neogene caribbean plate rotation and associated central american tectonic evolution during the neogene the caribbean plate moved eastward with respect to the north and south american plates reconstructing this motion by closing the cayman trough along its bounding transform faults creates a gore of ocean between northern central america and southern mexico we present instead a reconstruction which juxtaposes these two continental areas by strike slip motion using geological evidence from around the cayman trough the strike slip fault zones of northern central america and the continental margin of southern mexico as our constraints we propose that seafloor spreading began in the cayman trough at 30 5 ma and that subsequently there was 1100 km of relative plate displacement at an average rate of 3 7 0 6 cm yr this neogene plate motion cannot be achieved by rigid plate rotation about a single pole which implies that central america must have rotated anticlockwise relative to the rest of the plate there is evidence for internal plate deformation in central america consistent with such a sense of rotation our suggestion of an originally easterly trending arc in southern central america is more consistent with the timing and geometry of the collision of panama with northern colombia and the resultant deformation than were earlier models that depicted collision of a northerly trending arc

neotectonic and paleoseismicity studies on the urumaco fault northern falcon basin northwestern venezuela the northern falcon basin in northwestern venezuela is affected by several small active faults subordinated to the major right lateral east west trending oca ancon fault system a set of prominent nw se right lateral faults synthetic shears such as the urumaco rio seco lagarto and la soledad faults stands out among those the urumaco fault located between the lagarto and mitare rivers in the urumaco trough west of coro presents a rather complex active fault trace that comprises two nw se fault segments linked by an ene wsw reverse echelon all showing a restraining stepover geometry its western segment seems to continue to the north at sea conversely the eastern one dies out on land and its northern tip ends in a transtensive horse tail structure that disrupts an early pleistocene conglomerate this same unit is flexed and upheaved some 30 m at the restraining overlap the kinematics and present stress tensor the latest activity and the seismogenic potential of the eastern segment of the urumaco fault have been assessed at a set of three river cuts of an ephemeral tributary stream of the urumaco river 3 km north of the urumaco village where the urumaco formation is truncated by a late pleistocene terrace 14 cd ate of 20 700 950 yr bp at the base of the urumaco river on the one hand one of these outcrops features the urumaco fault affecting the late miocene urumaco formation which comprises two prominent fault planes disposed as a wedge the southwestern bounding plane juxtaposes two different sequences whereas the northeastern one does not implying different slip behavior in fact the northeastern plane shows oblique slip striations 29on normal dextral whereas the other one shows perfectly horizontal striations right lateral on the other hand both updip plane prolongations in the overlying alluvial unit are not so sharp if the 17 cm throw of the erosive bottom of such terrace measured at the lowermost part of the southwestern plane is regarded as an artifact however a mudflat deposit within this unit is bent with a 14 cm throw right above the northeastern fault plane clearly affecting the underlying miocene unit the estimated total offset per event allows to infer the occurrence of two individual events of magnitude ranging between ms 5 8 and 6 4 on this strand of the eastern segment of the urumaco fault in the last 20 000 yr 1999 elsevier science b v all rights reserved

geomagnetic intensity variation during the last 4000 years abstract thellier type determinations of the ancient geomagnetic intensity are reported for a large number of samples from greece comprising ancient pottery and other archaeologically dated forms of baked clay comparison is made with results for other parts of the world of about the same latitude the near east china and the western u s a these data indicate that in the time range studied variation of the geomagnetic dipole moment is unlikely to have been the dominant influence it is suggested that the westward drift of a non dipole disturbance could have been responsible

the 9th generation international geomagnetic reference field summary the international association of geomagnetism and aeronomy has recently released the 9th generation international geomagnetic reference field the latest version of a standard mathematical description of the earth s main magnetic field used widely in studies of the earth s deep interior its crust and its ionosphere and magnetosphere the coefficients were recently finalized at the xxiii general assembly of the international union of geophysics and geodesy held at sapporo in japan in 2003 july the igrf is the product of a huge collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and from observatories and surveys around the world

secular variation of the geomagnetic field intensity during the past 2000 years in japan abstract we report the results of paleointensity determination with volcanic rocks of izu oshima and fuji volcano japan samples used for the present study were basaltic rocks from nine lava flow units of oshima volcano which erupted between ad 590 and 1950 and aokigahara lava flow derived from fuji volcano in ad 864 demagnetization and several rock magnetic experiments show that the samples have stable single component remanences which are carried by magnetite or titanomagnetite with the psd magnetic domain state thellier s method was used for the paleointensity experiments and reliable determinations for 10 eruptive units were obtained from 58 samples in total the unit mean values generally show good consistency with the previous archaeointensity and paleointensity results allowing us to construct a reference curve of the field intensity variation for the past 2000 yr in japan the reference curve has a general trend of decreasing intensity since ad 500 showing two peaks of the field strength around ad 500 and 1400 and two troughs around ad 1200 and 1700 since around ad 800 the field intensity predictions for japan by the inversion spherical harmonic models show good consistency with the reference curve suggesting that the peak and the troughs in this period have probably been produced mainly by non dipole sources the geocentric axial dipole variation extracted from the reference curve with the inversion model shows good agreement with the global averages of the virtual axial dipole moment except that our reference curve yields a significant peak around ad 500 this suggests that a temporal strengthening of the dipole moment might have occurred over a few hundred years around ad 500

environmental impact and geochemistry of old tailing pile from the sanggok mine creek republic of korea this study evaluates the pollution load on a creek based on the physicochemical and mineralogical properties of old tailings the sanggok mine is one of the largest lead zinc producers in the hwanggangri mining district republic of korea the vertical profile of the old tailings in the mine area can be divided into three units based on color change and mineralogical and textural variations as well as physical and chemical properties unit i surface accumulation and oxidized heterogeneous tailing soil has lower ph and higher eh than unit ii originally unoxidized dumped tailing soil and unit iii pebble bearing bottom soil the conductivity data indicates that unit i and ii have very high values compared to unit iii and basement the mine area consists mainly of carbonate rocks however mineral constituents of tailing soil and sediments near the mine were mainly composed of quartz mica feldspar amphibole calcite dolomite magnesite and clay minerals units i and ii are characterized by high abundances of siderite locally pyrite and dolomite precipitates in the mining drainage mainly included smectite illite berthierine quartz siderite hexahydrite and ca ferrate among the separated metallic minerals tailing soils and sediments of highly concentrated toxic metals are found some pyrite arsenopyrite chalcopyrite sphalerite galena malachite goethite various hydroxide and uncertain secondary minerals units i and ii are characterized by relatively high concentrations of ca fe mn and low contents of al mg k na ti rare earth elements rees that correlated with the proportion of secondary minerals potentially toxic elements such as ag as cd cu pb sb and zn are highly enriched in the upper two units this metal concentration can be influenced by changes in the depth because of oxic and suboxic zonal distribution the removal zone unit i has probably migrated below the elevation of the maximum enrichment layer due to deepening of the oxic suboxic boundary in most of the materials the enrichment index is higher than 3 62 the highest value of 42 55 is found in the oxidation surface soils of the tailing pile an average enrichment index of the profiles and precipitates are 27 62 and 22 62 respectively rocky basement soils have an average enrichment index of 6 63 which is influenced by overlying the tailing pile the water quality and habitat of the sanggok creek are severely polluted polluted surface water may also negatively impact the agricultural soil and groundwater

