Starship Asterisk*

dougettinger wrote:Some hot spots such as the Deccan traps are being associated with large meteorite impactors.

Where else can hot spots come from except from the Earth's core? Might there be another place ? Is there an astronomical relationship?

So here is my mystery of hot spots: I learned this fact in Ecuador just recently; Quito sits next to a subduction zone live volcano. Why do hotspot volcanoes consistently, spew out similar materials but are quite different from the materials that come from sub-duction zone volcanoes ?

And generally, the hotspot volcanoes, like the one in Hawaii, are not explosive like subduction zone volcanoes.

Let me add a confusing fact; hotspots are not stationary.

Chris Peterson wrote:If the theory of hotspots is correct (and it's got good supporting evidence), we are seeing mantle material (even deep mantle material) at the surface, whereas in subduction zones it's simply crustal material. So the fact that there are mineralogical differences should be expected.

The magma under subduction zone volcanoes is usually very hydrated, and also very viscous (because of a high silica content). As a result, it traps water and other volatiles, and this can produce explosive eruptions once it gets near the surface and the pressure drops. Low silica, unhydrated magmas are seen in deeper material, such as at mid-ocean ridges and hotspots. These have fewer volatiles, and what volatiles are present are unlikely to be trapped, so the material simply flows when it reaches the surface, typically forming shield volcanoes, sub-sea pillows, or basaltic floods like those of the Deccan Traps.

What does "stationary" even mean? Everything in and on the Earth is moving. In fact, hotspots are sometimes seen as being stationary with respect to the Earth's interior, and the crustal plates over them are treated as moving. It's all relative.

dougettinger wrote:The planet after its major accretion phase should have differentiated very quickly, within millions of years. The subduction zone volcanoes have a reason for volatiles and a higher proportion of silicates. Materials on the top of the diving divergent plates become scrapped off and collected under the subduction zones to be later released in volcanoes. What is the reason for volatiles, perhaps as much as 40 % of the erupted mass, being found in hotspot volcanoes ? Why did these volatiles not become squeezed upward from the mantle into forming the crust billions of years ago?

I don't like the current idea of plumes rising from the liquid core and rising through the present very dense and viscous mantle.

Chris Peterson wrote:

Doug Ettinger wrote:The planet after its major accretion phase should have differentiated very quickly, within millions of years. The subduction zone volcanoes have a reason for volatiles and a higher proportion of silicates. Materials on the top of the diving divergent plates become scrapped off and collected under the subduction zones to be later released in volcanoes. What is the reason for volatiles, perhaps as much as 40 % of the erupted mass, being found in hotspot volcanoes ? Why did these volatiles not become squeezed upward from the mantle into forming the crust billions of years ago?

The volatiles associated with subduction zone volcanoes are largely associated with water, which is usually dragged down into these zones in high amounts. Mantle volatiles are more complex. Why would you expect them to move upward or otherwise dissipate? They are dissolved in the mantle material, and are only released when the material ceases to be under high pressure. Volatiles are stable over large regions of the pressure-temperature phase space.

Doug Ettinger wrote:I don't like the current idea of plumes rising from the liquid core and rising through the present very dense and viscous mantle.

Chris Peterson wrote: Why don't you like it? In what way does it not describe what we observe? Or more specifically, in what way do our observations seem to argue against the idea of hotspots?

Chris Peterson wrote: I think that the collision that created the Moon probably heated up the Earth so much, and stirred things up so much that it essentially had to partially re-differentiate. We don't see the sort of isotopic differences between Earth and Moon rocks that we do between Earth rocks and meteorites. Certainly impactor material makes up parts of the core, mantle, and crust. But I've not seen anything to suggest that the behavior of the mantle or crust is tied to that impact. How would you test something like that?

A Los Alamos National Laboratory cosmic-ray observatory has seen for the first time two distinct hot spots that appear to be bombarding Earth with an excess of cosmic rays. The research calls into question nearly a century of understanding about galactic magnetic fields near our solar system.

