A few weeks ago I went on the third year Igneous field trip to the northern cape and southern Namibia. What an incredible part of the world. We drove north through Springbok, South Africa on the N7 and left the highway in a terrane of rounded granite "koppies" in a sea of red sand. The sun went down on us while the vans got increasingly stuck in this sand.
Here's the first time we got stuck... Turns out flash flooding a few weeks before had washed soft sand across the old sandy tracks in this desolate area of sheep herding. The ground surface was marked by mini-deltas, braided stream channels, and all kinds of tiny miniaturized flood features in the fine sand. We ended up leaving the vehicles in disarray all over the desert and hiked in the last couple of kilometers to the campsite.
In the morning, Chris handed out some aerial photos and we sent the students off into the desert while the instructor team got started on the digging out process.
Due to the mid-day heat, we started them out early in the morning and had them return to camp for lunch/siesta and back out for more mapping in the afternoon. This was the first time for me mapping in an essentially all-intrusive landscape. There was enough diversity in the intrusive suites that it's not too hard to tell them apart in the field. In contrast to mapping bedded rocks however, structures are often obscured and it's almost impossible to predict what you might see at the next outcrop since you have no "initial shape" model to work from. That means you have to actually visit every outcrop you can find. This makes things a bit slower...
Here's an intrusive contact between medium-grained pink granite (top) and porphyritic adamelite (bottom). The adamelite is easy to identify because it has those big squarish feldspar crystals. The intrusive contacts here are "soft" like this - and irregular.
The country rock to all these intrusives is the Orange River Volcanic Suite. These were generally some gritty, blackish-green actinolite metabasalt and some metasediments. Here's a quartz-talcy shear zone with a sheath folded quartz vein!!!! Props to Johann the metamorphic petrologist who found this and showed it to me!!
Here's the class checking out some of the amphibolites in the ORVS:
Duane caught this crazy beetle out of the air. They buzz around slow and lazy making a mini-helicopter sound.
Here's an awesome fault surface in the ORVS. The rock here is a quartz porphyry - maybe - but it might be a metasomatic product. The thin darker pink layer on the surface of the outcrop is a cataclasite layer, and the rounded quartz grains get stretched out into ellipsoids with increasing flattening toward the cataclasite layer - and oh yes, I got a gorgeous big oriented sample.