Dataset Identification:
Resource Abstract:
- description: The US Geological Survey, in cooperation with the National Park Service, mapped 35 7.5-minute quadrangles, within
a 2-mile-wide+ corridor centered on the Parkway, from BLRI (Blue Ridge Parkway) Mile Post (MP) 0 near Afton, Virginia southward
to MP 218 at Cumberland Knob, approximately 1.3 km south of the Virginia North Carolina State Line. Detailed bedrock geologic
mapping for this project was conducted at 1:24,000-scale by systematically traversing roads, trails, creeks, and ridges within
and adjacent to the 2-mile-wide+ corridor along the 216.9-mile length of the BLRI in Virginia. Geologic data at more than
23,000 station points were collected during this project (September 2009 February 2014), with approximately 19,500 included
in the accompanying database. Station point geologic data collected included lithology, structural measurements (bedding,
foliations, folds, lineations, etc), mineral resource information, and other important geologic observations. Station points
at the start of this project (September 2009) were located in the field using topographic reckoning; after May 2012 stations
were located using Topo Maps (latest version 1.12.1) for Apple IPad 2, model MC744LL/A. Since the start of the project, station
point geologic data and locational metadata were recorded both in analog (field notebook and topographic field sheets) and
digitally in ESRI ArcGIS (latest version ArcMAP 10.1). Station point geologic data were used to identify major map units,
construct contact lines between map units, identify the nature of those contacts (igneous, stratigraphic or structural), determine
contact convention control (exact located in field to within 15 meters; approximate located to within 60 meters; inferred
located greater than 60 meters), trace structural elements (faults, fold axes, etc) across the project area, and determine
fault orientation and kinematics. Geologic line work was initially drafted in the field during the course of systematic detailed
mapping; line editing occurred during office compilation in Adobe Illustrator (latest version CS 4). Final editing occurred
during conversion and compilation of Illustrator line work into the ArcGIS database, where it was merged with station point
geologic data. Station point geologic data, contacts and faults from previous work in the BLRI corridor were evaluated for
compilation and synthesis in the BLRI mapping project. Station point geologic data compiled from previous work are referenced
and marked with a C in the database. Compiled line work is also clearly tagged and referenced. The BLRI cuts at an oblique
angle nearly the entire width of the Blue Ridge Geologic Province in Virginia. Thus, the geology varies significantly along
its along its 216-mile traverse. North of Roanoke (BLRI MP 115), the Blue Ridge is defined as an orogen-scale, northwest-vergent,
northeast-plunging reclined anticlinorium, and from its start at MP 0 near Afton, Virginia, southward to Roanoke, the BLRI
traverses the western limb of this structure. Here, rocks range in age from Mesoproterozoic to Cambrian: Mesoproterozoic orthogneisses
and metamorphosed granitoid rocks of the Shenandoah massif comprise basement to Neoproterozoic to Cambrian mildy- to non-metamorphosed
to sedimentary cover rocks; the BLRI crisscrosses in many places the contact between cover and basement. Mesoproterozoic basement
rocks in the Shenandoah massif represent the original crust of the Laurentian (ancestral North American) continent; sedimentary
cover rocks were deposited directly on this crust during extension and breakup of the Rodinian supercontinent in the Neoproterozoic
to earliest Cambrian. Very locally, diabase dikes of earliest Jurassic age intrude older basement and cover sequences. These
dikes were emplaced in the Blue Ridge during continental extension (rifting) and the opening of the Atlantic Ocean in the
Mesozoic Era. From MP 103.3 to MP 110.3 near Roanoke, the BLRI crosses into and out of a part of the Valley and Ridge Geologic
Province. Unmetamorphosed sedimentary rocks of Cambrian to Ordovician age mostly shale, siltstone and carbonate occur here.
These rocks were deposited in a terrestrial to shallow marine environment on the Laurentian continental margin, after extensional
breakup of Rodinian supercontinent in the Neoproterozoic and earliest Cambrian, but before mid- to late-Paleozoic orogenesis.