Joining an international team of collaborators, Los Alamos researchers Brenda Dingus, Gus Sinnis, Gary Walker, Petra Hüntemeyer and John Pretz published the findings November 25 in Physical Review Letters.

“The source of cosmic rays has been a 100-year-old problem for astrophysicists,” Pretz said. “With the Milagro observatory, we identified two distinct regions with an excess of cosmic rays. These regions are relatively tiny bumps on the background of cosmic rays, which is why they were missed for so long. This discovery calls into question our understanding of cosmic rays and raises the possibility that an unknown source or magnetic effect near our solar system is responsible for these observations.”

Cosmic rays are high-energy particles that move through our Galaxy from sources far away. No one knows exactly where cosmic rays come from, but scientists theorize they might originate from supernovae—massive stars that explode— from quasars or perhaps from other exotic, less-understood or yet-to-be-discovered sources within the universe.

Researchers used Los Alamos’ Milagro cosmic-ray observatory to peer into the sky above the northern hemisphere for nearly seven years starting in July 2000. The observatory is unique in that it monitors the entire sky above the northern hemisphere. Because of its design and field of view, Milagro was able to record over 200 billion cosmic-ray collisions with the Earth’s atmosphere.

“Our observatory is unique in that we can detect events of low enough energies that we were able to record enough cosmic-ray encounters to see a statistically significant fractional excess coming from two distinct regions of the sky,” Dingus said.

Because cosmic rays are charged particles, magnetic fields from the Milky Way and our solar system change the flight paths of the particles so much that researchers had not been able to pinpoint their exact origin. Consequently, traditional wisdom has held that cosmic-ray events appear uniformly throughout the sky.

But because Milagro was able to record so many cosmic-ray events, researchers for the first time were able to see statistical peaks in the number of cosmic-ray events originating from specific regions of the sky near the constellation Orion. The region with the highest hot spot of cosmic rays is a concentrated bulls eye above and to the right visually of Orion, near the constellation Taurus. The other hot spot is a comma-shaped region visually occurring near the constellation Gemini.

The researchers created a graphic depiction of the hot spots that makes them appear as a pair of red cosmic rashes in a field of stars.

Milagro scientists are currently working with researchers in Mexico to build a second-generation observatory known as the High-Altitude Water Cherenkov (HAWC) experiment. If built, the HAWC observatory could help researchers solve the mystery of cosmic-ray origin.

In addition to the Los Alamos Milagro team, collaborators include nearly three dozen researchers from the following institutions: Naval Research Laboratory; University of California-Santa Cruz; University of Maryland; University of California-Irvine; George Mason University; New York University; Instituto de Astronomia, Universidad Nacionál Autonoma de Mexico; Michigan State University; NASA Goddard Space Flight Center; University of New Hampshire.

Funding for the research came from the U.S. Department of Energy’s Office of High-Energy Physics and Office of Nuclear Physics; Los Alamos National Laboratory’s Laboratory-Directed Research and Development fund and the Laboratory’s Institute for Geophysics and Planetary Physics; and the National Science Foundation.

dougettinger wrote:Thanks for your interesting discussion about cosmic ray hot spots which is completely new to me. However, the hot spots referred in this forum discussion are about hot spots that are created in the Earth's crust by some internal mechanism inside the Earth's mantle and/or core. These hot spots cause volcanic eruptions over long periods of time at random global locations such as Iceland and Yellowstone Park.

Chris Peterson wrote:

dougettinger wrote:Thanks for your interesting discussion about cosmic ray hot spots which is completely new to me. However, the hot spots referred in this forum discussion are about hot spots that are created in the Earth's crust by some internal mechanism inside the Earth's mantle and/or core. These hot spots cause volcanic eruptions over long periods of time at random global locations such as Iceland and Yellowstone Park.

The situation in Iceland is very different from the more mysterious hotspots you discussed. Iceland lies on the mid-Atlantic ridge. The reason for its volcanism is well understood.