DOI: 10.3897/geostudies.2.e126114

Authors: Petar Stavrev, Petya Trifonova, Metodi Metodiev

Abstract: Analysis and solution of the forward magnetic problem for models of disjunctive layered geological structures, such as faults and layer discontinuities, are developed in this paper. Magnetic anomaly components Z, H, T, ΔT and Ta resulting from disjunctive geologic structures are similar to those caused by thin-layer magnetic sources of finite size. Structures of a discontinuous horizontal layer, an up-thrown fault, inclined, normal or reverse faulted, an over-thrusted structure and also a thick-layer fault of the relatively small throw are examined. The composition of different forward magnetic models of disjunctive structures and their calculations can be facilitated by the applied specific properties of thin layers with unlimited depth extent. A method of rotation is proposed to analyse the anomalous magnetic effects caused by discontinuous crustal structures. The results shown are useful in analysing field magnetic data, recognising sources, inverting anomalies and interpreting geophysical data.

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DOI: 10.3897/geostudies.1.e115530

Authors: Neli Jordanova, Diana Jordanova

Abstract: Identification of magnetic minerals, which determine the magnetic properties of natural rocks, sediments and soils, is of crucial importance for any further interpretation of their magnetic signature in environmental or paleogeographical context. One of the major and widely used methods for determination of kind of magnetic phases in natural materials is by obtaining the Curie/Neel temperature of the respective magnetic mineral. In this contribution, we report a set of thermomagnetic measurements of high-temperature behavior of magnetic susceptibility for topsoils from the territory of Bulgaria, aiming to reveal the pedogenic and lithogenic signature. The data are considered and reported in respect to the parent rock type. Our results suggest that pedogenic magnetic minerals are represented mainly by fine-grained maghemite and/or hematite with possible Al-substitutions in the crystal lattice. This phase is expressed on the heating run of the thermomagnetic curve as a “hump” with a maximum at 250–300 °C. Coarse-grained magnetite is identified as a dominant lithogenic magnetic mineral. Hematite’s presence in a sub-set of red-colored soils is confirmed by additional analyses of isothermal remanence acquisition curves. Two hematite coercivity components were identified, related to pedogenic and lithogenic origin, respectively.

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