tectonic controls of the right lateral burro negro tear fault on paleogene structure and stratigraphy northeastern maracaibo basin the northeastern maracaibo basin in western venezuela was deformed by paleogene thrusting and an associated tear fault burro negro right lateral strike slip fault zone related to paleogene oblique collision between the caribbean and south american plates two different tectonic models have been previously proposed for the thick paleogene depocenter located along the northeastern margin of the maracaibo basin the first model proposes that the depocenter is a foreland basin controlled by southwestward directed overthrusting during a late paleocene middle eocene oblique collision between the caribbean and south american plates the second model supported by data presented in this study proposes that the asymmetric paleogene maracaibo sedimentary wedge was controlled by strike slip displacement along a right lateral tear fault separating southeast directed thrust sheets to the east lara nappes from a more stable platform area to the west maracaibo basin regional seismic lines recorded to 5 s two way traveltime reveal the structure of the asymmetric paleogene depocenter in the northeastern part of the maracaibo basin the approximately 100 km 62 mi long burro negro fault is a right lateral strike slip fault separating less deformed inner to outer shelf rocks of the western maracaibo basin from highly deformed deep marine rocks of the eastern maracaibo basin seismic lines northeast of the burro negro fault zone show elongate subsurface basins bounded by partially inverted reverse and strike slip faults filled with about 3 km 1 8 mi of oligocene and miocene clastic marine sedimentary rocks structural highs of eocene rocks are characterized at depth on seismic reflection lines by chaotic seismic reflections that underlie the more coherently stratified oligocene and miocene subbasins we interpret these structural highs as steeply dipping fault zones and shale diapirs activated during eocene oligocene oblique plate convergence the geology and overall structural configuration of the northeastern maracaibo basin and the burro negro fault zone support its origin as a right lateral tear fault in our model the burro negro fault zone accommodated southeastward migration of the thrust front in the deep water area east of the fault in the present day falcn region the paleogene clastic wedge of the maracaibo basin exhibits many common features of a classic foreland basin including onlap onto an arch or forebulge located near the center of the present day lake maracaibo this paleogeographic coincidence of the burro negro fault zone and the maracaibo shelf edge suggests that the paleotrend of the south american passive margin prior to collision was serrated in map view west to east migration of the caribbean south america oblique collision formed progressively younger parallel tear faults to the east of the maracaibo basin that may have formed by the same tectonic process as the burro negro fault zone

oblique collision and accretion of the netherlands leeward antilles to south america 1 accretion of the netherlands leeward antilles volcanic island arc to northern south america offshore venezuela was accompanied by deformation and clockwise block rotation structural analysis of aruba curacao and bonaire indicates that they were deformed during at least one ductile event d1 and three brittle events f1 f3 the first deformation phase d1 and f1 began in the early cretaceous at approximately 110 ma deformation features are consistent with displacement partitioning at the obliquely convergent caribbean atlantic proto caribbean plate boundary this deformation was accompanied by an approximate 90 clockwise rotation of the forearc terrane the onset of the second phase of deformation f2 occurred in the eocene 55 ma also accompanied by a small amount of rotation and structures are consistent with wrench tectonics in a pull apart regime this coincided with the collision of the caribbean plate with the great bahama bank and the initiation of convergence between north and south america the youngest deformation structures and rotation f3 are also associated with wrench faulting likely motion along the oca fault and the caribbean plate transform fault initiated a major restraining bend in the late paleogene beginning 12 ma the northeastward escape of the maracaibo block further increased the complexity of tectonism at the caribbean south american plate boundary deformation structures are consistent with a total of 135 clockwise rotation of the leeward antilles islands and regional diachronous deformation from west to east since the early cretaceous

broad trends in geomagnetic paleointensity on hawaii during holocene time paleointensity determinations have been obtained from 22 basaltic lava flows on the island of hawaii using the thelliers method radiocarbon dating indicates that these flows erupted at intervals ranging from about 200 to 1000 years and results of the experiments provide an estimate of broad trends in geomagnetic paleointensity during holocene time in the vicinity of hawaii most of the samples were obtained from quickly cooled flow margins and as a consequence typically contain two titanomagnetite populations only two of the 79 samples analyzed failed to yield an estimate of the paleofield demonstrating that paleointensities can be obtained from such samples if carefully selected virtual dipole moments calculated for the flows are compared with a published curve of dipole field intensity that was constructed using worldwide archeomagnetic data the large nondipole fields that were previously postulated for the vicinity of hawaii are confirmed and the present data indicate that they were present from about 5000 years b p to perhaps as recently as the past 200 years the data indicate however that these nondipole sources must have been virtually absent between about 12 000 and 5000 years b p as they are at the present time

a german catalogue of archaeomagnetic data summary a catalogue has been compiled of existing published and unpublished archaeomagnetic directional data from sites in germany the data comprise 125 results dated mainly in the past two millennia the stability of the natural remanent magnetization was proven for most structures with at least a thellier viscosity test although for the majority of the data the direction is based on the characteristic remanent magnetization obtained from demagnetization experiments rock magnetic experiments carried out on the samples from many of the sites reveal that the dominant magnetic carrier is magnetite often oxidized or with impurities for many sites the archaeological age estimate is supported by physical dating methods while the roman epoch 0 400 ad and the period from medieval to modern times 800 1700 ad are reasonably well covered with data the time interval in between and the first millennium bc are only poorly covered the geographical distribution of data throughout germany shows a concentration along the rhine valley during roman times with in general a better coverage to the north nevertheless this data set clearly shows the secular variation during the past three millennia and it extends the european archaeomagnetic data set considerably

