Isothermal Remnant Magnetization Research Articles

Magnetic susceptibility as a proxy for detection of total petroleum hydrocarbons in contaminated wetlands.

Soil petroleum hydrocarbon contamination in the wetlands could cause ecological risk, especially through leakage into water reservoirs. So, the detection of the spatial variability of total petroleum hydrocarbons (TPH) in these soils is very crucial. The variability of TPH and its associations with magnetic susceptibility (χlf) in contaminated soils around the Shadegan pond in southern Iran was investigated. TPH varied from 2.1 to 18.1% (w/w), by the variation of χlf from 14.08 to 713.93 × 10-8 m3kg-1. The highest variability (coefficient of variation, CV = 107.12%) was obtained for χlf indicating significant impacts of magnetic minerals induced by crude oil contamination. High positive correlations were detected among TPH, χlf, and different forms of iron (Fed: extracted by CBD, Feo: extracted by oxalate, and Fet: total iron). The results of mineralogy by powdery XRD and scanning electron microscopy (SEM), also revealed the formation of ferrimagnetic minerals (magnetite, maghemite) during the biodegradation of petroleum hydrocarbons. The stepwise multiple regression analysis showed that χlf and Fed made a great contribution and could explain about 74% of TPH variability in the studied sites. For the extension of this cost-effective and rapid technique, further work is needed to assay saturation isothermal remnant magnetization and isothermal remanet magnetization in contaminated sites.

Cyclostratigraphic calibration of the ca. 1.56 Ga carbon isotope excursion and oxygenation event recorded in the Gaoyuzhuang Formation, north China

Recent studies of the upper Gaoyuzhuang Formation (Fm) (ca. 1600–1540 Ma) in north China have suggested that Earth underwent an oxygenation event associated with a negative δ 13 C carb excursion and this event may have led to the expansion of eukaryotic life. However, the duration of this negative δ 13 C carb excursion, which is crucial to understand its origin, remains uncertain. Here, we report a floating astronomical timescale based on Milankovitch cycles extracted from the carbonate-dominated strata of the Member 3 of the Gaoyuzhuang Fm in north China, in which the oxygenation event is recorded. High-resolution magnetic susceptibility, anhysteretic remnant magnetization and saturation isothermal remnant magnetization series were obtained from the stratigraphic sections in the Jixian and Yanqing regions. Rock magnetic experiments suggest that the magnetic parameters are dominated by the detrital materials whose flux was likely controlled by orbitally forced climatic changes. Our results for the first time reveal well-constrained eccentricity, obliquity, and precession cycles from the Gaoyuzhuang Fm and demonstrate that the ca. 1560 Ma negative δ 13 C carb excursion and associated transient oxygenation event indicated by I/(Ca + Mg) had durations of ~1.7 Myr and ~6.2 Myr, respectively. The ca. 1560 Ma δ 13 C carb excursion is comparable with the short-term Neoproterozoic excursions in respect of duration, rather than with the long-term ones such as the ca. 574–567 Ma Shuram excursion. The similarity may indicate a common mechanism in origin of the short-term excursions in the Mesoproterozoic and Neoproterozoic time, which deserve testing by more investigations. • Cyclostratigraphic analyses revealed Milankovitch cycles from the ca. 1.56 Ga Gaoyuzhuang Formation • Durations of the δ 13 C carb excursion and the oxygenation event in the ca. 1.56 Ga are 1.7 Myr and 6.2 Myr, respectively • The duration of this δ 13 C carb excursion are comparable to the short-term ones in the Neoproterozoic

Anisotropy of Magnetic Susceptibility (AMS) of Bostonite Rocks, Um-Gir and El-Atshan-II Uranium Prospect Areas, Central Eastern Desert, Egypt

