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BASE104
climber
An Oil Field
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Well, it has come a long way. Powerful computers are getting very cheap. A 3D seismic volume has an unreal amount of numbers in it.
The big cost is acquisition.
The grabens in Nevada have had petroleum geologists salivating for ages. There is this one tiny field in Railroad Valley that had one well that for a while was the best onshore oil well in the continental US. The geology is horribly complicated, and people have been drilling dry holes all around that thing for ages.
The really cool stuff comes from attributes (just something that you can yank out of the straight data).
That link above is to a whole division at OU that does nothing but attribute analysis and development. They can see incredible things.
You see all of those igneous joint patterns? Well, you can see them in the igneous basement below sedimentary basins, and they control a lot of the structural geology.
The coolest one is called coherence. It is too much to just steal a picture, so here is a link to a good paper. Just look at the pictures and read the captions. It is uber cool.
http://www.cseg.ca/events/luncheons/2009/10oct/20091014-chopra.cfm
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dipper
climber
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Topic Author's Reply - Jan 7, 2010 - 02:59am PT
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More oddities from the west base of the Inyo Mountains. Any ideas what caused this?
A
zwei (detail of above shot)
3
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BASE104
climber
An Oil Field
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Cool abstract, TT! I was wondering if the hard rock guys are doing more of this. It is cheap and can tell you tons. I would go so far to say that if you are doing surface geology without it, you are kind of in the stone age. One of my professors was way into paleo mag. He had this device that filled a whole room. Inside of it, the earth's magnetic field was canceled out. By now, I bet you can go to Wal-Mart and buy the same device that will fit on your desk..but i dunno.
The biology department put all kinds of migrating things inside it like salamanders and what not. So they could show that they were using the earth's magnetic field to migrate with. Then they would disect the snot out of them, run stuff through a mass spec and find magnetite of some sort in the brain.
And of course the usual stuff. During this time period, this location was at such and such latitude as continents drifted around.
You can do a lot with paleomag. You can bang on rocks and work their spatial and temporal data to death, but a simple plug of rock will tell you a lot.
Doing geology without geophysics is really limiting yourself. With seismic, you see things that have different densities..and therefore velocities. I would love to see what it would look like if it was shot in a totally igneous area.
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Fritz
Trad climber
Hagerman, ID
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tuolumne_tradster: Glad you enjoyed my Sawtooths story. Re your question:
what's the mineral with the metallic luster?
The spessartine in the photo shows two different colors: the light orange most of us associate with spessartine, and that darker color. I don't think it is camera-angle. The crystals were fairly small, maybe 8mm at the largest. Per this closeup photo: the two colors just seem to merge.
I took that photo on a 2006 trip into the west side of the Sawooths. I have never seen garnet in the east side of the range. Apparently some places have a lot of spessartine, but it was new to me.
Keep those "geology talk" posts coming guys!
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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sometimes referred to as a melange
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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coast range ophiolite??
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franky
climber
Davis, CA
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This is a coal strip mine in PA. They excavated an entire coal bed from an anticline, leaving the clay below the coal perfectly exposed. That big feature in the middle is essentially the same bedding plane throughout. One of the sweetest outcrops in the world no doubt.
By the way, I didn't see anyone mention that the first photo was probably a good example of boudinage.
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dipper
climber
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Topic Author's Reply - Jan 7, 2010 - 03:38pm PT
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DMT,
Those shards that look as if from a chocolate cake were way slick. Would have made for great screeing. Yet, they were so pretty and fragile, I mostly stayed off them.
Here are 3 more postcards from a rock-scape. These are from Center Basin, where the JMT used to go before Forester Pass was blasted into existence.
1
2
3
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Fritz
Trad climber
Hagerman, ID
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bump for this thread over the other crap on ST tonight.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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back to the Franciscan Complex...
Blue schist knocker at Goat Rock beach, near Jenner CA
more glaucophane-schist facies metagrewacke...this stuff was buried deep (10s of kiliometers) in a subduction zone before it made its way back up to the surface
Metagreywacke lenses in a sheared argillite matrix
Hidden cove north of Jenner where the above photo was taken
Highly sheared serpentine in a fault zone...like pinching a pumpkin seed between your fingers
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Minerals: awesome photos from Nevada...especially the pyroclastic rocks and the deformed sedimentary rocks.
BASE104: those horizontal slices from your 3D seismic volume show incredible channel detail
Fritz: thanks for the zoom on the garnets
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Spider Savage
Mountain climber
SoCal
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BASE, What do you know about oil exploration under the Columbia basalts? Anything? (Since you seem to be in that field.)
Anyone else?