geochemistry and genesis of hydrothermal au ag pb zn deposits in the hwanggangri mineralized district republic of korea the hwanggangri mineralized district within the ogcheon metamorphic belt of the southern korean peninsula contains more than 60 w mo and cu pb zn au ag bearing metallic ore occurrences and lesser fluorite and talc occurrences related to intrusion of late cretaceous 83 90 ma i type and magnetite series granites fissure filling veins in the district differ in mineralogy with distance from the granites w mo vein deposits are located within or near 500 m the granites whereas cu pb zn vein deposits occur up to 5 km from the granites the geumsil and daehyun au ag pb zn mines are unique and represent the most distal deposits in the district they consist of quartz carbonate veins which contain economic concentrations of gold 3 g t and silver 250 g t in addition to abundant base metal sulfides 6 wt pb zn study of these au ag enriched mines provides a key to understanding ore forming processes in the outer portions of a very large batholith driven hydrothermal circulation system phase equilibria fluid inclusions and stable isotopes indicate that ore deposition was the result of interaction of progressively less evolved meteoric waters with earlier highly evolved meteoric waters early fe sulfide mineralization occurred at temperatures of 380 degrees to 310 degrees c from fluids delta 18 o 10 12ppm whose chemistry was controlled dominantly by reactions with granite and carbonate bearing host rocks main base metal au ag mineralization occurred at temperatures of 250 degrees to 210 degrees c from fluids delta 18 o 6 7ppm whose chemistry changed rapidly as a result of fluid unmixing and cooling late postore carbonates were deposited at temperatures of 250 degrees to 165 degrees c from fluids whose stable isotope compositions delta 18 o 1 4ppm delta d 89ppm and salinities 3 wt nacl reflect increasing meteoric water dominance the most intriguing result of our studies is that gold deposition occurred from fluids whose chemistries were controlled dominantly by granites and wall rocks at temperatures well below magmatic conditions 250 degrees c at great distances from the intrusion the occurrence of increased gold and silver grades in these distal areas bodes well for increased exploration for au ag pb zn deposits at relatively great distance from granite batholiths

carbonate hosted talc deposits in the contact aureole of an igneous intrusion hwanggangri mineralized zone south korea geochemistry phase relationships and stable isotope studies many talc deposits occur in the hwanggangri mineralized zone hmz in dolomitic marbles of the cambro ordovician samtaesan formation within 1 km of the contact with the cretaceous muamsa granite talc commonly forms fine grained fibrous aggregates or pseudomorphs after tremolite abundant tremolite is included as impurities in the talc ore talc generally was derived from tremolite in calc silicate rock within the dolomitic marble calc silicate rock consisting mainly of tremolite and diopside was generated from silicic metasomatism during the prograde stage which promoted decarbonation reactions until dolomite was exhausted locally hydrothermal alteration of calc silicate rock to talc is marked by the addition of mg and si and the leaching of ca cr co and ni were relatively immobile during the retrograde stage contact metamorphism related to the granite intrusion generated the successive appearance of tremolite diopside and forsterite or wollastonite bearing assemblages in the marble depending on the bulk rock composition the xco2 content of the metamorphic fluids rose initially above xco2 0 6 and decreased steadily toward a water rich composition with increasing temperature above 600 c in the calcitic marble while buffered reaction of the dolomitic marble occurred at higher xco2 conditions above 600 c talc mineralization developed under metastable conditions with infiltration of large amounts of igneous fluids along a fault shattered zone during the retrograde stage and is characterized by the loss of ca2 with the addition of mg2 oxygen and carbon isotopic variations of carbonate and calc silicate minerals are in agreement with theoretical relationships determined for decarbonation products of contact metamorphism talc formation temperatures obtained from oxygen isotope fractionation t xco2 relationships and activity diagrams range from 380 to 400 c

a late quaternary geomagnetic secular variation record from lake waiau hawaii and the question of the pacific nondipole low a continuous paleomagnetic record for the last 13 000 years was obtained from the sediments of lake waiau located near the summit of mauna kea volcano on the island of hawaii the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the hypothesis that there has been anomalously low geomagnetic sv in the central pacific was tested using angular dispersion analysis the inclination record has a mean value of 27 that is much lower than the 35 predicted by the geocentric axial dipole hypothesis the spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100 2000 3300 and 7800 years the approximately 8000 and 3500 year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation respectively the approximately 1100 and 2000 year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections in addition bauer plots of the magnetic vector are dominated by clockwise motion the angular dispersion calculated from lake sediments is 5 9 with respect to the mean virtual geomagnetic pole vgp and 9 1 with respect to the geographic pole both values are much lower than the 13 5 expected from paleosecular variation model g which separates the angular dispersion into components from the dipole and the quadruple families our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central pacific furthermore this geomagnetic behavior persists on time scales of 104 years regional anomalies in temperature topography or electrical conductivity at the core mantle boundary are inferred to cause the low sv

late quaternary marine deposits of the paraguana peninsula state of falcon northwestern venezuela preliminary geological observations and neotectonic implications abstract four marine terraces are identified on paraguana at 80 m 40 50 m 15 20 m and 6 m skirting the inselberg of cerro santa ana besides the holocene marine deposits patches of correlative sediments are only associated with the two youngest terraces within a narrow strip along the seashore because older quaternary marine terraces are mainly erosional surfaces that truncate the uppermost limestone of the pliocene paraguana formation diverse marine deposits are observed between seashore and 5 6 m sand barriers mud flats salt flats stromatolites mats coquinas and coral reefs in living position some of these facies are undoubtfully holocene but some others proved to be older than the 14 c dating limit therefore the latter ones should be ascribed to isotope stage 5 but further sampling and dating are required to confirm their chronology it is worth mentioning that probable stage 5 facies of paraguana are as high as its worldwide undeformed equivalents implying a certain tectonic stability during late pleistocene however the assumption of a stable paraguana block has to be modified since the existence of staircased marine terraces implies a certain amount of uplift even if it is rather slow 0 8 mm year

gallium germanium indium and other trace and minor elements in sphalerite as a function of deposit type a meta analysis abstract while a significant amount of analytical data on trace and minor element concentrations in sphalerite has been collected over the last six decades no meta analysis of this data has ever been conducted in this study the results of such an analysis are presented while the study focusses on ga ge and in data for six other elements ag cd co cu fe and mn was also included the results show that there are systematic statistically significant differences in the mean concentrations of fe ga ge in and mn in sphalerite from different deposit types while cd and cu concentrations show no such differences and ag and co concentrations are only significantly different for vein type deposits a principal component analysis demonstrates that the differences between deposit types are approximately one dimensional being expressible in terms of a single number this number correlates strongly with the homogenisation temperature of fluid inclusions r 2 0 82 p 16 it may be expressed as follows pc 1 ln c ga 0 22 c ge 0 22 c fe 0 37 c mn 0 20 c in 0 11 with ga ge in and mn concentrations in ppm and fe concentration in wt the relationship is sufficiently strong to be used as a geothermometer ggimfis the empirical relationship between pc 1 and the homogenisation temperature t is t c 54 4 7 3 pc 1 208 10 our results indicate a strong control of sphalerite chemistry by fluid temperature particularly for the concentrations of ga r 2 0 40 ge r 2 0 65 fe r 2 0 30 and mn r 2 0 60 and to a lesser degree in r 2 0 10 the concentrations of ag cd co and cu appear to be independent of temperature as a consequence of the strong temperature control on pc 1 metamorphic overprinting of pb zn deposits even by lower greenschist facies events may lead to significant changes in sphalerite composition namely a relative decrease in ga and ge concentrations and increase in fe mn and to a lesser degree in concentrations the closure temperature of sphalerite in regional metamorphic events appears to be around 310 50 c such that higher grade events will not be reflected in its composition factors other than temperature such as differences in fluid salinity or source rock composition do not appear to be responsible for differences between deposit types but rather appear to cause differences between individual deposits particularly the cu activity in ore forming systems appears to have a strong influence on in concentrations in sphalerite the observed trends in sphalerite compositions provide a useful tool for future studies of different types of pb zn deposits as well as for mineral exploration they should be particularly relevant for the identification of new resources of ga ge and in

