Titanomagnetite Research Articles

Oxidation kinetics of typical high FeO ferrous spinels

In this study, the isothermal oxidation kinetics of magnetite (OM), high-Mg magnetite (MM), titanomagnetite (TM), and chromite (CM) were investigated by applying thermogravimetry (TG) analysis at temperatures ranging from 1073 K to 1223 K. The results show that different high-FeO spinels possess distinct oxidizability. The oxidation process of OM in the temperature range from 1073 K to 1223 K is faster than others, followed by MM and TM. While CM exhibits the poorest oxidizability, and generally undergoes complex phase transitions. In the initial stage of oxidation, high FeO spinels have a higher oxidation rate due to the surface oxidation of spinel particles. However, the oxidation rate gradually declines in the later stages of oxidation due to increased internal diffusion resistance. The results of oxidation kinetics indicate that the initial oxidation stage of four spinels can be described as random nucleation and subsequent growth mechanism. The average apparent activation energies of the initial oxidation stage of OM, MM, TM, and CM are 25.09 kJ/mol, 32.39 kJ/mol, 58.10 kJ/mol, and 82.42 kJ/mol, respectively.

Application of MgO-Titanomagnetite mixture in high-temperature catalytic pyrolysis of radiata pine

This study aimed to investigate the effect of MgO and titanomagnetite mixture on the high-temperature pyrolysis of radiata pine wood in a fluidised bed reactor at 850 °C. The catalytic performance of the MgO-titanomagnetite (MgO-TM) mixture was experimentally evaluated based on product distribution, gas composition, gas properties, and tar composition. The results revealed that addition of MgO-titanomagnetite resulted in a decrease in gas yield (67.2 wt.%) compared to addition of titanomagnetite (TM) alone (72.9 wt.%), but an improvement was found compared to addition of MgO alone (63.9 wt.%). The hydrogen concentration in the gas product was significantly enhanced (23.2 vol.%) compared to titanomagnetite alone (12.8 vol.%) or to non-catalytic (NC) pyrolysis (14.1 vol.%) but was similar to that with addition of MgO alone (22.6 vol.%). However, the addition of MgO and titanomagnetite mixture resulted in a reduction in CO concentration to 2.7 vol.% in the gas product whereas increased the CO2 and light olefins formation. It was also found that the addition of the MgO and titanomagnetite mixture significantly increased the total concentration of ethylene and propylene (18.3 vol.%) compared to addition of titanomagnetite (5.8 vol.%), MgO (9.0 vol.%), or non-catalytic pyrolysis (12.0 vol.%). The lower heating value of the gas product and the H2 to CO ratio (17.5 MJ/Nm3 and 8.7) were also improved with addition of the MgO-titanomagnetite mixture. These findings demonstrate that application of physically mixed MgO and titanomagnetite as catalyst is a promising method for converting biomass into a H2-rich gas product via high-temperature pyrolysis. This study offers a useful reference for the development of novel catalytic systems for biomass conversion.Graphical

The Properties of Thermochemical Remanent Magnetization Acquired by Slow Laboratory Cooling of Titanomagnetite-Bearing Basalt Samples from Different Temperatures and the Results of the Thellier Method

—The experiments have been carried out on the acquisition of thermochemical remanent magnetization (TCRM) in basalt samples containing titanomagnetite (TM) with the Curie temperature Тс ~200°C by their rapid heating to maximum temperatures Т* from 450 to 530°C followed by slow cooling in the laboratory magnetic field Blab. At different stages of the preliminary thermal treatment of the initial samples, a set of magnetomineralogical studies including electron microscopy, X-ray diffraction and thermomagnetic analyzes, and measurements of magnetic hysteresis parameters were performed. It is shown that as early as the very beginning of the cooling process, all samples demonstrate explosive growth of TCRM corresponding to the stage of rapid single-phase oxidation of the initial titanomagnetite fraction of basalt, and that TCRM is acquired by the increase of Тс and volume of single-phase oxidized parts of TM grains as well as by the growth of the volume of Ti-depleted (relative to the initial TM) cells of microstructure of the subsequent oxidative exsolution. The Arai–Nagata diagrams for the samples carrying TCRM have a form of a broken line consisting of two linear segments. The low-temperature interval T < Т* corresponds to a mixture of thermochemical and thermoremanent (TRM) magnetizations and gives a slightly overestimated Blab because of the effect of a low cooling rate during the acquisition of TCRM and TRM. The high-temperature interval corresponds to pure TCRM and the Blab strength determined from this interval is underestimated by 20–27%. It is recommended to reject samples whose Araii–Nagata diagram has two or more linear segments against the background single-component NRM.

