Published: Jun 1998
Pages: 181 - 192
Authors: OTO ORLICKY
Abstract: The carriers of magnetic properties of rocks were studied using: (1) fully automated measurements of magnetic susceptibility (κ) change of sample influenced by temperature in the range of -196 to 700 °C, (2) reflected light microscopy, (3) electron microprobe analysis, (4) Mössbauer spectroscopy, (5) X-ray powder diffraction analysis. The carriers of magnetic properties of the neogene volcanics have been grouped into seven dominant groups (B, C, D, F, G, I, J) on the basis of the results of method (1) for about 670 individual samples. Groups B–F contain titanomagnetites (Tms) of two magnetic phases of different Curie temperatures (TC1 ,TC2); Groups B, C: first phase (TC1 ≈ 130–220 °C) contains quasi homogeneous or partly oxidized Tms of composition Fe2.35Ti0.65O4-Fe2.5Ti0.5O4, second phase (TC2 ≈ 570–575 °C) contains oxidized Tms of unknown composition. Groups D, F: both magnetic phases correspond to oxidized Tms of unknown composition. Group D — dominant phase of TC1 ≈ 480 °C and second magnetic phase of TC2 ≈ 590 °C. Group F contains oxidized Tms, a first magnetic phase of TC1 ≈ 420 °C and TC1 ≈ 530 °C, and a second one of TC2 ≈ 600 °C, TC2 ≈ 590–600 °C. magnetic phases of TC ≤ 585 °C also contain small portion of hematite-ilmenites. Group G contains one magnetic phase of TC ≈ 580 °C (and Verwey transition temperature of TV ≈ -153 °C), which corresponds tu pure multidomian magnetite. Group I contains two magnetic phases, a first phase of TC1 ≈ 560–600 °C corresponds to nonstoichiometric magnetite (exceptionally an oxidized TM can be present), and a second phase of TC2 ≈ 600–630 °C corresponding to hematite-ilmenites. The J group contains only one phase of TC ≈ 610–640 °C. This magnetic phase corresponds to hematite-ilmenites. The magnetic phases of TC ≈ 585–640 °C correspond to hematite-ilmenites, probably of composition within the range x ≈ 0.09–0.04 (of equation Fe2-xTixO3). Dominant occurrences of the groups B–J have been delineated in the geological schemes.
Keywords: Neogene volcanics, 7 dominant groups of Fe-Ti magnetic mineralsDownload PDF document