Waypoint 015 - the biggest layers

This first photo shows the area where PP59 was sampled. You can see the corner of a flattened, sheath-like fold in this photograph. the axial area is the sample PP59. I have taken slabs of the axis and there is beautiful viscous folding of different layers, some cuspate-lobate structure between fine layers and coarse layers. I began to trace these layers from the slab to make a sketch because as Toshi-san said in his email, "it's too dark to imagine inside". I will post the tracing here when I have a chance to scan it.

This next two photos show another large feature which may be a sheath-like fold but we are not sure because we have not seen the layers bending around the axis. You can see here the deformation of layers of different flow properties at the left side of the fold. Also in the second photo you can see where the big layer of "black material" thins down at the edge of the outcrop. You can see the sandstone hanging wall and argillite cataclasite footwall.

Finally, here are two more photos from the outcrop. These are taken westward (to the left) of the previous photos. We noticed in particular the beautiful cross-cutting of the cataclasite footwall, the banding and folding which is very fluid-like in the left photo. In the right photo notice how there are flakes or sheets of cataclasite material in between layers of black material, very planar.

I am looking forward to hearing your impressions of these photos.

Other Injection Structures - the fabulous Wpt 014


In fact there are a lot of injection-type structures at Pasagshak Point, but most of them are not as typical as the ones I posted yesterday. At Wpt 014 there are some which resemble the structures formed by soft sediment deformation. In these first two pictures you can see a vein of black material (2-3cm thick) which cross cuts the cataclastic fabric at a low angle. The top of the vein resembles "flame structures" with the black material (lower viscosity) ductilly intruding upwards into the cataclasite (must have been higher viscosity) similar to a mud layer forming flames into an overlying sand layer. In fact, the "flames" are also sheared (top to the left in this photograph) and some are even disconnected from the source vein.

The subtle vertical cleavage you may see cutting the black material is a steep weak pressure solution cleavage which cross-cuts all subduction related faulting.

Along the same source vein we find this large sill/dike complex. The injection of the black material upward from the source vein deformed the cataclastic fabric of the fault zone. The cataclastic fabric is defined by the alignment of sandstone clasts which are tectonically rounded and have slickenlined surfaces. In some places there are elongated boudins and stringers of sandstone and hyaloclastite also along the fabric. This injection was also shown in our paper of 2005 which you can also download now from the links at the side of this page.

Your comments please!
--Christie

Hi Everybody! Welcome to the Kodiak Fault Rocks discussion blog. Putting this in a blog format was inspired by Gaku-san and his excellent blog, which unfortunately I can't read but the photographs are lovely. This blog will be moderated by Christie Rowe. In order to participate, sign up for an account by creating a username and password at blogger.com (this will allow you to post comments to any thread on this blog). Pick a username which allows others in this discussion to identify you. To be empowered to begin your own threads on this blog, send me your blogger account name and the email address you would like to use for this (be aware there is a risk of added spam) and I will add you to the "members" list for this blog so you can post pictures and start new questions.

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