Thank you so much, Eman... you've answered my question and more. If my thoughts are forming in the right direction, the Sabine uplift also helped to create the Ouachita Mtns. in OK/AR. For all you non-southerners, that's pronounced as Wah-shuh-taw.
Again, thanks for the info.
Lin
PS Did you know at one time that Hicks Dome was thought to have formed via a bolide impact? I've been all around the area and I tried to figure out how a large convex structure could ever be considered as such.
On Wed, Apr 23, 2014 at 12:48 AM, MEM <mstreman53@yahoo.com> wrote:
The Jackson MS paleo-volcano is problematic but probably has been best explained by a process of snapback/tension relaxation related to the same process that formed the Sabine uplift of East Texas( 85mybp)--mainly through exclusion of other explanations, even it it was a 100million year loop from rift to eruption.
The Triassic Rift 190mybp left several smaller plates between the North and South America plates that had weighed down the new shelf margins. As the last tensions on the Gulf of Mexico's opening were unloaded, continental crust which had been thinnned and stretched snapped back (on geological time-scales where the crust had thinned during the failed rift related to the New Madrid (Failed Rift ) Seismic Zone and Missippi River Embayment. This could have been like squeezing a pimple where magma was slowly pooling but then squeezed to the surface.
Others include:
Chicxulub triggered but the Jackson Volcano was active 10-20my before that impact. Remember Chicxulub was a lot closer to Mississippi 65mybp but can't resolve the ages and an asteroid can't cause a volcano 20million years before it hits.
Passage over the Bermuda Hot Spot. From Kansas to Bermuda along the 38th parallel which, funny you should mention, is probably the cause for Hicks Dome. The Bermuda hotspot is an "intermittent" (for lack of a better word), eruptive hotspot which probably expended a lot of magma under the continental crust as the North American plate passed westward over it. I have seen formations called "pillow and column" which were attributed to strong seismic shaking. I was told that this was believed to be due to the passing of the Bermuda hotspot. A good theory is that in Permian, when Pangaea came together, the mantle was "overcrowed" with slabs being forced into it. On geological speeds the reaction was to squeeze up a plume. The area of the Bermuda plume was the weakest spot/link, so magma began seeping upwards only to meet thick continental crust --Otherwise we'd have more volcanoes in Tennessee. Incidentally, while the name escapes me, I believe there is a subducted slab of unknown origin ( Central California mini slab suture sequence?) which lies partially absorbed underneath the eastern US and may have something to do with the Yellowstone plume as well but the combined thickness of the mantle and crust is bulged under us. Couple that with the yet rebounding crust from the roots of the older Appalachains, the crust under the Eastern US is thicker than normal and the door of volcanic opportunity was and is closed for another100my.
On Tuesday, April 22, 2014 9:38 PM, Lin Kerns <linkerns@gmail.com> wrote:
Here's some of the fossils I've collected from the Coon Creek formation and the surrounding area:
http://1roxxfoxx.blogspot.com/2012/04/adventures-in-fossils-part-1.html
Eman...I have a question. Is the extinct volcano sitting beneath the coliseum in Jackson, MS related to this suture?
Thanks!LinOn Tue, Apr 22, 2014 at 8:33 PM, Allison Maricelli-Loukanis <allison.ann@att.net> wrote:
Really interesting.. I would love to go and sit on that gorgeous coast. Allison
From: MEM <mstreman53@yahoo.com>
To: "geology2@yahoogroups.com" <geology2@yahoogroups.com>
Sent: Tuesday, April 22, 2014 6:12 PM
Subject: Re: [Geology2] Piece of Africa Found Under Alabama
In case any list members are planing a field trip to the South East--As to Georgia And Alabama geology which gave rise to the geography: this is why there is volcanic-derived soil on the South Georgia plane that make onions from Vidallia so sweet.
It also accounts for the kaolin belt between Columbus and Macon where the basement rock was uplifted to the surface and hydro- theromal broke them down into constituent parts and then sorted them into layers.( Collecting vic Butler, GA) The water saturated clays are plastic/buoyant and squeeze up into the red New Providence Formation. They behave somewhat like the salt of salt domes in Louisiana and Texas. See New Providence State Park aka The Grand Canyon of Georgia.
These heated waters also broke down the graniteoid bedrock vic La Grange Georgia ( GA/AL stateline) where at the Hogg Mine( fee dig) literal boulders of gemy rose quartz formed as micro-needles of plagioclase feldspar were carried along with the rock quartz by that process. To the west of La Grange but to the east of Talladega AL is a large deposit of black tourmaline/schorl in quartz. Mapquest "Tourmaline Road" and you are there -lol.
This suture generally follows what is known as the "fall line" which is a string of "rapids" from Columbus to Athens and gave rise to the industry/mills in those towns along its transition of resistant basement --now surface rocks onto the sedimentary clays, marls, and chalks which make up mid southern Georgia. (Columbus, Macon, Athens and others were important heavy industry towns during the Civil War owing to the natural hydro-power the falls offered).
