magnetism and transmission electron microscopy of fe ti oxides and pyroxenes in a granulite from lofoten norway granulites from southwest lofoten norway often carry intense and stable components of natural remanent magnetization nrm coercivities in excess of 100 mt and blocking temperatures up to 580 645 c are common several phases in these rocks can carry stable components of nrm clinopyroxenes augite with exsolved pigeonite and orthopyroxene usually contain abundant fe ti oxides the majority of which are too small to be studied conclusively with visible light additionally these rocks typically contain coarse grained 100 1000 m exsolution intergrowths of rhombohedral fe ti oxides and coarse grained magnetite we have studied the magnetism and mineralogy of the titanohematite and the inclusion bearing augites in one granulite sample using transmission electron microscopy tem and magnetic experiments to understand better the remanence properties of naturally occurring fe ti oxides and their relationships to silicate minerals the coarse grained titanohematite has a coercivity of 350 mt and a laboratory saturation remanence that unblocks at 570 600 c the hysteresis characteristics of this titanohematite are typical of much smaller 10 m sized single domains which apparently reflects the presence of exsolved ilmenite lamellae as small as 10 nm in thickness these lamellae presumably inhibit 1 domain wall nucleation and 2 movement of walls that manage to nucleate the inclusions in the augites serve as carriers of lower coercivity remanence with blocking temperatures less than about 560 c magnetite hematite and ilmenite are present in the augite and intergrowth of the rhombohedral phases revealed by tem persists down to the 20 nm scale the distribution of the magnetite inclusions in the augite appears to be unrelated to any silicate microstructure while that of the rhombohedral fe ti oxides is strongly controlled by silicate microstructure with intergrowths of these oxides commonly decorating lamellae of pigeonite orthopyroxene and clinoamphibole within the augite the nrm of this sample possibly dates from the amphibolite facies metamorphism that the region experienced about 1000 m y ago paleomagnetic studies of these rocks could readily recover virtual geomagnetic poles dating from this event in addition to the included oxides the augites display a number of unusual features that probably result from the protracted polymetamorphic history of these granulites pigeonite lamellae are not parallel to the b crystallographic axis pigeonite lamellae cut across those of orthopyroxene and numerous included minerals occur rare earth elements are concentrated within inclusions that reside in the augite

chondrules in h3 chondrites textures compositions and origins major and minor element bulk compositions of 90 individual chondrules and 16 compound chondrule sets in unequilibrated type 3 h group chondrites were determined in polished thin sections by broad beam electron probe analysis and the chondrules were classified petrographically into six textural types barred olivine porphyritic olivine porphyritic pyroxene barred pyroxene radiating pyroxene fine grained although analyses of individual chondrules scatter widely the mean composition of each textural type except barred pyroxene is rather distinct as verified by discriminant function analysis al2o3 tio2 and na3o are correlated in chondrules but al2o3 and cao do not correlate compound chondrule sets were found to consist almost entirely of chondrules or partial chondrules of similar texture and composition the data suggest that composition played a conspicuous role in producing the observed textures of chondrules though other factors such as cooling rates and degrees of supercooling prior to nucleation were also important if compound chondrules formed and joined when they were still molten or plastic then the data suggest that chondrules of each textural type could have formed together in space or time the correlation of al2o3 and tio2 with na2o and not with cao appears to rule out formation of chondrules by direct equilibrium condensation from the nebula we conclude that the most reasonable model for formation of the majority of chondrules is that they originated from mixtures of differing fractions of high intermediate and low temperature nebular condensates that underwent melting in space a small percentage of chondrules might have formed by impacts in meteorite parent body regoliths

role of fluids in migmatites co2 h2o fluid inclusions in leucosomes from the deep freeze range migmatites terra nova bay antarctica the metasedimentary sequence of the deep freeze range northern victoria land antarctica experienced high t low f metamorphism during the cambro ordovician ross orogeny the reaction bt sil qtz grt crd kfs melt was responsible for the formation of migmatites peak conditions were c 700 750 c c 3 5 5 kbar and xh2oc 0 5 distribution of fluid inclusions is controlled by host rock type 1 co2 h2o fluid inclusions occur only in graphite free leucosomes 2 co2 ch4 h2o fluid inclusions are the most common type in leucosomes and in graphite bearing mesosomes and gneiss and 3 co2 n2 ch4 fluid inclusions are observed only in the gneiss and subordinately in mesosomes co2 h2o mixtures 41 co2 58 h2o 1 nad mol are interpreted as remnants of a synmig matization fluid their composition and density are compatible p t ah2o conditions of migmatization c 750 c c 4 kbar xh2oc 0 5 co2 h2o fluid in graphite free leucosomes cannot originate via partial melting of graphite bearing mesosomes in a closed system this would have produced a mixed co2 ch4 fluid in the leucosomes by a reaction such as bt sil qtz c h2o grt crd kfs l co2 ch4 we conclude that an externally derived oxidizing co2 h2o fluid was present in the middle crust and initiated anatexis high density co2 rich fluid with traces of ch4 characterizes the retrograde evolution of these rocks at high temperatures and support isobaric cooling p t anticlockwise path in unmigmatized gneiss mixed co2 n2 ch4 fluid yields isochores compatible with peak metamorphic conditions c 700 750 c c 4 4 5 kbar they may represent a peak metamorphic fluid that pre dated the migmatization

lodestone natures only permanent magnet what it is and how it gets charged magnetite and titanomagnetite exhibit magnetic properties which are attributable to the micro structures developed during oxidation and exsolution all magnetite iron ores which are lodestones contain maghemite these lodestones have hc between 10 and 30 mt sirm between 8 and 18 am kg and ri between 0 10 and 0 26 magnetite titanomagnetite and metals have rem values ratio of nrm to sirm 0 05 samples called fulgarites obtained from the smithsonian institution have rem values ranging from 0 45 to 0 92 the rem value serves as a witness parameter to the magnetic fields associated with the lightning bolt if a high rem value say 0 1 can be verified as not to be due to contamination by man and does not contain md hematite then the rock has lrm lightning remanent magnetization the magnetic field associated with lightning can be revealed from an isothermal remanent acquisition ra curve

a remanent and induced magnetization model of magsat vector anomalies over the west african craton scalar and vector magsat anomalies over the west african craton are analysed by forward and inverse models a forward model of the man shield is based on liberia induced magnetization contrasts due to sporadic iron formations and to regional metamorphic rocks and a contrast in remanent magnetization within the lower crust are included this combination reproduces the location magnitude and adopted local zero level of anomalies in the initial magsat maps an inverse model of the reguibat shield estimates the magnetization contrast of its lithosphere and when magnetism is restricted to shallower than 75 km both shields can be represented by a susceptibility contrast of 0 02 a residual anomaly between the shields involves a relative deficiency of induced magnetization along with other causes

nitrogen isotopic compositions and concentrations in marid xenoliths abstract nitrogen isotopic compositions and concentrations in micas from kimberlite hosted marid mica amphibole rutile ilmenite diopside suite of xenoliths from the kimberley area of the kaapvaal craton south africa were measured using continuous flow isotope ratio mass spectrometry and fourier transform infrared spectroscopy fourier transform infrared spectroscopy data suggest that the nitrogen in marid phlogopite is from ammonium in the mica structure the replacement of potassium by ammonium is the major mechanism for the storage of nitrogen within these phlogopites the 15n values of micas from marid xenoliths range from 11 to 9 and nitrogen contents range between 113 and 272 ppm the 15n enrichment of most samples relative to the average upper mantle 15n value of 5 suggests that the nitrogen reflects a recycled reservoir from subducted material within their source region the presence of nitrogen from a recycled reservoir indicates that sedimentary organic nitrogen in the sub continental lithosphere is not effectively cycled to the surface resulting in a geochemically heterogeneous upper mantle

