THE JURASSIC KING CREEK PLUTON AND INDEPENDENCE DIKES, SOUTHERN RITTER RANGE, SIERRA NEVADA, CA: IMPLICATIONS FOR JURASSIC MAGMATISM AND TECTONICS

The Sierra Nevada Batholith (SNB) is a long-lived continental arc and orogen that evolved with three magmatic and tectonic flare-ups in the Triassic, Jurassic, and Cretaceous, respectively. Although most of the central SNB has been overprinted by the Cretaceous flare-up, new geologic mapping and U-Pb geochronology of the King Creek pluton sheds light on the Jurassic tectonic history of the SNB. U-Pb LA-ICP-MS zircon geochronology yields a ~168 Ma age of the King Creek granodiorite and a ~153 Ma age of basaltic to rhyolitic dikes that intrude both the King Creek granodiorite and Jurassic-Triassic metavolcanics. The dikes and the King Creek pluton, which intrude steeply SW dipping and deformed Jurassic meta-voclanics, experienced Jurassic solid-state deformation. The dikes preserve both magmatic sheath folds and solid-state boudinage, as well as record pre- and syn-emplacement faulting. The ~153 Ma age and composition of the dikes suggest that they are part of the Jurassic Independence Dike Swarm.

Variation in the strikes of the Independence dikes has been used as evidence for rotation of rigid blocks (e.g., Mojave blocks), whereas the Sierra Nevada block is thought to have experienced little to no rotation due to a consistent dike strike. However, compilation of detailed geologic maps shows a change in dike strike from NW-SE in the southern SNB to WNW-ESE in the central SNB, the latter linking to the EW striking Sonora dike swarm. The King Creek dikes occur within the transition zone of dike strike. Preliminary mapping of the dikes in the King Creek area show a WNW-ESE trend, compatible with ~13% local extension during sinistral transpression. The variation in dike strike within the Sierra Nevada block indicates that changes in the mean strike of Independence dikes is not solely caused by tectonic rotation and instead may reflect spatial and/or temporal variations in local stress fields across the Jurassic Cordilleran margin.