Mid-Cenozoic dikes, sills, and plugs emplaced along transition between the Rocky Mountains and Great Plains physiographic provinces form a patchy discontinuous belt that represents the most distal periphery of Cordilleran magmatism. In axial to eastern New Mexico, these small-volume intrusions are found ~50-200 km east of the nearest broadly coeval alkaline magmatic centers. In the state of New Mexico, these small-volume intrusions stretch from the Yeso Hills, near the NM-TX state line in southernmost Eddy County (Allen and Attia, 2021), to at least as far north as Garita near the border between San Miguel and Guadalupe Counties (see map). This belt may be linked to mid-Cenozoic precursor magmatism along the eastern Jemez lineament potentially including the Two Buttes sill complex in southeastern Colorado (the easternmost Cordilleran igneous exposures!!). Even further north in Colorado, Cretaceous-Paleogene intrusions and lavas are found at the Rocky Mountains-Great Plains transition near Golden, Boulder, and Lyons Colorado. To the far south, minor igneous exposures just east of the Davis Mountains may represent equivalent occurrences distal to the Trans Pecos magmatic province.
Although generally known for over 100 years (e.g. Ogilvie, 1902), these igneous occurrences have received little study and we presently know very little about them. Studying these features will help us to reconstruct the landscape development of New Mexico in between the building of the Rocky Mountains and the formation of the widespread Ogallala Caprock. These rocks are also key to our understanding of the tectonic significance of mid-Cenozoic magmatism in the southwestern United States.
We propose that these distal igneous rocks form a distinct Cordilleran magamtic peripheral belt that represents extremely small-volume melting beneath the western margin of the Great Plains. To test this hypothesis, we have begun initial reconnaissance and are building towards collaborative studies addressing basic aspects of these occurrences through mapping, petrography, geochemistry, geochronology, and thermochronology.
Please reach out if you have any questions! We are currently recruiting a graduate student to work on this topic with funding from a related EDMAP grant, more info available here!
For more information, contact:
Dr. Snir Attia— Field Geologist
Results
- Attia, S., and Ricci, J., in revision, Latest Eocene 40Ar/39Ar age from the Yeso Hills dikes, Eddy County, New Mexico, in Land, L., and Hutchinson, P.L., eds., Southeastern New Mexico: New Mexico Geological Society 73rd Annual Fall Field Conference Guidebook.
References
- Allen, B.D., and Attia, S., 2021, Geologic map of the Rattlesnake Springs 7.5’ quadrangle, Eddy County, New Mexico: New Mexico Bureau of Geology Open-file Geologic Map 291, scale 1:24,000.
- Ogilvie, I.H., 1902, An Analcite-Bearing Camptonite from New Mexico: The Journal of Geology, v. 10, n. 5, p. 500-507.