EGU21-3409, updated on 18 Apr 2021
https://doi.org/10.5194/egusphere-egu21-3409
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Comprehensive palaeomagnetic study of San Borja and Jaraguay monogenetic volcanic fields, Baja California (28–30°N): considerations on latitudinal corrections

Ahmed Nasser Mahgoub1,2, Bernardo Ignacio García-Amador3, and Luis Manuel Alva-Valdivia1
Ahmed Nasser Mahgoub et al.
  • 1Laboratorio de Paleomagnetismo, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, México
  • 2Assiut university, Faculty of Science, Geology department, Assiut, Egypt (anmahgoub@gmail.com)
  • 3Posgrado en Ciencias de la Tierra, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, México

We report 24 palaeomagnetic directions and 10 high-quality Thellier-derived palaeointensity (PI) values, obtained from 27 sites located in Baja California Peninsula, northwestern Mexico. Sampling was done in four rock units (magnesian andesites, calc-alkaline lavas, ignimbrites, adakites) belonging to San Borja and Jaraguay monogenetic volcanic fields. These units were erupted between ~ 15 and 2.6 Ma (previous K-Ar and 40Ar/39Ar data), hence results are presented in two consecutive periods: middle-late Miocene and Pliocene. Based on previous geological and geophysical records, the kinematic evolution of the region was carefully considered, allowing for the independent restoration of the palaeoposition of each sampled site. The identified main magnetic minerals are titanomagnetite, magnetite, and minor hematite, of variable grain size, present as intergrowths, which reflect varying oxidation/reduction conditions during emplacement of high-temperature magmas. We did not observe a clear relationship between the magnetic properties of the different sites and their success rate for PI experiments. This is with the exception of the FORC analysis which showed a fairly good correlation with PI success. Pliocene (Dec=359.2°; Inc= 47.4°; α95=7.6°; and k= 41.43) and Middle-late Miocene (Dec=353.9°; Inc= 38.5°; α95=9.2°; and k= 28.56) mean directions were calculated from 20 sites (10 sites per period), and PI mean values of 29.2 ± 9.1 μT and 23.2 ± 6.3 μT were determined for the two periods, respectively. Compiling global filtered PI data, together with our results, indicates that the strength of the geomagnetic field during middle-late Miocene was weak (virtual dipole moment = 5.0±2.2×1022 Am2) compared to Pliocene (6.4±2.8× 1022 Am2), and also relative to the present-day value (7.6 × 1022 Am2). This indicates the global nature of the low dipole moment during the middle-late Miocene, which is consistent with what was previously concluded that from the past 30 Ma to the present time the magnetic field strength has increased. However, issues related to the Spatio-temporal distribution of PI data still present an obstacle to validating these suggestions; therefore, more reliable data are still needed.

How to cite: Mahgoub, A. N., García-Amador, B. I., and Alva-Valdivia, L. M.: Comprehensive palaeomagnetic study of San Borja and Jaraguay monogenetic volcanic fields, Baja California (28–30°N): considerations on latitudinal corrections, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3409, https://doi.org/10.5194/egusphere-egu21-3409, 2021.

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