GP21A-01
Hydromagnetic Dynamos in a Non-uniformly Stratified Spherical Shell
Magnetic fields in the universe are generated by a hydromagnetic dynamo which acts in a liquid part of their interiors. The geomagnetic field is generated similarly, i.e. by the Geodynamo action in the outer Earth's core. The outer Earth's core is probably non-uniformly stratified due to thermodynamic processes acting in this area. The most part of the outer Earth's core is unstably stratified, only very thin sublayer close to core-mantle boundary (CMB) is stratified stably. Similarly, the interiors of Giant planets are also non-uniformly stratified, especially the regions, in which the hydromagnetic dynamo action is situated. In these cases the hydromagnetic dynamo action is apparently influenced by non-uniform stratification. The numerical modelling of a hydromagnetic dynamo in a rotating non-uniformly stratified spherical shell using the control volume method is presented. Our results showed that the influence of a non-uniform stratification and viscosity to a hydromagnetic dynamo (the Geodynamo) action is slight. They are very similar to the case of an uniformly stratified spherical shell (this case will be presented for the parameters of the numerical dynamo benchmark). The generated magnetic fields are mostly dipole dominated. It is expected that the influence of a non-uniform stratification to a hydromagnetic dynamo (the Geodynamo) action will be strong in the study of turbulence.
GP21A-02
The Dipole and Cuadrupole Aproximation of the Earth Magnetic Field for Monitoring the Temporal Evolution
In the present work are compiled the coefficients of spherical harmonics analysis representing the dipole and cuadrupole aproximation of the Earth Magnetic Field, from 1550 to 2005 years. The temporal variation of each coefficient are approximately by a non linear function in the interval of study and then forecasting the values up to year 2100. The position of the excentric dipole aproximation and also the energy for the dipolar and cuadrupolar components and their relationship are evaluated. A conclusion is that the changes for the year 2100 will be a very important transition to a multipolar expression of the Earth Magnetic Field after year 2100. Will be possible that the South Atlantic Anomaly shows very low values for total magnetic intensity, and the energy of cuadrupole will be 14% of the dipole energy comparatively to the 5% in the year 2005.
GP21A-03
Ultrasensitive Geomagnetic Field Temporal Variations and its Relationship to Stress in the Earth's Crust: an Experiment in the Oaxaca Coast, Mexico.
We present the different assignments developed since June 2004 designed to set up an ultrasensitive
magnetometer (Supergrad) built by GEM Systems (Canada).
Several geomagnetic surveys, micro-surveys, regional profiles, and Declination-Inclination absolute
measurements were carried out, as well as magnetic diurnal variation recording during these tasks. The
objective was to reveal areas with a stable magnetic anisotropy inside the site of at least a 200m X 400m area, in
order to install three supergradiometer's high sensitivity potassium sensors. This project is undergoing in one of
the most seismogenic areas in Mexico: El Trapiche, San Francisco Cozoaltepec, in Santa Maria Tonameca
municipality (state of Oaxaca).
Different methods of measurement are assessed and a short base gradient method explained. Supersensitive
(50fT), potassium 3 sensor gradiometer is described and some field data presented.
In the up-to-date significant investments in Earthquake studies and especially in detection of Earthquake
precursors there is a lot of emotional and in general non-critical measurements of precursors. We are trying to
establish some kind of reference conditions for detection of precursors. For this purpose we are supported by the
Supergrad resolution (0.001 pT) and sampling rate (20 Hz). At the same time, a Geomagnetic data-base will be
achieved in order to examine the relationship between Earth crust stress and its influence in local geomagnetic
field.
