NEW GEOLOGIC MAPPING AND AGE CONSTRAINTS IN THE HYCO ARC OF THE CAROLINA TERRANE IN ORANGE COUNTY, NORTH CAROLINA
New U-Pb (zircon) crystallization ages for the top of the pyroclastic sequence in southern Orange County from a dacitic tuff (630 ± 1 Ma) from Morgan Creek and a dacite (628.5 ± 1 Ma) from the American Stone Quarry, coupled with previously published dates, indicate southern Orange County is dominated by ~ 630 Ma primary pyroclastics, associated lavas and intrusives. In northern Orange County, a new U-Pb age (613 ± 1 Ma) from a felsic tuff interlayer in a dominantly epiclastic unit, coupled with previously published dates from adjacent northern Durham County, indicate that the area is dominated by ~ 615 Ma lithologies.
Past workers designated the study area as part of the Hyco and Aaron formations of the Virgilina sequence, in which epiclastic rocks were assigned to the regionally extensive Aaron formation. Previously reported youngest detrital zircon ages of ~ 578 and ~ 588 Ma from two separate locations in the Aaron formation prevent direct correlation of texturally similar rocks in the Orange County area. It is speculated that each volcanic center had its own volcaniclastic apron that likely interfingered with volcaniclastic aprons of adjacent volcanic centers. Based on the new data, we have tentatively identified Upper (~ 615 Ma) and Lower (~ 630 Ma) members (informal) of the Hyco Arc.