South of Roanoke, the Blue Ridge Geologic Province quickly transitions from an anticlinorium to a stack of imbricated thrust
sheets. After crossing the southern end of the Shenandoah Mesoproterozoic basement massif (MP 124.1 to MP 144.4), the BLRI
enters the eastern Blue Ridge province, a fault-bounded geologic terrane comprised of high-metamorphic-grade sedimentary and
volcanic rocks deposited east of the Laurentian continental margin from the Neoproterozoic to early Paleozoic. These rocks
were significantly metamorphosed, deformed, and transported westward onto the Laurentian margin along major orogenic faults
during Paleozoic orogenesis. Sixty bedrock map units underlie the BLRI in Virginia. These units consist of one or more distinguishing
lithologies (rock types), and are grouped into formal and informal hierarchal frameworks based on age, stratigraphy (formations-groups),
and tectonogenesis. Many of these units exhibit characteristics and field relationships that are critical to our understanding
of Appalachian orogenesis. Most of these units are named based on the dominant occurring lithology; other units follow formal
nomenclature, some of which was developed and has been used for more than 100 years. Oldest rocks occurring along the BLRI
corridor are Mesoproterozoic orthopyroxene-bearing basement rocks of the Shenandoah massif, in the core of the Blue Ridge
anticlinorium. Preliminary SHRIMP U-Pb zircon geochronology (J. N. Aleinikoff, this study) shows that these rocks can be grouped
based on crystallization ages: Group I (~1.2 to 1.14 Ga) are strongly foliated orthogneisses and Group II (~1.06 to 1.0 Ga)
are less deformed metagranitoids. Group I orthogneisses, which occur discontinuously from near Irish Gap (MP 37) to Cahas
Overlook (MP 139), comprise 10 map units: leucogranitic gneiss (Yllg); megacrystic quartz-monzonitic gneiss (Yqg); granitic
gneiss (Yg); lineated granitoid gneiss (Ylgg); garnetiferous leucogneiss (Yglg); Sandy Creek gneiss (Ysg); porphyroblastic
garnet-biotite leucogranitic gneiss (Ygtg); dioritic gneiss (Ydg); Pilot gneiss (Ypg); and megacrystic granodioritic gneiss
(Ygg). Group II metagranitoids, which are first encountered along the BLRI at Reeds Gap (MP 14) and occur discontinuously
to Roanoke River Overlook (MP 115), comprise 8 map units: megacrystic meta-quartz monzonitoid (Yqm); massive metagranitoid
(Ymgm); megacrystic metagranitoid (Ypgm); mesocratic porphyritic metagranitoid (Ygpm); metagranodioritoid (Ygdm); Vesuvius
megaporphyritic metagranitoid (Yvm); quartz-feldspar leucogranitoid (Yqfm); and Peaks of Otter metagranitoid (Ypom). An additional
relatively undeformed metagranitoid with a preliminary SHRIMP U-Pb zircon age of ~1.12 Ga is assigned to the Bottom Creek
Suite (Ybcm), and well layered migmatitic gneiss (Ymg) near Irish Gap (MP 37) has a a preliminary SHRIMP U-Pb zircon age of
~1.05 Ga. Other rocks of Mesoproterozoic age include orthogneisses in the Fries thrust sheet between MP 139 and MP 144.5 that
range in age from ~1.19 to ~1.07 Ga: biotite-muscovite leucogneiss (Ymlg); biotite granitic augen gneiss (Ybgg); blue-quartz
gneiss (Ybqg); and biotite leucogneiss (Yblg). Latest Mesoproterozoic rocks include paragneiss and pegmatite (Yprg) near Porters
Mountain Overlook (MP 90), and a suite of igneous intrusive nelsonites and jotunites (Yjn). Two units, foliated metagreenstone
(Zdm) and foliated metagranitoid (Zgm), locally intrude older Mesoproterozoic rocks in the core of the Blue Ridge anticlinorium.
