geoforschungszentrum anomaly magnetic map gamma a candidate model for the world digital magnetic anomaly map the world digital magnetic anomaly map wdmam is an ongoing effort toward the mapping of worldwide available aeromagnetic data it is led by a task force of the international association for geomagnetism and aeronomy iaga and aims at distributing a global map in printed and digital forms in this paper we describe in detail our candidate model which has to be evaluated by the iaga task force together with five other candidate maps after discussing the quality of the available data we show a simple but effective method applied to successfully process reduce and merge together individual compilations the near surface data are corrected using global field models and further refined with two dimensional polynomial corrections after the upward continuation to 5 km altitude data are resampled to a 3 minute grid and merged together we then calculate a spherical harmonic model up to degree 199 and analyze the magnetic spectrum of the global map this helps us to confirm that wavelengths larger than 400 km are spurious at a global scale in aeromagnetic compilations therefore we substitute them using a satellite based lithospheric field model mf5 to degree 100 finally our proposed candidate map for wdmam is presented

petrogenesis of the hercynian tichka plutonic complex western high atlas morocco trace element and rbzsr and smznd isotopic constraints the late tectonic hercynian tichka plutonic complex in morocco was emplaced in the lower cambrian volcanosedimentary sequence of the western high atlas and displays an exceptional acid basic association which consists of five well defined plutonic intrusions gabbros diorites granodiorites tonalites monzogranites and two types of leucogranites biotite amphibole leucogranites and two mica leucogranites with the exception of the late two mica leucogranites the plutonic suites present field relationships clearly indicating an almost synchronous magmatic emplacement the monzogranites and biotite amphibole leucogranites plot along the same rbzsr isochron and most of them also plot along the same smznd isochron yielding respectively ages of 291 5 ma and 283 24 ma with initial87sr 86sr and143nd 144nd ratios of 0 70348 4 and 0 51243 4 major and trace element data together with the rbzsr and smznd isotopic results rule out any genetic process involving a unique homogeneous source the smznd isotopic heterogeneity even at the scale of one unit implies the existence of contrasting source rocks and the combination of different mechanisms the gabbro and diorite magmas are assumed to be derived from the melting to different degrees of a depleted upper mantle source in a within plate geotectonic environment whereas a combined wallrock assimilation fractional crystallisation model is proposed for the evolution of the diorite suite in contrast the granitoids are mainly the result of the anatexis of a dominant basic to intermediate igneous heterogeneous continental crust

age geodynamic setting and mantle enrichment processes of a k rich intrusion from the meissen massif northern bohemian massif and implications for related occurrences from the mid european hercynian the plutonic complex of the meissen massif northern margin of the bohemian massif comprises dioritic to mainly monzonitic and granitic rocks the diorite to monzonite intrusions show major and trace element patterns typical for shoshonitic series the chemical signatures of less crustally contaminated diorites are similar to arc related shoshonitic rocks derived from continental lithospheric mantle clm sources previously enriched by subduction of altered oceanic crust laser step heating 40ar 39ar analyses on actinolitic to edenitic amphiboles from geographically different occurrences of the monzonitic intrusion yielded concordant plateau ages as well as total gas ages ranging from 329 1 1 4 to 330 4 1 4 ma and from 330 4 2 1 to 330 6 1 8 ma respectively these cooling ages are indistinguishable from sensitive highresolution ion microprobe shrimp 238u 206pb intrusion ages measured on magmatic zircon rims from the monzonite nasdala et al submitted this shows that the monzonite intrusion is probably not related temporally to active subduction because it postdates eclogites of the adjacent saxonian erzgebirge by approximately 20 ma the shoshonitic magmas intruded during strike slip tectonism along the elbe valley zone the enrichment of their mantle sources may be of upper devonian lower carboniferous age or older intrusions of shoshonitic to ultra potassic k rich rocks during the upper visean namurian are widespread in the moldanubian zone based on similar ages and structural relationships a similar post collisional setting to the meissen shoshonitic rocks can be demonstrated most of these occurrences cut high grade nappe units which were subducted during the upper devonian lower carboniferous in contrast to the meissen massif at least the ultra potassic members of the central and the south bohemian batholiths were derived from clm sources enriched by fluids or melts released from subducted oceanic crust and by greater portions of crustal material despite the similar post collisional geodynamic setting of the k rich intrusions different enrichment processes generated mid european hercynian clm sources with heterogeneous major and trace element and isotopic signatures