Integrated Pliocene-Pleistocene magnetostratigraphy and tephrostratigraphy of deep-sea sediments at IODP Site U1424 (Yamato Basin, Japan Sea)

Sediments from the semi-enclosed Japan Sea are sensitive to paleoclimatic perturbations and they offer great opportunities for many regional and global paleoceanographic and paleoclimatic studies. These studies often require a robust chronology. However, due to rare preservation of calcareous microfossils and drastic changes in surface water salinity during glacial lowstands, the construction of a traditional oxygen isotope stratigraphy for Japan Sea sediments is often difficult. Here, we use sediments recovered at Integrated Ocean Drilling Program (IODP) Expedition 346 Site U1424 to build an integrated Pliocene-Pleistocene reference magnetostratigraphy and tephrostratigraphy for sedimentary sequences from the region. Rock magnetic experiments indicate that magnetic remanence of Site U1424 sediments are carried primarily by (titano)magnetite with small contributions from high coercivity minerals (e.g., hematite) and possibly iron sulphides (pyrrhotite and/or greigite). Dark-colored sediments appear to contain less (titano)magnetite probably due to reductive diagenesis under euxinic conditions. Natural remanent magnetization (NRM) of u-channel samples covering a continuous ~ 167.6 m sediment sequence at Site U1424 was repeatedly measured at 1 cm intervals before and after stepwise demagnetization. Despite lower NRM intensity in dark-colored sediments, NRM directional data from both dark- and light-colored sediments are considered suitable for the construction of magnetostratigraphy. Site U1424 sediments clearly recorded the majority of the polarity chrons and subchrons within the last ~ 4.89 Myr, with the Cobb Mountain subchron, the end of Kaena subchron, and the onset of Nunivak subchron less well preserved. Sixteen tephra layers from the site were sampled for chemical composition analyses and the results were correlated to reference tephrostratigraphy of the region. Ages of the identified tephras are consistent with and can be well integrated with the magnetostratigraphy. The resulting age model suggests that sedimentation rates at Site U1424 range between ~ 1.7 and 7.6 cm/kyr with an average of ~ 3.3 cm/kyr. The acquired magnetostratigraphy and tephrostratigraphy at Site U1424 provide a reference chronology that can be correlated with and transferred to other sediment sequences in the region to study paleoceanographic and paleoclimatic changes of the region as well as their links to other regional and global changes.Graphical abstract

Determination of the Formation Field of Artificial CRM and pTRM by the Thellier Method at Different Oxidation Stages of Natural Titanomagnetite

Artificial chemical remanent magnetization (CRM) created on a basalt rock from the Red Sea rift zone, originally containing titanomagnetite (TM) with a Curie temperature of 203–208°С, is studied at various oxidation stages. CRM was formed by annealing the samples at temperature T = 355°C during 4.5–350 h in the magnetic field with induction of 100 μT. The thermomagnetic analysis has shown that with the increase of the annealing time, a single-phase oxidation process takes place, the degree of the oxidation increases and reaches its maximum after annealing during 110 hours. It is established that the subsequent heating of the samples to 600°C in argon leads to the homogenization of the single-phase-oxidized titanomaghemite. When the annealing time increases to 350 h, oxi-exsolution of titanomaghemite begins. CRM as well as the sum of CRM and partial thermoremanent magnetization (pTRM) have been investigated by the Thellier–Coe procedure. The magnetic field Bcalc calculated in the temperature interval 355–475°C from chemical magnetization formed at the annealing times of 4.5, 16.5, and 40.5 h (CRM4.5, CRM16.5 and CRM40.5) proved to be underestimated by 55, 48–52, and 16–34%, respectively. The difference between the calculated and true field decreases with the growth in the degree of single-phase oxidation. The Bcalc values calculated in the temperature interval 475–580°С from CRM40.5 and CRM110 corresponding to the high degree of single-phase oxidation turned out to be underestimated by 69–72 and 62–63%. The last result is caused by the mineral transformations of titanomaghemite at heatings in the Thellier–Coe experiments. During paleointensity determination, it is proposed to control mineral transformations not only using the check-point procedure but also based on the difference in the removal of remanent magnetization in the Thellier experiments and by thermal demagnetization.

