EDIACARAN VOLCANIC REMNANTS OF THE STIRLING QUARTZITE, NEVADA: PETROGENETICS AND POTENTIAL RELATIONSHIP TO CONTINENTAL RIFTING EVENTS

The predominantly fluvial Stirling Quartzite of eastern Nevada contains depositional remnants of basalt flows that in total are up to 46 to 21 m thick. These mafic flows are typically approximately and experienced very low-grade metamorphism. Basalts locally form columns, indicating relatively fast cooling in a static environment, and contain peperitic textures that relate to lenses of mudstone and locally cross-bedded sandstone intercalated with interpreted flows. These basalts primarily exhibit porphyritic textures, with abundant pseudomorph crystals from plagioclase and pyroxene. Diopside crystals are also present a rich plagioclase groundmass. Basalts have low SiO₂ concentrations (45.2% - 51.4%) and geochemically and petrographically can be characterized as meta-basalts and meta basaltic-andesites with a subalkaline signature. Norm CIPW show silica oversaturated magmatism consistent with tholeiitic characteristics. Petrogenetic diagrams suggest an E-MORB signature, from sources that were moderately enriched and typical of continental rifting. Together, these results indicate a possible relation between the Stirling Quartzite volcanism and magmatism associated with a portion of the Ediacaran to Cambrian volcanics known from California, Utah, British Columbia, and Sonora. Stratigraphic succession suggest that the rifting process was discontinued or aborted.