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

Abstract

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/degree/C prior to approximately 250 Ma. The samples of Tioga ash bed from Pennsylvania have an average apatite fission-track apparent age of 220 /plus minus/ 4 Ma, which decreases to the east to 153 /plus minus/ 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 /plus minus/ 37 Ma in the west to 110 /plus minus/28 Ma in the central section. This decreases to 95 /plus minus/ 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 /plus minus/6 Ma for five samples. Confined fission-track length distributions for the sediment and ash bed samples from the central and southern Appalachians rangemore » from 12.3 /plus minus/ 1.9 /mu/ in the east to 13.1 /plus minus/1.5 /mu/ in the west. These mean track lengths are shortened from an initial track length of 16 /mu/. Exposure to temperatures in the range of 20/degree/-125/degree/C during the last 200 m.y. can produce the observed track lengths.« less