaceous mainly diorite and granodiorite. In other areas they range from felsic to mafic.
http://geomaps.geosci.unc.edu/quads/quads.htm
It's called a "dike swarm" because there are 1,000s of dikes that intruded overlying rocks from a magma below during a fairly narrow range of geologic time (late Jurassic to early Cretaceous). These dikes extend about 300 kms from the Transverse Range, Mojave desert and up through the eastern Sierras.
Some cool photos of dikes in the Indpendence area from the website that Levy posted.
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'Pass the Pitons' Pete
Big Wall climber
like Ontario, Canada, eh?
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Feb 20, 2011 - 06:55pm PT
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^^ I'll take dikes on bikes over chicks with dicks any day.
P.S. How could anyone resist clicking on a Bill Leventhal post entitled "Dike Swarms"? Sheesh. Thank you, Dingus - it was looking far too geological. Where's Locker when we need him?
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Feb 20, 2011 - 11:43pm PT
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dudes: that's a swarm of independent dykes not the independence dike swarm.
personally I prefer chicks with picks.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Feb 21, 2011 - 09:05pm PT
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QITNL: thanks for posting the link to that thread on granite...somehow I missed that one. Minerals has sure spent a lot of time sharing his geologic knowledge with fellow SuperTopoans.
Definition: A dike refers to a tabular intrusive igneous body. The thickness is usually much smaller than the other two dimensions. Thickness can vary from sub-centimeter scale to many meters in thickness and the lateral dimensions can extend over many kilometers. A dike is an intrusion into a cross-cutting fissure, meaning a dike normally cuts across or through other pre-existing layers or bodies of rock. Dikes are usually high angle to near vertical in orientation, but subsequent tectonic deformation may rotate the intruded sequence. Near horizontal or conformable intrusions along bedding planes between strata are called intrusive sills. Dikes often form as either radial or concentric swarms around plutonic intrusives or around volcanic necks or feeder vents in volcanic cones.
Here is a photo of one of the radial dikes at Shiprock, NM
If you've ever been to the Leap, you know that it is full of what climbers refer to as dikes. However, these features don't fit the above definition. They appear to be a "swarm" of quartz-feldspar rich "sills" in granite. Good thing they are present...otherwise climbing at the Leap would be very challenging.
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matty
Trad climber
under the sea
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Feb 22, 2011 - 03:40pm PT
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WTF? I thought this thread would be about restroom lines at the Lilith Fair!
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Feb 22, 2011 - 04:59pm PT
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weschrist: hydrothermal alteration...that's interesting. I agree they don't appear to be dikes or sills. That's why I put the "" on the sills. Since they are near horizontal they seem to fit the sill definition over dikes. I've always wondered about those features but have never seen any published work on them. Do you have a reference?
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Feb 22, 2011 - 07:28pm PT
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thanks weschrist for that info and the usgs link. I never looked that closely at those features when I climbed at the Leap. Since they form positive features I assumed they were quartz-rich and more resistant to weathering.
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Spider Savage
Mountain climber
SoCal
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Feb 22, 2011 - 07:50pm PT
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Levy reveals the secret location for the next great climbing area.
(He's already climbed everything else in CA.)
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