Effect of Ni Content on Iron-based Friction Material Prepared by In-situ Synthesized from Vanadium-bearing Titanomagnetite Concentrates

Effect of Ni Content on Iron-based Friction Material Prepared by In-situ Synthesized from Vanadium-bearing Titanomagnetite Concentrates

Investigation of the mechanism of solid-phase recovery of the titanomagnetite concentrate of Krapivensky deposit

В работе освещены результаты исследований по твердофазному восстановлению титаномагнетитового концентрата Крапивенского месторождения, характеризующегося высоким (до 25 %) TiO2 и сложным строением рудных зерен – на уровне распада твёрдого раствора. Выводы и положения минераграфических исследований проверялись изучением химического состава остаточных зерен титаномагнетита, а также фаз шлака и металла на разных этапах восстановления. Всего на лазерном микроанализаторе было выполнено около 200 анализов на содержание 12 элементов. Ниже нами излагается наше видение процесса твердофазного восстановления титаномагнетитового концентрата, и даются рекомендации по рациональной крупности концентрата и разработке технологических режимов его восстановлении.

Mechanisms and Kinetics of Solid State Reduction of Titano Magnetite Ore with Methane

Sustainable development aims to reduce energy demand and carbon footprint in all fields of industry. In this study, a new approach to decrease these has been performed. Methane, a hydrocarbon gas, has been employed as a reductant with better reducing properties than solid carbon and hydrogen separately. Reduction of a titano magnetite ore has been executed at temperature ranging from 800 to 1200 °C using methane contents between 10 and 30 vol% in the hydrogen–methane gas mixture. Due to the high carbon activity reaching up to approximately aC = 200, higher reduction degrees has been achieved at lower temperatures compared to ordinary carbothermic reductions. Kinetically, the reduction of titano magnetite ore was most likely mix controlled regardless of the methane contents used. The reduction process especially at the early stages displayed shrinking core behaviour. The calculated activation energies, based on the obtained experimental metallisation data, varied when assuming the reaction is controlled by diffusion (iron 25–28 kJ/mol, titanium: 335–355 kJ/mol) or chemical reaction rate (iron 21–25 kJ/mol, titanium 178–184 kJ/mol) indicating a likely mixed control process. Iron was fully reduced at 1000 °C after 1 h and at 1200 °C in half an hour. The calculated rate constants for metallisation of titanium, vanadium and iron varied too, i.e. Fe from 0.00454 to 0.01150. The possible reduction mechanism is presented and discussed based on the kinetics results achieved and SEM–EDS observations.

Anisotropy of Magnetic Susceptibility of Earthquake-Affected Soft Sediments: Example from Ther Village, Latur, Maharashtra, India

Anisotropy of magnetic susceptibility (AMS) of deformed and undeformed unconsolidated clay samples of Deccan Trap terrain from the ~2000-year-old palaeoearthquake site of Ther village, Maharashtra, India, was studied. Such deposits are rare in this region and give an exceptional opportunity to test the efficacy of AMS and other magneto petrofabric studies, which can have a bearing on magnetic granularity ellipsoids, inclination and declination directions impacting palaeomagnetic studies. The undeformed clay samples exhibit typical sedimentary fabric with an oblate AMS ellipsoid, whereas the deformed samples are tightly grouped in the inferred compression direction, probably effected by an earthquake, exhibiting prolate as well as oblate AMS ellipsoids. The temperaturedependent magnetic susceptibility revealed the occurrence of titanomagnetite and magnetite in both the deformed and undeformed samples signifying similar sediment material. The site mean ChRM direction for undeformed clay samples is D = 3 and I = 44.7 ( k = 92.7, α 95 = 4.5), whereas for deformed samples D = 336 and I = 39 ( k = 39, α 95 = 8). The present study reveals that sediments can be severely deformed without deflecting minimum susceptibility directions. AMS methodology can be effective in the DT region and can throw up new results to build the chronology of past earthquakes.

