Geo 730: Jan. 7, Day 372: From the Middle of Oceanic Crust

A photo by Dana, this is the same spot as yesterday's photo, with the hammer in the same position. I'm more confident about my tentative gabbro identification after looking through some of her shots. Again, the prominant ~2 cm basalt dike really stands out. If you look about 10 cm up from that, you can see another that's much lighter, but still a bit darker than its host rock. Those two, in turn, appear to be in a light-colored, fine-grained parcel, which is bounded below by material that's similar in color and tone, but coarser-grained. The variations are subtle, but I'm convinced they're real. The problem is that all of the dike material is of similar, basaltic, composition, and it's all been moderately metamorphosed. I don't see the green here; it's too subtle for me. But there are plenty of non-color cues that tell me there's a metamorphic overprint. Often, there are clearly evident variations in texture and tone that convey chilled rims- which we'll get at in the next few days- but to a large extent, it's much easier to distinguish the dike boundaries in person, as opposed to in photographs.

Photo by Dana Hunter, unmodified. May 8, 2013. FlashEarth Location largely hypothetical. Indexed