The Chazy Group, St. Lawrence Lowlands: anisotropy of magnetic susceptibility

1991 ◽  
Vol 28 (11) ◽  
pp. 1827-1833
Author(s):  
Nan-Hai Zhang ◽  
Maurice-K. Seguin
Keyword(s):  
Magnetic Susceptibility ◽  
Low Temperature ◽  
Flow Direction ◽  
High Energy ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Magnetic Minerals ◽  
Flat Bottom ◽  
The North ◽  
Microscopic Studies ◽  
Predominant Orientation

Magnetic susceptibility (K) and anisotropy of magnetic susceptibility (AMS) were measured on 69 specimens from five sites in the Chazy Group of the St. Lawrence Lowlands in southern Quebec. The K values depict an isotropic to slightly anisotropic character. The AMS ellipsoid shapes range from oblate to prolate. The axes of minimum susceptibility (Kmin) are mainly perpendicular to the subhorizontal bedding, whereas the other two axes (Kmax) and (Kint) are subparallel to it and somewhat scattered. These observations suggest that the Chazy seafloor was a relatively stable sedimentary platform, with a rather flat bottom, and was a high-energy depositional environment. A cluster analysis indicates a predominant orientation of the Kmax axes in the north-northwest – south-southeast direction. Microscopic studies have shown that detrital magnetic minerals in some specimens align in that direction as well. It is thus inferred that this direction reflects the flow direction of paleocurrents. K was measured also at low temperature (in liquid nitrogen). The results show that the paramagnetic contribution to K is relatively well detected at very low temperature, but it is hampered by diamagnetic contributions to K at room temperature. The specimens contain very few primary ferromagnetic mineral carriers, and therefore the sedimentary rocks of the Chazy Group are not appropriate for standard paleomagnetic investigation.

scholarly journals Anisotropy of Magnetic Susceptibility and Preferred Pore Orientation in Lava Flow from the Ijen Volcanic Complex, East Java, Indonesia

Geosciences ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 304 ◽  
Author(s):  
Fadhli Ramadhana Atarita ◽  
Satria Bijaksana ◽  
Nuresi Rantri Desi Wulan Ndari ◽  
Aditya Pratama ◽  
Reyhan Fariz Taqwantara ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Magnetic Susceptibility ◽  
Lava Flow ◽  
Igneous Rock ◽  
Flow Direction ◽  
Sampling Site ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Vertical Position ◽  
Volcanic Complex ◽  
Micro Computed Tomography

Anisotropy of magnetic susceptibility (AMS) has been used in various studies related to interpreting the direction of lava flow, some of which have shown ambiguity with regard to the data generated. In this study, we explored an alternative option to support the aforementioned application, using lava flow type igneous rock samples from the Ijen Volcanic Complex, East Java, Indonesia. We have investigated the preferred rock pore orientations from micro-computed tomography (μCT) images and quantified their directions. We then calculated their correlation with AMS data by calculating the angle between preferred pore orientation. The axis with the smallest gap to the preferred pore orientation of each sample was assumed to imply lava flow direction. Different lava flow direction preferences were obtained from different magnetic ellipsoids. Another important factor for consideration is the relative vertical position of the sampling site within a single lava flow unit. Only one out of five samples (ANY2) show good quantitative conformity between AMS data, preferred pore orientation, and topographical slope, despite these limitations. Our results point to a direction that seems to be correct and coherent on a physical basis. Additional research would likely clarify the issues involved. This encourages us to explore and work further in this field of research.

scholarly journals ANISOTROPY OF MAGNETIC SUSCEPTIBILITY (AMS) IN VOLCANIC FORMATIONS: THEORY AND PRELIMINARY RESULTS FROM RECENT VOLCANICS OF BROADER AEGEAN.