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Titanomagnetites (TMs) [pseudobinary (1 - x)Fe 3 O 4 · xFe 2 TiO 4 oxides, where, e.g., TM75 corresponds to x-0.75] are magnetic minerals with a spinel structure. Ulvospinel (Fe 2 TiO 4 ) and TMs were made using a solid-state synthesis technique, and transmission electron microscopy (TEM) characterization and measurement of the TM samples were performed to further confirm the homogeneity of the samples and cation site occupancies. The Mossbauer spectra in the TMs exhibited an anomalous composition dependence at x=0.95, when fitted with two instead of three quadrupole split doublets. This result was reinforced by the obtained dependence of the recoilless fraction on the composition, which exhibited an extremum at x=0.95.

Magma flow directions in the sheeted dike complex at superfast spreading mid-ocean ridges: Insights from IODP Hole 1256D, Eastern Pacific

Integrated Ocean Drilling Program (IODP) Hole 1256D successfully sampled a complete section of an intact oceanic crustal sheeted dike complex (SDC) (from 1061 to 1320 meters below seafloor; mbsf) on a 15 Ma old Cocos Plate. A series of rock magnetic measurements were carried out to understand the magmatic processes that accreted this end-member, superfast-spread (200 mm/yr full rate) oceanic crust. Results indicate that main ferromagnetic minerals are predominantly pseudo single-domain (titano)magnetite crystals, responsible for both anisotropy of magnetic susceptibility (AMS) and magnetic remanence signals. AMS fabrics were reoriented into a geographic reference frame using magnetic remanence data, and corrected for a counterclockwise rotation of the Cocos Plate relative to the East Pacific Rise (EPR) ca. 15 Ma. Corrected AMS fabrics were then compared with the orientations of chilled margins previously obtained from Formation MicroScanner (FMS) images of the SDC at Hole 1256D. For some samples taken from close to dike margins, a dike-normal orientation of the minimum AMS axes (Kmin) of prolate AMS ellipsoids mean that the long axis (Kmax) can be used to infer magma flow directions. Subvertical Kmin orientations in the interior of the dikes, however, may have required settling or compaction of the magma shortly after intrusion, thus rearranging the AMS fabric. Despite this orientation of Kmin axes, orientation of Kmax axes indicate a rather constant subhorizontal paleo-flow direction, suggesting that magmas most probably traveled to the surface considerable distances from source regions within the EPR system.

Synthesis and magnetic properties of single phase titanomagnetites

The focus of this paper is the study of cation distributions and resulting magnetizations in titanomagnetites (TMs), (1−x)Fe3O4−xFe2TiO4 solid solutions. TM remnant states are hypothesized to contribute to planetary magnetic field anomalies. This work correlates experimental data with proposed models for the TM pseudobinary. Improved synthesis procedures are reported for single phase Ulvöspinel (Fe2TiO4), and TM solid solutions were made using solid state synthesis techniques. X-ray diffraction and scanning electron microscopy show samples to be single phase solid solutions. M-H curves of TM75, 80, 85, 90, and 95 (TMX where X = at. % of ulvöspinel) were measured using a Physical Property Measurement System at 10 K, in fields of 0 to 8 T. The saturation magnetization was found to be close to that predicted by the Neel model for cation distribution in TMs. M-T curves of the remnant magnetization were measured from 10 K to 350 K. The remnant magnetization was acquired at 10 K by applying an 8 T field and then releasing the field. Experimental Neel temperatures are reported for samples in the Neel model ground state.

