Paleointensity derived from igneous rocks of Kamchatka volcanoes of the Late Pleistocene-Holocene epoch

2020 ◽  
Author(s):  
Iuliia Sleptsova ◽  
Valeriy Maksimochkin
Keyword(s):  
Magnetic Field ◽  
Curie Temperature ◽  
Lava Flow ◽  
Geomagnetic Field ◽  
Single Domain ◽  
Igneous Rocks ◽  
Lava Flows ◽  
Virtual Geomagnetic Pole ◽  
Temperature Oxidation ◽  
Curie Temperature Tc

<p>This work is devoted to paleomagnetic studies of lava samples from three volcanoes of Kamchatka in order to define the age of lava flows and to obtain data of paleosecular variations of the geomagnetic field for the Kamchatka region. We studied 53 samples from 7 sites from lava flows of the Avachinsky, the Gorely and the Tolbachik volcanoes. The study of paleosecular variations recorded in the magnetization of the lava flows of volcanoes makes it possible to create a magnetochronological scale for epochs of the same polarity.</p><p>According to the data of electron microprobe and thermomagnetic analyzes, the magnetic properties of samples from the lava flows of the Avachinsky volcano are mainly determined by titanic magnetite with a Curie temperature Tc = (540-580) °С. The study of magnetic mineral grains using electron and magnetic force microscopy showed the presence of decay structures in grains, indicating the high-temperature oxidation of titanomagnetite. Ferrimagnetic grains of samples from the Gorely and Tolbachik volcanoes are represented by titanomagnetite with a Curie temperature Tc = (200–300) °C. According to the hysteresis characteristics, the magnetic structure of the grains corresponds to a single-domain and pseudo-single-domain state. Thermal and magnetic cleanings showed the predominance of one component in the NRM. The geomagnetic field intensity was determined by the Thellier method in the Coe modification.</p><p>It was found that the paleointensity value H<sub>anc</sub> = 55±3 μT, determined from the NRM of samples of the 2012 eruption from the Tolbachik volcano, differs from the modern magnetic field in the area of this volcano by the IGRF-12 model by only 4% (Н<sub>IGRF</sub> = 53 μT). This indicates the reliability of our methodology for determining paleointensity from the most stable part of the NRM of igneous rocks.</p><p>A comparison of the coordinates of the paleomagnetic pole (N 66º±4º, E 266º±5º) and the virtual dipole magnetic moment of the Earth (VDM = 8.3±0.9*10<sup>22</sup> A*m<sup>2</sup>) with data on variations of the geomagnetic field over the past 10,000 years [Burlatskaya, 2007; McElhinny, 1982] allows us to conclude that the investigated lava flow belongs to the historical eruptions of 1827. The coordinates of the virtual geomagnetic pole (N 83º±3º, E 254º±21º) and the value of VDM = 8.0±0.3*10<sup>22</sup> A*m<sup>2</sup> determined from the samples belonging to the second lava flow of the Avachinsky volcano indicate that rocks are formed in the result of the eruption, which occurred 5-5.5 thousand years ago.</p><p>It was revealed that the magnitude (H<sub>anc</sub> =65±5μT) and the direction of paleointensity determined by the NRM of the samples from Gorely volcano significantly differ from the characteristics of the modern magnetic field. The assumption is made that the studied samples belong to the outpouring of lava, which occurred about 2.7 thousand years ago, during the "Sterno-Etrussia" geomagnetic excursion.</p><p> </p><p>This work was supported by the Russian Foundation for Basic Research, project 20-05-00573.</p>

scholarly journals Instability of thermoremanence and the problem of estimating the ancient geomagnetic field strength from non-single-domain recorders

2015 ◽  
Vol 112 (36) ◽  
pp. 11187-11192 ◽  
Author(s):  
Ron Shaar ◽  
Lisa Tauxe
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Geomagnetic Field ◽  
Single Domain ◽  
Standard Theory ◽  
Systematic Bias ◽  
The Past ◽  
Deep Interior ◽  
Relationship Of ◽  
Geomagnetic Field Strength

Data on the past intensity of Earth’s magnetic field (paleointensity) are essential for understanding Earth’s deep interior, climatic modeling, and geochronology applications, among other items. Here we demonstrate the possibility that much of available paleointensity data could be biased by instability of thermoremanent magnetization (TRM) associated with non-single-domain (SD) particles. Paleointensity data are derived from experiments in which an ancient TRM, acquired in an unknown field, is replaced by a laboratory-controlled TRM. This procedure is built on the assumption that the process of ancient TRM acquisition is entirely reproducible in the laboratory. Here we show experimental results violating this assumption in a manner not expected from standard theory. We show that the demagnetization−remagnetization relationship of non-SD specimens that were kept in a controlled field for only 2 y show a small but systematic bias relative to sister specimens that were given a fresh TRM. This effect, likely caused by irreversible changes in micromagnetic structures, leads to a bias in paleointensity estimates.

