I was thinking about doing an Aerosmith Edition a couple weeks ago, then when Saturday rolled around, I couldn't remember the group. Interzone Nickelle bought a vinyl version of this first album and reminded me of it just a few minutes ago. Toys In The Attic:
I've owned various copies of both the previous album and "Rocks," on which the lead song is Back In The Saddle:
This one *just* squeaks into the 80's; it was released November 8, 1989. This may well be my favorite song by this group, partly because of the power of the lyrics, partly because of the music, and partly because of how perfectly they go together. Janie's Got a Gun:
Volcanic necks (aka, chimneys, throats, plugs, etc.- I don't know if there's a "correct" term) such as this are pretty common in the Western Cascades, where thousands of feet of overlying volcanic and volcanic-derived debris has been removed by millions of years of erosion. For the most part, these "old Cascades" have not seen eruptive activity since the Pliocene, about 5 million years ago. The roughly cylindrical conduits that carried magma toward the surface, once cooled, are often more resistant to weathering and erosion than the surrounding, often fragmented, rock. Exacerbating this fact, the lava conduits themselves often create localized hydrothermal systems, which as we've seen in the series recently, can render resistant rock into piles of gloppy, utterly incompetent clays. As a result, the difference between the resistant core and less resistant host rock becomes even greater. So while tooling around in the Western Cascades watching the landscape, one often sees spires such as this sticking up. They're not all necessarily volcanic necks, and one should try to look for contacts to make sure it's not an isolated bit of, say, a dike or vein, but generally, in drive by, I'm generally comfortable identifying examples such as this as the conduit of an old volcano.
By the way, if you look at the FlashEarth Location, you should be able to pick out the spire above the curve in the road, to ENE of the crosshairs.
A final panorama of this alteration zone, shot from the pullout on the opposite side of the road, which shows the gradient from more or less unaltered rock down the hill to very highly altered in the area of the calcite veins. From here, we'll walk down the hill to the curve visible on the far right. There's a couple of fun surprises waiting behind the Douglas firs along the right edge of the photo...
Several small veinlets of calcite show up here, one near the bottom with the lens cap (52 mm), another in the upper right middle, and a nubbin up near the top- that latter one may a continuation of the second. Another characteristic of this outcrop comes through well in this shot: the rock is totally rotten, essentially just a pile of clay with veins shot through it. I may have, on past field trips, referred to this sort of stuff as "metacrappite." Or not.
The white calcite veins don't stand out well against the light clays of the altered volcaniclastic rocks, so I've highlighted a few patches below.
There's one large vein here, but myriads of smaller ones, ranging from a couple millimeters to maybe a centimeter or two. The calcite was emplaced into what appear to be faults; many show casts of slickensides. However, the rock itself is too rotted to be able to identify offsets or slicks in place. Only the mineralization hints at their existence.
The calcite vein is out of sight on the left, behind the alder growing in the ditch, but you can see how the nearby rock in the cut is a light, ashy gray, which slowly grades to black and basalt-like in the distance. This is the gradient from highly altered (nearby) to basically unaltered (distance) rocks. Also, in the foreground, you can see what looks to be crude layering, dipping maybe 25 degrees to the left.
This stop has been badly weathered over the years, but it's an interesting one in that it shows a gradient from a more or less unaltered lahar deposit(s) to highly altered near the vein showing above. The vein doesn't stand out well from the surrounding clay-rich material, but it's the diagonal slash in the rock face below the alder tree at the top. This is another stop that rewarded multiple visits; the weathered surface of the unaltered (by hot water) lahar material looks almost indistinguishable from basalt at a cursory glance. However, if you break open a fresh surface, it's pretty easy to tell it's volcaniclastic, not directly volcanic. For years I had told kids it was basalt, and had to change my story when an adult assistant found a bit of petrified wood.
Photo run through Paint.Net's auto-level routine for saturation and contrast. June 19, 2014. FlashEarth location.
After a few miles of these "peripheral clay patches," as I'll dub them, the Quartzville tour enters a stretch with minimal alteration- there are a few highly altered spots, such as the one I'll be featuring next, but by and large the rocks are fairly fresh. As I mentioned in The August first post, the effects of the hydrothermal alteration in this district are very patchy and discontinuous, especially in the outer portions. Toward the center, it's a more consistent, multi-generational quartz breccia, with multiple episodes of fracturing and silicification, but even there, just a few steps can take you from one rock type to something that appears very different.