Combined single-grain (U-Th)/He and U/Pb dating of detrital zircons from the Navajo Sandstone, Utah

Abstract

Radioisotopic dating of detrital minerals in sedimentary rocks can constrain sediment sources (provenance), elucidate episodes and rates of ancient orogenesis, and give information on paleogeography and sediment-dispersal patterns. Previous approaches have been restricted to the application of a single technique, such as U/Pb or fission-track dating, to detrital grains. These methods provide crystallization and cooling ages, respectively, of sediment sources (terranes). However, evidence for source regions from a single technique can be ambiguous because candidate source terranes often have similar ages for a given radioisotopic system. This ambiguity can be avoided by applying multiple radioisotopic systems to individual detrital grains. Here we present a method for measuring both (U-Th)/He and U/Pb ages of single crystals of detrital zircon, providing both formation and cooling ages (through ϳ180 ؇C). We applied this technique to zircons from the Lower Jurassic Navajo Sandstone, which represents one of the largest erg deposits in the geologic record. A large fraction of these zircons was derived from crust that formed between 1200 and 950 Ma, but cooled below ϳ180 ؇C ca. 500-250 Ma. This history is characteristic of Grenvillian-age crust involved in Appalachian orogenesis (and subsequent rifting) in eastern North America. Our finding requires the existence of a transcontinental sediment-dispersal system capable of moving a large volume of detritus westward (modern coordinates) throughout the late Paleozoic and early Mesozoic.

Tectonosedimentary Relations of Pennsylvanian to Jurassic Strata on the Colorado Plateau

“…Following retirement in 1991, he began working with University of Arizona professor George Gehrels to identify sandstone provenance using detrital-zircon U-Pb geochronology. This led to determination that much of the Pennsylvanian to Jurassic sandstone of the Colorado Plateau was derived from the orogenic belt now associated with the Appalachian Mountains (Dickinson and Gehrels, 2003; see also Rahl et al, 2003).…”

U–Pb and Th–Pb dating of apatite by LA-ICPMS

“…Combining U-Th-Pb apatite dating by LA-ICPMS with the apatite (U-Th)/He thermochronometer is slightly more challenging as (U-Th)/He dating is performed on whole crystals, not polished grain mounts. However several studies have undertaken U-Pb detrital zircon dating by LA-ICPMS on the exterior of unmodified zircon grains (e.g., Rahl et al, 2003), and modifying this procedure for apatite double dating is entirely possible. Combining U-Th-Pb apatite dating with Nd isotopic analysis (e.g., Foster and Vance, 2006) is also feasible.…”

Uplift, denudation, and their causes and constraints over geological timescales

“…The effective closure temperature for the first system is about 200-320°C, while for the second it is generally inferred to be in excess of 700°C. Similarly, Rahl et al (2003) combined zircon (U-Th)/He (closure temperature around 180°C) with zircon U-Pb, and Garver et al…”