http:www.geofisica.unam.mx
GP21A-04
New substorm index derived from high-resolution geomagnetic field data at low latitude and its comparison with real-time AE index
Geomagnetic field data with high time resolution (i.e., 1 second) become more popular recently. Using such high time resolution data, we can identify Pi2 pulsations which have a period of 40-150 s and an irregular waveform. It is generally accepted that Pi2 pulsations appear clearly in mid- or low-latitude ground station on the nightside in close connection with substorm onsets. Thus we can monitor substorm activity at any given time if we examine Pi2 activity at multiple geomagnetic observatories which distribute globally with longitudinal separation of ~120° or less. Here we propose a new index reflecting Pi2 wave power at low- and mid-latitude. This index is derived by wavelet analysis for geomagnetic field data obtained at three different longitudinal sectors, that is, the Asia, Europe, and North/Middle America sectors. Possible observatories are Kakioka, Teoloyucan, Iznik, and Füstenfeldbruck. We will make a comparison of substorm activity estimated from this new index and that from the AE index.
GP21A-05
A Small Autonomous Unmanned Aerial Vehicle, Ant-Plane 4, for aeromagnetic survey
Autonomous unmanned aerial vehicles (UAV) are expected to use in Antarctica for geophysical research due to economy and safety operations. We have developed the technology of small UAVwith autonomous navigation referred to GPS and onboard magnetometer, meteorolgical devices and digital camera under the Ant-Plane project. The UAV focuses on operation for use in the summer season at coastal area in Antarctica; higher temperature than -15C under calm wind. In case of Ant-Plane 4, it can fly continuously more than 500 km, probably more than 1000 km, although the flight in Antarcitca has not succeeded The UAV of FRP is pusher type drone consisting of 2.6m span and 2.0m length with 2-cycles and 2-cylinder 86cc gasoline engine (7.2 HP) navigated. The maximum takeoff weight is 25kg including 1kg of payload. Cruising distance 500 km at speed of 130 km/h using 10 litter of fuel. The UAV is controlled by radio telemeter within 5km from a ground station and autonomous navigation referred to GPS latitude and longitude, pitot tube speed and barometer altitude. The magnetometer system consists of a 3-component magneto-resistant magnetometer (MR) sensor (Honeywell HMR2300), GPS and data logger. Three components of magnetic field, latitude, longitude, altitude, the number of satellite and time are recorded every second during 6 hours. The sensitivity of the magnetometer is 7 nT and we use a total magnetic field intensity for magnetic analysis due to unknown direction of heading of the plane. We succeeded in long distant flight to 500km with magnetometer by Ant-Plane 4 collaborated with Geoscience Australia, in March 2006. The survey was performed in the area 10kmx10km at Kalgoorlie, Western Australia. The magnetic data are obtained from 41 courses (250m in interval) of EW direction. The altitude of the flight was 900m from sea level and 500m from the runway. MR-magnetometer sensor was installed at the tip of a FRP pipe of 1m length, and the pipe was fixed to the head of the plane in order to reduce the plane magnetization. After 4 hours 14 minutes from the takeoff, the 500km flight was accomplished and the magnetic data were stored in the data logger. The straight flight course was almost consistent with the way point course, but the course was drastically disturbed when the plane was turning. The resolution of magnetic field decreased to 30nT, when the plane flew to the tail wind. However, it is worse against the head wind. Obtained anomaly pattern was compared with the magnetic anomaly pattern published by Geoscience Australia. Both patterns were essentially consistent, although a part of pattern in the head wind flights was not resemble. Ant-Plane 4 flew up to 5700 m in altitude with aerosol counter, thermometer and hygrometer at northern part of Japan. A drastic change of temperature, humidity and particle number was observed at the inversion layer of atmosphere. Consequently we conclude that the small drone Ant-Plane 4 can be used for geophysical research. We are making effort to develop Ant-Plane for more simple assemblage and more easy operation.