Um-Gir and El-Atshan-II areas represent important structurally-controlled radioactive anomalies and have become promising areas for U exploration. The bostonite rocks represent the most promising rock unit in the two studied areas. They form the most promising rocks due to their high radioactivity and, hence uranium mineralization. Anisotropy of magnetic susceptibility (AMS) measurements was carried out for Um-Gir and El-Atshan-II bostonite rocks. The AMS results show that the mean magnitude of magnetic susceptibilities is low, of the order of 10-5 S.I. units. Consequently, the bostonite rocks of the two areas are considered as non-magnetic, reflecting the presence of hematite as the main ferromagnetic mineral. These results are in agreement with the measurements of initial remnant magnetization (NRM) and the results of isothermal remnant magnetization (IRM) for the two areas. Besides, the results of magnetic anisotropy degree (PJ), refer to and concluded that the magnetic fabric of bostonite of two the areas has secondary fabric. AMS results clearly show the differences between the bostonite dyke of Um-Gir and Bostonite sill of El Atshan-II. The lineation (P1) > foliation (P3), and the negative values of the ellipsoid shape (T) of Um-Gir bostonite reflect clearly magnetic lineation (prolate ellipsoid). However, in El Atshan-II, (P3 > P1), the values of T are positive, which indicate the predominance of magnetic foliation (oblate ellipsoid) over lineation. Furthermore, the foliation planes of the bostonite dyke of Um-Gir possess a shallow to moderate inclination and a nearly N-S direction, while, the foliation planes of the bostonite sill of El-Atshan-II show a shallow to moderate inclination and a NNE direction. Finally, the AMS method is a powerful tool for detecting the structures that affect the bostonite rocks of the two studied areas.

Rock Magnetic Properties during the Paleocene-Eocene Thermal Maximum (PETM): Records from P/E boundary Sections (Sinjar, Shaqlawa) in Iraq

Rock magnetic properties have been investigated across the Paleocene/Eoceneboundary in two distally separate sections of Paleogene marine sedimentary rocksfrom Iraq, namely the Sinjar and the Shaqlawa sections. The sediments at thestudied sections belong to the Aaliji and the Kolosh formations respectively, whichwere previously examined for their biostratigraphy by the authors using planktonicand benthonic foraminifera to delineate the Paleocene/Eocene (P/E) transition.Measured magnetic properties include; bulk magnetic susceptibility, hysteresiscycles, isothermal remnant magnetization (IRM) acquisition, and thermomagneticcurves analysis. Rock-magnetic results (i.e. low magnetic coercivity component)indicate greigite as the main magnetic phase at Aaliji rocks, while a mixture ofmagnetite and greigite with high magnetic coercivity has been observed at Koloshclastics. Magnetic susceptibility is induced by related to both biogenic minerals(mainly at Aaliji Formation) and transported terrigenous material sources. Multivaried magnitude phases of high bulk rock magnetic susceptibility observed inboth formations along PETM lithosomes are attributed to two sources: greigite orbiogenic iron oxides source and increase in terrigenous discharge source asinferred by anoxic to suboxic iron - sulfate-reducing conditions and lithologicalchange respectively. Both sources referred to some of environmental conditionsassociated with Paleocene - Eocene thermal maximum events such as methanedissociation, water stratification, enhanced hydrological and weathering cycles.

An environmental magnetic record of heavy metal pollution in Vembanad lagoon, southwest coast of India

Magnetic signature of the iron-bearing minerals archived in sediments is sensitive to change in environment and therefore, studied to reconstruct the signals linked with environmental processes. In the present work, we have analyzed 11 sediment cores from Vembanad lagoon, southwest coast of India, to estimate the magnetic fluctuations associated with environmental processes. Down-core variation in magnetic susceptibility and anhysteretic, isothermal and saturation isothermal remnant magnetization and S and H-ratios have been interpreted to map the degree and spatial distribution of anthropogenic pollution in and around the lagoon. Downcore variation of magnetic susceptibility of Vembanad lagoon sediments varies from 10 to 100 × 10−8 m3/ kg. The top layers of sediment samples from river mouth regions (Periyar and Muvattupuzha rivers) show higher susceptibility values and incidentally these samples are of coarse sized. The subtle variations in SIRM/χlf ratios suggest that there are magnetic grain size differences in the samples. The SIRM and χlf relation suggests that dominant magnetic grain size in sediments. The low ARM/χlf ratios suggest a relatively higher ferrimagnetic contribution and coarser magnetite grain size. Rock magnetism data reveal that the coarse magnetic grain size is affecting the pollution of Vembanad lagoon. We also analyzed downcore variability of metal concentrations such as Fe, Mn, Cu, Zn, Ni and Cr, and all these metals exhibit higher concentrations in the top layers of the cores. Our study suggests that higher values of magnetic parameters and metal concentrations are due to various anthropogenic sources.

