New Mexico Geological Society Annual Spring Meeting — Abstracts

Migration of magma at shallow levels of the crust is a fundamental process that has bearing on the construction of volcanoes, the associated hazards in active volcanic terranes, as well as igneous mass redistribution into near surface environments. This study examines a suite of Miocene dikes in the Española Basin, north-central NM, where Rio Grande Rift faulting has complicated the sourcing of mafic magmas. The problem addressed by this research involves a two-fold approach: 1) collect paleomagnetic data from thirty basaltic dikes with the intent to discern components of vertical-axis rotation across structural blocks, between separate dikes, and along strike within individual dikes, and 2) obtain anisotropy of magnetic susceptibility (AMS) data, thin section, and field observations, to infer magma flow within individual dikes and document any variation in magma flow patterns in the swarm.We plan to test the following hypotheses: 1) the mafic dikes experienced some degree of vertical axis rotation associated with rifting and 2) that the magma flow pattern within the dikes reflects lateral emplacement with flow directed away from the magma ascent location. Low-field susceptibility versus temperature results from the dikes yield a spectrum of temperature dependence reflecting typical thermomagnetic behavior of intermediate composition titanomagnetite while others exhibit a more complex behavior with the presence of two or more magnetic phases. Curie point estimates range from ~ 100°C to 575°C indicating a range of moderate Ti- to low Ti- titanomagnetite compositions as well as evidence of a Fe-sulfide phase. AMS fabric data reveal a combination of both prolate and oblate susceptibility ellipsoids. At several sites, the fabrics are oblate from the paired dike margins and reveal a unique magma flow direction. Susceptibility values are high and consistent with a ferromagnetic phase, likely low-Ti titanomagnetite, providing encouraging data that the remanence is likely a primary thermoremanent magnetization (TRM) and geologically stable. Paleomagnetic analysis is underway and should help further constrain the emplacement of the dikes and tectonic evolution of the study area. Additional paleomagnetic data will aide in constraining the tectonic and thermal history of the dikes and provide insight into the regional deformation of the area. AMS data should document the direction of magma flow within each intrusion allowing us to deduce the source region of the magma body.