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nature
climber
Flagstaff, AZ
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Topic Author's Original Post - Mar 10, 2005 - 12:05pm PT
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On geological rock types...
What is Quart Monzonite? What is Granite? Both are igneous rocks and both fall under the same classification scheme. They look the same because they formed under similar physical (high pressure/temp) and chemical regimes. The chemical composition at the time the magma crystalized determined the rock classification.
Igneous rocks (and plutonic rocks in general) such as these are classified on a ternary diagram (below). At the top is quartz, on the point bottom-right is plagioclase and on the left is orthoclase (K-spare).
In the rocks of Yosemite and Joshua Tree quartz is the clearest of the grains, plag is the opaque white grain, and k-spare typically takes on a flesh to pinkish color. Color, however, is not diagnostic of a particular variety of feldspar but it'll serve our purpose in Yosemite and Josh. Striations on cleavage faces are a better diagnostic of plagioclase.
Classifying the rock is pretty simple. A handlense is helpful. Looking at your rock you blank out all the dark minerals (they don't count unless >10%). This includes the mica's, pyroxene and hornblend. First determine what percentage of the light minerals is quartz. Then determine the ratio (in percentage) of plag to k-spar. After you figure that out you look for that spot on the diagram and you have your rock type.
In Yosemite your classification exercise might go:
Quartz: 45%
Feldspars: 55% (85% plag, 15% k-spar)
Turns out this makes most of the granitic looking rock in Yosemite a Granodiorite.
In Joshua Tree your classification might be:
Quartz: 15%
Feldspars: 85% (70% plag, 30% k-spar)
This classifies the rock as a Monzodiorite
OR :
Quartz: 15%
Feldspars: 85% (50% plag, 50% k-spar)
Classifying it as a Quartz Monzonite
I have a couple papers that I usually carry around with me that folks find of interest. Both are from California Geology. One covers some of the metamorphic aspects of Yosemite as well as the glacial aspects, the other is on the geomorphic evolution of Joshua Tree. It details the distribution of rock types in JTree. It also covers the tectonic evolution - explaining the higher elevations. If anyone is interested in finding these I can dig up the ref.
This about covers our Geology 419 topic for the day. Minerals has been missing from the supertopo geo seminar circuit. Figured I'd throw-down in his place.
For our next topic (we might get):
a) why is JTree rock so damn grainy?!?
b) What's up with all that desert varnish?
c) what the hell are those big black knobs at sugarloaf all about?
d) what nitwit sucked Owens Lake dry?
e) is there really cheese on the moon?
f) what makes the bishop tuff so special?
g) what's an exotic blue schist knocker?
h) why is there so much more quartz in the Yosemite rock?
i) why does orogeny lead to subduction?
j) what's a roof pendant and should i buy my wife/gf one?
k) desert pavement - what? they paved the desert?
One minute to go. gotta run. Enjoy!
Editors note: inspired by the discussion in the JTree/RRocks post. Most of this stuff isn't something covered in Geology 110 courses (geology for physical science majors). You'd learn this stuff in Minerology and Petrology courses - upper level shiztnitz.
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up2top
Big Wall climber
Phoenix, AZ
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Mar 10, 2005 - 02:18pm PT
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Cool. And here I thought it was all just granite. What about kniess (or is it kneiss)?
Ed
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Edge
Trad climber
New Durham, NH
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Mar 10, 2005 - 02:29pm PT
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Ed, it's "gneiss."
Me likey the gneiss....
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Donny... the OHHH!- Riginal
Sport climber
Boald'r Effin See Oh
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Mar 10, 2005 - 02:33pm PT
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Great Nature....how 'bout some NON-geological rock types?
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 10, 2005 - 02:36pm PT
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Ed - the prerequisite for this seminar was geology 110. In case you were out climbing the day they covered metamorphic rocks here's a url to get you caught up.
http://www.rocks-rock.com/gneiss.html
yeah... but what's up with gneiss? I've never climbed in an area where the attraction was the climbs on gneiss. You see it in the bands above the igneous rocks - like when hiking up to the Queen Mountain area in JTree. Where are areas where you climb on the stuff?
I'm sorry Donny, you'll have to enroll in "Busting Donny's moms' chop's 101" to get the graph to differentiate crack-cocaine and crystal meth.
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jfk
climber
Santa Barbara, CA
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Mar 10, 2005 - 02:51pm PT
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nature,
if you could cite the refs for those papers that would be cool.
thanks,
john
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Edge
Trad climber
New Durham, NH
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Mar 10, 2005 - 02:52pm PT
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Nature,
Some of the "gneissest" climbing in the country is in Western Mass at Farley, Great Barrington, and Happy Valley/the Hideaway. These are primarily bouldering destinations, although the cliffline at Farley is awesome as well. The stuff out here is awesome to climb on.
A close relative is schist, which is what you find at Rumney. Very sharp layers of stone, with some amazing features. I don't have a pic, but there are a few places where you see the strata twisted all pretzel-like. Truly amazing.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 10, 2005 - 03:24pm PT
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Yosemite ref is:
California Geology December 1991
Geology of The Joshua Tree National Monument - California Geology, April 1984
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Donny... the OHHH!- Riginal
Sport climber
Boald'r Effin See Oh
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Mar 10, 2005 - 03:28pm PT
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I was hopin' you'd come up with somethin' like Buddy Holly....and maybe Whitesnake.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 10, 2005 - 05:22pm PT
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I'm going to correct myself before someone else does. This will also add to the confusion. I found the paper on JTree Geology. I took a good hard look at the geological map.
Here's how they classified the rock types in various areas we all know:
Hidden Valley Campground, Wonderland or Rocks, Jumbo, Ryan all get mapped as:
Kwt - Cretaceous White Tank monzodiorite.
Split rock is mapped as:
Kgp Cretaceous Gold Park diorite
Queen Mountian is mapped as:
Kqm - Cretaceous Queen Mountian monzogranite
Around Indian Cove it's mosttly Kwt but there are pockets of Jtp - Jurassic Twntynine Palms porhyritic quartz monzonite.
Looks like there is very little Quartz Monzonite and no monzonite (edited that part out above) in JTree. Still, the idea is the same.
Geology after Dibblee, 1967 and 1968, Rogers 1961.
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jfk
climber
Santa Barbara, CA
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Mar 10, 2005 - 05:57pm PT
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thanks,
should be fun to hit up the library before i hit the road for a little post-climb fire-side education.
john
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up2top
Big Wall climber
Phoenix, AZ
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Mar 10, 2005 - 06:08pm PT
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Mt. Lemmon is all gneiss.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 10, 2005 - 06:36pm PT
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Thanks Ed. So it is gneiss. In fact it's 1.5 Billion year old Catalina gneiss. I've never climbed there. Tragedy really but the nothern part of this state is so loaded I rarely find a reason to drive the four hours to get there. Will have to check it out for sure now.
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Lambone
Ice climber
Ashland, Or
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Mar 10, 2005 - 10:50pm PT
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this all seems like Geology 101 to me...???
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troutboy
Trad climber
Newark, DE
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Mar 11, 2005 - 11:32am PT
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"Geology after Dibble, 1967 and 1968, Rogers 1961."
Just guessing (I don't have the cited pub) but would this be Dibblee, not Dibble ???
TS
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 11, 2005 - 11:33am PT
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Where did they give you the ternary diagagram and monzonite in 101?
