Ediacaran-Ordovician magmatism and REE mineralization in the Wet Mountains, Colorado, USA: Implications for failed continental rifting

Benjamin Patrick Magnin; Yvette Kuiper; Eric D. Anderson

doi:10.1029/2022tc007674

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Ediacaran-Ordovician magmatism and REE mineralization in the Wet Mountains, Colorado, USA: Implications for failed continental rifting

Benjamin Patrick Magnin·Yvette Kuiper·Eric D. Anderson

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Abstract

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

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Source-reported bounding extent: 37.59367717050884° to 38.78046120500633° latitude; -105.83697815705129° to -104.7497993335517° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Benjamin Patrick Magnin, Yvette Kuiper, Eric D. Anderson. 2023-04-11. Ediacaran-Ordovician magmatism and REE mineralization in the Wet Mountains, Colorado, USA: Implications for failed continental rifting. https://doi.org/10.1029/2022tc007674

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