Metagreenstone is fine-grained and mafic in composition, and occur as narrow dikes and sills; metagranitoid is medium-grained
and generally felsic in composition, and intrude basement rocks as small plutons, stocks, and a few narrow dikes. On the west
limb of the Blue Ridge anticlinorium, metamorphosed sedimentary and volcanic rocks of Neoproterozoic to Cambrian age crop
out discontinuously along the BLRI from near Afton (MP 0) to MP 103.3, in the vicinity Roanoke Mountain (MP 120 to MP 124),
to near Adney Gap (MP 136). These rocks are assigned to a formal stratigraphic sequence: Swift Run Formation; Catoctin Formation;
Chilhowee Group. Metasedimentary and meta-igneous rocks of lower Paleozoic (?) to Neoproterozoic age are assigned to the Alligator
Back Formation, Lynchburg Group, and Ashe Formation. These units crop out southeast of the Red Valley fault from MP 144.5
southwestward to the North Carolina Virginia State Line at Mile Post 216.9. Rocks assigned to the Alligator Back crop out
in the Blue Ridge Parkway corridor from Mile Post 174.5 southward to the North Carolina Virginia State Line: compositional-layered
biotite-muscovite gneiss (abg); garnet-biotite-muscovite-quartz schist (abs); quartzite and quartz-rich metasandstone (abq);
and marble (abm). The following lithologic map units along the BLRI corridor are correlated with Lynchburg Group formations:
graphitic schist (lgs), muscovite-biotite metagraywacke (lmg), and graphite-muscovite-quartz metasandstone (lms). These rocks
crop out between the Red Valley fault (Mile Post 144.5) and the Rock Castle Creek fault (Mile Post 174.5). Coarse-grained-
to conglomeratic metagraywacke (acm), underlying Lynchburg Group rocks west of the Rock Castle Creek fault in the vicinity
of Rakes Millpond (MP 162.3) and Rocky Knob Visitors Center (MP 169), are considered to be the lower metamorphic grade-equivalent
of the higher metamorphic-grade Ashe Formation at its type section in northwestern North Carolina. Five meta-igneous lithologic
map units occur as mappable bodies interlayered or intrusive into metasedimentary rocks of the Alligator Back Formation and
Lynchburg Group. Altered ultramafic and ultrabasic rocks (um) occur mostly within the Lynchburg Group, but few thin bodies
also occur within laminated amphibolite gneiss (aml) locally (laminated amphibolite gneiss is associated with rocks of the
Alligator Back Formation). Amphibolites of the Lynchburg Group include biotite-bearing amphibolite (amb), clinozoisite-bearing
amphibolite (amc) and quartz-layered amphibolite (amq). Map units that occur beneath the Blue Ridge fault are assigned to
the Valley and Ridge Province. In the BLRI corridor, these rocks are first exposed near Bearwallow Gap (MP 91) and continue
southward beyond Roanoke near MP 125. Oldest formations are Shady Dolomite (Cs) and Waynesboro Formation (Cw), which regionally
can be mapped in stratigraphic continuity with cover and basement rocks of the Blue Ridge anticlinorium. Conversely, nowhere
in the Appalachians can rocks of the Elbrook Formation (Ce) or Conococheague Formation (Cco) be mapped in direct stratigraphic
continuity with Mesoproterozoic basement rocks in the core of the Blue Ridge anticlinorium; however, they do stratigraphically
overlie older Waynesboro Formation and Shady Dolomite within imbricates of the Blue Ridge fault system. Ordovician Martinsburg
Formation (Omb) occurs beneath the Pulaski fault north of Roanoke River, about 0.85 km northwest of MP 108. Paleozoic mylonite
(Pzmy) is a tectonic rock unit that that occurs in high-strain fault zones in the core of the Blue Ridge anticlinorium from
near Afton (MP 0) to Adney Gap (MP 136). Jurassic diabase (Jd) occurs in narrow dikes that intrude older map units, just south
of Roanoke River near MP 118 and MP 125, north of James River near MP 56, and in the vicinity of Afton near MP 3 and north
of MP 0.; abstract: The US Geological Survey, in cooperation with the National Park Service, mapped 35 7.5-minute quadrangles,
within a 2-mile-wide+ corridor centered on the Parkway, from BLRI (Blue Ridge Parkway) Mile Post (MP) 0 near Afton, Virginia