The typical ingneous rock series taught in your first geo course is:
Granite, Diorite, Gabbro, Peridotite for the Intrusive rocks
Rhyolite, Andesite, Basalt for the extrusive.
Additionally you might also have to identify Obsidian, Tuff (or Breccia Tuff), Pumice and Scoria in your lab for the intrusives. I'd be surprised if Monzodiorite is lab test question in any into geo course.
Petrology
troutboy - yup, thanks for the catch. i fixed it
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Josh Higgins
Trad climber
San Diego
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Mar 11, 2005 - 08:18pm PT
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I heard a touron in J-Tree say, "See all the sand on the ground. This is all sandstone." That was classic. Great post.
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Haggis
Trad climber
Scotland
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Mar 12, 2005 - 01:52pm PT
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Ok
Ignore the ternary diagram for the moment and consider what you are doing to form these rocks.
Quartz Monzonite and Granites are evolved rocks. They start from a similar silca saturated magma sitting in two magma chambers, the quartz Monzonite system has more K, Ca, Na, Al and Fe etc in the melt than the granite system.
Ok start to cool the systems down.
Step one: both systems form Olivine then Plag’ and mag’ then Augite in this order as you cool. These sink to the bottom on the chamber and/or partly erupted out.
Hence the magma in both chambers has been reduced in K, Ca, Na, Al and Fe etc
Step two. Since your liquid line of descent is a Calcalkiline setting (has H2O in the Magma) therefore the next suit of minerals to for are Amphiboles and Biotites in that order hence further reducing the K, Ca, Na, Al and Fe etc: SiO2 Ratio. You plag compositions move down from Ca rich to Na rich
So after you have done all this what are you left with?
A lot of SiO2 which forms qtz, and some K which forms feldspars and a bit of Biotites that got left behind thus you have a granite. HOWEVER your quartz Monzonite system started with a great volume of K, Ca, Na, Al and Fe etc relative to silica. So there is more of this k, Ca, Na, Al and Fe etc kicking around that forms a lager quaintly of K feldspars and Na plag’.
Thus
Due to the starting composition of the magma. There is more aulimius material in the melt which remains through evolution and gets used up in the end when it all freezes in K feldspars and Plag.
So what is granite.
It is course grained evoloved silica rich igneous rock
What is quartz monoztie
It’s a course grained evolved peralikaline granite or Alkali rhyolite in the UK.
The only difference is the amount of K, Ca, Na, Al and Fe etc at the start.
Rob
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 14, 2005 - 09:22pm PT
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dingus... i'm taking that one on. I'm doing what any good geologist worth his weight in tuff would do - i'm doing some research/reading. I'm really stoked on the last two posts (dmt and Haggis) but need to give both some thought.
right now I'm leaning towards thinking that your/our understanding of the intrusive systems and how they should work are simply off-base.
Garlock faulting and some weirdness (whacko rotation) going on south breaks that model (basin and range extension) down easily. More complexity is going on towards the south than is easily explained from a tectonic perspective than the north.
Heck, explain this one. We're on the leading edge of a massive subduction zone. Why the Basin and Range (extensional)? Where did the compression go? (I bet DMT has a pretty good idea)
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bobh
climber
Bishop, California
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Mar 14, 2005 - 09:55pm PT
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Nature wrote:
"In Joshua Tree your classification might be:
Quartz: 15%
Feldspars: 85% (70% plag, 30% k-spar)
This classifies the rock as a Monzogranite"
I don't see monzogranite anywhere on your ternary diagram.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 14, 2005 - 10:18pm PT
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yeah... neither do i. Guess that should be monzodiorite. I've made the correction. thanks for catching that.
(though hmm... I typed it twice. Either I wrote it wrong after reading the paper or? - i gonna have to look at the paper again tomorrow).
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WBraun
climber
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Mar 15, 2005 - 01:23am PT
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I love this theoritical side of geology, much more so than identifying the rocks we pick up on the ground.
Why is that Dingus?
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Haggis
Trad climber
Scotland
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Mar 15, 2005 - 10:36am PT
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Re: the rocks being older in the west thing:
Older rocks are representations of smaller degrees of meting therefore are saturated in elements that do not like being in rocks. Silica likes being in rocks and things like CaTs and dolomite (yes it can be produced by igneous processes) does not thus really low melt fractions (with some CO2) will produce ultabasic rocks like nephilinites and weirder.
Thus as age increases melting increases magma changes composition to more silica rich when melting increase producing more quartz.
this also accounts for the colour.
just a theroy
Rob
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 15, 2005 - 11:26am PT
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"I love this theoritical side of geology, much more so than identifying the rocks we pick up on the ground"
I'm with DMT on that statement. Identifying rocks is basic geology. There isn't a ton of research science to do identifying rocks when compared to say the area of paleoclimate. Arm waving about peleoclimate shifts or plate rafting is fun stuff.
In the right circles, if you put for the "plate rafting" theory some folks will hit the roof. The debates will begin (as well as more beer consumption). I've seen it first hand. I was lucky enough at the time to not know enough to get involved (probably still don't when it comes to tectonic/ig-pet stuff). But I love to be in the middle of the paleoclimate discussion.
I should have masters in geology but I'm now beyond the term limitation on getting my thesis signed. My undergrad work was in NRPI (Natural Resources Planning and Interpretatioon) with emphasis in Interp (relating complex scientific ideas in laymans terms). My focus for my masters was soils geomorphology applied to paleoclimate studies in and around the Sierra. With folks like DMT participating I see no reason not to continue various Geo 419 threads.
thanks for the effort you put in to that post, DMT.
Haggis: "Silica likes being in rocks and things like CaTs and dolomite (yes it can be produced by igneous processes)" - please provide a citation for this statement regarding dolomite. Thanks.
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Minerals
Social climber
The Deli
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Mar 15, 2005 - 02:20pm PT
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Oh man, I don’t know where to begin. Lots of cool stuff here… my favorite… pluton emplacement… I guess I’ll start by getting some breakfast.
Rocks, rocks, rocks…
Hey, what happened to blueschist???
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Minerals
Social climber
The Deli
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Mar 15, 2005 - 06:42pm PT
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Intrusion, diking, magma mixing and mingling, jointing/fracturing, climbing.
How about this one?
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quickhiker
Trad climber
Seattle
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Mar 15, 2005 - 09:57pm PT
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Hmmm… a lot of cool stuff, and I always like the rocks…
A couple of points:
1) the map of Joshua Tree cannot be directly compared to the ternary diagram that looks like it was scanned out of Compton’s ‘Geology in the Field.’ This is because the names in the ternary classification shown in the original post postdate the 1961 map. To keep things extra confusing, some of the names were recycled- including quartz monzonite. The previous classification allows QM to have more quartz. Now it would be considered a granite or granodiorite based on modal assemblages.
2) Simple fractionation from a basaltic ‘parent’ magma to produce the granites of the sierras (or Cordillera Blanca, J Tree, K2, Cascades, etc…) isn’t really the concept in favor at this point (though, arguably, there are those that would still defend it as the holy grail and it still shows up in many 101 textbooks). In most cases the supposed ‘parent’ magma pointed to in the field has a different isotopic value than the granite, which is inconsistent with fractionation. Does fractionation happen? Of course. Is it the only game in town? No. Magma mixing, assimilation of host rocks deeper in the crust and other processes are important processes contributing to the compositional evolution of granites, etc. This stuff would show up in igneous petrology courses (or at least it should if your instructor is up to the times).
