Unearthing the mid-Cenozoic Cordilleran magmatic periphery of eastern New Mexico

The North American alkaline magmatic belt has long been recognized as a first-order feature of the western North American Cordillera. Even more distal, small-volume alkaline igneous occurrences are found in the far inboard Cordillera along the western edge of the Great Plains from Texas to northernmost Montana. In eastern New Mexico and southeastern Colorado, distal intrusions of mid-Cenozoic age are emplaced into little deformed Permian to Cretaceous strata, some 50 to 200 kilometers east of the nearest major alkaline magmatic centers. About ten late Eocene to mid-Miocene igneous occurrences stretching from the Yeso Hills dikes (Eddy County, NM) to the northeastern end of the Jemez lineament form the Cordilleran magmatic periphery of eastern New Mexico. Isolated minor dikes, sills, and plugs are generally alkaline and mafic to intermediate in composition, though data and descriptions are presently limited. These peripheral igneous occurrences may simply be far-travelled lateral offshoots of the alkaline magmatic centers in axial New Mexico. Alternatively, distal intrusions may represent transcrustal magmatic systems related to small-volume melting beneath the westernmost Great Plains. In the latter case, these minor alkaline igneous occurrences would constitute a coherent ‘Cordilleran magmatic peripheral belt’ distinct from the major magmatic centers of the North American alkaline magmatic belt emplaced into Laramide structures and rift flank uplifts to the west. We highlight the potential constitutive elements of the Cordilleran magmatic periphery of eastern New Mexico and future research to study these occurrences.