southward to MP 218 at Cumberland Knob, approximately 1.3 km south of the Virginia North Carolina State Line. Detailed bedrock
geologic mapping for this project was conducted at 1:24,000-scale by systematically traversing roads, trails, creeks, and
ridges within and adjacent to the 2-mile-wide+ corridor along the 216.9-mile length of the BLRI in Virginia. Geologic data
at more than 23,000 station points were collected during this project (September 2009 February 2014), with approximately 19,500
included in the accompanying database. Station point geologic data collected included lithology, structural measurements (bedding,
foliations, folds, lineations, etc), mineral resource information, and other important geologic observations. Station points
at the start of this project (September 2009) were located in the field using topographic reckoning; after May 2012 stations
were located using Topo Maps (latest version 1.12.1) for Apple IPad 2, model MC744LL/A. Since the start of the project, station
point geologic data and locational metadata were recorded both in analog (field notebook and topographic field sheets) and
digitally in ESRI ArcGIS (latest version ArcMAP 10.1). Station point geologic data were used to identify major map units,
construct contact lines between map units, identify the nature of those contacts (igneous, stratigraphic or structural), determine
contact convention control (exact located in field to within 15 meters; approximate located to within 60 meters; inferred
located greater than 60 meters), trace structural elements (faults, fold axes, etc) across the project area, and determine
fault orientation and kinematics. Geologic line work was initially drafted in the field during the course of systematic detailed
mapping; line editing occurred during office compilation in Adobe Illustrator (latest version CS 4). Final editing occurred
during conversion and compilation of Illustrator line work into the ArcGIS database, where it was merged with station point
geologic data. Station point geologic data, contacts and faults from previous work in the BLRI corridor were evaluated for
compilation and synthesis in the BLRI mapping project. Station point geologic data compiled from previous work are referenced
and marked with a C in the database. Compiled line work is also clearly tagged and referenced. The BLRI cuts at an oblique
angle nearly the entire width of the Blue Ridge Geologic Province in Virginia. Thus, the geology varies significantly along
its along its 216-mile traverse. North of Roanoke (BLRI MP 115), the Blue Ridge is defined as an orogen-scale, northwest-vergent,
northeast-plunging reclined anticlinorium, and from its start at MP 0 near Afton, Virginia, southward to Roanoke, the BLRI
traverses the western limb of this structure. Here, rocks range in age from Mesoproterozoic to Cambrian: Mesoproterozoic orthogneisses
and metamorphosed granitoid rocks of the Shenandoah massif comprise basement to Neoproterozoic to Cambrian mildy- to non-metamorphosed
to sedimentary cover rocks; the BLRI crisscrosses in many places the contact between cover and basement. Mesoproterozoic basement
rocks in the Shenandoah massif represent the original crust of the Laurentian (ancestral North American) continent; sedimentary
cover rocks were deposited directly on this crust during extension and breakup of the Rodinian supercontinent in the Neoproterozoic
to earliest Cambrian. Very locally, diabase dikes of earliest Jurassic age intrude older basement and cover sequences. These
dikes were emplaced in the Blue Ridge during continental extension (rifting) and the opening of the Atlantic Ocean in the
Mesozoic Era. From MP 103.3 to MP 110.3 near Roanoke, the BLRI crosses into and out of a part of the Valley and Ridge Geologic
Province. Unmetamorphosed sedimentary rocks of Cambrian to Ordovician age mostly shale, siltstone and carbonate occur here.
These rocks were deposited in a terrestrial to shallow marine environment on the Laurentian continental margin, after extensional
breakup of Rodinian supercontinent in the Neoproterozoic and earliest Cambrian, but before mid- to late-Paleozoic orogenesis.