GP21A-06
Magnetostratigraphy of the Neogene sediments of SW Uruguay
Preliminary results on the magnetostratigraphy of three Neogene formations from SW Uruguay are presented: Camacho, Raigón and Libertad, and a relative age from the record of reversions in the Earth's magnetic field polarity is proposed. The sediments outcrop in the SW region of Uruguay,and have been received attention due to their fossil contents. The oldest is the late Miocene-Pliocene Camacho Fm, of Huayquerian to Montehermosan affinities. A Pliocene-early Pleistocene age has been assigned to Raigón Fm, of Chapadmalalan affinities. The overlying Libertad Fm has been considered early-middle Pleistocene in age, and to have Marplatan-Ensenadan affinities. The lithology of this facies of Camacho Fm is identified by the presence of fine to very fine sandstones and is composed of silty-sandy and bioturbed silty deposits. The marine facies of this formation is rich in fossil content, as several invertebrate and vertebrate taxa are found. The upper Raigón Fm is formed by sandstones of varied grain size and includes lenses and levels of claystones and conglomerates. It shows the sedimentological features of a deep, pebble-rich braided fluvial system. The 383 vertebrate specimens found in the sandy facies and studied in a taphonomically-oriented study belong to 19 genera and 13 higher taxa. The bones are disarticulated, with smooth fractures and little weathered or abraded, which is congruent with a short time of contact, as observed in strong and sudden flows. The elements belong to the three Voorhies groups and fractured specimens are found along with well preserved materials, implying different taphonomical histories and reworking. The consequent inferred time averaging urges caution at using these remains for defining precise ages. The Libertad Fm, top of the sequence, is conformed by greenish clays, clayey fine sandstones, medium sized sandstones and conglomeratic levels, corresponding to deposits of continental origin under a semiarid climate, which allowed the accumulation of fine material through aeolic transport. Several genera of mammals have been found in that formation. Three localities were sampled; Mauricio, Arazatí and Kiyú. A reverse polarity was found for the specimens of the Camacho Fm sampled in the locality of Mauricio, assignable to the Gilbert magnetic zone. The sediments of Raigón Fm have normal polarity, both in those specimens from Mauricio and in those from Arazatí, interpreted as belonging to Gauss magnetic zone. The samples from Kiyú of Libertad Fm showed a reverse magnetic polarity, which we refer to Matuyama magnetic zone. However, in the samples of this Formation taken in the locality of Medina, a normal magnetic polarity was found, which suggests they correspond to Brunhes. The chronology is roughly compatible with that based on the fossil contents of those formations, although several details must be worked out.
GP21A-07
New Paleomagnetic Data for the Middle Cambrian and Middle Ordovician of the Siberian Platform: Llandeilian Magnetostratigraphy and new Evidence for Relative Rotations Between the Aldan and Anabar-Angara Blocks
Whether Siberia acted a s a coherent black throughout the Phanerozoic or whether significant rotations occurred in early Paleozoic times between the Anabar-Aldan and Angara blocks is still a matter of debate and it has argued repeatedly that differences in the Apparent Polar Wander Paths from both blocks result from incorrect correlations between sections from the two regions. Addressing this problem a detailed palaeomagnetic study combined with high resolution magnetostratigraphy was carried out on sedimentary sections of mid Cambrian and Llandeillian age along the rivers Lena, Maya, Kulumbe, and Stolbovaya, where a total of 150 oriented hand samples were collected. In addition, a section of llandeilian age was sampled near St. Petersburg, on the Russian Platform in order to obtain a magnetostratigraphic reference profile for further correlation. In all sections the material sampled are either redbeds or greyish, fine grained sediments. Stepwise thermal demagnetization experiments reveal a rather simple directional spectrum in almost all samples studied. after removal of recent magnetizations, and occasionally intermediate components of magnetization, a high temperature component is identified, either carried by magnetite and/or hematite. The resulting mean directions are of dual polarity, pointing either to the south (north) and up (down) as in the case of the Cambrian sections or more to the east (west) or southeast (northwest) and up (down) as in the case of the sections of Llandeilian age. However, no directions of normal polarity have been identified in the lower two thirds of the Llandeilo. Positive reversal and fold tests clearly demonstrate the primary character of these magnetizations. The resulting magnetostratigraphy has been used to unambiguously correlate the sections from Anabar-Angara and Aldan. As a result, we note significant differences in declination in the order of 20° between sections from both blocks which is indicative for early Paleozoic rotations and can be can be linked to the opening of the intervening, v-shaped Vilyui basin. The resulting Euler pole of rotation is located close to the northern shore of lake Baikal and is in good agreement with data from deep sounding seismic experiments which have been used for estimates of crustal thinning in the Vilyui basin.
