scholarly journals Mineralogical control on the magnetic anisotropy of lavas and ignimbrites: a case study in the Caviahue-Copahue field (Argentina)

2019 ◽  
Vol 220 (2) ◽  
pp. 821-838 ◽  
Author(s):  
Thiago R Moncinhatto ◽  
Maurício B Haag ◽  
Gelvam A Hartmann ◽  
Jairo F Savian ◽  
Wilbor Poletti ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Magnetic Anisotropy ◽  
Flow Direction ◽  
Volcanic Rocks ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Lava Flows ◽  
Magnetic Fabric ◽  
Volcanic Complex ◽  
Magnetic Mineralogy ◽  
Southern Volcanic Zone

SUMMARY Anisotropy of magnetic susceptibility is a petrofabric tool used to estimate the alignment of minerals at the site-scale, the imbrication between the magnetic foliation and the emplacement surface being an indicator of flow direction. However, despite numerous studies examining the flow direction in pyroclastic deposits and lava flows, the effect of magnetic mineralogy and the domain state of ferromagnetic phases on the magnetic fabric remains poorly understood. This paper describes the magnetic mineralogy and its influence on the magnetic fabric of Plio-Pleistocene lava flows and ignimbrites of the Caviahue-Copahue Volcanic Complex in the Andean Southern Volcanic Zone, Argentina. Rock magnetism, anisotropy of magnetic susceptibility and anhysteretic remanent magnetization and petrographic observations were performed on 30 sites of the volcanic complex. Results revealed the extrusive and pyroclastic rocks present varied magnetic mineralogy, formed in different stages of the magmatic evolution. Magnetic mineralogy variations strongly affect the anisotropy of magnetic susceptibility data in volcanic rocks and associated ignimbrites, providing ‘scattered’ fabrics when late Ti-rich titanomagnetite phases dominate the fabric, and ‘inverse’ or ‘intermediate’ fabrics when single-domain grains are present. ‘Normal’ fabrics are typically found when early crystallized pure magnetite is present. Our results highlight the complexity in the interpretation of magnetic anisotropy data in volcanic rocks and ignimbrites.

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 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).

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 The magnetic anisotropy of rocks: principles, techniques and geodynamic applications in the Italian peninsula

1997 ◽  
Vol 40 (3) ◽  
Author(s):  
A. Winkler ◽  
L. Alfonsi ◽  
F. Florindo ◽  
L. Sagnotti ◽  
F. Speranza
Keyword(s):  
Magnetic Susceptibility ◽  
Magnetic Anisotropy ◽  
Sedimentary Rocks ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Magnetic Fabric ◽  
Experimental Techniques ◽  
Rock Fabric ◽  
Italian Peninsula ◽  
Physical Principles

Magnetic anisotropy studies have recently come to the forefront as accurate, fast and inexpensive methods in the investigation of the rock fabric. In this paper we summarize the physical principles and the experimental techniques commonly used to resolve the Anisotropy of Magnetic Susceptibility (AMS) and the Anisotropy of Anhysteretic Remanence (AAR) tensors, and we give a description of the parameters which usually describe the magnetic anisotropy properties of a rock. A synthetic review of the magnetic fabric studies carried out on sedimentary rocks of the Italian peninsula is also given, discussing the potentiality of this technique in geodynamic studies.

On the influence of magnetic mineralogy in the tectonic interpretation of anisotropy of magnetic susceptibility in cataclastic fault zones

2018 ◽  
Vol 216 (2) ◽  
pp. 1043-1061 ◽  
Author(s):  
Teresa Román-Berdiel ◽  
Antonio M Casas-Sainz ◽  
Belén Oliva-Urcia ◽  
Pablo Calvín ◽  
Juan José Villalaín
Keyword(s):  
Magnetic Susceptibility ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Fault Zones ◽  
Magnetic Mineralogy ◽  
Tectonic Interpretation

Magnetic fabric from Quaternary volcanic edifices in the extensional Bransfield Basin: internal structure of Penguin and Bridgeman islands (South Shetlands archipelago, Antarctica)