South of Roanoke, the Blue Ridge Geologic Province quickly transitions from an anticlinorium to a stack of imbricated thrust
sheets. After crossing the southern end of the Shenandoah Mesoproterozoic basement massif (MP 124.1 to MP 144.4), the BLRI
enters the eastern Blue Ridge province, a fault-bounded geologic terrane comprised of high-metamorphic-grade sedimentary and
volcanic rocks deposited east of the Laurentian continental margin from the Neoproterozoic to early Paleozoic. These rocks
were significantly metamorphosed, deformed, and transported westward onto the Laurentian margin along major orogenic faults
during Paleozoic orogenesis. Sixty bedrock map units underlie the BLRI in Virginia. These units consist of one or more distinguishing
lithologies (rock types), and are grouped into formal and informal hierarchal frameworks based on age, stratigraphy (formations-groups),
and tectonogenesis. Many of these units exhibit characteristics and field relationships that are critical to our understanding
of Appalachian orogenesis. Most of these units are named based on the dominant occurring lithology; other units follow formal
nomenclature, some of which was developed and has been used for more than 100 years. Oldest rocks occurring along the BLRI
corridor are Mesoproterozoic orthopyroxene-bearing basement rocks of the Shenandoah massif, in the core of the Blue Ridge
anticlinorium. Preliminary SHRIMP U-Pb zircon geochronology (J. N. Aleinikoff, this study) shows that these rocks can be grouped
based on crystallization ages: Group I (~1.2 to 1.14 Ga) are strongly foliated orthogneisses and Group II (~1.06 to 1.0 Ga)
are less deformed metagranitoids. Group I orthogneisses, which occur discontinuously from near Irish Gap (MP 37) to Cahas
Overlook (MP 139), comprise 10 map units: leucogranitic gneiss (Yllg); megacrystic quartz-monzonitic gneiss (Yqg); granitic
gneiss (Yg); lineated granitoid gneiss (Ylgg); garnetiferous leucogneiss (Yglg); Sandy Creek gneiss (Ysg); porphyroblastic
garnet-biotite leucogranitic gneiss (Ygtg); dioritic gneiss (Ydg); Pilot gneiss (Ypg); and megacrystic granodioritic gneiss
(Ygg). Group II metagranitoids, which are first encountered along the BLRI at Reeds Gap (MP 14) and occur discontinuously
to Roanoke River Overlook (MP 115), comprise 8 map units: megacrystic meta-quartz monzonitoid (Yqm); massive metagranitoid
(Ymgm); megacrystic metagranitoid (Ypgm); mesocratic porphyritic metagranitoid (Ygpm); metagranodioritoid (Ygdm); Vesuvius
megaporphyritic metagranitoid (Yvm); quartz-feldspar leucogranitoid (Yqfm); and Peaks of Otter metagranitoid (Ypom). An additional
relatively undeformed metagranitoid with a preliminary SHRIMP U-Pb zircon age of ~1.12 Ga is assigned to the Bottom Creek
Suite (Ybcm), and well layered migmatitic gneiss (Ymg) near Irish Gap (MP 37) has a a preliminary SHRIMP U-Pb zircon age of
~1.05 Ga. Other rocks of Mesoproterozoic age include orthogneisses in the Fries thrust sheet between MP 139 and MP 144.5 that
range in age from ~1.19 to ~1.07 Ga: biotite-muscovite leucogneiss (Ymlg); biotite granitic augen gneiss (Ybgg); blue-quartz
gneiss (Ybqg); and biotite leucogneiss (Yblg). Latest Mesoproterozoic rocks include paragneiss and pegmatite (Yprg) near Porters
Mountain Overlook (MP 90), and a suite of igneous intrusive nelsonites and jotunites (Yjn). Two units, foliated metagreenstone
(Zdm) and foliated metagranitoid (Zgm), locally intrude older Mesoproterozoic rocks in the core of the Blue Ridge anticlinorium.