Microscopy and rock magnetism of fine grain-size titanomagnetite from the Jacupiranga Alkaline Complex, Brazil: unearthing Ti-magnesioferrite nanoparticles

Very fine samples from the mineralized zones of the Jacupiranga complex at the Cajati mine were selected for crystallographic identification of Ti-magnesioferrite (TMf) nanostructures embedded in titanomagnetite (TM) using high-resolution transmission electron microscopy (TEM). A magnetic concentrate obtained of pyroxenite samples (sites 4 to 7) was reduced and divided into fractions of distinct range sizes: 26±2 μm, 19±1 μm, 13±1 μm, 9±1 μm, 6±1 μm and 6-0.1 μm. The mineralized samples of carbonatite and pyroxenite were characterized by X-ray diffraction, transmitted and reflected light microscope, and scanning electron microscope with multielemental analysis. The finest magnetic concentrate sample (MC6) was analyzed under high-resolution transmitted electron microscopy (TEM) and high angle annular dark field and Raman spectroscopy. Magnetic properties were measured for the distinct granulometric fractions, showing drastic changes when grain sizes go beyond the frontier from micro to nanometer sizes. Frequency-dependent magnetic susceptibility percentage (÷fd%) report higher values (10.2%) for the finer fractions (6±1 μm and 6-0.1 μm) attributed to dominant fractions of superparamagnetic particles. Nanometer and < 6 μm grain size TMf in TM particles require a magnetic field up to 249 mT to reach saturation during the isothermal remanent magnetization experiment. Coercivity and remanent magnetization of these samples increase when the particle size decreases, probably due to parallel coupling effects. Magnetic susceptibility versus temperature experiments were conducted two times on the same (< 35 nm) sample, showing that the repetition during the second heating is probably due to the formation of new TMf nanoparticles and growth of those already present during the first heating process.

Magnetic petrology of high Fe‐Ti eclogites from the CCSD main hole: Implications for subduction‐zone magnetism

The high Fe‐Ti eclogites with exsolved lamellar in 530–600 m depths from the Chinese Continental Scientific Drilling (CCSD) main hole in the Sulu Ultra‐High Pressure (UHP) metamorphic belt, eastern China, record an anomalously high susceptibility (κ), natural remanent magnetization (NRM) and Köenigsberger ratio Q (NRM/Ji, Ji is induced magnetization). This provides us with a good opportunity to study the effects of magnetic minerals and exsolution lamellae on the magnetic properties of deep rocks. In this paper, we have measured systematically magnetic properties and mineral assemblage and structure for three special samples (No. 83, No.86 and No.89). Results show that these Fe‐Ti‐rich eclogites are the result of the fine‐grained (titano)‐magnetite exsolution in pyroxene and lamellar structure consisting of finely interlayered ilmenite and hematite in exsolved hemo‐ilmenite. We found that the dominant Fe‐bearing oxide minerals in samples studied are ilmenite, hematite (Hem + Ilm up to 25%), little (titano)magnetite and pyrite. The ferromagnetic susceptibility is mainly controlled by fine grained (titano)magnetite and NRM is closely related to the exsolved lamellar structure. We hence propose that the anomalous magnetism of these eclogites observed in our samples is the result of exsolution from homogenous pyroxene and ilmeno‐hematite during cooling and decompression processes. These Fe‐Ti‐rich eclogites might be one of the sources of high‐magnetic anomalies observed in the Sulu subduction zone, eastern China.

Dual polarity directions in basaltic-andesitic dykes-reversal record or self-reversed magnetization?