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

weathering mechanisms and their effects on landsliding in pelitic schist physical chemical and mineralogical analyses of undisturbed drill cores of pelitic schist from a landslide area in japan clarified the mechanisms of chemical weathering of pelitic schist oxidizing surface water percolates downward and reaches an oxidation front where chlorite is altered to al vermiculite graphite and pyrite are oxidized and depleted and goethite precipitates oxidation of pyrite also occurs just below the oxidation front probably by ferric iron pyrite oxidation yields sulphuric acid which penetrates further downward interacting with and weakening the rocks in addition to this chemical weakening stress release and shearing along schistosities form an incipient shear zone which propagates to a sliding zone that forms the rupture surface of a landslide once a sliding zone has developed it inhibits downward groundwater flow across it because of its low permeability slowing the downward propagation of the weathering zone until this filtration barrier is broken by landslide movement copyright 2010 john wiley sons ltd

timing of tibetan uplift constrained by analysis of volcanic rocks the tibetan plateau has had a central role in the development of recent models for the mechanics of mountain belts1 2 and cenozoic global climate change3 the present elevation and extensional deformation of the plateau probably result from uplift owing to convective thinning of the underlying lithospheric mantle1 2 an age for the uplift would provide a valuable constraint on these models but because recently proposed indicators of uplift are all climate dependent they are equivocal possibly reflecting global cooling rather than regional uplift4 here we present new geochemical data on post mid miocene lavas from the plateau which show that the lavas were derived from the lithospheric mantle simple thermal arguments indicate that the generation of such magmas also necessitates thinning of the lithospheric mantle thus volcanism is coincident with uplift providing a climate independent means of dating the onset of uplift dating by the laser 40ar 39ar technique places the beginning of this volcanism and therefore the time of uplift of the tibetan plateau at 13 myr ago

further studies on the use of quartz grains from fault gouges to establish the age of faulting abstract quartz grains were selected from samples of intrafauit material at two outcrop sites of the atotsugawa fault in central japan surface textures of the grains observed by scanning electron microscope were classified into texture groups i iv in the order from a simple feature through increasing undulations to a texture with cavities the defects in the quartz measured by electron spin resonance gave absolute ages using the grains the relative ages by surface texture groups were tentatively correlated to the absolute ages as determined by the electron spin resonance it was disclosed that subgroups ia and ib were stable during the period of 0 9 ma and changed through intermediate subgroup ic in a period ranging from 0 9 to 1 2 ma and then to group ii after 1 2 ma therefore the surface texture groups can change from subgroups ia and ib through intermediate subgroup ic to group ii with increasing age this indicates that the surface texture groups of quartz grains in the fault are effective for dating fault activity concisely

origin of late variscan granitoids from ne bavaria germany exemplified by ree and nd isotope systematics sm nd isotopic results are presented for late and post tectonic granitoids comprising peraluminous granites and subordinate metaluminous dioritic rocks redwitzites from the fichtelgebirge fg and northern oberpfalz nop ne bavaria the data combined with a number of earlier geochromological studies on these granitoids place severe constraints on the crustal evolution of this region during the carboniferous and pre carboniferous epoch redwitzites range in nd t from 4 to 0 inclusive data from p k holl and coworkers the nd t values of the granites s s are restricted to overlapping ranges of 8 to 3 fg and 8 to 2 nop in both domains the older granites 330 325 ma are characterized by nd t values of 4 whilst the younger granites 315 305 and 290 ma have nd t values of 4 the diversity observed in nd isotopic characteristic is interpreted in terms of different source material the nd isotopic compositions of the redwitzites exhibit source heterogeneity suggesting mixing between mantle magma and crust the nd isotopic features of the older granites are consistent with the magmatic precursors having been generated by partial melting of pre existing mature crust variably contaminated by mantle material or alternatively by melting of chemically less evolved crust resembling paragneisses of teh zev structural unit the origin of the younger granites can be confidently linked to anatexis of common moldanubian and saxothuringian metasediments two stage nd model ages tdm of the granitoids are in the range 1 1 1 7 ga these ages provide further support of substantial involvement of pre phanerozoic crust in the generation of the granitoids the leuchtenberg granite and the g2 and g3 granites yield late variscan sm nd isochron ages which are concordant with previous rb sr data on these granites by contrast the nd isotopic data for barnau and flossenburg define pseudo isochrons suggestive of mixing between contrasting felsic melts