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

plate motions in the north andean region repeated geodetic measurements with the global positioning system gps provide direct measurements of displacements due to plate motions and active crustal deformation in central america and northern south america an area of complex interaction of the nazca cocos caribbean and south american plates the displacement rates for the period 1988 1991 obtained from the results of the first three central and south america casa gps campaigns are in general agreement with the predictions of the nuvel 1 plate motion model but there are differences in detail between the observations and the model the nazca north andes convergence rate vector measured by gps is different from the nuvel 1 vector at 95 confidence the difference implies that the north andes are moving northward relative to south america the measured convergence between the caribbean plate and the north andes suggests that the southern margin of the caribbean plate is located in the south caribbean deformed belt the april 1991 costa rica earthquake and the cocos caribbean convergence rate determined by gps suggest the possibility of significant ongoing deformation between central america and the stable interior of the caribbean plate our gps results are consistent with deformation of the overriding plates at the convergent margins of central and south america and confirm that active convergence is occurring around much of the southern margin of the caribbean plate from colombia west to costa rica costa rica and panama are not part of the stable caribbean plate instead the south caribbean deformed belt and the north panama fold belt probably represent the southern margin of the caribbean plate

compass roses on the book of navigation kitab i bahriye declination data source for geomagnetic field models abstract the earth is surrounded by a geomagnetic field that is generated by dynamo processes in the core like a gigantic magnet the earth s geomagnetic field shifts with time and location there has been a comprehensive effort for modelling the geomagnetic field of the earth at regional and global scales by several researchers in the recent decades the magnetic data from historical sources have a great importance in geomagnetic field modelling the declination was the first measured geomagnetic field element with the early use of compasses for navigation in this study the declination values estimated from compass roses drawn on the book of navigation kitab i bahriye that are georeferenced by an artificial neural network are compared to the declination values based on the geomagnetic field models cals3k 3 and scha dif 3k the results show that the compass roses drawn on the portolan charts of kitab i bahriye can be used as declination data sources for regional or global geomagnetic field models

pleistocene ignimbrites of western armenia paleomagnetic and magnetic anisotropy constraints on flow direction and stratigraphy abstract voluminous early to middle pleistocene pyroclastic flow deposits were generated from mount aragats aragats volcanic province avp one of the largest volcanoes in the arabia eurasia continental collision zone here we report paleomagnetic results in combination with anisotropy of magnetic susceptibility ams analysis from 31 outcrops belonging to six ignimbrite units of the western part of the avp covering an area of more than 5000 km2 paleomagnetic directions analysis of samples from 26 outcrops of the three younger ignimbrite units yields a well defined normal polarity direction of d 339 2 i 55 7 k 278 4 and 95 1 7 the virtual coincidence of the paleomagnetic directions seems to point to an emplacement of the units within a restricted time of similar geomagnetic secular variation i e few hundred years however new isotope 40ar 39ar ages of the three units suggest two separated events at 0 65 and 0 75 ma we cannot fully exclude the possibility of similar paleomagnetic directions at 0 65 and 0 75 ma or the occurrence of a widespread remagnetization event at 0 65 ma but both scenarios are highly unlikely in contrast to that five sites from the three older units all show reversed magnetic polarity which implies an age of emplacement older than the last magnetic polarity reversal at 780 ka this agrees with recent 40ar 39ar ages of the three older units at 0 93 ma the paleomagnetic scatter of the older units is high compared to the younger ones even if paleomagnetic directions and radiometric age are similar available data cannot unequivocally indicate if the three older units were generated from the same or three different eruptions the high quality ams data result in three different types of fabric lineated foliated and undetermined that are all commonly observed in the studied pyroclastic deposits accordingly we use lineation tilt of foliation or both for the determination of paleoflow direction results reveal a radial flow pattern surrounding mt aragats which is however highly influenced by topographic features such as valleys even in proximity of the eruption center

basin formation along the bocono moron el pilar fault system venezuela within the boundary zone between the caribbean south america plates which includes the bocono moron el pilar right lateral fault system that has been active since the late tertiary there are several sedimentary basins in the venezuelan andes and the caribbean mountains these were formed in zones of crustal depression where faults diverge and as pull apart basins in zones of en echelon stepovers or along releasing bends in the faults in addition there are pull apart basins along the avila and la victoria faultzones in the caribbean mountains which are associated with the plate boundary the basins are filled with alluvial lacustrine fluvial and marine sediments mainly of quaternary age on the basis of model studies dimensions of the basins and age of their sedimentary fill it is estimated that right lateral offset necessary to form them along the bocono moron el pilar fault system varies from 2 to 125 km along the avila and la victoria fault zones this right lateral offset is estimated to range from 2 to 30 km on this basis the maximum right lateral offset along the southern caribbean plate boundary that can be documented along the bocono moron el pilar fault system has not exceeded 100 125 km if there has been larger offset it has to be documented by other means or it has taken place along other fault zones within the system

paleoseismology in venezuela objectives methods applications limitations and perspectives abstract the privileged location of venezuela along an active interplate deformation belt despite of being a so called developing country has led to a long paleoseismic tradition as attested by 45 trench assessments since 1968 since then a first 2 trench study was carried out by the american woodward clyde company across the oca fault at sinamaica since 1980 all further paleoseismic studies have been performed by funvisis and the uribante caparo hydroelectric project southern merida andes became their first assessment where 22 huge trenches were bulldozer dug except for these compania anonima de administracion y fomento electrico cadafe financed trenches and two others all other assessments were for petroleos de venezuela s a pdvsa in this paper geographic and geologic factors as well as logistic limitations conditioning success in paleoseismic studies by trenching shall be discussed based on the venezuelan experience developed over the years the scientific contribution of this approach refer to confirmation of holocene fault activity slip per event and average slip rate of a given fault or segment seismic potential repeat of maximum credible earthquakes of known faults fault segmentation fault interaction as consequence of stress loading by stick slip on contiguous faults time space distribution of seismic activity along a given tectonic feature seismotectonic association of historical earthquakes and landscape evolution on the short term and its implications on the long term evolution poorly discussed since this is really part of the field of neotectonics in recent years since 1999 a new approach has been introduced in venezuela consisting in complementing the seismic history derived from trenching studies with the evaluation of seismically induced perturbations in the continuous quaternary sedimentary record of either active or fossil lakes the future of this discipline in venezuela heads to more trenching and lake coring in order to gather more data on the previously mentioned aspects other paleoseismic approaches have been developed very little in venezuela since either climate or the geodynamic setting do not favor their application

