Characteristic features of the implantation of Al,Mg, and Mn impurity atoms into the titanomagnetite structure

Results of microprobe analysis of titanomagnetites and hemoilmenites from Cenozoic basalts of Mongolia and Iceland, Eastern Siberia Permo-Triassic traps (the Norilsk borehole), and Proterozoic and Paleozoic dike basaltoids on the White Sea coast of the Kandalaksha Gulf (Por’ya Bay), as well as data on titanomagnetites of Primorski Krai basalts [Shcheka et al., 1980], are used to examine specific features of the implantation of impurity atoms into solid solutions with various concentrations of the ulvospinel component.     

Petromagnetic features of sediments at the Mesozoic-Cenozoic boundary: Results from the Gams section

The paper continues a cycle of petromagnetic investigations of epicontinental deposits at the Mesozoic-Cenozoic (K/T) boundary and is devoted to the study of the Gams section (Austria). Using thermomagnetic analysis, the following magnetic phases are identified: goethite (T _C = 90–150°C), hemoilmenite (T _C = 200?300°C), metallic nickel (T _C = 350–360°C), magnetite and titanomagnetite (T _C = 550–610°C), Fe-Ni alloy (T _C = 640–660°C), and metallic iron (T _C = 740–770°C). Their concentrations are determined from M(T). In all samples, ensembles of magnetic grains have similar coercivity spectra and are characterized by a high coercivity. An exception is the lower coercivity of the boundary clay layer due to grains of metallic nickel and iron. With rare exceptions, the studied sediments are anisotropic and generally possess a magnetic foliation, which indicates a terrigenous accumulation of magnetic minerals. Many samples of sandy-clayey rocks have an inverse magnetic fabric associated with the presence of acicular goethite. The values of paramagnetic and diamagnetic components in the deposits are calculated. According to the results obtained, the K/T boundary is marked by a sharp increase in the concentration of Fe hydroxides. The distribution of titanomagnetite reflects its dispersal during eruptive activity, which is better expressed in the Maastrichtian and at the base of the layer J. The along-section distribution of metallic iron, most likely of cosmic origin, is rather uniformly chaotic. The presence of nickel, most probably of impact origin, is a particularly local phenomenon as yet. The K/T boundary is not directly related to an impact event.     

The microstructure and domain structure of multiphase oxidized titanomagnetites

An estimation of the domain state of 15 natural and synthetic samples containing both homogeneous and multiphase oxidized titanomagnetites was made by means of J_rs/J_s and H_cr/H_c ratios, the Lowrie-Fuller criterion, the thermomagnetic criterion, F criterion and the Preisach diagram. The J_rs/J_s and H_cr/H_c ratios and the Lowrie-Fuller criterion are shown to be not sufficiently informative for a determination of the domain state. In the case where the lamellae thickness became thinner than 0.1 μm, titanomagnetite grains demonstrate multidomain behaviour independent of the size of the interlamellar regions (cells). If the lamellae become thicker than 0.1 μm the domain state depends on the size of the cells. Single-domain behaviour is obtained for a cell size less than 1 × 1 μm; in agreement with the results of others, larger cells have multidomain properties.     

Unique phenomenon of the accumulation of <Emphasis Type="Italic">terrestrial</Emphasis> metal iron particles in lacustrine deposits: Zhombolok volcanic region,East Sayan

The native iron particles that were previously detected by thermomagnetic and microprobe analyses in the sediments of different age in many regions of the world are of extraterrestrial origin. The similarity in the compositions, grain shapes, and sizes observed in the extraterrestrial and terrestrial particles of native iron testifies to the common production conditions of iron particles during the formation of planets. In this paper, the single finding of terrestrial iron in the lacustrine sediments of the Zhombolok volcanic region, East Sayan, is discussed. The uniqueness of the results indicates that the spatial distribution of the particles of native iron is limited to a fairly narrow area around their source—volcanic eruption or/and the fall of a large meteorite.     

Paleomagnetism of Precambrian dikes in the Kola part of northeastern Fennoscandia and its relation to the Svecofennian orogeny

Based on the results of the preliminary paleomagnetic investigation of 57 Precambrian dikes of the Kola Peninsula, in 31 of them a stable monopolar component of natural remanent magnetization (NRM) is revealed (D = 353.2°, I = 53.0°, K = 58, and α95 = 3.4°). The peculiarities of the distribution of this magnetization component within the Kola Peninsula and the rock magnetic characteristics of the dikes in which this component is isolated suggest its secondary nature and relate the mechanism and formation time to the remagnetization processes which took place in the northwest of Fennoscandia about 1.8 billion years ago during the Svecofennian orogeny. The corresponding geomagnetic pole of Fennoscandia has the coordinates Plat = 54.5°, Plong = 224.0°, and A95 = 3.9° and is located in the immediate vicinity of the known Paleoproterozoic (1.9–1.7 Ga) poles of Baltica (Khramov et al., 1997; Veikkolainen et al., 2014).     

