soil metal pollution from former zn pb mining assessed by geochemical and magnetic investigations case study of the bou caid area tissemsilt algeria former zinc and lead mines that have been operating for half a century are located in the massif of bou caid tissemsilt algeria hazardous heavy metals emitted from the mines are abundant in the surrounding soil and cause strong metal pollution in the region this paper investigates the extent of lead and zinc mine activity derived pollution by characterizing both magnetic and geochemical properties of samples collected in the vicinity of the mines the results of the magnetic study show the coexistence of magnetic minerals such as magnetite hematite and goethite analyses on surface soils and weathered rocks suggest that hematite and goethite have ore related lithogenic origins magnetic susceptibility shows a positive correlation with lead content when present in low to medium concentrations 500 mg kg at higher lead concentrations there is no correlation with magnetic susceptibility the relationship between magnetic susceptibility and zinc content is not straightforward these observations are explained by the higher affinity of pb to iron oxides at lower pollution levels and their preferential bonding to carbonates when pb and zn contents are extremely high as demonstrated by iavazzo et al j geochem explor 113 56 67 2012 in a study of former zn pb mine in morocco based on the general features of the spatial maps of field measured magnetic susceptibility mass specific magnetic susceptibility pb and zn contents it is concluded that field magnetic measurements provide a good qualitative proxy of pollution spread out of the mining galleries while laboratory measurements afford a more detailed investigation of the links between iron oxides and the main heavy metals in the ore

selective dissolution of magnetic iron oxides with the acid ammonium oxalate ferrous iron extraction technique ii natural loess and palaeosol samples summary chemical extraction techniques are being introduced into environmental magnetism studies to aid in the interpretation of magnetic climate proxies previous studies have shown that the acid ammonium oxalate ferrous iron aao fe 2 extraction technique can be used to selectively dissolve very fine grained magnetite and maghemite from synthetic samples here we present the results of a study of this extraction technique to serve as a tool for selective dissolution of pedogenic magnetic minerals from a loess palaeosol transect before and after extraction the samples were subjected to classic mineral magnetic methods measurement of low field susceptibility and hysteresis parameters as well as first order reversal curve analysis in addition acquisition curves of the isothermal remnant magnetization irm were fitted with logarithmic distributions these analyses showed the magnetic dominance of lowcoercivity magnetic minerals by subtracting the irm remaining after extraction from that before extraction the magnetic fraction that was dissolved could be characterized as well supplying extra information concerning the performance of the extraction technique the aao fe 2 method successfully dissolved the superparamagnetic and part of the singledomain material from the palaeosol samples in one extraction step repeating the extraction resulted in hardly any further changes to the magnetic content of the samples the magnetic characteristics of the loess samples remained stable throughout the extraction experiment the combination of the aao fe 2 extraction with mineral magnetic analysis has successfully identified the pedogenic contribution in our samples therefore variations in the lithogenic fraction potentially present in pedogenically enhanced intervals can be assessed improving the merit of mineral magnetic climate proxy parameters

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

influence of fluorine on the solubility of manganotantalite mnta2o6 and manganocolumbite mnnb2o6 in granitic melts an experimental study abstract solubility experiments of manganotantalite mnta 2 o 6 and manganocolumbite mnnb 2 o 6 were conducted under nearly fluid saturated conditions in synthetic haplogranitic hpg and natural granitic ng melts containing different amounts of fluorine at 800 to 1000 c and 200 mpa the experiments were carried out in cold seal pressure vessels at 800 c with water or ar as a pressure medium and in internally heated pressure vessels 1000 c with ar as a pressure medium the f contents vary from 0 to 11 43 wt in experiments using hpg melts and from 0 61 to 3 78 wt in experiments using ng melts additionally the ng melt contains minor amounts of p 2 o 5 0 44 to 0 64 wt in hpg melts alumina saturation index including mn asi mn 0 88 to 0 99 the solubility product values at 800 c yield log k sp ta and log k sp nb ranging from 3 36 0 10 to 2 92 0 10 mol kg and from 3 01 0 11 to 2 87 0 06 mol kg respectively in ng melts the log k sp ta and log k sp nb vary from 3 00 0 04 to 2 35 0 13 mol kg and from 2 83 0 06 to 2 67 0 18 mol kg at 800 c respectively the solubility products of both mnta 2 o 6 k sp ta and mnnb 2 o 6 k sp nb are not significantly affected by the f content for a given melt composition data are virtually identical within error the variation of the solubility products observed in this study is rather attributed to the changes in melt structure e g polymerization and in particular to the alumina saturation index by contrast there is no evidence for the formation of complexes associating f and nb and or ta our results also indicate that the structural changes caused by the incorporation of f in natural water rich silicate melts are not expected to significantly influence the maximum concentrations of nb and ta in granitic or pegmatitic melts coexisting with manganotantalite and manganocolumbite

