Fold Links

General Fold Info:
Folds at Wikipedia - includes some photos, some general descriptions, mediocre

Folding of Rocks - some examples of fold types, with diagrams, good

Recumbent Fold:
Definition: A fold in which the axial plane is horizontal.

Isoclinal Fold:
Definition: A fold in which the limbs are parallel.

Sheath Fold:
Definition: A sheath fold is a conical fold in which the conical surface is completely closed in the neighbourhood of the cone's apex.

Sheath Folds and more:
Alsop, G.I., and Holdsworth, R.E., 2002, The geometry and kinematics of sheath folds [abs]: Geological Society of America Abstracts with Programs, v. 34, no. 6, p.561.

Alsop, G. I., Holdsworth, R. E., and McCaffrey, K.J.W., 2007, Scale invariant sheath folds in salt, sediments and shear zones: Journal of Structural Geology, 2007, v. 29, no. 10, p. 1585-1604; doi:10.1016/j.jsg.2007.07.012.

Kuiper, Y.D., 2006 ,The usefulness of non-cylindrical (sheath) folds in monoclinic and triclinic shear zones [abs]: Geological Society of America Abstracts with Programs, v. 38, no. 7, p. 19.

Moore, J., C., (unknown date), Shear Zones Ductile and Semi-brittle Zones of Distributed Deformation Around Faults, Especially Strike-slip Faults: "15ShearZones" page from University of California, Santa Cruz, Earth Sciences 150.

Searle, M.P, and Alsop, G.I., 2007, Eye-to-eye with a mega–sheath fold: A case study from Wadi Mayh, northern Oman Mountains: Geology, v. 35, no. 11, p. 1043-1046; doi: 10.1130/G23884A.1.

How to make a sheath fold:
1) Photo of sheath fold exposure (click "click here" for the diagrams).
2) How to make a sheath fold part 1 (then click "continue").
3) How to make a sheath fold part 2 (click "example" to return to the photo).
—Copyright: Dr R. Butler, School of Earth and Environment, Leeds University
—HTML by C. Gordon

(This post continues my ongoing project of cleaning out my drafts folder, which largely consists links collected while doing research of various sorts.)

Where on (Google) Earth #150

Above, the WoGE #150 image for y'all to give a shot at. I doubt it's very difficult, but don't know - they've all seemed impossible to me until the last one, and they've seemed hard to locate in cyberspace, also. I can only recommend that Peter Lufti's postings for WoGE be somehow added to the Allgeo feed so we can tell easily when and where it's been posted (since he wins so often!). But maybe we are just meant to search for it!

To play WoGE, post the location of the above place in the comments - latitude and longitude or a description. To win, post the location first! If you win, it passes to you. If you can comment about the geology, that would be great! I'm invoking the Schott Rule: wait one hour for every time you've won WoGE.

I've never won one of these things before - I used to try a lot, but finally stopped after realizing that even in an hour I usually wasn't even coming close. WoGE #149 looked very familiar to me, so I GoogleEarthed it quickly (I think that if you can Google something, then surely you can GoogleEarth a place - a new verb!), and then posted the answer as fast as possible, only stopping to look up a couple place names in my handy-dandy Oregon Atlas. And I checked out TerraServer, also [now MSR Maps].

Yes, it was the Three Sisters near Sisters, Oregon. For certain former Oregonian readers of mine, please click here to see the Three Sisters as seen from Google Earth! And please read the comments, Tuff Cookie of Magma Cum Laude gave a spectacular description of the geology of the Three Sisters, far surpassing mine!

Posted at 6:40 PM Pacific Daylight Time, (GMT -7 I think because of summer time) October 24, 2008.

UPDATE 04Apr2017: These are the Whipple Mountains, with Savahia Peak nearly centered. I've added this update so the blog will find this post when using the search "whipple" and "savahia." I've gotten tired of not being able to find the post easily.