co 2 co fluid inclusions in a composite peridotite xenolith implications for upper mantle oxygen fugacity fluid inclusions occur in a composite xenolith from the lunar crater volcanic field nevada u s a the xenolith is an amphibole bearing wehrlite that is cut by an andesine amphibole vein the compositions of individual fluid inclusions in both portions of the xenolith have been determined using microthermometry and micro laser raman spectroscopy fluids in the host wehrlite are nearly pure co2 99 mol whereas those in the vein contain from 8 5 to 12 0 mol co in co2 chemical modelling shows that the composition of the vein fluids at t room is representative of the composition at the high p t conditions of trapping graphite has not been observed by optical microscopy in any of the fluid inclusions graphite is probably absent although stable at t 800 c most probably because of the kinetically unfavorable co decomposition reaction and rapid quenching by combining the measured fluid compositions with fluid p v t data and the chemical equilibrium co2 co 1 2 o2 we have calculated the oxygen fugacity of the fluid inclusions at 1200 c log f o 2 8 6 vein and 6 host if the f o 2 of the fluid in the vein represents that in equilibrium with the magma that crystallized to produce the vein then the f o 2 of the basalt magma is near qfm at 1200 c and 10 3 kbar this is similar to values reported for extrusive basaltic lavas if the much lower intrinsic oxygen fugacity values for divines and spinels from alkali basalt nodules are representative of upper mantle conditions then oxidation of basaltic magmas must occur in the upper mantle prior to ascent to the surface implications for the origin of co2 rich fluids and carbon isotope geochemistry are also discussed

the role of hematite ilmenite solid solution in the production of magnetic anomalies in ground and satellite based data abstract remanent magnetization rm of rocks with hematite ilmenite solid solution hiss minerals at all crustal levels may be an important contribution to magnetic anomalies measured by ground and satellite altitude surveys the possibility that lower thermal gradient relatively deep in the crust can result in exsolution of hiss compositions with strong remanent magnetizations rm was studied for two bulk compositions within the hiss system samples from granulite terrane around wilson lake labrador canada contains titanohematite with exsolved ferrian ilmenite lamellae other samples from the anorthosite terrane of allard lake quebec canada contain ferrian ilmenite with exsolved titanohematite lamellae in both cases the final exsolved titanohematite has similar ti content and carries dominant magnetic remanence with rem nrm sirm where nrm is the natural remanent magnetization and sirm is the saturation isothermal remanent magnetization that is comparable to the ti free end member the rm was acquired prior to exsolution and the ilmeno hematite rich rock possesses thermal remanent magnetization trm whereas rocks with hemo ilmenite possess chemical remanent magnetization crm in both cases we found fairly large homogeneous grains with low demagnetizing energy that acquired intense rm the magnetism of the ilmeno hematite solid solution phases is not significantly perturbed by the continuous reaction ilmeno hematite titanohematite solid solution hence the occurrence of hiss in rocks that cooled slowly in a low intensity magnetic field will have an intense magnetic signature characterized by a large rem

a closer look at remanence dominated aeromagnetic anomalies rock magnetic properties and magnetic mineralogy of the russell belt microcline sillimanite gneiss northwest adirondack mountains new york a large distinct negative aeromagnetic anomaly of over 2000 nt associated with microcline sillimanite quartz gneisses in the russell area northwest adirondack mountains was previously shown to be remanence dominated although the carriers of remanence were not well documented russell belt gneisses have a strong natural remanent magnetization with steep remanence directions d 263 i 58 an average intensity of 3 6 a m and typical susceptibilities of 10 4 si the remanence is thermochemical in origin acquired during cooling from peak metamorphic conditions of 650 750 c during the ottawan orogen 1050 1080 ma the reversed polarity of remanence reflects a reversed paleofield rather than self reversed contrary to earlier suggestions the gneisses contain up to 3 oxide predominantly metamorphic titanohematite which accounts for the low susceptibility values and highly stable remanence optical observations show titanohematite grains with multiple generations of ilmenite pyrophanite rutile and spinel exsolution lamellae microprobe analyses confirm titanohematite compositions ranging from 72 to 97 fe2o3 with hematite83 being most typical in rare samples inclusions of magnetite were identified the ubiquitous presence of titanohematite and the rare occurrence of magnetite is supported by thermal and alternating field demagnetization studies saturation magnetization measurements hysteresis properties temperature hysteresis studies and low temperature remanence measurements numerous crustal granulites have titanohematite as part of the oxide assemblage and this may contribute a strong remanent component to what have previously been considered to be solely induced anomalies

magnetization of lower crust and interpretation of regional magnetic anomalies example from lofoten and vesteralen norway the interpretation of regional magnetic anomalies commonly observed over continental crust in both satellite and near surface magnetic data has remained enigmatic in its requirement for laterally extensive thick highly magnetic and deep seated sources presented here are the results of a detailed field analytical and experimental study of the magnetic mineralogy and magnetic properties of rocks from lofoten and vesteralen norway a province of deep seated origin with associated regional magnetic and gravity anomalies these rocks have a bulk magnetic character of surprising uniformity with susceptibilities hysteresis and curie temperatures defined solely by coarse grained magnetite stable remanence is observed in samples from sw lofoten but is not of significant magnitude the thermal enhancement of magnetic susceptibility the hopkinson effect is not important rocks from the deepest part of the section have the largest average susceptibilities 6 10 2 si and magnitudes of natural remanent magnetization nrm 5 10 4 a m2 kg these values of susceptibility together with the oft observed viscous character of the nrm suggest that these granulite facies lithologies particularly those of sw lofoten are perfect examples of lower crustal sources of typical regional magnetic anomalies furthermore these intermediate pressure granulites define a unique magnetic petrology especially for mafic compositions at higher grades of metamorphism high pressure granulites and eclogites or lower grades greenschist and amphibolite facies such magnetite bearing assemblages will be unstable and their high or low grade equivalents will be only weakly magnetic this evidence and these conclusions may be used to constrain models of lower crustal sources of regional magnetic anomalies over stable cratons it portrays the lower crust as a highly magnetic unit defined by metamorphic grade with a curie isotherm of 575 c magnetite and magnetization parallel to the ambient geomagnetic field induced and viscous components

the application of a multichannel laser raman microprobe microdil 28 to the analysis of fluid inclusions abstract the application to the analysis of fluid inclusions of laser excited raman microspectrometry with a multichannel detection system has two important features connected with the very short time needed to acquire one single spectrum 1 5 s the accumulation of a great number of the same spectral range results in an averaged spectrum with a very high signal to noise ratio with corresponding low detection limits and good counting statistics on the other hand the rapid acquisition of spectra enables the analysis of many individual inclusions in a relatively short time

