Geology Quiz

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kpinwalla2

Social climber
WA
Jan 1, 2010 - 05:50pm PT
It's a boudin!
cintune

climber
the Moon and Antarctica
Jan 1, 2010 - 11:54pm PT
Maybe it started out as chert and then got baked. If that stuff is even schist; could be just some weird folded mud beds or such.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Jan 2, 2010 - 12:56am PT
At first I thought it looked like Franciscan Chert, but on that side of the San Andreas Fault, your in the Salinian Block not Franciscan.

The photo you posted from the Pt Reyes area looks like younger Neogene shallow marine rocks, likely Purisima or Monterey Fm equivalent.

Looks like some type of nodule, perhaps a phosphate? or dolomite nodule in bedded Monterey Chert.
dipper

climber
Topic Author's Reply - Jan 2, 2010 - 01:27am PT
I used to date a woman that said that about my turbidites....


Sorry, the chocolate, red wine, white wine, mussels, crab, halibut, smoked trout and all the other yummy stuff I just ate are mixing.

Strange brew indeed.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Jan 2, 2010 - 01:36am PT
looks like some kind of biogenic sediment...my guess is a dolomite concretion in bedded chert in the Monterey Fm

I agree BASE104...too large for a nodule...more like a concretion

e.g. check out the photo on this website...
http://www.cnsm.csulb.edu/departments/geology/research/miocenemontereyformation.shtml
Minerals

Social climber
The Deli
Jan 2, 2010 - 01:59pm PT
Tradster, did you see the Lee Vining Canyon stuff in the Yosemite thread?


OK, how about another quiz, for armchairs only (for now). This one is too easy for you geo guys. Not in Yosemite…

What’s going on here?



tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Jan 2, 2010 - 02:58pm PT
Minerals: I just checked the Yosemite Documentary thread and posted on it. I'm thinking about this photo and will post up my '2 cents' later.
Minerals

Social climber
The Deli
Jan 2, 2010 - 03:32pm PT
Right on. That thread disappeared for a couple of days and I wasn’t sure if you saw what I posted, in response to your question.
Jaybro

Social climber
Wolf City, Wyoming
Jan 2, 2010 - 06:39pm PT
You hard rock guys crack me up....
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Jan 2, 2010 - 08:09pm PT
That's an interesting rock. It's difficult to see the matrix or the sedimentary texture. The rock is obviously stratified and bi-modal, so I'm thinking volcanic or sedimentary origin. The individual layers look like they are only a few centimeters thick. The large clasts look granitic but not sure...if granitic then it's probably sedimentary with granitic provenance. The clasts are not sharp and angular so I wouldn't call it a breccia...they're somewhat rounded so they've undergone some transport. I don't see any obvious upward fining or coarsening in the layering but it looks matrix supported and it's interesting how the finer grained layering is deformed around the large clasts, perhaps during burial or metamorphism. Looks like a metamorphosed debris flow or conglomerate, perhaps a distal alluvial or submarine fan. On the other hand it could be predominately volaniclastic. In which case it could be a pyroclastic rock that has undergone some metamorophism...so a metavolcanic rock.

That's my 2 cents.

Jaybro

Social climber
Wolf City, Wyoming
Jan 2, 2010 - 08:54pm PT
Okay, this one is a giveaway!

cintune

climber
the Moon and Antarctica
Jan 2, 2010 - 09:11pm PT
Whoa. The Elder Sign.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Jan 2, 2010 - 09:32pm PT
What do you make of the joint pattern in this Aplite dike near the summit of Mt Whitney?
dipper

climber
Topic Author's Reply - Jan 3, 2010 - 12:03am PT
Thanks all for the tips on the Point Reyes coastal meta-ice cream.

Nice rock pics.

Here is another nice one I spied in the Kern River headwaters area a few years back.

It was a little too heavy so I left it in place. Need to go back and visit it if I can.

Jaybro

Social climber
Wolf City, Wyoming
Jan 3, 2010 - 12:38am PT
Whitney was a Cubist?
Minerals

Social climber
The Deli
Jan 3, 2010 - 12:47am PT
Oooooh… Back to granite!