I've always been fascinated with those. A thousand feet and more of basalt.
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BASE104
climber
An Oil Field
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I dunno about the basalts in Columbia that you are talking about, but I do know that there are some sills in Mexico that have been imaged.
The problem you get into is that the densities (gram/CC) generally relates to velocity of the waves, so if the thickness varies, it creates problems. The thing with seismic is that you tie it in with the actual rocks that are drilled through. You can pull an Acoustic Velocity log and then model velocities in the area much better.
This is kind of the same bag of worms that the subsalt play in the gulf of mexico had to deal with. It took a while to model it and figure out, but now the subsalt data is incredible, even while the salt thickness varies hugely above it, with a wildly different velocity.
There is a basin in eastern Oregon..Harney, I think. It is ripe but covered with volcanics. It is also in a really sensitive wetlands area, so nobody messes with it as far as I know.
There are actually quite a few igneous oil reservoirs around. I was at a talk several months ago when the seismic guru started throwing up all of these shots of igneous fields in the seismic data. One was an actual volcanic cone. If you are in a sedimentary basin that has a good source rock, anything porous and permeable becomes a potential reservoir rock.
I am really jealous of the cali boys having ophiolites. I would love to get a free field trip the next time I am out there. I studied them and all that in school, but I have never laid eyes on one.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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BASE104: here's some info on the Cali ophiolites
Models for origin and emplacement of Jurassic ophiolites of northern California
Auteur(s) / Author(s)
INGERSOLL Raymond V. ;
Four Jurassic ophiolite complexes in northern California have crystallization ages of 170-160 Ma; the Coast Range (including Great Valley) ophiolite is oldest (170-165 Ma), the Smartville ophiolite, intermediate (164-160Ma), and the Josephine ophiolite, youngest (162 Ma). The Smartville ophiolite was obducted during the Sierran phase of the Nevadan orogeny (162-155 Ma), and the Josephine ophiolite was obducted during the Klamath phase of the Nevadan orogeny (153-150 Ma). The Great Valley ophiolite was not highly deformed during the Nevadan orogeny and became oceanic basement for the post-Nevadan forearc basin. Three conflicting models for origin of the Coast Range (including Great Valley) ophiolite have been proposed: (1) Formation by intra-arc and backarc spreading related to an east-facing intraoceanic arc, which collided with a west-facing continental-margin arc during the Nevadan orogeny (Sierran phase). (2) Formation by open-ocean seafloor spreading and incorporation into the continental margin during trench initiation outboard of an existing continental-margin trench. (3) Formation by forearc oblique rifting along the continental margin, followed by partial closure. Lithospheric rifting is favored where there is either thick continental crust or thin mantle lithosphere because continental crust is weaker than oceanic crust and both are weaker than mantle lithosphere. Favorable sites for rifting are extant rifts, intra-arc settings, suture belts, and areas where mantle lithosphere has been delaminated from overlying crust. Upon cessation of magmatism related to rifting or subduction, mantle lithosphere rapidly strengthens, so that by 20 m.y., lithosphere strongly resists extensional stresses. Forearcs cool and strengthen even faster because of refrigeration by subducted slabs. Mature forearcs are strong and unlikely to yield to stresses, especially when weaker intra-arc and backarc settings are nearby. Trench initiation is favored by (1) the presence of a preexisting lithospheric boundary, (2) the presence of thin oceanic lithosphere, (3) attempted subduction of buoyant crust, and (4) plate reorganization. Trench initiation in intact oceanic lithosphere older than 20 m.y. is implausible. The following facts render models for Jurassic trench initiation (model 2) or rifting (model 3) in forearc settings implausible: (1) Subduction began along the California margin in the Triassic, so that forearc lithosphere was considerably older than 20 m.y. by the Late Jurassic. (2) The Triassic-Jurassic magmatic arc related to this earlier subduction zone died in eastern California at the same time that the Jurassic-Cretaceous magmatic arc was initiated in the westernmost Sierra Nevada. (3) The colliding buoyant crust that forced this plate reorganization is found in the Sierran foothills. The most plausible model for formation of the Great Valley, Smartville, and Josephine ophiolites is by lithospheric rifting within and/or behind magmatic arcs. The Great Valley and Smartville ophiolites formed behind an east-facing intraoceanic arc. The west-facing continental-margin forearc of California was partially subducted beneath the east-facing intraoceanic arc, and this attempted subduction of buoyant crust resulted in the Sierran phase of the Nevadan orogeny, during which the Great Valley and Smartville ophiolites were obducted. North of this suture zone, no collision occurred, and the continental-margin arc expanded westward, resulting in intra-arc and/or backarc rifting to form the Josephine ophiolite. The Josephine ophiolite was then obducted over its arc during the Klamath phase of the Nevadan orogeny, as the Klamath trench propagated southward to trap the Great Valley ophiolite in the post-Nevadan forearc.
