Low-field Magnetic Susceptibility Research Articles

Hayabusa 2 returned samples reveal a weak to null magnetic field during aqueous alteration of Ryugu's parent body

The JAXA Hayabusa 2 mission returned 5.4 g of material from the C-type asteroid Ryugu. The Mn-Cr ages of dolomite in the returned samples indicate that Ryugu's parent body experienced aqueous alteration sometimes between <1.8 and 6.8 Myr after CAI formation. Because this time range overlaps with the lifetime of the solar nebula, we investigate the possibility that magnetite and pyrrhotite, which are aqueous alteration products found in Ryugu samples, acquired a remanent magnetization reflecting the nebula field intensity. We analyze the intrinsic magnetic properties and paleomagnetic record of three Ryugu samples of 0.82, 0.97 and 21.87 mg. None of the samples exhibit a stable natural remanent magnetization. This indicates that the aqueous alteration of Ryugu's parent body took place either in a field of a few µT, or in a very weak to null field. In the former scenario, the solar nebula field is the most likely magnetizing field, implying that aqueous alteration occurred before its dissipation, i.e., before ∼5 Myr after CAI formation. In the latter scenario, aqueous alteration must have occurred either after the dissipation of the nebula, or at an earlier epoch and a large heliocentric distance (> 5 au). The similarities between Ryugu samples and CI chondrites favor this second hypothesis. Our results contrast with another paleomagnetic study of two Ryugu samples, arguing for a paleofield intensity of 40 to 390 µT. Our interpretation of this discrepancy is that these samples were exposed to artificial magnetic fields (> mT) during preceding experiments. This highlights the importance of conducting, as much as possible, the paleomagnetic investigations of returned samples before any other experiment. We also demonstrate that the ratio of NRM over low-field magnetic susceptibility is a powerful, non-destructive indicator of magnetic contamination. We recommend measuring this ratio routinely before paleomagnetic investigations of meteorites and returned samples.

Emplacement of the paleoproterozoic Itareru tonalite (NE São Francisco Craton, Brazil) during arc-continent collision revealed by magnetic fabrics

The Itareru tonalite is one of the Paleoproterozoic plutonic rock units that intruded the Serrinha block, an Archean-Paleoproterozoic crustal fragment of the São Francisco Craton (Bahia, Brazil). It is characterized by a ca. 80 km long, NW-SE elongated leaf-shaped body, mainly comprised of tonalite-diorite to granodiorite rocks with numerous dioritic enclaves. Magnetic studies were performed on 26 sites of the Itareru pluton (including country rocks). Anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM) are coaxial, indicating that all minerals have the same orientation, partially controlled by regional strain. Rock-magnetism measurements reveal that paramagnetic–matrix minerals contributed significantly to the magnetic susceptibility and AMS while magnetite grains in the range of 2–5 μm are responsible for AARM. Magnetic fabrics in the central region of the pluton are probably primary (magmatic), which was acquired when the rocks were crystallized, reflecting magma flow linked to a magma feeder zone (magma chamber). The moderated magnetic lineation plunges in the northern part of the pluton suggest that this region was close to the feeder zone. In contrast, the southern region should be far from it, since the magnetic lineations are horizontal to sub-horizontal. The Itareru tonalite emplacement was also controlled by regional strains related to the collision of the Paleoproterozoic Rio Itapicuru greenstone Belt with the Archean basement.