Synthesis and Characterization of Ni-Ti Partially Substituted Hexaferrites for High-Density Magnetic Recording Applications

Synthesis and Characterization of Ni-Ti Partially Substituted Hexaferrites for High-Density Magnetic Recording Applications

Exposure to Indoor Ferromagnetic Particulate Matter Monitored by Strawberry Plants and the Occurrence of Acute Respiratory Events in Adults.

Exposure assessment of air pollution in epidemiologic research remains a challenge. Previous studies showed that magnetic monitoring of strawberry leaves, based on Saturation Isothermal Remnant Magnetization (SIRM), is a valid tool for estimating the concentration of ambient particulate matter (PM). This study uses this assessment method for the first time in epidemiologic research to quantify indoor exposure to PM. In a nested case control study, we evaluated the association between ‘waking up by cough’ and indoor air pollution measured by SIRM of dust deposition on leaves of strawberry plants located in the bedroom in the general adult population. A multiple logistic regression was used to estimate the association between ‘waking up by cough’ and exposure to ferromagnetic particles of PM controlling for age, gender and smoking status. A cut-off of 10 µA was decided to define exposure status (high versus low). Using logistic regression, a crude odds ratio (OR) of 1.80 (95% CI: 0.90–3.60) for ‘waking up by cough’ was found. This association remained approximately the same after controlling for age, gender and smoking status (adjusted OR: 1.76; 95% CI: 0.60–5.30). We found an association between exposure to ferromagnetic particles and ‘waking up by cough’ in adults; however, it was not statistically significant. This environmental exposure assessment method could be a valuable alternative for expensive personal exposure measurement devices.

Reentrant spin-glass and transport behavior of Gd4PtAl, a compound with three sites for Gd

We report temperature (T) dependence (2-330 K) of DC and AC magnetization (M), isothermal remnant magnetization (M_IRM), heat capacity (C), electrical resistivity (rho), and magnetoresistance (MR) of a ternary intermetallic compound, Gd4PtAl, crystallizing in a cubic (space group F-43m) structure. In this structure, there are three sites for the rare-earth. The magnetization data reveal that, in addition to a magnetic transition at 64 K, there is another magnetic feature below 20 K. The C(T) data reveal an upturn below 64 K, shifting to a lower temperature with increasing field, which establishes that the onset of magnetic order is of an antiferromagnetic type. However, there is no worthwhile feature near 20 K in the C(T) curve. AC susceptibility peak undergoes an observable change with frequency and, in particular, the peak around 20 K gets suppressed with the application of a dc magnetic field; in addition, M_IRM undergoes a slow decay with time and isothermal M exhibits low-field hysteresis below 20 K only, which is typical of spin-glasses. The results overall suggest that this compound is a reentrant spin-glass in zero-field. There are experimental signatures pointing to the existence of both antiferromagnetic and ferromagnetic components, competing with the variation of temperature and magnetic field, as a result of which electrical and magnetoresistance behaviors are peculiar. The results overall suggest this compound exhibits interesting magnetic and transport properties.

Study on the structural and magnetic properties of Fe/Co co-doped Bi4Ti3O12 ceramics

Polycrystalline Bi4(Ti3-xFex/2Cox/2)O12 (0 ≤ x ≤ 0.4) ceramics are prepared by solid state reaction method. The low temperature ferromagnetism is successfully induced by Fe/Co co-doping. Particularly, the x = 0.3 ceramics possess the largest remnant magnetization (2Mr) of about 0.272 emu/g at 100 K. Furthermore, all the doped ceramics undergo a ferromagnetic to paramagnetic transition, and show typical spin glass behavior, which is confirmed by the isothermal remnant magnetization and Memory Effect. The magnetic mechanisms probably originate from the coexistence and competition between ferromagnetic double exchange interactions and antiferromagnetic superexchange interactions, which lead to the appearance of the spin glass behavior in the doped ceramics and the strongest ferromagnetism in the x = 0.3 ceramics. The present work provides basic data and theoretical reference for the exploitation of the new multifunctional materials.