the moho as a magnetic boundary revisited we have re examined the question of whether it is generally true that in continental regions a relatively magnetic crust overlies a relatively non magnetic mantle whereas the original conclusion was based on limited data the present study is based on about 400 globally distributed xenolith samples while it is now clear that the moho represents a maximum velocity gradient in a complex transition from crust to mantle and while crustal magnetization is highly variable the original concept of a magnetic crust overlying a non magnetic mantle is strongly supported by the new data a large upper mantle xenolith suite of ultramafic composition is characterized by non magnetic chrome spinels and magnesian ilmenites such rocks are magnetic only where demonstrably altered the most significantly magnetic rocks within the crust are mafic types prograded to granulite grade or mafic melts of basaltic composition which crystallized deep in the crust at high pressure and temperature prograded rocks have characteristic magnetite curie points and are strongly magnetic especially the more mafic compositions while the mafic rocks formed by crystallization at depth have curie points between 400 570 c and are strongly magnetic induced magnetizations are commonly several a m and can readily account for long wavelength magnetic anomalies measured by satellite and aircraft thus there is no need to search for exotic sources for missing crustal magnetization no metal or other peculiar magnetic species have been observed by us in any of our unaltered samples mineral assemblages including magnetic components are consistent with oxidizing conditions close to the fmq buffer

a geotechnical study of evaporitic lacustrine sediments in the saline environment of the dead sea area this paper is the third by the authors relating to the geotechnical properties of the evaporitic lacustrine sediments of the saline environment in the dead sea area the earlier papers identified difficulties involved in establishing the water content of sediments in a saline environment a different approach was adopted whereby fluid content rather than water content was used to define geotechnical properties the present paper expands on the geological background presented in the previous papers and discusses additional geotechnical aspects of the materials behavior the three major sediment types encountered in the region are fluvial granular soil cohesive lime carbonate deposits and granular to massive halite sediments the granular soils composed predominantly of sand and pebbles of dolomite with minor chert and limestone have gradations which vary widely both with depth and laterally shear wave velocities are higher than those estimated from common existing correlations with standard penetration test spt blow counts while compression indices cc and cyclic shear response of the saturated lime carbonates are consistent with behavior of clay soils their effective friction angle of about 34 on average is significantly higher than that of clays the geotechnical properties of the rock salts encountered in the region are shown to be intimately related to the extent of diagenesis and burial with very significant difference between the younger more porous deposits of holocene age and the older mt sdom diapiric salt wall of upper miocene age the latter are seen to have properties consistent with those of older rock salt deposits at greater depths reported in the literature

grain size dependent potential for self generation of magnetic anomalies on mars via thermoremanent magnetic acquisition and magnetic interaction of hematite and magnetite abstract early in the history of planetary evolution portions of martian crust became magnetized by dynamo generated magnetic field a lateral distribution of the secondary magnetic field generated by crustal remanent sources containing magnetic carriers of certain grain size and mineralogy is able to produce an ambient magnetic field of larger intensity than preexisting dynamo this ambient field is capable of magnetizing portions of deeper crust that cools through its blocking temperatures in an absence of dynamo we consider both magnetite fe3o4 and hematite fe2o3 as minerals contributing to the overall magnetization analysis of magnetization of magnetic minerals of various grain size and concentration reveals that magnetite grains less than 0 01 mm in size and hematite grains larger than 0 01 mm in size can become effective magnetic source capable of magnetizing magnetic minerals contained in surrounding volume preexisting crustal remanence for example 250 a m relates to 25 of multi domain hematite can trigger a self magnetizing process that can continue in the absence of magnetic dynamo and continue strengthening and or weakening magnetic anomalies on mars thickness of the primary magnetic layer and concentration of magnetic carriers allow specification of the temperature gradient required to trigger a self magnetization process

formation of tonalite in island arcs by seawater induced anatexis of mafic rocks evidence from the lyngen magmatic complex north norwegian caledonides abstract the lyngen magmatic complex lmc of north norway consists of a western suite of layered gabbros of normal mid oceanic ridge basalt n morb affinity and an eastern suite of layered gabbronorites quartz bearing gabbros and diorites quartz diorites of iat island arc tholeiitte to boninitic affinity the boundary between the suites is defined by a large scale ductile shear zone the rypdalen shear zone rsz in this shear zone anatectic tonalites were generated by partial melting of the gabbro in the presence of an h 2 o bearing fluid phase quartz from the tonalites contains early secondary and secondary liquid dominated inclusions 88 99 wt h 2 o with an average salinity of 18 wt calculated as nacl eq combined gas and ion chromatography shows that the major ions in the fluid are cl ca 2 na with smaller amounts of k mg 2 sr 2 br and no 3 the dominant non h 2 o volatile species is n 2 0 5 10 and small amounts of co 2 ch 4 and other hydrocarbons are also present the cation concentrations in the fluid are variable due to element exchange during interaction of the fluids with the tonalites amphibolites and metagabbros of the rsz the fluid contributed na and k to the melt and gained ca 2 in exchange explaining the variable na ca 2 ratio of the fluid the br and cl contents of the fluid inclusions plot on the same line as evaporating sea water which strongly suggests a seawater origin for the fluid phase and a seawater source fits well with other geochemical signatures and the tectonic setting of the lmc it is suggested that seawater escaped from a subducting slab and was channelled along the rypdalen shear zone this caused anatexis of the gabbro generating tonalitic melts at 0 5 0 9 gpa and 680 800 c

magnetic properties of ultrahigh pressure eclogites controlled by retrograde metamorphism a case study from the zk703 drillhole in donghai eastern china parallel studies on rock magnetic properties petrology and mineralogy were conducted on 16 eclogite samples from the zk703 hole and magnetic susceptibilities and densities of 41 eclogite samples with different degree of retrograde metamorphism from fresh eclogite to fully retrograded eclogite from the chinese continental scientific drilling ccsd near the zk703 hole located at donghai southern sulu ultrahigh pressure metamorphic belt eastern china results show 1 that the high field slopes obtained from the hysteresis loops the paramagnetic fraction para and density have a positive correlation with the volume concentration of garnet omphacite a typical mineral assemblage used to semi quantify the degree of retrograde metamorphism the low field slopes obtained from hysteresis loops the ferrimagnetic susceptibility fraction ferri saturation isothermal remanent magnetization mrs and saturation magnetization ms have a positive correlation with the volume concentration of symplectite a mineral related to retrograded metamorphism therefore they could be potential indicators for quickly semi quantifying the degree of retrograde metamorphism of the eclogite units 2 the dominant magnetic carriers in retrograded eclogites are magnetite particles in pseudo single domain grain size region 3 the p t conditions during the retrograde decompressional process could first increase the concentration of magnetite which can reach up to 3 for extensively retrograded eclogite and then was dissolved for fully retrograded eclogite therefore change in the magnetite contents during the retrograde process is the major factor controlling the magnetism of retrograde eclogites

magnetic properties of exposed deep crustal rocks from the superior province of manitoba abstract a traverse across precambrian rocks of the superior province in central manitoba provided 56 samples for magnetic study from the pikwitonei granulite domain and the adjacent cross lake subprovince these rocks represent a cross section of the continental crust presently exposed at the surface thirty one samples are dominantly paramagnetic and three contain pyrrhotite twenty two samples from silicic plutonic rocks which make up about 80 of the section by volume contain nearly pure magnetite and have susceptibilities that are almost constant between room temperature and 540 c averaging about 1 10 2 si units the mafic supracrustal rocks with much higher iron content are about an order of magnitude less magnetic because they contain little or no magnetite susceptibility is generally independent of metamorphic grade or apparent depth in the crust the discrepancy between induced magnetizations of measured lower crustal rocks and the source requirements of long wavelength magnetic anomalies may be due to a high temperature viscous magnetization in the deep crust