Magnetic and Geochemical Properties of Zagreb City Area Soils

This study was performed to derive the first insight into the distribution of low-field volume magnetic susceptibility (MS) throughout Zagreb city, based on in situ field measurements. The most interesting locations were selected for soil sampling and their geochemical contents were determined using ICP-OES. A geostatistical approach was applied to the MS and geochemical results. A median of 0.245 × 10−3 SI units was proposed as the average MS value in Zagreb. The mean concentrations of heavy metals in Zagreb’s soils (in µg/g) are Pb (36.82), Zn (87.77), Cu (30.84), Cd (0.66), Cr (29.04), Co (11.89), and Ni (28.40), and these measurements are relatively low in comparison to the Croatian legislation and the European and world average. Boxplot analyses demonstrate that 45% of the studied elements do not feature any anomalies, while most of the remaining elements indicate only one weak anomaly located at the same site as the MS anomalies. Our statistical analysis found significant correlations between MS and the following elements: Cd, Co, Fe, Mn, Na, Pb, Sb, and Zn. In situ MS measurements proved to be an efficient tool for the initial screening of large areas with elevated concentrations of heavy elements, enabling the cheap and fast assessment of the state of the environment.

The Variations of Clinker Superparamagnetic Value from PT. Semen Padang by Using a Bartington Magnetic Susceptibility Meter Sensor Type B

Clinker is a significant material in the cement manufacturing process. Before clinker formation, the raw material is burned in a Rotary Kiln with a temperature of up to 1450℃. After that, it is cooled in a Greet Cooler to a temperature of 100℃ and produces clinker. During the clinker manufacturing process, always being test on samples, but there has been no test based on magnetic susceptibility. The purpose of this research is to know the variation of the superparamagnetic clinker value based on the magnetic susceptibility value. The method used is the rock magnetism method using a Bartington Magnetic Susceptibility Meter MS2B Type. A sampling of clinker is taken hourly every day from PT. Padang Cement. From the value of magnetic susceptibility based on low-field magnetic susceptibility , it was obtained that the values ​​varied from 3.2 × 10-8m3/kg to 22.6 ×10-8m3/kg. The frequency of dependents is also diverse, ranging from 0.0% to 7.4%. Based on the obtained, the type of grain produced also varies. 136 samples of clinker containing less than 10% superparamagnetic grains, and 32 samples belonging to Medium have a percentage of 2%-10% where the sample comprises superparamagnetic grains. Between 10% and 75% is a mixture of fine and coarse superparamagnetic grains.

Is biomagnetic leaf monitoring still an effective method for monitoring the heavy metal pollution of atmospheric particulate matter in clean cities?

The development of a reasonable method for predicting heavy metals (HMs) pollution in atmospheric particulate matter (PM) remains challenging. This paper presents an elution-filtration method to collect PM from the surface of Osmanthus fragrans in a very clean area (Guiyang, China). The aim is to evaluate the effectiveness of biomagnetic leaf monitoring as a simple and rapid method for assessing HMs pollution in clean cities. For this purpose, we determined the magnetic parameters and concentrations of selected HMs in PM samples to investigate their relationships. The results showed that the magnetic minerals in PM samples were mainly low coercivity ferrimagnetic minerals, with a small amount of high coercivity minerals. The types of magnetic minerals were generally single, and the magnetic domain state was pseudo-single domain (PSD). There was a significant correlation between magnetic parameters and the heavy metal (HM) concentrations in PM. Low-field magnetic susceptibility (χ) could be used as an ideal proxy for determining anthropogenic HM pollution. Traffic emissions were the main atmospheric pollution source in urban Guiyang. Due to the incomplete traffic network and large traffic flow, traffic congestion (TC) often occurred at road intersections in the northwest and southwest corners of the city, resulting in the highest concentration of magnetic minerals and the most severe PM pollution. To mitigate atmospheric PM pollution and protect public health, it is strongly recommended that municipal authorities prioritize urban planning and traffic management to address TC. Measures should be implemented urgently to alleviate stop-and-go traffic.

Structural and magnetic properties of superconductive YFeSb1.2 compound

The structural and magnetic analysis of the YFeSb[Formula: see text] compound synthesized by the solid-state reaction method was observed. At room temperature, the compound exhibits the ThCr2Si2-type structure with the space group of [Formula: see text]. Low-field DC magnetic susceptibility property of the YFeSb[Formula: see text] compound has been examined. An obvious oscillation of the remanent magnetization, [Formula: see text] with temperature was observed. The YFeSb[Formula: see text] compound exhibits large irreversibility at low fields below the coercivity fields due to freezing spins at low temperatures. At higher temperatures, the susceptibility obeys perfectly to modified Curie–Weiss behavior. Each magnetic ion on a microscopic scale and each magnetic cluster on a nanoscale experience reveal a local random anisotropy.

