PROVENANCE, DETRITAL ZIRCON U-PB GEOCHRONOMETRY, AND TECTONIC SIGNIFICANCE OF PERMIAN TO LOWER TRIASSIC SANDSTONE IN SOUTHEASTERN QUESNELLIA, BRITISH-COLUMBIA AND WASHINGTON

U-Pb ages of Permian detrital zircons within eastern Quesnellia are si milar to ages of western and southwestern Laurentian basement province s, suggesting sedimentologica ties between the Quesnellian arc terrane and the Laurentian continental margin. The Permian to Lower Triassic Mount Roberts Formation forms the easternmost exposures of the Harper Ranch subterrane of Quesnellia. The formation consists of interbedded lithic graywacke, argillite, limestone, and volcanic rocks deposited w ithin an ensimatic arc environment. Petrology of Mount Roberts Formati on sandstones indicate derivation from lithologically diverse sources that consisted predominantly of volcanic rocks but also included signi ficant amounts of sedimentary, metamorphic, and plutonic rocks. U-Pb a ges of 27 individual detrital zircons from a single Permian to lower T riassic sandstone of the Mount Roberts Formation indicate that detritu s was derived from source terranes with ages of approximately 0.37-0.4 0 Ga, 1.0-1.3 Ga, 1.50 Ga, 1.61-1.66 Ga, 1.8-2.1 Ga, 2.36 Ga, 2.48 Ga, and 2.5-2.7 Ga. Devonian zircons are interpreted to represent first-c ycle detritus derived from an igneous source terrane that may make up local basement to the Mount Roberts Formation. Most Precambrian zircon s are well rounded by sedimentary abrasion and thus were probably deri ved from older sedimentary rocks. The ultimate sources of 1.0-1.66 Ga detrital zircons are unknown, but it is unlikely that they were derive d from the presently adjacent craton. Zircons 1.0-1.66 Ga may represen t detritus ultimately derived from southwestern Laurentia. Zircons 1.8 -2.7 Ga are similar in age to geologic provinces within western Lauren tia, suggesting presently adjacent provinces within the Laurentian cra ton as ultimate sources of some Precambrian detritus within the Mount Roberts Formation. Although Laurentia may have been the ultimate sourc e of Precambrian detritus within the Mount Roberts Formation, sediment ologic and petrologic data and regional geologic considerations strong ly suggest that most of this detritus was recycled from craton-derived sedimentary and metasedimentary rocks that composed part of Quesnelli a.