aspects of the validation of magnetic remanence in meteorites meteorite magnetic records constitute physical evidence of processes acting during early solar system evolution consequently the validation of these records is important in meteorite research the first step in the validation process should be the rem value the rem value is the ratio of natural remanence nrm to saturation remanent magnetization imparted by a 1 t magnetic field sirm the rem values range over 3 to 4 orders of magnitude for stony meteorites and for chondrules from allende c3v s1 bjurbole l4 s1 and chainpur ll3 s1 meteorites the rem values computed from published nrm and sirm data identify many orders of magnitude range in the rem values including rem values 100 10 3 these data suggest a dependence for the nrm intensity on the curatorial location from which the sample was obtained any earth rock acquiring thermoremanent magnetization trm in the geomagnetic field has a restricted range in rem mostly between 5 and 50 10 3 the exception being the mineral hematite in the multidomain size range the only terrestrial samples with rem much greater than 100 10 3 are those struck by lightning the rem value provides a physical basis for recognition between valid records and those that might be contaminated the isothermal remanence acquisition ra curve is presented as a contamination curve that allows an indication of the level of magnetic field contamination required to give the computed rem rm sirm value in the case of the bjurbole and chainpur chondrules with rem values 100 10 3 the ra curve indicates that unrealistically large contamination magnetic fields would be required to give rem values greater than 100 10 3 this would suggest contamination other than by a hand magnet that is normally available to an experimenter this would require an explanation that would involve large magnetic fields during chondrule formation or some extraordinary remanence acquisition mechanism that remains to be described magnetic contamination experiments using 80 and 40 mt magnets demonstrate that the rem values and extent of modification of the magnetic vector record are mineralogy dependent and this is mostly related to the amount and characteristics of the mineral tetrataenite the complexity of the meteorite records suggest validation of the record as a first step the rem value is the first physical statement that can be made in this validation

high density nitrogen inclusions in barite from a giant siderite vein implications for alpine evolution of the variscan basement of western carpathians slovakia contrasting compositions and densities of fluid inclusions were revealed in siderite barite intergrowths of the dro diak polymetallic vein hosted in variscan basement of the gemeric unit central european carpathians primary two phase aqueous inclusions in siderite homogenized between 101 and 165 c total salinity ranged between 18 and 27 wt and cacl2 nacl cacl2 weight ratios were fixed at 0 1 0 3 by contrast mono and two phase aqueous inclusions in barite exhibited total salinities between 2 and 22 wt and the cacl2 nacl ratios ranged from nacl to cacl2 dominated compositions the aqueous inclusions in barite were closely associated with very high density 0 55 0 745 g cm 3 nitrogen inclusions in some cases containing up to 16 mol co2 crystallization p t conditions of siderite 175 210 c 1 2 1 7 kbar constrained by the vertical oxygen isotope gradient along the studied vein isochores of fluid inclusions and the k na exchange thermometer corresponded to minimal palaeodepths between 4 3 and 6 3 km assuming lithostatic load and average crust density of 2 75 g cm 3 maximum fluid pressure during barite crystallization attained 3 6 4 4 kbar at 200 300 c and the most dense nitrogen inclusions maintained without decrepitation the residual internal pressure of 2 2 kbar at 25 c contrasting fluid compositions increasing depths of burial 4 14 km and decreasing thermal gradients 40 15 c km 1 during initial mineralization stages of the dro diak vein reflect alpine orogenic processes rather than an incipient permian rifting suggested in previous metallogenetic models siderite crystallized at rising p t in a closed rock buffered hydrothermal system developed in the variscan basement during the north vergent cretaceous thrusting and thickening of the gemeric crustal wedge variable salinities of the barite hosted inclusions reflect a fluid mixing in open hydrothermal system and re equilibration textures lengths of decrepitation cracks proportional to fluid inclusion sizes correspond to retrograde crystallization trajectory coincidental with transpression or unroofing maximum recorded fluid pressures indicate 12 km thick pile of imbricated nappe units accumulated over the gemeric basement during the cretaceous collision

metamorphic evolution and fluid composition of garnet clinopyroxene amphibolites from the tatra mountains western carpathians relics suggesting an early high pressure eclogite facies stage have been identified in the garnet and clinopyroxene bearing amphibolites of the tatra mountains in the variscan basement of the western carpathians slovakia in these rocks primary omphacite cpx i has been wholly converted to symplectites of diopside cpx ii and plagioclase apart from minor inclusions in the garnet cores amphibole and plagioclase are secondary minerals formed in the kelyphitic rims between garnet and clinopyroxene several generations of amphibole pargasite hornblende cummingtonite actinolite are evidence of a transformation down to greenschist facies conditions thermobarometric calculations from mineral inclusions in the garnet cores yield 670 700 c and 10 15 kbar recording the initial path from upper amphibolite to eclogite facies conditions the attainment of the eclogite facies stability field is inferred from the composition of a reconstructed omphacite jd36 implying a minimum peak pressure of 15 16 kbar conditions of around 650 c and 8 10 kbar record the post eclogite breakdown and partial re equilibration in the amphibolite facies region the earliest fluid inclusions contain high density nitrogen dominated water absent fluid younger are polyphase brines and two phase h2o n2 ch4 inclusions with signs of heterogeneous entrapment of coexisting gas rich and water rich immiscible phases pure nitrogen 0 5 mol ch4 is considered to have been the major component during the high pressure metamorphism in contrast the later aqueous inclusions are interpreted to represent retrogression related fluids the brines have originated by leaching and re entrapment of saline melt inclusions observed in tonalitic trondhjemitic layers of the amphibolite enclosing the eclogitic relics a similar mechanism is assumed for the origin of the h2o n2 ch4 inclusions these represent relics of the primary eclogite facies related n2 inclusions re equilibrated and re entrapped during retrogression under increasing water activity a possible source of n2 and cl rich fluids was primary amphibole which decomposed during the prograde metamorphism from the amphibolite to the eclogite facies the metamorphic pt path is generally clockwise reflecting a steep increase in pressure and temperature during burial followed by decompression and cooling the retrograded eclogites occur in boudins within an allochthonous unit of an inverted metamorphic sequence their exhumation was facilitated by tectonic transport along a ductile shear zone during the variscan orogeny

unique thermoremanent magnetization of multidomain sized hematite implications for magnetic anomalies intense magnetic remanence 100 1000 a m associated with md hematite and or titanohematite and associated with high koenigsberger ratios 40 1000 indicate that magnetic remanence may dominate the total magnetization if these minerals are volumetrically significant titanohematite behaves similarly to hematite and thus the grain size dependence of trm acquisition in hematite is considered as a generalization the transition between truly md behavior and tendency towards sd behavior in hematite has been established to be between grain sizes of 0 1 and 0 05 mm in contrast to magnetite and titanomagnetite hematite exhibits inverse grain size dependence with md hematite acquiring a relatively intense trm in the geomagnetic field comparable to sub micrometer sized magnetite and only an order of magnitude less than sd magnetite consequently md hematite and by analogy titanohematite remanence may be of significance as a source of magnetic anomalies at all scales md hematite exhibits trm weak field acquisition behavior that is different from all other magnetic minerals being the only magnetic mineral having an rem trm sirm value e0 1 for trm acquisition in the geomagnetic field the very different trm behavior of md hematite in contrast to magnetite is due to two factors the first is the lesser influence of demagnetizing energy with respect to wall pinning energy at temperatures almost up to the curie temperature for hematite the second is the greater importance of the magnetostatic energy in the applied field which for hematite dominates the total energy at high temperatures fl 2000 published by elsevier science b v all rights reserved