Magnetic Behavior of Trigonal (Bi-)pyramidal 3d8 Mononuclear Nanomagnets: The Case of [Ni(MDABCO)2Cl3]ClO4.

This paper attempts to shed light on the origin of the magnetic behavior specific to trigonal bi- and pyramidal 3d8 mono- and polynuclear nanomagnets. The focus lies on entirely unraveling the system's intrinsic microscopic mechanisms and fundamental quantum mechanical relations governing the underlying electron dynamics. To this end, we develop a self-consistent approach to characterize, in great detail, all electron correlations and the ensuing fine structure of the energy spectra of a broad class of 3d8 systems. The mathematical framework is based on the multiconfigurational self-consistent field method and is devised to account for prospective quantum mechanical constraints that may confine the electron orbital dynamics while preserving the properties of all measurable quantities. We successfully characterize the experimentally observed magnetic anisotropy properties of a slightly distorted trigonal bipyramidal Ni2+ coordination complex, demonstrating that such compounds do not exhibit intrinsic huge zero-field splitting and inherent giant magnetic anisotropy. We reproduce qualitatively and quantitatively the behavior of the low-field magnetic susceptibility, magnetization, low-, and high-field electron paramagnetic resonance spectroscopy measurements and provide an in-depth analysis of the obtained results.

Initial results of the colorimetric indices of the oldest exposed pedocomplex (Titel loess plateau, Serbia)

n this study we present an in-depth description of the colorimetric values for the lowest section of the Dukatar Loess Palaeosol Sequence (LPS) pedocomplex S5. Formed during the Marine Isotope Stage (MIS) 13-15, it represents the oldest pedocomplex exposed at the base of the Titel loess plateau (TLP), near the confluence of the Tisa and Danube rivers in Vojvodina (northern Serbia). The results of low-field magnetic susceptibility measurements (χlf) were compared to colour properties (obtained by conventional methods as well as instrumental measuring) and quantified Soil Development Indices (SDI). Of these measurements we found that the Redness Index (RI1) yielded the most useful results, as this index appears most sensitive to lithological changes and soil development intensity. It was also observed that a high level of correlation existed between χlf, and a* chromaticity. The initial results of this study highlight the utility of colorimetric methods as an interdisciplinary tool when evaluating the presence of ferromagnetics, and the application of rock magnetism to the Middle and Upper Pleistocene LPS of the Middle Danube Basin. The presented approach can be used to observe the evolution of climatic and ecological conditions in the given study area, and for establishing correlations between sites extending over the Eurasian LPS provinces.

Rock Magnetism and Magnetic Fabric Study of the Icelandite and Rhyodacite Long Volcanic Sequence at Mauna Kuwale, Wai’anae Volcano, Oahu, Hawaii, USA

