Thermal History of Central and Southern Appalachian Basin Based on Apatite Fission-Track Thermochronology

M. K. Roden

Seventy samples from the Tioga ash bed and Upper Devonian Hampshire and Chemung Formations were collected throughout the central and southern Appalachian basin for apatite fission-track analysis. Apatite fission-track apparent ages younger than depositional age (390 Ma) indicate that the sediments were subjected to temperatures greater than 100°C prior to approximately 250 Ma.

The samples of Tioga ash bed from Pennsylvania have an average apatite fission-track apparent age of 220 ± 4 Ma, which decreases to the east to 153 ± 6 Ma at Swatara Gap, Pennsylvania. This range is consistent with CAI contours that indicate higher temperatures (deeper burial) in eastern Pennsylvania.

In Maryland, northeastern West Virginia, and northwestern Virginia, apatite fission-track apparent ages range from 246 ± 37 Ma in the west to 110 ± 28 Ma in the central section. This decreases to 95 ± 18 Ma in the east. These relationships are consistent with the CAI values, which increase eastward from 3.0 to a maximum of 4.0. In southwestern Virginia, the mean apatite fission-track apparent age is 182 ± 6 Ma for five samples.

Confined fission-track length distributions for the sediment and ash bed samples from the central and southern Appalachians range from 12.3 ± 1.9 µ in the east to 13.1 ± 1.5 µ in the west. These mean track lengths are shortened from an initial track length of 16 µ. Exposure to temperatures in the range of 20°-125°C during the last 200 m.y. can produce the observed track lengths.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.