Provenance of the Neoproterozoic Johnnie Formation and Stirling Quartzite, southeastern California, determined by detrital zircon geochronology and Nd isotope geochemistry

Abstract

Detrital zircon geochronology coupled with Nd isotopic data constrains the provenance of the Neoproterozoic Johnnie Formation and Stirling Quartzite in the southern Nopah Range, southeastern California, and provides data to test a model of the early tectonic evolution of the southwestern Laurentian continental margin. A total of 228 detrital zircon grains from four samples of quartzose arenite, were analyzed by sensitive high resolution ion microprobe – reverse geometry (SHRIMP-RG). To supplement the provenance information derived from these grains, whole-rock Nd isotopic compositions of four coarse- and fine-grained samples were analyzed from the Rainstorm Member of the Johnnie Formation. Paleo- and Mesoproterozoic zircons dominate the lower Johnnie Formation and upper Stirling Quartzite, whereas the middle Johnnie Formation and lower Stirling Quartzite have a greater proportion of late Grenville-aged detritus, lesser amounts of older ∼1400Ma Mesoproterozoic grains, and a scattering of Paleoproterozoic grains. Archean-aged zircons occur in both samples of the Johnnie Formation and both samples of the Stirling Quartzite. We interpret this distribution to indicate a source area composed of a mixture of local and distal provenance components. Sedimentary rock Nd isotopic compositions are characterized by low ɛNd (0) values that range from −16.1 to −20.0, are independent of grain size or 147Sm/144Nd ratios, and suggest derivation from Nd Provinces 2 and 3 (Yavapai and Mazatzal provinces). Shifting provenance patterns from the Johnnie Formation and superjacent Stirling Quartzite and Wood Canyon Formation indicate an evolving provenance recorded by a general up-section increase of late Grenville-aged detritus. These data support a Laurentian provenance for Johnnie Formation detritus composed of contributions from both distal source areas in the cratonic interior and local source areas in the rift shoulder, which is consistent with its deposition as part of a post-rift, early-stage, passive-margin succession.