In order to understand further the emplacement (i.e., volcanic growth) of 22 Icelandite and 3 Rhyodacite cooling units in one of the long volcanic sequences known as Mauna Kuwale of the Wai’anae volcano (ca. 3.3 Ma), Oahu Hawaii we have conducted appropriate rock magnetic experiments described below as well as anisotropy of magnetic susceptibility (AMS) studies of such 25 units. We have undertaken rock magnetic investigations such as continuous and partial thermo-magnetic cycles of low field magnetic susceptibility versus temperature dependence, (k-T) curves experiments. We classified the k-T heating-cooling dependence of susceptibility in three groups A, B and C. Type A: yielded two components of titano-magnetite with a predominat Ti rich phase and occasionally a relevant magnetite component phase. Type B: samples are characterized by Ti poor magnetites. Magnetite dominates as the main magnetic carrier. Type C: k-T curves show one single phase of titanomagnetite, and Ti poor magnetite. The coercivity or remanence, determined by back field magnetization is always &lt;60 mT, which suggest the predominance of magnetic components of low coercivity, like magnetite. Usually, two coercivity components are identified in the specimens. In addition we also conducted magnetic granulometry analyses on 27 specimens to determine the domain state of the flows. The ratio of hysteresis parameters (Mr/Mrs versus Hcr/Hc) show that overall samples fall in the Pseudo-Single Domain (PSD) region with high values of Mr/Mrs and very low values of Hcr/Hc. Only two samples from cooling units 17 and specially 22 show a Single Domain (SD) magnetic behavior and a sample from one unit approaches the SD-MD mixture region. We measured the magnetic susceptibility of all cooling units and we found out that in all analyzed units the magnetic susceptibility is low 13.7 ± 8.8 (10−3 SI). Magnetic anisotropy/magnetic fabric is used as a tool in rock fabric analyses to investigate the preferred orientation of magnetic minerals in rocks. Magnetic anisotropy is low on all (measured) flows from the Icelandite cooling units from 1 to 17 (mean P’ = 1.010), but becomes noticeably distinct and high in rhyodacite cooling units 23, 24 and 25 (mean P’ = 1.074). Four units show a magnetic fabric with k3 axes vertical to sub-vertical which may be denoted as normal for the horizontal to sub horizontal units. Two Icelandite cooling units display oblate shapes and two other cooling units triaxial shapes. K1 axes are horizontal but point in different directions, i.e., NE and NW. Remaining cooling units show different magnetic fabric. Units 17, 23, 24 and 25, despite important variations in anisotropy (low for units 25 and high for units 23 and 24) and shape of ellipsoid (oblate in cooling unit 23, prolate in 24 and triaxial in 25) the k3 axes show the same orientation, SW to SSW dipping around 45° and a very steady magnetic lineation azimuth NW nearly horizontal to sub horizontal. The magnetic mineralogy and magnetic fabric indicate that both the Icelandite and Rhyodacite cooling units the magmatic evolution during the shield stage of the entire Wai’anae volcano and that such growth was not affected by tectonic deformation.

Rapid Magnetic Susceptibility Characterization of Coastal Morphosedimentary Units at Two Insular Strandplains in Estonia

Coastal archives of changing hydrometeorological conditions include mineralogical anomalies, such as heavy-mineral concentrations (HMCs) of variable thickness and intensity, which contain varying ferrimagnetic (e.g., magnetite) fractions. As an effective alternative to laborious mineralogical and granulometric analysis, we present the first set of bulk-volume low-field magnetic susceptibility (MS) databases from beach and dune lithosomes in the Western Estonian archipelago: Harilaid cuspate foreland (westernmost Saaremaa Island) and Tahkuna strandplain (northernmost Hiiumaa Island). Readings were conducted both in situ from trench walls and on core subsamples. At the Tahkuna site, late Holocene beach ridges reveal substantially lower values: quartz-dominated dune sequences grade from 5–20 μSI downward to diamagnetically dominated (−1–7 μSI) beach facies. Values are higher (20–140 μSI) in historically reactivated parabolic dunes that are encroaching southward over the strandplain. At the Harilaid site, four beach dune ridges (height: 2–3 m) that span the past 250–300 years show a general increase in mean MS from 320–850 μSI with decreasing age, with peaks of 1000–2000 μSI below the dune crests (depth: ~0.3–0.6 m) likely related to contemporary wind acceleration during ridge aggradation. The highest mineralogical anomalies range from 2000–5500 μSI in the historic dune sections and exceed 8000 μSI along the actively eroding upper-berm segments, typical of HMCs generated by moderate storms. MS anomalies are likely correlated with high-amplitude electromagnetic signal responses in georadar records and provide useful information for optical luminescence sampling strategies. Our study demonstrates that magnetic susceptibility trends provide a useful means of rapidly assessing relative temporal changes in overall wave/wind climates, help identify and correlate discrete anomalies related to extreme events, serve as local beach/dune boundary indicators, and represent potentially quantifiable paleo-energy indices.

