Characterizing the Geomagnetic Field at High Southern Latitudes: Evidence From the Antarctic Peninsula

• Published in: Journal of Geophysical Research: Solid Earth
• Main Authors: Biasi, Joseph, Kirschvink, Joseph L., Fu, Roger R.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Geophysical Union 2021
• Subjects: James Ross Island; paleomagnetism; paleointensity; Antarctica; volcanology; tangent cylinder; Space and Planetary Science; Earth and Planetary Sciences (miscellaneous); Geochemistry and Petrology; Geophysics; Antarctic; Antarctic Peninsula; Ross Island; The Antarctic; Antarc*
• Online Access: https://doi.org/10.1029/2021jb023273

Due to a dearth of data from high-latitude paleomagnetic sites, it is not currently clear if the geocentric axial dipole (GAD) hypothesis accurately describes the long-term behavior of the geomagnetic field at high latitudes. Here we present new paleomagnetic and paleointensity data from the James Ross Island (JRI) volcanic group, located on the Antarctic Peninsula. This data set addresses a notable lack of data from the 60°–70°S latitude bin and includes 251 samples from 31 sites, spanning 0.99–6.8 Ma in age. We also include positive fold, conglomerate, and baked contact tests. Paleointensity data from three methods (Thellier-Thellier, pseudo-Thellier, and Tsunakawa-Shaw) were collected from all sites. The Thellier-Thellier method had low yields and produced unreliable data, likely due to sample alteration during heating. Results from the Tsunakawa-Shaw and pseudo-Thellier methods were more consistent, and we found a bimodal distribution of paleointensity estimates. Most sites yielded either <15 μT or >40 μT, which together span a range of estimates from long-term geomagnetic field models, but do not favor any model in particular. Alternating-field demagnetization of these samples, when combined with preexisting data, yields a revised paleomagnetic pole of −87.5°, 025°, α95 = 3.6° for the Antarctic Peninsula over the last ∼5 Ma, which suggests that the current data set is sufficiently large to "average out" secular variation. Finally, the C2r/C2n transition was probably found at a site on JRI, and further geochronological and paleomagnetic study of these units could refine the age of this reversal. © 2021. American Geophysical Union. Issue Online: 24 December 2021; Version of Record online: 24 December 2021; Accepted manuscript online: 14 December 2021; Manuscript accepted: 11 December 2021; Manuscript revised: 09 December 2021; Manuscript received: 18 September 2021. The authors would like to thank their fellow team members: Jennifer Buz, David Flannery, Ross Mitchell, Joe O'Rourke, ...