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

geomagnetic jerks as chaotic fluctuations of the earth s magnetic field 1 the geomagnetic field is chaotic and can be characterized by a mean exponential time scale after which it is no longer predictable it is also ergodic so time analyses can substitute the more difficult phase space analyses taking advantage of these two properties of the earth s magnetic field a scheme of processing global geomagnetic models in time is presented to estimate fluctuations of the time scale here considering that the capability to predict the geomagnetic field is reduced over periods of geomagnetic jerks we propose a method to detect these events over a long time span this approach considers that epochs characterized by relative minima of fluctuations in time scale i e those periods when a geomagnetic field is less predictable are possible jerk occurrence dates we analyze the last 400 years of the geomagnetic field covered by the gufm1 model to detect minima of fluctuations i e epochs characterized by low values of the time scale most of the well known jerks are confirmed through this method and a few others have been suggested finally we also identify some short periods when the field is less chaotic more predictable than usual naming these periods as steady state geomagnetic regime to underline their opposite behavior with respect to jerks

archaeomagnetic research in the andean highlands abstract eleven archaeomagnetic samples were collected from several sites near porco bolivia as part of the proyecto arqueologico porco potosi these samples were collected in order to 1 explore the availability of appropriate sample materials in the bolivian andes and 2 assess the feasibility of pursuing reference curve research for this region in addition this research explored the archaeomagnetic dating application of reference curves constructed from the global geomagnetic field model gufm1 jackson et al 2000 which covers the period from ad 1590 1990 this model is particularly applicable to our project since many of the project sites are late prehispanic pre ad 1532 and early historic ca ad 1532 1825 in age of the 11 samples three appeared to contain an insufficient amount of ferromagnetic minerals to provide reliable results while eight samples produced acceptable to good results the data from the eight good samples were compared to a reference curve for the period of ad 1600 2000 that was calculated for this project from the global field model gufm1 the archaeomagnetic dates obtained for two of the samples agreed with archaeological expectations while those for four other samples marginally or greatly postdated the archaeological age expectations two additional samples produced significantly different directions and could not be dated against the reference curve it is likely that the age discrepancies for four of the samples stem from inaccuracies in the archaeomagnetic data the archaeological age expectations the calculated reference curve or some combination of these factors

the direction of the earth s magnetic field at london 1570 1975 the observations of magnetic declination and dip made in london over the past 400 years comprise one of the longest and most complete series of such data for anywhere in the world they give an indication of secular change on a time scale intermediate between that of recent observatory measurements and of archaeomagnetic measurements we have attempted to catalogue all direct measurements of declination and dip paying particular attention to completeness in the earlier years and tracing the data to their original source wherever possible sufficient details of the observations are given for an assessment of their reliability and accuracy the data are then corrected to a single site fitted with a continuous smooth curve and discussed

age and spreading history of the cayman trough as determined from depth heat flow and magnetic anomalies the opening of the cayman trough records aspects of relative motion between the north american and caribbean plates essential to accurate reconstruction of caribbean evolution assessment of opening rates based upon basement subsidence analysis as well as magnetic anomaly interpretation shows that the trough may have opened at one third to one half previously proposed rates depths to basement show that the crust has subsided away from the present axis in two stages a younger stage characterized by substantial and asymmetric greater to the east subsidence preceded by an older stage of slight increases of depth with distance depth to age relations calculated from subsidence curves which accommodate lateral as well as vertical cooling of the accreting slab indicate that the trough has opened at an overall rate of less than 15 mm yr since 25 30 ma and at 20 30 mm yr prior to 30 ma marine magnetic anomalies show lineations perpendicular to the trough including a distinct central anomaly but the pattern is neither well defined nor symmetrical about the present axis however partial anomaly sequences can be identified on both sides of the axis and the distribution of these sequences indicates that spreading may have involved frequent short ridge jumps mostly eastward the overall rate of opening as indicated by this interpretation of the magnetics is about 15 and 30 mm yr since and prior to 26 ma both subsidence and magnetics indicate that the trough opened by at least 45 50 ma

an overview of the petroleum system of maracaibo basin the geologically complex maracaibo basin in northwestern venezuela is one of the most prolific hydrocarbon basins in the world having a basinal area of 50 000 km2 19 300 mi2 the basin has produced more than 30 billion bbl of oil with estimated recoverable oil reserves of more than 44 billion bbl the central elements of the petroleum system of the basin include 1 a world class source rock upper cretaceous la luna formation deposited on a shelf to slope environment under anoxic conditions and modified by intermittent oxygenated periods and tectonic events 2 high quality clastic reservoir rocks deposited in eocene and miocene fluviodeltaic settings 3 two main periods of rapid tectonic subsidence responsible for two pulses of voluminous hydrocarbon generation first during paleogene caribbean south american oblique plate collision and second during the neogene uplift of the sierra de perij mrida andes and 4 lateral and vertical migration of oil along strike slip normal and inverted faults as well as a regional unconformity of late eocene oligocene age the maturation migration and trapping of hydrocarbons were closely controlled by the tectonic evolution of the maracaibo basin during the paleogene the development of a foredeep along the northeastern margin of the basin and the strike slip reactivation of the rift related jurassic faults on the maracaibo platform controlled the early structural setting of the source and reservoir rocks hydrocarbons migrated updip from source rocks beneath the north northeastern margin of the basin along north south strike slip faults and into overlying eocene clastic reservoirs in the south central parts of the basin the second period of the maracaibo basin petroleum system developed during subaerial exposure of most of the maracaibo basin during oligocene miocene uplift of the adjacent sierra de perij and mrida andes uplift of mountain ranges surrounding the basin folded and depressed the interior of the basin to form the extensive maracaibo syncline because of the formation of the maracaibo syncline oil generation began in the central and southern parts of the synclinal basin and migrated northward hydrocarbons migrated up the flanks of the maracaibo syncline along reactivated strike slip faults and into miocene rocks adjacent to the uplifted mountain ranges escaping oil has formed numerous surface seeps along the edges of the maracaibo basin

