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Shear bands in the Grassy Portage Sill

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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

Friday fold: a granite dike

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This Friday, I give you a fold from the shores of the Rockfish River, south of Charlottesville, in Virginia’s Blue Ridge basement complex, and just down the road from the Lawhorne Mill High Strain Zone. The fold distorts (and improves) a felsic dike cutting the darker granite of the basement. You can make this (stitched … Read more

Friday fold(s): the Outdoor Lab

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Today’s Friday fold takes me back 25 years, to when I visited the Outdoor Lab with my science class in Arlington County Public Schools. I revisited this exemplary outdoor education facility on Tuesday, at the invitation of its director, Neil Heinekamp. Neil wanted a geology “expert” to take a look at their rocks, and I … Read more

Tavşanlı Zone field trip, part 6

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Part 5 of the Tavşanlı Zone field trip left us eating lunch amid some fine blueschists. Of course, nothing tops off a blueschist lunch like… more blueschist. So after our meal, we took another stroll through the countryside in search of more interesting subduction zone rocks… I’;ve got a bunch more photos for you today. … Read more

Accretionary Wedge #28: Deskcrops

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In honor of this month’s Accretionary Wedge (geoblog carnival; this month the theme is “deskcrops”), I recorded the following short video, showcasing some samples I have in my office: stromatolite (western Montana), conglomerate (Patagonia), schist (New Hampshire), anorthosite (New York), amygdular meta-basalt (Virginia), amphibolite (California), hematite concretions (eastern Montana), and a stretched-pebble lineated meta-conglomerate (Turkey).

Tavşanlı Zone field trip, part 3

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Picking up where we left off last time, we were in some partly-serpentenized peridotite, part of the Burham Ophiolite in Turkey’s Tavşanlı Zone, an ancient tectonic suture. Our next stop on the field trip allowed us to visit some diabase dikes: Here’s a close-up of the right contact of the dike with the host peridotite: … Read more

Tavşanlı Zone field trip, part 2

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Yesterday, I shared a few thoughts about the first couple of stops on the field trip I took earlier this month from Istanbul to Ankara, prior to the Tectonic Crossroads conference. Today, we’ll pick up with some images and descriptions from the next few stops. After lunch, our next stop brought us to a relatively … Read more