The Ripley formation of "Coon Creek fame" is one of those marls. Lynn lives a top some of its exposures, this formtion covers much of the area below the fall line and curves all the way up through East Memphis and into Missouri--perhaps into Iowa. Very few of the out-wash sediments in this area lithofied( turned to rock) so fossil collecting is easier than most other places. And those fossils are preserved in great detail. Follow gullies and runoffs aside the roads. I have shells from the Ripley and Ewtoh formations that have hair thin spines still intact. Shark and skate teeth are common.
I would be remiss to not mention Wetumpka Crater where an asteroid 81-81 mybp formed a 4-5 mile wide crater. And in Beckly and Dodge Counties east of Macon are where Georgia tektites have been found (although rarely and not in recent years). These are splatter forms from the Chesapeake Astrobleme 34mybp. Graves Mountain south east of Atlanta is likely related to the suture and is open to organized clubs/collecting groups several times a year.
While the soils from the volcanic island arc remain in south Georgia--forming as the Africa plated closed in on the NA plate in the Permian( 250mybp), there is strangely no evidence of basalt flows filling the gap during the rift at the beginning of the Triassic( 190mybp) like we see outside New York City and Paterson NJ. Perhaps these beds if they exist are deeply buried by Cretaceous and earlier sediments Above the fall line the rocks are 1.2-1.3 billion years old. Walk down stream a few feet and the rocks(sic) are 82-68 million years old. 3 miles further and they are post-cretaceous. 60-40Mybp.
Much of the soil below the suture is very, very, sandy so if in Americus, stop in and see Jimmy Carter's peanut farm or if you are headed to the Froggy Bottom-- Ripley collecting area, Westville in Lumpkin Georgia is a working 1840's town where you can help wash kaolin clays for the pottery works.
If you've read this far most of these exposures/sites/formations can be visited over a 3 day trip. So pack your collection bags--rock hammer optional.
EmanOn Tuesday, April 22, 2014 6:22 PM, Lin Kerns <linkerns@gmail.com> wrote:
A scene from Alabama's Gulf Coast.Piece of Africa Found Under Alabama
Apr 22, 2014 // by Larry O'HanlonGeoscientists have identified a chunk of Africa stuck onto the southeastern United States.A long mysterious zone of unusual magnetism that stretches from Alabama through Georgia and offshore to the North Carolina coast appears to be the suture between ancient rocks that formed when parts of Africa and North America were pressed together 250 million years ago. If so, Africa could have left a lot more behind in the American southeast when the conjoined continents rifted apart and formed the Atlantic Ocean."There are some large faults in the magnetic data," said geologist Robert Hatcher of the University of Tennessee in Knoxville, regarding what is called the Brunswick Magnetic Anomaly and other magnetic features in the region. "They have not been active for a very long time. They are strike-slip faults like the San Andreas today. But there's also younger fall with opposite direction."
Play Video
On a recent dinosaur dig Kasey-Dee Gardner noticed that fossils not only come in all shapes and sizes, but also in all different colors.The faults appear to be the remains of the collision and then messy divorce of Africa and North America."There was an attempt to rip away Florida and southern Georgia," said Hatcher. "So you have a failed rift there. We know there's a suture there between African crust and newer crust from the Appalachians. There are pieces of crust that started in Africa."A rift is what happens when the crust is pulled apart. When that happened 200 million years ago, 50 million years after African and North America collided, it appears to have started near the old collision zone, but then shifted to weaker crust to the east.That rift zone split open and caused volcanic eruptions which created new oceanic crust -- what is today the crust of the Earth under the Atlantic Ocean. The rifting continues today at what's called the Mid-Atlantic Ridge."The age of the suture zone is believed to be about 250 million years old, but that's not very well constrained," said geologist Elias Parker, Jr., of the University of Georgia in Athens. He published a paper reviewing what's known about the Brunswick Magnetic Anomaly in the latest issue of GSA Today.The big challenge in sorting out the history of the southeast U.S. is that there are intriguing magnetic signals, as well as gravimetric measurements, but there is not enough deep borehole studies or seismic data to confirm the faults and the proposed scenarios."There are deeper faults and more shallow features," said Parker. "It makes the interpretation really challenging."Among the seismic projects that could help increase the resolution of the structures, said Parker, is the Southeastern Suture of the Appalachian Margin Experiment (SESAME) and the Suwanee Suture and Georgia Rift Basin Experiment."This is just the start to understanding the structure of the southeast U.S.," said Parker. "What I'm trying to do is come up with a simple explanation for this."
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There were a lot more asteroid strikes in the Cretaceous than just Chicxulub and so far as I am aware no volcanism has been linked to any of them. Wetumpka would have hit along to time of Jackson's emergence and is the closest geographically but still not matched geologically.
Of passing note: the Cave in the Wall complex was abandoned and allowed to totally fill with water, sad to say. However, a part of that fluor-spar district lies in Marion County KY where the Columbia Mine is located. They have night digs several times a year. If you can't make Franklin NJ, I hear Marion County is a pretty good substitute.
Eman
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