In the last few years Anisotropy of Magnetic Susceptibility (AMS) in undeformed clay sediments ha... more In the last few years Anisotropy of Magnetic Susceptibility (AMS) in undeformed clay sediments has been increasingly used to unravel the tectonic history of sedimentary basins formed both in compressional and extensional tectonic settings. In extensional sedimentary basins it was demonstrated that the magnetic lineation is tectonically controlled and is oriented perpendicular to the normal faults. The origin of the
During the past few years, the anisotropy of magnetic susceptibility (AMS) has been increasingly ... more During the past few years, the anisotropy of magnetic susceptibility (AMS) has been increasingly considered as a successful method to study subtle deformation in sediments where conventional strain markers are not available, such as clay sediments. In the Mediterranean region, AMS studies on Neogene to Quaternary clay sediments located in different tectonic settings show a systematic correspondence between the observed
The investigation of rocks and minerals in low magnetic fields may be a good and relatively inexp... more The investigation of rocks and minerals in low magnetic fields may be a good and relatively inexpensive alternative of the more or less standard high-field rock magnetic techniques. The Multi-Function Kappabridge Set measures the "in phase" susceptibility, the relative changes of the "out of phase" susceptibility and the magnetic loss angle in variable magnetic fields, at variable operating frequencies, and
The magnetic properties of a sediment core from a high altitude lake in the Swiss Alps were compa... more The magnetic properties of a sediment core from a high altitude lake in the Swiss Alps were compared with palynological and geochemical data to link climatic and mineral magnetic variations. According to pollen data, the sediments extend from the present to the Younger Dryas, i.e., they cover more than 10,000 years of environmental change in the Alps. The major change
ABSTRACT Magnetotactic bacteria produce chains of magnetite nanoparticles, which are called magne... more ABSTRACT Magnetotactic bacteria produce chains of magnetite nanoparticles, which are called magnetosomes and are used for navigational purposes. We use these cells as a biological template to prepare a hollow hybrid material based on silica and magnetite, and show that the synthetic route is nondestructive as the material conserves the cell morphology as well as the alignment of the magnetic particles. The hybrid material can be resuspended in aqueous solution, and can be shown to orient itself in an external magnetic field. We anticipate that chemical modification of the silica can be used to functionalize the material surface in order to obtain multifunctional materials with specialized applications, e.g. targeted drug delivery.
A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscov... more A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscovite powders, in order to gain a better understanding of how texture develops in impure carbonate rocks. The development of the microstructure and the crystallographic preferred orientation (CPO, texture) during the preparation process is described. The synthetic rocks have been fabricated from powders of calcite and muscovite
ABSTRACT Anisotropy of magnetic susceptibility (AMS) measured in the presence of low and high fie... more ABSTRACT Anisotropy of magnetic susceptibility (AMS) measured in the presence of low and high fields, at ambient and low emperatures(17K), has been used to separate ferromagnetic(s. l.), paramagnetic and diamagnetic sub-fabrics from a highly deformed, low-grade metamorphosed marble shear zone in southwest Switzerland. The AMS and bulk susceptibility obtained from these marbles reflect developmentof crystallographicpreferred orientations, as well as the ratio of diamagneticmatrix calcite to paramagnetic secondary phases. The magnetic fabrics in two of the three study locations is produced by iron-rich calcite, and display an inverse relationship to structural cleavage. Preferred orientations of calcite c-axes correspond to the directions of the separated diamagnetickmax•
ABSTRACT The anisotropy of magnetic susceptibility(AMS) has been used as an indicator of deformat... more ABSTRACT The anisotropy of magnetic susceptibility(AMS) has been used as an indicator of deformation, and in certain cases strain, in rocks for over fifty years. Advantages of using AMS to describe deformation is that low-field AMS is relatively fast to measure and it is very sensitive in detecting mineral alignment. However interpretation of AMS results is not always straightforwardand requires a good understanding of the mineral phase or phases, which contribute to the magnetic fabric. Numerous studies use the intensity of bulk susceptibilityto interpret whether diamagnetic, paramagnetic or ferromagneticminerals control the observed fabric. Such a criterion can be misleading since minerals responsible for the anisotropy are not always the minerals that make the largest contribution to the bulk susceptibility. Exampleswill be given from differentrock types to illustratethe role that mineralogy has on interpretingAMS results.
The structure of columnar-jointed lava flows and intrusions has fascinated people for centuries a... more The structure of columnar-jointed lava flows and intrusions has fascinated people for centuries and numerous hypotheses on the mechanisms of formation of columnar jointing have been proposed. In cross-section, weakly developed semicircular internal structures are a near ubiquitous feature of basalt columns. Here we propose a melt-migration model, driven by crystallization and a coeval specific volume decrease inside cooling and solidifying columns, which can explain the observed macroscopic features in columnar-jointed basalts. We study basalts from Hrepphólar (Iceland), combining macroscopic observations, detailed petrography, thermodynamic and rheological modelling of crystallization sequences, and Anisotropy of Magnetic Susceptibility (AMS) of late crystallizing phases (that is, titanomagnetite). These are all consistent with our proposed model, which also suggests that melt-migration features are more likely to develop in certain evolved basaltic lava flows (with early saturatio...