a new chronology for the middle to late miocene continental record in spain abstract the first detailed chronology for the middle to late miocene continental record in spain is presented based on high resolution magnetostratigraphic data of mammal bearing sections which were studied in several basins calatayud daroca teruel valles penedes duero and jucar cabriel our results indicate that these sections compose an almost complete magnetostratigraphic succession from the lower aragonian mn4 to the middle turolian mn12 seven successive mammal neogene mn zone boundaries are directly dated in these sections which often contain faunas of two successive zones in superposition the three oldest boundaries are dated in the aragonian type area calatayud daroca basin the mn4 mn5 boundary vargas section occurs in chron c5cr o with a corresponding age of 17 26 0 01 ma the mn5 mn6 boundary aragon section in chron c5acn 0 8 with an age of 13 75 0 03 ma and the mn6 mn7 8 boundary aragon section in the interval c5ar 1n c5ar 3r with an age of 12 75 0 25 ma the mn7 8 mn9 aragonian vallesian boundary occurring in chron c5r 1n at 11 1 ma and the mn9 mn10 boundary in chron c4ar 3r at 9 7 0 1 ma are recorded in the valles penedes basin vallesian type area and are supported by the results from the duero basin torremormojon section in the turolian type area teruel basin the mn10 mn11 vallesian turolian boundary la gloria section occurs in chron c4an y at 8 7 0 1 ma taking into account the pre existing data from the jucar cabriel basin the mn11 mn12 boundary cabriel valley section is recalibrated to c4n 1n at an age of 7 5 0 1 ma

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

zoning in columbite tantalite crystals from the granitic pegmatites of the erajarvi area southern finland abstract electron microprobe analyses of zoned columbite tantalite crystals from the granitic pegmatites of the erajarvi area in orivesi southern finland indicate wide compositional variation within the series fenb2o6 feta2o6 mnnb2o6 mnta2o6 especially in specimens from thin pegmatite dikes most crystals show gentle progressive zoning characterized by small scale variations in the major elements where the compositional variation is large backscattered electron images indicate oscillatory or patchy zoning or various replacement textures the zones in oscillatory zoned crystals are usually 1 50 m in width exceptions reaching 50 120 m the wider zones often consist of a group of very narrow subzones of only slightly different composition zoning is due mainly to the compositional variation in ta and nb in two of these crystals the oscillations in mn follow the strongest oscillations in nb content patchy zoned crystals exhibit corroded cores of early columbite tantalite surrounded by later zones enriched in ta the mottled appearance of such crystals results from two or more successive replacements replacement tongues or network like replacement textures are typical in the rims of some crystals the zoning of the columbite tantalite is related to the complex crystallization history of the pegmatite dikes the main factors controlling oscillatory zoning are considered to be the growth dynamics of the crystals the concentration and diffusion of the main elements and the successive flows of the magma in an intrusion channel the generation of a corrosive supercritical vapor phase at the end of magmatic crystallization caused resorption patchy zoning and the replacement of the columbite tantalite

paleomagnetism of the moenkopi formation colorado plateau basis for long term model of acquisition of chemical remanent magnetism in red beds paleomagnetic studies of moenkopi samples from several sites on the colorado plateau including a complete 427 m section at sinbad valley western colorado reveal the following 1 the presence of both normal and reversed triassic components in many of the same samples at many localities 2 the close correlation of the magnetic polarity and intensity of magnetic remanence with the lithologic characteristics in the sinbad valley section 3 a streaked pattern of the remanence directions in any one member in the sinbad valley section similar to that expected from polar wander 4 a lack of progressive change from the base upward and 5 the common intermediate remanence directions of weak intensity suggesting the presence of two or more nearly balanced anti parallel components throughout the formation the results of our investigation combined with previously reported petrographic and paleomagnetic studies of the moenkopi formation have led us to conclude that the principal remanence carried by the formation is chemical remanent magnetism crm acquired diagenetically over a geologically long time interval from the available data we have formulated the following model to explain how the crm was acquired through natural processes acting intermittently at geologically reasonable rates when initially deposited the moenkopi sediments consisted primarily of first cycle detritus containing a few percent of iron bearing accessory minerals such as biotite hornblende magnetite and ilmenite at some time after deposition under favorable subsurface conditions intrastratal alteration began involving breakdown of iron bearing silicate and oxide minerals partial replacement of some iron rich silicate grains by hematite martitization of magnetite growth of hematite pods and blebs in ilmenite and biotite and precipitation of crystalline hematite in both primary and secondary voids the authigenesis spanned at least two polarity events and probably continued over several tens of millions of years stratigraphic units with grossly similar lithologies underwent similar diagenetic alterations at rates and to extents that were different from other stratigraphic units having different lithologies because of variations in the rate and duration of alteration and variations in the length of normal versus reversed polarity events any given lithologic unit tended to be dominated by one polarity the model given above seems to be capable of explaining not only those magnetic and petrographic features found in the moenkopi formation but also those of most other red beds

