Looking For Detachment

Just the other day, Monday to be precise, I was walking around above town thinking about the signs of fall that were all around: dry, straw-colored bunch grass (unknown variety), yellow blooms of rabbitbrush (right foreground), golden-brown blooms of sagebrush (left middleground), and yellow to bright red aspen on the distant mountain.
This closer view of the Duck Creek Range, with Camel Peak to the right, shows the aspens better - a yellow to red patch to the right of the central saddle, just above the folded Cambrian limestone.
Two days later - Wednesday to be precise, because I shot this pic yesterday morning - there was snow on the mountain, and many leaves had fallen off the aspen trees. Today, the snow is mostly gone, except for some patches on north slopes under a few trees.
The same two photos, enlarged, for easier comparison.
Exactly one year ago yesterday, on September 30, 2007, I happened to be at the top of the saddle north of the aspen trees, and I took this somewhat faded-looking photo with my old camera. The same aspen trees - located just above the light gray Cambrian limestone and just below the pointy-looking peak, Camel Peak - had mostly dropped their leaves. Saddle location in Google Maps. Oh, and btw, that's an exposure of mylonitic quartzite in the foreground!

Ah, the vagaries of weather, year to year.

As for our garden, it experienced our first hard freeze (it got down to 14°F at the airport, but was already 39°F when I checked our thermometer at almost 9:00 am, and 32°F at the airport at the same time - we are in the banana belt). The tomatoes have wilted and are falling over, the leaves of our zucchini plant are lying flat on the ground, and the marigold leaves have wilted and turned blackish green. The kale is just fine, and so is the chocolate mint. Yay for the chocolate mint!

In a continuation of a meme event that took place in the GeoBlogosphere late last year, Garry Hayes is hosting the current Accretionary Wedge - February, #16 - at his site, Geotripper:

What are the places and events that you think should all geologists should see and experience before they die? What are the places you know and love that best exemplify geological principles and processes?

Rather than create a new list of 100, or even 25, I thought I'd just mention a few places not on the original list, that I think should be considered.

Snake Range, Nevada: a place to collect mylonites.

1. See a metamorphic core complex - metamorphic core complexes are common in a belt in North America, from British Columbia south into Mexico, and also occur in other places in the world, including Slovakia, Greece, Turkey, Iran, Tibet, China, and New Zealand. One should see a metamorphic core complex, preferably as part of a tour or field trip, just so one can get involved in the lively discussions about how they form, but also in order to see and collect wonderful samples of mylonites!

2. While in Tibet, check out the Tibetan Plateau - just because it's there. It's the "largest, highest area in the world today" - and it was created by a magnificent convergence of two continental plates.

3. While in China, be sure to see the South China Karst, which is now a UNESCO World Heritage Site, and which contains some unusual rock formations formed by dissolution and re-precipitation of limestone: Guizhou Libo Karst, Yunnan Shilin Karst, and Chongqing Wulong Karst. I don't know of other similarly magnificent regions of karst that could replace this one.

Those are my three additions or suggestions. I have seen number one: several metamorphic core complexes in the western United States.

Accretionary Wedge #16: Is One Life Enough?

On a fairly recent road trip to Baker, NV (gee, I almost wrote Baker, CA - yikes! - so many *fond* memories from there), I took the opportunity to look around while MOH was getting gas, and discovered that you can see the Snake Range decollement or detachment fault from town.
In case you need to have the low-angle fault pointed out, here's a great photo with a power line running parallel to the fault! Upper plate rocks are dipping westward (to the left), and lower plate rocks, besides the white-line mylonite right along the fault, are obscure.
Ah, then we drove up Wheeler Peak, where the road is closed part way up the mountain to the upper campground, and we had this great view of part of the Snake Range detachment fault, with a snow-covered mountain in the background. The detachment fault is a little difficult to see, but is essentially following a somewhat curved or arched line where all the tilted upper plate rocks end. The snow-covered mountain might be Mount Moriah, one of the highest peaks in Nevada.
And here's the Snake Range detachment fault again, this time from the rock glacier on Wheeler Peak. Bristelcone pines grow on the rock glacier, and can be seen in this photo mostly toward the far edge of the glacier. More info can be found about the detachment fault, the geology of the area, and the bristlecones in my series on Wheeler Peak.

