pichi
 
Reply Wed 17 Jan, 2018 04:02 pm
One more from me.
Here is a representative sample in thin section:
https://drive.google.com/file/d/1cqqDRmcV7hAfUG1IPinUaiZvq4UaoKnV/view?usp=sharing

https://drive.google.com/file/d/1kFCI3sjD2k2c9Kd3qV1kqsTv5cGCg3FM/view?usp=sharing

Here is a video of the rock in thin section:
https://drive.google.com/open?id=1-FiW0JUarPNdfIjxRqDQtGn1LMvSWUDH

The texture reminds me of a basalt (elongated plagioclase), but it seems that a large part of them have been replaced by sericite like in this video:

https://drive.google.com/open?id=130mC00E4LyhHgG2KuUljWOE-AMxhfGdf

Furthermore, the presence of stilpnomelane reinforces the idea of a metamorphic rock. But... i noticed there are some things which seems clasts giving the appareance of sedimentary (althought maybe are replaced mineral, some of them have sharp faces, even prismatic forms), these are replaced by calcite or some carbonate.
See this pictures (the dark ones under PPL, notice the octogonal shape):

https://drive.google.com/file/d/1Cq35E1JU45u9TTCg4A-S7OdwWguhIOHw/view?usp=sharing
https://drive.google.com/file/d/158LMWSx05OOFEkOENwcH8ZKDAYv4lBJ_/view?usp=sharing

https://drive.google.com/file/d/1j6mM8VAO1F71Lnfu1Y6oTerF03EWhuHf/view?usp=sharing
https://drive.google.com/file/d/1wa5G1jxPe5Kz1HS-pgIqEKmv__AeORpd/view?usp=sharing

So.. what do you think? is it a metabasalt or something else? Thanks
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Type: Question • Score: 0 • Views: 1,150 • Replies: 4

 
farmerman
 
  3  
Reply Wed 17 Jan, 2018 04:35 pm
@pichi,
Whats the structural neighborhood. The ser would certainly indicate a met rock. (It looks also like kyanite on rotation) Im just needing to sense some idea whether it was a hydrothermal alteration?

I didnt look at all the slides (just the one where you rotate on the pet scope). Are those teeny garnets or some magnetite in the mix. arent they a giveaway?
pichi
 
  1  
Reply Thu 18 Jan, 2018 08:44 pm
@farmerman,
Where did u see kyanite? the one replacing the feldspar?
There are no garnets, it must be magnetite.
farmerman
 
  2  
Reply Fri 19 Jan, 2018 04:14 am
@pichi,
yeh, it looked like the colors I am used to when you rotate to extinction. I assume you made the thin sections and did the "Quartz thickness check".

pichi
 
  1  
Reply Fri 19 Jan, 2018 10:11 am
@farmerman,
The samples were donated to the university. I am classifying them and giving them names (which is what has cost me the most so far).
As for the mineral, it has very little relief to be kyanite. It looks more like Sericite or Muscovite in the low relief, or not?
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