Where in the West: Wheeler Peak

I'll be away when this post comes out, hiking and camping on Wheeler Peak. Since I already posted pictures of this peak, and because coconino already correctly identified it and the formations making up the peak, I won't have a regular July Where in the West.

Wheeler Peak is in the Snake Range of eastern Nevada, not very far west of the Utah border. It reaches an elevation of 13,063 feet, making it the second highest peak in Nevada, a close second to Boundary Peak at 13,141 feet.

Wheeler Peak is inside Great Basin National Park, which was created in 1986, some 8 years after I first drove up the paved road that goes to the upper campground while on days off from a helicopter camp in Caliente. The upper campground is at an elevation 9,886 feet, in a wonderful aspen grove and meadow, with Lehman Creek gurgling by on the south side of the camp. The Bristlecone, Glacier, and Wheeler Peak Summit Trails all begin at the campground, although I'd recommend parking at the upper trailhead for the Wheeler Peak Summit Trail, thereby cutting off about 300 feet of elevation on an already strenuous and long hike. The combined Bristlecone and Glacier Trail goes to a Bristlecone Pine grove and to the only active glacier in Nevada, a rock glacier. [The Glacier Trail is a continuation of the Bristlecone Trail, the entire journey from trailhead to glacier and back to trailhead being 4.6 miles.]

[Correction: it is a small glacier that is active or has been within the last decade or two, not the rock glacier - see later posts.]

The Wheeler Peak Scenic Drive, 12 miles of paved road that switchbacks and winds up the mountain at up to 8% grades, provides several scenic overlook stops of Wheeler Peak itself, and also of the distant basins and ranges in Utah. If you carefully stop in the right places, you can also get a good view of the northern Snake Range decollement or detachment fault. The photo header for this blog, Looking for Detachment, was taken from the Wheeler Peak Scenic Drive.

While winding up the mountain on the scenic drive, you will pass through late Precambrian to early Cambrian Prospect Mountain Quartzite, and possibly through a bit of Osceola Argillite. I'm not that familiar with the Osceola Argillite, but it's part of the late Precambrian McCoy Creek Group, described here. The Osceola Argillite is one of coconino's favorite rock formations.

Of course, a lot more could be said about the Wheeler Peak area and Great Basin Park - don't forget Lehman Caves or the nearby Osceola mining district. Osceola produced the largest gold nugget in Nevada [archived], which weighed in at 25 lbs and was valued - at the time - at $6000.

Hopefully I'll have a few photos when I return! In the words of California's erstwhile governator, "I'll be Bach."


Some geologic maps:

Miller, E. L., Gans, P. B., and Grier, S. P., 1994, Geologic map of Windy Peak 7.5' quadrangle, White Pine County, Nevada: USGS Open-File Report OF-94-687.

Miller, E.L., Brown, J.L., Miller, D.M., Crane, M.P., and McCarthy, P.T., 1993, Minerva Canyon, Nevada; Wheeler Peak, Nevada: Stanford University, scale 1:24000.

Elizabeth L. Miller, Phillip B. Gans, and the Stanford Geological Survey, "Geologic Map of Wheeler Peak and Minerva Canyon 7.5'Quadrangles, White Pine County, Nevada," Unpublished USGS Open FileReport, somewhere in the USGS CR, 1993. Draft available via web.

Miller, E.L., Grier, S.P., and Brown, J.L., 1995, Geologic map of the Lehman Caves quadrangle, White Pine County, Nevada: U.S. Geological Survey, Geologic Quadrangle Map GQ-1758, scale 1:24000.