Way out west, they got a name
For rain and wind and fire
The rain is Tess, the fire's Joe and
They call the wind Mariah [Moriah, in this case.]

See these sites for lyrical references.

I'm finally getting back to the first Brunton I ever used, an old K+E given to my dad by my mom when he graduated from college with his geology degree.

Brunton on eastward-dipping Cambrian-Precambrian Prospect Mountain Quartzite (or possibly it's part of the Precambrian McCoy Creek Group).

Case for said Brunton sitting on the same outcrop. Coconino, what do you think - Prospect Mountain Quartzite? Anyone else have an opinion?

The same Brunton resting parallel to lineations in mylonitic quartzite within 100 feet of the previous outcrop.

A more photogenic picture of the same Brunton sitting on a nearby quartzite outcrop.

Location of the last two outcrop photos, on the whitish eastward-dipping quartzite seen in the foreground, with Wheeler Peak in the background.

This month's Accretionary Wedge is up at Lounge of the Lab Lemming: Geohmms (Accretionary Wedge 6). He runs down the many interesting geological articles quite well.

One thing I wonder - is a particular kind of "blue quartz" really associated with ore deposits - ore deposits of the gold kind? Some have postulated this idea: for example, here and here. A familiar example to me would be an unusual bluish quartz found in the Silver Peak mining district, on top of Mineral Ridge, near Silver Peak, NV (the town, not the peak). I noticed blue quartz while working there long ago, especially in and around the old Gold Wedge and Oromonte claims above the Mary Mine. The quartz occurs in granitic rock (including in what I would call alaskite), and I've seen it most commonly near the relatively flat-lying quartz veins or ledges of the area. It appears to be an alteration feature or late stage intrusive feature, though the granitic rocks are entirely within the lower plate of a core complex and are often mylonitized or mylonitic. The timing of quartz veining and the gold-mineralizing event is unclear, at least in the sense that the many mining companies that looked for gold there (in the 1970's to 1980's in particular) all seemed to use different deposit models, from Carlin-type to exhalite-type to some variation of Mesquite-type, and even, possibly, to some variation of Mother-Lode-type (mesothermal veins). At this juncture, it would be a good idea to show an example of the blue quartz. If I have any examples, they are packed in boxes in the garage from my last move in 2001. I haven't been to the top of Mineral Ridge since the day after New Year's Day in 2000 (a geo-millennial thing, I guess), and at that time, the entire area was fenced off from recently shut-down mining operations, operations which appeared to have placed a heap-leach pad over part of a gold deposit discovered in the late 1980's by Former Mining Company. From this Google Earth image, it looks like the best outcrop of blue quartz might be almost or entirely gone!

Silver Peak, by the way, is another "outback" Nevada town or village. It was the largest town in Esmeralda County in the mid-1980s when its population was about 1500 because of silver and lithium-brine mining, and the population of Goldfield, the county seat and only other town in Esmeralda County was a third of that or less.

Silver Peak is A Virtual Paradise.










Updated slightly 23Feb2025

Yesterday started out cold and icy - with an orangey sunrise over the nearby mountains to the east. Later, the sun came out and everything around started melting and dripping.

If you look closely, you can see a fold or monocline concealed partly by snow. Folded limestone atop a reddish limestone breccia sits on Precambrian to Cambrian, possibly mylonitic quartzite. And speaking of mylonites (once again), it turns out that mylonitic quartzite was rock of the week at All of My Faults Are Stress Related. What a coincidence!

I just wanted to share this article about mylonites: The Sound of Mylonites. Mylonites are one of my favorite types of rocks, and long ago I had a wonderful introduction to them in the Snake Range, a metamorphic core complex with mylonites along and below the main décollement, a low-angle normal fault sometimes referred to as a detachment fault.

On the home front: today I am mailing our 2007 Newsletter. I'm just now sending it out!

I'll now be walking down the steep snowy street one block away from our little house, and then will walk downhill to the main part of town. I will be out for a late brunch: I'm on days off! All for now, Sfx.