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Minerals

Social climber
The Deli
Jul 11, 2012 - 04:52pm PT

“Fe3O4”




Magnetite sand concentration derived from the weathering of Cathedral Peak Granodiorite, seen at the high-water mark along the Tuolumne River, just west of Tuolumne Meadow, summer solstice, 2010. Yes, you can pick it up with a magnet.

Minerals

Social climber
The Deli
Oct 2, 2012 - 07:58pm PT
Going for the Moho…

http://www.cnn.com/2012/10/01/tech/mantle-earth-drill-mission/index.html?hpt=hp_c1



(CNN) -- Humans have reached the moon and are planning to return samples from Mars, but when it comes to exploring the land deep beneath our feet, we have only scratched the surface of our planet.

This may be about to change with a $1 billion mission to drill 6 km (3.7 miles) beneath the seafloor to reach the Earth's mantle -- a 3000 km-thick layer of slowly deforming rock between the crust and the core which makes up the majority of our planet -- and bring back the first ever fresh samples.

It could help answer some of our biggest questions about the origins and evolution of Earth itself, with almost all of the sea floor and continents that make up the Earth´s surface originating from the mantle.

Geologists involved in the project are already comparing it to the Apollo Moon missions in terms of the value of the samples it could yield.

However, in order to reach those samples, the team of international scientists must first find a way to grind their way through ultra-hard rocks with 10 km-long (6.2 miles) drill pipes -- a technical challenge that one of the project co-leaders Damon Teagle, from the UK's University of Southampton calls, "the most challenging endeavor in the history of Earth science."

Their task will be all the more difficult for being conducted out in the middle of the ocean. It is here that the Earth´s crust is at its thinnest at around 6 km compared to as much as 60 km (37.3 miles) on land.

They have already identified three possible locations -- all in the Pacific Ocean -- where the ocean floor was formed at relatively fast spreading mid-ocean ridges, says Teagle.

The hole they will drill will be just 30 cm in width all the way from the ocean floor to inside the mantle -- a monumental engineering feat.

"It will be the equivalent of dangling a steel string the width of a human hair in the deep end of a swimming pool and inserting it into a thimble 1/10 mm wide on the bottom, and then drilling a few meters into the foundations," says Teagle.

To get to the mantle scientists will be relying on a purpose-built Japanese deep-sea drilling vessel called Chikyu, first launched in 2002 and capable of carrying 10 km of drilling pipes. It has already set a world-record for the deepest hole in scientific ocean drilling history, reaching 2.2 km into the seafloor.

What makes the task even more difficult is that, currently, the drill bits have a limited lifespan of between 50-60 hours before needing to be replaced, meaning drilling could take many years unless technology improves.

The first attempts to reach the Earth's mantle actually began back in the early 1960s. Dubbed "Project Mohole" after the Croatian meteorologist Andrija Mohorovicic who first discovered the boundary between the Earth's crust and mantle, a team of U.S. scientists managed to drill a few meters into the oceanic crust off Guadalupe Island in the eastern pacific. The achievement was recognized by a telegram from President John F. Kennedy but the project was closed down in 1966.

Since then, a Russian-project in the far north Kola Peninsula during the 1980s has taken over the record for the deepest borehole ever drilled, reaching 12 km into the earth's crust.

And In 2011, the oil giant Exxon Mobil recorded an even longer borehole at just over 12 km in eastern Russia. However, it wasn't drilled vertically downwards and only reached soft sedimentary rocks.

While neither of these record-drilling projects got close to the Earth's mantle, they did give the geologists leading the new project -- The Integrated Ocean Drilling Program (IODP) -- confidence that recent advances in drilling techniques have made their plans more feasible than ever before.

"Many of the technologies required are conventional deep-drilling technologies that are presently being used in the oil and gas industry," explain IODP geologists.

However, given the challenges and the likely cost of $1 billion plus, much of which still needs to be raised, skeptics may question the necessity of the mission.

For Teagle, reaching the Earth's mantle would provide a "legacy of fundamental scientific knowledge" and "inspire" future generations.

"I was giving a lecture to a group of 15-year-old high-school students recently and they [and their teachers] were fascinated by the technology and the thought that we could re-enter a hole just a few centimeters across with a drill string dangled from a ship in the open ocean 4 km above."

