DETRITAL ZIRCON GEOCHRONOLOGY FROM THE CAMBRIAN-ORDOVICIAN BLISS SANDSTONE, NEW MEXICO: EVIDENCE FOR CONTRASTING GRENVILLE-AGE AND CAMBRIAN SOURCES ON OPPOSITE SIDES OF THE TRANSCONTINENTAL ARCH

Cambrian sandstones of the SW U.S. record deposition above a major unconformity on the rift margin of Laurentia. Detrital zircon ages from the Cambro-Ordovician Bliss Sandstone in New Mexico are used to test models for the influence and significance of the Transcontinental Arch. We obtained U-Pb zircon ages of basement rocks to test potential local source rocks in New Mexico. Two samples of the Florida Mts. granite underlying the Bliss Sandstone yield ages of 500-506 Ma, and these distinctive ages can be used as tracers for transportation paths. The Bliss was studied from 8 localities; three are west of the Cambrian Florida granite. The most abundant zircon population has a main peak at 1250 Ma. Other significant peaks are at 1465 Ma, 1710 Ma, 1850 Ma, and 1625 Ma. There are only 5 Archean zircons out of a total of 966 analyses. Cambrian detrital zircons are present in the Florida Mts., directly overlying the Cambrian granite. They are also present in the Burro Mts. NW of the Florida Mts. and in the Little Hatchet Mts. to the SW. Localities east of the Florida Mts. did not have any Cambrian zircons. We interpret these data as indicating that the Cambrian intrusions of the mid-Continent were not a source for the Cambrian zircons in the Bliss Sandstone. The Tapeats Sandstone in the Grand Canyon does not have Cambrian zircons and has a minor Grenville peak at 1070 Ma (Gehrels et al., 2011), significantly younger than the 1250 Ma Grenville peak in the Bliss Sandstone. We interpret these differences as being related to different source areas on opposite sides of the Transcontinental Arch. The differences in the specific ages of Cambrian plutons between the Oklahoma rift and the Florida Mts. granite can be used to test depositional models for other Cambrian sandstones of the southwest U.S. and in Mexico.