detrital remanent magnetization in hematite heavy mineral placer layers within channel sandstones of the morrison formation western united states have been shown to contain a very stable accurate record of the jurassic geomagnetic field these laminae are composed almost entirely of hematite grains in particular they are largely the hematite pseudomorph of magnetite martite the laminae record the correct geomagnetic field direction during a period of rapid apparent polar wander which suggests an early acquisition of the remanence several other remanence characteristics imply that the remanance is probably a detrital remanent magnetization drm 1 there is large directional dispersion in one lamina which had been heavily burrowed by organisms measurement of individual burrows shows that the burrowing disrupted and randomized the magnetization held in the martite grains 2 directions of laminae that were deposited on sloping surfaces are significantly deflected from the directions of the flat lying laminae 3 more than 50 of the martite grains have high temperature oxidation features suggesting that they may have been martite at the time of deposition these characteristics in particular the burrowing disturbance strongly suggest that the martite was deposited as martite and that the remanence is a drm as opposed to deposition of magnetite grains which were altered to hematite after deposition examination of recent weathering debris on igneous outcrops shows a substantial amount of martite on these outcrops this observation provides further evidence in support of the idea that hematite and in particular martite can be a deposited mineral in sedimentary rocks and thus can carry a drm

astronomical forcing of sedimentary cycles in the middle to late miocene continental calatayud basin ne spain abstract a high resolution cyclostratigraphic and magnetostratigraphic study was carried out on cyclically bedded successions of middle miocene lacustrine to distal alluvial fan floodplain deposits from the calatayud basin in northeast spain eight partially overlapping subsections near the village of orera are correlated in detail using distinct sedimentary cycle patterns or by following marker beds in the field together they form the orera composite section ocs sedimentary cycles are recognised on at least two different scales the basic small scale cycles in the ocs consist of an alternation of grey and occasionally red clays with white dolomite rich carbonate beds they are arranged in larger scaled so called large scale cycles based on repetitive changes in the overall carbonate clay lithology two other but less distinct types of intermediate scale cyclicity are also recognised in terms of depositional environment the cycle hierarchy is interpreted to represent periodic lake expansion over the palaeo alluvial fan floodplain area the palaeomagnetic results yield a reliable magnetostratigraphic record which confirms the cyclostratigraphic correlations between the subsections in detail rock magnetic experiments reveal that haematite is the main magnetic carrier of the primary component the magnetostratigraphy of the ocs is correlated straightforwardly with the geomagnetic polarity time scale this resulted in an age of 10 7 12 8 ma for the entire succession which is supported by fossil micromammal findings in addition it also reveals the presence of two possibly three short new polarity intervals based on the number of cycles in the ocs the average periodicity of the basic small scale cycles is approximately 23 000 yr while the large scale cycle indicates a periodicity of 400 000 yr this suggests that these sedimentary cycles are controlled by astronomically induced climate changes causing lake level fluctuations and thus resulting in the deposition of carbonate clay cycles the continental sequences of the ocs provide a unique opportunity to extend the astronomical polarity time scale into the middle miocene the overlap of such continental sequences in the mediterranean area with time equivalent astronomically induced marine sequences is fundamental for establishing marine continental bed to bed correlations and for understanding regional climate change

rock magnetic properties of multicomponent natural remanent magnetization in alluvial red beds ne spain summary an earlier study of the cyclic miocene red bed sequence of la gloria spain by krijgsman et al indicated complicated behaviour of the natural remanent magnetization nrm in parts of the section particularly close to reversal boundaries we resampled part of the section with high resolution and used extensive rock magnetic analyses to characterize the magnetic remanence carriers below a conspicuous hydromorphous layer the magnetic contributions of haematite and magnetite are approximately equal while in the brown layers on top of the hydromorphous layer the contribution of magnetite is drastically reduced this is probably related to a change in hydrological conditions the nrm is characterized by 1 a low temperature 200 360 c overprint of unknown age 2 a medium temperature 360 580 c component interpreted as the characteristic remanent magnetization chrm and 3 a high temperature haematite component 600 680 c carrying the same directions as the medium temperature component there is no perceivable delay in nrm acquisition between the medium and the high temperature components they are both regarded as primary the behaviour of the nrm seems to be similar in the cyclic lithologies the acquisition of nrm thus seems to be independent of lithology in the cyclic part of the section the higher sampling resolution yielded the detection of a new polarity zone which probably represents a geomagnetic feature according to rock magnetic properties however the more detailed magnetostratigraphy of the resampled part of the section indicates that the earlier correlation to the geomagnetic polarity timescale is no longer tenable therefore the la gloria section should no longer be used as a magnetostratigraphic dating tool of mammal biochronology

timing of remanent magnetization acquisition in red beds a case study from a syn folding sedimentary basin abstract red beds have been recognized as a useful source of ancient geomagnetic field however the timing of remanence acquisition in red beds is still incompletely understood fold tests may be used for an estimation of the timing of red bed remanence acquisition but an essential ability of this kind of test is to conclude whether magnetizations are acquired before or after folding even a positive fold test does not necessarily represent a primary nature of magnetization because the relationship between the timing of fold growth and sedimentation is well understood for a small syn folding sedimentary basin we select such a sedimentary basin as a focus of study a case study example examining the timing of red bed remanence acquisition based on fold tests is described in this paper it shows that the observed remanence directions carried by hematite are given a syn folding nature this syn folding nature is more observable in the lower part of the sedimentary sequence that was under the more intense folding during its sedimentation than the upper part a pure depositional remanent magnetization when beds were horizontal is not applicable to this case but a post depositional remanent magnetization with possible existence of an initial slope of the deposition surface is considered to have been imparted prior to complete lithification microscopic observations showing the presence of hematite as sedimentary particles can be used for an independent estimation supporting the detrital origin chemical compositions of the hematite grains agree well with the maximum laboratory unblocking temperatures of the samples and we draw the conclusion that these grains are the carrier of the detrital magnetization

