Influence of magnetic interactions on the anisotropy of magnetic susceptibility: the case of single domain particles packed in globule aggregates     

Gregory Fanjat  Valera Shcherbakov  Pierre Camps 《Studia Geophysica et Geodaetica》2012,56(3):751-768

The influence of magnetic interactions on the anisotropy of magnetic susceptibility (AMS) have been largely studied by several theoretical models or experiments. Numerical models have shown that when magnetostatic interactions occur, the distributions of particles over the volume rather than their individual orientations control the AMS. We have shown recently from a comprehensive rock magnetic study and from a theoretical 2-dimensional (2-D) model that single domain particles closely packed in globule aggregates could produce strong local random interaction magnetic fields which could influence the magnetic susceptibility and decrease the degree of anisotropy. In this paper, we first present in detail this 2-D theoretical model and then we extend it to the 3-D case. The possible distribution function of the magnetostatic interaction fields comprises two extreme states: it is either isotropic or ordered. The former case corresponds to the thermal-demagnetized state while the second case corresponds to the alternating field (AF) demagnetized state. We show that when easy axes of magnetization are not uniformly distributed, the degree of anisotropy decreases as the interaction field increases in both AF- and thermal-demagnetized states in 2-D and 3-D geometry. Thus we conclude that random magnetic fields generated by a random arrangement of magnetic particles over the sample volume decrease the degree of anisotropy of AMS and may alter the magnetic fabric.  相似文献   

Eclogite trace in evolution of Late Cenozoic alkaline basalt volcanism on the southwestern flank of the Baikal Rift Zone: Geochemical features and geodynamic consequences     

A. B. Perepelov  M. I. Kuzmin  S. S. Tsypukova  E. I. Demonterova  A. V. Ivanov  Yu. D. Shcherbakov  M. Yu. Puzankov  D. Odgerel  D. Bat-Ulzii 《Doklady Earth Sciences》2017,476(2):1187-1192

Eclogitized material from the oceanic lithosphere are the most likely source of alkaline basalt magmas in the formation of Late Cenozoic volcanic areas on the southwestern flank of the Baikal Rift Zone. Basaltic trachyandesites of the early stage of volcanism (Pg₃² ~ 28–23 Ma) are rich in high field strength elements (HFSE), P₂O₅, F, Zn, Ga, Sr, Sn, and light rare earth elements (LREE); they are characterized by high values of the following ratios: Fe/Mn = 72–77, Sm/Yb = 7.7–8.5, Sr/Y = 57–63, and Ga/Sc = 2.1–2.3. At this stage, magmas are formed under conditions with a 2–8% degree of partial melting of the mantle substrate enriched with the material of the eclogite source (50–70%) (Cpx/Grt = 1.5–1.7). Basaltoid magmas of the final stage of volcanism (N₁³–N₂¹ ~ 6–4 Ma) are formed from melting (1.5–4%) of a less fertilized mantle (Cpx/Grt = 2.1–3.1, Fe/Mn = 62–71, Sm/Yb = 3.5–4.6, Sr/Y = 29–44, Ga/Sc = 1.0–1.4). The directed variations of the compositions of the successive basaltoid magmas, which were formed in the Late Cenozoic, create an “eclogite trace” in this area.  相似文献   

Petrology of mafic enclaves in the 2006–2012 eruptive products of Bezymianny Volcano,Kamchatka     

V. O. Davydova  V. D. Shcherbakov  P. Yu. Plechov  A. B. Perepelov 《Petrology》2017,25(6):592-614

This paper reports the results of the first comprehensive petrological study of mafic enclaves widespread in the products of recent (2006–2012) eruptions of Bezymianny Volcano, Kamchatka. Four types of mafic enclaves were distinguished on the basis of the composition and morphology of minerals, P–T conditions of formation of mineral assemblages, and structural and textural characteristics of the rocks. Disequilibrium assemblages of mafic enclaves indicate a complex structure of the magmatic plumbing system of the volcano, including a shallow chamber with andesite–basaltic andesite magmas and a deep reservoir filled in part with plagioclase–hornblende cumulates and fed by basic magmas with mantle harzburgite xenoliths. The mafic enclaves were formed at different levels of the magmatic plumbing system of the volcano and correspond to different degrees of mixing of interacting magmas. The most abundant enclaves were formed during magma ascent from the deep reservoir (960–1040°C, 5–9 kbar) into the shallow andesitic chamber (940–980°C). Enclaves of plagioclase–hornblende cumulates from the basic magmas feeding the deep reservoir (T > 1090°C and P > 9 kbar) are much less common.  相似文献   

On the suitability of the Thellier method of palaeointensity determinations on pseudo-single-domain and multidomain grains     

V. P. Shcherbakov  V. V. Shcherbakova 《Geophysical Journal International》2001,146(1):20-30

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Experimental modeling of the chemical remanent magnetization and Thellier procedure on titanomagnetite-bearing basalts     

S. K. Gribov  A. V. Dolotov  V. P. Shcherbakov 《Izvestiya Physics of the Solid Earth》2017,53(2):274-292

The results of the experimental studies on creating chemical and partial thermal remanent magnetizations (or their combination), which are imparted at the initial stage of the laboratory process of the oxidation of primary magmatic titanomagnetites (Tmts) contained in the rock, are presented. For creating chemical remanent magnetization, the samples of recently erupted Kamchatka basalts were subjected to 200-h annealing in air in the temperature interval from 400 to 500°С under the action of the magnetic field on the order of the Earth’s magnetic field. After creation of this magnetization, the laboratory modeling of the Thellier–Coe and Wilson–Burakov paleointensity determination procedures was conducted on these samples. It is shown that when the primary magnetization is chemical, created at the initial stage of oxidation, and the paleointensity determined by these techniques is underestimated by 15–20% relative to its true values.  相似文献   

Experimental Model of the Formation of Nanophase Metallic Iron in the Lunar Regolith     

Sorokin  E. M.  Yakovlev  O. I.  Slyuta  E. N.  Gerasimov  M. V.  Zaitsev  M. A.  Shcherbakov  V. D.  Ryazantsev  K. M.  Krasheninnikov  S. P. 《Doklady Earth Sciences》2020,492(2):431-433

Doklady Earth Sciences - One of the signs of “space weathering” on the Moon, including the effect of the solar wind and micrometeorite bombardment, is the formation of nanophase...  相似文献