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Author Topic:   Exploring the Grand Canyon, from the bottom up.
Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 45 of 283 (295519)
03-15-2006 11:44 AM
Reply to: Message 43 by jar
03-15-2006 10:45 AM


Re: Can we head back towards the topic.
There was some rock forming event at some time in the past.

That rock was worn down into sand.

The sand was transformed in sandstone and then later into the
Vishnu Schist.

During the process there was a tectonic event and Zoroaster
Granite intruded into the Vishnu Schist.

Now there is no speculation in this summary so far that I can see.

You can almost say that was the order except for the last step. If I remember my geology correctly then a Schist is a metamorphic rock. Sedimentary rock can change into metamorphic rock in a number of way. It can buried and compressed due to the depth and heat at that depth or can be heated due to its proximity to a magma body. The latter is called contact metamorphism and there are some distinguishing characteristics for which I cannot recall at the moment. Rox or IRH might be able to help show us which it is.

Since this particular Shist is so close to the granite my first guess would be contact metamorphism which would change the order of events a bit.

1. Some silicate rock somewhere gets eroded into sand.
2. That sand is deposited which later becomes the Vishnu Sandstone.
3. A magma body intrudes into the sandstone causing contact metamorphism turning the sandstone into schist.
4. The magma never makes it to the surface and therefore cools as granite.

Certainly our resident geology experts may have a better explanation as to the type of metamorphism that created the Schist.

What is fun to note is that young or old the order of events does not change.


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 48 of 283 (295544)
03-15-2006 12:37 PM
Reply to: Message 47 by IrishRockhound
03-15-2006 12:27 PM


Re: Can we head back towards the topic.
But really there is also another scenario depending on the evidence where no contact metamorphism is necessary. The granite could have formed and been exposed before the sandstone was even deposited.

This case should be easy to identify though if there is an erosional unconformity between the granite and the schist. If there is then probably all the metamorphism is compressional.

So really the first question we have to ask is if the granite is an intrusion or not.


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 50 of 283 (295551)
03-15-2006 12:48 PM
Reply to: Message 49 by jar
03-15-2006 12:43 PM


Re: on the ordering
Unless, like I said in my most recent post, there is an erosional unconformity between the granite and the schist. The granite really has to be an intrustion for that scenario to work. This might have been cleared up before but I don't recall. Sorry if it has.


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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 Message 49 by jar, posted 03-15-2006 12:43 PM jar has responded

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Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 53 of 283 (295569)
03-15-2006 1:40 PM
Reply to: Message 52 by PaulK
03-15-2006 1:26 PM


Re: Can we head back towards the topic.
That is the evidence for an intrusion that we need. If there is a dike then there is no doubt. Then we are back to what IRH said which is that there was probably a combination of the types of metamorphism. We just may need someone to show us what to look for if this was the case.

I seem to recall someone mentioning the grade of the metamorphism and that part of the schist was more metamorphosed (is that even the right word?) than other parts. If that scales with distance from the granite then it seems like contact metamorphism is our most likely and probably sole canidate. This is just my armchar knowledge speaking though and I hope rox or IRH or someone else can confirm or correct.


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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 Message 54 by roxrkool, posted 03-15-2006 2:57 PM Jazzns has responded

  
Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 57 of 283 (295617)
03-15-2006 3:45 PM
Reply to: Message 54 by roxrkool
03-15-2006 2:57 PM


Re: Can we head back towards the topic.
Awesome! Thanks Rox!

the highest degree of alteration is typically located immediately adjacent to the intrusion (again especially if the rock is cold) and the alteration becomes progressively less pronounced the further away from the heat source we move.

I had just remember you posting something earlier about the difference is grade of the schist. I wasn't sure how far out the heat from a contact metamorphism scenario would go or it if was uniform. Sounds like it is not.

Thanks again for all the great info!


