Ellicott City Granodiorite

Ranges from biotite granodiorite along margin of body to quartz monzonite in core; age of quartz monzonite core 420 +/- 50 m.y. * by radiogenic dating.
State Maryland
Name Ellicott City Granodiorite
Geologic age Silurian
Lithologic constituents
Major
Igneous > Plutonic > Syenitic > Quartz-monzonite
Minor
Igneous > Plutonic > Granitic > Granodiorite
Comments Radiogenic date from Wetherill et al., 1966 (ref. MD003). Also second age date reference from USGS Geologic Names lexicon (ref. MD004): Isotopic dating (Rb-Sr) of the Ellicott City Granodiorite indicates the unit is of Silurian age (425 Ma).
References

Cleaves, E.T., Edwards, J., Jr., and Glaser, J.D., 1968, Geologic Map of Maryland: Maryland Geological Survey, Baltimore, Maryland, scale 1:250,000.

In 1995 the Water Resources Division of the U.S. Geological Survey digitized the geologic map of Maryland from the 1968 paper map (Reference MD001). Information about products from the Maryland Geological Survey can be found at http://www.mgs.md.gov/.

Wetherill, G.W., Tilton, G.R., Davis, G.L., Hart, S.R., and Hopson, C.A., 1966, Age measurements in the Maryland Piedmont: Journal of Geophysical Research, v. 71, p. 2139-2155.

USGS Geologic Names lexicon found at: http://ngmdb.usgs.gov/Geolex/

https://ngmdb.usgs.gov/Geolex/search

NGMDB product
Counties Baltimore - Howard