Paper No. 9
Presentation Time: 3:30 PM
WEATHERING, PROVENANCE, AND TECTONIC SETTING OF THE NEOPROTEROZOIC STIRLING QUARTZITE, DEATH VALLEY AREA, CALIFORNIA: A GEOCHEMICAL PERSPECTIVE
The Neoproterozoic to Cambrian age stratigraphic succession along the Cordilleran margin in eastern California preserves a stratigraphic record that passes through several significant stages, including initial fault-controlled rift-basin development followed by subsequent thermal-mechanical and loading subsidence of a passive margin. Major-, trace-, and rare-earth-element (REE) geochemistry of the Stirling Quartzite are used to evaluate the nature of provenance in an effort to reconstruct the tectonic setting of sediment formation. In A-CN-K compositional space Stirling sediments define a linear array that suggests the unweathered source has a granodioritic composition. Such scatter indicates that fluvial systems incised most parts of a well developed weathering profile. Chondrite-normalized REE patterns are of uniform shape with a negative Eu anomaly (Eu/Eu* = 0.66), LREE enrichment (chondrite normalized La/Sm=4.17), and a flat heavy REE distributions (chondrite normalized Gd/Yb=1.69) that are characteristic of average upper crust, average shale, and bedrocks of the Mojave region. A plot of Th/Sc vs. Zr/Sc suggests that Stirling sediments experienced zircon enrichment due to sedimentary sorting and recycling, a result suggestive of passive margin sedimentation. Variation in CIA vs. stratigraphic position shows an upward excursion from intensely weathered towards toward less weathered values (CIA: 74 to 53, PIA: 98 to 78) from the lower to middle Stirling Quartzite. In the absence of a tectonic event to drive such changes, such compositional variation is likely to result from variations in weathering.