archaeomagnetic results from mural paintings and pyroclastic rocks in pompeii and herculaneum abstract this work investigates the magnetic remanence associated with red pigments from murals at pompeii and compares their directions to those of the pyroclastic rocks from the vesuvius ad 79 eruption the remanence of the murals is shown using x ray analyses to be carried by haematite murals in thermae stabianae known to have been painted a few years before ad 79 yield an archaeomagnetic direction d 1 2 i 58 0 95 5 5 indistinguishable from that of a nearby kiln d 358 0 i 59 1 95 1 7 evans and mareschal 1989 probably last used immediately prior to the eruption the directions are also consistent with those of fine grained pyroclastic rocks from the eruption d 351 2 i 57 9 95 3 4 and lithic and tile fragments embedded within them d 358 5 i 60 4 95 8 5 other paintings of the 1st century ad yield similar directions with a lower statistical definition this study shows that murals can retain their remanent magnetization for centuries and demonstrates the viability in principle of pictorial remanence as an archaeomagnetic tool

the paleomagnetism and u th dating of mexican stalagmite das2 a 72 cm high stalagmite from mexico das2 has been analyzed for its paleomagnetism and has provided a record of secular variation beginning about 1200 years ago to present the stalagmite did not grow uniformly and a low content of magnetic material has rendered the record less precise in some parts a topographic test involving the magnetic measurement of coeval specimens from the sides of the stalagmite has shown that the record is detectably free from depositional errors age data were provided by the u th method and concordancy checked by14c and226ra methods shallow inclinations at the base of the record are followed by a partial anticlockwise loop in the declination inclination plot there is good agreement between the das2 data and the southwest u s a archeomagnetic record and with a lacustrine record from oregon from 750 to 1400 ad comparison of the record with the present field at the site latitude shows that westward drift of the field has persisted for at least 1200 years at a drift rate of about 0 30 yr 1 a close match in declinations with the present field at the site latitude suggests that the stalagmite may have recorded the passing of the northern edge of the gulf of guinea negative anomaly about 1000 years ago though the corresponding inclination feature is not present in the record an archeomagnetic synthesis by merrill and mcelhinny of worldwide data to estimate positions of the main dipole shows that it was tilted away from mexico from 500 to 1250 ad and this may account for the shallow inclinations seen at the start of the record

quaternary tectonics and present stress tensor of the inverted northern falcon basin northwestern venezuela abstract the tertiary falcon basin in northwestern venezuela has a privileged position in the geodynamic puzzle of northwestern south america occurring in a region where several major plates caribbean south america and nazca and minor lithospheric blocks maracaibo bonaire and western colombia are interacting a combination of good exposures due to aridity and a near continuous sedimentary record in a now inverted basin helps to unravel the neogene and quaternary geodynamic evolution of this region a neotectonic and microtectonic investigation of the plio quaternary sedimentary rocks of the northern falcon basin reveals that this region is subject to a compressive to transpressive regime at present this regime is characterized by a nnw sse oriented maximum horizontal stress and a ene wsw trending intermediate or minimum horizontal stress as is confirmed by focal mechanism solutions this stress field is in agreement both with the nne directed extrusion of the maracaibo and bonaire blocks in western venezuela where the falcon basin is located and present day transpression along the caribbean south america plate boundary zone

multi decadal ingredients of the secular variation of the geomagnetic field insights from long time series of observatory data abstract the temporal evolution of the geomagnetic field is shown on data from 24 observatories with 100 150 years long time series of annual means to be composed of several ingredients which we call the steady the 80 year the 22 year and the 11 year variations the latter is the result of incomplete averaging out in the annual mean of external effects and shows a characteristic 11 year solar cycle related evolution with an amplitude of 10 40 nt in h and z and within 0 05 in d the other three characterize the main field while the steady variation carries the largest part of the main field and is smoothly increasing or decreasing in time the 80 year variation shows changes with amplitudes amounting to several hundred nt in the intensity components h and z and of 0 2 0 7 in declination the 22 year variation changes with much smaller amplitudes of 20 60 nt in h and somewhat larger in z 20 100 nt and of about 0 05 0 15 in d the analysis of the first time derivative of declination for the 24 study observatories showed that the 80 year variation dominated the secular variation in the last 100 years and that the 22 year variation has gotten its importance in defining the time evolution of the first time derivative of declination jerks included since 1960 the external contribution is decisive though in establishing the very short time scale characterizing jerks and to some extent also the amplitude and timing of the jerk the analysis of 400 years long declination time series from three european locations london munich rome resulted in tracing back of the 80 year variation to the 15th century and showed that what we called steady variation based on 150 years of observatory data proves to be only a part of a larger timescale variation when 400 years of data are available according to our results the term jerk loses its presently accepted meaning of sudden change in the temporal evolution of secular variation a more complex concept in describing the secular variation of the main field namely the superposition of several quasi periodic effects corresponding to specific core processes at various time scales should be used instead

changes in solar quiet magnetic variations since the maunder minimum a comparison of historical observations and model simulations magnetic measurements going back to the 18th century offer a unique opportunity to study multi centennial changes in the upper atmosphere we analysed measurements from rome and mannheim from may 1782 to may 1783 and measurements from greenwich st helena cape of good hope and singapore from may 1841 to may 1842 a comparison of the daily magnetic variations in these historical data with modern day observations from 2010 at nearby stations where available showed notable differences in the amplitude and or phase of the x and y components model simulations indicated that these can be explained at least to some extent by changes in the earth s main magnetic field changes in the main field strength and the north westward movement of the magnetic equator in particular in the region of the south atlantic anomaly have caused changes in the positioning shape and strength of the equivalent current vortices in the ionosphere that result in the magnetic perturbations on the ground differences in solar activity between the historical and modern epochs which were all near solar minima were too small to have a notable effect on the ground magnetic perturbations however in regions where main magnetic field changes have been relatively small for the last 400 years e g in singapore the effects of a long term increase in solar activity from maunder minimum conditions to normal solar minimum conditions an increase in f10 7 of 35 solar flux units were comparable to the effects of geomagnetic main field changes

paleomagnetic directions and thermoluminescence dating from a bread oven floor sequence in lubeck germany a record of 450 years of geomagnetic secular variation 1 a record of about 450 years of geomagnetic secular variation is presented from a single archaeological site in lubeck germany where a sequence of 25 bread oven floors has been preserved in a bakery from medieval times until today the age dating of the oven floor sequence is based on historical documents 14c dating and thermoluminescence dating it confines the time interval from about 1300 to 1800 a d paleomagnetic directions have been determined from each oven floor by means of 198 oriented hand samples after alternating field as well as thermal demagnetization experiments the characteristic remanent magnetization direction was obtained using principal component analysis the mean directions of 24 oven floors are characterized by high fisherian precision parameters 146 and small 95 confidence limits 1 2 4 6 for obtaining a smooth curve of geomagnetic secular variation for lubeck a spherical spline function was fitted to the data using a bayesian approach which considers not only the obtained ages but also stratigraphic order correlation with historical magnetic records suggests that the age estimation for the upper 10 layers was too young and must date from the end of the sixteenth to the mid of the eighteenth century for the lowermost 14 layers dating is reliable and provides a secular variation curve for germany the inclination shows a minimum in the fourteenth century and then increases by more than 10 declination shows a local minimum around 1400 a d followed by a maximum in the seventeenth century this is followed by the movement of declination about 30 to western directions

