High-coercivity magnetic minerals in archaeological ceramics: new insights from remanence acquisition and demagnetization measurements at elevated temperatures

2020 ◽  
Author(s):  
Andrei Kosterov ◽  
Mary Kovacheva ◽  
Maria Kostadinova-Avramova ◽  
Pavel Minaev ◽  
Nataliya Sal'naya ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Basic Research ◽  
Parent Material ◽  
High Coercivity ◽  
Firing Process ◽  
Magnetic Minerals ◽  
Magnetic Mineralogy ◽  
Archaeological Ceramics ◽  
Magnetically Hard ◽  
Basic Research Grant

<p>The thorough understanding of magnetic mineralogy is a prerequisite of any successful palaeomagnetic, and in particular, archaeomagnetic study. Magnetic minerals in archaeological ceramics and baked clay may be inherited from the parent material, or, more frequently, formed during the firing process. The resulting magnetic mineralogy may be complex, including ferrimagnetic phases not commonly encountered in rocks. Towards this end, we carried out a detailed rock magnetic study on a representative collection of archaeological ceramics (baked clay from combustion structures and bricks) from Bulgaria and Russia. Experiments included measurement of isothermal remanence acquisition and demagnetization as a function of temperature between 20°C and >600°C, and a variant of Lowrie 3-axis IRM test with measurements performed at elevated temperatures. For selected samples, low-temperature measurements of saturation remanence and initial magnetic susceptibility between 1.8 K and 300 K have been carried out.<br>All studied samples contain a magnetically soft mineral identified as maghemite probably substituted by Al and/or Ti. Stoichiometric magnetite has never been observed, as evidenced by the absence of the Verwey phase transition. In addition, one or two magnetically hard mineral phases have been detected, differing sharply in their respective unblocking temperatures. One of these unblocking between 540°C and 620°C is believed to be substituted hematite. Another phase unblocks at much lower temperatures, between 140°C and 240°C, and its magnetic properties correspond to an enigmatic high coercivity, stable?, low unblocking temperature (HCSLT) phase of McIntosh et al. [McIntosh, G., M. Kovacheva, G. Catanzariti, M. L. Osete, and L. Casas (2007), Geophys. Res. Lett., 34, L21302, doi: 10.1029/2007GL031168]. In a few samples high- and low-unblocking temperature magnetically hard phases appear to coexist, in the others the HCSLT phase is the only magnetically hard mineral present. We finally compare the samples performance in archaeointensity experiments with their respective magnetic mineralogy.<br>This study is supported by Russian Foundation of the Basic Research, grant 19-55-18006, and Bulgarian National Science Fund, grant KP-06-Russia-10.</p>

High-coercivity magnetic minerals in archaeological baked clay and bricks

2020 ◽  
Vol 224 (2) ◽  
pp. 1256-1271
Author(s):  
Andrei Kosterov ◽  
Mary Kovacheva ◽  
Maria Kostadinova-Avramova ◽  
Pavel Minaev ◽  
Natalia Salnaia ◽  
...  
Keyword(s):  
Parent Material ◽  
High Coercivity ◽  
Firing Process ◽  
Magnetic Minerals ◽  
Magnetic Mineralogy ◽  
Archaeological Ceramics ◽  
Mineral Phases ◽  
Initial Magnetic Susceptibility ◽  
Magnetically Hard ◽  
Saturation Remanence

SUMMARY The thorough understanding of magnetic mineralogy is a prerequisite of any successful palaeomagnetic or archaeomagnetic study. Magnetic minerals in archaeological ceramics and baked clay may be inherited from the parent material or, more frequently, formed during the firing process. The resulting magnetic mineralogy may be complex, including ferrimagnetic phases not commonly encountered in rocks. Towards this end, we carried out a detailed rock magnetic study on a representative collection of archaeological ceramics (baked clay from combustion structures and bricks) from Bulgaria and Russia. Experiments included measurement of isothermal remanence acquisition and demagnetization as a function of temperature between 20 and >600 °C. For selected samples, low-temperature measurements of saturation remanence and initial magnetic susceptibility between 1.8 and 300 K have been carried out. All studied samples contain a magnetically soft mineral identified as maghemite probably substituted by Ti, Mn and/or Al. Stoichiometric magnetite has never been observed, as evidenced by the absence of the Verwey phase transition. In addition, one or two magnetically hard mineral phases have been detected, differing sharply in their respective unblocking temperatures. One of these unblocking between 540 and 620 °C is believed to be substituted hematite. Another phase unblocks at much lower temperatures, between 140 and 240 °C, and its magnetic properties correspond to an enigmatic high coercivity, stable, low-unblocking temperature (HCSLT) phase reported earlier. In a few samples, high- and low unblocking temperature, magnetically hard phases appear to coexist; in the others, the HCSLT phase is the only magnetically hard mineral present.

