Ediacaran‐Ordovician Magmatism and REE Mineralization in the Wet Mountains, Colorado, USA: Implications for Failed Continental Rifting

Structures associated with Ediacaran-Ordovician alkaline magmatism and the timing of rare earth element (REE) mineralization in Wet Mountains, CO, were analyzed using field, geophysical, U-Th-Pb isotope methods to interpret their tectonic setting context previously proposed rift models. The Mountains are known for thorium REE failed rift-related, intrusions veins. Structural field data indicate that dikes mineralized veins controlled by a system northwest-striking, high-angle faults tension fractures formed 040°-directed extensional regime. Magnetic surface expressions Democrat Creek McClure Mountain complexes show elongation toward ∼045°, consistent NE-directed extension. also suggest existence fourth, unrecognized mafic-ultramafic complex inferred Cambrian age similar elongated orientation. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) 208Pb/232Th analysis low-uranium zircon from carbonatite situ 206Pb/238U LA-ICP-MS monazite yielded 465 ± 18 Ma 489 33 ages, respectively. These ages expected based on slightly older, cross-cut syenite hypothesized Ordovician end rift-related magmatism. magmatic rocks northeast-directed extension direction those along-strike, Ediacaran-Cambrian Southern Oklahoma Aulacogen. Therefore, is interpreted be northwestern continuation Aulacogen thorium/REE representing late intrusive phases.