geomagnetic variation on decadal time scales what can we learn from empirical mode decomposition 1 the effects of core fluid dynamics are observable as variations in the geomagnetic field at time scales of decades to many thousands of years a non classical method empirical mode decomposition emd is performed on globally distributed observatory records of declination and inclination to study decadal variations of the geomagnetic field we use waveform analysis to test the robustness of emd and find an 11 5 year signal consistent with the solar cycle periods of 30 5 62 and 81 years are also identified in the observations and compared with results from core flow inversions these signals are likely to be of internal origin potentially the manifestation of torsional oscillations in the fluid core finally we analyse a new 600 year time series from munich and suggest that a longer 160 year period exists

unbiased analysis of geomagnetic data sets and comparison of historical data with paleomagnetic and archeomagnetic records reconstructions of the past geomagnetic field provide fundamental constraints for understanding the dynamics of the earth s interior as well as serving as basis for magnetostratigraphic and archeomagnetic dating tools such reconstructions when extending over epochs that precede the advent of instrumental measurements rely exclusively on magnetic records from archeological artifacts and farther in the past from rocks and sediments the most critical component of such indirect records is field intensity because of possible biases introduced by material properties and by laboratory protocols which do not reproduce exactly the original field recording conditions large biases are usually avoided by the use of appropriate checking procedures however smaller ones can remain undetected in individual studies and might significantly affect field reconstructions we introduce a new general approach for analyzing geomagnetic databases in order to investigate the reliability of indirect records this approach is based on the comparison of historical records with archeomagnetic and volcanic data considering temporal and spatial mismatches with adequate weighting functions and error estimation a good overall agreement is found between indirect records and historical measurements while for several subsets systematic bias is detected e g inclination shallowing of lava records we also demonstrate that simple approaches to analyzing highly inhomogeneous and internally correlated paleomagnetic datasets can lead to incorrect conclusions about the efficiency of quality checks and corrections consistent criteria for selecting and weighting data are presented in this review and can be used to improve current geomagnetic field modeling techniques

paleoseismicity studies on the oca ancon fault system northwestern venezuela abstract the e w trending right lateral oca ancon fault system extends eastward for 650 km from the colombian caribbean coast near the city of santa marta to the town of boca de aroa located on the eastern coast of falcon state northwestern venezuela across the goajira peninsula the outlet of lake maracaibo the coastal plains of buchivacoa and the central falcon range this system is very conspicuous west of the city of maracaibo where its single trace sharply truncates the northern ends of the santa marta block and the perija range fault related landforms along the system trace e g displaced beach strandlines at sinamaica and fault scarplets in the buchivacoa plains suggest that it may have been active during holocene times a first trenching attempt carried out north of maracaibo at sinamaica in 1969 only confirmed its holocene tectonic activity on the western coastal plains of falcon state and east of lake maracaibo the system is less simple as it is composed of two parallel fault strands but they are clearly evidenced by holocene paleoseismic scarplets recently this system has been paleoseismically evaluated by means of two trenches placed across each of the two parallel branches known as the oca and the ancon faults dimensions of these bulldozer dug trenches are 80 m long and 8 m deep various lines of evidence obtained from these exploratory trenches indicate that a three surface rupture events dated slightly prior to 7755 320 6240 39 and 1945 630 yr b p have occurred along the oca fault b one surface rupture event has occurred within the past 3125 185 yr on the ancon fault c the holocene slip rate of the system is close to 2 mm yr and d either of the faults can generate a maximum event of magnitude 7 4 7 5 recurrence of such earthquakes on the ancon fault is close to 1900 years while it is about 4300 years on the oca fault

estimation of relative site effect coda q and scattering strength from the records obtained by a large airgun experiment abstract by using a large capacity marine airgun we carried out a seismic refraction experiment around the bandai volcanic area in the southern part of tohoku ne japan the analysis of the observed waveform data from the airgun shots shows that the coda wave amplitude is independent of hypocentral distance after a lapse time of about 9 s at any observation site with epicentral distance q c 1 n where the power n is found to be about 0 8 in the earlier part of the lapse time the coda wave energy concentrates around the seismic source which indicates that the scattering effect is very strong in the study area the shapes of waveform envelopes at 5 10 and 20 hz show that the forward scattering factor is stronger at higher frequency than that at lower frequency

jerks abound an analysis of geomagnetic observatory data from 1957 to 2008 we present a two step method for the removal of external field signals and the identification of geomagnetic jerks in magnetic observatory monthly mean data providing quantitative uncertainty estimates on jerk occurrence times and amplitudes with minimal a priori information we apply the method to the complete time series of x y and z components at up to 103 observatory locations in the period of 1957 2008 we find features fitting the definition of jerks in individual components to be frequent and not globally contemporaneous identified regional jerks have no consistent occurrence pattern and the most widespread in any given year is identified at 30 of observatories worldwide whilst we identify jerks throughout the period of study relative peaks in the global number of jerk occurrences are found in 1968 71 1973 74 1977 79 1983 85 1989 93 1995 98 and 2002 03 with the suggestion of further poorly sampled events in the early 1960s and late 2000s the mean uncertainties on individual jerk occurrence times and amplitudes are found to be 0 3 yrs and 2 1 nt yr2 respectively for all field components jerk amplitudes suggest possible periodic trends across europe and north america which may be related to the 6 yr periods detected independently in the secular variation and length of day

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

a historical declination curve for munich from different data sources abstract long series of geomagnetic field changes are important for studying processes in the earth s core we have compiled 635 historical declination values for southern germany and surrounding areas indirect estimations including the oldest ones from back in the 15th century come from 185 sundials and compasses with declination information and 15 historical maps measurements carried out by monks in the time interval 1668 1854 amount to 122 annual mean values and data related to the orientation of mine shafts contributes by 313 annual values for several locations all these data can be useful to improve historical geomagnetic field models previously compiled german church orientations however are shown to be no reliable sources of the past declination the compiled new declination curve for munich shows general agreement with previously published curves for london and paris and allows to detect geomagnetic jerks with a temporal uncertainty of 10 years more or less regular impulses on a decadal time scale ranging from 30 to 60 years are identified for most of the time interval 1400 2000 but the century from about 1760 to 1860 seems to be devoid of sudden secular variation changes