Diverse erosional indicators along a rapidly retreating Holocene strandplain margin, leeward Hiiumaa Island, Estonia

A diverse suite of erosional features along the shoreline of Lehtma (Hiiumaa Island, Estonia) is used to assess their morphodynamic context and preservation potential. The Holocene strandplain along the east-facing (leeward) shoreline has experienced rapid retreat due to the anthropogenically induced sediment deficit. The study site is located just updrift of the erosional-depositional fulcrum segment, with southerly longshore transport resulting in the accumulation of eroded sand along a drift-aligned spit. The most prominent erosional indicators are mature pine trees in different stages of undercutting, toppling, fragmentation, and burial. Morphological features include scarps in paleo-beach/dune ridges (height: &gt; 1 m), as well as modern berm scarps. Mineralogical indicators are exemplified by heavy-mineral concentrations (HMCs) of variable thickness (some &gt; 2 cm) and concentration. Representative samples show a substantial increase in bulk low-field magnetic susceptibility ranging from &lt; 10 µSI common to the nearby Holocene coastal lithosomes to &gt; 8,000 µSI in second-cycle HMCs within berm enrichment zones. A conceptual morphosedimentary model describing the recent and current state of the system, as well as the preservation potential of specific structures and recognition in geological research (e.g., georadar signatures of buried trees and HMCs) is proposed. The approach presented in this study can be used to assess the distribution and preservation potential of erosional indicators along the Baltic Sea coast and mineralogically heterogeneous, forested sandy shorelines worldwide.

Rockmagnetic Characterization of the Quaternary Fluviolacustrine Sediments of the Thimi Section, Kathmandu Valley, Nepal

The fine-grained silt/clay sediments sampled at 38 levels of a 21 m thick segment at the Thimi outcrop in the Kathmandu valley have been studied for their rockmagnetic properties. These sediments have yielded consistently normal magnetic polarity and 14C ages determined by various workers between 20 and 45 kyrs or even more. They were measured for a set of rock magnetic parameters: low-field magnetic susceptibility, parameters derived from isothermal remanent magnetization (IRM) acquisition and demagnetisation (IRM0.3T, IRM3T, MDFIRM), anhysteretic remanent magnetization (ARM) (ARMtot, ARM(30 mT)/ARMtot, χARM), hysteresis parameters, etc. Several relationships between these parameters have been suggested for the Kathmandu valley sediments. Four rockmagnetic zones, based on the minor variations in magnetic mineral types and grain size parameters, are proposed and their possible relationship to the published pollen data has been discussed.

Fine Structure and the Huge Zero-Field Splitting in Ni2+ Complexes.

We perform a thorough study of the ground state magnetic properties of nickel-based 3d8 complexes. This includes an in-depth analysis of the contribution of the crystal field, spin exchange and spin-orbit interactions to the ground state magnetic properties. Of particular interest to the current investigation are the presence and occurrence of non-trivial zero-field splitting. The study focuses on the cases of Ni2+ ideal octahedral, trigonal bipyramidal, square planar and tetrahedral geometries. We provide results for the complete energy spectrum, the fine structure related to the ground state and the second set of excited states, low-field magnetic susceptibility and magnetization. In addition, we examine the zero-field fine structure in square pyramidal, trigonal pyramidal and trigonal planar complexes. The obtained results unequivocally show that a moderate or highly coordinated 3d8 complex can neither exhibit spin-orbit-driven large and giant magnetic anisotropy nor a huge zero-field splitting. Moreover, in the trigonal bipyramidal coordination, a fine structure associated to the ground state cannot result from the spin-orbit coupling alone.

