NEW DETRITAL ZIRCON U-PB DATA FROM NORTHERN NEVADA: CAMBRIAN MIOGEOCLINAL STRATA AND HARMONY FORMATION

New U-Pb detrital zircon ages document marked changes in provenance with time for two unrelated stratigraphic units from northern Nevada. The eleven samples (n=959) included: (1) six samples from the Cambrian Osgood Mountains Quartzite and Preble Formation in and near the Osgood Mountains, and (2) five samples from the Harmony Formation in the Osgood Mountains, Sonoma Range, and Galena Range. The Osgood Mountains Quartzite and the Preble Formation are stratigraphically continuous, and are part of the Neoproterozoic-Early Paleozoic miogeocline. The Harmony Formation is a distinctive arkosic unit of the Roberts Mountains Allochthon, and has been identified as either Cambrian or Devonian. The samples from the Osgood Mountains and vicinity record a change in provenance with time. One Osgood Mountains Quartzite sample yielded mainly ca 980 Ma-1.2 Ga and 1.7-1.8 Ga ages, consistent with derivation from the Grenville orogen and Yavapai Province, respectively. The other two Osgood Mountains Quartzite samples and those from the overlying Preble Formation yielded mainly ca. 1.64-1.89 Ga, ca 1.3-1.5 Ga, and ca 2.4-2.9 Ga ages, consistent with derivation from the Mazatzal and Yavapai Provinces, the midcontinent region, and the Achaean craton, respectively. The Harmony Formation samples show a similar dichotomy in detrital zircon provenance. Two of the Harmony Formation samples, both from the Galena Range, yielded mainly ca 990 Ma-1.2 Ga and 1.7 Ga-1.8 Ga ages, consistent with derivation from the Grenville orogen and Yavapai Province, respectively. The other samples, one each from the Galena Range, the Sonoma Range, and the Osgood Mountains, yielded mainly 1.73 Ga-1.9 Ga and 2.6 Ga-2.8 Ga ages, consistent with derivation from the Yavapai Province and the Achaean Craton, respectively. These new results from the Osgood Mountains vicinity record the initial deposition of Grenville-rich sands onto the emerging Cordilleran miogeocline, and a younger Grenville-poor sand being deposited from more proximal Yavapai-Mazatzal source rocks. They are similar to detrital zircon ages reported from Neoproterozoic-Early Paleozoic rocks in southeast Idaho, northern Utah, and southern and eastern Nevada. The overall pattern of Harmony Formation detrital zircon provenance is similar to that of the Osgood-Preble section.