I don't major in petrology, so I will greatly appreciate if anyone would like to give me some suggestions.
The rock of the thin section is red sandstone (red bed). Thin section graphs were taken in reflected light and the bright white minerals are hematite which were corroborated by Raman spectrum and Energy Disperse Spectroscopy (EDS).
Conventionally, hematite in the red bed is mostly thought to be detritus origin. But according to the thin section I think this is not the case. I think the hematite is a secondary one (or grew in a later stage), and probably formed in response to the regional tectonics since a collision followed shortly after the forming of the rock.
But I don't know when exactly nor how do the hematite form. Any suggestions will be welcome. Thank you!
Dear Yalun Liang,
My interpretation of the images shown is as follows:
Image 1 and 2: The hematite forms pseudomorphic shape relics after probably magnetite and / or ilmenite. Hematite is a secondary product and cemented the older quartz grains.
Image 3: A primary inclusion of probably ilmenite and / or magnetite showing twin lamellae was secondarily pseudomorphic replaced by hematite.
Image 4: Here you can see a relatively complicated crystallization and deformation history: The net-like bent hematite agggregate inside the quartz grain was deformed ductile. The bent network probably represents tectonically stressed twin lamellae.The hematite aggregate broken into individual fragments between older quartz grains has been deformed brittle. In both cases there are pseudomorphs of hematite probably after ilmenite and / or magnetite.
I think your opinion is right that all shown haematites are secondary products.
Best regards,
Guenter Grundmann
Dear prof. Guenter Grundmann,
Thank you for your prompt reply, it helps a lot !
Best regards,
Yalun liang
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