The magnetic susceptibility of Pleistocene paleosols as a martian paleoenvironment analog

This work aims to introduce and test various semiquantitative field methods and environmental magnetic measurements to help prepare future planetary missions on Mars. For analog observations, paleosols of loess successions in various stages of soil development were investigated and were used as models to infer environmental change during environmental change on early Mars. Methods commonly used in terrestrial soils and sediment environments, such as soil development indices and low field and frequency-dependent magnetic susceptibility, are introduced and evaluated as potential proxies to constrain paleoenvironmental conditions and climate change on Mars billions of years ago. These methods include the following: 1) low field magnetic susceptibility, which may aid in the identification of weathered horizons (e.g., palaeosols) and provide insight into the degree of weathering intensity; 2) frequency-dependent magnetic susceptibility can constrain nanoscale magnetic contributions, including some with possible biogenic/bacterial origin, but its applicability to indicate the degree of pedogenesis is limited; and 3) the vertical distribution of low field magnetic susceptibility, i.e., the pattern of magnetic susceptibility curves, seems to work well in the indication of the balance between the sedimentary and pedogenic environment. Analysis of magnetic susceptibility curves may contribute to the identification of Martian paleosols, the characterization of the transition period between the soil-forming and subsequent sedimentary periods (Noachian-Hesperian and Hesperian-Amazonian transitions) and the identification of climate cycles; thus, these may be used as a frame of reference for evaluating paleoclimatic changes on Mars to e.g., the Noachian warm Mars and”Snowball Mars” periods.The results also suggest that the time dependence of the magnetic enhancement of paleosols seems to be nonlinear compared to the length of the pedogenic period itself, and magnetic susceptibility may work as a relative chronometric parameter, which can help to constrain the duration of pedogenic alteration and soil formation on Mars.

A detailed magnetic record of Pleistocene climate and distal ash dispersal during the last 800 kyrs - The Suhia Kladenetz quarry loess-paleosol sequence near Pleven (Bulgaria)

Loess-paleosol sequences (LPS) from the Lower Danube area are valuable terrestrial archives of environmental change in SE Europe during the Pleistocene. A twenty-seven meters thick sequence has been sampled in Central North Bulgaria near the city of Pleven within the Suhia Kladenetz (SK) quarry. The sedimentary sequence consists of seven loess units and six interbedded paleosol complexes covering the last 800 kyrs. The continuous 2 cm resolution sampling depth interval enabled the recovery of several cryptotephras in addition to a ~ 20 cm thick tephra deposit observed in the field within the L2 loess unit. All cryptotephras are clearly identified in laboratory analyses by their strong magnetic signal, particularly well expressed by concentration – dependent anhysteretic susceptibility (χARM), isothermal remanence (IRM), low field magnetic susceptibility (χlf) and in some cases by frequency dependent magnetic susceptibility (Δχ), coercivity of remanence (BCR), and hard isothermal remanence (HIRM2.0–0.3T). Complementary optical and scanning electron microscope analyses of single grains from the tephra deposit and cryptotephra intervals reveal the presence of volcanogenic grains with smooth glassy surfaces and vesicular internal structure; fluidal grains with bulbous surfaces and dense irregular grains. Grain size sensitive magnetic ratios χARM/χlf, ARM/IRM100mT, IRM2T/χlf are not always discriminative, suggesting that (crypto)tephras do not have a single uniform source. Preliminary correlative age models are used to estimate ages for the (crypto)tephras and propose likely associated volcanic eruptions. Finally, strong pedogenic magnetic enhancement of the younger paleosols (S4, S3, S2 and partly S1) contrasts with the smeared and low magnetic signal of the older paleosols (S6 and S5). Moreover, an enhanced content of low-coercivity hematite observed from the upper part of the S5 paleosol upwards to the present and a sharp increase in the concentration of maghemite at the expense of magnetite observed for the S3, S2 and S1 paleosols provides strong evidence for a significant paleoenvironmental change. The timing of this change, based on the SK LPS age models, is compatible with the mid-Brunhes climate transition.

