FRINGE BENEFITS: PALEOMAGNETIC AND GEOCHRONOLOGIC DATA FROM DYKES ON THE MARGINS OF THE MCCLURE MOUNTAIN IGNEOUS COMPLEX, COLORADO

The western Cordillera exposes rocks spanning a wide swath of geologic time. The McClure Mountain/Iron Mountain igneous complexes are alkalic intrusive centers in the northern Wet Mountains of southern Colorado. They were emplaced in early Cambrian time into gneissic/granitic Proterozoic host rocks. A number of dykes are associated with the complex, primarily along the western edge. The utility of dykes as high-fidelity recorders of paleomagnetic data has been well-known – and is now being increasingly combined with site-level geochronological analysis for unequivocal position-time results. Previous paleomagnetic investigations into these dykes (French and Van der Voo, 1977; Lynnes et al., 1984) revealed several stable magnetizations with a tri-modal distribution. Those data suggest several stages of dyke emplacement. Although the main intrusive nepheline syenite body is well-dated (and indeed is used a dating standard); the age(s) of the surrounding dykes and of the magnetizations are mostly unconstrained. Paleomagnetic samples were collected from dykes associated with the McClure Mountain igneous complex. Sample collection focused on providing field tests of magnetization – specifically baked contact tests. Geochronologic samples were also collected from sampled dykes. Natural remanent magnetizations were consistent within sites, and fell into two groups. Thermal and alternating field demagnetization methods were used to determine characteristic remanent magnetizations. Paleomagnetic data from these dykes will be shown and compared to previous results, as well as new geochronologic data from some of the sampled dykes.