scholarly journals Magnetic stratigraphy of the Villafranchian type-section:(Villafranca d'Asti, Italy)

1999 ◽  
Vol 42 (1) ◽  
Author(s):  
P. Boano ◽  
D. Bormioli ◽  
F. Carraro ◽  
R. Lanza
Keyword(s):  
Remanent Magnetization ◽  
Bedding Plane ◽  
Magnetic Fabric ◽  
Isothermal Remanent Magnetization ◽  
Type Section ◽  
Inclination Shallowing ◽  
Polarity Transition ◽  
Clayey Silt ◽  
Normal Polarity ◽  
Nw Italy

A detailed magnetostratigraphic investigation has been carried out along the section of the Fornace RDB quarry (Villafranca d'Asti, NW Italy), which is the type-section of the Villafranchian and has provided many of the land mammal remains used by Azzaroli (1977) to define the Val Triversa faunal unit (zone MN16a). Poorly consolidated clay and clayey silt are the prevailing lithologies and samples were collected with plastic boxes. Isothermal remanent magnetization measurements showed that haematite is the main ferromagnetic mineral and occurs through the section, whereas iron sulphide is subordinate and only occurs in the lower part. Alternating field demagnetization usually succeeded in isolating a stable component and was used to derive the characteristic remanence by demagnetizing the specimens at 4 to 7 steps in the range 15 to 80 mT. The magnetic fabric was investigated by measuring the anisotropy of the magnetic susceptibility. It was always well defined and characterized by a horizontal foliation matching the bedding plane. The anisotropy of isothermal remanent magnetization was measured on some specimens and yielded fully comparable results. This consistency shows that detrital haematite carries the primary magnetization in these sediments and explains the 20° inclination shallowing of the site mean palaeomagnetic direction. Only one reverse to normal polarity transition has been detected and a direct correlation with the GPTS reference scale of Cande and Kent (1992, 1995) is thus not possible. The age of the Triversa fauna has been much debated in recent literature. Some authors have recently suggested that it is transitional between Ruscinian and Villafranchian, i.e. a little older than previously assumed. According to this hypothesis, the lower part of the RDB section would correlate to the chron C2Ar (upper Gilbert) and the upper part to the chron C2An.3n (lower Gauss), whereas according to the traditional interpretation correlation is to one of the polarity inversions within the middle Gauss (Kaena and Mammoth). An independent age constraint based on magnetostratigraphy will only be possible when other Ruscinian and Villafranchian sections are investigated in the same detail and a correlation between palaeosecular variation is established.

Paleomagnetism of the Keweenawan Chipman Lake and Seabrook Lake carbonatite complexes, Ontario

1992 ◽  
Vol 29 (6) ◽  
pp. 1215-1223 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
Magnetic Field ◽  
Remanent Magnetization ◽  
Pole Position ◽  
Alteration Zone ◽  
Contact Aureole ◽  
Isothermal Remanent Magnetization ◽  
Abitibi Subprovince ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Host Rocks

The Chipman Lake complex crops out as a series of carbonatite and related alkalic mafic dikes in the Wabigoon Subprovince of the Superior Province, whereas the Seabrook Lake complex crops out as an alkalic syenite – carbonatite stock in the Abitibi Subprovince. Paleomagnetic analysis was done on specimens from 23 and 19 sites located in and around the Chipman Lake and Seabrook Lake complexes, respectively, using detailed alternating-field and thermal step demagnetization and isothermal remanent magnetization tests. Contact tests with adjacent Archean host rocks show that both complexes retain a primary characteristic remanence (ChRM). The Chipman Lake's ChRM is retained in 11 dikes with normal polarity and one dike with reversed polarity and at one site with normal polarity and one site with reversed polarity from the fenite alteration zone. Its ChRM gives a pole position at 186°E, 38°N (dp = 7°, dm = 11°), which corresponds to a Keweenawan age of 1098 ± 10 Ma, suggesting that younger K–Ar amphibole ages do not date emplacement. The ChRM of the host rock, the Chipman Lake diorite stock, gives a pole at 49°E, 51°N (dp = 8°, dm = 13°), showing that it is not part of the Keweenawan complex but may be a 2.45 Ga Matachewan intrusive. The Seabrook Lake complex's ChRM is found at six normal polarity sites from within the complex and at four normal and three reversed polarity sites from within the fenitized Archean granite and Matachewan diabase of the contact aureole. It gives a pole position at 180°E, 46°N (dp = 11°, dm = 17°), which corresponds to a Keweenawan age of 1103 ± 10 Ma, agreeing with K/Ar biotite ages. The paleomagnetic data indicate that no significant motion on the Kapuskasing Structural Zone occurred after emplacement of the complexes excluding minor vertical uplift of less than about 4 km, and that there were multiple polarity transitions of a symmetric Earth's magnetic field during Keweenawan time.