3) The age relations in the Sierras span a large chunk of time (40 million years between ellery lake and olmstead point alone). Part of this is likely due to changes in the angle at which the Farallon Plate was subducting below North America. Part of it is likely due to more local tectonics. Many of the sierran plutons were emplaced along transcurrent faults (mixed extension and strike-slip motion) so their locations are moderately controlled by fault geometries (there are some great examples of fault control on pluton emplacement in Death and Panamint Valleys, albeit in a different tectonic environment and 11-15 million years old). If you look at the age relationships in the Tuolumne Intrusive suite (TIS), there is a bullseye pattern, which is roughly commensurate with increasing silica and shift in Strontium isotopic values. This is a subject of ongoing research. These ‘nested’ plutonic complexes are common throughout the sierras and the world. Another good example is around Mt. Whitney, for those who venture beyond the Valley neighborhood. Regardless, the ages pulled from the TIS they span ~10 million years. Contact relationships indicate that most of the units were partially molten at the same time as their outer neighbor and that they were exchanging material. So, this provides a neat window into the timescales over which a magmatic system is ‘viable.’ Keep in mind that there were probably many generations of volcanic expression at the surface over those 10 my as most volcanic centers, per se, last about 0.5 to 1 million years (rough, of course).
4) Yep, you can find good quality sierra granites in Santa Cruz that were transported north along the san andreas system of faults. I say system because plate boundaries are very messy places and the SA fault has evolved considerably over its slightly more than 20 million years of activity.
I’ll stop there before I get too carried away. I’d be happy to answer any specific questions on granite. I spent enough years of my life studying it and writing about it that it’s nice to put some of it to work now that I’ve moved on to other ventures.
Oh yeah… Minerals… Is the lower picture from the upper part of Tenaya Canyon, maybe a half mile from the Sunrise Trail as the crow flies? Composite dike with basaltic andesite, surrounded by aplite surrounded by host granodiorite, with its own set of mafic inclusions. Pretty cool outcrops. I spent an afternoon documenting those a few years ago and have always thought it would be fun to map them out a bit more. Order of operations:1) crystallization of granodiorite to at least about 80% crystals/ 20% melt (or less) along with some mixing and stirring for the mafic inclusions; 2) intrusion of aplite dike, possibly related to the large aplite body further down Tenaya Canyon (making the inner gorge gorgeous); 3) basaltic andesite dike follows path of least resistance and follows mushy aplite. This partially remelts and partially disaggregates the aplite; 4)Basaltic andesite quenches preserving some pretty neat mixing and assimilation textures.
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Lambone
Ice climber
Ashland, Or
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Mar 15, 2005 - 11:17pm PT
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whoa...now there's someone who knows his rocks!
I look at those pics and see climbing lines, holds and friction smears...someone else see's "mafic intrusions"...nice!
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WBraun
climber
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Mar 15, 2005 - 11:32pm PT
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The one mind blower for me has always been that the continent of North America has been in diorite on El Cap. How does one explain that?, especially since it’s in such good detail.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 16, 2005 - 12:11am PT
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yes yes yes! minerals is here! oh man! and quickhiker too! thanks for sorta saving my ass from further making a fool. As stated, this area isn't my specialty so I'm so happy ya'll found this post and participated. yes! (though I will say I sorta hoped I'd bait BL into this :-)
quickhiker - yup it was from compton's. I should have cited that. Can you expand on the statement or provide another classification to defend " Joshua Tree cannot be directly compared to the ternary diagram"? Hey... what's your background/education? Obviously you know your stuff so I'm just wondering where you learned it and how far you took it. In fact, as I re-read your stuff it's clear it's packed and pretty thick!
quickhiker (QH) - do you know John Longshore?
QH - 20 million on the SA activiation. I've always had 40 M stuck in my head (subduction of the rift and eastern section of the Pacific plate thus activating the SA). Can you cite to correct/help my understanding?
Werner - it's shape is 100% random. The fractionation(?) to allow the shape I'm sure is best left to try to be explained by our experts that just joined this fun.
QH - STOP? NO! don't stop!
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golsen
Social climber
kennewick, wa
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Mar 16, 2005 - 12:13am PT
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Really cool stuff. Nice pics...I bagged geology in school to be an engineer and I need some of you guys to help with a question concerning basalt. Not looking for a dissertation here just a laymans explanation. Devils tower, smith rock gorge, Vantage in Washington is all what I call basalt (I am sure they are different types) but they all seem to form columns that are pentagon shaped. My understanding is that this was due to the crystal structure and how it cooled? Is this even remotely correct?
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Jaybro
Social climber
The West
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Mar 16, 2005 - 12:16am PT
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Dingus said it all. If I may combine some bites;
"I love this theoritical side of geology, much more so than identifying the rocks we pick up on the ground. - Professional geologists ... have to know it all and have to know how to find the oil, or .... "
I was drawn to geology, esp. paleontology, just for this detective-like peicing together of ideas and theories. I was briefly a well core anaylising oil pimp and it soured me on the profession. Now, as an amatuer, a climber and roadcut driver by-er , I have much more latitude, I find there is no limit to things to think about. I like being part of the john Mcphee school more than being a tool for pig oil.
I wonder about what made the topography the way it is. Why is the glue in Maple canyon strong enough to hold those river stones solidly enough that we can climb on them when most similar formations are choss?
I'm tempted to think of the black Diorite 'North America," inclusion on El cap as an anomolus coincidence, but, as Werner suggested, it's too perfect. Is it's shape, and that of the continent most of us here live on some sor tof naturally ( inevitably) recurring fractle pattern? If so, how does that effect a physical, metaphysical interpretation?
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WBraun
climber
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Mar 16, 2005 - 12:16am PT
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I ain’t buyin the ”random” shape of the North American continent in diorite on El Cap. It’s just too coincidental for me to say it’s random. It’s definitely a mind blower.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 16, 2005 - 12:17am PT
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remotely correct it is (and I'm pretty sure all the places you refer to are basalts). The jointing is also part an artifact of the cooling and degassing of the basalt.
The columnar jointing is also what suckers people into thinking Owens River Gorge is Basalt - it's not. It's the 763,000 year old (paleomag reversed) Bishop Tuff. My jaw stats flappin' when folks call it basalt. It's the youngest paleo-mag reversed rock unit that has been radiometrically dated. It's the big player in nailing down the timing of the Brunhes-Matuyama magnetic flip.
Werner - I sorta didn't think you'd bye the random part of that but oh well. You'll be hard pressed to find a better "explaination". Think of it this way. If you added 500 feet to the section of the wall - 500 feet thicker - would it look the same? I doubt it.
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WBraun
climber
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Mar 16, 2005 - 12:49am PT
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That means that this universe is just a random event that occurred for no apparent cause whatsoever. Why does the Earth move around the Sun? Is it for no apparent reason? Why does the grass grow at a specific temperature?
It cannot be for no apparent reason.
There is no such thing as randomness since there is a cause to this universe. If random things happen, then that means they have no cause.
Yes Dingus
The captain has a nose an eye and a heart. And it's in North America.....
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WBraun
climber
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Mar 16, 2005 - 12:53am PT
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Yes
And where comes the source of beauty
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WBraun
climber
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Mar 16, 2005 - 01:05am PT
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Ok, very nice, you are happy toulomne*. I hope you get some nice outside time soon.
