CRETACEOUS MAGMATISM WITHIN THE MIDHILLS QUADRANGLE, TEUTONIA BATHOLITH, MOJAVE NATIONAL PRESERVE

Late Cretaceous plutons of the Mojave Desert are uniquely situated for examining the current tectonic models related to the timing and style of transition from the Sevier to the Laramide orogeny. For example, the large and compositionally diverse Teutonia batholith presents a unique opportunity to study magmatism generated in the Mojave between ~82 to ~88 Ma. A better understanding of the timing, sources, and tectonic control on magmatism that occurred during this period will help constrain this event that shaped the geology present within the western US.

The Rock Springs Monzogranite, described by Beckerman et al. (1982), is one of six plutons within the Teutonia batholith related to this event. Although some description and major element geochemistry has been conducted, the overall genetic history of the unit and how it fits into the Cretaceous magmatic history of the Mojave is poorly understood. Recent field observations show the Rock Springs magma interacted with the surrounding host rocks and plutons in a complex manner. Within the Mid Hills quadrangle, the Rock Springs monzogranite is intermingled with magmas of the Black Canyon gabbro and the Mid Hills monzogranite. In addition, the Mid Hills monzogranite has been shown to have three distinct units: theproposed Round Valley granite is distinguished by porphyritic k-feldspar phenocrysts and elongated planar mafic enclaves, and the proposed Wild Horse Canyon monzogranite contains diagnostic potassium felspar megacrystsup to 80mm in length. Magmatic fabrics measured throughout the region indicate regional strain fields and local magmatic properties.

Planned major and trace element geochemistry, as well as high precision geochronology, of the previously mentioned sub-units of the Mid Hills monzogranite, including the Rock Springs monzodiorite, will lead to a better understanding of the styles and sources of Teutonia batholith magmatism and help to constrain the timing of the shift from Sevier to Laramide orogenesis.