GP21A-08
Paleomagnetism of paleoproterozoic mafic and felsic volcanic rocks of the Rio Negro- Juruena Province, Southwestern Amazonian Craton, Brazil
Several paleogeographic configurations for the Amazonian Craton have been suggested along its geological history. Paleomagnetic tests for suggested configurations are however restricted due to very sparce and low quality paleomagnetic data, especially for Paleoproterozoic. In an attempt to improve our understanding of the geodynamic evolution, a paleomagnetic study was performed on felsic volcanic rocks of the Colider Suite, and associated mafic rocks in the Rio Negro-Juruena Province, southwestern Amazonian Craton. These rocks have well dated zircon U-Pb ages between 1.80-1.78 Ga. Very stable northern (southern) directions with moderate to steep negative (positive) inclinations were isolated during AF and thermal demagnetization. Rock magnetism experiments show that the magnetization, which is probably of primary origin, in the felsic rocks is carried by hematite and in the mafic rocks by Ti-poor titanomagnetite. A preliminary mean direction (D=187.4°, I=50.9°, N=16, A95=11.3°, K=11.7) yield a paleomagnetic pole located at 289.4°E, 65.4°S (A95=12.9°), which is classified with quality factor of Q=5. Paleogeographic reconstructions using key Paleoproterozoic poles suggest that Laurentia, Baltica, North China, and Amazonian Craton were located in laterally contiguous positions forming a large continental mass at 1.83-1.77 Ga ago.
GP21A-09
Paleomagnetism of Pleistocene Lava Flows in the Cascade Range Near McKenzie Bridge, Oregon
Paleomagnetic study of a sequence of dozens of basalt flows near Mackenzie Bridge, Oregon, was undertaken to investigate magnetic field behavior during a magnetic reversal. These basalt flows are believed to be of Pleistocene age and exhibit both normal and reversed polarities (Conrey, pers. comm.), suggesting that they may record the Matuyama-Brunhes magnetic reversal of about 780,000 years ago. In 2006, six flows were sampled and examined. Samples from each flow were demagnetized using stepwise alternating field (AF) demagnetization effectively erasing secondary magnetizations. A minimum of two samples from each site was also thermally demagnetized in a shielded oven for comparison with AF results and to help determine magnetic mineralogy. A mean direction for the six flows has a declination of 334.4° and an inclination of 65.8°. The Virtual Geomagnetic Pole (VGP) indicated by these results shows a latitude of 71.9° and a longitude of 169.7°, located in eastern Siberia. Results are similar to results from two studies performed on 24 flows lying atop these 6 flows (LeValley and Valentine, 2005; White and Valentine, 2005). These data suggest three possible conclusions. First, the upper flows of this sequence of basalts erupted during a narrow window of time and do not adequately average paleosecular variation, indicating the pole was stagnant at this location during eruption. Second, that counter clockwise rotation has occurred since formation, affecting declination but not inclination. Finally, that these flows do depict a portion of a reversal, and that the location of VGPs in Siberia is in accord with models for Siberian preferred paths and patches for poles during reversals. It is hoped that examination of numerous flows underlying those already sampled will help resolve which of these possibilities is most plausible.