Tradster, that is a way cool photo! Wild pattern! Aplite dikes are commonly fractured when the host granitic rock is not – this is due to the difference in competence between the coarse-grained granite(?) and the fine-grained aplite – the materials behave differently. As far as the two sets of fractures at right angles to each other, I’m not sure why exactly this pattern forms. I’d like to take a class on fracture mechanics. Cleo and others can probably explain this stuff a lot better than I can.

I did see your “pretty” outcrop before it disappeared… reminded me of “Snoopy” on the way to the Black Rock.


Nice mirror image, Dipper! Looks like a chunk of well-foliated granodiorite(?) that hosts a stretched mafic enclave that hybridized with the granitic host by “ingestion” of small feldspar crystals from the host (white dots - xenocrysts). Foliation probably formed during magmatic flow, as the enclave was stretched. Both rock types are cut by younger aplite/pegmatite dikes (white bands) that may offset the enclave slightly (can’t tell). Or something like that…
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Jan 3, 2010 - 03:17am PT
I pulled the pretty face on the granite boulder in the Alabama Hills...much to silly for this serious thread. Feast your eyes on these lovely glacier polished feldspar phenocrysts in Cathedral Peak Granodiorite. If I recall correctly, this photo was taken along the cascade behind Pywiack.

Cathedral Peak Granodiorite, Sierra Nevada Batholith, California: A Big, Mushy, Magma System?
Burgess, S. D.; Miller, J. S.; Matzel, J. P.

The broad geochemical and isotopic data are consistent with bulk fractionation in the Cathedral Peak Granodiorite. However, the geochemical spatial variation (especially trace elements) and field evidence suggest that fractionation was highly disorganized and involved mixing and remobilization of crystal mush as it solidified, possibly triggered by new inputs of isotopically uniform magma (i.e., recharge from the magma source).


Minerals

Social climber
The Deli
Jan 3, 2010 - 01:51pm PT
Oh, man, Tradster… You are going to open a can of worms with that one!

Seth Burgess is/was a student at San Jose State – I met him briefly at a poster session at a GSA meeting in San Jose in 2005. I have spent a day or two in the field with Jonathan Miller, a professor from San Jose State.

An abstract, similar to what you found?

http://adsabs.harvard.edu//abs/2006AGUFM.V11A0551B


A Big, Mushy, Magma System? Ummmmmm...

Bulk fractionation at the final emplacement level is so 1979………

I don’t want to get into this in this thread… way too complicated and it should be reserved for a Tuolumne-specific geo thread… someday.


For now, those are some pretty orthoclase megacrysts!



More geo quizzes!!!
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Jan 3, 2010 - 01:59pm PT
Opening worm cans...isn't that what the Taco Stand is all about? Hey I understand..no problem. I'm trying to learn from you guys. I've spent a lot of time in Tuolumne climbing on the domes during the last 30 years but never delved too deeply into the geology. I've always been fascinated by the rocks that make up the roof pendants. I'll wait for your Tuolumne Intrusive series thread before posting anymore photos/abstracts like that. BTW, that was an AGU 2006 Fall mtg abstract.

I'm not a hard rocker...the only hard rock work experience I've had is a summer job with a mining company back in 1978 working on a scheelite-bearing Skarn deposit outside of Mina, NV (Gunmetal mine). It was mined for Tungsten during WWII for armor-piercing munitions. Mostly I described core and did some surface and subsurface mapping. Many cool contact metamorphic minerals, pyroxenes, epidote, etc...I had no idea what many of the minerals were. I would use a UV lamp on the cores & outcrops at night to estimate the scheelite content. One of the lessons I learned that summer was that working in a mine is very dangerous. I wish I had photos from that time period but I don't.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Jan 4, 2010 - 08:19pm PT
Fans of Geoporn, feast your eyes on this optical televiewer image of a borehole wall. The image is generated with a wireline digital camera. It is oriented in geographical coordinates and is essentially the borehole wall displayed as a 2D image (i.e., North is at both ends of the image).


For scale, the image is ~1 meter of the borehole
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