The use of giant Gaussian process models to study the paleomagnetic field of the Kiaman superchron

• Ano de defesa: 2020
• Autor(a) principal: Brandt, Daniele Cornellio de Paiva Caldeira
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: análises direcionais de forma e escala; directional distributions; distribuições direcionais; Formação Mafra; giant Gaussian process; Kiaman superchron; Mafra Formation; Paleomagnetism; Paleomagnetismo; paleosecular variation; processo Gaussiano gigante; shape and scale directional analyses; Superchron Kiaman; variação paleo-secular
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/14/14132/tde-29052021-131709/

The assessment of the long-term paleosecular variation (PSV) of the geomagnetic field is frequently based on a class of statistical models known as giant Gaussian processes (GGP). The shape of the distributions of the paleomagnetic directions predicted by the most recent GGP model (TK03) calculated for the last 5 Ma, is used as a reference even for older ages. However, its validity was not confirmed for the Paleozoic Era. Particularly, during superchrons, there is evidence that the field has a steadier behavior with depleted PSV. In this work, the Kiaman Superchron field is approached by two different ways for testing the validity of the TK03 model and determining its directional PSV based on GGP models. First, a new paleomagnetic dataset from the rhythmites of the Paleozoic Mafra Formation (southern Brazil) was tested and compared to predictions of elongation E of directions and dispersion S_F of virtual geomagnetic poles (VGPs) from synthetic directions drawn from the TK03 model (a Monte Carlo procedure). Second, an extensive directional paleomagnetic database from the Kiaman magnetic interval (Kiaman database) was evaluated using a new approach based on the scale and shape of the distributions of directions compared to predictions given by numerical integration of directional probability density functions of GGP models. The Mafras results (E = 2.08_1.44^3.13; S_F=10.9_9.8^11.8) revealed incompatible with the TK03 model. Simulations of different versions of GGP models producing reduced S_F, also found in other studies, imply in distributions with a different shape than the TK03 model, mainly at the Equator. The latitudinal dependence of the proposed measures of PSV (_E and _N) provided useful diagnostics for testing the validity of a GGP model. For the Kiaman, the latitudinal dependence of _N and _E calculated for an extensive directional paleomagnetic database (Kiaman database) composed of 1419 paleomagnetic directions of igneous rocks, merged into paleolatitudinal bands showed two characteristics: (1) an elongated and more dispersed distribution near the Equator; (2) an almost constant behavior of more concentrated and circular distributions for latitudes greater than 10°. Two GGP models, with parameters KRS_m =( , ,g_1^0 )=(6.2 T,3.4,18 T) and KRS^\'_m =(3.6 T,6.6,18 T), were found, including and excluding the equatorial band data, respectively. However, for both Kiaman models, the misfit is larger than the data uncertainties, indicating that simplified GGP models are not able to describe the Kiaman PSV, or the common experimental noise is overshadowing its suppressed PSV.