PROVENANCE IMPLICATIONS OF NEW U-PB DETRITAL ZIRCON DATA FROM CAMBRIAN PASSIVE MARGIN STRATA OF NORTHERN NEVADA
LINDE, Gwen M., Geological Sciences, University of Nevada, Reno, NV 89557, CASHMAN, Patricia H., Geological Sciences, University of Nevada, Reno, Reno, NV 89557, DICKINSON, William R., Department of Geosciences, University of Arizona, Tucson, AZ 85721 and TREXLER, James H., Department of Geological Sciences and Engineering, University of Nevada, MS 172, 1664 N Virginia St, Reno, NV 89557, email@example.com
New analysis of detrital zircons from continuous Neoproterozoic-Early Paleozoic passive margin stratigraphy in Nevada reveals a systematic change in provenance of the Neoproterozoic-early Paleozoic Laurentian passive margin. The six samples (n=757) include: (1) three samples from the Cambrian Osgood Mountains Quartzite and (2) three samples from the Cambrian Preble Formation. Both units are in the Osgood Mountains and vicinity. The older Osgood Mountains Quartzite sample yielded mainly ca 980 Ma-1.2 Ga, 1.3-1.4 Ga, and 1.7-1.8 Ga ages, consistent with derivation from the Grenville orogen and Yavapai Province, respectively. The two younger 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. These new results from the Osgood Mountains and vicinity record the initial deposition of Grenville-rich sands onto the emerging Laurentian passive margin, and younger Grenville-poor sands being deposited from more proximal Yavapai-Mazatzal source rocks.
Examination of detrital zircon ages reported from Neoproterozoic-Early Paleozoic passive margin rocks in Idaho, Utah, and California reveals a similar change in provenance with time. Older strata, the Kelly Canyon and Mutual formations of Utah, the Caddy Canyon Quartzite of Utah and Idaho, and the Johnnie Formation of California, yield detrital zircon ages similar to the older Osgood Mountains Quartzite. The younger strata, the Middle Windy Pass and Geersten Canyon Formations and the Prospect Mountain Quartzite of Utah, and the Zabriskie Formation of California, yield detrital zircon ages similar to the younger Osgood Mountains Quartzite and Preble Formation. We hypothesize that the flexural uplift of a major crustal feature, such as the Transcontinental Arch, blocked the transport of sediments rich in Grenville-age detritus from mid-Laurentia to the western passive margin in early Cambrian time. Timing of this provenance shift may allow correlation of rocks that are otherwise difficult to date.