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quickhiker
Trad climber
Seattle
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Mar 16, 2005 - 01:16am PT
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Columnar jointing is a cooling phenomenon, rather than being related to crystal structure. The scaling is different. The columns result from fracture intersections at 120 degrees (times three is 360). Do that a few times and propagate them, and you get a column. The 120 comes from energy minimization as the material shrinks during cooling. Since cooling is along a gradient (cooler at the surface, for example), the shrinking is the greatest where coldest and thus there is a gradient in stress. Therefore, it isn't too big a stretch to see that the cracks are perpendicular to the cooling front and propagate with time/cooling into the rock. The regularity of the columns is a function of cooling rate and order in the cooling front (planar or curvy). If you look at examples of lavas cooled against glaciers, you get some pretty neat patterns.
As to how far I went in school... let's just say my family is glad to see me finally have a job.
As to north america wall... the mafic material is actually a tabular body in three dimensions that obliquely intersects the east face of el cap. give it a few meters of weathering and it won't look like NA anymore. The human mind is designed to look for patterns... take a look around whatever space you are in and see how many things you can see that look like human faces. Does this make anything less beautiful or worthy of respect? I would hope quite the contrary.
I may have spoken out of context... the rocks at J Tree are perfectly classifiable using the IUGS ternary diagram. No Problemo. The classifications from the 1961 map are apples and oragnes in terms of names. Similar vintage rock classifications include terms like 'alaskite', which would simply be a high K (and Al) granite in the IUGS scheme. Purely semantic jargon crap, but kinda useful if you go back into some of the older literature (there is some great stuff from the 1930s-50s on the sierras).
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Lambone
Ice climber
Ashland, Or
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Mar 16, 2005 - 01:22am PT
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"I ain’t buyin the ”random” shape of the North American continent in diorite on El Cap. It’s just too coincidental for me to say it’s random. It’s definitely a mind blower."
I concur.
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quickhiker
Trad climber
Seattle
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Mar 16, 2005 - 01:32am PT
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Anyways, I'm definitely stopping for a few days while I'm in the field, in the sun, and away from the 'puter.
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golsen
Social climber
kennewick, wa
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Mar 16, 2005 - 02:39am PT
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thanks quickhiker. I get the cooling and I understand that it takes place at a gradient. I am missing the 120 degrees? That must be energy minimization on a molcular level? My PhD chemist girlfriend tells me that pentagons dont form at the moleculr level. These things are pretty uniform pentagons which I think would be 360/5 = 72 degrees. Oh well, they sure are fun to climb on.
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Haggis
Trad climber
Scotland
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Mar 16, 2005 - 09:57am PT
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nature:
ive left my notes at home
ill write a repy regarding the dolimite tomorrow when im back in my flat.
it has a lot to do with trace elements in melts and how they are very abundant in low melt fractions.
Rob
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 16, 2005 - 10:29am PT
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bobh noted quartz monzogranite isn't on the ternary diagram so I assumed I had typed it wrong. I have not. So now maybe quckhikers statement regarding "not classifiable" has validity. Dibblee and others did map it as monzogranite. That must be the old nomenclature. quicktimer (or minerals or anyone) can you tell me how/where to look up classification of the monzogranite - how does it relate to the IUGS diagram?
Rob - looking forward to the explaination.
OK QH can I at least get out of you where you did your work? Was it UW?
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Lambone
Ice climber
Ashland, Or
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Mar 16, 2005 - 11:04am PT
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you won't hear from QH for a few days because he is out in the field...but yes, UW. he recently earned his phd....but he's too modest to tell anyone that. he'd probly rather take personal questions of line, send him an email.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 16, 2005 - 11:36am PT
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Lambone - thanks. I figured as much. I didn't mean to get personal with the questions and will email him directly. I do understand how asking about timing (length, etc.) might be a bit personal. I guess I really just wanted to know the level of eduction (I had guessed phd), where the degree was granted and the specialty. Seems right within context of this thread.
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Lambone
Ice climber
Ashland, Or
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Mar 16, 2005 - 11:38am PT
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yeah...all I know is he did most of his Thesis feild work in Toulomne! I can't pronounce or even come close to spelling his specialty, but I know it's more on the structural side.
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Haggis
Trad climber
Scotland
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Mar 17, 2005 - 10:36am PT
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i hope this makes sence
ok lets consider what happens when you just start to melt the mantle at high pressure.
starting with a undersaturated Basalt what happens if we remove SiO2?
Note I know and so should you that you cannot remove silica from the melt I will explain at the end just run with it
Your K2O + NaO : SiO2 ration increases
Basalt consists of Olivine Augite and Plag
Therefore the Plag starts to break down by losing the SiO2
This forms CaTs or CaTiTs as so CaAl2Si2O8 – SiO2 => CaAl2SiO6
It also forms Nepheline as so NaAlSi3O8 – 2SiO2 => NaAlSiO4
This produces Ol + Neph + TiAugite (Ti looks like Si so they replace each other very well)
Note there is no longer any Plag
Ok now hike the pressure up a bit more thus further reducing the SiO2 concentration
Your K2O + NaO : SiO2 ration increases again
Diopside now starts to loose SiO2
4CaMgSi2O6 – 3SiO2 => 2Ca2MgSi2O6 + MgSiO4
Diopside – silica reacts to form Melilite + Fosterite
thus we now have 2Ol + Mel + Neph
HOWEVER
this is where it gets really weird
you are now such low melt fractions that all of the incompatibles (Li Rb La’s Ac’s and volatiles like H2O and CO2) are concentrating in the melt and silica is not melting thus you start forming a lot of strange minerals
in the presence of lots of CO2 the system must stabiles and obey the laws of thermodynamics and le chatalites (SP?) principle
thus Fosterite + Diopside + carbon Dioxide => Dolomite + Ensatite
2Mg2SiO4 + CaMgSi2O6 + CO2 => CaMg(CO3)2 + 4MgSiO3
if you count the silica’s then they haven’t changed however you have not formed Mel which is a very unstable structure it has been replaced by dolomite also note that we are not taking about pheocryst phases and this stuff very rarly makes it to the surface becasue the mantel melts by decompression
ok now the hard bit
you cannot remove silica from the melt as its liquidus is higher than the liquiduses of the minerals above, thus you must melt to such a small degree that you start from Dolomite + Ensatite + Faylite + Neph and as you increase the melt you increase the silica and these react away to form undersat MORB
thus you start with what I have ended with and work backwards in real life its just better shown when you start with minerals that most people know and take for granted
in essence all really undersaturated Basalt starts life as this but when the melt increases it forms more stable species.
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Haggis
Trad climber
Scotland
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Mar 17, 2005 - 10:50am PT
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this may make things easier to grasp here
Rob
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Jaybro
Social climber
The West
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Mar 17, 2005 - 11:08am PT
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I concur that the NA intrusion is a mind blower. but, if it's not random what is it? Or, is the point just to ask the question?
The spider web intrusion that tells you where the east ledge rappells are is a mindblower, though it doesn't look like anything more than a vague spider web pattern. IMHO,It doesn't have to resemble anything else to be remarkable.
Vedauwoo, with it's hoodoos, Mushroom boulders and plethora of balanced rocks is one of the most mind blowingly surreal landscapes anywhere.
In both (and many more) cases it's not "random," Cause and affect and a nitpickingly tedious series of events lead to what's there.
