Ellicott City Granodiorite

Ellicott City Granodiorite
Stratigraphic range: Ordovician
An outcrop on Main Street, Ellicott City
Typeigneous
Location
RegionPiedmont of Maryland
ExtentHoward and Baltimore Counties
Type section
Named forEllicott City, Maryland
Named byKnopf and Jonas, 1929[1]
Photomicrograph of Ellicott City Granodiorite under crossed polarized light. Field represents approximately 0.85 cm.
Former quarry wall of the granodiorite in Baltimore County southeast of Ellicott City

The Ellicott City Granodiorite is a Silurian or Ordovician granitic pluton in Howard and Baltimore Counties, Maryland. It is described as a biotite granodiorite along the margin of the intrusion which grades into a quartz monzonite in its core.[2] It intrudes through the Wissahickon Formation and the Baltimore Gabbro Complex.

In 1964, C. A. Hopson grouped the Ellicott City Granodiorite with the Guilford Quartz Monzonite and the Woodstock Quartz Monzonite as "Late-kinematic intrusive masses."[3]

In 1980, Crowley and Reinhardt of the Maryland Geological Survey remapped the Ellicott City Quadrangle and referred to this unit as the Ellicott City Granite, rather than granodiorite.[4]

  1. ^ Knopf, E.B., and Jonas, A.I., 1929, Baltimore County report: Maryland Geological Survey County Report, 420 p.
  2. ^ USGS Mineral Resources On-Line Spatial Data
  3. ^ 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)
  4. ^ Crowley, W.P. and Reinhardt, Juergen, 1980, Geologic map of the Ellicott City quadrangle, Maryland: Maryland Geological Survey, scale 1:24,000. (online)