scholarly journals Anisotropy of (partial) isothermal remanent magnetization: DC-field-dependence and additivity

2019 ◽  
Vol 218 (2) ◽  
pp. 1428-1441 ◽  
Author(s):  
Andrea R Biedermann ◽  
Mike Jackson ◽  
Dario Bilardello ◽  
Joshua M Feinberg
Keyword(s):  
Applied Field ◽  
Remanent Magnetization ◽  
Magnetic Fabric ◽  
Data Uncertainty ◽  
High Coercivity ◽  
Isothermal Remanent Magnetization ◽  
Wide Range ◽  
Principal Directions ◽  
Definition Of ◽  
Applied Fields

SUMMARY Anisotropy of isothermal remanent magnetization (AIRM) is useful for describing the fabrics of high-coercivity grains, or alternatively, the fabrics of all remanence-carrying grains in rocks with weak remanence. Comparisons between AIRM and other measures of magnetic fabric allow for description of mineral-specific or grain-size-dependent fabrics, and their relation to one another. Additionally, when the natural remanence of a rock is carried by high-coercivity minerals, it is essential to isolate the anisotropy of this grain fraction to correct paleodirectional and paleointensity data. AIRMs have been measured using a wide range of applied fields, from a few  mT to several T. It has been shown that the degree and shape of AIRM can vary with the strength of the applied field, for example, due to the contribution of separate grain subpopulations or due to field-dependent properties. To improve our understanding of these processes, we systematically investigate the variation of AIRM and the anisotropy of partial isothermal remanence (ApIRM) with applied field for a variety of rocks with different magnetic mineralogies. We also test the additivity of A(p)IRMs and provide a definition of their error limits. While A(p)IRM principal directions can be similar for a range of applied field strengths on the same specimen, the degree and shape of anisotropy often show systematic changes with the field over which the (p)IRM was applied. Also, the data uncertainty varies with field window; typically, larger windows lead to better-defined principal directions. Therefore, the choice of an appropriate field window is crucial for successful anisotropy corrections in paleomagnetic studies. Due to relatively large deviations between AIRMs calculated by tensor addition and directly measured AIRMs, we recommend that the desired A(p)IRM be measured directly for anisotropy corrections.

IRMITS: A MATLAB program for analyzing isothermal remanent magnetization (IRM) data

2020 ◽  
Author(s):  
Adika Bagaskara ◽  
Christopher Salim ◽  
Muhammad Archie Antareza ◽  
Kevin Dwimanggala Tjiongnotoputera ◽  
Mariyanto Mariyanto
Keyword(s):  
Remanent Magnetization ◽  
Isothermal Remanent Magnetization ◽  
Matlab Program

Evidence of Single-Domain Magnetite in the Michikamau Anorthosite

1971 ◽  
Vol 8 (3) ◽  
pp. 361-370 ◽  
Author(s):  
G. S. Murthy ◽  
M. E. Evans ◽  
D. I. Gough
Keyword(s):  
Remanent Magnetization ◽  
Theoretical Models ◽  
Natural Remanent Magnetization ◽  
Single Domain ◽  
Isothermal Remanent Magnetization ◽  
Mineral Separation ◽  
Domain Configuration ◽  
Plagioclase Felspar ◽  
Magnetite Particles ◽  
Theoretical Evidence

