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 Post subject: cause of magma
PostPosted: Mon Aug 13, 2007 7:40 am 
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whilst travelling around new zealand a few years back,i paid a visit to a museum in wellington & in the geology section i was very interested to read that nobody was sure what causes magma,but it is thought that is produced by the gravitational pull on iron deposits in the earth,causing friction & heat,thus causing the magma.
is the formation of magma which gives birth to our precious gems & minerals really a mystery?i'm thinking nobody can ever know?
do i need to get out more? :^o :smt002

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PostPosted: Mon Aug 13, 2007 10:52 am 
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Interesting....I never really thought it was a mystery, unless there has been some new evidence in the last few years that discounts the former theories.

We have found, as evidenced in drill holes, that the temperature increases about 1 degree Fahrenheit for every 60 feet in depth. If this increase was consistent to the center of the earth, the temperature at the core would be 100,000 degree Celcius.

It is universally agreed, that the earth's core is not that hot so it has been hypothesized that the temperature increase slows with depth. I have heard estimates of core temperature vary from 3000 to 7000 degrees Celcius.

These estimates are derived from theoretical modeling and laboratory experiments. Of course, the results are speculative, but they would certainly explain the existence of molten rock and magma.


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PostPosted: Mon Aug 13, 2007 12:04 pm 
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I've been reading on that topic recently. Current theory relates continental magma creation to the subduction of oceanic tectonic plates under continental plates. Tremendous force and friction is created in the collision and pockets of fiery magma expand toward the surface. The volcanic Ring of Fire around the Pacific Ocean is an expression of that process.

The eruption of Mt. St. Helen's in the U.S. was a recent example. It's merely one of a large number of active volcanos extending down our West Coast, from Washington's Mt. Rainier to the beautiful but ominous Long Valley Caldera here in California. Last week's earthquake near L.A. was a little reminder that the plates are always on the move.

Most of the very rich gem deposits from Burma to China resulted from magma created when the Indian subcontinent smacked forcefully into the Asian plate and raised the Himalayas. That process continues today, with the mountains gaining an inch or two in altitude a year.

Another important factor contributing to subterranean heat is energy released by the slow decay of radioactive elements in the earth's crust.

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PostPosted: Mon Aug 13, 2007 7:08 pm 
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It seems to me that taking the rocks to depth has more of an effect on melting than friction....Think about it, if friction were the primary cause you would have melt zones on fault planes, as a fault moves at much higher speed than a plate being sbducted.


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PostPosted: Mon Aug 13, 2007 8:53 pm 
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Sorry if I conveyed the idea that magma production is entirely due to friction. I thought I mentioned heat at depth from radioactive decay of elements like uranium, potassium and thorium, which combines with pressure and the tremendous forces of plate subduction to generate magma under continental plate margins.

Disclaimer: I'm not a geologist and I didn't stay at a Holiday Inn Suites last night.

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 Post subject: boiling hot magma muhhahahahahah
PostPosted: Mon Aug 13, 2007 9:02 pm 
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It seems that a combination of the 'geothermal gradient' i.e the rise in temperature for every km in depth and 'radioactive decay' will cause sufficient heat to form magma.

Also pressure can cause melting by compression or the opposite 'decompression melting' where melting rock eventually gives way to the immense pressure and releases its magma usually vertically through fault lines or weak spots in the overlying rock,with a bouyant effect as it is less dense than the rock its travelling through,this can cause further formation of magma.

The various compositions of the effected strata will determine the rates and temperatures of the resulting magma formation.

Crystalline rock will have formed from aqueous solution or from molten magma. the form of crystallization depends primarily on the conditions under which they solidified.i.e slow cool quick cool high/low pressure etc.

There we are now,my mini thesis on magma :wink: whaddya think!!


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PostPosted: Mon Aug 13, 2007 11:14 pm 
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Yes, quite impressive...
I would still love to know who might have thought that magma is a mystery...Dingtong, is there something about your conversation in New Zealand that we're just not understanding?


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PostPosted: Thu Aug 16, 2007 5:20 pm 
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If you have enough mass, you can get a little fusion going on. Just ask the sun. I go with the depth/mass theory.

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PostPosted: Thu Aug 23, 2007 10:09 am 
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i may have the attention span of a gnat in museums,& only read what i find interesting. :D
i found this at wikipedia under geothermal;

sources (heat)

1.Much of the heat is believed to be created by decay of naturally radioactive elements. An estimated 45 to 85 percent of the heat escaping from the Earth originates from radioactive decay of elements concentrated in the crust.
2.Heat of impact and compression released during the original formation of the Earth by accretion of in-falling meteorites.
3.Heat released from the sinking of abundant heavy metals (iron, nickel, copper) as they descended to form the Earth's core.
4.Some heat may be created by electromagnetic effects of the magnetic fields involved in Earth's magnetic field.
5.Heat generated within the Earth's core may be in the range of 4–10 TW.]
6.Heat may be generated by tidal force on the Earth as it rotates, since land cannot flow like water it compress and distorts, generating heat.

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PostPosted: Thu Aug 23, 2007 10:13 am 
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So, I guess we've cleared up this mystery and we can all agree we understand why magma exists. :D


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