Paleodirections and paleointensity of the Zimbros dikes (South Brazil): evidence for ultralow fields and hints of a dipole in the mid-Ediacaran

Abstract

Ediacaran (635–538 Ma) paleomagnetic records from multiple continents are associated with populations of paleopoles nearly synchronous in time but widely separated in space. Some hypotheses to explain these data appeal to rapid motions of the solid Earth, whereas others invoke a non-geocentric axial dipole (GAD) or an extremely weak GAD field with high paleosecular variation and frequent reversals. We present new directional and absolute paleointensity constraints obtained from two mafic dikes of the Zimbros Intrusive Suite (ca. 590 Ma) in the Dom Feliciano Belt (DFB), southern Brazil. Magnetite and low-Ti titanomagnetite are the main magnetic carriers, associated with pseudo-single-domain to multidomain magnetic behavior. Directional ana- lyses reveal that the dikes host two distinct magnetization components. The low-temperature component is attributed to pyrrhotite, likely related to late-stage tectonic events. The high-temperature component, held by low-Ti titanomagnetite/magnetite, is interpreted as the characteristic remanent magnetization. This compo- nent’s directions are antipodal and compatible with a dominantly GAD field, but a high degree of directional dispersion may reflect an unstable field. Absolute paleointensity experiments yielded 19 reliable estimates with virtual dipole moments (VDM) of 0.38 ± 0.15 × 1022 and 0.89 ± 0.33 × 1022 Am2. The validity of these ultra-low estimates was confirmed by their stability under progressively stricter selection criteria based on curvature analysis, indicating the estimates' internal consistency. The obtained VDMs are consistent with coeval results from Laurentia and Baltica, and with an existing time-averaged field estimate from the DFB. Together, these results provide additional evidence of a remarkably weak Ediacaran geomagnetic field.