Rock magnetic analyses were performed on basaltic-andesitic dyke samples from the Lhasa Block, which were previously used for palaeomagnetic investigations of the India–Asia collision. The aim of the study is to prove whether antipodal directions separated in these samples represent different polarities of the Earth's magnetic field or a self-reversal magnetization. Reflected light microscopy, domain pattern observations and energy dispersive X-ray analyses revealed two generations of titanomagnetite (TM) grains, one consisting of large-sized (∼20 μm to more than 100 μm) and inhomogeneous Ti-poor TM, and another with small (smaller than ∼10 μm) and rather homogeneous Ti-rich TM grains. Partial thermoremant magnetization experiments and reflected light microscopy show that magnetostatic or superexchange interaction between these two phases is unlikely. Temperature dependence of saturation magnetization and low-temperature curves of isothermal remanent magnetization disprove a possible N-type behaviour of the samples. A self-reversal due to ionic reordering can be ruled out as it requires a high degree of oxidation of the Ti-rich TMs, which was not observed. In summary, a self-reversal magnetization is very unlikely in the studied dyke samples, and therefore the observed antipodal directions most probably represent a record of different polarity epochs of the Earth's magnetic field. This conclusion implies that the time of remanence acquisition in the studied dykes was sufficiently long to average out paleosecular variation, supporting the significance and reliability of the palaeomagnetic results.

Magnetic fabric and its significance in the sills and lava flows from Taimyr fold-belt, Arctic Siberia

Magnetic fabric research on the emplacement of the Taimyr fold-belt is still absent. Therefore, we have performed magnetic fabric studies on samples collected from 23 sites from mafic igneous rocks (75°N, 100°E) in South Taimyr. This study indicates a correlation between the anisotropy of magnetic susceptibility (AMS), magma flow and fold-related compression in the rocks. AMS measurements on 183 unheated and 122 heated samples reveal the magma flow directions. The magma flow direction is mainly parallel to the ESE–WNW and secondarily parallel to the SSW from the NNE in the mafic sills. The unheated and heated basaltic flows reveal a NE-trending flow vector. In some of the sills, AMS shows a tight clustering of the maximum K 1 axes close to the bedding pole, which is not thought to define the flow direction. Corresponding AMS measurements on igneous rocks allow us to infer the existence of magnetic fabrics of tectonic origin linked to the main folding episode that occurred subsequent to the Mid-Triassic magmatic event in latest Triassic–Early Jurassic times. In the sills, the distribution of most maximum K 1 axes is close to NS that corresponds to the maximum compressive stress or folding directions; contrarily, the minimum K 3 axes have an elongated distribution along the EW direction or parallel to the fold axis before exchanging K 1 and K 3 axes for inverse fabrics, but close to the NS stress direction after exchanging K 1 and K 3 axes for inverse fabrics. In the basaltic flows, the minimum K 3 axes almost parallel to the NS folding direction. The structural interpretation of all AMS data taken from the igneous bodies is in accordance with a NNW–SSE stress-related folding taking place around 198 Ma in the Taimyr Peninsula (Arctic Siberia). The relationship of susceptibility axes to bedding surfaces and magnetic foliation planes is a criterion that permits differentiation of normal magnetic fabrics from inverse fabrics in the igneous samples. Single-domain (SD) and small pseudo-single-domain (PSD) magnetite crystals in the sill samples are the main carriers of the AMS fabrics, implying the abundance of inverse magnetic fabrics. PSD and multidomain (MD) titanomagnetite (TM) grains as well as minor hematite are identified in the basalt flows, suggesting the occurrence of more normal magnetic fabrics in the basalts than in the sills.

First occurrence of titanomagnetites from the websterite dykes within Balmuccia peridotite (Ivrea-Verbano zone): crystal chemistry and structural refinement

Periodico di Mineralogia (2011), 80, 1 (Special Issue), 19-26 - DOI: 10.2451/2011PM0002 Special Issue in memory of Sergio Lucchesi First occurrence of titanomagnetites from the websterite dykes within Balmuccia peridotite (Ivrea-Verbano zone): crystal chemistry and structural refinement Davide Lenaz* and Francesco Princivalle Dipartimento di Geoscienze, Universita di Trieste, Italy *Corresponding author: lenaz@units.it Abstract The crystal chemistry of three ulvospinels from the websteritic dykes within the Balmuccia peridotites has been investigated by means of X-ray single crystal diffraction and electron microprobe. They are very similar each other with cell edge about 8.43 A and oxygen positional parameter between 0.2565 and 0.2570. Ti content is about 0.32 a.p.f.u. As they are embedded in a glass with syenite composition it is supposed they quenched during the rapid cooling of a melt pervading the websteritic dykes. This is the first finding of similar spinels in the studied area. Key words : Balmuccia peridotite; websterite dykes; ulvospinel; crystal chemistry; structural refinement.