I just don't buy the assertion of design, that the rejection of the 'Random' ( for lack of a better word) model seems to imply. Doesn't that lead to an unknowable infinite regression?
Gtanted, on some level it's all unkowable, anyway.
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Jaybro
Social climber
The West
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Mar 17, 2005 - 12:01pm PT
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Maybe a rough draft?
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 17, 2005 - 01:53pm PT
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but the layer that looks like NA wasn't exposed until after the NA took shape.
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quickhiker
Trad climber
Seattle
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Mar 18, 2005 - 12:46am PT
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Haggis, I think you have a lot of neat ideas, and certainly have done a bit of chemistry to look at forumulae and not run screaming, and to have heard of Le Chatlier's principle. You opened a bit of a pandora's box, with a lot of neat, neat stuff in it. You may wish to look at a program called MELTS put together by Mark Ghiorso and Richard Sack (yes, that is his name). This program looks at equilibrium mineral assemblages in association with a melt. It doesn't deal with high silica melts (say dacite and above) very well, or metamorphic at all, but is exceptional at melting in the mantle. A few rules of thumb: increasing pressure will reduce melt fraction by stabilizing more compact crystal forms (volume/entropy tradeoff); dolomite is, sensu stricto, a sedimentary rock, the metamorphic changes you are referring to are part of a prgression towards pyroxenites, a very active field of research for those interested in the mantle; Le Chatliers principle is fundamentally based on energy arguments (G=H-TS is the simplest relation), and CO2 can happily exist separately in the mantle as a supercritical fluid (this is indirectly the source of DeBeers wealth as diamonds when you spawn kimberlites). A neat brother of Le Chatlier's principle that is relevant here is the somewhat obscure Darken relation.
The 120 degree geometric relationship is an energy minimization in a slightly different sense- more of a stress orientation thing. The intersections are at 120, though they can form columns of many shapes (pentagons, etc) depending on how the intersections are aligned. Individual fractures will curve into the stress field around other fractures. Mudcracks show the same thing, and the physics are actually pretty similar. You can actually figure out which cracks propagated first. The first ones will have nice 120 intersections. If you see a crack intersecting a line at 90, it happened later. Most of the time the crack will noticably curve in to be perpendicular to the straight edge. Repeat ad nausem and you can figure out the order of cracking. Not a great use of time, but something to do while you are waiting for people to catch up on a trail.
Since Lambone blew my cover... I did my PhD at UW which included field work in Tuolumne looking at mixing relationships between the various units and a second project at Chaos Crags in Lassen Volcanic National Park. Before that I did my BS and MS at UCSC doing structure/tectonics research. Fun stuff, but academia didn't leave nearly enough time for all the other things in life.
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Ed Hartouni
Trad climber
Livermore, CA
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Mar 18, 2005 - 02:10am PT
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Truely awesome to watch the Rock Jocks go at it here... makes me wish my brain were wired differently so I could actually do that science, geology.
As for randomness vs. purpose, our conscious existence results in a propensity for interperting that randomness as an intentional act or as some more purposeful event. It is one of the motives that drive scientific investigation as well as spiritual investigation. These are two path ways to enlightenment, I can't judge which is the more valid, but I do know which I have choosen.
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quickhiker
Trad climber
Seattle
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Mar 18, 2005 - 02:25am PT
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Yes. Who says those paths are separate? Chaos theory, non linear dynamics and related fields show that relatively moderate actions have impacts and can shift systems between stable states, into oscillations or into unstable trajectories (be it weather or populations or the chemistry of our bodies). In many ways, this is a back door to the holistic view of interconnectedness. Why not skirt the middle between the two? The divide between creative and emotive life and science is artificial, to me at least.
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Haggis
Trad climber
Scotland
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Mar 18, 2005 - 09:46am PT
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i am fortunate to have a really good lecturer and a basic understanding of chemistry
if you understand the diagram I posted above then you can do 90% of igneous geology with a little common sense.
Its only when we start raving on about carbonatites, kimberlites and other oddities that things start breaking at the edges.
I found out about a volcano called Ol Doingo Lengia in Tanzania today that erupts sodium carbonate how cool is that!! The lava flows are about 5cm think and are as runny as hot mud. They also dissolve in H2O so they don’t exist in the record.
Very strange
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 18, 2005 - 09:48am PT
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A quick google search on your name and a lucky guess on the school and I had many web pages and all I needed to know. Though since you disclosed UCSC did you know a Rick Koehler while you were there?
Le Chatelier's priciple: "A system in equilibrium responds to stress in a manner that tends to relieve that stress".
G = H-TS
Gibbs = Enthalpy - Temp * Entropy
Speaking of screaming. Geochem flashbacks with Don Garlick. Gibbs always made me start to lose it. Of course, that equation is too simple (for Don). He wrote "if you memorize anything memorize this equation!"
dG =< VdP - SdT
yikes! (and that's not a equal to or greater than - dunno how ot properly get that symbol in but I'm sure the thermo folks know what it's suppose to be)
QH - maybe you missed this from above (where I wrote):
bobh noted quartz monzogranite isn't on the ternary diagram so I assumed I had typed it wrong. I have not. So now maybe quckhikers statement regarding "not classifiable" has validity. Dibblee and others did map it as monzogranite. That must be the old nomenclature. quicktimer (or minerals or anyone) can you tell me how/where to look up classification of the monzogranite - how does it relate to the IUGS diagram?
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bobh
climber
Bishop, California
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Mar 18, 2005 - 11:33am PT
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Nature, I've got an igneous petrology book from the 1940's somewhere, but I couldn't find it last night. I'll let you know if I find it.
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Minerals
Social climber
The Deli
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Mar 18, 2005 - 12:42pm PT
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I have been kinda out of touch with geology recently. All I can think about is dirt bikes. Racing every weekend, pimping out my new ride, and rebuilding the 500. But, I’ve got to start working on a poster for a GSA meeting at the end of April.
How’s it going, Glen? Good to hear that you have finished your PhD. Nice work! Will you be at the GSA meeting in San Jose? I’m working on ladder dikes hosted in metavolcanics by Steelhead Lake. Have you seen these? Here’s a picture of one of the ladder dikes by the Tuolumne River, as described by Reid (1993).
Anyone have any comments or suggestions for me? Have you seen the ‘Vortex’ on the SE flank of DAFF Dome? It’s a brain twister for sure!
Ladder Dike in Cathedral Peak granodiorite:
Glen, have you seen Walt’s dissertation or the paper in Geology that he wrote with Glazner and Coleman? Neat stuff.
Nature, I'm not sure about old nomenclature...
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Lambone
Ice climber
Ashland, Or
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Mar 18, 2005 - 01:03pm PT
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"Since Lambone blew my cover..."
sorry bro, but you should be prowd of your work at UW.
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Minerals
Social climber
The Deli
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Mar 18, 2005 - 02:16pm PT
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Proud. Prowd is the name of my route on LB.
Yeah, Glen, upper Tenaya Canyon. I remember some pics that you had on your site a while back. One section of the dikes has some pretty crazy mixing and mingling, eh? Hibbard thought someone could do a thesis on that one square meter of outcrop. Wild.
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quickhiker
Trad climber
Seattle
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Mar 18, 2005 - 06:41pm PT
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Part of the reason for the old/new nomenclature was to standardize everything into one format. Previously, there were multiple names for the same rock because different people were using different nomenclature. So, with regard to JTree, I would say the most direct route would be to look for the rock descriptions that accompany the map and see if they give modal information, or use it as an excuse for a climbing trip and make the observation yourself.
Brian, good to hear you are still looking at rocks. Did you ever end up taking Glazner up Cathedral? I've poked around a bit in the ladder dikes and they are certainly interesting. I think they are part of a continuum of features that show up in granites including the classic schlieren and some pretty dramatic layering out in the eastern part of the TIS. I think I sent you some of the pics a while back. Anyways, we had an MS student take a look at them and start trying to tease some info out of them. I think there is still a link to a pretty comprehensive image gallery from James Loetterle's page c/o George Bergantz's page. It is certainly worth a 2 minute glance just to know they are there, if anything.
Had I taken a faculty position, one of my plans was to put a few ms or senior thesis students on the Tenaya outcrops. It is a very rich site with a lot of neat things with ramifications for magma mixing processes. But, maybe I'll just do it on my own some summer for fun. There is a really cool kayaking video of some guys running a line that goes over/through the huge potholes in early spring. Crazy!
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 20, 2005 - 12:59pm PT
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I finally did the right Google search and have answered my own question
stolen from:
http://tesla.jcu.edu.au/Schools/Earth/EA1001/Igneous/4.%20IgClassification.html
"Where the proportions of alkali feldspar and plagioclase are relatively even (neither one being more than twice the amount of the other) it is a monzogranite."
I'm not going to change my post above to correct myself. But if all the pieces I'm putting together add up correctly then JTree rock that we climb on is actually granite and not monzonite or quartz monzonite. I'd like to know who started calling it monzonite.
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WBraun
climber
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Mar 20, 2005 - 01:46pm PT
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JTree rock.....is actually granite and not monzonite or quartz monzonite.
Whatever it is .... It sure is rough stuff that wears out all your gear incredibly fast.
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Jaybro
Social climber
The West
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Mar 20, 2005 - 05:00pm PT
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"JTree rock.....is actually granite and not monzonite or quartz monzonite.
Whatever it is .... It sure is rough stuff that wears out all your gear incredibly fast. "
Josh granite is the roughest, rougher than Vedauwoo. Sandpaper vs smoothness bearing knobs (phenocrysts). And yet, they're both granite. There are major differences between the two in age and composition; Sherman granite (vedauwoo ( shoshone for earth born spirit, always loved that)) is older and has more k-spar (potassium feldspars)
Kinda like, lumping a disparate group together as climbers.
¿More binding similarities than differences? no matter how we factionate?
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Mar 21, 2005 - 01:35am PT
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D. D. Trent
Geology of the Joshua Tree National Monument
California Geology - April1984
"The light-colored, Cretaceous White Tank monzogranite predominates in the more accessible parts of the Monument. The rock was originally recognized as a monzonite by Miller (1938), later as a quartz monzonite by Rogers (1954, 1961) and Dibblee (1968), but is now named a monzogranite (Brand and Anderson, 1982; Powell, 1982) in accordance with the modified version of Streckeisen's classification (1973) of igneous rocks. It resembles the Queen Mountain monzogranite but differs by being finer-grained, and by containing very small amounts of biotite and/or muscovite but no hornblend (Brand, personal communication). Areas underlain by the White Tank monzogranite included Indian Cove, the Wonderland of Rocks, Jumbo Rocks, White Tank, and the Lost Horse Valley (Photo 3)."
I looked through my Vogel guide and he doesn't mention quartz monzonite.
igpet folks - am I missing something? (yeah yeah i've lost it). All these years of calling it a monzonite and it's a true-blue granite? I feel like a loser. I don't need a climbing trip to "observe" fity:fity alk-spar:k-spar and >20% qtz.
Duh'g
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Minerals
Social climber
The Deli
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Apr 10, 2005 - 09:12pm PT
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Man, I thought this thread disappeared into geologic time… It’s getting pretty long so maybe we should start another geo thread.
Nature, are you still there? Glen? Anyone……..?
There it is… Streckeisen.
Nature, you haven’t lost it. So what if you used to call it a monzonite. NBD. I don’t really know Josh (only been there once) but if we look at any of the granitic rock around Yosemite, specific units vary in composition. For example, if you look at modes in Bateman’s ’92 paper (*) you will see that some Cathedral Peak granodiorite is actually granite and some El Capitan granite is actually granodiorite or even tonalite. As for the rock at Josh, it’s a granitoid. I wouldn’t worry about it. You are doing fine.
* Bateman, P. C., 1992, Plutonism in the central part of the Sierra Nevada batholith, California: U. S. Geological Survey Professional Paper 1483, 185 p.
Where are areas where you climb on the stuff? (gneiss)
The rock at my local crag is not a true, banded gneiss but it is super compact and has a gneissic texture with discrete cm-scale shear bands. Maybe it’s a proto-gneiss, or something like that. Anyways, it was originally a granodiorite or tonalite (protolith) but has since been deformed. There are also felsic dikes in the host rock (folded phyllites and slates) that have been boudinaged. I think there is a localized shear zone in the area but need to do more fieldwork… Mapping by dirt bike is so efficient; it’s almost cheating!
Schist? Yeah, what happened to our blueschist?
As for the earlier question about the map-pattern of ages of Sierra plutons, an older reference would be (in addition to the answers given by others above):
Stern, T. W., Bateman, P. C., Morgan, B. A., Newell, M. F., and Peck, D. L., 1981, Isotopic U-Pb ages of zircon from the granitoids of the central Sierra Nevada, California: U.S. Geological Survey Professional Paper 1185, 17 p.
The Bateman reference above also explains this, and a lot more.
And the NA diorite??? Give the San Andreas another 10 million years or so and an ice age to depress Hudson Bay and the dike on El Cap might look similar to the real thing. How about Europe? You know, the diorite that surrounds the Grey Circle? And how about all of the wisps and dikes of tonalite that are cut by the NA diorite? For more info on the NA diorite and other mafic intrusions on El Cap see:
Ratajeski, K., and Glazner, A. F., 1999, Mesozoic convergent margin of central California: Geological Society of America Special Publication 119, p. 118 – 135.
Ratajeski, K., Glazner, A. F., and Miller, B. V., 2001, Geology and geochemistry of mafic to felsic plutonic rocks in the Cretaceous intrusive suite of Yosemite Valley, California: Geological Society of America Bulletin, v. 113, p. 1486 – 1582.
Reid, J. B., Evans, O. C., and Fates, D. G., 1983, Magma mixing in granitic rocks of the central Sierra Nevada, California: Earth and Planetary Science Letters, v. 66, p. 243 – 261.
Did you ever end up taking Glazner up Cathedral?
Glen, yeah and we had a lot of fun. I was able to show him the epidote and miarolitic cavities towards the top. We did Northwest Books the following year.
I have seen James’ web page before as well as the layering on the east side of the TIS and most of the outcrops that are listed on his page. Thanks for reminding me though. He did a great job with the site. It’s good to look at that stuff again. I would like to post one of his pictures here because it is beautiful and shows great cross-cutting relationships, but I should ask him first. Some of the craziest schlieren that I have seen is in this area and in some of the outcrops to the east and to the north. Super-cool! Hey, if you (or anyone else) ever want to check out the Tenaya dikes again and do some mapping, let me know.