As well as the technical achievement of bringing back samples, the samples themselves will clarify many of the assumptions we have about how our planet works. Despite making up 68% of the Earth´s mass, Teagle says we only have a "reasonable" idea of what the mantle is made of and how it works.

"[The mantle] is the engine that drives how our planet works and why we have earthquakes and volcanoes and continents. We have the textbook cartoons but detailed knowledge is lacking," he says.

The Japanese government has already invested substantially in the project through the construction of Chikyu, with some scientists regarding the mission as the country's "moon project."

If Japanese support can be combined with other funding, Teagle says they could start drilling before the end of the decade, making it possible for humans to finally reach the Earth's mantle by the early 2020s.

BASE104

Social climber
An Oil Field
Oct 2, 2012 - 10:00pm PT
Minerals,

When I got my B.S., the last class you take is field geology, which in our case was at the OU Field Camp near Canon City, CO.

A lot of it was mapping structure and stratigraphy of sedimentary rocks, but we had a week of geophysics. This included doing gravity and magnetic surveys.

Well, we had worked an igneous area a couple of weeks before, and it had huge chunks of magnetite. I must have saved twenty pounds of the stuff. We had to divide up into small teams to use the magnetometer and gravity meter. My group of four was up second on the magnetic survey, which passed over a complicated ultramafic system.

I got the bright idea of tossing out about five pounds of magnetite at a couple of the mag survey flags that everyone took their readings at. Nobody caught on, but the area had been surveyed over and over each year and the prof knew the numbers. So 9/10 of the class had wild readings at two stations.

Nobody caught on. It just looks like a dark cobble, and that fit in well with the crap laying around.....

I was a little turd.

Also, that black crystal included into quartz above is 99% probability of tourmaline. I've seen the exact same stuff several times. Most tourmaline is not only not gem quality, it will fall apart in yer hands.
mechrist

Gym climber
South of Heaven
Apr 4, 2013 - 01:05pm PT
Interesting (but shallow) article about a study of the (deep) structure under CA

http://www.nature.com/news/how-the-west-was-built-1.12724
john hansen

climber
Apr 4, 2013 - 01:42pm PT
TT, this is probably out there but could that cylindrical hole be caused by a "tree mold"?

If a mud flow solidified around a tree stump and the stump eventually rots away.

They are fairly common when lava flows surround tree trunks. Could happen the same with a mud / slurry flow.
mechrist

Gym climber
South of Heaven
Apr 4, 2013 - 01:46pm PT
^ I'd say that is a good possibility, especially given the nature of the deposit. But I've seen similar things in grainite (not quite as long), which were clearly not formed by trees.
mechrist

Gym climber
South of Heaven
Oct 17, 2013 - 01:25pm PT
Man, searching soopertaco is a pain in the ass!

Probably a better thread for this, but I ain't spending the time to find it.

If you ever get a chance to play in the 3D simulator, you should. It is a blast.

http://www.isgtw.org/feature/3d-tectonic-modeling-answers-age-old-geology-question
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Oct 17, 2013 - 02:06pm PT
"Flat subduction" of the Farallon Plate is also evoked to explain mountain building during the Laramide Orogeny in the Rocky Mountains at the end of the Cretaceous.

http://1.bp.blogspot.com/-J2oEQPJQcVc/TlDdBjXBXdI/AAAAAAAAAc0/R9gVPko1Ct4/s1600/Farallon+subduction.jpg

http://www.gps.caltech.edu/~gurnis/Papers/2010_Liu_etal_NatureGeosci.pdf

john hansen: that's the best explanation I've heard so far. We find a lot of wood, including whole tree trunks, in the Neroly Fm that are petrified.

Here's one for Minerals..."cross bedding" in granite. Photo taken near Tenaya Lake.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Oct 17, 2013 - 03:00pm PT
My impression of the Basin & Range is a large-scale thermal dome extending from the Owens Valley to the Rocky Mts and underlain by a still active subducted oceanic ridge and melting Farallon Plate. Many of the regional extensional faults are reactivated thrust faults.

However, the complexity of B&R geology at the outcrop to 7.5 min quad scale can be overwhelming and has lead many geologists to drink.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Oct 17, 2013 - 04:04pm PT
not sure what the problem is...seems pretty straight forward ;-)

Grapevine Mts

Titus Cyn
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