AMS data of the Santa Angélica pluton

Published: 13-05-2020| Version 2 | DOI: 10.17632/3xth2s5cp9.2
Contributors:
Filipe Temporim,
Ricardo Trindade,
Eric Tohver,
Caroline Soares,
Lucas Pequeno Gouvêa,
Marcos Egydio-Silva,
Caio Amaral,
Gelson Souza Jr.

Description

This dataset is part of the work "Magnetic fabric and geochronology of a Cambrian “isotropic” pluton in the Neoproterozoic Araçuaí orogen". Such work presents results of an integration of U-Pb SHRIMP and a detailed anisotropy of magnetic susceptibility (AMS) study to determine the emplacement mechanisms of the Santa Angélica. This pluton was emplaced at the mid-crustal section of the Araçuaí orogenic system, and is located along its southern toe. Its internal fabric pattern will provide information on the final deformation partitioning at the waning stages of mountain building across this crustal level that is presently inaccessible in modern orogens. In this dataset we filed anisotropy of magnetic susceptibility (AMS), thermomagnetic experiments and anisotropy of anhysteretic remanence magnetization (AARM) data.

Files

Steps to reproduce

In the laboratory 759 specimens were cut into standard specimens that were 2.2 cm in length. All measurements were carried out in the Laboratório de Paleomagnetismo at the Universidade de São Paulo (USPmag). The anisotropy of magnetic susceptibility (AMS) of individual samples was measured using an Agico Kappabridge MFK 1A. Statistical evaluation of the magnetic anisotropy in individual sites was obtained using the methods of Jelínek (1978), implemented in the ANISOFT program package (Hrouda et al., 1990). Each station is characterized by the mean anisotropy parameters of a minimum of five specimens. The AMS directional data from individual sites were filtered to eliminate sites with high internal dispersion (ε12, ε 23), removing sites with uncertainty estimates >26.5°. We investigated the contribution of specific minerals to the bulk rock magnetic susceptibility in order to better understand the results of the AMS measurements. Thermomagnetic experiments were acquired under argon flux to prevent excessive oxidation during heating using a CS-2 furnace attached to an Agico Kappabridge KLY 4 CS. All thermomagnetic K-T curves (susceptibility K as function of temperature T) were performed at a temperature interval from -200 to 700°C. Measurement of the anisotropy of anhysteretic remanence magnetization (AARM) was carried out on samples from five sites, selected to represent all rock types and structural domains within the Santa Angelica pluton. The measured AARM fabric reflects the pure contribution of ferromagnetic phases to the magnetic fabric of the rock (Jackson, 1991), in contrast with the more commonly measured AMS, which reflects the summed contributions of diamagnetic, paramagnetic, and ferromagnetic mineral phases. AF demagnetization and anhysteretic remanence acquisition were achieved with a LDA-3 (AGICO) demagnetizer/magnetizer, and remanence was measured with a JR6-A magnetometer (AGICO), both kept in the magnetic field-free room of USPmag. Before AARM measurements samples were AF demagnetized at a peak AF field of 100 mT. The magnitude and orientation of the principal axes of the AARM ellipsoid were determined for each specimen after anhysteretic remanence acquisition along fifteen different orientations with a peak field of 50 mT and a biasing field of 100 μT following the procedure described in Trindade et al. (2001).