High-temperature three-axis IRM Lowrie test

2021 ◽  
Author(s):  
Leonid Surovitskii ◽  
Andrei Kosterov ◽  
Mary Kovacheva ◽  
Maria Kostadinova-Avramova ◽  
Natalya Salnaya ◽  
...  
Keyword(s):  
High Temperature ◽  
Elevated Temperatures ◽  
Basic Research ◽  
Archaeological Sites ◽  
High Coercivity ◽  
Variable Degree ◽  
Hard Component ◽  
Classical Procedure ◽  
Temperature Spectra ◽  
Basic Research Grant

<p>The three-axis isothermal remanent magnetization (IRM) test (the Lowrie test; Lowrie, 1990, Geophys. Res. Lett., 17, 159-162) is a useful tool to identify ferromagnetic minerals by their coercivity and unblocking temperature spectra. In this study, we explore a variant of the Lowrie test in which measurements are conducted directly at elevated temperatures, and compare its performance with the results of the conventional stepwise procedure. IRM acquisition fields applied along three orthogonal axes were 1 T, 200 mT and 40 mT, respectively. The field value for the soft component was chosen so as to include ca. 90% of its coercivity spectrum. For the hard component the maximum available field was used. The test is applied to characterize the magnetic mineralogy of archaeological baked clays and bricks from Bulgaria and Russia. Bulgarian samples are baked clays from various Neolithic (5700-5300 BCE) archaeological sites and several bricks of the Roman epoch (III-IV c. AD). Samples from Russia are bricks originating from several regions with ages from XIII to early XIX c. AD.</p><p>The low- and intermediate-coercivity components of IRM in the studied samples are typically demagnetized by 520-550°C, compatible with substituted or cation-deficient magnetite or, possibly, maghemite. This is supported by the absence of the Verwey transition in studied samples (Kosterov et al., 2021, Geophys. J. Int., 224(2), 1256-1271). The high-coercivity component appears to be carried by two mineral phases with very distinct unblocking temperatures, 120-200°C and 500 to 640°C. The first phase is similar to the high coercivity, low unblocking temperature (HCSLT) phase described by McIntosh et al., 2007 (Geophys. Res. Lett., 34, L21302, doi: 10.1029/22007GL031168), and the second one appears to be hematite with variable degree of substitution.</p><p>Performance of the high-temperature variant of the Lowrie test compares favorably with the classical procedure, while the former is also significantly faster and yields a superior temperature resolution.</p><p>This study is supported by Russian Foundation of the Basic Research, grant 19-55-18006, and by Bulgarian National Science Fund, grant KP-06-Russia-10.</p>

Secular geomagnetic field variations in Bulgarian lands during Classical Age and Late Antiquity – new archaeomagnetic data

2021 ◽  
Author(s):  
Maria Kostadinova-Avramova ◽  
Petar Dimitrov ◽  
Andrei Kosterov ◽  
Mary Kovacheva
Keyword(s):  
Material Culture ◽  
Late Antiquity ◽  
Basic Research ◽  
Reference Points ◽  
Archaeological Sites ◽  
Historical Sources ◽  
National Science ◽  
Basic Research Grant ◽  
National Science Fund ◽  
Research Grant