Sedimentary Rock Magnetic Response to Holocene Environmental Instability in the Pearl River Delta

Located on the northern coast of the South China Sea, the densely populated Pearl River Delta has experienced the combined effects of sea-level change, monsoon-driven discharge, and especially human activity, since the late Holocene. However, how these factors have regulated the regional environmental and sedimentary evolution remains unclear. To better understand these processes, we conducted a high-resolution rock magnetic investigation of the Holocene sediments of core DS01, drilled in the vicinity of the West River channel in the head area of the Pearl River deltaic plain. The magnetic grain-size proxy of the ARM/κlf ratio (the ratio of anhysteretic remanent magnetization to low-field magnetic susceptibility) indicates a long-term fining trend of the magnetite grain size, which may be a response to an increase in the weathering intensity in the Asian monsoon region during the Holocene. An interval with an enhanced concentration of magnetic minerals (mainly magnetite and hematite) occurred during 7.7–4.8 kyr BP (calendar years before 1950), coinciding with a period of delta progradation. During the marine transgression in the early Holocene, two similar intervals of magnetic enrichment may reflect regional hydrodynamic shifts associated with cooling events at ∼9.5–9.3 kyr BP and 8.2 kyr BP. The subsequent 4.2 kyr BP cooling event possibly induced a cold and dry environment in the sediment source area. From ∼800 yr BP onward, there was a major increase in the sedimentary magnetic mineral content, likely in response to intensified agricultural and industrial activities.

Magnetic Susceptibility of Volcanic Rocks from Pahae Julu Region, North Sumatera Province

Pahae Julu is a sub-district located in North Tapanuli Regency, North Sumatra. This area is often found with volcanic material from the eruption of Mount Toba (Youngest Toba Tuff). The Youngest Toba Tuff eruption occurred ~74,000 years ago with a volume of 2,800 km3. When there is an eruption, the lava on the earth's surface undergoes a relatively fast freezing process to form volcanic igneous rock. These rocks contain various minerals, one of which is magnetic minerals that can be used as a track record of volcanic processes from Mount Toba. However, no document records the magnetic susceptibility value of the Youngest Toba Tuff volcanic rock in the Pahae Julu area. This research aimsbfor knowing the abundance of magnetic minerals by the low-field magnetic susceptibility. To achieve this goal, the rock magnetism method is used. This way is very effective, cheap, sensitive, and non-destructive. Magnetic susceptibility measurements are done using the Bartington Magnetic Susceptibility Meter MS2B sensor. Rock samples analyzed are pumice which is the result of the Youngest Toba Tuff eruption. The results showed that the magnetic susceptibility value obtained for the sample was between 85.0 x 10-8m3/kg – 183.1 x 10-8m3/kg with an average of 119.78 x 10-8m3/kg. Based on this value, it is assumed that the magnetic mineral properties are Antiferromagnetic. The average value of χ fd% obtained is 0.95%, indicating that the Youngest Toba Tuff volcanic rock in the Pahae Julu area has almost no Superparamagnetic grains.

Long-term development archive of the Yellow River since the Neogene in the central Jinshaan Gorge, China

Formation and development of the middle Yellow River have been debated for a long time. In this study, we carried out detailed field investigation, sedimentological and stratigraphic analyses in the central Jinshaan Gorge area. Our field work reveals that six terraces have been well preserved in the central Jinshaan Gorge. Sedimentological features of the conglomerates on all terraces indicate that these terraces were abandoned by an ancient south-flowing river, that is, the Yellow River. Based on previous paleomagnetic study on the Weijiawa Red Clay section, the oldest conglomerate was abandoned 8.1 Ma and the Yellow River along the western piedmont of the Lüliang Mountain at least occurred at that time. Powder samples were collected from five aeolian sections and low field magnetic susceptibilities were measured in a bid to establish correlation with the known sections and constrain formation ages of the terraces. Our results demonstrate that the Yellow River had trenched a 3.5 km wide valley (T6) since it occurred in the Liulin area and then the river gradually incised 4 Ma which finally trenched another 5-km-wide paleovalley (T5). Aggradation in the 5-km-wide paleovalley initiated in the Pliocene under the control of climate and ceased in the early Pleistocene which resulted in deposition of the up to 58-m-thick conglomerate. Fluvial sediments on T2-T4 are directly covered by aeolian loess-paleosol sequence (LPS). The basal units of the LPSs on T2, T3 and T4 are S3, S14 and L21 based on field stratigraphic markers and magnetic susceptibilities. Formation ages of these three terraces are 0.34 Ma, 1.19 Ma and 1.5 Ma respectively in the light of the astronomical ages. Our analysis on the driving factors suggests that climate might play an important role in river evolution in the central Jinshaan Gorge.

