Wednesday, June 14, 2006

Injection Structures

Hi, I thought we'd start off the discussion with looking at some of the injection veins people have been asking about. Here are two field photos showing injection veins. The first photo (from wpt009) shows an upward/oblique injection, the boundaries are sharp irregular and may be controlled by pre-existing joints or deformation bands in the sandstone hanging wall.

The lower photo shows a downward directed intrusion at almost 90degrees to the fault surface. It also intrudes sandstone. At this particular location (just north of wpt 015) the fault core widens and sandstone blocks seem to float in the very fine, hard, black material. I would guess that this is a pooling zone of the black material as it thins rapidly to the north (right in this photo).

In both cases, the sandstone wall of the fault suffers fracture and injection, while the argillite cataclasite wall of the fault does not.

Comments welcome! --Christie


Blogger giulio said...

Hi Christie,

this looks really like a pseudotachylyte injection vein.
Heve you sampled this vein?

1:08 PM  
Blogger Fault Rocks said...

Hi Giulio -
Like most of the coolest structures, we didn't destroy this particular vein. However I assure you I will make a big hole in it this summer. Very sad to think about destroying some of these outcrops but we must remove some to get our answers. We will search carefully for more small intrusion veins like this since we found two rather large ones without knowing to look for them, there may be more! --christie

1:31 PM  

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