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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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