The Piedmont and Blue Ridge Project is a geologic mapping project supported by the USGS National Cooperative Geologic Mapping Program. The Piedmont Blue Ridge Project aims to understand the geologic framework and tectonic evolution of terranes and basins in the Appalachian Piedmont and Blue Ridge, and their significance for water, mineral and energy resources, natural hazards, and engineering/infrastructure applications. The mapping-based research is separated into an eastern task, Piedmont Geology Along the Southeast Fall Zone, Virginia and North Carolina (PIGONSOFA), and western task, Blue Ridge-Inner Piedmont (BRIP), that will converge to cover areas of needed mapping. Collectively, these tasks are expected to (1) characterize the geologic framework of the Piedmont and Blue Ridge; (2) produce detailed geologic maps (1:24,000 and 1:100,000) and geodatabases; (3) document and quantify the availability of natural resources; (4) understand and recognize potential natural hazards; and (5) apply advanced technology to resolve geologic problems.
The Piedmont and Blue Ridge provinces extend from southeastern New York to Alabama and include parts of eleven states in the Eastern U.S. and part of Washington, D.C (Figure 1). Blue Ridge physiography is characterized by the highest topography east of the Mississippi River, with elevations ranging from 1,000 ft to over 6,600 ft, and moderate to steep vegetated slopes. The Piedmont is located east of the Blue Ridge and characterized by rolling hills and isolated monadnocks. The Blue Ridge is bordered on the west by the Valley and Ridge Province, and the Coastal Plain Province onlaps the Piedmont to the east and southeast, and the Blue Ridge to the southwest. Major streams and rivers draining the Blue Ridge flow west into the Mississippi River and Gulf of Mexico, and east across the Piedmont and Coastal Plain into the Atlantic Ocean; the latter drainage systems are actively capturing headwaters of westward flowing streams.
The geologic framework of the Piedmont and Blue Ridge provinces is complex. The Blue Ridge is generally faulted over Paleozoic strata of the Valley and Ridge, while the rocks of the Piedmont continue in the subsurface beneath the Coastal Plain onlap.Mesozoic rift basins overlie parts of the Piedmont crystalline rocks and contain hundreds to thousands of meters of Early Triassic to Jurassic sediment and igneous rocks (Olsen and others., 1991).The Piedmont and Blue Ridge consist of complex, polydeformed Mesoproterozoic to Paleozoic crystalline rocks, and comprise various lithostratigraphic terranes that were assembled during multiple orogenies (Hibbard and others, 2006; Hatcher, 2010; Hatcher and others, 2007). The oldest rocks are 1.3–1.0 Ga crystalline gneisses and granitoids, Grenville basement, exposed in various massifs in the Blue Ridge and Piedmont (Southworth and others, 2010; Tollo and others, 2010, 2017).Neoproterozoic to Paleozoic metasedimentary and metavolcanic rocks compose the majority of the different Appalachian terranes, both Laurentian and exotic (peri-Gondwanan affinity), and record the Mesoproterozoic to Paleozoic accretion and collision of different terranes to the Laurentian margin (Hibbard and others, 2006; Hatcher and others, 2007).
Collectively, the orogenies experienced by the Blue Ridge and Piedmont provinces include: Grenville orogeny (1.3–1.0 Ga), Taconic orogeny (460–450 Ma), Acadian/Neoacadian orogeny (395-340 Ma), and Alleghanian orogeny (335–260 Ma) (Hatcher and others, 2007; Hibbard and others, 2007, 2010; Hatcher, 2010; Merschat and others, 2017). These were punctuated by periods of extension, including intracontinental rifting (780–750 Ma), break-up of supercontinent Rodinia and the opening of the Iapetus ocean (~570 Ma), and finally the break-up of supercontinent Pangea and the opening of the modern Atlantic Ocean (~200 Ma). These orogenic events are responsible for the crustal structure, fracture and fault zones, mineralization and ore deposits, geochemical, and geophysical properties of the Piedmont and Blue Ridge. The magmatic, thermal, and deformational history of the Blue Ridge and Piedmont terranes controlled mineralization and formation of ore deposits. Magmatism, arc- or rift-related, localized gold and other precious metal mineralization, including massive sulfide deposits (e.g., Ducktown, TN, Cabarrus County, NC, Mineral, VA). Major faults, which bound these terranes, developed highly foliated and/or fractured rocks that are weak and more susceptible to landslides and other forms of mass wasting (landslides). Highly fractured rocks associated with faults may also be important aquifers, and aquicludes (Johnson and Dunstan, 1998; Shapiro, 2002; Goode and others, 2007). Many other properties of the rocks (composition) may affect groundwater quality (Ayotte and others, 2011; Bradley and Campbell, 2012). Further, geologic framework studies have identified the spatial relationship between geologic/tectonic structures and the localization of intraplate earthquakes and seismic zones (e.g., Hughes and others, 2014; Burton and others, 2015; Horton and others, 2017), and 3D seismic-velocity structure of the Earth, and seismic hazards (Thomas and Powell, 2017). Understanding the complex orogenic events, and the tectonic and geologic processes involved—arc magmatism, mantle plumes, partial melting of the crust, fracturing and faulting of the crust, structural inheritance and reactivation, etc.—will help better understand and locate ore deposits, locate and mitigate geologic hazards, and better evaluate water resources. Detailed geologic mapping and framework studies of the Piedmont and Blue Ridge Project look to address these complex geologic problems.
References Cited
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Below are other science projects associated with this project.
Blue Ridge and Inner Piedmont Geologic Mapping
Below are other science projects associated with this project.