Fingerprinting Sediment Transport in River‐Dominated Margins Using Combined Mineral Magnetic and Radionuclide Methods

AbstractBoth magnetic properties and radionuclides are widely used to trace sediment transport in aquatic environments; however, these methods have not been used in combination. In this study, the East China Sea (ECS), a typical river‐dominated margin, was chosen to demonstrate the advantages of combining these two methods to track sediment movements on a seasonal to annual timescale. The ratios between saturation isothermal remnant magnetization and anhysteretic remnant magnetization (χARM/SIRM) and 7Be/210Pbex activity ratios as well as mass balance of 7Be provide information on the seasonal transport of sediment from the Changjiang Estuary to the neighboring shelf. Both 210Pb budget and SIRM distribution in the inner shelf of the ECS show that a small fraction (at most 14% of annual Changjiang sediment discharge) of particles could be transported offshore. Most of 7Be activities in inner shelf sediments of the ECS were below detection limit due to relatively lower residence times and dilution by the older sediment. The observation that radionuclide activities exhibit a better correlation with χARM/SIRM ratios than with grain size suggests that iron oxides are the primary carriers of 7Be, 210Pb, and 234Th. The absorption of radionuclides onto magnetic minerals further reinforces the reliability of this combined approach in tracing sediment transport. Our study indicates that radionuclides, with different half‐lives, can be utilized for quantifying sediment dynamics, whereas magnetic properties can yield more detailed information on sediment transport directions. The combined analysis of magnetic parameters and radionuclides offers a better understanding of sediment transport in river‐dominated areas.

Magnetic measurements and geochemical characterization of the road-deposited sediments (RDS), Allahabad city, India: impact of climatic perturbations on sediment composition and provenance tracing

Magnetic measurements provide quantitative data on urban pollution (including heavy metal content) which correlate significantly with geochemical analysis and better constrain the source character of pollutants. The present study is aimed to map the distribution of heavy metals in road-deposited sediments (RDS) and identify the possible provenance of the sediments during the pre-monsoon and post-monsoon (mainly fog) periods of Allahabad city, India. In all, 442 RDS samples from 60 representative locations were collected over 3 years, and the different magnetic parameters and metal concentrations were determined. The magnetic minerals were identified using X-ray diffraction (XRD) and backscatter electron-scanning electron microscopy (BSE-SEM) while principal component analysis (PCA) was used for the provenance tracing of the RDS. The samples record high magnetic susceptibility (χlf; $$ \overline{\mathrm{x}}: $$ 174.44–604.36 × 10−8 m3 kg−1), saturation isothermal remnant magnetization (SIRM; $$ \overline{\mathrm{x}}: $$ 1586.30–2421.51 × 10−5A m2 kg−1) and anhysteric remnant magnetization susceptibility (χARM; $$ \overline{\mathrm{x}}: $$ 461.64–1099.68 × 10−8 m3 kg−1) values independent of seasonal change. The magnetic minerals in the sediments lie in pseudo-single domain (PSD) and multi-domain (MD) from anthropogenic sources while stable single domain (SSD) is associated with both natural and anthropogenic sources. PCA of magnetic proxies with heavy metal concentrations suggests the derivation of the RDS from multiple (crustal, anthropogenic, traffic, and industrial) sources. The XRD analyses confirm the presence of magnetite and hematite, in addition to quartz, feldspar, gypsum, apatite, calcite, and dolomite in the RDS. Limited geochemical analysis of the RDS comprising Na, Mg, Al, K, Ca, Ti, Mn, Fe, Sc, V, Cr, Ni, and Rb suggests a predominance of anthropogenic load in RDS compared to geogenic sources. The magnetic measurements coupled with XRD and BSE-SEM analyses suggest the dominance of magnetic grains and heavy metals in pre-monsoon samples compared to those collected during the fog period. The geochemical data also support the seasonal control for the elevated heavy metal concentration in the RDS and their derivation from geogenic as well as anthropogenic sources.

Influence of Mn-substitution on the magnetic and thermal properties of TbCrO3

Studies on the Mn-substitution induced modification in the structural, thermal, magnetic and magnetocaloric properties of TbCrO3 orthochromite are presented. The phase formation and purity of the samples were examined by analyzing X-ray diffraction (XRD) patterns. Magnetization measurements as a function of temperature reveal the antiferromagnetic ordering of Cr3+ spins (TN1) at ∼ 157 K and Tb3+ spins (TN2) ∼ 5 K for TbCrO3 sample. The substitution of Mn-atoms at Cr-site results in a decrease in TN1 whereas an increase in TN2. The isothermal magnetization measurements reveal the presence of metamagnetic transition at 5 K and 2 K. Results of, ac and dc magnetization and isothermal remnant magnetization suggest a spin-glass like ordering below TN2. The heat capacity measurements show peaks corresponding to the magnetic ordering of Cr3+ and Tb3+ spins. The temperature variation of magnetic entropy change (-ΔSm) for different ΔH suggests the presence of the magnetocaloric effect in the vicinity of TN2. It is found that values of -ΔSm decreases with the increase in Mn-substitution. Present results have been understood in terms of modifications in magnetic exchange interactions introduced by the Mn-substitution at Cr-site.