15 n enriched gondwana lamproites eastern india crustal n in the mantle source abstract a comagmatic suite of lamproites ultramafic lamprophyres and minettes was intruded at 100 ma into thick siliciclastic sequences deposited in five intracratonic basins which developed during gondwana rifting in eastern india lamproites are dominated by microphenocrysts of ti rich phlogopite and olivine pseudomorphed by serpentine and talc with variable modal abundances of aegirine amphibole apatite carbonates cr spinel fluorite perovskite priderite and titanomagnetite compositionally lamproites are characterized by extremely high contents of tio2 4 2 10 wt k2o and p2o5 over a range of mg from 80 to 75 in keeping with lamproites worldwide they have high abundances of ba th u and ree 1019 5400 ppm with pronounced fractionation of ree where la smcn 3 5 5 6 and gd ybcn 7 3 18 consistent with residual garnet in the mantle source nitrogen isotope compositions range from 1 6 to 8 7 with an average of 3 8 and n contents average 107 ppm mantle 15n averages 5 with a n content of 2 ppm whereas continental crust varies from 2 to 6 with 30 90 ppm n atmospheric n2 is sequestered by n fixing microorganisms and stored as kerogen with an average 15n of 3 in sedimentary rocks some of the organic n is converted to nh4 which substitutes for k in crustal k silicates the 15n enriched lamproites are interpreted to have formed from partial melting of enriched harzburgitic mantle lithosphere by decompressional melting accompanying extension enrichment resulted from subduction erosion of continental crust or subduction of sediments low degree partial melting hybridization of the melts with mantle lithosphere and incubation prior to decompressional melting consequently some crustal n is recycled to the mantle

sapphirine bearing paragneiss from the northern grenville province in labrador canada protolith composition and metamorphic p t conditions sapphirine has recently been found to be abundant throughout proterozoic 1 7 1 6 ga granulite facies quartzofeldspathic paragneiss in central labrador the pressure temperature p t trajectory of metamorphism culminated at 900 c and 9 kbar and was succeeded by nearly isobaric cooling the paragneiss has 18 o enrichment and chemical compositions which suggest that the protolith was probably highly oxidized shale chemical constraints render the involvement of partial melting during the formation of the paragneiss unlikely

n2 and co2 in deep crustal fluids evidence from the caledonides of norway abstract high pressure metamorphic rocks eclogites and high pressure granulites occur along the entire length of the norwegian caledonides and have formed from a variety of protoliths in some cases the relationship between protoliths high pressure rocks and their later retrogression products have been preserved in situ fluid inclusion data suggest a simple correlation between metamorphic grade and metamorphic fluid composition 1 eclogites and high pressure granulites contain n 2 bearing fluids pure n 2 or mixtures with co 2 or h 2 o with x n 2 5 in some eclogite facies rocks co 2 1bn 2 inclusions are associated with aqueous brine inclusions ca 30 wt nacl the two compositions representing immiscible fluids at peak metamorphic conditions 2 granulite facies protoliths and eclogites reworked in the granulite facies contain pure co 2 or co 2 dominated fluids with less than 2 5 n 2 3 rocks retrograded in the amphibolite facies contain h 2 o 1bnacl fluids immiscibility between brine and anhydrous n 2 1bco 2 fluid and between anhydrous fluid and waterbearing aluminosilicate melt have taken place in some eclogites during high grade metamorphism nitrogen may be incorporated in minerals as nh 4 substituting for k or it may occur as n 2 in the free fluid phase the partitioning of nitrogen between minerals and fluids depends upon the water activity and oxygen fugacity during metamorphism low a h 2 o and or high f o 2 partitioning nitrogen to the fluid phase a rock interacting with a carbonic fluid at granulite facies pt conditions will be depleted in mineralogically bound nitrogen in cases where the protoliths of high pressure rocks have been through a previous granulite facies event a local source for the nitrogen contained in high pressure fluid is therefore unlikely

evidence for a nitrogen flux directly derived from the european subcontinental mantle in the western eger rift central europe in the czech german border region of the vogtland and nw bohemia western eger rift central europe chemical and isotopic compositions c n he ar of free gas from a thermal water escape fluorite mine schonbrunn two mineral springs eisenquelle bad brambach sprudel iii bad elster and a mofette bublak located along an 40 km long traverse are reported the gases of bublak and bad brambach are co2 rich 99 vol and have 13c values of 1 95 and 4 29 respectively with distance from the center of co2 degassing bublak the 13c values decrease most likely due to physico chemical fractionation of co2 between gaseous and aqueous phases rather than to admixture of organic biogenic co2 the 15n values range between 3 2 and 0 6 compared to an upper mantle value of 4 0 1 0 the four locations are characterized by 3he 4he ratios decreasing from 5 9 ra in the center bublak to 0 8 ra in the periphery schonbrunn and give evidence for mixing of he from a deep seated magmatic source with a crustal source the location with the highest 3he 4he ratio 5 9 ra is accompanied by the highest 40ar 36ar 550 we argue that the nitrogen of the bublak mofette gas is a mixture of predominantly atmospheric and mantle derived components whereas at the other three locations crustal nitrogen may also be present the bublak 15n value of 4 5 1 0 represents the first free gas 15n reference from the european subcontinental mantle escm and indicates that in contrast to the 3he 4he ratios the 15n values are equal for escm and morb respectively

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

fe ti oxides in metamorphic basites from the eastern alps austria a contribution to the formation of solid solutions of natural fe ti oxide assemblages the development of fe ti oxide assemblages in basic rocks from the penninic series of the southern venediger rea austria during polyphase alpine metamorphism has been studied textural and compositional relations indicate thorough reequilibration of the opaque mineral assemblages during late barrovian metamorphism at essentially static conditions of lower amphibolite to greenschist facies in contrast silicate mineralogy of the preceeding blueschist to eclogite facies metamorphism might still be preserved to a large extent

how accurately can nrm sirm determine the ancient planetary magnetic field intensity abstract the present study tested grain size dependence of thermoremanent magnetization trm saturation isothermal remanent magnetization sirm as well as its stability against demagnetization the trm sirm ratio is dependent on the grain size of magnetite suggesting that a strong constraint on grain size characterization is necessary to be used as a paleointensity proxy in planetary magnetism in addition the trm sirm ratio increases as the alternating field increases for fine grained magnetite accuracy of trm sirm was investigated using historic showa lava erupted in 1946 it was observed that the natural remanent magnetization nrm sirm ratio of 0 032 is comparable to the field intensity of 46 80 t however the uncertainty of nrm sirm was an order of magnitude larger than that of the companion thellier estimation therefore the nrm sirm ratio can only provide crude estimations on the absolute planetary magnetic field intensity in practice anisotropy correction is advisable to reduce the scatter of nrm sirm