Studying the Dynamics of Cosmic Dust Flux on the Earth’s Surface from Peat Deposits

Izvestiya, Physics of the Solid Earth - Peat cores sampled from different climatic zones are studied. The petromagnetic and microprobe methods are used to find peat layers enriched with cosmic...     

Magnetic and mineralogical characteristics of rocks at the Mezmaiskaya cave Paleolithic site (Northern Caucasus)

The results of magnetic and microprobe studies of the rock sequences in the Mezmaiskaya cave at the unique multilayer Paleolithic site are discussed. The magnetic properties of rocks are analyzed for 17 layers (upwards from layer 4 to layer 1\1) dated from over 73 ka ago to recent times. The rocks of layer 1C (Early Upper Paleolithic, ∼38 ka) are found to have the highest magnetic susceptibility (K) (up to 2500 × 10⁻⁶ SI), which is related to the intensive activity of [Homo sapiens]. The minimum K corresponds to the rocks of layer 2, which is overlain by layer 1D. The sizes of magnetic grains vary throughout the rock section. The largest grains are found in the middle part of the section in the Middle Paleolithic layers 2B3, 2B2, 2B1, 2A, and 2. The superparamagnetic fraction is identified in all layers. This fact supports the view that the cave was open as early as the formation of layer 4. According to the thermomagnetic data on the saturation magnetization and the temperature curves of magnetic susceptibility, magnetite is the main carrier of the rock magnetization; some samples contain iron hydroxides. Samples with iron sulfides (pyrite) are abundant. The study of the hysteresis parameters of rocks showed that the question on whether sulfide-bearing rocks are suitable for reliable paleomagnetic determinations requires further laboratory research into the origin of magnetite in the rocks. The chemical composition of rocks composing layer 2B3 and layers 1D (∼39 ka) and 2B1 (∼45 ka), in which the presence of volcanic ash has been previously established according to the presence of volcanic glass, was determined by detailed microprobe analysis. A wide variety of chemical elements (up to 18 items) was recognized in layers 1D and 2B1. The iron, titan, chrome, manganese content, and concentrations of other components vary from grain to grain. The microprobe analysis of samples from layers 1D and 2B1 revealed a set of magnetic particles with compositions characteristic of volcanic rocks, which supports the ash origin of these layers. Layer 2B3 is established not to be volcanic ash. The results on the volcanic glass in the rocks of layers 1D and 2B1 were published by Golovanova and her colleagues in Current Anthropology in October 2010 [Golovanova et al., 2010].     

Magnetic minerals in sediments at the Cretaceous/Paleogene boundary (the Gams Section,Eastern Alps)

The paper presents results of detailed magnetomineralogical and microprobe studies of sediments at the Cretaceous/Paleogene (K/T) boundary in two epicontinental sections in the Eastern Alps (Austria), where deposits, including the K/T boundary, outcrop along the Gams River and its tributaries. K/T boundary layers in these sections are similar in the set of such magnetic minerals as iron hydroxides, ferrospinels, hemoilmenite, titanomagnetite, magnetite, hematite, and metallic iron. However, the boundary layer in the Gams-1 section is distinguished by the presence of metallic nickel and its alloy with iron and by the absence of iron sulfides, whereas nickel has not been discovered in the Gams-2 section, which, however, contains iron sulfides of the pyrite type. Therefore, these minerals occur locally. It is suggested that enrichment in iron hydroxides of a common origin can be regarded as a global phenomenon inherent in the K/T boundary and unrelated to an impact event.     

Cosmic dust and micrometeorites in the transitional clay layer at the Cretaceous-Paleogene boundary in the gams section (Eastern Alps): Morphology and chemical composition

Results of investigation of the cosmic matter in the transitional clay layer at the Cretaceous-Paleogene boundary in the Gams section, Eastern Alps, are presented. A great diversity of iron microspherules and particles of different morphologies, pure nickel spherules, awaruite (Fe₃Ni) particles, and diamond crystals are discovered. Iron microspherules are also met in the overlying Paleocene deposits, but their diversity there is not great. The discovered metallic microspherules and particles are described, their chemical compositions are presented, and their origin is discussed.