Implications of Fission-Track Ages from Kaplan Geothermal-Geopressure Zone, Vermilion Parish, Louisiana: ABSTRACT

Abstract

Apatite and zircon mineral separates were extracted from cores from near the bottom of two geopressured-geothermal wells in Vermilion Parish, southern Louisiana, and dated by the fission-track method. Samples were taken in the sandstone units of the Oligocene age Frio Formation. The purpose of the study was to determine if fission-track clocks had been affected by long-term heating within the zone. Downhole temperature measurements indicate that the samples are currently at ~277°F (136°C) and ~338°F (169°C). Fission-track clocks, such as apatite and zircon, lose their tracks when subjected to temperatures of ~212°F (100°C) and ~ 347°F (175°C), respectively, for geologically significant periods of time (1 m.y.). Results show that apatite clocks were reset to 0 m.y. whereas zircon yielded ages of 82 and 88 m.y. (Cretaceous). If bottomhole temperatures are reliable, then the data suggest the following. (1) Zircon ages are relict, reflecting times of cooling of the volcanic, plutonic, or metamorphic source. The Frio Formation in southern Louisiana was at least in part derived from a Cretaceous or older source. Such cooling ages are common in the Ouachitas, southern Appalachians, and the Gulf coast plain. (2) Reset apatite and relict zircon ages suggest that temperatures within the geopressured zone have probably not been any higher than the 347°F (175°C) they are today. End_of_Article - Last_Page 1428------------