Yerington Day 1

Day 1 of the field trip was an overview of the Yerington mining district, a touring day of driving here and there along with a couple moderately long (or steep) hikes. We started at Weed Heights, just above the old Anaconda open-pit, the dumps of which are visible from the town of Yerington. We had a round of introductions - geologists present were largely from outside the United States, most were from Canada but countries included Mongolia, Italy, Sweden, Mexico, a few South American countries, and one American living in Australia and working in southern Africa. Several languages were spoken, the dominant ones being English, Spanish, and French. We had one or two students on the trip (or more?), several relatively young geologists working mostly in Canada, and a number of older geologists. The day was cool and partly cloudy, and every time we stopped, we got out a set of maps, cross-sections, and diagrams and had mini-lectures standing in front of one of the vans, which was used as a magnetic bulletin board.

Weed Heights Post Office:


Yerington pit, with ducks swimming in the non-acidic, non-copper-colored blue-green water (acidic water with a lot of copper in it is often a deep or bright blue-green):

Our fearless leaders, Dick Tosdal and John Dilles:

Anaconda mined the deposit from 1951 through 1978. A brief history and summary on the tires below (enlarge as needed):

The field trip was very interesting, both geologically and with regard to scenery, plant life, and wildlife. Geologically speaking, the field trip could be called, "Detached or Not: the 200% Extension of a Major Porphyry Copper Center in Western Nevada." This is the area mapped first by Proffett and Proffett, by Proffett and Dilles, and by Dilles, Proffett, and Einaudi, and also by others.

Normal faults, which are now dipping 20 degrees in most places, but which initiated at 60 degrees or more, have essentially cut the district and the porphyry copper system into large and thick tectonic slices. One can now view the Jurassic porphyry system essentially in cross-section by looking at it on a map after turning the north arrow to point to the right. "Jurassic Up," the direction that was up in Jurassic time, is then at the top of the map - west - with the now tilted Tertiary unconformity that eroded the upper, shallower part of the porphyry system sitting on top of the older rocks in what amounts to a cross-sectional view. The porphyry dikes, which in actuality strike east-west and dip about 30 degrees to the north, will - after rotation of the geologic map as I just described above - appear to be vertical, as if in cross-section.

In the upper (real) cross-section, you can see the major low-angle normal faults that have cut the Jurassic through Tertiary into thick slices and tilted the entire section. Apparently, if these faults sole downward into any kind of regional detachment fault or fault system, it has not been discovered and is probably too deep to be found, if present. That is, no brittle-ductile contact zone - such as is found in major core complexes like the one in the Snake Range of eastern Nevada (see banner photo), or the Ruby Mountains near Elko, Nevada - is known or has been recognized. The lower (real) cross-section shows a fold affecting Triassic to Jurassic sedimentary (and volcanic) formations, probably folded in Jurassic time prior to intrusion of the Yerington batholith (if my f.t. notes serve me correctly).

The area visited during day one is thoroughly covered by the enlarged geologic map shown above, with north up and the larger squares equal to about one mile (a township section). Below, I've rotated the map so that north is to the right and west is up. I've labeled the Singatse Fault in yellow, one of the major low-angle normal faults; the Tertiary unconformity is in turquoise in two places in the upper, western part of the map; a cupola of the Yerington batholith, also in turquoise, is in the lower, eastern part of the map; and the approximate axis of the fold is in dark blue near the left or southern part of the map. Porphyry dikes cut through the center of the map in a mostly westerly direction (WNW). They come out of and intrude the cupola of the batholith and then cut through other plutons of the batholith complex, which are in a kind of beige color.

With the rotation of this map so that "Jurassic Up" is located to the top of the map, one is now viewing the area in a cross-sectional fashion, except for the various normal faults that have sliced things up. The anticline is now seen as a mostly upright fold; the dikes shoot "upward" out of the cupola and into the rest of the porphyry system; and the Tertiary unconformity, which has an erosional conglomerate or breccia sitting on top of it, that overlain be Tertiary volcanic rocks, is now seen to overlie the entire mass of pre-Tertiary rocks. It's not a perfect "cross-section" that one looks at in this fashion, but it shows the main elements very well.

