USING URANIUM-LEAD AGE DATING OF DETRITAL ZIRCONS TO IDENTIFY SEDIMENT PROVENANCE FOR THE MESOZOIC SANDSTONES OF THE HARTFORD BASIN

The Hartford Basin formed due to the break up of Pangaea and exposes Late Triassic to Early Jurassic alluvial fan, lacustrine, and fluvial sedimentary rocks. The provenance of the Hartford Basin sediments is not well understood due to poorly exposed outcrops and structural complexities. Zircon is a durable mineral found in virtually all sandstones and can be used to determine provenance through the use of U-Pb ages in individual grains. The ages of the zircons can then be matched with ages of surrounding rock units, thus indicating the potential source rocks. In this study, detrital zircon U-Pb ages from four sandstone samples were used to study the provenance of the sediment deposited within the Hartford Basin. Two samples were collected each from the Triassic New Haven Arkose Formation and the Jurassic Portland Formation. The samples were pulverized, sieved, panned, and washed in order to prepare for density separation with lithium metatungstate. A Frantz magnetic separator was then used to separate away the magnetic heavy minerals from the non-magnetic heavy minerals. The zircons were hand-picked from the sample using binocular and petrographic microscopes and sent to the Arizona LaserChron Center at the University of Arizona for U-Pb analyses on a Laser Ablation Inductively Coupled Plasma Mass Spectrometer. The New Haven Arkose sample was dominated by zircons with an age spectrum from 420 to 460 Ma, which coincides within the Taconic Orogeny. Additionally, the sample yielded a secondary cluster of ages between 360 and 380 Ma, which corresponds to the Acadian Orogeny. Also, there was a small group of ages between 600 and 640 Ma, which may be associated with the Avalon terrane. Given these ages, the source area may be from the local Bronson Arc terrane to the east. The zircons from the Portland Formation yielded two primary age spectra; one from 350 to 380 Ma, which corresponds with the Acadian Orogeny, and another from 440 to 480, which coincides with the Taconic Orogeny. Additionally, a minor cluster of zircons dated within a range of 1000 to 1600 Ma, which suggests a Grenville source. This preliminary analysis of the detrital zircons in the Hartford basin suggests an eastern source in the New Haven Arkose whereas the Portland Formation indicates sediment derived from both the east and west.