resolving mantle and crustal contributions to ancient hydrothermal fluids hear isotopes in fluid inclusions from dae hwa wmo mineralisation south korea abstract helium and argon isotopes from fluid inclusions in individual colour zones b c d and e of a large scheelite crystal from the 88 ma dae hwa w mo deposit south korea trace the source and history of the ore fluids a gradual decrease of the fluid 3 he 4 he 3 he 36 ar and 40 ar 36 ar from the core to the edge of the scheelite reflects the progressive dilution of a magmatic fluid by meteoric water and is consistent with the previously observed decrease of 18oh2o and fluid inclusion homogenisation temperatures th shelton et al 1987 the covariation of fluid inclusion he ar isotope systematics with 18o and th defines a magmatic component with 3 he 4 he 1 2 10 6 3 he 36 ar 0 01 and 40 ar 36 ar 1000 anomalously high helium and argon isotope ratios in zone d fluids represents undiluted magmatic noble gases this may reflect local variation in the magmatic gas flux or gas loss due to boiling of the hydrothermal fluids prior to mixing with magmatic gas helium and argon isotope systematics constrain mantle and crustal components in the hydrothermal fluids 40 ar 3 he 4 5 104 are close to the mid ocean ridge basalt value implying that 40ar is mantle in origin radiogenic isotope ratios of the mantle endmember 40 ar 4 he 0 69 0 06 are similar to contemporary geothermal fluids the coincidence of mantle derived he and ar in the fluids is strong evidence that mantle melting during late cretaceous subduction triggered the crystal melting responsible for granite formation 40 ar 4 he of the meteoric fluid 0 007 0 001 is far lower than the crystal production ratio 0 2 implying an origin in crust below 200 c

hydrogeochemistry of mine surface and groundwaters from the sanggok mine creek in the upper chungju lake republic of korea the sanggok mine used to be one of the largest lead zinc mines in the hwanggangri mining district republic of korea the present study characterizes the heavy metal contamination in the abandoned sanggok mine creek on the basis of physico chemical properties of various kinds of water samples mine surface and groundwater hydrochemistry of the water samples is characterized by the relatively significant enrichment of ca2 hco3 no3 and cl in the surface and groundwaters whereas the mine water is relatively enriched in ca2 mg2 heavy metals and hco3 and so4 2 the more polluted mine water has a lower ph and higher eh conductivity and tds values the concentrations of some toxic elements al as cd cu fe mn pb se sr pb and zn are tens to hundreds of times higher in the mine water than in the unpolluted surface and groundwaters however most immobile toxic pollutants from the mine drainage were quickly removed from the surface water by the precipitation of al and fe oxyhydroxides geochemical modeling showed that potentially toxic heavy metals might exist largely in the forms of mso4 2 and m2 in the mine water these metals in the surface and groundwaters could form m2 co3 2 and oh complex ions computer simulation indicates that the saturation indices of albite alunite anhydrite chlorite fluorite gypsum halloysite and strontianite in the water samples are undersaturated and have progressively evolved toward the saturation condition however barite calcite chalcedony dolomite gibbsite illite and quartz were in equilibrium and only clay minerals were supersaturated ground and mine waters seemed to be in equilibrium with kaolinite field but some surface water were in equilibrium with gibbsite and seceded from the stability field of quartz this indicates that surface water samples in reaction with carbonate rocks would first equilibrate with carbonate minerals then gibbsite to kaolinite investigations on water quality and environmental improvement of the severely polluted sanggok creek as well as remediation methods on the possible future pollution of the groundwater by the acid mine drainage from the abandoned metal mines are urgently required

very high resolution paleosecular variation record for the last 1200 years from the aral sea 1 a record of geomagnetic paleosecular variation psv spanning the last 1200 years has been obtained from two lacustrine sediment cores from the north part of aral sea kazakhstan magnetic susceptibility and nrm intensity have been used for correlating between cores and reconstructing composite core data the main swings and fine details of declination and inclination records correlate well between both cores a very high sedimentation rate up to 25 mm per year due to recent tectonic activity of the region provides a very high resolution psv record for the interval from 450 100 years bp to 655 65 years bp the results which have been dated by eight ams radiocarbon age determinations suggest that a 200 400 years secular variation period with amplitudes in declination and inclination up to 10 15 existed regularly during the time interval 0 1200 bp amplitudes of the psv record from aral sea are not reduced and smoothed by postdetrital magnetization processes they adjoin to the historical data model and are considered to represent a reliable paleosecular variation record for the aral sea region for the last 1200 years

time dependent mapping of the magnetic field at the core mantle boundary we consider the problem of constructing a time dependent map of the magnetic field at the core mantle boundary we use almost all the available data from the last 300 years to produce two maps one for the period 1690 1840 and the other for 1840 1990 we represent the spatial dependency of the field using spherical harmonics the time dependency using a cubic b spline basis and seek the smoothest solutions compatible with the observations particular attention must be paid to the effects of the crustal field in the data we argue that for observations from permanent magnetic observatories the most efficient strategy is to use first differences of annual means for satellite data the most efficient strategy is simply to limit the number of data used so as to minimize any tendency to map the crustal field into the core field the resulting model fits the observatory data better than any previous model yet has less power in the secular variation than previous models demonstrating that very simple models fit the data the resulting time dependent field map exhibits much of the same structure in the field and its secular variation identified in earlier studies

construction of type curves of geomagnetic secular variation for dating lake sediments from east central north america type curves of palaeomagnetic secular variations of declination and inclination through the last 12 000 radiocarbon years have been constructed by combining data from the minnesota lakes with paral

present day tectonics of the southeastern caribbean and northeastern venezuela four telemetered seismic arrays were operated in northeastern venezuela during the summer of 1979 an analysis of the data collected has resulted in accurate locations for about 100 microearthquakes and four new focal mechanism solutions on the basis of these new data an in depth analysis of teleseismic data and geologic evidence we propose a new plate tectonic framework for the southeastern caribbean in this model underthrusting of the atlantic seafloor along the lesser antilles is extended to the southeast of trinidad the subducted slab is shown to dip northwesterly beneath trinidad and the caribbean sea penetrating depths of at least 150 km this subduction appears to terminate abruptly in the vicinity of the los bajos el soldado fault zone which trends wnw nw and is located in the gulf of paria west of trinidad geologic evidence shows right lateral strike slip rlss motion in this fault zone probably initiated in the late pliocene this wnw nw trending fault zone joins up with the e w trending el pilar casanay fault system in northeastern venezuela which also moves right laterally the el pilar fault is apparently offset by nnw trending faults that exhibit rlss motion as well as normal faulting this complex motion on an en echelon series of faults is interpreted to be the result of wnw motion of south america relative to the caribbean plate in our interpretation the e w component of relative motion is accommodated by rlss motion on e w faults and results in normal faulting on nnw sse faults the smaller component of n s convergence is reflected by rlss motion on nnw trending faults and is accommodated by some internal deformation the timing of the initiation of rlss motion on the los bajos fault zone and the known total amount of displacement on it as well as other geologic indicators lead us to suggest that this complex mode of strike slip motion began only a few m y ago and that the average rate of relative plate motion in this region is probably 0 9 0 2 cm yr