<p>Numerous historical sources and archaeological monuments attest the age of Antiquity in Bulgaria – from both the early Roman period (I – III c.) and Late Antiquity (IV – VI c.). Owing to systematic archaeological excavations, lasting more than 100 years, plenty of information has been accumulated concerning not only all aspects and manifestations of its material culture, but also their evolution and chronology.  This in turn allows for interdisciplinary fields such as archaeomagnetism to progress.</p><p>There are many archaeomagnetically studied archaeological structures from the Antiquity. The results included in the Bulgarian database form 74 reference points. However, only 20 of them are full-vector determinations because 70 % of the investigated materials are bricks. Hence, the secular variation of declination is poorly constrained within the considered period. Moreover, the reuse of bricks in the constructions occurred quite often (especially in the Late Antiquity) providing for possible errors in archaeological dating. In addition, stronger effects of magnetic anisotropy and cooling rate are usually expected for bricks than for hearths, domestic ovens, production kilns or burnt dwelling remains (there are no results from pottery in the Bulgarian dataset) and both factors are not evaluated for most of the older results. All this can explain the contradictions observed between some of the experimental results juxtaposed over the absolute time scale. In an attempt to clarify these contradictions 13 baked clay structures from eight archaeological sites were archaeomagnetically studied producing seven new directional and eight new intensity data. The samples collected possess variable magnetic properties suggesting differences in clay sources and/or firing conditions. Magnetically soft minerals prevail in seven structures but in the remaining six, abundant HCSLT phase is detected. The success rate of archaeointensity determination experiments vary from 49 to 100 %. It appears that samples containing HCSLT phase always produces good araeointensity results unlike those with the dominant presence of soft carriers.</p><p>The new reference points are compared with the present compilation of Bulgarian archaeomagnetic dataset and with the data from the neighboring countries.</p><p> </p><p>This study is supported by the grant KP-06-Russia-10 from the Bulgarian National Science Fund and Russian Foundation of the Basic Research grant 19-55-18006.</p>

Analysis of Strong-Field Hysteresis in High Coercivity Magnetic Minerals

2019 ◽  
pp. 127-142 ◽  
Author(s):  
A. Kosterov ◽  
E. S. Sergienko ◽  
A. G. Iosifidi ◽  
P. V. Kharitonskii ◽  
S. Yu. Yanson
Keyword(s):  
Strong Field ◽  
High Coercivity ◽  
Magnetic Minerals

Mineral assemblage within secondary crystallized melt inclusions in olivine of mantle xenoliths from the Bultfontein kimberlite pipe (Kaapvaal craton, South Africa)

2021 ◽  
Author(s):  
Alexey Tarasov ◽  
Igor Sharygin ◽  
Alexander Golovin ◽  
Anna Dymshits ◽  
Dmitriy Rezvukhin
Keyword(s):  
Melt Inclusions ◽  
Basic Research ◽  
Kimberlite Pipe ◽  
Mantle Xenoliths ◽  
Mantle Minerals ◽  
Source Regions ◽  
Basic Research Grant ◽  
Carbonate Composition ◽  
First Time ◽  
Ca Carbonate

