Petrophysical studies of igneous and metamorphic complexes of the Olkhon geodynamic polygon

The purpose of the study of igneous and metamorphic complexes of the Olkhon region is to develop a petro physical legend for a new generation aerospace geological map as a basis for interpreting geophysical survey materials, geodynamic reconstructions, etc. Using modern methods and equipment, field work was carried out to select oriented sam ples, conduct laboratory petrophysical and analytical studies. Scalar and vector physical parameters (density, magnetic susceptibility, vectors of remanent and total magnetisation, Königsberger coefficient) characterising modern and ancient (paleomagnetic) state of the objects under investigation were obtained. Statistical processing of the primary measurements showed that the studied complexes are conditionally divided into two petromagnetic complexes: weakly and strongly mag netic. Since the basites (dolerites, gabbros and beerbachites) of the second petromagnetic complex may prove to be prom ising objects for geodynamic reconstructions, they were subjected to reconnaissance geochemical, magnetomineralogical and paleomagnetic surveys. Unaltered magnetite (Fe > 90 %) with a Curie point of about 580 °C is found to be the main mineral-carrier of natural remanent magnetization vectors in the studied formations. In the course of laboratory demagne tisations by alternating magnetic field and temperature, the considered geological formations retained the vectors of char acteristic natural remanent magnetization, which can be used for paleogeodynamic reconstructions of the Olkhon terrane.

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