DEAR COLLEAGUES
I RECENTLY VISITED THE HILL OF THORIKON NEAR LAURION. IT HAS AN IGNEOUS FORMATION ON THE TOP. OLD MAPS CALL IT AN OPHIOLITE. I SEND THREE PHOTOS. WHAT KIND OF ROCK DO YOU THINK IT IS?
BEST REGARDS
IOANNIS
The third image could depict hyaloclastites, i.e. glassy or devitrified tuffitic rocks, formed by rapid cooling of mostly basaltoid rocks below the water surface.
THANK YOU FOR YOUR INTERESTING ANSWER DALIBOR. COULD THE FORMATION BE AN ULTRAMAFIC PIPE?
BEST REGARDS
IOANNIS
I agree with Dalibor. It looks as if there are pillows in the upper part of the third photo, above the hyaloclastite. Basaltic as far as I can guess.
Dear Ioannis: yes, it is definitely a hyaloclastite, the name comes comes hyalos, glass, and clastos, fragment. They form when magmas are erupted under water, and are always associated with pillow lava, usually basaltic, but it could be of other lithologies. So this portion of the ophiolite in that hill corresponds to basaltic oceanic crust, which is the most mineralized and contained in the past the famous silver mines which gave ancient Athens all its richness and power, at Laurion. I've been studying recently a section of pillows and lavas in NW Venezuela, but these don't crop out, they are cores extracted from 9000 feet depth in the Falcon Basin. The cores look a lot like your rock in that hill, if somebody studied that rock in thin section he or she might have found an interesting alteration to saponite, and fragmented glass cemented with analcite and carbonate. Regards, Sebastián Grande. Caracas, Venezuela.
THANK YOU FOR YOUR DETAILED ANSWER SEBASTIAN. THE OUTCROP IS NEAR THE SILVER MINES OF LAURION. OLD MAPS SHOW THAT THIS ROCK WAS TECTONICALLY EMPLACED (UPTHRUSTED) IN TOP OF THE THORIKON HILL.
BEST REGARDS
IOANNIS
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts