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View Diary: BREAKING: Meteor airburst over Chelyabinsk (318 comments)

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  •  The answer lies in asteroid formation itself. (1+ / 0-)
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    Just Bob

    Asteroids (except for the handful of largest, like Ceres and Vesta) don't have enough gravity to have differentiated interiors - i.e., the different elements don't separate out, and there's no erosive process that would evenly distribute them either, so they occur in heterogeneous blobs throughout the interior.  Not blobs of one pure substance, obviously, but highly enriched ones.  When they impact, lighter material is mostly blasted away while the heavier material is mostly deposited.  

    Over time the crust where the impact occurred moves and fragments, and once parts of it get uplifted into mountains, the continental crust is eroded and exposes the veins of precious metal.  This also means pieces of it can wash downstream, but as the history of any gold rush will tell you, finding gold in a river means the main strike is somewhere up in the mountains closer to the river's source.  It's not that there's more gold to be found in mountains than flat land - it's just where the material is more likely to have been exposed by erosive processes.

    So that's why these metals occur in heterogeneous blobs on Earth: Because they occur in heterogeneous blobs in the asteroids that deliver them.

    Pour yourself into the future.

    by Troubadour on Fri Feb 15, 2013 at 06:41:10 PM PST

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    •  More meteorites strike the oceans than on land (1+ / 0-)
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      Troubadour

      Of course any fragments are buried under miles of ocean sediment and isolated from chemical reactions and transport other than upthrusts.

      There are sea shells found on Sandia Crest at an elevation of 10,700 feet. That implies exposure to weathering, transport, and concentration. Of course that area has also had huge lava flows from time to time.

      http://vulcan.wr.usgs.gov/...

      It seems that each of the Southwestern states has an apparent geologic specialty. If so, and Arizona is the big Canyon state, Utah is the Mesozoic fauna state, and Colorado is the big snow-capped Rocky Mountains state, then what is New Mexico? New Mexicans need only look out their windows for the answer: New Mexico is the Volcano state. New Mexico has one of the greatest concentrations of young, well-exposed, and uneroded volcanoes on the continent. And as a bonus, it is also the Rift Valley state; it has one of only four or five big continental rifts in the world, East Africa being one of the other ones. The fact is, New Mexico is one of the best places to study the natural history of volcanoes. Twenty percent of the U.S. National Parks and Monuments based on volcanic themes are in New Mexico. There are more here than Arizona, Idaho, Oregon, and Washington combined.

      Volcanism in New Mexico is not "extinct," but is dormant. The record of volcanism in New Mexico is continuous over tens of millions of years, and there is no reason to think it stopped magically 3000 years ago with the eruption of several cubic kilometers of basalt (McCartys lava flow, El Malpais). New Mexico has one of only three large mid-crustal active magma bodies (Socorro) in the continent. (The others are Long Valley, California and Yellowstone, Wyoming.) The Socorro area is one of the few areas where there is a dearth of young volcanoes, so perhaps the Rift is working on filling out its volcano landscaping.

      Every major type of volcanic landform (composite volcano, shield volcano, volcanic caldera, major ash-flows, pahoehoe and aa lava, maar crater, fissure eruptions, cinder cones) occurs in New Mexico.

      "There's gold in them thar hills!"

      http://geoinfo.nmt.edu/...

      Our staff have prepared a free packet of information about gold panning in New Mexico (in PDF format 5.14 Mb). It includes a brief history of gold mining in NM, where to look, what equipment is required, what regulations apply and who to contact, and an extensive reference list.

      Others have simply gotten old. I prefer to think I've been tempered by time.

      by Just Bob on Fri Feb 15, 2013 at 06:59:26 PM PST

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