Sm-Nd and Rb-Sr ages of gabbroids, granitoids, and titanomagnetite ores from layered intrusions of the Kusa-Kopan Complex (South Urals)

732 A band of layered gabbro intrusions belonging to the Kusa–Kopan Complex is confined to the zone of the Zyuratkul riftogenic fault in the eastern part of the Bashkir Meganticlinorium, where it consists of several massifs (Matkal, Kopan, Medvedevo, Kusa) with the Ryabinovka and Gubenskii granitoid massifs located in the hanging wall (Fig. 1). The gabbro massifs enclose synonymous ilmenite–titanomagnetite deposits of the Urals in the form of stratified series, vein, and lenticu� lar lodes of continuous and disseminated ores, which alternate with gabbroids. These deposits were discov� ered in the 1930s, and since that time their geological structure and composition of ores and host rocks have been studied by many researchers. The primary atten� tion was paid to the most debatable factors responsible for strong lateral variations in the composition of rocks and ores within the complex, represented by horn� blende gabbro and gneiss–granites in the Kusa and Gubenskii massifs and ilmenite–magnetite ores in the Kusa and Medvedevo deposits in the north and by gab� bronorites (Matkal and Kopan massifs), porphyroid granophyric granites (Ryabinovka Massif), and titano� magnetite ores in the south. Some researchers explain such differences in the mineral composition by the influence of superposed metamorphic processes on rocks and ores of the Kusa Massif [1, 2], which occurred substantially after the formation of intru� sions. Our petrological studies performed in recent years revealed that the formation depth of granitoids, gab� broids, and enclosed ores increases along this band in the northerly direction from 3–4 km in the south to 20–30 km in the north. Accordingly, the P–T param� eters of rock and ore formation vary in the same direc� tion: = 0.5–3.0 kbar and T = 900–1100°C in the south (Kopan and Matkal gabbro massifs and associ� ated deposits, Ryabinovka granite massif) and P = 6– 9 kbar and T = 600–900°C in the north (Kusa and Medvedevo gabbro and Gubenskii granite massifs,

Magnetic granulometry of recent sediments from the Huguang Maar and its implication for provenience

To understand the origin and its climatic implications of the Huguang Maar sediments, we conducted laser grain size analysis and rock mangtic measurement for the recent deposits from the Huguang Maar and for the volcanic rocks of the caldera for comparison. The grain size distributions are dominated by clayey silts for both the bulk sediments and magnetic separates. Acquisition of isothermal remanent magnetization (IRM) and thermal demagnetization of IRM suggest (titano) magnetite as the dominating magnetic mineral in the sediments; high coercivity minerals are not detected. Therefore, the ratio of the susceptibility of anhysteretic remanent magnetization (k ARM) to the weak field magnetic susceptibility (k), k ARM/k can be used to estimate the grain size of magnetite. The sediments and volcanic rocks yield values of 13.7 and 11.8 for the k ARM/k, respectively, corresponding to grain size values of ∼0.03 µm and ∼0.05 µm. The magnetic granulometry of lake sediments is distinctive from one of the Chinese loess, in which published data suggest a value of 6.0 for k ARM/k, and grain size of ∼0.1 µm, but is akin to the nearby volcanic rocks. Although a Loess Plateau source of the lake sediments cannot be fully ruled out, the catchment is most probably the main source. We explain the slightly finer magnetite grain size in sediments than in the volcanic rocks as being disintegrated of particles during erosion and transportation. We conclude that there is no evidence for aeolian input of the Loess Plateau dusts into the Huguang Maar, and the relationship between magnetic parameters of the lake sediments and winter monsoon intensity is probably more complicated than previously thought.

Characterization of a mechanochemically activated titanium-hematite mixture: Mössbauer spectroscopy study

Fil: Cristobal, Adrian Alberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingenieria. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales; Argentina