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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 Message 54 by roxrkool, posted 03-15-2006 2:57 PM roxrkool has not yet responded

  
Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 76 of 283 (295954)
03-16-2006 12:47 PM
Reply to: Message 75 by jar
03-16-2006 12:30 PM


Re: A few more questions before moving on to the Bass Limestone.
Q1. Rox or someone will have to answer that for certain.
Q2. I suppose the answer to that question would be that we can never know because erosion has destroyed that evidence. All we can say is that the sandstone came first and the instrusion after. How far they extened is unanswerable. For all we know there were a dozen other layers above the sandstone that the magma also intruded into that are now lost to erosion. (Acutually this might not be totally unknowable depending on the position of the schist and other layers that might not have been eroded somewhere else other than the GC. Just given this information alone it is unknowable.)
Q3. According to Rox's last post it sounds like the metamorphism and the melting of the granite happened sort of at the same time which sort of makes sense if some of the metamorphism is due to the magma. Rox had a good description of how some of the intrusions spread along the lines of deformation suggesting that they were all contemporaneous. The granite though may not have fully solidified until later. Granite in particular is a result of slow cooling.


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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 Message 75 by jar, posted 03-16-2006 12:30 PM jar has responded

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Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 119 of 283 (297096)
03-21-2006 4:09 PM
Reply to: Message 118 by jar
03-21-2006 1:39 PM


Re: Okay, trying a summary and see if we are ready to move on.
This means we see the land lowering to allow the sea in, and then later in the process gradually rising again to make the sea retreat.

I don't think this statement can be made definitivly. Sea level can rise by both the land dropping and more water being put into the oceans. Vice versa sea level can drop by the land raising or water being removed from the oceans. Most sea level changes (correct me rox or IHR or edge) that you see in transgression/regression sequences occur due to the cyclic nature of ice ages on earth. During an ice age more water is trapped in ice and sea level lowers. Of course this is just the mainstream view so if we are trying to be 'controversy' correct all we can say is that the water rose and fell in comparison to the land via EITHER the land or water raising or lowering.


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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 Message 118 by jar, posted 03-21-2006 1:39 PM jar has responded

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Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 123 of 283 (297108)
03-21-2006 5:23 PM
Reply to: Message 122 by jar
03-21-2006 5:05 PM


Re: Cause of sea level changes and marine transgressions onto land
I don't know if it was brought up or needs to be brought up but the description of the sea level changes takes in the existance of the specific layer we are talking about and its relationship to the other layers in the group. So the conclusion about the changes are more of a big picture type of concusion instead of something that you get just from looking at the Bass Limestone.

I know you spoke about how you wanted to just take it a layer at a time. Then you may want to just postpone any discussion of this until we finish this group since it relates to all the layers in this group not just the Bass.


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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 Message 122 by jar, posted 03-21-2006 5:05 PM jar has not yet responded

  
Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 213 of 283 (436784)
11-27-2007 3:09 PM
Reply to: Message 212 by jar
11-27-2007 2:20 PM


Re: Read it and Nankoweap
I guess I'm just old, but why does one formation end up sandstone, another shale or mudstone?

Its all about the size of the particles which relate to the energy, or lack thereof, which is transporting the particles.

It takes more energy to transport a particle of sand than it does a smaller particle of silt even if they are made from the same material. So up high in a mountain stream, water and wind will pick up sand and silt both and carry them away.

Near a beach though, the energy of the wind and water is much lower and so sand which makes it there goes no further, but silt can continue on.

Silt that makes it out into deeper and deeper water will eventually hit the point where there is little to no energy to keep in moving so it will settle out.

The different force of weathering energy at different geographic locations basically sorts material out over the course of its transport. One only needs to look at how energetic a mountain stream is compared to the mouth of any of the great rivers to see the effect.


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
This message is a reply to:
 Message 212 by jar, posted 11-27-2007 2:20 PM jar has responded

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Jazzns
Member (Idle past 2166 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 215 of 283 (436791)
11-27-2007 3:40 PM
Reply to: Message 214 by jar
11-27-2007 3:19 PM


Re: Read it and Nankoweap
From most to least active we would see:

1. sandstone
2. siltstone
3. shale
4. mudstone

I think that list looks right. I forget exactly which is smaller shale or mud.

There is some above sandstone though, IRH can help me with the exact correctness of this but it goes.

1. Breccia - Large and jagged pieces of rock mixed in with sizes of particles all the way down to silt sized. (there is nothing preventing smaller particles from sticking around with bigger ones)
2. Conglomerate - Large pieces of rock that are rounded off usually indicating that they were transported at least a little bit.
3. Sandstone
4. Siltstone
5. Shale
6. Mudstone


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
This message is a reply to:
 Message 214 by jar, posted 11-27-2007 3:19 PM jar has responded

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