Tuesday, October 27, 2015

Finding a Thesis: A Bit O' Geology in the Palmetto Mountains

My (very) rough interpretation of the Walker Lane on Google Earth.
As for the broad geology of the Palmetto Mountains area, what I knew back in the spring or early summer of 1976 was quite broad, and it probably wouldn't have filled up the trunk of my '72 Opel. The main thing I knew—besides that the region was known for its silver mining, and that the silver mines were presumably of the Betty O’Neal type (see more here; I can’t actually expound upon this much further anymore because that terminology never came into wide use)—was that I was in that confusing realm in western Nevada known as the Walker Lane (or Walker line, Walker belt, Walker Lane belt, Walker Lane strike-slip belt, and even Walker Lane mineral belt; we geologists can be overly broad and rather sweeping at times).

The Walker Lane, first named by Locke et al. (1940), is a somewhat vaguely defined, and yet locally precisely defined zone of abnormal structural trends, a zone that acts as or is the transition between the Sierra Nevada structural block and the Basin and Range province. Albers and Stewart (1972) described it thusly:
“a zone of disrupted structure at least 300 miles long and 50 to 100 miles wide that forms a transition between the northwest-trending Sierra Nevada block to the west and the north-northeast-trending ranges of the Great Basin province to the east.”
(Please note that this use of "Great Basin" may be incorrect, depending on where one terminates the Walker Lane to the north and south; i.e., the Walker Lane would be at least partly outside the Great Basin if it extends north of the Madeline Plains, and it is outside the Great Basin if it extends as far south as Las Vegas.)

(And also, by the definitions above, which reference the Sierra Nevada, the Walker Lane shouldn't continue north of about Susanville, CA; or farther south than about Las Vegas, NV, Kingman, CA, or maybe Parker, AZ.)

Different maps and figures show different boundaries for the Walker Lane, and as you can see from my interpretation on the Google Earth image, the zone gets vague to the north (or disappears) where it runs into the Cascades, and it gets vague (or meaninglessly broad) as it goes southward toward and past Vegas and the Mojave Desert. Looking at Google Earth and zooming way out, it appears that the entire Mojave could be included in this belt, and that the general trend continues southward into Mexico where the caterpillars are marching to the northwest. I don’t mean to formally extend the Walker Lane to the south like that, because as a definable and distinct structural entity it then becomes quite nebulous.

Anyway, not only was I cognizant of the existence of the Walker Lane back in '76, but I also knew that the Palmetto Mountains were located along the southern portion of the larger Silver Peak-Palmetto-Montezuma (SPPM) oroflex (Albers, 1967), a feature that is broadly part of the Walker Lane (and may have been caused by motion along Walker Lane strike-slip faults). I hypothesized (possibly fancifully; I didn't get to check it out) that an east-west structure defined by Lida Canyon on the east and Palmetto Wash on the west formed a break between the larger, well-defined SPPM oroflex to the north and a poorly formed Sylvania-Magruder oroflex to the south (which may not exist).
I've drawn the approximate trace of the Silver Peak-Palmetto-Montezuma oroflex on a Google Earth image.
Oroflex, as defined by Albers (1967, p. 145):
"a mountain range with an arcuate trend that is believed to have been inherited from tectonic bending of the crust"
Well, so much for that. Yes, we’re in the Walker Lane (and have been since before coming to the Klondyke District). Yes, there has been an oroflexural bending of the structures or mountain ranges of the area during formation of the Walker Lane—if that is, indeed, what really happened—sorry to be vague about this; read more at Faulds and Henry (2008) and Petronis et al. (2009). Tectonic issues can be kinda complicated!

As for Lida and the Palmettos, I would make my way back into this area a couple times in later years—and I'll probably get into these visits a little before moving on to my next thesis stop: Silver Peak.

Selected References:
Albers, J. P., 1967, Belt of sigmoidal bending and right-lateral faulting in the western Great Basin [abstract only]: Geol. Soc. America Bull, v. 78, p. 143- 156.

Albers, J.P., and Stewart, J.H., 1972, Geology and mineral deposits of Esmeralda County, Nevada [for purchase only]: Nevada Bureau of Mines and Geology Bulletin 78, 80 p., 1:250,000.

Billingsley, P., Locke, A., 1941. Structure of ore districts in the continental framework. Transactions of American Institute of Mining and Metallurgical Engineers 144, 9–59.

Faulds, J. E., Henry, C. D., and Hinz, N. H., 2005, Kinematics of the northern Walker Lane: An incipient transform fault along the Pacific–North American plate boundary [pdf]: Geology, v. 33, no. 6, p. 505-508.

Faulds, J. E., and Henry, C. D., 2008, Tectonic influences on the spatial and temporal evolution of the Walker Lane: An incipient transform fault along the evolving Pacific [pdf]: – North American plate boundary: Arizona Society Digest 22, p. 433-466.

Locke, Augustus, Billingsley, P. R., and Mayo, E. B., 1940, Sierra Nevada tectonic pattern [abstract only]: Geol. Soc. America Bull., v. 51, p. 513-539.

Petronis, M.S., Geissman, J.W., Oldow, J.S., and McIntosh, W.C., 2009, Late Miocene to Pliocene vertical-axis rotation attending development of the Silver Peak–Lone Mountain displacement transfer zone, west-central Nevada [abstract only], in Oldow, J.S., and Cashman, P.H., eds., Late Cenozoic Structure and Evolution of the Great Basin–Sierra Nevada Transition: Geol. Soc. America Special Paper 447, p. 215–253.

Stewart, J.H., 1980, Geology of Nevada: a discussion to accompany the Geologic map of Nevada: Nevada Bureau of Mines and Geology, Special Publication 4, 136 p.

Wesnousky, S. G., 2005, The San Andreas and Walker Lane fault systems, western North America: transpression, transtension, cumulative slip and the structural evolution of a major transform plate boundary: Journal of Structural Geology, v. 27, p. 1505–1512.

Previous Posts in this Series:
Thesis: Finding an Area
Finding a Thesis: Battle Mountain to Austin to Gabbs
Finding a Thesis: Pole Line Road
Finding a Thesis: Pole Line to Belmont
Finding a Thesis: Klondyke District
Finding a Thesis: A Joshua Tree Aside
Finding a Thesis: Into the Palmetto Mountains
Finding a Thesis: Farther into the Palmetto Mountains

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