2004 ◽  
Vol 36 (3) ◽  
pp. 1308 ◽  
Author(s):  
I. Zananiri ◽  
D. Kondopoulou
Keyword(s):  
Magnetic Susceptibility ◽  
Flow Direction ◽  
Source Region ◽  
Physical Property ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Magnetic Fabric ◽  
Local Flow ◽  
Magma Flow ◽  
Preliminary Results ◽  
Scalar Properties

The anisotropy of magnetic susceptibility (AMS) is a physical property of rocks widely used in petrofabric studies and other applications. It is based on the measurement of low-field magnetic susceptibility in different directions along a sample. From this process several scalar properties arise, defining the magnitude and symmetry of the AMS ellipsoid, along with the magnetic foliation, namely the magnetic fabric. Imaging the sense of magma flow in dykes is an important task for volcanology; the magnetic fabric provides a fast and accurate way to infer this flow direction. Moreover, the AMS technique can be used in order to distinguish sills and dykes, a task that is almost impossible by using only field observations. Finally in the case of lava flows, the method can be applied to define the local flow conditions and to indicate the position of the "paleo" source region. However, this technique is quite new in Greece. Some preliminary results from volcanic formations of continental Greece and Southern Aegean are presented (Aegina, Almopia, Elatia, Gavra, Kos, Patmos, Samos, Samothraki and Santorini).

Anisotropy of magnetic susceptibility in salt rocks from the German Zechstein Basin, Sondershausen mine

2019 ◽  
Vol 219 (1) ◽  
pp. 690-712
Author(s):  
Frances C Heinrich ◽  
Volkmar Schmidt ◽  
Michael Schramm ◽  
Michael Mertineit
Keyword(s):  
Magnetic Susceptibility ◽  
Magnetic Anisotropy ◽  
Rock Salt ◽  
Impurity Content ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Deformation History ◽  
Magnetic Minerals ◽  
Accessory Minerals ◽  
Salt Rocks ◽  
Rock Types

SUMMARY The anisotropy of magnetic susceptibility (AMS) of rocks reflects the alignment of certain minerals, and therefore it can be used to investigate the deformation history of rocks. However, for salt rocks, very few studies on the AMS of salt rocks and the influence of accessory minerals exist. In this study, we analysed the potential to use the AMS of salt rocks with low impurity content for fabric characterization. Samples of rock salt, sylvinite and carnallitite from a salt mine in Sondershausen (Germany) from the Late Permian (Zechstein 2, Stassfurt series) are investigated. The results of low-field AMS (LF-AMS) measurements show a very weak but significant magnetic anisotropy for sylvinite, carnallitite, and rock salt with an elevated content of accessory minerals. The AMS results are consistent in individual layers of the same rock type. In order to identify the magnetic minerals, which cause the magnetic anisotropy, the high-field AMS (HF-AMS) was measured using a torque magnetometer in order to separate ferrimagnetic and paramagnetic contributions to the AMS. A significant paramagnetic subfabrics exists, which reflects the alignment of phyllosilicates. The magnitude of the LF-AMS is considerably greater than that of the paramagnetic subfabric. This indicates the existence of a ferrimagnetic subfabric due to magnetite, which can have a different orientation than the paramagnetic subfabric. Differences in the orientation of the AMS in samples from two sites suggest a relationship of deformation history and AMS. At a site with dipping layers, the AMS orientation is independent of the bedding and shows large differences between individual lithological layers. In a tight fold, the AMS of all rock types has similar shape and orientation. We conclude that AMS in salt rocks can give meaningful information on the mineral fabric, which could be used in the analysis of the deformation history.

Palaeomagnetic and anisotropy of magnetic susceptibility data bearing on the emplacement of the Western Granite, Isle of Rum, NW Scotland

2008 ◽  
Vol 146 (3) ◽  
pp. 419-436 ◽  
Author(s):  
M. S. PETRONIS ◽  
B. O'DRISCOLL ◽  
V. R. TROLL ◽  
C. H. EMELEUS ◽  
J. W. GEISSMAN
Keyword(s):  
Magnetic Susceptibility ◽  
Country Rock ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Magnetic Fabric ◽  
Contact Aureole ◽  
Data Set ◽  
The North ◽  
Early Paleocene ◽  
Magma Emplacement

