Magnetic properties of intrusive traps of the Siberian platform: Evidence for a self-reversal of the natural remanent magnetization

2008 ◽  
Vol 44 (10) ◽  
pp. 822-838 ◽  
Author(s):  
A. K. Gapeev ◽  
S. K. Gribov
Keyword(s):  
Magnetic Properties ◽  
Siberian Platform ◽  
Remanent Magnetization ◽  
Natural Remanent Magnetization

The Mid-Atlantic ridge near 45° N. VII. Magnetic properties and opaque mineralogy of dredged samples

1970 ◽  
Vol 7 (2) ◽  
pp. 239-256 ◽  
Author(s):  
C. M. Carmichael
Keyword(s):  
Magnetic Properties ◽  
Remanent Magnetization ◽  
Complex Structure ◽  
Magnetic Anomalies ◽  
Natural Remanent Magnetization ◽  
Coarse Grained ◽  
X Ray Diffraction ◽  
Field Polarity ◽  
Fine Grained ◽  
Mid Atlantic Ridge

Measurements of the magnetic properties, paleomagnetic field intensity, and the inferred paleomagnetic field polarity have been made using fine grained basalt and coarser grained rock samples dredged from the mid-Atlantic ridge near 45° N and supplied by the Geological Survey of Canada. The opaque mineralogy of the samples was studied by microscope, Curie point, and X-ray diffraction techniques. The natural remanent magnetization of the basalt is of the order of 5 to 10 × 10−3 e.m.u./cm3 with some values from the center of the median valley reaching 10−1 e.m.u./cm3. Magnetic anomalies over the ridge can be accounted for by the remanent magnetization of a few hundred meters of this basalt. The coarse grained rocks were relatively weakly magnetized, and while they contribute little to the magnetic anomalies, their diverse character suggests that the major portion of the oceanic crust, below a thin veneer of fine grained basalt, has differentiated into a complex structure.

scholarly journals Magnetic Mineralogy of Speleothems From Tropical-Subtropical Sites of South America

2021 ◽  
Vol 9 ◽  
Author(s):  
Plinio Jaqueto ◽  
Ricardo I. F. Trindade ◽  
Joshua M. Feinberg ◽  
Janine Carmo ◽  
Valdir F. Novello ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
South America ◽  
Remanent Magnetization ◽  
Drainage Basin ◽  
Environmental Magnetism ◽  
Rank Correlation ◽  
Natural Remanent Magnetization ◽  
Magnetic Minerals ◽  
Magnetic Mineralogy ◽  
Diverse Range

Fe-bearing minerals are a tiny fraction of the composition of speleothems. They have their origin in the karst system or are transported from the drainage basin into the cave. Recent studies on the magnetism of speleothems focused on the variations of their magnetic mineralogy in specific time intervals and are usually limited to a single sample. In this study, we describe a database of environmental magnetism parameters built from 22 stalagmites from different caves located in Brazil (South America) at different latitudes, comprising different climates and biomes. The magnetic signal observed in these stalagmites is dominated by low-coercivity minerals (∼20 mT) whose magnetic properties resemble those of the magnetite formed in pedogenic environments. Also, a comparison with few samples from soils and the carbonate from cave’s walls shows a good agreement of the magnetic properties of speleothems with those of soil samples, reinforcing previous suggestions that in (sub-)tropical regimes, the dominant magnetic phase in speleothems is associated with the soil above the cave. Spearman’s rank correlation points to a positive strong correlation between magnetic concentration parameters (mass-normalized magnetic susceptibility, natural remanent magnetization, anhysteretic remanent magnetization, and isothermal remanent magnetization). This implies that ultrafine ferrimagnetic minerals are the dominant phase in these (sub-)tropical karst systems, which extend across a diverse range of biomes. Although the samples are concentrated in the savannah biome (Cerrado) (∼70%), comparison with other biomes shows a higher concentration of magnetic minerals in speleothem underlying savannahs and lower concentration in those underlying moist broadleaf forests (Atlantic and Amazon biome) and dry forests (Caatinga). Thus, rainfall, biome, and epikarst dynamics play an important role in the concentration of magnetic minerals in speleothems in (sub-)tropical sites and indicate they can be an important target for paleoenvironmental research in cave systems.

The Mid-Atlantic Ridge near 45° N. XIII. Magnetic properties of basalt bore-core

1970 ◽  
Vol 7 (6) ◽  
pp. 1515-1527 ◽  
Author(s):  
J. Brooke ◽  
E. Irving ◽  
J. K. Park
Keyword(s):  
Magnetic Properties ◽  
Coercive Force ◽  
Physical Properties ◽  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
The Core ◽  
Mid Atlantic Ridge ◽  
Technical Interest

Three bore-cores containing basalts have been obtained from the Mid-Atlantic Ridge at 45° N. The material is fresh and ideal for the study of physical properties. The drilling record and the nature of the core itself suggest that much of the basalt is from detached boulders, although one core may be in situ. In one core, variations in coercivity by a factor 2 occur within a distance of 5 cm. The coercive force spectra of anhysteretic and natural remanent magnetization are similar, but there are small differences due to secondary components which are used to predict correctly the polarity of 11 out of 12 specimens studied. This result may be of technical interest only since there is no guarantee that the material is in situ.

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