Here’s a sweet little sample of migmatite (~470 Ma late Ordovician Taconian Orogeny, U/Pb date from zircon), that my students and I spotted last week on the Billy Goat Trail, downstream of Great Falls in Maryland’s metamorphic Piedmont province: Note the white translucent quartz, the orangey (partially kaolinitized and rusty stained) opaque potassium feldspar, and … Read more
Here’s a sample that my Physical Geology students see on their field trip to the Billy Goat Trail:
Following on yesterday’s post about the kink bands within the strained metagraywacke of the Laurel Formation in DC, let’s take the opportunity today to go to Klingle Valley, site of a different facies within the Laurel Formation: a strained metaconglomerate. Though the exposure isn’t as great as the Purgatory Conglomerate, I think you’ll find plenty … Read more
The Friday before last, I was in DC for a fun geology/botany field trip, and I got the opportunity to stroll around the barn at historic Peirce Mill, a historical grain mill along Rock Creek in Rock Creek Park, Washington, DC. The barn is immediately south of Tilden Street NW. It appears to have been … Read more
Another thing I saw last Friday on my DC field trip was this fine boulder exhibiting spheroidal weathering: Annotated: It’s a boulder of the Laurel Formation, a clast-poor metamorphic unit found east of the Rock Creek Shear Zone in DC. This is the first time I’ve seen it exhibit this sort of mechanical weathering. Compare … Read more
On Duck Creek (Ellendale, NC quadrangle), you can see folded xenoliths within the Toluca Granite (383 Ma, 378 Ma, or 368 Ma, depending on which mineral you ask). The granite there contains xenoliths that contain pre-exisiting fabrics and structures, and we stopped at Duck Creek on the pre-GSA-Charlotte field trip I took to the Neoacadian … Read more
The Friday fold comes from a stop on the “Neoacadian Inner Piedmont” field trip that Callan attended prior to the GSA meeting in Charlotte, North Carolina, last week.
Quartzite, shattered and healed and shattered again and again and again. It’s cataclasite, seen in the North Carolina Piedmont and inferred to be Mesozoic in age due to its brittle style of deformation.
Today, I’ve got a batch of additional photos of the Walker Top Granite to share, variably mylonitized (sheared out under ductile conditions)… Nice garnets in some spots: Delta porphyroclast: Lovely sheared-out rocks…
My students Chris Johnson and Robin Rohrback have been busy adding to the Mid-Atlantic Geo-Image Collection. Check out a few of these new GigaPan images: [gigapan id=”117788″] link [gigapan id=”117786″] link [gigapan id=”117390″] link [gigapan id=”117346″] link [gigapan id=”116919″] link