the origin of magnetic anomalies in lower crustal rocks labrador mid to lower crustal granulites near wilson lake in central labrador exhibit pronounced aeromagnetic anomalies areas characterized by high and low field strength correlate with the wilson lake allochthon and the surrounding autochthon respectively the induced magnetization in both units has mean values of 0 34 a m allochthon and 0 33 a m autochthon however the mean values of remanent magnetizations are 9 2 a m allochthon and 3 3 a m autochthon in directions contributing to the present geomagnetic field therefore the remanent magnetization plays the main role in generating the observed magnetic anomaly thermal demagnetizations indicate that titanhematite is stable to 585 600 c the absence of significant verwey transitions indicates that titanhematite is the predominant carrier in some rocks and a significant carrier along with magnetite in others any interpretation of the magnetic anomalies above these rocks must consider magnetic remanence as the principle anomaly source

exchange bias identifies lamellar magnetism as the origin of the natural remanent magnetization in titanohematite with ilmenite exsolution from modum norway abstract large and stable negative magnetic anomalies in southwestern sweden southern norway the adirondacks usa and quebec canada are related to rock units with a magnetic fraction consisting primarily of ilmeno hematite or hemo ilmenite it has been suggested that the unusual magnetic stability of these rocks results from lamellar magnetism this is a type of magnetic remanence carried by uncompensated magnetic layers at interfaces between nanoscale exsolution structures of antiferromagnetic afm hematite and paramagnetic ilmenite here we present the first direct proof that this lamellar magnetism indeed is responsible for the natural remanent magnetization nrm of a rock from modum norway our argument expands a previous observation that in mineral grains from this rock the cooling of a positive induced remanence from room temperature to 5 k which is well below the ordering temperature of ilmenite 57 k leads to a large negative shift of the low temperature lt hysteresis loop this can only be explained by exchange bias due to exchange coupling across the hematite ilmenite interfaces in a different experiment we now have cooled the original nrm of untreated grains to 5 k and then measured the hysteresis loop again in several separate grains we observed large shifts of the hysteresis curves this shows that exchange bias develops also from the untreated nrm this observation proves that the moments which carry the nrm also participate in the exchange coupling at the hematite ilmenite interfaces therefore the nrm is not carried by defect moments or stress induced moments which occur in normal bulk hematite a closer look at the nrm induced lt loops shows that exchange bias acts in both field directions though one direction is clearly predominant this observation can be interpreted as a frozen equilibrium of different proportions of oppositely directed lamellar moments a key feature of the original lamellar magnetism hypothesis we discuss lamellar aggregation and the formation of exchange coupled clusters to explain the observed high efficiency of lamellar nrm we also conclude that remanence carried by lamellar moments should not be used for paleointensity estimates of terrestrial or extraterrestrial material

nitrogen in fluids effecting retrogression of granulite facies gneisses a debatable mantle connection abstract the abundance patterns of nitrogen and chlorine in retrogressed granulite facies gneisses from southern east greenland exhibit strong enrichment in the vicinity of small scale shear zones sulfur in the shear zones occurs at the same concentration levels as in the adjacent country rock but is depleted in the transition zone between shear zone and country rock within the shear zone sulfur occurs as sulfate whereas in the country rock granulites it occurs as sulfide recrystallization of rock in the shear zone to scapolite bearing hornblende absent assemblages along with changes in the major element chemistry demonstrates that these zones define migration pathways of chemically reactive fluids consideration of the computed fluid compositions and of the mass ratios of chlorine sulfur and nitrogen sulfur demonstrate that the fluid equilibrated with continental crust prior to its passage through gneisses in the study area previous suggestions have been made that the mantle may act as a source region for nitrogen rich fluids however equilibration of these s n and cl rich fluids with crustal material precludes the use of element abundances to identify a mantle signature the bulk of these fluid constituents must be considered crustal derived

magnetic mineralogy in an archean crustal cross section implications for crustal magnetization a traverse across precambrian rocks from the kapuskasing uplift in ontario provided 31 samples from a crustal cross section that is now exposed at the surface about half the samples are dominantly paramagnetic magnetite accompanied in a few samples by minor amounts of pyrrhotite is the only significant magnetic mineral in the other half magnetic susceptibilities of these samples are constant between room temperature and about 540 c above which temperature they drop rapidly to zero magnetic susceptibility does not depend on rock type apparent original depth in the crust or degree of metamorphism the average induced magnetization of the most magnetic units in this section is less than 1 a m which is much lower than the source requirements for the deep crust deduced from aeromagnetic and satellite magnetometer surveys

multi stage magma ascent beneath the canary islands evidence from fluid inclusions gabbroic and ultramafic xenoliths and olivine and clinopyroxene phenocrysts in basaltic rocks from gran canaria la palma el hierro lanzarote and la gomera canary islands contain abundant co2 dominated fluid inclusions inclusion densities are strikingly similar on a regional scale histogram maxima correspond to one or more of the following pressures 1 minimum 0 55 to 1 0 gpa within the upper mantle 2 between 0 2 and 0 4 gpa the moho or the lower crust 3 at about 0 1 gpa upper crust fluid inclusions in several rocks show a bimodal density distribution the lower density maximum comprising both texturally early and late inclusions this is taken as evidence for an incomplete resetting of inclusion densities and simultaneous formation of young inclusions at well defined magma stagnation levels for gran canaria pressure estimates for early inclusions in harzburgite and dunite xenoliths and olivine phenocrysts in the host basanites overlap at 0 9 to 1 0 gpa indicating that such magma reservoir depths coincide with levels of xenolith entrainment into the magmas magma chamber pressures within the mantle inferred to represent levels of mantle xenolith entrainment are 0 65 0 95 gpa for el hierro 0 60 0 68 gpa for la palma and 0 55 0 75 gpa for lanzarote the highest density fluid inclusions in many canary island mantle xenoliths have probably survived in situ near isobaric heating at the depth of xenolith entrainment inclusion data from all islands indicate ponding of basaltic magmas at moho or lower crustal depths and possibly at an additional higher level strongly suggestive of two main crustal accumulation levels beneath each island we emphasize that repeated magmatic underplating of primitive magmas and therefore intrusive accretion are important growth mechanisms for the canary islands and by analogy for other ocean islands comparable fluid inclusion data from primitive rocks in other tectonic settings including iceland etna and continental rift systems hungary south norway indicate that magma accumulation close to moho depths shortly before eruption is not however restricted to oceanic intraplate volcanoes lower crustal ponding and crystallization prior to eruption may be the rule rather than the exception independent of the tectonic setting

magnetic petrology of deep crustal rocks ivrea zone italy magnetic petrology is an extension of petrology integrating magnetic property studies with conventional petrology for the purpose of understanding the development and modification of the magnetization in rocks the magnetic properties of a suite of samples from the ivrea zone northern italy are described with the aim of developing a magnetic petrology for deep crustal rocks samples studied include a variety of metamorphosed mafic granulites granofelses plagioklasfelse amphibolite pyriclasite and pelitic quartzo feldspathic rocks acid granulites stronalite and kinzigite gneisses schists and representative ultramafic rocks phlogopite peridotite pyroxenite hornblendite ilmenite is the chief oxide mineral in a majority of the samples but in a few mafic rocks magnetite is the principal oxide constituent cr al spinel is common in ultramafic samples and rutile is present in some metapelites sulfides are generally subordinate in abundance to oxide minerals the mafic rocks in the ivrea section have the broadest range of magnetic properties and include the most strongly magnetic samples the ivrea ultramafic rocks are moderately magnetic the magnetite present appears to be secondary and is associated with crustal alterations while pelitic and quartzo feldspathic lithologies are dominantly paramagnetic or only weakly magnetic the main ferromagnetic mineral in all strongly magnetic samples is magnetite that is nearly pure fe3o4 in composition consequently curie temperatures are 565 580 c for these rocks pyrrhotite contributes to the magnetism in several ultramafic and mafic rocks and it is the sole ferromagnetic mineral in the pelitic and quartzo feldspathic samples the results of our study indicate that certain mafic rock types amphibolites mafic granulites pyriclasites are the most likely source of the ivrea zone s regional scale magnetic anomalies if the ivrea zone represents a tectonically exposed cross section of continental crust the geographic distribution of these rock types suggests the presence of multiple and variably thick strongly magnetic layers with magnetite curie temperatures in the deep crust petrographic evidence suggests however that the magnetic mineralogy of the sampled ivrea rocks might have been changed subsequent to peak metamorphic conditions therefore considerable care must be taken in evaluating the magnetic record in these crustal cross sections particularly if they are to be used to model the magnetic characteristics of the lower crust

