A baked horizon in the Columbia River flood basalts
How did this bold orange layer develop? It’s seen in an outcrop near Wilson Creek, Washington, in the Columbia River basalts.
metamorphism
Four new GIGAmacro images
Here are a few new images I’ve been working on with my home-based Magnify2 imaging system from GIGAmacro. Archean basement complex gneiss from the Gallatin Range of Montana: Link (If this looks familiar, that’s because one of the samples I imaged with the Photoscan 3D modeling technique and published on Sketchfab the week before last.) … Read more
Three new 3D rock sample models
Pahoehoe “ropes” on a basalt, sample site unknown: Archean gneiss from the Gallatin Range of Montana: Tafoni in Malmesbury Group turbidites, South Africa:
A GIGAmacro view of the front and back of an anorthosite cobble
Here are two views of a single anorthosite cobble, collected in the Adirondack Mountains of upstate New York: Raw, natural surface: Link Slabbed and polished surface: Link As you zoom in and explore these GIGAmacro images, see if you can find the delicate little “necklaces” (reaction rims) of garnet wrapping around the few isolated pyroxenes!
Friday fold: disharmony in the Old Lyme Gneiss
Happy Friday – it’s the end of a very busy week for me, and I hope you too are looking forward to a fun and rejuvenating weekend. Here’s your Friday fold – like last week, a guest submission from Joe Kopera: Wowzers; that’s a looker! What are we looking at here? Joe writes: This photo … Read more
Friday fold: Catalina Island #1
My friend Sarah Penniston-Dorland, of the University of Maryland, supplied this week’s Friday fold. it comes from Catalina Island, California, where Sarah just wrapped up some field work with two of her students. All three of them have given me permission to post the images here: The Catalina Schist is a suite of subduction-related metamorphic … Read more
Friday fold: Cho La Pass, Himalayas
Today’s Friday fold comes from Martin Schmidt, who has shared a few previous folds with Mountain Beltway readers. It shows a folded ptygmatic vein from the Himalayas. Pretty sweet, amiright? Thanks, Martin. Happy Friday, all!
Serpentinite mélange on Marshall’s Beach
South of the Golden Gate Bridge in San Francisco, there are beachside exposures of serpentinite mélange: tectonically sheared-out former oceanic crust accreted to western North America as part of an accretionary wedge.
Friday fold: Apennine phyllites
Another one from Samuele Jæger Papeschi: NE verging recumbent F2 folds in Paleozoic phyllites – Filladi di Buti fm., Punta Bianca, N. Apennines, Italy
Friday fold: recumbent folds in metapelites and metalimestones, Apennines, Italy
Anotehr one from Samuele Jæger Papeschi: Recumbent SW verging folds in alternating metalimestones and phyllites in the Metacalcari e Filladi formation, seen at Anisian, Punta Bianca, La Spezia, N. Apennines, Italy
The Sykesville Formation, in 6 new GigaPans
As part of my work on the GEODE project, I’m always looking for good imagery to teach key concepts in geoscience. One important concept that I’ve been thinking about lately is the principle of relative dating on the basis of inclusions. Just as you can’t bake a loaf of raisin bread without already having raisins … Read more
Purcell Sill, layer-jumping
After reading the post last weekend about the discordant offshoot of the Purcell Sill, Rich Gashnig (post-doc at Georgia Tech) sent me a few photos he shot at Piegan Pass (at the head of a side-canyon adjacent to the one containing Grinnell Glacier). They show the Purcell Sill leaving one stratigraphic horizon and jumping to … Read more
Epidotized tuff, Tucson Mountains, Arizona
I was in Tucson this past weekend for a book project meeting, and my editor and coauthor and I took a hike on Sunday morning in the Tucson Mountains to Wasson Peak. Not far from the summit, we saw an epidotized tuff, where the fiamme and pumice blobs had undergone reactions to produce pods of … Read more
Building stones of the Acropolis (Athens, Greece)
As a follow-up to my post about the geology of the Acropolis klippe in Athens, Greece, and in the spirit of my post on the building stones of the Haghia Sophia in İstabul, Turkey, let’s turn our attention today to the various rocks that ancient Greeks used to construct the buildings of the Acropolis, such … Read more
Friday folds: Cabbage Island, Maine
Devonian metamorphic rocks (garnet-bearing gneiss) exposed on the western side of Cabbage Island, Maine: And here it is in GigaPan form: link
Friday fold: Santorini schist
Happy Friday! Here’s some folded schistocity in the schist of Santorini’s Cycladean subduction complex: The blunt crest of the fold in the second photo appears to be a folded marble boudin. Neato!
In search of Santorini’s blueschist, part 2: finding fault
As mentioned last week, I took a solo field trip north of Perissa, Santorini, Greece, in search of subducted rocks. The contact between the two main rock types (marble and schist) was prominent and visible from a great distance (see photos in previous post), but what was the nature of this contact? Did it represent … Read more
In search of Santorini’s blueschist, part 1: into the Valley of the Shadow of Ash
While in Santorini, Greece, your humble geoblogger braves a warm afternoon to search the hillsides for evidence of subduction.
Friday fold: En route to Santorini over the Cyclades
A glimpse out an airplane window reveals some Cycladean geology in the Aegean Sea. Somewhere down there among the metamorphic rocks is our Friday fold… but nary a volcano in sight.
Charnockite at Swift Run Gap
Over the weekend, I ran a 1-credit field course for NOVA, on the geology of Shenandoah National Park. I was about eight minutes early getting to the meet-up location, so that allowed me to check out a promising new outcrop of rock along the road (route 33, ~100 m west of Swift Run Gap). Here … Read more