Here is a link to my ladder dike abstract:
http://gsa.confex.com/gsa/2005CD/finalprogram/abstract_85770.htm
Here is some work that I have been helping my profs with:
http://gsa.confex.com/gsa/2004AM/finalprogram/abstract_80584.htm
Here is a link to Roberto Weinberg’s site and magmatic structures in plutons in Brazil. Check it out; this stuff is way cool! Follow the links to other sections of his site.
http://www.earth.monash.edu.au/%7Eweinberg/Borborema_granites3.htm
I don't come at it from a sample collection angle.
Dingus, you are very lucky. Trust me.
If I had to move all of my rocks from storage, I would have to rent a moving truck. It’s a bad addiction.
I have enjoyed reading your posts and it has prompted me to pull out my copy of Moore’s book. Check out the wonderful pictures of schlieren (p. 223), comb-layering (p. 228), and orbicular granite (p. 230). Nice book.
Ok, what’s next? A new thread?
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Jaybro
Social climber
The West
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Apr 11, 2005 - 02:01am PT
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Thanks you guys, for keeping this going.
Rock types are cool, though a lot in Ca. could be lumped into "Granitic."
Farther east there is a place I used to climb a lot that has been described as a volcanic plug and currently the prefered theory is that it's a Lacolith. 'basaltic'- er, features ( don't want to completely give it away), comes up a lot in describing this place.
Word is, now, (and has been for some time) that it's made of a Phonolytic porphory. The idea being that the sound that the rocks make when dropped on each other are diagnostic of the type. I've experimented informaly with this and it sounds true to my untrained ear.
Trivia-What place is this? (FPS-recuse)
Anyone out there ever hear of more than one climbing area made of Phonolytic Rock? It would be fun to find another one.
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TGT
Social climber
So Cal
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Apr 11, 2005 - 11:03am PT
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There's a long "ladder dike" on Lost Mule Wall, J Tree. It's to the right of the upper part of the Bartlet route, 40 Acres and a Mule. At least 60 ft long, 1 ft wide and may go all the way from top to bottom, (or the stuff lower down fell off the upper part, didn't really check it out that closely). The only one I've seen at Josh I think. BTW this is one of the worst choss piles at J tree, but, "you can't climb quality all the time".
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KarlP
Social climber
Queensland, NorCal, Iceland
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Apr 12, 2005 - 03:51pm PT
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Jaybro: Devils Tower?
Another place where you can climb on gneiss is Gallatin Canyon, Montana.
And for my own questions....
What is aplite? It seems to only ever be in intrusions/dikes (and what's the difference anyway? Do dykes/sills only flow into fractures, and intrusions melt their way in?
And, can anyone tell me more about what this is...
http://www.tweak.net.au/pics2/2004/October/bigbendday2/pichtml/web_crw_7484_jfr.html
The black band is about 1cm thick. This was in big bend national park. This was in the creek bed walls, just above Ernst Tinaja, if that helps identify the parent rock, (I know big bend has LOTS of different rocks floating around)
Cheers,
Karl P
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bobh
climber
Bishop, California
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Apr 12, 2005 - 04:44pm PT
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Minerals wrote:
"Here is some work that I have been helping my profs with: "
Are you working on a dissertation with Schweikert? I took structural from him a long while back as an undergrad.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Apr 12, 2005 - 05:08pm PT
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Minerals - I'm around. Just got back from two days playing in Red Rocks. WOW! That place is amazing. Starting another thread might be good. I planned on keeping the Geology 419 theme going. I'll give some thought to the next topic. I posed all those questions (in the first thread) to see who wanted to bite on the discussion.
Aplite - A fine-grained, light-colored granitic rock consisting primarily of orthoclase and quartz. In granitics dikes and sills are filled fractures caused by cooling of the intrusive unit. Still molten material fills the fractures and typically forms Aplite. Aplite is fine grained because it cooled quickly. If the material is allowed to cool slowly very course grains can form (the size of the entire dike) and would be termed a pegmatite dike. You can tell the difference because Aplite dikes won't exhibit cleavage planes while the pegmatite will.
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Jaybro
Social climber
The West
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Apr 12, 2005 - 11:15pm PT
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Karl P you nailed it, know of any more similar?
The photo; a z-fold into a carnivorous water buffalo? talismanic.
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Minerals
Social climber
The Deli
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Apr 12, 2005 - 11:22pm PT
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"Rock types are cool, though a lot in Ca. could be lumped into "Granitic.""
No way! I would love to see a VERY detailed plutonic map created before I die that encompasses everything from the Mexico border to the Canada border, through the southern and northern Sierra, northern Nevada, and the Idaho Batholith. Now that would be freeeeeekin’ cool. Better get to work…
Yes, isn’t Devil’s Tower phonolite porphyry? (thanks Google…) (edit... I guess so...)
"I took structural from him a long while back as an undergrad."
No way! I met with him earlier today. He is a super nice guy and pays for my lunch way too often. He is also an incredible wealth of knowledge on all sorts of stuff. Great guy. Did you go to UNR? Rich was my advisor when I was taking classes there.
No, I’m not really working on a thesis but I always seem to be working on several different projects that could each be a thesis. I have been out of school for two years now (still don’t have a degree (unless granite is a degree…)). The fieldwork with him is more for fun and self-education but I get paid too. I need to go back to school.
"What is aplite?"
Nature’s answer pretty much explains it.
Aplite, alaskite, leucogranite, leucocratic granitoid… Pretty much jargon for white granite – it’s got a sugary texture. In addition to cooling rates, grain size (aplitic vs. pegmatitic) can also be controlled by diffusion rates and nucleation rates in the melt.
"It seems to only ever be in intrusions/dikes…"
Yes, mostly in dikes and pods/masses/intrusions of varying size. Quartz and orthoclase (potassium feldspar) are some of the last minerals to crystallize from a melt (see Bowen’s Reaction Series (old stuff)). Aplite dikes, etc. form during the last stages of pluton solidification; dikes may form as fluid pressure in the remaining melt takes advantage of linear cooling fractures, seismic events, etc. and forces its way through the surrounding rock mass as planar sheets; space (volume) is made by dilation of the fracture surfaces as the fracture propagates in length. Brittle fracturing can occur before a granitic magma has completely crystallized; fracturing may begin to be possible during cooling as the crystal/melt ratio reaches roughly 70% crystals or more.
"…(and what's the difference anyway? Do dykes/sills only flow into fractures, and intrusions melt their way in?"
That is a good question and something that could take a long time to answer…(if we only knew...). Do intrusions melt their way in? By what mechanism is space created to allow the emplacement of granitic magma into the crust?
Here’s an aplite/pegmatite question:
Are the aplite/pegmatite dikes on El Cap related to the Intrusive Suite of Yosemite Valley (103-104 Ma) and part of the whole El Cap granite – Taft granite system or are they actually dikes from the Tuolumne Intrusive Suite (~85-93 Ma), maybe related to Half Dome granodiorite, that have traveled quite a ways beyond the limits of the TIS? I have always wondered…
Look at the cover of your ST Walls book, 1st ed. – 5th pitch of the Trip. See all of the aplite/pegmatite dikes? There are at least two episodes of felsic diking present. The older, sub-vertical dikes are cut and offset by the horizontal dikes - simple geologic cross-cutting relations. If the sub-vertical dikes were not offset, you would have to look closely at the rock itself, which would tell you their age relation (they sometimes talk, you know…).
Right on, Nature. Sounds like a plan. Question c) looks like something that I might have fun with. But since you just got back from RR, maybe a little soft rock geo and some tectonics are in order…? Edumacate me (with a new thread…)!
