Archaeomagnetism

The Archaeomagnetism Laboratory, which belongs to the Center's geochronology laboratories, boasts all of the necessary instruments for the study of the magnetic properties of rocks in order to develop magnetostratigraphies in sediments. This enables the determination of the magnetic remanence, demagnetization, IRM and ARM in sediments, rocks and archaeological artefacts and also makes it possible to obtain hysteresis loops, FORC diagrams and susceptibility and anisotropy. The 2G magnetometer, the laboratory's main piece, enables the automatic measurement of standard samples and "u-channel" probes of up to 150 cm in length, as the basis for chronostratigraphic studies.

Methods

Paleomagnetism is the study of the terrestrial magnetic field recorded by rocks at the time of their formation or during relevant geological processes that took place afterwards (e.g. metamorphism). It is based on this three basic assumptions:Equipo 2

  • Axial geocentric dipole: The terrestrial magnetic field is similar to that produced by a geocentric dipole that is parallel to the rotational axis of the Earth (at least the mean over a specific period of time). Therefore, the paleomagnetic poles calculated within a specific area will coincide with those of the rotational axis.
  • Record of the primary magnetic field: The ferromagnetic minerals contained in rocks can record the past terrestrial magnetic field.
  • Unchanged record over time: The magnetization acquired by a rock at the time of its formation may remain unchanged over time.

The laboratory deals mainly with magnetic stratigraphy issues (reverse polarity), rock magnetism and anisotropy of magnetic susceptibility in various sedimentary environments.

Individual samples (of up to 12 cubic centimeters), or 2 x 2 cm probes of 150 cm in length, are used to obtain records of a higher resolution and greater continuity. Furthermore, the characterization of the remanence-carrying magnetic phases in rocks and sediments is carried out, along with the study of sedimentary fabrics based on measurement of the preferred orientation of minerals (AMS).

At present, laboratory techniques, along with superconductive instruments, make it possible to precisely establish the orientation, polarity and intensity of the record for almost any type of rock, thus obtaining highly valuable information of two different kinds:

Geochronology: The sequence of changes in magnetic polarity (called inversions) makes it possible to date local stratigraphic sequences. Paleo-orientation of geological bodies: The deviation of the orientation of the magnetic field recorded in rocks in relation to the expected benchmark enables the reconstruction of the deformation processes on different scales.

Facilities and equipment

Equipo 1

  • Cryogenic magnetometer (SQUID) (755 SRM, 2G Enterprises), equipped with a three-coil system with the capacity to apply a field of up to 170 m Tesla for alternating field demagnetization and for the acquisition of ARM.
  • Thermal Demagnetizer model ASC TD48-SC (ASC Scientific), with the capacity to demagnetize up to 48 individual samples at the same time.
  • MicroMag 3900 vibrating magnetometer (VSM - Princeton Measurements Crop.) with cryostat and furnace, which makes it possible to obtain hysteresis loops at a variable temperature and FORC (First Order Reversed Curves) diagrams for magnetic characterization.
  • Kappabridge MFK1-FA susceptometer (AGICO) and Bartington MS2 susceptometer to measure magnetic susceptibility and anisotropy
  • ASC IM10-30 impulse magnetizer with the capacity to create magnetic fields of up to 5 Teslas and enabling the application of isothermal remanent magnetization (IRM) for the characterization of the ferromagnetic phases.
  • Helmholtz Coil 3D coil system (ASC)
Applications and Services
  • Measurements of several different magnetic properties of both natural and artificial materials, such as magnetic susceptibility (ASM) and anisotropy; remanent magnetization; hysteresis loops; curves of acquisition of remanent magnetization; Curie curves at low and high temperatures, etc.
  • Development of rock magnetic cyclostratigraphy.
  • Geochronologic studies based on magnetostratigraphic analysis and environmental magnetism studies. The measurements of magnetic soil parameters, airborne dust, etc., are directly connected to the emission of pollutants.
  • In general, paleomagnetic studies for varying purposes: structural, magnetostratigraphic, etc.