DETRITAL ZIRCON PROVENANCE OF CAMBRIAN TO TRIASSIC MIOGEOCLINAL AND EUGEOCLINAL STRATA IN NEVADA

U-Pb analyses have been conducted on 176 abraded single detrital zirco ns from Cambrian to Triassic miogeoclinal and eugeoclinal strata in Ne vada. Concordant to slightly discordant ages for 154 of these grains r ecord derivation from a wide range of crystalline provinces in central and western North America. Miogeoclinal strata apparently received mo st of their detritus from: (1) cratonal rocks in a wide area of the we stern and central United States during Early Cambrian time (Osgood Mou ntains Quartzite), (2) the Peace River arch area of northwestern Canad a during Middle Ordovician time (Eureka Quartzite), (3) basement rocks of the southwestern United States during Middle Devonian time (Oxyoke Canyon Sandstone Member of the Nevada Formation), and (4) basement ro cks of the southwestern United States, Cambrian plutons in the Colorad o-Oklahoma region, and a Cordilleran-margin Triassic arc system during Late Triassic time (Chinle Formation). Comparison of detrital zircon ages in miogeoclinal strata with grains in eugeoclinal strata of the H armony and Valmy formations of the Roberts Mountains allochthon indica tes that Harmony detritus was derived primarily from off-shore basemen t exposures rather than the cratonic Salmon River arch, whereas the Va lmy is a lateral facies equivalent of the Eureka Quartzite and is comp osed of detritus derived from the Peace River arch region. Correlation of the Eureka and Valmy formations supports previous interpretations that the Roberts Mountains allochthon is composed of slope, rise, and basinal sediments deposited just offshore from the Cordilleran margin. Comparison of zircons in a Triassic basinal assemblage (Osobb Formati on of the Auld Lang Syne Group) that overlies rocks belonging to the G olconda allochthon with Chinle zircons supports previous interpretatio ns that the Osobb is a linked facies equivalent of the Chinle. This ti es the Golconda allochthon and perhaps other rocks of the Sonomia terr ane to the Cordilleran margin by Late Triassic time.