remagnetization in bituminous limestones of the neoproterozoic araras group amazon craton hydrocarbon maturation burial diagenesis or both 1 neoproterozoic carbonates of the araras group exhibit two distinct magnetic components across the same carbonate succession in a cross section between the amazon craton and the paraguay fold belt pink dolostones of the mirassol d oeste formation carry a dual polarity primary component whereas black bituminous limestones of the guia formation yield a secondary postfolding component magnetic signatures of the guia limestones such as high anhysteretic remanence magnetization saturation isothermal remanence magnetization ratios high frequency dependent magnetic susceptibility and contradictory lowrie fuller and cisowski tests are typical of remagnetized carbonates unblocking temperatures suggest that the stable high temperature remanence is carried by both pyrrhotite and magnetite for which an authigenic origin is suggested by scanning electron microscope observations the different magnetic properties noted between dolostones with or without bitumen and between dolostones and limestones in the same metamorphic conditions lead to the hypothesis that the amount of hydrocarbon as well as the lithology influence nucleation of authigenic magnetic minerals in these rocks presence of magnetite pseudoframboids and euhedral iron sulphide crystals occurring in fracture and voids are in favor of a chemical remanence crm the presence of pyrrhotite as one of the main carriers of crm in these rocks and its association with bitumen in fractures is probably related to an epigenetic enrichment of sulfur due to hydrocarbon seepage however hydrocarbon maturation solely could not explain the differences of the magnetic mineralogy observed in the craton and the fold belt enhanced magnetite formation in the thrust and fold belt is interpreted to be the result of higher temperatures leading to stronger diagenesis of clay minerals

cyclicity and nrm acquisition in the armantes section miocene spain potential for an astronomical polarity time scale for the continental record the results are presented of a detailed study of a short 250 kyr interval from a cyclically bedded continental sequence that is composed of alternating reddish silts and whitish limestones armantes section central spain the lithology as well as the carbonate and gamma ray records indicate that five small scale cycles are developed in one large scale cycle implying that the small scale cyclicity is related to precession and thus caused by climate forcing rock magnetic experiments show that the nrm is carried by hematite and magnetite maghemite and that the relative contribution of hematite is related to lithology the positions of the reversal boundaries can reliably be determined even though reversals of the magnetite and hematite components appear to be recorded at slightly different levels we conclude that the well developed cyclicity and the good paleomagnetic properties of the sediments will enable the construction of an astronomical polarity time scale apts for the continental realm

aragonian stratigraphy reconsidered and a re evaluation of the middle miocene mammal biochronology in europe abstract the recently collected fauna of armantes 1a in chron c5br of the armantes section necessitates reinterpretation of the previous bio and magnetostratigraphical correlations between the armantes and vargas sections calatayud daroca basin central spain w krijgsman m garces c g langereis r daams j van dam a j van der meulen j agusti l cabrera a new chronology for the middle to late miocene continental record in spain earth planet sci lett 142 1996 367 380 the long reversal in the vargas section is now correlated to c5br instead of to c5cr on the basis of the biostratigraphical correlation of armantes 1a to the faunas of fuente sierra 2 and 3 in the vargas section which are situated in the basal part of the middle aragonian mn5 this leads to the revised age of 16 0 ma for the early middle aragonian mn 4 5 boundary our age estimate of the mn5 6 boundary is maintained at ca 13 75 ma the vargas section is now considered to start in chron c5cn 2r and to end in c5bn 1n as a result of the revised correlation the duration of the time gap between the fossiliferous parts of vargas and the younger aragon section previously estimated as ca 1 5 myr is now reduced to less than 200 000 years the tie points of the european mammal units mn4 mn6 to the geomagnetic polarity time scale f f steininger w a berggren d v kent r l bernor s sen j agusti circum mediterranean neogene miocene and pliocene marine continental chronologic correlations of european mammal units in r l bernor v fahlbusch h w mittmann eds the evolution of western eurasian neogene mammal faunas columbia univ press new york 1996 pp 7 46 are evaluated our age estimates of the mn4 5 and mn5 6 boundaries are compatible with the new magnetostratigraphic calibration of middle miocene mammal zones in the swiss molasse basin o kempf t bolliger d kalin b engesser a matter new magnetostratigraphic calibration of early to middle miocene mammal biozones of the north alpine foreland basin in j p aguilar s legendre j michaux eds actes du congres biochrom 97 mem trav e p h e 21 1997 547 562