GP21A-10
Palaeomagnetic and AMS Study of the Tarfaya Coastal Basin (Morocco): a new Cenomanian/Turonian (~94 Ma) Paleopole for the African Plate
The Cenomanian/Turonian oceanic anoxic event (OAE2) is a transgressive phase that is registered as a cyclic marine sedimentation in the outcrops from the Tarfaya coastal basin. Very high sedimentation rates (av. 5-10 cm/ka) enables the investigation of past geomagnetic field record at high temporal resolution. With the aim of studying the magnetic signature of these key sediments, 114 samples have been sampled along a 15m vertical profile (approximately 150-300 ka) of orbital-scale forced sedimentation. Rock magnetic investigations reveal mineralogy principally controlled by the diamagnetic and paramagnetic matrix, along with very low concentrations of low coercivity, ferromagnetic material which is probably an iron sulphide. Anisotropy of magnetic susceptibility is dominated by the dia-/para-magnetic matrix. A well-defined fabric can be seen with the minimum susceptibility axis perpendicular to the foliation plane, and the magnetic lineation oriented NNW-SSE. The magnetic lineation, rotated to the position of Africa in the late Cretaceous, is compatible with extension associated with the opening of the proto-North Atlantic Ocean and/or the paleocurrent associated with the upwelling system deposition that occurred during the late Cenomanian/early Turonian marine transgression. Thermal and Alternating Field demagnetizations of the marine samples from Tarfaya Basin show a single, stable, low coercivity and low unblocking temperature directional component. Some intervals of reversal polarity have been found (apparently without a lithological control), suggesting the record of very short reversal polarities events (even assuming an "early" diagenetic remanence blocking in the entire section), though contradictory magnetic interactions related to iron-sulphide ferromagnetic minerals can't be excluded. The new paleopole obtained in this African craton platform, 94 Ma ago, confirm the Late Cretaceous segment of the synthetic Apparent Polar Wander path proposed for Africa (BC02).
GP21A-11
Magnetic signature of the Yamato 000593/749/802 paired nakhlites
Yamato 000593 consists of coarse-grained clinopyroxene and augite associated with olivine and minor amounts of Ti-rich magnetite and was classified as a typical nakhlite (Imae et al., 2002). The 87Rb/86Sr age was obtained to 1269±240 Ma by (Nakamura et al., 2002). Yamato 000749 and 000802 are most probably paired with Yamato 0000593. Here we give an overview of the magnetic signature and the NRM carriers of these Martian meteorites. The NRM intensities of 3 samples of Y000593 were between 4.02E-5 and 6.07E-5 Am2/kg. One of the samples having the direction of I=40 and D=215 was cut into 3 oriented subsamples. The directions of the subsamples were scattered to I=-53 and D=113 with α95=57 which is inconsistent with their parents. A subsample was demagnetized by AF field up to 100 mT in steps of 5 mT. The AF demagnetization of the NRM intensity showed a decreasing curve with zigzag variation. The direction has relatively smooth change to 30 mT, while it changed drastically between 30 and 100 mT. Thermal demagnetization of the NRM under vacuumed condition revealed a quick demagnetization of the intensity below 80C, a clearly defined NRM blocking temperature between 280 and 330C and a small directional shift to one direction was observed. The unblocking temperature may be consistent with a monoclinic pyrrhotite Curie point. Although the small intensity variation with a convex curve appeared between 330 and 630C, it may be insignificant due to the large variation of directions. The temperature dependence of HC (6.8 mT) revealed that the coercivity reached almost zero at 550C in the heating curve. A polished surface was prepared for the observations by reflected right microscope. Larger euhedral magnetite grains up to 300μm in diameter with ilmenite exsolution lamellae and elongated-shaped magnetite grains of about one micron appeared in olivine. Small amounts of sulfide grains less than 50μm in diameter were included. When magnetotactic bacteria were applied to the surface compulsively magnetized by IRM, the bacteria made strong clusters on the magnetite grains and small ones on the sulfide grains. Imae et al. (2002) described magnetite grains with ilmenite exsolution lamellae and small amount of pyrrhotite grains. Mikouchi et al. (2003) introduced symplectic inclusions composed of magnetite (less than a few μm) and augite in olivine grains. In the thermomagnetic analysis, pure magnetite and/or low Ti-magnetite are dominating magnetic minerals. The moderate coercivity of HC=6.8 mT seems to be carried by exsolution lamellae in larger magnetite grains. Iron sulfide is confirmed to be monoclinic ferrimagnetic pyrrhotite due to the forming of clusters of magnetotactic bacteria. The NRM was thermally demagnetized between 280 and 330C which consists with a blocking temperature of monoclinic pyrrhotite. Probably MD grains low-Ti magnetite might acquire IRM and/or VRM (demagnetized before 30 mT) in the terrestrial magnetic field. Fritz et al. (2005) estimated the peak pressure above 40 GPa in nakhlites including Yamato nakhlites. This pressure is one order larger than a high-pressure transformation of monoclinic pyrrhotite (Rochette et al., 2003), providing an explanation for the missing magnetic anomalies on all known impact craters in the Mars crust.