The Michikamau anorthosite possesses very stable natural remanent magnetization, some of which resists alternating fields up to 1800 Oe. The rock contains two types of opaque grains, fine opaque needles of order 10 × 0.5 μ in the plagioclase felspar, and large equidimensional magnetite particles. Ore microscope studies suggest, but do not establish, that the needles are composed of magnetite. Saturation isothermal remanence and thermal demagnetization studies indicate magnetite as the carrier of remanent magnetization. In order to distinguish the effects of the large grains from those of the needles, mineral separation was used to show that an artificial specimen of essentially pure plagioclase had very similar isothermal remanent magnetization properties to the whole rock. Both indicated magnetite as the magnetic mineral. Thermoremanent properties of the separated mineral fractions indicated magnetite as the dominant magnetic constituent but showed some evidence of laboratory-produced hematite. Theoretical models of grains elongated along [111] and [110] axes are used to show that magnetite needles can exist in stable single-domain configuration in the size and shape ranges of the needles observed in the Michikamau anorthosite. There is thus considerable experimental and theoretical evidence for the conclusion that the stable remanent magnetization of the Michikamau anorthosite is carried by fine single–domain needles of magnetite in the plagioclase felspar.

scholarly journals Feasibility of applying viscous remanent magnetization (VRM) orientation in the study of palaeowind direction by loess magnetic fabric

2018 ◽  
Vol 10 (1) ◽  
pp. 699-717
Author(s):  
Xingjun Xie ◽  
Xianghui Kong ◽  
Yajuan Du ◽  
Qiufang Chang ◽  
Ling Tang ◽  
...  
Keyword(s):  
Remanent Magnetization ◽  
Magnetic Fabric ◽  
Chinese Loess Plateau ◽  
Field Orientation ◽  
Significance Level ◽  
Chinese Loess ◽  
The North ◽  
Significant Difference ◽  
Temperature Ranges ◽  
Drilling Core

AbstractThe loess formation sampling method on the Chinese Loess Plateau generally involves the acquisition of samples from the basset section and the drilling core. Constraints imposed by the precision of the drilling machine operation make it difficult to determine the orientation of the samples due to the rotation of the core.Although researchers have proposed solutions for reconstructing the north direction of the samples by adopting the viscous remanent magnetization (VRM) orientation, it remains uncertain whether this approach can be adopted in studies that use the magnetic fabric to trace the palaeomonsoonal direction, and the degree to which this approach will change the magnetic fabric results.Based on the achievements of other researchers, we adopted the VRM orientation of the basset section samples oriented in the field. By determining how the VRM orientation changes the magnetic fabric of loess over different demagnetization temperature ranges, we can draw the preliminary conclusion that there is no significant difference between the magnetic fabric information of the loess obtained at 100–150°C VRM orientation and that obtained from the field orientation (the statistical bin size is 22.5°, significance level α = 0.05). This indicates that the VRM orientation approach is feasible for studying non-oriented drilling core samples to determine the prevailing surface paleowind direction with appropriate precision.

Photo-induced magnetic behavior in the amorphous spin-glass material Co3(SbTe3)2

1994 ◽  
Vol 9 (4) ◽  
pp. 909-914 ◽  
Author(s):  
Biao Wu ◽  
Lianwei Ren ◽  
Charles J. O'Connor ◽  
Jinke Tang ◽  
Jin-Seung Jung ◽  
...  
Keyword(s):  
Spin Glass ◽  
Remanent Magnetization ◽  
Magnetic Behavior ◽  
Freezing Temperature ◽  
Specific Resistivity ◽  
Metathesis Reaction ◽  
Isothermal Remanent Magnetization ◽  
Magnetization Data ◽  
Magnetizing Field ◽  
Thermal Remanent Magnetization

A new ternary material Co3(SbTe3)2 was prepared by using a rapid precipitation metathesis reaction between the Zintl material K3SbTe3 and CoCl2 in aqueous solution. The dc specific resistivity of this material is in the region for metallic conductors (p = 2.75 × 10-3 Ω-cm). The dc magnetic susceptibility of Co3(SbTe3)2 is reported over a 2.2 K-300 K temperature region, and the material is characterized as a spin glass with a freezing temperature of about 5 K. Magnetization data are also reported as both thermal remanent magnetization and isothermal remanent magnetization as a function of magnetizing field and temperature. When cooled well below the glass freezing temperature, the frozen spin glass has been observed to exhibit photomagnetic effects consistent with a disruption of the spin-glass state caused by uv-radiation.

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