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Minerals
Social climber
The Deli
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Apr 12, 2005 - 11:33pm PT
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Oh yeah... Karl's photo. Do we get any hints? Is it igneous or is it some sort of limestone/marble?
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KarlP
Social climber
Queensland, NorCal, Iceland
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Apr 13, 2005 - 12:20pm PT
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It was "just above" the limestone layer in a creekbed. The rock above the limestone is ???? orange, generic rock for the big bend area. The bottom picture at http://www.nps.gov/bibe/virtualvisit/ernsttinaja.htm shows the area I was in. It appears that the orange rock above is also limestone? *shrugs* I really don't know. It was just this really neat pod, wich wayyyyy more folding than anything around it.
Cheers,
Karl P
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rja
Trad climber
somewhere between LA and Baja
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Nov 23, 2005 - 11:42pm PT
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message deleted
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Apr 6, 2007 - 11:47pm PT
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shameless bump
Medium Soooze Edit: OMFG I make me laugh... I just read what I wrote two years ago and almost sprayed my screen with green label "I'm sorry Donny, you'll have to enroll in "Busting Donny's moms' chop's 101" to get the graph to differentiate crack-cocaine and crystal meth."
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Phil_B
Social climber
Hercules, CA
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Nature, thanks for bumping this thread. It's pretty cool and I just spent the last hour or so going through all the posts.
Haven't talked rocks in quite a long time. I totally sucked at it in school. Fun to do when out boating with fellow geo dudes (and dudettes) though.
Anyone else do the roadside geology books? They're pretty low level for you guys that really know your stuff, but they're pretty fun for me.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Apr 7, 2007 - 01:19am PT
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The roadside books are really pretty good.
Wow, an hour - that's really cool.
and I still read my quote from two years ago and laugh.
bustin' Donny's Moms' chops! - Killin me!
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L
climber
The Rebel L Gang
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I read that too, Nature. Cracked me up.
What amused me was that you and Donny have the same wonderful relationship today as you did 2 years ago. You appear to relate to each other in the exact same way, same words even.
Rather funny to see how the more things change, the more they remain the same.
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Klimmer
Mountain climber
San Diego
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Hey Geo-gurus,
Just got back from Bishop for Spring Break with the family. Enjoying the thread. Read it from end to end. Good stuff.
HS science teacher here teaching Physics and now, finally, San Diego Unified School District has brought Earth Science back, so a collegue and I are teaching Earth Science at our HS as well. Having to dust off a lot of my college texts. This is good stuff. I really enjoy these discussions. You all are leading me to great resources and "I be learning" a great deal from the discussion. Thanks.
I'll have to come up with some good questions, and try to contribute to the mineral discussions as well.
My personal collecting weaknesses are Fluorescent Minerals (great cross-over with Physics and Mineralogy - and the color is just intense, a major "wow" effect on people) and Meteorites. There is something very special about holding a rare meteorite in hand with bizarre mineralogy (and sometimes with unique minerals and assemblages not found anywhere on Earth) and having a formation age dating to the beginning of our Solar System 4.6 + Billion years, and sometimes even older (Nebular).
Love this stuff.
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Donny... the OHHH!- Riginal
Sport climber
Straight outta Compton!
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Strange coincidence too....this from two years ago...
"I'm sorry Donny, you'll have to enroll in "Busting Donny's moms' chop's 101" to get the graph to differentiate crack-cocaine and crystal meth." from Nature
Then this from yesterday's "Rockhounds of the world unite" thread.
"(btw, can't see any pics except Donny's mom's stash... otherwise I would comment cus I love rocks)." from Weschrist
You people need to leave my crack-head mother out of these bashings...I'm dead serious.
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nature
climber
Flagstaff, AZ
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Topic Author's Reply - Apr 7, 2007 - 01:56pm PT
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yeah wes, those circles make the discussion of topics like rap bolting vs ground-up Lite&trade.
in regards to changing from a subduction zone to a transitional strick-slip boundary. If I'm reading that right, which I think I am, from everything I remember that is the accepted theory: The spreading center was subducted - well, the plate east of the center, and the boundary became what we now call the San Andreas (not sure what the historic subduction zone boundary was called). The theory explains a whole bunch of things - like why we have extension (local and regional) along a compressional boundary.
I tried to follow your isotope clock discussion but I never really wrapped my brain around that stuff back in the day so i'll have to re-read it just to understand it (and not comment as I really won't know what I'm talking about there).
surface process and landscape evolution == the darkside?!?!?!? WHAT?!?!?! Say it ain't so! even darker, then, I suppose would be soils geomorphology. Darth is my dad.
I think you should buy us a beer anyway. And then we can buy you a beer and so on and so on. All the while discussing isotopes, slab windows, plate rafting, or any geomorphic topic that comes to mind. We'll just need help picking up the bottles in the morning.
Donny: I'm sorry about the comments regarding your mom. Rehab is an option though...
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Phil_B
Social climber
Hercules, CA
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Did I hear something about subduction under North America? My tectonics professor at UCSB, Tanya Atwater, wrote the paper that is always referenced when talking about that:
Implications of plate tectonics for the Cenozoic tectonic evolution of western North America. Bull. Geol. Soc. Amer., v. 81, p. 3513-3536.
The cool thing is that she's also put out some animated gifs and Quicktime movies that show it very well.
http://www.seismo.unr.edu/ftp/pub/louie/class/333/atwater/
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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DMT: just read your post ^^^ more carefully about discovering granitic rocks where you wouldn't expect them. Astute observation on your part. When I saw this earlier today, I knew Stony Creek Formation rang a bell. Turns out a friend of mine at UC Davis, Paul Bertucci, back in the late 1970s, did an MS Thesis on...Petrology and Provenance of the Stony Creek Formation, Northern Sacramento Valley, CA
http://archives.datapages.com/data/pac_sepm/048/048001/pdfs/1.htm
Those granitic rocks you found in that conglomerate may have been derived from as far north as the Klamath Mountains and originally deposited as the initial pulse of Great Valley Sequence deposition in a submarine environment by a turbidity current. Although there's not a lot of granitic material described in the Stony Creek Fm according to these papers.
Some more info here...
http://www.ucmp.berkeley.edu/science/profiles/erwin_0609geology.php
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Cragar
climber
MSLA - MT
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Thanks nature!! Love this stuff! Another fun thread to catch up on..
Do you work for the USGS in Flag? When I lived there I did a couple rides in Sedona with 2 guys from the USGS, younger guy on an SS-Surly and I can't remember the other but they are friends of Gullo...
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Surpless, K.D., Graham, S.A., Covault, J.A., & Wooden, J.L. (2006). Does the Great Valley Group Contain Jurassic Strata? Reevaluation of the Age and Early Evolution of a Classic Forearc Basin. Geology, 34(1), 21-24. doi: 10.1130/G21940.1
The Great Valley Group has been linked to the Klamath Mountains from its earliest depositional history by south-directed paleocurrent indicators (Ingersoll, 1983), Klamath-derived chert-rich conglomerate (Bertucci, 1983), and distinctive sandstone compositions (Ingersoll, 1983; Short and Ingersoll, 1990)
Also, this Ingersoll paper...
Ingersoll, R.V., 1983, Petrofacies and provenance of late Mesozoic forearc basin, northern and central
California: American Association of Petroleum Geologists Bulletin, v. 67, p. 1125–1142.
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