Late Holocene sea-level changes and paleoclimate recorded in Lake Lungué, southern Mozambique

We report on late Holocene paleoenvironmental and sea-level changes in southern Mozambique, based on analysis of diatom stratigraphy, mineral magnetic susceptibility, Saturation Isothermal Remnant Magnetization (SIRM) and organic carbon content in a sediment core from Lake Lungué, located ca. 30km north of Xai Xai City in the Limpopo River floodplain. Eleven radiocarbon dates performed on terrestrial shells allowed establishment of an age-depth model. High content of brackish-marine taxa, especially Diploneis suborbicularis and Navicula yarrensis, suggests that the Lake Lungué basin was part of the Indian Ocean coastal zone between ca. 740 and 910CE, suggesting higher relative sea-level during this phase. A similar diatom distribution in older parts of the sequence, of unknown age, indicates that the site was connected to the Indian Ocean also at some stage prior to 740CE. Between ca. 910 and 1130CE the basin was under a combined effect of sporadic marine water influx and Limpopo River actions. A freshwater lake was established sometime between 1130 and 1360CE, when the basin became less affected by marine influences due to lower sea-levels. Instead, the lake system was more influenced by Limpopo River meandering dynamics and flooding events, and eventually isolated into a more or less independent lake ecosystem where diatom diversity most likely responded to lake levels fluctuations driven by shifts in relative humidity and rainfall amounts within the floodplain and also from upstream sources. During this phase, high abundance of freshwater planktonic species, i.e. Aulacoseira granulata and A. ambigua, indicates high lake levels and wetter conditions dated to ca. 1360–1560CE. From 1560CE until present, the lake has been subject to drier conditions and higher evaporation as indicated by lower lake levels, reported by a decline in freshwater planktonic taxa and increase in brackish taxa, e.g. Amphora robusta.

Kinematics of the crust around the Tanggula Shan in North–Central Tibet: Constraints from paleomagnetic data

We have conducted a paleomagnetic investigation on the Middle–Upper Jurassic marine strata exposed in the hanging wall of the Tanggula Thrust system near the Yanshiping area, northern Tibet. Progressive demagnetization experiments successfully isolated stable magnetization over a broad spectrum of demagnetization temperatures. The mean direction of the characteristic remanent magnetizations for the Middle–Late Jurassic Yanshiping Group in stratigraphic coordinates (D/I (Declination/Inclination)=5.6°/60.3°, k=22.9, α95=12.9°, N=7s) is much more clustered than the mean direction in geographic coordinates (D/I=345.5°/37.2°, k=2.5, α95=48.4°), indicating magnetization was not acquired after folding. Although the conventional fold test is positive, incremental untilting test on the characteristic remanent magnetization reveals that a maximum value of precision parameter k occurs at 82.1±4.6% untilting (D/I=3.3°/57.8°, k=43.9, α95=9.2°), which indicates the ChRMs are probably acquired during Late Cretaceous folding. This synfolding magnetization component is therefore secondary. The corresponding pole position (84.4°N, 119.4°E with dp/dm=13.5/9.9°) is inconsistent with Jurassic–Early Cretaceous paleopoles of the region, but the paleolatitude is consistent with the Late Cretaceous paleolatitude observed in the Qiangtang terrane and its periphery. The synfolding component is carried by both magnetite and hematite, which were identified by isothermal remnant magnetization acquisition experiments, unblocking temperatures of stable magnetic components, and Curie temperature determination and correlated with observed hydrothermal veins. Available geological evidences indicate that the synfolding magnetization is probably the result of chemical remagnetization caused by orogenic fluids or hydrothermal sources during the early uplift of the Tibetan Plateau.