The Tertiary faults that tilted the Tertiary and older rocks began about 14 to 15 million years ago. Prior to Tertiary tilting, Jurassic tilting of the porphyry system and older rocks had amounted to about 20 degrees. Tertiary tilting took place on three sets of normal faults, all of which can be seen in the upper (real) cross-section. The earliest set, about 14 to 15 Ma, are the ones now dipping about 20 degrees, like the Singatse fault. The second set of normal faults were active from about 12 to 9 million years ago, cutting and tilting the earlier set of normal faults. The third set of normal faults, amounting to the Basin and Range faults of this area, became active about 7 to 8 Ma. These faults cut all previous faults, and have added somewhat to the tilting of the faults and strata of the area. Tertiary faults have tilted section and all units about 60 to 70 degrees, resulting in a total tilting of about 80 to 90 degrees since the Jurassic.

Just for all you volcanology fans, I've included a cartoon of the Tertiary volcanic section below.

Some references:

Dilles, J. H., 1983, The petrology and geochemistry of the Yerington batholith and the Ann-Mason porphyry copper deposit, western Nevada, Stanford Ph.D dissertation.

Dilles, J.H., 1987, The petrology of the Yerington batholith, Nevada: Evidence for the evolution of porphyry copper ore fluids: Econ. Geol., v. 82, p. 1750-1789. Econ. Geol. online.

Dilles, J.H., and Einaudi, M.T., 1992, Wall-rock alteration and hydrothermal flow paths about the Ann-Mason porphyry copper deposit, Nevada--A 6- km vertical reconstruction: Econ. Geol., v. 87, p. 1963-2001.

Dilles, J. H., Proffett, J., and Einaudi, M. T., 2000, Field trip day two: Magmatic and hydrothermal features of the Yerington Batholith with emphasis on the porphyry Cu-(Mo) deposit in the Ann-Mason area, in Thompson, T. B., ed., Society of Economic Geologists Guidebook, 32, p. 67-89.

Dilles, J.H., Proffett, J. and Einaudi, M. T., 2005, Magmatic and Hydrothermal Features of The Yerington Batholith with Emphasis on the Porphyry Cu(-Mo) Deposit in the Ann-Mason Area, in Geological Society of Nevada, 2005 Symposium Field Trip, Guidebook 9 Porphyry Deposits of the Great Basin.

Dilles, J.H., Solomon, G.C., Taylor, H.P., Jr., and Einaudi, M.T., 1992, Oxygen and hydrogen isotopes characteristics of hydrothermal alteration at the Ann-Mason porphyry copper deposit, Yerington, Nevada: Econ. Geol., v. 87, p. 44-63.

Dilles, J.H., and Wright, J.E., 1988, The chronology of early Mesozoic arc magmatism in the Yerington district, Nevada, and its regional implications: Geol. Soc. America Bull., v. 100, p. 644-652.

Proffett, J.M., 1977, Cenozoic geology of the Yerington district, Nevada, and implications for the nature and origin of basin and range faulting: Geol. Soc. America Bull., v. 88, p. 247-266.

Proffett, J.M., and Dilles, J.H., 1984, Geologic map of the Yerington district, Nevada: Nevada Bur. Mines Geology, Map 77.

Proffett, J.M., and Dilles, J.H., 1991, Middle Jurassic volcanic rocks of the Artesia Lake and Fulstone Spring sequences, Buckskin Range: Geol. Soc. Nevada, Field trip 16 guidebook compendium, v. 2, p. 1031-1036.

Proffett, John M., and Dilles, John H., in press 2006, Lower Mesozoic sedimentary and volcanic rocks of the Yerington region, Nevada, and their regional context: Geol. Soc Amer Spec Paper, editors, John Shervais and Jim Wright.

Proffett, J.M., Jr., and Proffett, B.H., 1976, Stratigraphy of the Tertiary ash-flow tuffs in the Yerington district, Nevada: Nevada Bureau of Mines and Geology Report 27, 28 p.