GP21A-12
Thermal Fluctuation Tomography: Analysis of Single-Domain Grain Populations
In Néel's thermal-activation theory for the magnetization of single-domain grains, the thermal fluctuation field varies strongly with temperature T and with particle volume V. Thermal fluctuation tomography uses this relationship to calculate the joint distribution f(V,Hk0) of particle volumes and microcoercivities from backfield remanence curves measured over a range of temperatures. We have previously applied the method to shape-anisotropy-dominated nanoparticle populations that span the boundary between the superparamagnetic and stable-single-domain states at room temperature, using low-temperature backfield data sets. Here we extend the approach to larger single-domain populations that are thermally stable at room temperature, using new data sets for different strains of magnetotactic bacteria and for the Tiva Canyon Tuff, measured both below and above room temperature. We address some of the issues that become increasingly important with larger particle sizes, including incoherent reversal modes and alteration related to the required high-temperature measurements. We also apply thermal fluctuation tomography to characterize materials in which the anisotropy is dominantly magnetocrystalline rather than shape-controlled, for example the monoclinic magnetite polymorph at temperatures below the Verwey transition.
GP21A-13
Compositional, thermal, and orientation dependency of olivine magnetic properties
Olivine is an orthosilicate solid solution between forsterite Mg2SiO4 (Fo100) and fayalite Fe2SiO4 (Fo0). Cations such as Si4+ and Mg2+ are responsible for the diamagnetic behavior, whereas Fe2+ and other cations, present as defects in the lattice, such as Fe3+, Cr2+, and Mn2+, contributes to the paramagnetic behavior of the olivine. Yet, most natural and even synthetic olivines contain ferromagnetic iron oxide exsolutions similar to those commonly reported in other mafic silicates. Olivine is one of the most abundant constituents in the upper mantle of rocky planets, in meteorites, and in cosmic dust. Olivines with composition ranging form Fo100 to Fo0 are then exposed to temperatures that vary widely from about 5 K, away from the Sun in space, to about 1773 K at the 410 km olivine-wadsleyite transition. Below the Néel temperature (TN< 65 K), natural and synthetic fayalites exhibit a magnetic transition interpreted as the change from paramagnetic to antiferromagnetic behavior. A second low-temperature transition has been described around 20 K in fayalite and was attributed to a change from collinear to canted antiferromagnetic state. The magnetic properties of fayalite are also varying with crystal orientation. At decreasing temperature, just below TN, the magnetic susceptibility along the b axis stops following the Curie-Weiss law and begins to decrease. This drastic change is a clear indication of the antiferromagnetic behavior. The variation of magnetic susceptibility as a function of decreasing temperature along the two other axes, a and c, remains practically constant through the Néel transition. At the second low temperature transition (Tt), around 23 K, the variation of magnetic susceptibility with temperature changes along the c axis whereas no changes are noted along a and b. Experiments were performed on natural and synthetic ferromagnesian olivines of various iron contents between 4 and 300 K to further investigate their magnetic properties, regarding low-temperature transitions, compositional dependency, and magnetic anisotropy. Measurements were carried out in high magnetic fields, above the saturation of the ferromagnetic exsolutions to get access to the paramagnetic or diamagnetic properties of olivine.
