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17 November 2011
Shear zone in basement complex
Callan visits a new outcrop of highly-sheared rocks in the basement complex of Virginia’s Blue Ridge province.
10 November 2011
Shear bands in the Grassy Portage Sill
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 like: …Except where it doesn’t. In places, it looks like this, instead: Zooming in a …
17 June 2011
Friday fold: a granite dike
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 composite) picture bigger by clicking it: Here’s the texture of the dike granite: Here’s the …
27 May 2011
Friday fold(s): the Outdoor Lab
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 wanted a chance to check out their rocks as part of my expanding examination of …
8 December 2010
Focusing on S-C fabrics
An animated image showing changing focus on a microscope camera aimed at a sample of S-C fabric is shared. Readers are encouraged to brainstorm uses for animated GIF images in the geosciences.
8 November 2010
Tavşanlı Zone field trip, part 6
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. Let’s start with this fine “schisty” example of a blueschist, with big needles of glaucophane …
28 October 2010
Accretionary Wedge #28: Deskcrops
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).
26 October 2010
Tavşanlı Zone field trip, part 3
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: The field notebook’s long edge is ~18 cm. And here it is again, annotated: Near …
21 October 2010
Tavşanlı Zone field trip, part 2
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 low-metamorphic-grade outcrop of sheared graywacke (dirty sandstone) and shale. As you can imagine, it wasn’t …
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.