<p>I am trying to get into early-Earth geochemistry, and the cratons piqued my interest. They would need a very specific density to float, and the right heat resistance to not melt. What composition would the early cratons have?</p>

CC BY-SA 3.0
2016-04-24T07:54:14.437Z
Archean cratons are dominated by TTG: tonalite-trondhjemite-granodiorite rock suites. When you say that they need a very specific density to float, what should they float on? The mantle? Magma? Please clarify. Also, why would they melt? What range of temperatures are you suggesting they experienced, and what is the range they should melt at?
Gimelist
CC BY-SA 3.0
2016-04-24T09:38:27.237Z
I am very new to this, so actual numbers are beyond me. But as I understand it, the initial cratons formed in planet-wide lava, because they A: Were light enough to float to the (cooler) surface, and B: where hardy enough to not melt in the temperatures that reigned (whatever they were; I have not gotten that far yet). The details are actually what I am trying to unravel, sloooowly...
Henry Stone
CC BY-SA 3.0
2016-04-24T09:47:37.103Z
Answeing that would be extremely long and hard. Giving you the necessary background is more than the scope of an answer here. I recommend that you read some of these links: [one](https://en.wikipedia.org/wiki/History_of_Earth#First_continents) [two](https://www.reddit.com/r/geology/comments/2oselk/question_how_were_cratons_formed/) [three-(technical)](http://www.currentscience.ac.in/Volumes/104/07/0871.pdf) [four](http://all-geo.org/metageologist/2012/12/cratons-old-and-strong/). Other than that, I vote to close this question as too broad. Maybe post a more specific question when you have one?
Gimelist
CC BY-SA 3.0
2016-04-24T09:50:21.183Z
Well, your TTG answer essentially answered my question, but I am opening the links you provided right now. I have no idea how to mark a comment as a correct answer, though.
Henry Stone
CC BY-SA 3.0
2016-04-24T09:51:26.857Z
You can't, because it's a comment, not an answer :) Anyway, have a read. I'm pretty sure you will end up having more questions, but ones that can be answered relatively easy. I'll be more than happy to help you once you get there!
Gimelist
<geochemistry><earth-history>
What composition would the early cratons have?
Henry Stone
# What composition would the early cratons have?

(Asked by: username_0 on 2016-04-23)

I am trying to get into early-Earth geochemistry, and the cratons piqued my interest. They would need a very specific density to float, and the right heat resistance to not melt. What composition would the early cratons have?

**Tags:** geochemistry, earth-history

> **Comments:**
> **username_1**: Archean cratons are dominated by TTG: tonalite-trondhjemite-granodiorite rock suites. When you say that they need a very specific density to float, what should they float on? The mantle? Magma? Please clarify. Also, why would they melt? What range of temperatures are you suggesting they experienced, and what is the range they should melt at?  
> **username_0**: I am very new to this, so actual numbers are beyond me. But as I understand it, the initial cratons formed in planet-wide lava, because they A: Were light enough to float to the (cooler) surface, and B: where hardy enough to not melt in the temperatures that reigned (whatever they were; I have not gotten that far yet). The details are actually what I am trying to unravel, sloooowly...  
> **username_1**: Answeing that would be extremely long and hard. Giving you the necessary background is more than the scope of an answer here. I recommend that you read some of these links: [one](https://en.wikipedia.org/wiki/History_of_Earth#First_continents) [two](https://www.reddit.com/r/geology/comments/2oselk/question_how_were_cratons_formed/) [three-(technical)](http://www.currentscience.ac.in/Volumes/104/07/0871.pdf) [four](http://all-geo.org/metageologist/2012/12/cratons-old-and-strong/). Other than that, I vote to close this question as too broad. Maybe post a more specific question when you have one?  
> **username_0**: Well, your TTG answer essentially answered my question, but I am opening the links you provided right now. I have no idea how to mark a comment as a correct answer, though.  
> **username_1**: You can't, because it's a comment, not an answer :) Anyway, have a read. I'm pretty sure you will end up having more questions, but ones that can be answered relatively easy. I'll be more than happy to help you once you get there!  

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