Draft:Piney Branch Complex
Submission declined on 25 October 2025 by GreenRedFlag (talk).
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|  |
| Piney Branch Complex | |
|---|---|
| Stratigraphic range: 635–509 Ma | |
| Type | Mélange |
| Unit of | Piedmont terrane |
| Lithology | |
| Primary | Schist |
| Other | Serpentinite; Greenschist; Soapstone; Actinolite-Schist |
| Location | |
| Location | Fairfax County, Virginia |
| Coordinates | 38°49′24″N 77°21′56″W / 38.8234°N 77.3656°W |
The Piney Branch Complex is a geological formation located in Fairfax County, Virginia. It’s a heterogeneous assemblage of metamorphosed peridotite, pyroxenite, and gabbro; dominant rock-types include Serpentinite, Soapstone, and Actinolite, Tremolite, and Schist..[1]. Its formation was heavily deformed during the Taconic orogeny (the 1st of 3 mountain building events during the formation of Pangea). It's also notorious for a large amount of naturally occuring asbestos rocks, which could pose long term health concerns due to the risk of mesothelioma.[2]
Geology
[edit]The Piney Branch Complex formed between 635-509 Ma in the ancient Iapetus Ocean. It started as a forearc or back-arc basin of a island arc subduction zone that was later accreated onto Laurentia (ancient North America). It is part of a larger ultra-mafic and serpentinite mélange complex associated with many different exotic island arc terrane collisions with Laurentia. Other examples of these include:
– Dadeville Complex, in Alabama
– Hamlett Grove meta-igneous suite, in South Carolina
–The Buck Creek ultramafic body, in North Carolina
–the Ashe and Alligator Back Metamorphic Suites, in North Carolina
– The Baltimore Mafic Complex (BMC), Maryland–southern Pennsylvania.)[3]
These ophiolites made their way to the surface through subduction and/or rifting processes. The material from the upper mantle became saturated and serpentinized. This led to the formation of ultra-mafic complexes.[3]
Natural asbestos
[edit]The Piney Branch Complex has a large amount of naturally occuring asbestos. The asbestos rocks found here are tremolite, actinolite, and serpentinite. The first documented case of asbestos was brought to the Fairfax County Air Pollution Control Division (Fairfax APCD) in 1987. Construction workers were building an underground parking garage. While digging, workers encountered a large vein of tremolite asbestos. Due to drilling, grinding, digging, and crushed rock material, the worksite was covered in a fine dust of tremolite. After a medical investigation was conducted, it was confirmed that the dust was indeed large amounts of tremolite asbestos.[4]
Since 1987, Fairfax County, (including the cities of Fairfax and Braddock which are over the Piney Branch Complex) have grown into large suburbs of Washington, D.C.. This potentially exposes large amounts of people to asbestos risks, including mesothelioma.
References
[edit]- ^ "Piney Branch Complex | Natural Atlas". naturalatlas.com. USGS. Retrieved 20 October 2025.
- ^ YETMAN, JOHN; DUSEK, JAMES. "Control and-Prevention of Asbestos Exposure from Construction in Naturally Occurring Asbestos" (PDF). TRANSPORTATION RESEARCH RECORD. Retrieved 20 October 2025.
- ^ a b Guice, George L.; Ackerson, Michael R.; Holder, Robert M.; George, Freya R.; Browning-Hanson, Joseph F.; Burgess, Jerry L.; Foustoukos, Dionysis I.; Becker, Naomi A.; Nelson, Wendy R.; Viete, Daniel R. (5 February 2021). "Suprasubduction zone ophiolite fragments in the central Appalachian orogen: Evidence for mantle and Moho in the Baltimore Mafic Complex (Maryland, USA)". Geosphere. 17 (2): 561–581. Bibcode:2021Geosp..17..561G. doi:10.1130/GES02289.1.
- ^ Dusek, James; Yetman, John. "Control and-Prevention of Asbestos Exposure from Construction in Naturally Occurring Asbestos" (PDF). TRANSPORTATION RESEARCH RECORD. Retrieved 21 October 2025.
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