Paleomagnetism and tectonics from the late Pliocene to late Pleistocene in the Xalapa monogenetic volcanic field, Veracruz, Mexico
The Xalapa monogenetic volcanic field, Veracruz, Mexico is located at the eastern end of the Trans-Mexican Volcanic Belt. This study uses 196 specimens collected from 20 sampling sites in, 0.8 ka to 5.96 ± 0.156 Ma, Xalapa lavas and 34 specimens from 3 sampling sites in, 4.5 ± 0.028Ma, La Concha Ignimbrite. For the lavas, the study (1) identifies the magnetic mineralogy by reflected light microscopy, thermomagnetic curves and UnMix curves; and (2) defines the magnetic domain size distribution by hysteresis plots, day diagrams, and First Order Reversal Curves. For the basalts and the ignimbrite:(1) characteristic remanent directions and virtual geomagnetic poles are calculated; (2) paleosecular variation is defined, which is coherent with the expected values; (3) net rotation experienced, at each site, since the emplacement is calculated. The results are used to improve some of the already published radiometric dates. Calculation of net rotation allowed the identification of the rotation domains, active since past ~2.5 Ma, due to a major system previously proposed by other authors in the region. This, in-turn, supports the identification of new strikeslip faults system, in the previously known normal faults. The study establishes a relationship between the translational fault systems and the distribution of volcanoes. Finally, a caution is raised for the future studies and the importance of analyzing the site-specific paleomagnetic information with respect to the local geological setting is emphasized.