paleomagnetism of the moenkopi and chinle formations in central new mexico implications for the north american apparent polar wander path and triassic magnetostratigraphy in central new mexico red sedimentary rocks unconformably overlying permian carbonates of the san andres formation have been correlated with the early middle triassic moenkopi and late triassic chinle formations of the colorado plateau paleomagnetic samples from triassic sections exposed on basement cored uplifts along both the east and west side of the rio grande rift near albuquerque yield upon thermal and chemical demagnetization well defined high unblocking temperature dual polarity magnetizations carried by hematite the characteristic magnetization is interpreted as an early acquired chemical remanent magnetization based on a positive intraformational microconglomerate test and bedding parallel magnetization polarity zonation the moenkopi and lowermost chinle formations produced paleomagnetic poles respectively at 57 6 n 100 3 e n 36 sites k 74 1 a95 2 8 and 60 8 n 88 9 e n 17 sites k 130 3 a95 3 1 these data plus previously published and additional results from the underlying permian strata suggest that portions of central new mexico have experienced a small clockwise rotation i e less than 10 similar to that of the colorado plateau with respect to the north american craton the paleomagnetic directions of the chinle formation and related strata in eastern new mexico document about 12 great circle distance of rapid apparent polar wander during mid carnian to late norian times along a track which contains other cratonic poles of similar age we present a preliminary magnetic polarity time scale for the triassic that incorporates the present new mexico data and previously published data mostly form continental red bed sequences this magnetic polarity scale provides a basic framework which can be tested with future data from triassic sections where additional biostratigraphic control exists

palaeogeographic implications of differential inclination shallowing in permo carboniferous sediments from the donets basin ukraine abstract we present new palaeomagnetic data from upper carboniferous and lower permian grey and red sediments from the donets basin ukraine part of the palaeozoic east european platform detailed demagnetization of these units reveals two ancient components of magnetization component b which is carried by magnetite and pigmentary haematite and a high unblocking temperature component c present only in the red beds carried by detrital haematite the b and c components both pass fold tests indicating a primary or a near primary origin for magnetizations the c component however yields palaeolatiudes that are consistently lower by up to 12 of latitude or 1330 km than those derived from the b component and we argue that this is due to significant inclination shallowing of the c component a comparison with european reference palaeomagnetic data reveals that the reference data also span a large spread of palaeolatitudes for this time and we argue that unrecognized shallowing may have crept into the reference data when based on sedimentary units a more rigorous approach to selecting reference palaeomagnetic data may well be key to resolving palaeogeographic controversies at this time

mineral chemistry of columbite tantalite from spodumene pegmatites of kolmozero kola peninsula russia abstract compositional variation results of electron microprobe analyses and mass spectrometry analyses of columbite group minerals cgm from fully differentiated albite spodumene pegmatites at kolmozero in the kola peninsula is evaluated concentric zoning typical of rare metal pegmatites was not observed in the kolmozero pegmatites columbite group minerals occur in all main parageneses of the pegmatites and form four generations reflecting the sequence of pegmatite formation these minerals demonstrate wide variations in the content of major and trace elements the composition of cgm ranges from columbite fe to tantalite mn fractionation trends were observed in mn mn fe versus ta ta nb diagrams and trace element abundances plotted versus xta and xmn the early cgm paragenesis is characterized by homogeneous oscillatory and progressive oscillatory zoning and corresponds to a primary magmatic type late generation cgm show patchy irregular internal textures replacing earlier regular patterns of zoning the irregular zoning points to metasomatic replacement processes for the first time it is shown that distributions of rare earth elements ree in cgm reflect the evolution of a pegmatite forming system at kolmozero the main trend of ree variation from early to late generations of cgm involves decreasing total ree contents due to a decrease in heavy ree and y decreasing negative eu anomaly and decreasing magnitude of m shape tetrad effect between gd and ho these changes are accompanied by gradual flattening of the bird like patterns of chondrite normalized ree distribution all these features are typical for late differentiates of granitic volatile rich magma late metasomatic tantalite mn is characterized by sharp changes in its ree distribution pattern decreasing total ree contents changing shape of the ree distribution pattern the absence of eu anomaly and tetrad effects and the appearance of a negative ce anomaly the textural characteristics and mineral chemistry of cgm indicate that the pegmatite forming system underwent several stages of evolution the earliest magmatic stage can be divided into two sub stages involving direct crystallization and collective recrystallization respectively and was succeeded by a late hydrothermal metasomatic post magmatic stage variations in chemical composition among the different generations of cgm are explained by the interplay of several processes fractional crystallization competitive crystallization of main rock forming feldspar muscovite spodumene and accessory triphylyte lithiophilite spessartine fluorapatite zircon microlite minerals and evolution of the mineral forming environment from a melt to a hydrothermal metasomatic fluid

melt composition control of zr hf fractionation in magmatic processes zircon zrsio4 and hafnon hfsio4 solubilities in water saturated granitic melts have been determined as a function of melt composition at 800 and 1035 c at 200 mpa the solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt moreover the molar ratio of zircon and hafnon solubility is a function of melt composition although the solubilities are nearly identical in peralkaline melts zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts accordingly calculated partition coefficients of zr and hf between zircon and melt are nearly equal for the peralkaline melts whereas for metaluminous and peraluminous melts dhf dzr for zircon is 0 5 to 0 2 consequently zircon fractionation will strongly decrease zr hf in some granites whereas it has little effect on the zr hf ratio in alkaline melts or similar depolymerized melt compositions the ratio of the molar solubilities of zircon and hafnon for a given melt composition temperature and pressure is proportional to the hf zr activity coefficient ratio in the melt the data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts however it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached for most ferromagnesian minerals in equilibrium with a depolymerized melt dhf dzr typical values of dhf dzr range from 1 5 to 2 5 for clinopyroxene amphibole and titanite because of the change in the hf zr activity ratio in the melt the relative fractionation of zr and hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite it is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in zr hf whereas fractional crystallization of depolymerized melts tends to increase zr hf there is no need to invoke fluid metasomatism to explain these effects results demonstrate that for ions with identical charge and nearly identical radius crystal chemistry does not alone determine relative compatibilities rather the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice