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Minerals
Social climber
The Deli
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OK… gotta catch up a bunch here…
Back to the photo of the metaconglomerate that I posted a few pages back (post #29)… Nice description, Tradster! This outcrop is on the east side of Sonora Pass, before the bottom of the grade. The reason why I like this photo is because it is a good example of how different materials (rock types) behave under deformation. Yes, the large clasts are granitic and are much “stronger” than the other non-granitic clasts and the matrix; this causes the foliation to “wrap around” the granitic clasts. Don’t know the exact geologic unit of this rock, but it’s neat…
Trdaster, nice Google image of the Gunmetal mine area! Google Earth is so cool, and what a fantastic resource for geologists, not to mention desert rats who want to explore. My caption for the view from the Desert Scheelite mine should have read southeast and not east – that view is towards Tonopah.
“The contact metamorphic zone or skarn consisted of a solid layer of garnets several feet thick that contained scheelite & molybdenite.”
Now I am going to have to go up there… maybe find some molybdenite… MoS2… neat stuff!
http://en.wikipedia.org/wiki/Molybdenite
Haven’t been into the Pine Creek mine but have hiked past it. Someone talked about a tour through the mine, somewhere back in the Supertopo pages…
“It appears to be a high angle (arctan of 30/6 = 79 degrees)reverse fault because the beds are lower in the foot wall than the hanging wall...correct?”
Sounds right to me.
“Have you seen the "Sand Stone Intrusion" on Power Dome at Courtwright Res?”
Guyman, no I haven’t. Got a photo or a link? The stuff at Courtwright looks really cool, from the photos that I’ve seen. Would like to check the place out at some point, for sure.
Wes, I recognize a couple of your photos from a previous post. Are those deformed aplite/pegmatite dikelets in a metavolcanic rock or is that a migmatite? Tahoe area, did you say?
Cool metacherts with neat structure, Tradster.
Jfailing, where did you map the Poleta? Looks like somewhere in the desert. I think there are bits of Poleta, caught up in the granites in the southern Sierra, as metamorphic roof pendants. I’ve seen a little out in Esmeralda County, NV, but not enough to remember any details. Saw more of the Wyman Fm and lots and lots of granitic rock.
Got more to type…
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Minerals
Social climber
The Deli
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From post #63:
“Here are some dikes. Is the goo that filled the cracks aplite? I saw that term mentioned above. Is that similar to plagioclase feldspar?”
Nice photos of dikes, Dipper! I like the rock texture in your first photo – looks like porphyritic granodiorite with orthoclase (feldspar) and hornblende or biotite phenocrysts.
Porphyry (rock type) and porphyritic texture:
http://en.wikipedia.org/wiki/Porphyritic
Here’s some info on dikes, from a previous ST thread with a bunch of info on granites:
http://www.supertopo.com/climbing/thread.php?topic_id=731799&msg=744514#msg744514
Here’s an explanation of granitic rock types from earlier in the same thread:
http://www.supertopo.com/climbing/thread.php?topic_id=731799&msg=732325#msg732325
Your 4th photo is of a series of joints (fractures) in granitic rock – these would not be considered dikes.
Tradster, those are cool photos from the Avawatz! Yeah, I think it’s safe to say that if you have vertically-dipping Quaternary alluvial fan deposits, you are in a tectonically “active” area.
Killer Wyoming photos! That stuff just screams the word “geology”!!! Very nice!
BASE104, interesting bit on the Ames Hole. Like Jfailing, when I first saw your graphic image, I thought it looked like an impact crater but figured that it must be some weird structural deal. Neat!
http://search.datapages.com/data/doi/10.1306/522B34E3-1727-11D7-8645000102C1865D
Dipper, thanks for the photo of the chunk of Cathedral Peak granodiorite with a bunch of orthoclase megacrysts! The question is, how do all of those megacrysts get packed together so tightly if they form entirely in a magmatic state? In many cases, simple crystal accumulation is mechanically impossible and cannot explain some of the very-tightly packed “rafts” of megacrysts seen in outcrop. But, I am going to open my bottle of beer instead of a can o’ bait!
Is “gamma” a Cyclops with a mafic enclave for an eye?
BASE104, thanks for the link to the seismic articles! I saved the one on igneous stuff in Mexico and will look over the list of articles in more detail. Also saved the article on subsurface joints.
