New Mexico Geological Society Annual Spring Meeting — Abstracts

The 5 km-long Buena Vista dike, intrudes the Cretaceous Benton Group and outcrops on the eastern side of the Sangre de Cristo Mountains near the transition between the Rocky Mountains and the Great Plains.  At the northernmost outcrop, at least three compositionally distinct intrusions are exposed ranging from augite porphyritic basalt, quartz diorite and diorite.  We hypothesize that the Buena Vista dike may be sourced from or genetically related to the Ocate Volcanic field.  Rock magnetic, paleomagnetic, and anisotropy of magnetic susceptibility analyses are being conducted on core samples taken from 13 sites.  Preliminary rock magnetic tests reveal that the primary magnetic phase is a cubic, Fe-Ti oxide phase of a restricted magnetic grain size.  The Curie point temperature ranged from 480 to 540 degrees Celsius indicating that the samples contain a titanomagnetite phase with low to moderate Ti substitution.  We see little contribution to the AMS fabric from paramagnetic phases and conclude that the AMS fabric is carried by a ferromagnetic phase of psuedosingle domain to a multi-domain grain size.  AMS data indicate that most sites are oblate. The shape factor T values for the sites range from 0.209 to 0.903. Further work, including geochronology, paleomagnetism, and petrographic analyses, is aimed at determining the origin and time of emplacement of the Buena Vista dike and understanding Cenozoic magmatism east of the Rio Grande Rift.