Theoretically, within a given pelitic rock in which the main paramagnetic carriers are white mica... more Theoretically, within a given pelitic rock in which the main paramagnetic carriers are white mica and chlorite and in which, judging from the AMS parameters, AMS is controlled by the paramagnetic carriers, the results of X-ray pole figure goniometry should show a qualitative relationship with AMS. This idea is tested on single-phase deformed, low-grade pelites of the Lower Palaeozoic Brabant
In the last few years Anisotropy of Magnetic Susceptibility (AMS) in undeformed clay sediments ha... more In the last few years Anisotropy of Magnetic Susceptibility (AMS) in undeformed clay sediments has been increasingly used to unravel the tectonic history of sedimentary basins formed both in compressional and extensional tectonic settings. In extensional sedimentary basins it was demonstrated that the magnetic lineation is tectonically controlled and is oriented perpendicular to the normal faults. The origin of the
During the past few years, the anisotropy of magnetic susceptibility (AMS) has been increasingly ... more During the past few years, the anisotropy of magnetic susceptibility (AMS) has been increasingly considered as a successful method to study subtle deformation in sediments where conventional strain markers are not available, such as clay sediments. In the Mediterranean region, AMS studies on Neogene to Quaternary clay sediments located in different tectonic settings show a systematic correspondence between the observed
The investigation of rocks and minerals in low magnetic fields may be a good and relatively inexp... more The investigation of rocks and minerals in low magnetic fields may be a good and relatively inexpensive alternative of the more or less standard high-field rock magnetic techniques. The Multi-Function Kappabridge Set measures the "in phase" susceptibility, the relative changes of the "out of phase" susceptibility and the magnetic loss angle in variable magnetic fields, at variable operating frequencies, and
The magnetic properties of a sediment core from a high altitude lake in the Swiss Alps were compa... more The magnetic properties of a sediment core from a high altitude lake in the Swiss Alps were compared with palynological and geochemical data to link climatic and mineral magnetic variations. According to pollen data, the sediments extend from the present to the Younger Dryas, i.e., they cover more than 10,000 years of environmental change in the Alps. The major change
ABSTRACT Magnetotactic bacteria produce chains of magnetite nanoparticles, which are called magne... more ABSTRACT Magnetotactic bacteria produce chains of magnetite nanoparticles, which are called magnetosomes and are used for navigational purposes. We use these cells as a biological template to prepare a hollow hybrid material based on silica and magnetite, and show that the synthetic route is nondestructive as the material conserves the cell morphology as well as the alignment of the magnetic particles. The hybrid material can be resuspended in aqueous solution, and can be shown to orient itself in an external magnetic field. We anticipate that chemical modification of the silica can be used to functionalize the material surface in order to obtain multifunctional materials with specialized applications, e.g. targeted drug delivery.
A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscov... more A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscovite powders, in order to gain a better understanding of how texture develops in impure carbonate rocks. The development of the microstructure and the crystallographic preferred orientation (CPO, texture) during the preparation process is described. The synthetic rocks have been fabricated from powders of calcite and muscovite
ABSTRACT Anisotropy of magnetic susceptibility (AMS) measured in the presence of low and high fie... more ABSTRACT Anisotropy of magnetic susceptibility (AMS) measured in the presence of low and high fields, at ambient and low emperatures(17K), has been used to separate ferromagnetic(s. l.), paramagnetic and diamagnetic sub-fabrics from a highly deformed, low-grade metamorphosed marble shear zone in southwest Switzerland. The AMS and bulk susceptibility obtained from these marbles reflect developmentof crystallographicpreferred orientations, as well as the ratio of diamagneticmatrix calcite to paramagnetic secondary phases. The magnetic fabrics in two of the three study locations is produced by iron-rich calcite, and display an inverse relationship to structural cleavage. Preferred orientations of calcite c-axes correspond to the directions of the separated diamagnetickmax•
ABSTRACT The anisotropy of magnetic susceptibility(AMS) has been used as an indicator of deformat... more ABSTRACT The anisotropy of magnetic susceptibility(AMS) has been used as an indicator of deformation, and in certain cases strain, in rocks for over fifty years. Advantages of using AMS to describe deformation is that low-field AMS is relatively fast to measure and it is very sensitive in detecting mineral alignment. However interpretation of AMS results is not always straightforwardand requires a good understanding of the mineral phase or phases, which contribute to the magnetic fabric. Numerous studies use the intensity of bulk susceptibilityto interpret whether diamagnetic, paramagnetic or ferromagneticminerals control the observed fabric. Such a criterion can be misleading since minerals responsible for the anisotropy are not always the minerals that make the largest contribution to the bulk susceptibility. Exampleswill be given from differentrock types to illustratethe role that mineralogy has on interpretingAMS results.
The structure of columnar-jointed lava flows and intrusions has fascinated people for centuries a... more The structure of columnar-jointed lava flows and intrusions has fascinated people for centuries and numerous hypotheses on the mechanisms of formation of columnar jointing have been proposed. In cross-section, weakly developed semicircular internal structures are a near ubiquitous feature of basalt columns. Here we propose a melt-migration model, driven by crystallization and a coeval specific volume decrease inside cooling and solidifying columns, which can explain the observed macroscopic features in columnar-jointed basalts. We study basalts from Hrepphólar (Iceland), combining macroscopic observations, detailed petrography, thermodynamic and rheological modelling of crystallization sequences, and Anisotropy of Magnetic Susceptibility (AMS) of late crystallizing phases (that is, titanomagnetite). These are all consistent with our proposed model, which also suggests that melt-migration features are more likely to develop in certain evolved basaltic lava flows (with early saturatio...
Theoretically, within a given pelitic rock in which the main paramagnetic carriers are white mica... more Theoretically, within a given pelitic rock in which the main paramagnetic carriers are white mica and chlorite and in which, judging from the AMS parameters, AMS is controlled by the paramagnetic carriers, the results of X-ray pole figure goniometry should show a qualitative relationship with AMS. This idea is tested on single-phase deformed, low-grade pelites of the Lower Palaeozoic Brabant
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Papers by Ann Hirt