Vertical ascent and lateral extrusion: emplacement of the Ortiz Mountain intrusion, Cerros Del Rio volcanic field, New Mexico

The processes governing magma ascent from subvolcanic reservoirs to emplacement at shallow crustal levels continue to pose a central challenge in volcanological research. To contribute to this long-standing scientific debate, we examine the vent-dike-lava flow system of the Ortiz Mountain volcanic complex, which intrudes Pliocene Rio Grande rift sediments, basaltic volcanic rocks, and older Oligocene sediments. Our study investigates the magmatic plumbing architecture, focusing on the relationships between an exposed intrusion and the surface volcanic features. Twenty sampling sites were collected for anisotropy of magnetic susceptibility (AMS), paleomagnetic, rock magnetic, and structural studies to characterize the magma emplacement, remanence behavior, and the overall vent-dike-lava flow system. Paleomagnetic data from half the sampling sites yield high-quality demagnetization data that are well grouped at the site level. The site mean directions of these locations are discordant to the Pliocene reversed polarity expected field direction. Thin section and rock magnetic experiments constrain the magnetic mineralogy to a cubic Fe-Ti oxide, likely titanomagnetite, some maghemite, minor Fe-sulfides, and traces of titanomaghemite. The magnetic domain size ranges from pseudosingle to multidomain grains. AMS ellipsoids are predominantly oblate, indicating magma flow directions that are either steeply inclined or sub-horizontal and directed away from the central vent. Combined field observations and laboratory data suggest initial magma ascent through a centralized vertical conduit, contributing to cone construction. A disruption in the plumbing system led to southwestward dike propagation (~800 m), which ultimately breached the surface and erupted as a lava flow. The resulting volcanic construct illustrates a vent-dike-lava flow system, where subsurface magmatic processes are spatially and temporally linked to surface volcanic features. The results underscore the importance of integrated field and laboratory approaches to reveal the hidden plumbing architecture of small volcanic systems as well as the dynamic pathways magma follows from depth to eruption.