Southwestern Virginia Case Study
Geologic Map
Elizabeth A. Johnson
Map
This is the map of the area (without annotations):click on the image to enlarge.
Here is an annotated map of the area, showing approximate sample locations and towns, as well as the Fries Fault and major structural units:
Rock Units
| Formation | Age | Sample # | Rock Type | Protolith |
| Ashe Formation | Protolith Age: 600 Ma (Late Proterozoic). Age of metamorphism: 450-430 Ma. | A1 B2, A3 schist | Staurolite Schist (Pelite) | Fine-grained mudstone |
| A1 amph, A3 Amph | Amphibolite | Basalt or Gabbro | ||
| UM1 | Soapstone / serpentinite | Ultramafic (peridotite) | ||
| Fries Fault Zone | Fault Age To Be Determined | A4 Mylonite 1 | Mylonite | Cranberry Gneiss |
| A4 Mylonite 2 | Mylonite | Ultramafic or mafic protolith | ||
| Cranberry Gneiss | Protolith Age: ~1.1 Ga (billion years) Age of metamorphism: gneissic fabric – 900 Ma? faulting age is unknown. | Cranberry | Orthogneiss | Granite |
| S5 Cranberry | Paragneiss | Sedimentary | ||
| Striped Rock Granite | Crystallization age ~690 Ma. Perhaps associated with Mt Rogers volcanics (~750 Ma)? | S6 Striped Rock | Granite | Not applicable |
| Unicoi Formation | Early Cambrian (like the Chilhowee Group near JMU) | Unicoi 1 | Shale / mudstone | Not applicable |
| Unicoi 2 | Greenstone | Basalt | ||
| Unicoi 3 | Conglomerate | Not applicable |
Field Bulletin
The map and field descriptions of this area (by Stose and Stose) are available here: https://www.dmme.virginia.gov/commercedocs/BUL_72.pdf
And from this page (it is free to download, even though it is the DMME “store”): https://www.dmme.virginia.gov/commerce/ProductDetails.aspx?productID=2272
Like most map bulletins, the text is first, and the maps are at the very end of the .pdf document.
Media Attributions
- Map from BUL_72 v2
- Galax map annotated 2
