Using your relative dating prowess to determine which of these two rock units is older, the schist (dark gray) or the granite (light pink): Click to enlarge Click to enlarge Justify your answer by citing a principle of relative dating.
At Morton Pass, where highway 34 crosses the crest of the Laramie Range, you can see a nice set of (younger) mafic dikes cutting (older) granite/gneiss basement complex. The pink stuff is Archean; the black stuff is Paleoproterozoic; around 2 billion years old. Click to enlarge I got to check out this outcrop on Tuesday … Read more
This is my final post on the pre-GSA-Minneapolis structural geology field trip to the Superior Province. The photo above shows a roadcut exposure of boudinage in xenolith-bearing Vermillion Granitic Complex. Here’s another, smaller, more brittle example of boudinage, from another site, the following morning: Gee, it only took me 1.5 years to blog that trip … Read more
A week ago, I featured six new GigaPans here, of the extraordinary rocks in Klingle Valley, DC. I hadn’t been able to get the next phase of imaging that site ready in time for the post, but here it is: an annotated view of the outcrop. Annotation color code: PINK = Granite contact BLUE = … Read more
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
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
Last week, we took a closer look at the xenoliths (MME’s?) in the Boulder Batholith. Here is a look at a fracture, perhaps a small fault, in that same outcrop. There are no marker units by which we could detect offset here, so we can’t say for sure it’s a fault. But definitely weathering has … Read more
The Boulder Batholith outside of Butte, Montana, is actively weathering, and shedding off grus. In the third installment of the Transitions of the Rock Cycle series, we watch an igneous rock turn to sediment.
Migmatite is a special rock that is partly metamorphic and partly igneous. Let’s take a look at it in Part 2 of Callan’s “Transitions of the Rock Cycle” series.
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.