GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 169-2
Presentation Time: 9:00 AM-6:30 PM


DECK, Eric, Geography-Geology, Illinois State University, Campus Box 4400, Normal, IL 61761, MALONE, David H., Geography-Geology, Illinois State University, Campus Box 4400, Normal, IL 61790-4400 and CRADDOCK, John P., Geology Department, Macalester College, 1600 Grand Avenue, St. Paul, MN 55105,

More than 1500 m of Paleozoic strata occur in the Sacramento Mountains, making this one of the largest and most complete exposures of Paleozoic strata in North America. The core of the Sacramento Mountains reveal compressional structures associated with the Pennsylvanian-Permian Ancestral Rocky Mountain Orogeny. The Permian Abo Formation consists of interbedded sandstone, conglomerate, limestone and shale and rests above the Ancestral Rocky Mountain unconformity. U-Pb analysis of detrital zircons extracted from quartzite clasts in basal conglomerates reveal a maximum depositional age of their protolith to be 1110 ± 15 Ma. Most (>40%) of the detrital zircon age spectrum is Grenville (1000-1300 Ma) in age, with a peak age of 1209 Ma. Midcontinent Granite-Rhyolite (1300-1500 Ma) comprise about 33% of the ages, and have a peak age of 1431 Ma. Smaller age populations of Yavapai-Mazatzal (1600-1800 Ma; age peak =1676 Ma), Trans-Hudson (1800-2000 Ma; peak age = 1820 Ma), and Archean (>2.5 Ga, age peak = 2819 Ma) also are present). U-Pb Detrital zircon ages from these quartzite clasts indicate that these clasts were likely derived from the Proterozoic Lanoria Formation, which is exposed now in the Franklin Mountains >150 km to the south. The Lanoria is identical to the Abo clasts in terms of maximum depositional age and detrital zircon age peaks. The protolith sandstone of these quartzite clasts was derived from the Grenville highlands of the Llano region of central Texas, and then transported west to the Rodinian continental margin at ~1110 Ma, where they were eventually buried and metamorphosed to quartzite. These quartzites were subsequently uplifted and eroded during the Ancestral Rocky Mountain Orogeny and transported north and west from the Pedernal Uplift to the adjacent Orogrande Basin during the early Permian.