determination of magnetic properties of rocks by analysis of demagnetization curves hematite ilmenite bearing rocks from sw sweden granulites from the high grade sveconorwegian corresponding to grenvillian gneiss terrane of sw sweden were investigated in order to relate magnetic properties to the granulite facies mineralogy and the amphibolite facies retrograde mineralogy we used standard paleomagnetic techniques susceptibility measurements electron and optical microscopy and a new way to analyze demagnetization curves based on vector difference sums the new technique allowed quantitation of the relative contributions of partial natural remanent magnetization nrm components as well as numerical extraction of thermal and coercive force alternating field af unblocking data two major components were identified one stable which is carried by hematite ilmenite and one less stable carried by multidomain md magnetite the age of the hematite ilmenite component is circa 930 ma and it has steep negative inclination coercivities in excess of 150 mt and unblocking temperatures between 540 degrees c and 640 degrees c two corresponding poles are reported 1 paleolatitude paleolongitude plat plong 218 degrees 24 3 with dp dm 9 4 degrees 9 9 degrees paleopole and 2 plat plong 203 degrees 51 degrees with d p d m 4 4 degrees 5 6 degrees vgp the md magnetite component is a recent or cretaceous paleogene steeply positive inclined nrm component associated with strong induced magnetization plat plong 2 degrees 74 degrees and d p d m 11 degrees 14 degrees vgp the md magnetite was unblocked at conditions of 6 40 mt and 60 400 degrees c our new analysis method was successful in showing that retrograde amphibole formation strongly decreases the importance of the hematite ilmenite component on behalf of the md magnetite it has a diminishing effect on a negative aeromagnetic anomaly in the area the 930 ma components constitute 80 0 of the vector difference sums depending on rock composition however as this fraction goes down to 60 the induced magnetization seems to outweigh the hematite ilmenite influence on aeromagnetic anomalies due to its opposite direction these rocks still have a strong and stable hematite ilmenite dominated nrm less

recurrence pattern of holocene earthquakes along the dead sea transform revealed by varve counting and radiocarbon dating of lacustrine sediments abstract a high resolution holocene seismic history of the dead sea transform dst is established from laminated sedimentary cores recovered at the shores of the dead sea radiocarbon dating and annual laminae counting yield excellent agreement between disturbed sedimentary structures identified as seismites and the historical earthquake record all recent and historical strong events of the area were identified including the major earthquakes of a d 1927 1837 1212 1033 749 and 31 b c the total of 53 seismites recognized along the entire holocene profile indicate varying recurrence intervals of seismic activity between a few and 1000 years with a conspicuous minimum rate at 2100 31 b c and a noticeable maximum during the past six to eight centuries most of the epicenters of the correlated earthquakes are situated very close to the dead sea within 150 km or up to 400 km north of it along the dst between 1000 b c and a d 1063 and from a d 1600 to recent time the epicenters are all located on the northern segment of the dst whereas prior to 1000 b c and between a d 1000 and 1600 they appear to scatter along several segments of the dst we establish how the local intensity exerts a control on the formation of seismites at historically estimated intensities greater than vii all well documented earthquakes are correlated whereas at intensities smaller than vi none are matching the periods with enhanced earthquake rate along the dst correlate with those along the north anatolian fault as opposed to the intervening east anatolian fault this may indicate some elastic coupling on plate boundary scale that may also underlie escape and extrusion tectonics typical of continental collision

magnetic petrology of high fe ti eclogites from the ccsd main hole implications for subduction zone magnetism 1 the high fe ti eclogites with exsolved lamellar in 530 600 m depths from the chinese continental scientific drilling ccsd main hole in the sulu ultra high pressure uhp metamorphic belt eastern china record an anomalously high susceptibility natural remanent magnetization nrm and koenigsberger ratio q nrm ji ji is induced magnetization this provides us with a good opportunity to study the effects of magnetic minerals and exsolution lamellae on the magnetic properties of deep rocks in this paper we have measured systematically magnetic properties and mineral assemblage and structure for three special samples no 83 no 86 and no 89 results show that these fe ti rich eclogites are the result of the fine grained titano magnetite exsolution in pyroxene and lamellar structure consisting of finely interlayered ilmenite and hematite in exsolved hemo ilmenite we found that the dominant fe bearing oxide minerals in samples studied are ilmenite hematite hem ilm up to 25 little titano magnetite and pyrite the ferromagnetic susceptibility is mainly controlled by fine grained titano magnetite and nrm is closely related to the exsolved lamellar structure we hence propose that the anomalous magnetism of these eclogites observed in our samples is the result of exsolution from homogenous pyroxene and ilmeno hematite during cooling and decompression processes these fe ti rich eclogites might be one of the sources of high magnetic anomalies observed in the sulu subduction zone eastern china

trm in low magnetic fields a minimum field that can be recorded by large multidomain grains abstract thermally acquired remanent magnetization is important for the estimation of the past magnetic field present at the time of cooling rocks that cool slowly commonly contain magnetic grains of millimeter scale this study investigated 1 mm sized magnetic minerals of iron iron nickel magnetite and hematite and concluded that the thermoremanent magnetization trm acquired by these grains did not accurately record the ambient magnetic fields less than 1 t instead the trm of these grains fluctuated around a constant value consequently the magnetic grain ability to record the ambient field accurately is reduced above the critical field trm acquisition is governed by an empirical law and is proportional to saturation magnetization m s the efficiency of trm is inversely proportional to the mineral s saturation magnetization m s and is related to the number of domains in the magnetic grains the absolute field for which we have an onset of trm sensitivity is inversely proportional to the size of the magnetic grain these results have implications for previous reports of random directions in meteorites during alternating field demagnetization or thermal demagnetization of trm extraterrestrial magnetic fields in our solar system are weaker than the geomagnetic field by several orders of magnitude extraterrestrial rocks commonly contain large iron based magnetic minerals as a common part of their composition and therefore ignoring this behavior of multidomain grains can result in erroneous paleofield estimates

an equivalent layer magnetization model for australia based on magsat data abstract an equivalent layer magnetization model for australia and adjacent oceanic areas is presented the model is obtained by linear inversion of magsat anomaly data measured in the altitude range 325 550 km the anomaly data set has been isolated from the raw data set by use of models of the core field and very long wavelength external fields and is internally consistent certain major structural features of the australian continent are geographically associated with magnetization anomalies a first order difference is seen between the tasman zone and the precambrian cratonic areas magnetization anomalies are much more subdued in the former possibly reflecting a shallowing of the curie isotherm within the crust a profile of the vertical integral of magnetization is presented for a crustal section extending from the gawler block to the southeast coast it is shown that the magnetization variations are probably due partly but not wholly to depth to curie isotherm variations gross magnetization variations among at least three distinct crustal units must be involved

