PALEOMAGNETIC DATA BEARING ON DRAG FOLDING ALONG THE SANTA CLARA FAULT SYSTEM

Late Miocene basalt flows of the Lobato volcanic sequence erupted between 9 to 10 million years ago on the northeast side of the Jemez Mountains, NM. These rocks are mostly fine-grained and vesicular olivine- and plagioclase-phyric basalts. The Lobato flows are subhorizontal for nearly 2 Kms southeast from the Clara Peak volcanic center, then moderately dip to the east before abutment against the Santa Clara fault, a major structure on the SW margin of the Espanola Basin. We are attempting to distinguish between (1) lava flow emplacement into a paleovalley prior to motion along the Santa Clara fault system or (2) post-emplacement drag folding against the Santa Clara fault post 10 Ma. Overall, this study helps to constrain the role of the Santa Clara fault system as a major structure in accommodating stress along the western margin of the Rio Grande Rift. Remanent magnetizations were measured using a AGICO JR6-A Dual-Speed magnetometer at the New Mexico Highlands University paleomagnetic-rock magnetic laboratory. Specimens were progressively AF demagnetized in 10 to 15 steps to a maximum field of 120 mT to isolate the geological important characteristic remanent magnetization. Preliminary paleomagnetic data reveal a single component magnetization that decays to the origin with less than 10 percent of the natural remanent magnetization remaining after treatment in 120 mT fields. Tentative results from sites located on the subhorizontal limb and those from the eastern tilted limb yield statistically indistinguishable remanence directions prior to and after unfolding for the inferred tilt of the flows. If ongoing paleomagnetic studies demonstrate that both limbs yield identical remanence directions, then it is probable that the lava flows were emplaced into a paleovalley. On the other hand, if data from both limbs are statistically distinct, then it is likely that the flows were deformed after remanence acquisition due to motion along the Santa Clara fault.