<p>For the first time, snapshots of crystallized melts in olivine of sheared garnet peridotite xenoliths from the Bultfontein kimberlite pipe have been studied. This type of xenoliths represents the deepest mantle rocks derived from the base of lithosphere (at depths from 110 to 230 km for various ancient cratons). According to different models, such type of inclusions (secondary) in mantle minerals can be interpreted as relics of the most primitive (i.e., close-to-primary) kimberlite melt that infiltrated into sheared garnet peridotites. In general, these secondary inclusions are directly related to kimberlite magmatism that finally formed the Bultfontein diamond deposits. The primary/primitive composition of kimberlite melt is poorly constrained because kimberlites are ubiquitously contaminated by xenogenic material and altered by syn/post-emplacement hydrothermal processes. Thus, the study of these inclusions helps to significantly advance in solving numerous problems related to the kimberlite petrogenesis.</p><p>The unexposed melt inclusions were studied by using a confocal Raman spectroscopy. In total, fifteen daughter minerals within the inclusions were identified by this method. Several more phases give distinct Raman spectra, but their determination is difficult due to the lack of similar spectra in the databases. Various carbonates and carbonates with additional anions, alkali sulphates, phosphates and silicates were determined among daughter minerals in the melt inclusions: calcite CaCO<sub>3</sub>, magnesite MgCO<sub>3</sub>, dolomite CaMg(CO<sub>3</sub>)<sub>2</sub>, eitelite Na<sub>2</sub>Mg(CO<sub>3</sub>)<sub>2</sub>, nyerereite (Na,K)<sub>2</sub>Ca(CO<sub>3</sub>)<sub>2</sub>, gregoryite (Na,K,Ca)<sub>2</sub>CO<sub>3</sub>, K-Na-Ca-carbonate (K,Na)<sub>2</sub>Ca(CO<sub>3</sub>)<sub>2</sub>, northupite Na<sub>3</sub>Mg(CO<sub>3</sub>)<sub>2</sub>Cl, bradleyite Na<sub>3</sub>Mg(PO<sub>4</sub>)(CO<sub>3</sub>), burkeite Na<sub>6</sub>(CO<sub>3</sub>)(SO<sub>4</sub>)<sub>2</sub>, glauberite Na<sub>2</sub>Ca(SO<sub>4</sub>)<sub>2</sub>, thenardite Na<sub>2</sub>SO<sub>4</sub>, aphthitalite K<sub>3</sub>Na(SO<sub>4</sub>)<sub>2</sub>, apatite Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>(OH,Cl,F) and tetraferriphlogopite KMg<sub>3</sub>FeSi<sub>3</sub>O<sub>10</sub>(F,Cl,OH). Note that carbonates are predominant among the daughter minerals in the melt inclusions. Moreover, there are quite a lot of alkali-rich daughter minerals within the inclusions as well. During the last decade, some research groups using different approaches proposed a model of carbonate/alkali‑carbonate composition of kimberlite melts in their source regions. This model contradicts to the generally accepted ultramafic silicate nature of parental kimberlite liquids. This study is a direct support of a new model of carbonatitic composition of kimberlite melts and also shows that alkali contents in kimberlite petrogenesis are usually underestimated.</p><p>This work was supported by the Russian Foundation for Basic Research (grant No. 20-35-70058).</p>

Model of Daytime Oxygen Emissions in the Mesopause Region and Above: New Results

2021 ◽  
Author(s):  
Valentine Yankovsky ◽  
Ekaterina Vorobeva ◽  
Rada Manuilova ◽  
Irina Mironova
Keyword(s):  
Molecular Oxygen ◽  
Excited States ◽  
Lower Thermosphere ◽  
Basic Research ◽  
Vibrationally Excited ◽  
Mesopause Region ◽  
Mesosphere And Lower Thermosphere ◽  
Basic Research Grant ◽  
The 19Th Century ◽  
Excited Oxygen

<p>Atmospheric emissions of atomic and molecular oxygen have been observed since the middle of the 19th century. In the last decades, it has been shown that emissions of excited oxygen atom O(<sup>1</sup>D) and molecular oxygen in electronically-vibrationally excited states O<sub>2</sub>(b<sup>1</sup>Σ<sup>+</sup><sub>g</sub>, v) and O<sub>2</sub>(a<sup>1</sup>Δ<sub>g</sub>, v) are related by a unified photochemical mechanism in the mesosphere and lower thermosphere (MLT). The current study is performed in the framework of the state-of-the-art model of ozone and molecular oxygen photodissociation in the daytime MLT. In particular, the study includes a detailed description of the formation mechanism for excited oxygen components in the daytime MLT and presents the comparison of widely used photochemical models. The study also demonstrates new results such as i) new suggestions about possible products of collisional reactions of electronically-vibrationally excited oxygen molecules with atomic oxygen and ii) new estimates of O<sub>2</sub>(b<sup>1</sup>Σ<sup>+</sup><sub>g</sub>, v = 0 – 10) radiative lifetimes which are necessary for solving inverse problems in the lower thermosphere. Moreover, special attention is given to the Barth’s mechanism in order to demonstrate that its contribution to O<sub>2</sub>(b<sup>1</sup>Σ<sup>+</sup><sub>g</sub>, v) and O<sub>2</sub>(a<sup>1</sup>Δ<sub>g</sub>, v) populations is neglectable in daytime conditions regardless of fitting coefficients. In addition, possible applications of the daytime oxygen emissions are presented, e.g., the altitude profiles O(<sup>3</sup>P), O<sub>3</sub> and CO<sub>2</sub> can be retrieved by solving inverse photochemical problems where emissions from electronically vibrationally excited states of O<sub>2</sub> are used as proxies. The funding of V.Y., R.M. and I.M. was partly provided by the Russian Fund for Basic Research (grant RFBR No. 20-05-00450).</p>

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