Texture Evolution In Fe-1%Si as a Function of High Magnetic Field

2005 ◽  
Vol 105 ◽  
pp. 151-156 ◽  
Author(s):  
Tricia A. Bennett ◽  
R.A. Jaramillo ◽  
David E. Laughlin ◽  
J.B. Wilgen ◽  
R. Kisner ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Grain Size ◽  
Field Strength ◽  
Curie Temperature ◽  
High Magnetic Field ◽  
Texture Component ◽  
Texture Evolution ◽  
Goss Texture ◽  
Drastic Increase ◽  
Curie Temperature Tc

The effect of a 1.5T, 15T and 30T magnetic field on texture evolution in Fe-1%Si was investigated by annealing samples for 1 hour at 787°C, (27° above the Curie temperature, Tc = 760°C). The intensity of the Goss texture component increased with increasing field strength accompanied by a drastic increase in grain size.

Paleointensity study of late Miocene igneous rocks from British Columbia, Canada

1970 ◽  
Vol 7 (1) ◽  
pp. 176-181 ◽  
Author(s):  
D. T. A. Symons ◽  
E. J. Schwarz
Keyword(s):  
Magnetic Field ◽  
British Columbia ◽  
North America ◽  
Late Miocene ◽  
Igneous Rocks ◽  
Lava Flows ◽  
Basaltic Lava ◽  
Remanent Magnetism ◽  
South Central ◽  
Demagnetizing Fields

Sixty-nine specimens representing 49 late Miocene (10–15 m.y. ago) basaltic lava flows and 4 associated gabbroic intrusive plugs were studied in an attempt to estimate the paleointensity of the earth's magnetic field in south-central British Columbia. The paleointensity determination was based on the comparison of the decay of natural remanent magnetism intensity with that of an artificial thermoremanent magnetism (H = 0.35 Oe) in progressively higher alternating demagnetizing fields (peak: 800 Oe). Only 22 of the 69 specimens were considered to yield reliable paleointensity determinations which give an estimated average equatorial intensity for the late Miocene earth's field of 0.18 Oe ± 0.11. This result agrees reasonably well with those from contemporaneous rocks from North America, Japan, and Iceland. Several low determinations with consistent, normal, or reversed remanence directions suggest that the intensity of the non-dipole components of the late Miocene earth's field must have been very small in the sampled area.

scholarly journals 14C Dating and Magnetostratigraphy

Radiocarbon ◽  
1983 ◽  
Vol 25 (2) ◽  
pp. 229-238 ◽  
Author(s):  
Roy Thompson
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Cosmic Ray ◽  
Lava Flows ◽  
Earth’S Magnetic Field ◽  
14C Dating ◽  
Fine Grained ◽  
Magnetic Remanence ◽  
Earth's Magnetic Field ◽  
History Of

The history of the earth's magnetic field is preserved in the fossil magnetism of archaeologic specimens, natural rocks and sediments. Samples such as lava flows and baked sherds that acquired a thermoremanent magnetization on cooling can be used to estimate ancient geomagnetic field intensities and directions. Paleofield directions can also be obtained from fine-grained sediments that acquired detrital magnetic remanence when deposited. Study of the earth's magnetic field over the last few tens of thousands of years yields information on geomagnetic dynamo theories, causes of fluctuations in cosmic-ray activity, and the formulation of a new regional chronologic tool.

scholarly journals Magnetic and Magneto-Caloric Properties of the Amorphous Fe92−xZr8Bx Ribbons

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5334
Author(s):  
Xin Wang ◽  
Qiang Wang ◽  
Ben Zhen Tang ◽  
Ding Ding ◽  
Li Cui ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Curie Temperature ◽  
Saturation Magnetization ◽  
Maximum Entropy ◽  
Entropy Change ◽  
Boron Addition ◽  
Magnetocaloric Properties ◽  
Curie Temperature Tc

Magnetic and magnetocaloric properties of the amorphous Fe92−xZr8Bx ribbons were studied in this work. Fully amorphous Fe89Zr8B3, Fe88Zr8B4, and Fe87Zr8B5 ribbons were fabricated. The Curie temperature (Tc), saturation magnetization (Ms), and the maximum entropy change with the variation of a magnetic field (−ΔSmpeak) of the glassy ribbons were significantly improved by the boron addition. The mechanism for the enhanced Tc and −ΔSmpeak by boron addition was studied.

Investigations of Some Magnetic and Mineralogical Properties of the Laschamp and Olby Flows, France

1971 ◽  
Vol 1 (4) ◽  
pp. 511-521 ◽  
Author(s):  
John Whitney ◽  
H. P. Johnson ◽  
Shaul Levi ◽  
Bernard W. Evans
Keyword(s):  
Magnetic Field ◽  
High Temperatures ◽  
Geomagnetic Field ◽  
Remanent Magnetization ◽  
Single Domain ◽  
Field Reversal ◽  
Ambient Magnetic Field ◽  
Mineralogical Properties ◽  
Magnetite Particles

