22 Everyday Geoscience (Posters)

This session will focus on elevating the importance of geoscience through geoscience education (e.g., curricula development, leading fieldwork experiences, etc.) and/or convergence research (e.g., using community-focused research frameworks/methods, community-engaged research, etc.).

Tuesday, 19 May 2026
8:00 AM - 5:30 PM
Alvarado D/E

Preliminary Paleomagnetic Results from the Oligocene Galisteo Dike (El Creston): A record of Unusual Geomagnetic Field Behavior

Paper number: 22-0
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Located in the north central New Mexico, within the Galisteo Basin, Sante Fe. The Oligocene Galisteo dike (El Crestón) is a prominent, ridge-forming basaltic-andesite intrusion approximately 8 km long. Its age is estimated at 26.55 Ma. The dike exhibits a speckled black and white texture, composed of plagioclase, potassium feldspar, augite, biotite, apatite, and opaque minerals set in a glassy groundmass. In map view, the dike consists of numerous right-echelon, overlapping segments ranging from 60-350 meters in length and up to five meters thick. In order to characterize the magnetic fabrics and the stability of the remanent magnetization, we conducted multiple rock magnetic experiments, including Curie point analysis, anisotropy of magnetic susceptibility (AMS), and paleomagnetic studies from three locations along strike and several sites across the width of the intrusion. The demagnetization behaviour of the rocks along strike and across the width of the intrusion shows evidence of variations in magnetic mineralogy, domain state, and the stability of the remanence. Some samples display a rapid magnetization drop at low applied fields (<20 mT), consistent with a low-coercivity, multi domain magnetite phase. Other samples yield a behaviour more consistent with single domain and/or vortex state magnetite grains with demagnetization experiments yielding a linear trend towards the origin indicating a stable characteristic remanent magnetization (ChRM). The directional data from the samples yielding a ChRM deviate significantly from the late Oligocene expected field direction. The mean sample results yield shallow positive and negative inclinations with declinations to the northeast, southeast, and southwest. Overall, the dike preserves a reliable record of Earth’s magnetic field at the time of formation. AMS fabrics are carried by a ferromagnetic mineral of variable titanomagnetite composition. The AMS data at the site level yield steep planar fabrics likely related to primary magmatic flow. Other sites yield erratic fabric data with no discernible flow pattern. Curie point experiments reveal temperature estimates between 400C-500C suggesting a moderate Ti titanomagnetite mineral phase. The non-reversible behavior during cooling suggests probable oxidation of the Fe–Ti oxide phase during heating. Preliminary Paleomagnetic results from the Galisteo dike (El Crestón) show that the samples preserve a stable characteristic remanent magnetization (ChRM) that deviates significantly from the expected late Oligocene field direction, likely recording a non-dipole geomagnetic field event.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410690

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