Insight into the magnetism of a distorted Kagome lattice, Dy3Ru4Al12, based on polycrystalline studies

The layered compound with distorted Kagome nets, Dy3Ru4Al12, was previously reported to undergo antiferromagnetic ordering below (TN=) 7 K, based on investigations on single crystals. Here, we report the results of our investigation of AC and DC magnetic susceptibility (χ), isothermal remnant magnetization (MIRM), heat-capacity, magnetocaloric effect and magnetoresistance measurements on polycrystals. The present results reveal that there is an additional magnetic anomaly around 20 K, as though the Néel order is preceded by the formation of ferromagnetic clusters. We attribute this feature to geometric frustration of magnetism. In view of the existence of this phase, the interpretation of the linear-term in the heat-capacity in terms of spin-fluctuations from the Ru 4d band needs to be revisited. Additionally, in the vicinity of TN, AC χ shows a prominent frequency dependence and, below TN, MIRM exhibits a slow decay with time. This raises a question whether the antiferromagnetic structure in this compound is characterized by spin-glass-like dynamics. In contrast to what was reported earlier, there is a change in the sign of the magnetoresistance (MR) at the metamagnetic transition. A butter-fly-shaped (isothermal) MR loop (interestingly spanning over all the four quadrants) is observed at 2 K with distinct evidence for the magnetic phase co-existence phenomenon in zero field after travelling through metamagnetic transition field. The results on polycrystals thus provide additional information about the magnetism of this compound, revealing that the magnetism of this compound is more complex than what is believed, due to geometric frustration intrinsic to Kagome net.

Using magnetic susceptibility to discriminate between soil moisture regimes in selected loess and loess-like soils in northern Iran

This study used discriminant analysis to determine the efficacy of magnetic measures for discriminating between four soil moisture regimes in northern Iran. The study area was located on loess deposits and loess-like soils containing similar parent material. Four soil moisture regimes including aridic, xeric, udic, and aquic were selected. A total of 25 soil profiles were drug from each regime and composite soil samples were collected within the moisture control section. A set of magnetic measures including magnetic susceptibility at low (χlf) and high (χhf) frequencies, frequency-dependent magnetic susceptibility (χfd), saturation isothermal remnant magnetization (SIRM), and isothermal remnant magnetization (IRM100mT, IRM 20mT) were measured in the laboratory. Dithionite citrate bicarbonate (Fed) and acid oxalate (Feo) contents of all soil samples were also determined. The lowest and highest χlf and χhf were observed in aquic and udic moisture regimes, respectively. A similar trend was obtained for Fed and Fed–Feo. The significant positive correlation between Fed and SIRM (r=0.60; P<0.01) suggested the formation of stable single domains (SSD) due to pedogenic processes. The results of discriminant analysis indicated that a combination of magnetic measures could successfully discriminate between the selected moisture regimes in the study area (average accuracy=80%). It can thus be concluded that magnetic measures could be applied as a powerful indicator for differentiation of soil moisture regimes in the study area.

Magnetic mineral characterization close to the Yingxiu-Beichuan fault surface rupture zone of the Wenchuan earthquake (Mw 7.9, 2008) and its implication for earthquake slip processes

The 2008 Mw 7.9 Wenchuan Earthquake produced two major rupture zones: one in the Yingxiu-Beichuan fault zone (YBF) and another in the Anxian-Guanxian fault zone (AGF). A shallow trench was dug in Bajiaomiao village, Dujiangyan, Sichuan Province, which experienced a ∼4.3m vertical offset during this large earthquake. The hanging wall of the YBF in this trench includes fault gouge and breccia. Optical microscope observations and X-ray diffraction (XRD) measurements show obvious differences between the fault gouge and breccia. Moreover, rock magnetism measurements were collected and include mass magnetic susceptibility (MS), Isothermal Remnant Magnetization (IRM), Saturation Isothermal Remnant Magnetization (SIRM), high-temperature thermo-magnetism (K–T) and magnetic hysteresis loops. Several cm-thick magnetic mineral anomalies are observed close to the Wenchuan Earthquake surface rupture zone of the YBF. Magnetite and Fe-sulfide are the main magnetic carrier materials for the fault rocks close to the surface rupture zone, including 3cm-thick fault gouge and 3cm-thick fault breccia, while the other fault breccia, further from the surface rupture zone, contains the paramagnetic minerals. The possible magnetic change is attributed to newly-formed magnetite from paramagnetic minerals at high temperatures (>500°C) during the large earthquake, implying that the YBF has ever experienced high-temperature thermal pressurization earthquake slip dynamics. Moreover, the YBF has also experienced high-temperature frictional melting earthquake slip dynamics, constrained by the multiple vein pseudotachylite. These high-temperature earthquake slip processes may be responsible for the high dip angle thrust characteristic of the YBF.