2021 ◽  
Author(s):  
B Oliva-Urcia ◽  
J López-Martínez ◽  
A Maestro ◽  
A Gil ◽  
T Schmid ◽  
...  
Keyword(s):  
Flow Direction ◽  
Orientation Distribution ◽  
Scoria Cone ◽  
Lava Flows ◽  
Magnetic Fabric ◽  
Scattered Electron ◽  
Magnetic Lineation ◽  
South Shetlands ◽  
Bransfield Basin ◽  
Electron Imaging

Summary Studying the magnetic fabric in volcanic edifices, particularly lava flows from recent eruptions, allows us to understand the orientation distribution of the minerals related to the flow direction and properly characterize older and/or eroded flows. In this work, the magnetic fabric from recent (Quaternary) lava flows (slightly inclined in seven sites and plateau lavas in two sites), pyroclastic deposits (two sites from a scoria cone) and volcanic cones, domes and plugs (three sites) from Penguin and Bridgeman islands, located in the Bransfield back-arc basin, are presented. The volcanism in the two islands is related to rifting occurring due to the opening of the Bransfield Strait, between the South Shetlands archipelago and the Antarctic Peninsula. The direction of flow of magmatic material is unknown. Rock magnetic analyses, low temperature measurements and electron microscope observations (back-scattered electron imaging and Energy Dispersive X-ray analyses) reveal a Ti-poor magnetite (and maghemite) as the main carrier of the magnetic fabric. Hematite may be present in some samples. Samples from the center of the lavas reveal a magnetic lineation either parallel or imbricated with respect to the flow plane, whereas in the plateau lavas the magnetic lineation is contained within the subhorizontal plane except in vesicle-rich samples, where imbrication occurs. The magnetic lineation indicates a varied flow direction in Bridgeman Island with respect to the spreading Bransfield Basin axis. The flow direction in the plateau lavas on Penguin Island is deduced from the imbrication of the magnetic fabric in the more vesicular parts, suggesting a SE-NW flow. The volcanic domes are also imbricated with respect to an upward flow, and the bombs show scattered distribution.

scholarly journals Distinguishing the Mélange-Forming Processes in Subduction-Accretion Complexes: Constraints from the Anisotropy of Magnetic Susceptibility (AMS)

Geosciences ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 381 ◽  
Author(s):  
Claudio Robustelli Test ◽  
Andrea Festa ◽  
Elena Zanella ◽  
Giulia Codegone ◽  
Emanuele Scaramuzzo
Keyword(s):  
Magnetic Susceptibility ◽  
Late Cretaceous ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Magnetic Fabric ◽  
Early Eocene ◽  
Accretionary Complex ◽  
Geodynamic Evolution ◽  
Structural Investigations ◽  
Laboratory Investigations ◽  
Magnetic Features

The strong morphological similitude of the block-in-matrix fabric of chaotic rock units (mélanges and broken formations) makes problematic the recognition of their primary forming-processes. We present results of the comparison between magnetic fabric and mesoscale structural investigations of non-metamorphic tectonic, sedimentary, and polygenetic mélanges in the exhumed Late Cretaceous to early Eocene Ligurian accretionary complex and overlying wedge-top basin succession in the Northern Apennines (northwest Italy). Our findings show that the magnetic fabric reveals diagnostic configurations of principal anisotropy of magnetic susceptibility (AMS) axes orientation that are well comparable with the mesoscale block-in-matrix fabric of mélanges formed by different processes. Broken formations and tectonic mélanges show prolate and neutral-to-oblate ellipsoids, respectively, with magnetic fabric elements being consistent with those of the mesoscale anisotropic “structurally ordered” block-in-matrix fabric. Sedimentary mélanges show an oblate ellipsoid with a clear sedimentary magnetic fabric related to downslope gravitational emplacement. Polygenetic mélanges show the occurrence of a cumulative depositional and tectonic magnetic fabric. The comparison of field and laboratory investigations validate the analysis of magnetic features as a diagnostic tool suitable to analytically distinguish the contribution of different mélange forming-processes and their mutual superposition, and to better understand the geodynamic evolution of subduction-accretion complexes.

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