Magnetic anisotropy of a sub-ophiolitic metamorphic sole (Mersin ophiolite, Turkey)

The Mersin ophiolite of southern Turkey is a well-exposed, Late Cretaceous, Neo-Tethyan supra-subduction zone ophiolite. It is underlain by metamorphic sole rocks inferred to have formed at the top of a down-going plate during subduction. These have a well-developed foliation and lineation observable in the field (defined by the preferred orientations of hornblende and plagioclase crystals). Here we present the first magnetic fabric data reported from the Mersin ophiolite with such settings. Anisotropy of low field magnetic susceptibility ellipsoids in sampled amphibolites have clustered, NW-plunging minimum principal axes representing poles to a SE-dipping magnetic foliation that aligns with the macroscopic metamorphic foliation plane seen in the field. Maximum AMS principal axes define a SE-plunging magnetic lineation that is parallel to the macroscopic metamorphic lineation. Oblate magnetic fabrics at specimen-level and an overall triaxial fabric at locality-level in these rocks are consistent with the development of the dominant metamorphic fabric by a combination of pure shear flattening and simple shearing during the formation and exhumation of the Mersin sole rocks. These observations are compatible with a recent tectonic model for the evolution of the ophiolite based on paleomagnetic data that invokes flattening and exhumation of the down-going slab in an incipient subduction zone during supra-subduction zone spreading.

Two-stage strike-slip faulting of the Altyn Tagh Fault revealed by magnetic fabrics in the Qaidam Basin

The timing and mechanism of the changes in the stress/strain field direction on the northeastern Tibetan Plateau are controversial, which limits our understanding of the tectonic evolution of the northeastern Tibetan Plateau and the Altyn Tagh Fault (ATF). Here, we conducted a detailed anisotropy of low-field magnetic susceptibility analysis of successive fluvial-lacustrine sediments deposited since the early Oligocene at Eboliang in the middle-western Qaidam Basin. Magnetic fabrics of the upper part (the Qigequan Formation) are predominantly considered to be primary sedimentary magnetic fabrics, while those of the lower-middle parts (the Shangganchaigou to Shizigou Formations) are mainly pre-folding, layer-parallel shortening induced embryonic tectonic fabrics. The magnetic lineation revealed ~50° successive clockwise rotations of the compressional strain orientations from nearly N-S to NE-SW in the middle-western Qaidam Basin during ~15–7 Ma. The nearly N-S compressional event is consistent with the generally N-S-directed India-Asia collision and thus was attributed to its far-field effects, whereas the post-mid-Miocene transition of ~50° clockwise rotations of the compressional strain orientations is consistent with the tectonic deformation in the basin interior. This transition lagged far behind that in the northern Qaidam marginal thrust belt (NQMTB), which began in the early Oligocene. The laterally diachronous transition in compressional strain orientation and deformations in the middle-western and northern Qaidam Basin were most likely due to the two-stage, sinistral strike-slip faulting of the ATF, with confined sinistral shear occurring along the ATF and partially transferred into the NQMTB during the early Oligocene to middle Miocene, while distributed sinistral shear occurred on the northeastern Tibetan Plateau beginning in the middle Miocene. A bidirectional propagation of compressional strain variation and tectonic deformation from the northern Qaidam Basin since the early Oligocene is proposed to reflect the tectonic evolution of the northeastern Tibetan Plateau.