Friday, November 21, 2014

Re: [Geology2] Small earthquake rattles west Alabama



Yes I just looked at a model and it underlies much of the central US and Canada.  Not syre how deep without reading up some more.  Interesting how a plate subducted what? 250 million years ago-- and still has some left over identity not absorbed into the mantle.  This is probably one of the slabs i mentioned the other day that retains some identity

 
From: "Kim Noyes kimnoyes@gmail.com [geology2]" <geology2@yahoogroups.com>
To: Geology2 <geology2@yahoogroups.com>
Sent: Friday, November 21, 2014 5:17 PM
Subject: Re: [Geology2] Small earthquake rattles west Alabama

 
Eman,

Where is the Farallon Plate relative to all of this? Deeper down in the mantle below the North American Plate?

Kimmer



On Fri, Nov 21, 2014 at 2:09 PM, MEM mstreman53@yahoo.com [geology2] <geology2@yahoogroups.com> wrote:
 
Eutaw, for which the Cretaceous marl formation is named, lies just off on the extended axis of the Appalachian Mountains where buried basins would be. Some researchers believe the Appalachians  took a "downwarp" and is an enigma how or why congenital crust would do so.  Some researchers using earthquake histories say they have tracked the orogeny all the way into Mexico as a syncline( downwarp).   

There is a pre-Cambrian formation of granite and gniess( 1.3 billion ybp) which takes a deep down slope to the west from where it surfaces along the Alabama/Georgia border around Columbus/ Phenix City.  It is hard to envision the interplay, as most geological research was directed at surface and mid depth oil and gas deposits.    Only recently was it announced that a huge batholith of igneous rock under Pennsylvania accounts for the kink in the Appalachians there in the edge of New England.

While this doesn't say much about the origin of the Eutaw quake, it is food for thought.  BTW many quakes at this depth are attributed to cavern collapse in limestone formations.

Eman






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Posted by: MEM <mstreman53@yahoo.com>



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