high density co2 n2 inclusions in eclogite facies metasediments of the munchberg gneiss complex se germany the eclogite facies metasedimentary rocks in the munchberg gneiss complex t 630 30 c p 17 24 kbar locally contain co2 n2 rich fluid inclusions of extremely low molar volumes 32 cm3 mol in quartz these fluid compositions are mainly found in rocks intercalated with calcsilicate bands densities were determined from low temperature phase transitions like stable or metastable homogenization l v l partial homogenization s l v s l and the transition s l l l liquid v vapour s solid the high fluid densities are in agreement with eclogite facies pressure and temperature and subsequent amphibolite facies co2 n2 inclusions were not observed in adjacent eclogites nor in non calcareous metasediments these rock types contain predominantly h2o rich inclusions correlating with amphibolite facies conditions the variation of fluid composition with lithological differences indicates local fluid gradients and speaks against a pervasive fluid flow during eclogite facies metamorphism

magnetization of exsolution intergrowths of hematite and ilmenite mineral chemistry phase relations and magnetic properties of hemo ilmenite ores with micron to nanometer scale lamellae from allard lake quebec hemo ilmenite ores from allard lake quebec were first studied over 50 years ago interest was renewed in these coarsely exsolved oxides based on the theory of lamellar magnetism as an explanation for the high and stable natural remanent magnetizations nrms 32 to 120 a m reported here to understand the magnetism and evolution of the exsolution lamellae the microstructures and nanostructures were studied using scanning electron microscopy and transmission electron microscopy tem phase chemistry and relations between mineral chemistry and the hematite ilmenite phase diagram cycles of exsolution during slow cooling resulted in lamellae down to 1 2 nm thick combined electron microprobe tem and x ray diffraction xrd results indicate that hematite hosts reached a composition approximately ilmenite ilm 14 4 and ilmenite hosts ilm 98 the bulk of the very stable nrm which shows thermal unblocking 595 620 c was acquired during final exsolution in the two phase region canted antiferromagnetic r3c hematite r3 ilmenite hysteresis measurements show a very strong anisotropy with a stronger coercivity normal to than parallel to the basal plane orientation of the lamellae magnetic saturation m s values are up to 914 a m compared to 564 a m predicted for a modally equivalent spin canted hematite corrected for 15 r 2 tio 3 substitution low temperature hysteresis ac susceptibility measurements and mossbauer results indicate a neel temperature t n of the geikielite substituted ilmenite at 43 k the low temperature hysteresis and ac susceptibility measurements also show a cluster spin glass like transition near 20 k below t n of ilmenite an exchange bias occurs with a 40 mt shift at 10 k

nitrogen rich fluid in the upper mantle fluid inclusions in spinel dunite from lanzarote canary islands fluid inclusions ranging from pure n2 to pure co2 occur in olivine porphyroclasts in spinel dunite xenoliths chrome diopside suite from two localities within the quaternary to historic alkaline lavas of lanzarote canary islands this is the first report of fluid inclusions containing major amounts of n2 in mantle xenoliths the nitrogen rich fluid inclusions predate at least one generation of nitrogen free carbon dioxide inclusions textural evidence indicates that the inclusions were trapped within the upper mantle some of the nitrogen rich fluid inclusions are intimately associated with solid inclusions of spinel the nitrogen rich fluid was most likely produced in situ by oxidation dehydration reactions destabilizing ammonium bearing silicate minerals phlogopite amphibole increasing oxygen fugacity or possibly increasing temperature of the mantle this process could be related to an event of co2 and silicate melt injection at 6 8 kbar neumann et al in press or to some earlier event in the evolution of the mantle beneath lanzarote the existence of a n2 rich fluid phase in at least some mantle lithology ies at certain conditions is demonstrated by these data this discovery has consequences for the understanding of the evolution of the mantle below the canary islands as well as for the global nitrogen budget

new insights into the origin of the evate apatite iron oxide carbonate deposit northeastern mozambique constrained by mineralogy textures thermochronometry and fluid inclusions the evate deposit represents the largest resource of apatite in south east africa 155 mt ore grading 9 3 wt p2o5 accumulated in up to 100 m thick magnetite carbonate apatite horizons conformable to the granulitic gneiss of the monapo klippe baddeleyite and zircon from early iron oxide magnetite geikielite spinel apatite and forsterite bearing rocks have been dated to 590 6 ma using the la icpms u pb method whereas monazites from anhydrite apatite carbonate rocks show a concordant u pb th age corresponding to 449 2 ma temperatures inferred fromcalcite dolomite solvus data and graphite structural ordering span the interval from 815 to 276 c primary and secondary fluid inclusions in apatite document calciocarbonatite melts associated with early apatite and co2 bearing sulfate chloride brines progressively dilutedwith low salinity probably meteoric waters towards ultimate stages of the deposit formation the calciocarbonatite melts have initially coexisted with liquid nitrogen and later with sulfate chloride brines mixed with n2 co2 gas crystallization of spinel around baddeleyite by the mechanismof ostwald ripening nucleation of graphite spherules along pyrrhotite carbonate boundaries the occurrence of molybdenite baddeleyite to zircon transformation and high crystallization temperatures inferred from graphite structural ordering and calcite dolomite thermometry suggest a magmatic origin of the early mineral assemblages in contrast microthermometric characteristics of primary aqueous inclusions in the late apatite and the presence of zeolites thomsonite ca mezolite is diagnostic of a low temperature hydrothermal crystallization formation of the early magnetite apatite forsterite assemblage is thought to be coeval with mafic alkalic intrusions of the mazerapane suite superimposed on the granulite facies metamorphism of the monapo klippe the low temperature anhydrite bearing mineralization was associated with the massive circulation of sulfate rich brines along fractures activated during the late cambrian ordovician extension origin of the sulfate rich brines may be genetically related either with the magmatic hydrothermal differentiation or with the remobilization of crustal evaporites

nitrogen bearing aqueous fluid inclusions in some eclogites from the western gneiss region of the norwegian caledonides minerals in eclogites from different localities in the western gneiss region of the norwegian caledonides age 425 ma contain a variety of fluid inclusions the earliest inclusions recognized are contained in undeformed quartz grains protected by garnet and consist of h2o n2 with x text h text 2 text o geqslant 0 8 the reconstructed p v t x properties of these fluid inclusions are compatible with peak or early retrograde metamorphic conditions matrix minerals quartz garnet apatite plagioclase contain a complex pattern of mostly truly secondary inclusions dominated by co2 and n2 the textural patterns and p v t x properties of these inclusions are incompatible with the high pressures of the eclogite forming metamorphic event but suggest that they were formed during uplift by a combination of remobilization of preexisting inclusions and influx of external fluids the fluid introduced at a late stage was dominated by co2 and did not contain n2 the present data agree with theoretical predictions of eclogite fluids from mineral equilibria and highlight the differences between granulite co2 and eclogite h2o n2 fluid regimes the provenance of the nitrogen in the eclogite fluid inclusions represents an important but unsolved question in the petrology of high pressure metamorphic rocks