Metagreenstone is fine-grained and mafic in composition, and occur as narrow dikes and sills; metagranitoid is medium-grained
and generally felsic in composition, and intrude basement rocks as small plutons, stocks, and a few narrow dikes. On the west
limb of the Blue Ridge anticlinorium, metamorphosed sedimentary and volcanic rocks of Neoproterozoic to Cambrian age crop
out discontinuously along the BLRI from near Afton (MP 0) to MP 103.3, in the vicinity Roanoke Mountain (MP 120 to MP 124),
to near Adney Gap (MP 136). These rocks are assigned to a formal stratigraphic sequence: Swift Run Formation; Catoctin Formation;
Chilhowee Group. Metasedimentary and meta-igneous rocks of lower Paleozoic (?) to Neoproterozoic age are assigned to the Alligator
Back Formation, Lynchburg Group, and Ashe Formation. These units crop out southeast of the Red Valley fault from MP 144.5
southwestward to the North Carolina Virginia State Line at Mile Post 216.9. Rocks assigned to the Alligator Back crop out
in the Blue Ridge Parkway corridor from Mile Post 174.5 southward to the North Carolina Virginia State Line: compositional-layered
biotite-muscovite gneiss (abg); garnet-biotite-muscovite-quartz schist (abs); quartzite and quartz-rich metasandstone (abq);
and marble (abm). The following lithologic map units along the BLRI corridor are correlated with Lynchburg Group formations:
graphitic schist (lgs), muscovite-biotite metagraywacke (lmg), and graphite-muscovite-quartz metasandstone (lms). These rocks
crop out between the Red Valley fault (Mile Post 144.5) and the Rock Castle Creek fault (Mile Post 174.5). Coarse-grained-
to conglomeratic metagraywacke (acm), underlying Lynchburg Group rocks west of the Rock Castle Creek fault in the vicinity
of Rakes Millpond (MP 162.3) and Rocky Knob Visitors Center (MP 169), are considered to be the lower metamorphic grade-equivalent
of the higher metamorphic-grade Ashe Formation at its type section in northwestern North Carolina. Five meta-igneous lithologic
map units occur as mappable bodies interlayered or intrusive into metasedimentary rocks of the Alligator Back Formation and
Lynchburg Group. Altered ultramafic and ultrabasic rocks (um) occur mostly within the Lynchburg Group, but few thin bodies
also occur within laminated amphibolite gneiss (aml) locally (laminated amphibolite gneiss is associated with rocks of the
Alligator Back Formation). Amphibolites of the Lynchburg Group include biotite-bearing amphibolite (amb), clinozoisite-bearing
amphibolite (amc) and quartz-layered amphibolite (amq). Map units that occur beneath the Blue Ridge fault are assigned to
the Valley and Ridge Province. In the BLRI corridor, these rocks are first exposed near Bearwallow Gap (MP 91) and continue
southward beyond Roanoke near MP 125. Oldest formations are Shady Dolomite (Cs) and Waynesboro Formation (Cw), which regionally
can be mapped in stratigraphic continuity with cover and basement rocks of the Blue Ridge anticlinorium. Conversely, nowhere
in the Appalachians can rocks of the Elbrook Formation (Ce) or Conococheague Formation (Cco) be mapped in direct stratigraphic
continuity with Mesoproterozoic basement rocks in the core of the Blue Ridge anticlinorium; however, they do stratigraphically
overlie older Waynesboro Formation and Shady Dolomite within imbricates of the Blue Ridge fault system. Ordovician Martinsburg
Formation (Omb) occurs beneath the Pulaski fault north of Roanoke River, about 0.85 km northwest of MP 108. Paleozoic mylonite
(Pzmy) is a tectonic rock unit that that occurs in high-strain fault zones in the core of the Blue Ridge anticlinorium from
near Afton (MP 0) to Adney Gap (MP 136). Jurassic diabase (Jd) occurs in narrow dikes that intrude older map units, just south
of Roanoke River near MP 118 and MP 125, north of James River near MP 56, and in the vicinity of Afton near MP 3 and north
of MP 0.
Citation
- Title Detailed geologic mapping geodatabase for the Blue Ridge Parkway in Virginia.
-
- creation Date
2018-06-08T11:57:11.100783
Resource language:
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- URL: http://dx.doi.org/10.5066/F7DN434F
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Linkage for online resource
- name Dublin Core references URL
- URL: http://dx.doi.org/10.5066/F7DN434F
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Metadata data stamp:
2018-08-06T20:58:32Z
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- notes: This metadata record was generated by an xslt transformation from a dc metadata record; Transform by Stephen M. Richard, based
on a transform by Damian Ulbricht. Run on 2018-08-06T20:58:32Z
Metadata contact
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pointOfContact
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CINERGI Metadata catalog
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- electronic Mail Address cinergi@sdsc.edu
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Metadata record format is ISO19139 XML (MD_Metadata)