Dipper, the float in your photos from the Inyo Mountains looks like a pile of chopsticks! My guess is that whatever the rock type (metased?), the chopsticks form because of at least two dominant cleavage angles in the rock, which when exploited by physical weathering, produce the slender rock fragments. So basically, the chopsticks form because of structural weaknesses in the rock.
Cleavage (the geology kind…):
http://en.wikipedia.org/wiki/Cleavage_(geology);
(Cut and paste screwy link again…)
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Minerals
Social climber
The Deli
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As far as the two different colors in the garnet that Fritz posted a photo of… I’m wondering if the darker colored garnet is of a slightly different composition, like almandine. Spessartine, almadine, and pyrope (all garnets) form a solid solution series.
Spessartine:
http://en.wikipedia.org/wiki/Spessartine
Solid solution series:
http://en.wikipedia.org/wiki/Solid_solution
Dipper, the first two photos in your above post have a light “X” pattern that is mirrored between the two blocks. The lighter-colored lines are due to minor chemical alteration of the primary igneous minerals in the granitic rock from hydrothermal fluid flow along joints and small fractures. The plagioclase feldspar appears “bleached” because calcium has been leached from the mineral, shifting its composition more towards a sodium-rich plagioclase, which is lighter in color. Epidote and sometimes chlorite are common secondary minerals that are found in altered zones in granitic rock.
Feldspar:
http://en.wikipedia.org/wiki/Feldspar
Epidote:
http://en.wikipedia.org/wiki/Epidote
(This is the pistachio-green colored mineral that is quite commonly seen in metamorphic rocks and sometimes fills joints as a secondary mineral in some granitic rocks.)
Chlorite:
http://en.wikipedia.org/wiki/Chlorite_group
Getting addicted to Wiki…
Neat Franciscan photos, Tradster!
Hey Anders… You asked about glaucophane? It’s the primary mineral that makes up blueschist, a high-pressure, low-temperature metamorphic rock that is diagnostic of a subduction zone environment. I wrote a 12+ minute song (Blueschist – The Metamorphic Song) back in the early 90’s and used the chemical formula of glaucophane for the time signature in one section of the song – one measure of this section turned out to be in 42/8 time, but it still sounded cool. Glaucophane – Na2(Mg,Fe)3Al2Si8O22(OH)2
Glaucophane:
http://en.wikipedia.org/wiki/Glaucophane
I need to scan some photos of Turtle Rock, my favorite blueschist knocker of all time…
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dipper
climber
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Topic Author's Reply - Jan 8, 2010 - 09:17pm PT
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Minerals,
Many thanks for taking the time to educate. I missed those prior links and have scanned them, but will go back and do them slow roast style for better retention (me hopes).
Man, you know rocks. That chunk o' chickenheads may/may not have once sat in the upper Budd Creek area.
Cyclops came from roadside campsite in Owens Valley somewhere long ago.
I have a chunk of Epidote, if weather and time permits tomorrow, I will post up smore of my collection of treasures.
Your explanations are most appreciated.
-Dipper, the geo-dilletante (Cinclus dilletantus phenocrysti)
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Minerals
Social climber
The Deli
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Glad that this stuff is helping you out, Dipper! It’s fun to post and is a good chance for me to brush up on some things, as well as learn more about new things. I enjoy teaching people about the geology that I have learned! What else ya got?
Hey, a question for the extrusive folks out there…
In post #86, I’m not sure of the origin of the breccia zone in volcanic rock in the photos that I posted. I have looked at this outcrop many times over the years, and not knowing too much about the extrusive stuff, have wondered if this breccia zone is of volcanic origin or is tectonic. What do you guys think?
OK… a reach for a granite guy, but still my home turf………….
Stewart Valley Fossils, Mineral County, NV:
http://gsa.confex.com/gsa/2002CD/finalprogram/abstract_35258.htm
http://researcharchive.calacademy.org/research/entomology/Entomology_Resources/fossils/index2.htm
A sign in need of replacement…
Is the “cracking” of the sign due to Basin and Range extension or Walker Lane transtension?
Where’s Obama’s stimulation when you need it??? What’s with all of the pseudo en echelon fracturing and chemical alteration…? :)
Miocene seds… complete with a little cross-bedding and mini fossils
Fresh-water mini crustaceans from BITD, but not too far back
Jaybro, am I starting to speak your language?
How ‘bout this?
http://skywalker.cochise.edu/wellerr/fssl-inv-links/list.htm
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Minerals
Social climber
The Deli
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Jan 10, 2010 - 12:52am PT
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Central Nevada:
Limestone
Tertiary volcanics
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SuperTopo on the Web
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Let us know!