The Norbeck Intrusive Suite is an Ordovician granitic pluton in Montgomery County, Maryland. The intrusive suite was originally mapped as the Norbeck Quartz Diorite by Hopson,[1] and is shown as such on the Geologic Map of Maryland of 1968.[2] A. A. Drake later revised the name after more detailed mapping.[3] It intrudes through the Wissahickon Formation.
| Norbeck Intrusive Suite | |
|---|---|
| Stratigraphic range: Ordovician | |
 Outcrop of tonalite at Greenwood Local Park, Brookeville | |
| Type | igneous |
| Lithology | |
| Primary | tonalite, metadiorite, metagabbro |
| Location | |
| Region | Piedmont of Maryland |
| Extent | Montgomery County |
| Type section | |
| Named for | Norbeck, Maryland |
| Named by | C. A. Hopson, 1964[1] |
Description
editThree lithologies were mapped in the Kensington quadrangle by Drake:[3]
- medium- to coarse-grained, fairly massive to foliated biotite-hornblende tonalite that contains xenoliths and/or autoliths of more mafic rock
- medium-grained, quartz-augite-hornblende metagabbro that forms small bodies within the tonalite
- dark-green, well-foliated ultramafic rocks of serpentine and lesser soapstone
References
edit- ^ a b 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)
- ^ Geologic Map of Maryland, 1968. Maryland Geological Survey.
- ^ a b Drake, A.A., Jr., 1998, Geologic map of the Kensington quadrangle, Montgomery County, Maryland: U.S. Geological Survey Geologic Quadrangle Map, GQ-1774, scale 1:24,000