textural features and chemical evolution in tantalum oxides magmatic versus hydrothermal origins for ta mineralization in the tanco lower pegmatite manitoba canada tantalum a key element in the electronics industry is produced mainly from rare element granitic pegmatites although their internal structure mineralogy and petrogenesis have been extensively investigated the processes that control tantalum mineralization remain poorly understood in particular the role of fluids in the crystallization of tantalum ore one of the major problems arises from the difficulty in distinguishing primary magmatic from secondary hydrothermal textures in such complex rocks in the tanco pegmatite manitoba canada tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite eight different families of tantalum oxides occur in various associations and compositions the tanco lower pegmatite is an isolated body beneath the main pegmatite body that contains abundant tantalum associated with mica alteration tantalum mineralization in the tanco lower pegmatite occurs as three different styles facies 1 is hosted by the wall zone and hosts primary magmatic ta oxides with simple textures progressive and oscillatory zoning facies 2 is hosted by the lower and upper intermediate zones where most mineralization occurs with dendritic amblygonite facies 3 is hosted by the central zone which is affected by mica alteration in this latter facies the oxides show particularly complex textures evident from x ray mapping by combining information obtained from textural observations and chemical analyses we are able to determine the paragenesis for each ta oxide bearing mineral assemblage and hence to evaluate the relative contributions of magmatic versus hydrothermal processes in complex associations we observe relics of primary ta phases that are replaced or overgrown by secondary ta phases we propose the paragenetic sequence columbite group minerals microlite early primary magmatic columbite wodginite group minerals microlite late primary magmatic wodginite group minerals microlite secondary magmatic ferrotapiolite secondary magmatic in addition chemical variations were identified in the columbite and wodginite group minerals both at the crystal scale and at the pegmatite scale columbite and wodginite group minerals show the typical ta ta ta nb and mn mn mn fe atomic ratios increase from earlier to later zones at the crystal scale the increase in ta and mn with fractionation in the columbite group is explained by the higher solubility of the ta end member relative to the nb end member and the crystallization of other minerals that shift the melt composition toward mn enrichment the fractionation trend in the wodginite group shows fe enrichment which is consistent with experimental results that show a higher solubility of the fe end member relative to the mn end member in columbite group minerals considering the available experimental data as well as the intimate association of ta oxides with zircon observed in this study we conclude that tantalum mineralization is a product of direct crystallization from the melt rather than hydrothermal in origin fluids are attributed an indirect role only as they could have brought minor elements fe mn or ca into the melt which resulted in the crystallization of secondary ta phases textural evidence shows that the late secondary phases were formed at the same time as mica alteration we suggest that mica alteration was due to a late melt rather than a hydrothermal fluid that reacted with the blocky k feldspar of the central zone during the alteration event tantalum was remobilized from primary phases and incorporated in new secondary ta oxide species

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

iron oxide mineralogy in late miocene red beds from la gloria spain rock magnetic voltammetric and vis spectroscopy analyses abstract free ferric oxides of a red bed series were analyzed by rock magnetic techniques irm component analysis and by two less traditional methods visible spectroscopy and voltammetry all three methods have low limits of detection making them suited for this type of analysis the red bed samples studied contained clay minerals quartz and calcium carbonate as major constituents free fe oxides occurred at a concentration of 0 3 2 1 i e in the majority of the samples below the detection limit of x ray powder diffraction the combination of the employed analytical techniques enabled to characterize the mineralogy of free ferric oxides and to estimate the ratio of goethite and to hematite this ratio changes substantially within the section that probably indicates paleoclimatic changes

evolution of early middle miocene rodent faunas in relation to long term palaeoenvironmental changes abstract cluster and principal components analyses have been applied to the composite sequence of 59 rodent assemblages from ramblian to lower vallesian deposits in the daroca calamocha area in the calatayud teruel basin north central spain the studied record is thought to represent the interval from the late aquitanian to the end of the serravallian i e early to middle miocene from ca 22 10 5 ma ago the quantitative results are interpreted by using individual rodent taxa as environmental indicators and by extrapolating the predominant adaptive strategies of recent taxonomic groups which also seem to form natural groups on a demographic scheme french et al 1975 a general warming trend starts in the rambian early miocene and continues into the middle aragonisn early middle miocene the cooling in the middle to late aragonian boundary interval is correlated to the middle miocene cooling phase another cooling occurred around the aragonian vallesian boundary late middle miocene we relate a major increase of aridity in the beginning of the middle aragonian ca 16 5 ma to the spread of low biomass vegetation due to intensification of the subtropical belt wolfe 1985 a notable feature around the early middle aragonian boundary indicating a major shift of climatic belts is the reversal of the relationship between our relative temperature and humidity curves before the reversal we find a positive correlation after it a negative correlation around the middle to late aragonian boundary humidity increased again and a further increase of humidity is indicated by the earliest vallesian faunas our data suggest that the nature of favoured adaptive strategy amongst rodents is related in the end to the degree of climatic humidity

