Abstract

New geochronologic data show that Jurassic dikes in the western Mojave Desert and Eastern Transverse Ranges are part of the Independence dike swarm of eastern California .These occurrences extend the length of the dike swarm to more than 500 km. U/Pb zircon concordia intercept ages for dikes near Stoddard Well in the western Mojave Desert and Big Wash in the Eagle Mountains are identical within analytical uncertainties to 148 Ma zircon ages for Independence dikes north of the Garlock fault. Recognition of this widespread magmatic and tectonic event with a restricted age has important ramifications. (1) Crosscutting relations between the dikes and pre-Upper Jurassic and Cretaceous rocks help establish relative ages. (2) Persistence of dikes across several inferred terrane boundaries constrains terrane accretion ages. (3) The dike rocks represent magmatic processes in a wide range of wall-rock settings. (4) The dikes are structural markers that record translations and rotationsof crustal flakes. (5) Regional persistence and dilational emplacement of the Independence dike swarm suggest that it is the last extension in a series of alternating extensional and compressional events during the Jurassic. The tectonic regime responsible for the Independence dikes may be related to arc-normal extension, changes in plate motions, or oblique subduction with left-lateral shear.

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