Catoctin Formation - Metabasalt breccia (low titanium)

Metabasalt breccia (low-titanium) (Espenshade, 1986). Blocky or angular fragments of grayish-green, fine grained rock in a fine-grained, ge erally schistose matrix. Breccia fragments range from 1 to 20 cm long, and form rough, knobby surfaces on weathered outcrops. Where present, this breccia occurs at or near the base of Catoctin metabasalt (CZc) on the southeast limb of the Blue Ridge anticlinorium; the unit is as much as 3000 feet thick. Furcron (1939) mapped both high- and low-titanium breccias as Warrenton agglomerate; R.L. Smith (personal communication in Espenshade, 1986) interpreted the breccias as subareal agglutinates. Kline and others (1990) presented evidence that the breccias are hyaloclastite pillow breccias, erupted in a subaqueous environment. Reed (1955) recognized a mappable stratigraphy within the Catoctin, and made the interpretation that the greenstones were metamorphosed tholeiitic flood basalts that originated in a "nonorogenic" setting. Rankin (1975) considered the Catoctin to have originated during continental volcanism associated with the opening of a proto-Atlantic Iapetus ocean in Latest Precambrian time, and included the Catoctin in the Crossnore volcanic-plutonic group. Badger and Sinha (1988) studied chemical stratigraphy within individual fl ows and dated Catoctin metabasalts at 570 ± 36 Ma using Rb-Sr systematics on samples showing little evidence of elemental mobility during metamorphism. This date is consistent with radiometric age data from Catoctin metarhyolite, discussed above, and with the occurrence of Early Cambrian-age Rusophycus stratigraphically above the Catoctin near the base of the Chilhowee Group (Simpson and Sundberg, 1987). These constraints suggest that some portion of the Catoctin may be as young as Cambrian in age. Regional mapping suggests that metabasalts and amphibole gneisses within the Ashe (Zaa), Alligator Back (CZas), and Bassett Formations (CZba) are volcanogenic rocks that are correlative with the Catoctin in a lithostratigraphic sense and in terms of tectonic setting, but not necessarily in a strict time sense. Catoctin volcanism likely spanned a considerable time period; correlative units to the southwest were probably time-transgressive to a degree.
State Virginia
Name Catoctin Formation - Metabasalt breccia (low titanium)
Geologic age Proterozoic Z-Cambrian
Lithologic constituents
Major
Metamorphic > Metaigneous > Metavolcanic > Metabasaltmeta-basalt breccia
Comments Blue Ridge Anticlinorium (Central)
References

Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000.

Virginia Division of Mineral Resources, 2003, Digital Representation of the 1993 Geologic Map of Virginia, Publication 174, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, scale 1:500,000.

NGMDB product
Counties Culpeper - Fauquier