timing of diagenetic haematite growth in red pelagic limestones from gubbio italy abstract magnetite haematite and to a minor extent maghaemite are recognised in the cretaceous and paleocene red pelagic limestones at gubbio the magnetite is detrital or biological whereas the haematite grew during diagenesis from a goethitic precursor thermal and af demagnetization of samples collected from close to reversal boundaries indicate that the various magnetization components do not record the polarity reversal at exactly the same stratigraphic level in the few tens of centimetersbelow a recorded geomagnetic reversal defined by the magnetite magnetization some of the haematite grains are magnetized in the post reversal field the blocking temperature spectra of this haematite fraction with post reversal magnetization are found to shift toward higher temperatures as the reversal boundary is approached the blocking temperature spectra reflect the grain size spectra of the haematite which we interpret as arising by the continual nucleation of grains down to a certain burial depth where the conditions are no longer conducive to further haematite growth the depth below reversal boundaries to which haematite with post reversal magnetization can occur is estimated to be about 60 cm after compaction and is equivalent to a time of about 105 years for these particular sediments a detailed study of the magnetization components at reversal boundaries indicates that the first diagenetic growth of haematite through the single domain critical volume occurs prior to the mechanical fixation of the detrital or biological magnetite subsequently the diagenetic haematite grains do not rotate in response to the ambient geomagnetic field polarity as easily as the magnetite because of their occurrence as pigmentary coatings on larger non magnetic grains

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

transition stratigraphy and the problem of remanence lock in times in the siwalik red beds the record of paleomagnetic polarity transitions can provide relative time information in the stratigraphic record on scales of hundreds to thousands of years transition stratigraphy is here used to determine the relative lock in times of several components of magnetization in the siwalik red beds

coercivity analysis of magnetic phases in sapropel s1 related to variations in redox conditions including an investigation of the s ratio 1 abstract the most recent sapropel s1 in the eastern mediterranean has been extensively investigated with geochemical and rock magnetic techniques different redox conditions prevailed in different zones of the sediment through time the oxidized sapropel zone is particularly interesting because earlier studies indicated that new magnetic material was formed including possible magnetosomes here we utilize component analyses of isothermal remanent magnetization irm acquisition curves and the analysis of first order reversal curves forc to further investigate the magnetic mineralogy in the entire box core abc26 the original input of eolian dust consisted of both magnetite and hematite in the oxidized sapropel and in the active oxidation zone an additional magnetite component is present this magnetite component has a higher coercivity than the eolian magnetite and a very small coercivity dispersion suggesting a narrow grain size distribution this is a strong indication that magnetosomes which are formed in the active oxidation zone are the magnetic carriers of this coercivity fraction forc diagrams support these findings the s ratio is forwardly modeled for mixed magnetic mineralogies with varying coercivity distributions to explain the down core s ratio behavior close to 1 in the top sediment and in the oxidized sapropel a drop in values in the active oxidation zone and again close to 1 in the syn sapropel the observed s ratio pattern in the oxidized sapropel and in the active oxidation zone can be explained by the recovered irm components whereas both oxidized sapropel and active oxidation zone contain the extra magnetite component their s ratios are different because of the differences in coercivity characteristics coercivity and dispersion of the two magnetites in these zones thus in these zones the s ratio does not reflect variations in the relative contributions of hematite to magnetite but variations in the characteristics of the individual magnetite assemblages also in the rest of the core the s ratio depends on the coercivity characteristics of the magnetite component rather than on the relative contributions of high versus low coercivity minerals the s ratio thus appears to be an unsuitable parameter to describe variations in the magnetic mineralogy especially when more than two components are present therefore the classical interpretation of the s ratio should be treated with caution

reconciling cretaceous paleomagnetic and marine magnetic data for iberia new iberian paleomagnetic poles 1 the cretaceous paleogeography and the kinematic evolution of the iberian plate are poorly constrained especially problematic is to reconcile iberian paleomagnetic data with paleomagnetic data of the neighboring plates and with euler poles derived from seafloor magnetic anomalies the first limitation arises from the cretaceous normal polarity superchron where paleogeographic reconstruction using marine magnetic anomalies is handicapped the second arises from the paucity of reliable paleomagnetic poles with satisfactory statistical criteria and age in order to address these shortcomings and provide new high quality paleomagnetic poles for iberia we conducted a detailed rock magnetic and paleomagnetic study of two cretaceous magmatic sills the paco de ilhas pi and foz da fonte ff sills from the lusitanian basin portugal recently dated at about 88 and 94 ma respectively our results show that the magnetic mineralogy of the sills is primary i e acquired during magma cooling and essentially represented by titanomagnetite the corresponding paleomagnetic poles match the synthetic apwp from the african plate at 80 and 100 ma on the basis of a rigorous selection of iberian cretaceous poles we then calculated mean paleomagnetic poles for different time intervals and found that iberian paleomagnetic data fit well the global apwp between 70 and 120 ma but move far away from the apwp at pre rift times our approach shows that new and better constrained paleomagnetic poles can aide in solving part of the contradiction between iberian and african apwps

