GEOLOGY OF THE CHERRY HILL 7.5-MINUTE QUADRANGLE, VIRGINIA

The Cherry Hill Quadrangle straddles the Coastal Plain and Piedmont provinces in the fall zone of southeastern Virginia (Tidewater Fall Line of Weems, 1998). Rocks of the Roanoke Rapids terrane crop out in the western part of the quadrangle and consist of Neoproterozoic greenschist- to amphibolite-facies felsic to intermediate metavolcanics, greenstone, metasiltstone, and metadiorite and metagabbro. Most of these rocks are strongly foliated and isoclinally folded, but some preserve primary bedding and volcanic layering. Cambrian mica schist, Silurian-Devonian foliated metagranite, and Mississippian massive and porphyritic granite crop out in the eastern part of the quadrangle and are part of the Dinwiddie terrane and the late Paleozoic De Witt pluton. Upper greenschist- to lower amphibolite-facies mica schist contains porphyroclasts of staurolite that preserve an earlier foliation as inclusion trails. Foliation in granites of the De Witt pluton may be magmatic. Greenschist-facies, highly strained granitic mylonite within the Nottoway River fault zone separate the Dinwiddie terrane from the Roanoke Rapids terrane.

Sand and gravel deposits of the Atlantic Coastal Plain overlie Piedmont rocks. Two units assigned to the upper part of the Neogene-Pleistocene Chesapeake Group occur at elevations up to 90 meters above sea level in the central part of the quadrangle. Two units of the Quaternary Bacons Castle Formation occupy elevations up to 55 meters above sea level in the eastern part of the quadrangle. In the western part of the quadrangle, multiple levels of terrace deposits are the fluvial equivalent of estuarine to marine units of the Coastal Plain to the east.

Brittle faults juxtapose Piedmont rocks against sediments of the Chesapeake Group. These Cenozoic faults were uncovered in mine excavations in the late 1990s; new mapping indicates that many of these faults are reactivated silicified cataclasites that occur throughout the Piedmont rocks of the quadrangle. Silicified cataclasites are typically mineralized with iron and iron sulfide minerals. The quadrangle was the focus of mining for heavy minerals, including ilmenite and zircon, in upland Coastal Plain deposits beginning in the mid-1990s. Precious metals, brick clay, crushed stone, and millstones have also been prospected or quarried.