Magnetic fabric and flow directions in magmatic rocks of the Franz Josef Land, Arctic Ocean

2020 ◽  
Author(s):  
Anna Chernova ◽  
Viktor Abashev ◽  
Dmitry Metelkin ◽  
Valery Vernikovsky ◽  
Nikolay Mikhaltsov
Keyword(s):  
Lava Flow ◽  
Complex Analysis ◽  
Flow Direction ◽  
Lava Flows ◽  
Magnetic Fabric ◽  
Basaltic Lava ◽  
Magma Flow ◽  
Franz Josef Land ◽  
Degree Of Anisotropy ◽  
Flow Directions

<p>Here, we present the results of a study of the anisotropy of magnetic susceptibility (AMS) completed in the Early Cretaceous magmatic complexes from the Franz Josef Land (FJL). AMS was measured in the framework of paleomagnetic research as a leading indicator of the rock magnetic fabric to help in understanding the lava flow directions and forming mechanisms. The three types of magmatic bodies were available in these studies: dolerite sills, dykes and basaltic lava flows from several islands (Alexandra, Hall, Ziegler, Jackson and Heiss Islands) among FJL. During the experiments the different parameters of AMS ellipsoids were obtained which have a good correlation with the igneous body shapes and also could illustrate lava flows direction parameters. The degree of anisotropy P is 1.01-1.06 for most sites that is typical for the primary igneous magnetic fabric. The form factor T characterizing the shape of the AMS ellipsoids demonstrates both planar and linear magnetic fabric in studied magmatic bodies. What is remarkable the part of the dykes is characterized strictly oblate magnetic fabric and another dykes have the prolate AMS ellipsoids. The linear magnetic structure is also more typical for lava flows with the maximum axes K1 lying in the flow plane that is obviously could point to the flow direction. The part of the igneous bodies are characterized by the inverse type of magnetic fabric, when the principal axis K1 of the ellipsoid is oriented perpendicularly to the plane of the flow or the sill, that was likely caused by the effect of secondary processes. The previous studies (Abashev et al., 2019) demonstrated that the primary orientation of the AMS ellipsoid could be recovered after temperature demagnetization. Noticeable changes were revealed at heating up to ~450 deg C, which generally corresponds to deblocking temperatures of titanomagnetites identified in the rocks by rock-magnetic methods. The degree of anisotropy was decreased after heating in 2-3 times. The heating also resulted to the redistribution of magnetic axes and in several cases the axes becomes more grouped. Analysis of the AMS results from the basaltic lava flows of the Aleksandra Island defined the magma flow direction to be NW-SE. Similar behavior of the AMS ellipsoids and lava flow orientation is typical for Ziegler Island. Generally our results show that complex analysis of AMS data in basaltic rocks is promising for identifying magma flow direction and it can give more detailed information about forming mechanisms of the different magmatic bodies.</p><p>This work was supported by the RSF (project no. 19-17-00091) and the RFBR (project nos. 18-35-00273, 18-05-70035).</p>

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.

Optimizing barrier placement for lava flow hazard and risk mitigation

2020 ◽  
Author(s):  
Giuseppe Bilotta ◽  
Annalisa Cappello ◽  
Veronica Centorrino ◽  
Claudia Corradino ◽  
Gaetana Ganci ◽  
...  
Keyword(s):  
Lava Flow ◽  
Risk Mitigation ◽  
Flow Direction ◽  
Economic Loss ◽  
Lava Flows ◽  
Mount Etna ◽  
Area Of Interest ◽  
Lava Flow Hazard ◽  
Mitigation Action ◽  
The Impact

<p>Mitigating hazards when lava flows threaten infrastructure is one of the most challenging fields of volcanology, and has an immediate and practical impact on society. Lava flow hazard is determined by the probability of inundation, and essentially controlled by the topography of the area of interest. The most common actions of intervention for lava flow hazard mitigation are therefore the construction of artificial barriers and ditches that can control the flow direction and advancement speed. Estimating the effect a barrier or ditch can have on lava flow paths is non-trivial, but numerical modelling can provide a powerful tool by simulating the eruptive scenario and thus assess the effectiveness of the mitigation action. We present a numerical method for the design of optimal artificial barriers, in terms of location and geometric features, aimed at minimizing the impact of lava flows based on the spatial distribution of exposed elements. First, an exposure analysis collects information about elements at risk from different datasets: population per municipality, distribution of buildings, infrastructure, routes, gas and electricity networks, and land use; numerical simulations are used to compute the probability for these elements to be inundated by lava flows from a number of possible eruptive scenarios  (hazard assessment) and computing the associated economic loss and potential destruction of key facilities (risk assessment). We then generate several intervention scenarios, defined by the location, orientation and geometry (width, length, thickness and even shape) of multiple barriers, and compute the corresponding variation in economic loss. Optimality of the barrier placement is thus considered as a minimization problem for the economic loss, controlled by the barrier placement and constrained by the associated costs. We demonstrate the operation of this system by using a retrospective analysis of some recent effusive eruptions at Mount Etna, Sicily.</p>

scholarly journals Emplacing a Cooling-Limited Rhyolite Lava Flow: Similarities with Basaltic Lava Flows

2017 ◽  
Vol 5 ◽  
Author(s):  
Nathan Magnall ◽  
Mike R. James ◽  
Hugh Tuffen ◽  
Charlotte Vye-Brown
Keyword(s):  
Lava Flow ◽  
Lava Flows ◽  
Basaltic Lava ◽  
Rhyolite Lava

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 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>

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