Age, Provenance, and Potential Correlations of the Rocks of Slumgullion, Castle Dome Mountains, Southwest Arizona

The ages and depositional environments of Mesozoic metasedimentary and metavolcanic rocks in the southwest United States have occasioned considerable debate. One such sequence, the low-grade metamorphic rocks of Slumgullion, located in the Castle Dome Mountains of southwest Arizona, has previously been considered Jurassic. From the rocks of Slumgullion, we obtained zircon ages from three quartz arenites, two arkoses, one lithic arenite, and one dacite. We also determined a zircon crystallization age of a monzogranite, which previous workers interpreted as having intruded the rocks of Slumgullion.

The quartz arenites yielded zircons with peaks at ca. 90–230, 400–650, 900–1200, 1400, 1600–1800, and 2500–2750 Ma. One quartz arenite, however, contains a ca. 120 Ma zircon, in contrast to the 193 Ma minimum age obtained from the other two samples. The arkose samples exhibit a large peak at 150–200 Ma. Smaller groupings occur at ca. 400–850, 1000–1200, and 1300–1400 Ma. The lithic arenite has three main peaks at ca. 80, 170, and 1400 Ma. The dacite and monzogranite yielded Middle to Late Jurassic crystallization ages.

Zircon patterns from the quartz arenites are remarkably similar to those from the Jurassic ergs of the Colorado Plateau (Dickinson and Gehrels, 2003). However, the presence of the ca. 120 Ma age suggests reworking of Jurassic sediments during the Cretaceous. Zircons in the less mature arkoses and lithic arenite appear to have been derived largely from local Jurassic to Proterozoic basement rocks. The dacite and monzogranite are older than the metasediments and likely represent the depositional basement to the Slumgullion sedimentary basin. The depositional ages, bulk-rock compositions, and zircon age distributions of the rocks of Slumgullion suggest affinities with the McCoy Mountains Formation of southeast California and southwest Arizona and the Winterhaven Formation of southeastmost California.