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National Geologic Map Database
Map showing publication footprint
  • Usage in publication:
    • Georgetown complex
  • Modifications:
    • Named
  • Dominant lithology:
    • Gabbro
    • Diorite
    • Quartz diorite
  • AAPG geologic province:
    • Piedmont-Blue Ridge province
Publication:

Hopson, C.A., 1964, The crystalline rocks of Howard and Montgomery Counties: Maryland Geological Survey County Report, 337 p., Reprinted from Cloos, Ernst, and others, "Geology of Howard and Montgomery Counties," p. 27-215


Summary:

Name given to poorly exposed complex of ultramafic, gabbroic, dioritic, and dark quartz dioritic rocks that underlie a large part of Washington, D.C., and adjacent parts of Montgomery Co., MD. Age is early Paleozoic.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Georgetown complex
  • Modifications:
    • Age modified
  • AAPG geologic province:
    • Piedmont-Blue Ridge province
Publication:

Reed, J.C., Jr., and Obermeier, S.F., 1982, The geology beneath Washington, D.C.; the foundations of a nation's capitol, IN Legget, R.F., ed., Geology under cities: Reviews in Engineering Geology, v. 5, p. 1-24.


Summary:

Briefly described as large body of igneous rocks ranging from tonalite to granite. Age of Piedmont rocks in DC area in dispute. Recent work suggests very late Proterozoic or early Paleozoic age

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Georgetown Intrusive Suite
  • Modifications:
    • Overview
  • AAPG geologic province:
    • Piedmont-Blue Ridge province
Publication:

Rader, E.K., and Evans, N.H., 1993, Geologic map of Virginia; expanded explanation: Virginia Division of Mineral Resources, 80 p.


Summary:

Georgetown Intrusive Suite used on VA State map. Description from Flemming and others (in press). Cambrian age indicated by map symbol.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Georgetown Intrusive Suite*
  • Modifications:
    • Age modified
    • Geochronologic dating
  • AAPG geologic province:
    • Piedmont-Blue Ridge province
Publication:

Map showing publication footprint
  • Usage in publication:
    • Georgetown Intrusive Suite*
  • Modifications:
    • Overview
  • AAPG geologic province:
    • Piedmont-Blue Ridge province
Publication:

Fleming, A.H., Drake, A.A., Jr., and McCartan, Lucy, 1994, Geologic map of the Washington West quadrangle, District of Columbia, Montgomery and Prince Georges Counties, Maryland, and Arlington and Fairfax Counties, Virginia: U.S. Geological Survey Geologic Quadrangle Map, GQ-1748, 1 sheet, scale 1:24,000 [http://ngmdb.usgs.gov/Prodesc/proddesc_277.htm]


Summary:

The Georgetown Intrusive Suite is divided into six mappable units in the map area and consists of a biotite tonalite, garnetiferous biotite-hornblende tonalite, biotite-hornblende tonalite, quartz gabbro and quartz diorite, metapyroxenite and hornblendite, and serpentinite and talc schist. The Georgetown is predominantly made up of the mafic biotite-hornblende tonalite, and the quartz gabbro and biotite tonalite make up smaller plutons. Possibly five intrusive phases can be identified within this intrusive suite that intrudes surrounding metasedimentary rocks. The Georgetown Intrusive Suite is of Early Ordovician age.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Georgetown Intrusive Suite*
  • Modifications:
    • Revised
    • Age modified
    • Areal extent
  • AAPG geologic province:
    • Piedmont-Blue Ridge province
Publication:

Drake, A.A., Jr., and Froelich, A.J., 1997, Geologic map of the Falls Church quadrangle, Fairfax and Arlington Counties and the City of Falls Church, Virginia, and Montgomery County, Maryland: U.S. Geological Survey Geologic Quadrangle Map, GQ-1734, 1 sheet, scale 1:24,000


Summary:

Georgetown Complex of Hopson (1964) is here revised as Georgetown Intrusive Suite because it consists of rocks of only one genetic class (igneous) (North American Commission on Stratigraphic Nomenclature, 1983, art. 36,37). Unit is extended to VA. Rocks are intruded by Kensington Tonalite (revised). The Georgetown is of Early Ordovician age.

Source: GNU records (USGS DDS-6; Reston GNULEX).


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Asterisk (*) indicates published by U.S. Geological Survey authors.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

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