Friday, June 3, 2011

Megabreccia II: More Photos

Because breccia is one of my favorite rock types, I've got a few more photos of the Titus Canyon megabreccia from our Death Valley and Mojave trip in 2009. In this first photo, the large breccia fragment in the lower left of the canyon wall is about 5 to 6 feet high (scale here and here). Looking carefully at this face of the Titus Canyon narrows, you can see that the breccia extends quite a ways up the canyon wall, into the darkly stained area where textures are difficult to see. The often angular clasts of the dark gray carbonate rock are angular to subrounded, and they are usually matrix supported by white to very pale orange to cream-colored calcite. In places, some of the fragments could easily be put back together, as if they were part of a jigsaw puzzle; in other places, the breccia pieces don't seem to fit.

Within the stunning exposure area in the canyon narrows, the breccia shows quite a bit of variability.
This one face of the canyon wall — man's hand on the right for scale — shows a lot of the white calcite that often forms the breccia matrix. There is seemingly more matrix than usual, although a large fragment or two could lie just behind the rock face, changing the apparent fragment:matrix ratio.
We'll zoom in on the area almost obscurred by the hand in the previous photo. Above the two large dark fragments, we see a large mass of the white calcite.
Looking more closely at the area above the two dark fragments, the main calcite mass can seen to be fractured and brecciated. But there's a complication: a heterolithologic breccia of dark carbonate rock and white calcite is shooting through the rock just to the right of my hand. This second breccia has subrounded to rounded clasts, and appears to be cemented by a reddish, hematitic material (possibly consisting of ground up pieces of both the original dark wall rock fragments and the secondary calcite cement).
This photo of the breccia provides some scale, by way of my truck, for the next photo, which is just to the left of this one.
What I see here is a relatively narrow banded zone that may be a calcite-cemented or calcite-filled fault, dipping off toward the left. Is it a fault? The answer appears to lie upward, requiring rock climbing, or finding a way around to the top from some other direction. Note the diffuse contact between breccia below and fairly solid rock above, just left of the banded zone. We'll zoom in on that...soon.

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