Saturday, February 4, 2012

Top 10 reasons I love detachment faults / core complexes

Not sure about the order of these things, but here's a go at the geoblogosphere's most recent spontaneous meme, as started by Erik Klemetti, and followed by Siim Sepp and Callan Bentley. Oh, and by the way, I also love volcanoes, sand, and structure — among other geologic subjects and subdivisions — not necessarily in that order.

* They are not everywhere. Detachment faults associated with metamorphic core complexes are generally found in a band running from British Columbia, into Washington and Idaho, through eastern Nevada, into Arizona and the Mojave Desert of California, and down into Mexico (and also in other parts of the western U.S. and in other parts of the world). They run through my general neck of the woods, in other words, but occur in rather specialized geologic settings. This is all right by me. (If they were everywhere, we would miss out on other types of geology.)

* Detachment faults are found in Nevada. I love working in Nevada! Has anyone noticed that?

* Detachment faults and core complexes are found in the Mojave Desert. At first I kind of disliked working in the Mojave Desert because, although similar to Nevada in some ways, it isn't Nevada: it's hotter than Nevada, it's dustier and hazier than Nevada, and the mountain ranges are often older, more worn down, and farther apart than those in Nevada. The roads are cruddier, the small towns less inviting or pleasant in many ways (e. g. Baker, CA). You can find some strange people in the Mojave, and the place doesn't seem as safe as Nevada. I gradually grew to like the Mojave Desert, maybe largely for the exceptional geologic exposure, maybe for all it's weirdnesses, maybe because someday, perhaps, Nevada will look more like the Mojave. I also love to hate cholla cactuses, especially ones growing around the Whipple Mountains core complex.

* Detachment faults are often well exposed. Good exposure of detachment faults is, perhaps, largely associated with their general location in areas that have good exposure, but being of regional extent by definition, they consist of large faults that can often be found around or on top of entire mountain ranges. (I love exposure.)

* A good detachment fault is a thing of beauty. It's relatively flat-lying, very smooth, often shiny, and has wonderful slickenlines and grooves all over it's surface, often aligned in a nearly east-west direction.

* A core complex is complex (surprise). Core complexes aren't easy to understand, and every one seems a bit different from it's nearest neighbor. Geologists dispute the formation and development of these things, allowing for great arguments over beers, great field trips and arm-waving sessions, and exceptional reason for practising down-to-earth to wild-eyed geo-speculation.

* Core complexes and detachment terrane in general are good places to study all kinds of geology. I love all kinds of geology for all kinds of reasons. You can find all rock types — sedimentary, metamorphic, and igneous (often plutonic, sometimes volcanic) — associated with core complexes and detachment terrane, along with great structure.

* Core complexes are mega structural features. I love structural geology, and core complexes and associated detachment faults provide excellent terrain for studying all kinds of structure, from mega to micro scales, including often unexpected but sometimes present contractional structural features.

* Detachment faults are a good place to find breccias: microbreccia, chlorite breccia, etc. I love breccias!

* Core complexes can contain ore deposits. Sometimes older ore deposits have been smeared or extended in the lower plate below the detachment fault; sometimes ore deposits are found along the detachment fault in possibly genetic association; sometimes pre-detachment ore deposits have been extremely sliced and diced by the detachment fault and its related upper-plate faults. Exploration for ore deposits is what I do. (Read a few discovery stories here.)


Nina F said...

When I was a student at SUU we took a couple of fun field trips to the Northern Snake Range. Kind of hard to wrap my mind around core complexes until a few years later, but I finally got a handle on the concept.

Silver Fox said...

Core complexes are complex! ;)

Utemike said...

Nevada smells better than the Mojave after a rain. Smells like home...

Dan McShane said...

I did a huge amount of research on detachment faults prior to my start of some field work in the North Cascades of Wasington State. Sadly I discovered that the detachment fault cutting trough the core complex we were investigating did not exist. Three years later my field work killed another major detachment fault in British Columbia. Ever since I have been very fond of detachment faults and still wish I could have determined the timing of detachment. But as you stae say well, core complexes are complex.
Nice write up.

Silver Fox said...

Dan, you've got to stop killing detachment faults! ;)