a paleomagnetic and geochemical record of the upper cochiti reversal and two subsequent precessional cycles from southern sicily italy abstract a detailed paleomagnetic and geochemical study of the upper cochiti n r reversal recorded in marine marls on southern sicily shows two consecutive and very rapid transitions r n and n r that coincide with distinct lithological boundaries a fe migration model is presented in which magnetite is formed under different diagenetic conditions during sulphate reduction originally formed primary magnetite is preserved this primary magnetite has recorded the pre transitional normal polarity after burial migration of ferrous iron occurs and subsequent oxidation produces secondary magnetite which records the post transitional reversed polarity and produces the two apparent transitions in addition low temperature lt and high temperature ht components record the reversal in a slightly different way the ht component being acquired with a delay it is probable that both components reside in magnetite but have a different origin and grain size distribution giving different blocking temperature spectra the actual upper cochiti reversal occurs at a level with an estimated astronomically calibrated age of 4 165 ma

statistical characteristics and origin of oscillatory zoning in crystals complex intracrystalline zoning patterns in hydrothermal garnet and vesuvianite and magmatic plagioclase were analyzed by statistical methods to test for fractal behavior the zoning data were collected by electron and proton microprobe and backscattered electron images and polarized micrographs were digitized the analysis shows that self affine fractal geometry can be used to characterize the zoning patterns of vesuvianite and some garnet patterns the range of power law scaling extended up to two decades the results from the plagioclase samples were not sufficient to determine whether or not the zoning patterns were self affine the measured hurst exponents are mostly in the range 0 25 0 45 indicating fractal scaling and anti persistent behavior this means that an increasing compositional trend in the past favors a decreasing trend in the future and vice versa no distinct periodic components of the zoning patterns were found the influence of environmental changes external fluctuations on a simple crystal growth model was investigated by numerical simulations the concentration at the boundary of a diffusion layer was allowed to vary as a brownian motion curve and the effect of the external fluctuation on diffusion and local growth kinetics was investigated we conclude that factors operating on scales much larger than the local interface processes are most important in controlling the zonation

kinematics and flow patterns in deep mantle and upper mantle subduction models influence of the mantle depth and slab to mantle viscosity ratio 1 three dimensional fluid dynamic laboratory simulations are presented that investigate the subduction process in two mantle models an upper mantle model and a deep mantle model and for various subducting plate mantle viscosity ratios sp m 59 1375 the models investigate the mantle flow field geometrical evolution of the slab sinking kinematics and relative contributions of subducting plate motion and trench migration to the total rate of subduction all models show that the subducting plate is always moving trenchward resulting from slab pull furthermore all deep mantle models show trench retreat as do upper mantle models in the initial stage of subduction before slab tip transition zone interaction upper mantle models with a low sp m 66 217 continue to show trench retreat after interaction upper mantle models with a high sp m 378 709 show a period of trench advance after interaction followed by trench retreat upper mantle models with a very high sp m 1375 show continued trench advance after interaction the difference in trench migration behavior and associated slab geometries is attributed to both sp m and the mantle depth to plate thickness ratio tm tsp which both affect the slab bending radius to mantle thickness ratio rb tm four subduction regimes can be defined regime i with rb tm 0 3 trench retreat slab draping and a concave trench regime ii with 0 3 rb tm 0 5 episodic trench migration slab folding and a concave trench regime iii with rb tm 0 5 trench advance slab rollover geometries and minor trench curvature and regime iv with rb tm 0 8 trench retreat slab draping and a rectilinear trench in all models slab parallel downdip motion induces poloidal mantle flow structures in addition trench retreat and rollback motion of the slab induce quasi toroidal return flow around the lateral slab edges toward the mantle wedge rollback induced poloidal flow around the slab tip is not observed in any of the experiments finally comparison between the slab geometries observed in the upper mantle models and slab geometries observed in nature imply that the effective viscosity ratio between slab and ambient upper mantle in nature is less than 103 and of the order 1 7 102 with a best estimate of 1 3 102

secular variation in permian red beds from dome de barrot se france the do me de barrot red beds se france were deposited during the permo carboniferous reversed superchron pcrs near the palaeo equator the natural remanent magnetisation nrm resides in detrital hematite which is very resistant against thermal demagnetisation microprobe analyses reveal the presence of titanium in hematite grains indicating the volcanic and thus detrital origin therefore the nrm is a detrital remanent magnetisation and nrm variations reflect changes in the geomagnetic field tuning of the proxy parameter magnetic susceptibility to periods of the earth orbit during permian times provides relative time control the inferred average sedimentation rate is 11 8 cm 1000 yr 31 the variation in nrm directions is similar to present day secular variation sv this suggests that sv was not suppressed during at least part of the pcrs fl 2000 elsevier science b v all rights reserved