DETRITAL ZIRCON AND MAGMATIC U-PB GEOCHRONOLOGY OF MESOPROTEROZOIC BASEMENT UNITS, WEST TEXAS, U.S.A.: IMPLICATIONS FOR GRENVILLIAN FORELAND BASIN EVOLUTION ALONG THE GRENVILLE FRONT TECTONIC ZONE

The Grenville orogen lacks a foreland basin along nearly its entire exposed length in North America, precluding examination of orogenic evolution recorded in foreland basin sediments. New U-Pb detrital zircon geochronology is presented for the late Mesoproterozoic Hazel and Lanoria Formations (West Texas), purported Grenvillian foreland clastic sequences, with new U-Pb zircon crystallization ages for magmatic rocks that overlie and intrude the Lanoria and constrain its depositional age. These new data permit comparisons with the Middle Run Formation, the only other known Grenvillian foreland sequence (US midcontinent subsurface), and other late Grenvillian clastic sequences across Laurentia. The Lanoria Formation (quartz arenite and feldspathic arenite) is overlain by Thunderbird rhyolite (1117 +/- 8Ma [2 sigma]) and intruded by Red Bluff Granite (1109 +/- 8 Ma). The Hazel Formation (eolian litharenite-fluvial conglomerate redbed sequence) was deposited on a 1260-1240 Ma volcanic-sedimentary sequence (Allamoore and Tumbledown Formations) and contains clasts of those units. The Hazel and underlying formations were interfolded within the Grenville Front Tectonic Zone footwall at ca. 1035 Ma. The Lanoria Formation is dominated by ages correlated with central Laurentian (1510-1360, 1800-1600 Ma) and eastern Laurentian Grenvillian (1280-1120 Ma) basement age provinces, with minor Archean ages (2900-2500 Ma). The Hazel Formation is dominated by central Laurentian Proterozoic and Archean basement ages, proximal sources within the exhuming Grenville orogen (1380-1320, 1280-1230 Ma), and ca. 1100 Ma ages correlated with the southwest Laurentia large igneous province, which was emplaced into central Laurentian terranes. The Lanoria is thus dominated by distal cratonic and eastern Laurentian orogenic input. The Hazel contains a mix of proximal syn-orogenic and distal cratonic input. Age constraints require that the Lanoria and Hazel Formations are not time-correlative, paired distal-proximal facies of a Grenvillian foreland basin, as was previously proposed. The Hazel Formation is lithologically identical to the Middle Run Formation and was deposited during a similar syn- to late Grenvillian time span. This is consistent with the presence of a foreland basin receiving cratonic and orogenic sediment input extending along the US midcontinent region during the Grenvillian orogeny.