Rock-magnetic, paleomagnetic and petrologic properties of samples from the Laschamp and Olby basalt formations in France were studied to aid in determining the validity of the Laschamp geomagnetic field reversal reported by Bonhommet and Babkine. The Laschamp flow contains ilmenomagnetite, with partial alteration of the magnetite to hematite. Ilmenomagnetite in the Olby flow has largely recrystallized at high temperatures to a composite mozaic intergrowth of pseudobrookite, titanohematite and magnesioferrite, with rare residual magnetite and lamellae of ilmenite. The remanent magnetization is stable and resides primarily in single-domain magnetite particles. Our results indicate that the magnetizations of the Laschamp and Olby flows faithfully record the direction of the ambient magnetic field in which they cooled.

scholarly journals Predictions of the geomagnetic secular variation based on the ensemble sequential assimilation of geomagnetic field models by dynamo simulations

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Sabrina Sanchez ◽  
Johannes Wicht ◽  
Julien Bärenzung
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Wave Number ◽  
Main Magnetic Field ◽  
Candidate Model ◽  
Uncertainty Estimates ◽  
Geomagnetic Field Models ◽  
Dipole Configuration

Abstract The IGRF offers an important incentive for testing algorithms predicting the Earth’s magnetic field changes, known as secular variation (SV), in a 5-year range. Here, we present a SV candidate model for the 13th IGRF that stems from a sequential ensemble data assimilation approach (EnKF). The ensemble consists of a number of parallel-running 3D-dynamo simulations. The assimilated data are geomagnetic field snapshots covering the years 1840 to 2000 from the COV-OBS.x1 model and for 2001 to 2020 from the Kalmag model. A spectral covariance localization method, considering the couplings between spherical harmonics of the same equatorial symmetry and same azimuthal wave number, allows decreasing the ensemble size to about a 100 while maintaining the stability of the assimilation. The quality of 5-year predictions is tested for the past two decades. These tests show that the assimilation scheme is able to reconstruct the overall SV evolution. They also suggest that a better 5-year forecast is obtained keeping the SV constant compared to the dynamically evolving SV. However, the quality of the dynamical forecast steadily improves over the full assimilation window (180 years). We therefore propose the instantaneous SV estimate for 2020 from our assimilation as a candidate model for the IGRF-13. The ensemble approach provides uncertainty estimates, which closely match the residual differences with respect to the IGRF-13. Longer term predictions for the evolution of the main magnetic field features over a 50-year range are also presented. We observe the further decrease of the axial dipole at a mean rate of 8 nT/year as well as a deepening and broadening of the South Atlantic Anomaly. The magnetic dip poles are seen to approach an eccentric dipole configuration.

scholarly journals Anatomy of a Paroxysmal Lava Fountain at Etna Volcano: The Case of the 12 March 2021, Episode

2021 ◽  
Vol 13 (15) ◽  
pp. 3052
Author(s):  
Sonia Calvari ◽  
Alessandro Bonaccorso ◽  
Gaetana Ganci
Keyword(s):  
Lava Flow ◽  
Ground Deformation ◽  
Monitoring Network ◽  
Lava Flows ◽  
Etna Volcano ◽  
Lava Fountain ◽  
Eruptive Episode ◽  
Lava Fountains ◽  
Borehole Strainmeter ◽  
Ash Plume

On 13 December 2020, Etna volcano entered a new eruptive phase, giving rise to a number of paroxysmal episodes involving increased Strombolian activity from the summit craters, lava fountains feeding several-km high eruptive columns and ash plumes, as well as lava flows. As of 2 August 2021, 57 such episodes have occurred in 2021, all of them from the New Southeast Crater (NSEC). Each paroxysmal episode lasted a few hours and was sometimes preceded (but more often followed) by lava flow output from the crater rim lasting a few hours. In this paper, we use remote sensing data from the ground and satellite, integrated with ground deformation data recorded by a high precision borehole strainmeter to characterize the 12 March 2021 eruptive episode, which was one of the most powerful (and best recorded) among that occurred since 13 December 2020. We describe the formation and growth of the lava fountains, and the way they feed the eruptive column and the ash plume, using data gathered from the INGV visible and thermal camera monitoring network, compared with satellite images. We show the growth of the lava flow field associated with the explosive phase obtained from a fixed thermal monitoring camera. We estimate the erupted volume of pyroclasts from the heights of the lava fountains measured by the cameras, and the erupted lava flow volume from the satellite-derived radiant heat flux. We compare all erupted volumes (pyroclasts plus lava flows) with the total erupted volume inferred from the volcano deflation recorded by the borehole strainmeter, obtaining a total erupted volume of ~3 × 106 m3 of magma constrained by the strainmeter. This volume comprises ~1.6 × 106 m3 of pyroclasts erupted during the lava fountain and 2.4 × 106 m3 of lava flow, with ~30% of the erupted pyroclasts being remobilized as rootless lava to feed the lava flows. The episode lasted 130 min and resulted in an eruption rate of ~385 m3 s−1 and caused the formation of an ash plume rising from the margins of the lava fountain that rose up to 12.6 km a.s.l. in ~1 h. The maximum elevation of the ash plume was well constrained by an empirical formula that can be used for prompt hazard assessment.

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