Incipient mylonitization of a granite/granitoid, as displayed in a sample on a shelf of one of the meeting rooms adjacent to the Reading Room of the Geological Sciences building at the University of Texas at El Paso. Same side, slightly different lighting conditions: I’d call this a protomylonite. Some of you might prefer the term … Read more
Today the Friday fold comes with copious bonus structures. It’s the first stop we hit on Day 3 of the pre-GSA Minneapolis field trip to examine the structural geology of the subprovince boundaries within the Superior Craton. This particular site showed granitoid dikes that had been deformed during dextral transpression into a variety of structures … Read more
Callan visits a new outcrop of highly-sheared rocks in the basement complex of Virginia’s Blue Ridge province.
Continuing now with the discussion of my pre-GSA meeting field trip to examine the structural geology of the Quetico-Wabigoon subprovince boundary within the Superior Craton of southern Ontario, Canada. Our penultimate stop on the second day of the trip was a roadcut exposing the gabbro of the Grassy Portage Sill. This is what it looks … Read more
After the awesome outcrops and pavements of strained metaconglomerates from the Quetico / Wabigoon subprovince boundaries of the Superior Craton, my pre-GSA field trip visited the most charmingly-named magma chamber I’ve ever seen, the cuddly-sounding Ottertail Pluton. This is an Algoman-type pluton which is discordant to tonalite-composition gneisses in the area. As with the Giants … Read more
I’m on the plane home from the annual meeting of the Geological Society of America, held this year in Minneapolis, Minnesota. This annual event features a robust smorgasbord of science, with talks and posters detailing the research efforts of thousands of geoscientists from the US and other countries. It’s an amazing experience on many, many … Read more
Lily poses with amphibolite boudin (showing extensional veins) on the road in Kootenay Bay, British Columbia.
Callan attends a field trip in the Blue Ridge of Virginia, looking first at a Paleozoic shear zone that disrupts (and improves) Mesoproterozoic basement complex rocks.
While exploring the Rock Creek Cemetery last week, I noticed a couple of other interesting graves. This one, made of limestone, shows nice “reverse” cross-bedding: Here; I dialed up the contrast a bit to highlight these cool primary structures: It’s “reverse” because the tilting direction of the cross-beds switches from left (at the bottom) to … Read more
Walking back to my hotel after departing the Northeastern / North-central GSA section meeting on Sunday, I noticed this fine shear band cutting across a polished slab of granite on the exterior of an office building in downtown Pittsburgh: You’ll notice some grain-size reduction along that shear zone, and what looks to be a decent … Read more