AbstractThe Western Granite is the largest of several granitic bodies around the margin of the Rum Central Igneous Complex. We report palaeomagnetic and anisotropy of magnetic susceptibility (AMS) data that bear on the emplacement and deformation of the Western Granite. The collection includes samples from 27 sites throughout the Western Granite, five sites in adjacent feldspathic peridotite, and two sites in intermediate to mafic hybrid contact aureole rocks. Palaeomagnetic data from 22 of the 27 sites in the granite provide an in situ group mean D = 213.2°, I = −69.5°, α95 = 5.5° that is discordant to an early Paleocene reverse polarity expected field (about 184°, −66°, α95 = 4.3°). The discrepancy is eliminated by removing an inferred 15° of northwest-side-down tilting about a best fit horizontal tilt axis trending 040°. Data from the younger peridotite and hybrid rocks of the Rum Layered Suite provide an in situ group mean of D = 182.6°, I = −64.8°, α95 = 4.0°, which is statistically indistinguishable from an early Paleocene expected field, and imply no post-emplacement tilting of these rocks since remanence acquisition. The inferred tilt recorded in the Western Granite, which did not affect the younger Layered Suite, suggests that emplacement of the ultrabasic rocks resulted in roof uplift and associated tilt of the Western Granite to make space for mafic magma emplacement. Magnetic fabric magnitude and susceptibility parameters yield two subtle groupings in the Western Granite AMS data set. Group 1 data, defined by rocks from exposures to the east and south, have comparatively high bulk susceptibilities (Kmean, 29.51 × 10−3 in SI system), stronger anisotropies (Pj, 1.031) and oblate susceptibility ellipsoids. Group 2 data, from rocks in the west part of the pluton, have lower values of Kmean (15.89 × 10−3 SI) and Pj (1.014), and triaxial susceptibility ellipsoids. Magnetic lineations argue for emplacement of the granite as a tabular sheet from the south–southeast toward the north and west. Moderate to steeply outward-dipping magnetic foliations, together with deflection of the country rock bedding in the north, are consistent with doming accompanying magma emplacement.

scholarly journals Preferred Pore Orientation as a Complement to Anisotropy of Magnetic Susceptibility: A Case Study of Lava Flows From Batur Volcano, Bali, Indonesia

2020 ◽  
Vol 8 ◽  
Author(s):  
Nuresi Rantri Desi Wulan Ndari ◽  
Putu Billy Suryanata ◽  
Satria Bijaksana ◽  
Darharta Dahrin ◽  
Fadhli Ramadhana Atarita ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Lava Flow ◽  
Magnetic Measurements ◽  
Flow Direction ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Lava Flows ◽  
Micro Computed Tomography ◽  
Petrographic Analyses ◽  
Sample Position ◽  
Batur Volcano

Anisotropy of magnetic susceptibility (AMS) analyses have been used widely in many applications that include studying lava flows. In this paper, we introduce an auxiliary parameter, i.e., preferred pore orientation, on the use of AMS for lava flow studies on the basaltic lava samples from Batur Volcano in Bali Indonesia. We also examine the effect of sample position in lava flow outcrop to the relationship between preferred pore orientation and AMS. The samples are subjected to petrographic analyses as well as to magnetic measurements and micro-computed tomography (μCT) imaging. Preferred pore orientations were obtained by quantified the long-axis of the vesicles from the images. The correlation was evaluated by measuring the angle between the maximum susceptibility axes and the preferred pore orientations. All samples show that the maximum susceptibility axes are parallel with the flow direction. Three out of six samples of two lava flows from the same eruption show a positive correlation between AMS and preferred pore orientation, where both parameters point to the northeast direction. A difference of sample position in the outcrop of lava flow was observed as a possible factor that influenced the results for the preferred pore orientations. Samples which were taken from the summit of the lava flow have pore orientation parallel to the lava flow direction. While samples which were taken from the foot slope of the lava flow have pore orientation perpendicular to the lava flow direction. This study provides further evidence that pore orientation might be positively correlated with the AMS.

scholarly journals Anisotropy of magnetic susceptibility (AMS) of lava and volcanoclastic flows of the Stephano-Permian Cadi basin (central-eastern Pyrenees)

2020 ◽  
Author(s):  
Ana Simon-Muzas ◽  
Antonio M Casas-Sainz ◽  
Ruth Soto ◽  
Josep Gisbert ◽  
Teresa Román-Berdiel ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Flow Direction ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Lava Flows ◽  
Magnetic Fabric ◽  
Magnetic Mineralogy ◽  
Thin Sections ◽  
Andesitic Lava ◽  
Magnetic Fabrics ◽  
Standard Specimens

