Domain structure of volcanics’ ferromagnetic grains: A case study of the Saatly ultradeep well, Azerbaijan

Z A Novruzov

doi:10.24028/gzh.0203-3100.v41i3.2019.172474

Abstract

Various magnetic properties of magnetic minerals show strong grain-size depen-dence. This dependency occurs because these parameters are influenced by the magnetic grain-size (domain state) of the samples. Natural rocks often contain a mixture of different magnetic minerals with different grain-size (domain states). Thus determination of the domain state is important. The Saatly ultradeep well’s volcanics were used as a research material. In the depth intervals of 3540—8126 m the volcanics had been revealed by the borehole. According to data of the petrographic and microprobe analysis the volcanogenics of the ultradeep borehole is conditionally divided into a two parts: 1) the upper part (an interval of depths of 3540—5500 m); 2) the bottom part (an interval of depths of 5500—8126 m). In the upper part of section according to microprobe analysis of volcanogenic rocks ore grains are presented by two generations: 1) large grain of titanomagnetites (Ti-poor), homogeneous or with a decay structures; 2) small-sized usually well faced grain of practically stoichiometric magnetite. So, homogeneous small-sized grains or fragments of decay large grains (which are strongly changed chemically) can have properties of single-domain particles. Here the ferromagnetic grains (especially in the depth interval 3540—5000 m) are often noted as a pseudo-single domain. In the bottom part of the section the presence of multidomain grains of the Ti-poor titano-magnetite is noted. And since depths of 7000 m the oxidized magnetite is also observed. The pseudo-single-domain grains are fixed much less than in the upper section. And, since a depth mark of 7300 m and deeper, they are absent wholly. In the result of rese-arch it turned out that the ferromagnetic is presented by basically multidomain grains. It should be noted that Lauri—Fuller’s Criterion is not applicable at identification of a domain structure of the complex ensemble of the ferromagnetic grains.

Highlights

For the first time magne Environmental conditions of generation tometric researches of volcanogenic rock co of ferromagnetic minerals and changes of re of the super deep Saatly well have been them leave traces on magnetic domain struc conducted by the staff of department “Geo ture [Stackey, Banerjee, 1974]
For magnetic researches of a core of the Saat- realization of this purpose we used four mag ly super deep well has been dictated by ne netic criteria
The criteria are based on cha ed in obtaining the petromagnetic data used racteristics of various magnetic parameters at interpretations of results of geophysical of magnetic grains with different magnetic activity

Summary

Introduction

Of 15 km) is spaced in the Kur basin placed Object of our researches are the volcabetween the Greater Caucasus and the Les nics located in the depths interval of 3540—. Debatable idea of crustal structu The depth interval of 3540—3900 m is chare within the Saatly local gravitational maxi racterized by plagioclase basalts and is mamum was formed in two points of view. To the second — the Earth crust is single The depth interval of 3900—4850 m conlayer and it is presented by mafic rocks on tains porphyritic olivine-pyroxene-plagioly. Along with low-potas thermal remanent magnetization (TRM) wesium basalts potassium-enriched groups ha re measured on a magnetometer JR-4 In the depth interval of 5209—6100m the on an automatic thermomagnetometer with double-pyroxene-plagioclase basalts and an sensitivity 110-4 A/m.

Stepwise demagnetization by increasing

SD basalt