GP21A-14
Magnetic Mineralogical Transformations in Experimental Fires and Implications to Archaeomagnetic Studies
It is well known that fire is a primary mechanism responsible for the magnetic enhancement experimented by iron minerals in soils. However, these mineralogical transformations involve complex processes highly dependent of factors like availability of pre-existing iron minerals, degree of heating, fuel employed or heat penetration with depth that strongly influence the final magnetic signal. We present here the results obtained from experimental fires conducted in the field with the objective to get a better understanding of the magnetic mineral transformations due to burning, emphasizing the direct implications for archaeomagnetism and archaeological research. During four days twice per day, a clay soil matrix was burned to temperatures ranging from 400ºC to 650ºC approximately. The temperatures were recorded with an array of thermocouples disposed along the surface and at different depths. Oriented and bulk samples were extracted before and after carrying out the heating in order to perform a complete set of magnetic mineral analyses. Both thermal and alternating field demagnetization were performed as well as several rock-magnetic measurements such as magnetic susceptibility, hysteresis cycles, Isothermal remanent magnetization (IRM) and backfield curves (± 2T), FORCS, Thermomagnetic curves and the analyses of the IRM coercivity components. We conclude that burning produce the reduction of a weak antiferromagnetic mineral (hematite) to a strong ferrimagnetic phase (magnetite). Mineralogical changes are focused to a limited depth (approx. up to 5 cm) but are particularly effective in the first 2-3 cm. where single-domain magnetite is noticeable. The record of p-TRMs and TRMs is a valuable tool in the identification of fires in archaeological contexts, but the changes in composition, concentration and granulometry of magnetic minerals can be also used as effective criterion in the study of fire. Understanding these processes and their effects is decisive in order to carry out archaeomagnetic analyses on fired archaeological materials.
GP21A-15
Mexico City Top Soils Magnetic Properties and Geochemical Characteristics as Pollution Indicators
Metal pollution of soils by human activities is one of the greatest environmental problems, and Mexico City urban area is not the exception. The geochemical methods are widely employed, but they are expensive and time consuming. The correlation between the magnetic minerals contents and the pollutants allow employing rock magnetism methods to determine the rate and spatial variations of them. We collected more than 120 samples from roadways and parks covering an area of 160 km2. Magnetic measurements were carried out on routine magnetic parameters, including low frequency mass magnetic susceptibility (χ), frequency dependence susceptibility (χfd) , anhysteretic remanent magnetization (ARM) and isothermal remanent magnetization (IRM). Correlation factors between χ and several metals were obtained. With Pb the correlations factors are the highest. Intermediate values were obtained with Al2O3, Na2O, Sr, Ba, Cu, Zn and Cr+Ni. The lower factors have been obtained with MgO, CaO, K2O, P2O5, Zr, and V. The values of χ are ranging between 49 and 952 x 10-8 SI. Parameters from IRM, ARM and hysteresis loops were analyzed in order to distinguish pollution sources and to define better correlation factors between magnetic properties and geochemical contents.
GP21A-16
Magnetic Screening and Multivariate Techniques in Antarctic Soils, Marambio Station
Antarctic stations are an interesting and particular field for pollution research because of the small area of influence and the reduced number of sources. The present contribution constitutes one of the first studies of magnetic screening and heavy metal pollution on Antarctica (Marambio station, 64° 14'S; 56° 37'W), being a suitable method for contamination assessment in Antarctic areas. Among magnetic studies, magnetic susceptibility, anhysteric and isothermal remanent magnetisation and thermal studies were carried out. Magnetite-like carriers are especially dominant in samples collected near pollution sources. Among several heavy metals, lead and zinc are the main trace elements reaching high values, both are end products derived from fuel combustion and residues, solid waste and paints. The magnetic and heavy metal measurements, and related maps of this case study can be considered as a reference in the area for future work. The correlation results between magnetic and chemical variables show moderate relationships varying from 0.409 to 0.663. Moreover, canonical correlation analysis showed very good canonical correlations: R= 0.950. On the other hand, other multivariate techniques were studied in order to classify the data according to the degree of contamination, principal coordinates and discriminant analyses, as well as the comparison of several multivariate means were performed. Therefore, three groups were distinguished, which were well classified at a low margin of error and quite different from each other at a significant level: 0.01.