<p>The aim of this work is to apply the anisotropy of magnetic susceptibility (AMS) to determine the primary and tectonic fabrics of lava flows and volcanoclastic materials in one of the Pyrenean Stephano-Permian basins.</p><p>The Pyrenean Range is a double vergence orogen located at the northern end of the Iberian Peninsula. During Carboniferous-Early Permian times the extensional or transtensional regime dominant during the progressive dismantling of the Variscan belt resulted in the development of E-W elongated intra-mountainous basins. This process was coeval with an exceptional episode of magmatic activity, both intrusive and extrusive. The Cadí basin represents a good example of these structures were Stephano-Permian rocks are aligned along an E-W continuous outcrop and reach thickness of several hundreds of meters. The stratigraphy of the study area is characterized by fluviolacustrine sediments changing laterally to volcanoclastic and pyroclastic rocks with interbedded andesitic lava flows.  </p><p>A total of 75 sites (733 standard specimens) were studied and analysed throughout the volcanoclastic, volcanic and intrusive materials of the Stephano-Permian outcrops in the Cadí basin. Samples were drilled in the field along 5 sections with N-S or NW-SE direction in the Grey and Transition Unit. Afterwards, standard specimens were measured in a Kappabridge KLY-3 (AGICO) at the Zaragoza University to characterise the magnetic fabric. The susceptibility bridge combined with a CS-3 furnace (AGICO) was used for the temperature-dependent magnetic susceptibility curves (from 20 to 700 °C) to recognize the magnetic mineralogy. In addition, textural and mineralogical recognition in thin-sections of the samples was carried out in order to recognize the relationship between magnetic and petrographic fabrics.</p><p>The results shows that the bulk magnetic susceptibility of the specimens ranges between 118 and 9060·10<sup>-6</sup> SI but most of the values are bracketed between 160 to 450·10<sup>-6</sup> SI. Taking into account magnetic parameters (Km, Pj and T) there is no correlation between magnetic fabrics and magnetic mineralogy and there is a dominance of triaxial and prolate ellipsoids. Thermomagnetic curves indicate the dominance of paramagnetic behaviour in all the samples and except in one case there is a ferromagnetic contribution due to the generalised presence of magnetite.</p><p>Magnetic ellipsoids can be divided into four main types depending on the orientation of the main axes and associated with the lithologic types: 1) K<sub>max</sub> vertical and K<sub>int </sub>and K<sub>min</sub> horizontal for small intrusive bodies (no restoring); 2) K<sub>max </sub>horizontal or subhorizontal and K<sub>int </sub>and K<sub>min </sub>included in a subvertical plane (before and after restitution) for volcanic breccias; 3) K<sub>min</sub> vertical (after restoring) and three directional maxima for lava flows and 4) non-defined fabric for the explosive materials (probably due to their complex depositional mechanisms). In general, a dominant E-W magnetic lineation is observed in many sites, resulting either from dominant flow direction, or to secondary processes. This is the case for some of the magnetic ellipsoids, that seems to be affected by deformation, K<sub>min</sub> is not normal to bedding and therefore, they do not become vertical after bedding restitution.</p>

scholarly journals Structure and internal deformation of thrust sheets in the Sawtooth Range, Montana: insights from anisotropy of magnetic susceptibility

2019 ◽  
Vol 487 (1) ◽  
pp. 189-208 ◽  
Author(s):  
Dave J. McCarthy ◽  
Patrick A. Meere ◽  
Michael S. Petronis
Keyword(s):  
Magnetic Susceptibility ◽  
Strain Analysis ◽  
Anisotropy Of Magnetic Susceptibility ◽  
North American Continent ◽  
The North ◽  
Magnetic Fabrics ◽  
Structural Regime ◽  
Thrust Sheets ◽  
Internal Deformation ◽  
East West

AbstractGeological strain analysis of sedimentary rocks is commonly carried out using clast-based techniques. In the absence of valid strain markers, it can be difficult to identify the presence of an early tectonic fabric development and resulting layer parallel shortening (LPS). In order to identify early LPS, we carried out anisotropy of magnetic susceptibility (AMS) analyses on Mississippian limestones from the Sawtooth Range of Montana. The Sawtooth Range is an arcuate zone of north-trending, closely spaced, west-dipping, imbricate thrust sheets that place Mississippian Madison Group carbonates above Cretaceous shales and sandstones. This structural regime is part of the cordilleran mountain belt of North America, which resulted from accretion of allochthonous terrains to the western edge of the North American continent.Although the region has a general east–west increase in thrust displacement and related brittle deformation, a similar trend in penetrative deformation or the distribution of tectonic fabrics is not observed in the field or in the AMS results. The range of magnetic fabrics identified in each thrust sheet ranges from bedding controlled depositional fabrics to tectonic fabrics at a high angle to bedding.

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