Near-vertical, northwest- and north-trending diabase dikes of Early Jurassic age were emplaced during the extensional event that led to the opening of the Atlantic Ocean. The diabase is fine to coarse grained, massive, dense, and composed of plagioclase, augite, olivine, and quartz. These dikes occur along northwest and north-northeast strikes, and in north-northwest-striking, right-stepping en echelon trends. An 40Ar/39Ar radiometric date of 200 Ma (Kunk and others, 1992) was obtained from the 4.5-m-wide granophyric diabase dike on the B&O railroad cut along the Potomac River (chemical samples 23-26, table 1, and isotopic sample 1, fig. 3). Two of the diabase dikes cut the Short Hill fault.
U.S. Geological Survey, U.S. Department of the Interior
This page is https://pubs.usgs.gov/bulletin/b2123/jurassic.html
Contact: Scott Southworth
Last modified 08.29.00
This page is https://pubs.usgs.gov/bulletin/b2123/jurassic.html
Contact: Scott Southworth
Last modified 08.29.00