Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: OokieWonderslug on 20/05/2011 03:55:28
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I recently went to Morrow Mtn state park and while I was there I noticed that the signs on the top of the mountain have been changed. They used to say that Morrow Mtn was a volcano 500,000,000 years ago. Now it says that it was a blob of magma that never reached the surface 400,000,000 years ago.
That begs the question. Where are the volcanoes? The sediments of the Carolina Slate belt are volcanic ash, mud, clay, and pyroclastic flow remnants. This means there had to be volcanoes. When I was younger and did not know any geology I thought that Crowder's Mtn, Pilot Mtn, and Morrow Mtn were all the remains of volcanoes. I have since learned that none of them are.
They had to be here, or the sediments would not be what they are. Having read over and over that approx 5 miles of sediment has been eroded away from the area, wouldn't that leave a magma pipe sticking out somewhere as a mountain? Wouldn't there at least be a mountain that was just a rubble pile of basalt? If there had been a miles long pipe of magma going to what was the surface at one time wouldn't it leave a trace? I imagine a huge pile of broken igneous rocks.
Or were the volcanoes on a lower level than the ground is at now and are still buried? How would the ash be here and the source be at a lower level? There are numerous plutons in the area that never made it to the surface. Why isn't there evidence of where they did make it to the surface?
Logically there should be at least one column of igneous material jutting up from the piedmont. Basalt does not erode as quickly as metamorphosed ash. Or clay.
There were never glaciers here to "wipe away" the bases of the volcanoes. They seem to be missing from the landscape. Why?
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The Carolina Slate Belt is highly deformed, highly metamorphosed, and highly eroded. The ash and pyoclastics came from higher level volcanoes that have long since been eroded away. The granites and diorites you refer to may be remnant "roots" of these volcanoes. "May" because some of these were intruded later or were intruded as plutons that never had a surface expression as a volcano.
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Reading about the geology of the Appalachian Mountains, there seem to be multiple phases.
http://en.wikipedia.org/wiki/Appalachian_Mountains#Geology
Early volcanoes.
Followed by erosion.
Followed by upheaval.
So the peaks you are seeing today were likely caused by upheavals, rather than the original volcanoes.
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The Carolina Slate Belt is highly deformed, highly metamorphosed, and highly eroded. The ash and pyoclastics came from higher level volcanoes that have long since been eroded away. The granites and diorites you refer to may be remnant "roots" of these volcanoes. "May" because some of these were intruded later or were intruded as plutons that never had a surface expression as a volcano.
After much thought and research on this subject, I think I found the volcanoes. Your answer is impossible. You can't have ash deposits below where the volcano that created them is to any extent. Sure, flows go downhill, but the lava plug would still be lower than any deposits.
While searching for the African counterpart to the Appalachian mountains I found evidence of the lava plugs that woulds HAVE to remain after depositing such an enormous amount of ash. One of the most likely spots is: 22 34 46 07N by 14 17 15 76W. I would have expected the volcanoes to have remained closer, but didn't take into account the possibility that Avalonia split in half when the Atlantic was created. Which it apparently did and took the volcanoes with it.
Couldn't find the remnant African Appalachians though. Not where they should be at least.
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One of the hardest things in geology is to understand the timescales and the changes that we belive have occurred over hundreds of millions of years.
The second hardest thing is visualising processes that occurred over geological timescales.
The third hardest thing is understanding dating techniques and in particular their drawbacks and shortcomings - paticularly in relation to heavily metamorphosed rocks where the "clocks" may have been reset and where techniques have improved, leaving some dating suspect.
A lot of the evidence and sources of rock have simply been erased or is under other rocks.
If you are interested in the Caledonian - Appalacian Orogeny I would recomend tracking down
http://sp.lyellcollection.org/content/38/1/local/front-matter.pdf
from a library.