Magnetic parameters indicate the intensity of chemical weathering developed on igneous rocks in China

Continental weathering plays a key role in earth surface processes by linking Earth's spheres and producing material for cycling. Previous studies have proposed numerous weathering indices for the evaluation of chemical weathering intensity. However, few research efforts are devoted to the changes of sediment physical properties during weathering processes and on the correlations between weathering and mineralogical/chemical alteration. This study investigates mineral transformation and magnetic properties of two weathering profiles developed on granodiorite and basalt in China. The notable differences in magnetic properties between the two profiles, i.e., magnetic susceptibility (χ), percentage frequency-dependent susceptibility (χfd%), anhysteretic remanent magnetization (χARM) and saturation isothermal remnant magnetization (SIRM), are ascribed to the combined effects of parent rock lithology and climate conditions on the formation and alteration of magnetic components during weathering/pedogenesis. Parent rock lithology (e.g., Fe-bearing basalts and relatively Fe-poor granites) determines the initial magnetic susceptibilities. Warm and humid climate favors rock weathering and thus enhances the magnetic intensity, whereas changes in redox conditions lead to inhomogeneous degree of chemical weathering, and thus alter the spatial distribution of magnetic minerals. This study further suggests that the weathering intensity in geologic profiles can be evaluated by magnetic indicators such as χfd% and χARM/SIRM based on their positive correlations with the chemical index of alteration (CIA). The research findings may shed new light on the constraints on continental weathering and detrital sediment cycling in the East Asian continental margin.

Paleo-environment and flooding of the Limpopo River-plain, Mozambique, between c. AD 1200–2000

Multi-proxy analysis was performed on a radiocarbon-dated core, collected from a relic oxbow lake in the Limpopo River-plain, Mozambique, with the aim to reconstruct paleo-environment and past flooding of the lower river system over the past c. 800years. An additional objective was to evaluate and investigate the potential use of different proxies as recorders of paleo-flooding events and paleo-environmental variability within the floodplain. The proxies applied in this study were: mineral magnetic properties, grain-size distribution, organic carbon content and diatom microfossil assemblages. We found that sediment grain-size and mineral magnetic properties of the minerogenic fraction were the most sensitive proxies in terms of detecting signals from high-intensity river-discharge events. In the 800year long sequence, variations in sand content, magnetic susceptibility and saturation isothermal remnant magnetization suggest at least four major flooding events at the site during the reconstructed period; in the mid-1200, late-1300, mid-1500AD and during the last century. The diatom proxy reflects the development of the site from an open oxbow lake to a mainly terrestrial area. The diatom assemblage indicates that open lake conditions prevailed at the site between c. AD 1200–1400, with periodic inundation by marine water, most likely due to late Holocene sea-level changes. From c. AD 1400 and onwards, diatoms were rarely deposited at the site, which indicates drier conditions. This was a result of soil formation and gradual in-filling of the lake, a process which possibly was accentuated by a regionally dry climate situation. Our study shows that oxbow lakes and the proxies used here have great potential for reconstructing flooding events, a knowledge that is crucial for potential prediction and mitigation of flooding events in Mozambique in the future. Although chronological uncertainties limit comparisons to other paleo-environmental records, it seems that the flooding events recorded at our site occurred both during regionally wet and dry periods. Our data infer however, that flooding was probably more clearly recorded during the lake-stages than during infilled stage, probably as the terrestrial environment was more exposed to erosion.

Super spin dimensionality of a mono-dispersed and densely packed magnetic nanoparticle system

The dynamics of a dense near mono-dispersed assembly of maghemite nanoparticles is investigated by measurements of the temperature dependence of the isothermal remnant magnetization induced by temporal application of weak magnetic fields at constant temperature. The results suggest that the dimensionality of the super spins of the particles is of Heisenberg character at high temperatures but crossover to become Ising like at lower temperatures.