rb sr and k ar dating of clay diagenesis in jurassic sandstone oil reservoir north sea rb sr and k ar isotopic determinations were combined with scanning electron microscopy sem observations and x ray diffractometry xrd controls to date the diagenetic formation of clay minerals from oil bearing sandstones of the middle jurassic brent sandstone in the north sea the separated clay fractions often contain detrital components especially k feldspars which are reduced to sizes smaller than 0 4 m either by intense in situ alteration or by destructive sample preparation direct rb sr and k ar isotopic dating of diagenetic illite therefore was not possible isotopic data obtained on mixtures of detrital and newly formed components showed however that illite formed about 40 to 45 ma this value also was obtained directly on clay fractions separated by a gentle method of disaggregation illitization is related to emplacement of hydrocarbons and associated waters into the formation aqueous and hydrocarbon fluids simultaneously trapped in quartz overgrowth inclusions indicate late silicification contemporaneous with this fluid migration minimum trapping temperatures of at least 110 c for these fluid inclusions are too high for the present burial depth hot fluids are assumed to have originated in deep source rocks beneath the brent reservoirs and migrated upward during the middle eocene

shoshonitic magmas in nascent arcs new evidence from submarine volcanoes in the northern marianas volcanoes in the northern mariana arc between uracas lat 20 n and minami iwo jima 24 n are very active yet entirely submarine in contrast to the predominantly low k basaltic magmas of the central mariana arc the northern mariana arc is dominated by more siliceous melts in the south and by shoshonites in the north the northern arc melts have enrichments in ba 800 ppm rb 70 ppm sr 1000 ppm ce 50 ppm and ce yb n 24 which increase to the north as far as iwo jima lavas from volcanoes north of iwo jima lack these enrichments and are indistinguishable from those of the central maranas the shoshonites are unusual in occurring along the magmatic front of a primitive intra oceanic arc we hypothesize that they represent the reconstruction of a magmatic arc following melting of enriched mantle due to the propagation of the mariana trough spreading center northward through the volcano arc shoshonites thus may characterize the initial stages of arc construction after an episode of back arc rifting and need not be restricted to the mature stages of arc evolution this situation contrasts with subduction zone initiation where first melts may be boninites or low k tholeiites these differing initial melts converge toward tholeiitic and calc alkaline compositions as arcs evolve

gigantic low gradient landslides in the northern periphery of the crimean mountains ukraine abstract large scale low gradient ancient landslides estimated at 5 4 18 9 km 2 in area and 0 2 1 2 km 3 in volume have been studied in the northern hilly periphery of the crimean mountains ukraine they originated on slopes along wide water gaps of rivers belbek kacha alma and biyuk karasu crossing the cuestas of the northern foothills the slopes generally consist of slightly northward tilting miocene mainly sarmatian limestones overlying weak clay rich lower neogene palaeogene substratum with a significant content of smectite although the region is characterised by the least active contemporary morphodynamics within the crimean mountains the landslides which were studied are of the same size or even larger than various types of landslides occupying active geomorphic domains of the highest mountain range in the southernmost part of the peninsula the landslides are generally a spreading type but the sliding mechanics were probably very complex involving toppling rotational slides gravitational folding and translational block slides all the landslides which were studied are located in the vicinity of regional faults and three of them have headscarps aligned along faults a common feature is also a location close within several km to the mesozoic suture zone which is the most important tectonic feature in the northern periphery of the crimean orogene this suture was formerly classified as aseismic however evidence of strong low frequency palaeoearthquakes was collected during the last decade within both the mesozoic suture and the low lying northern part of the crimean peninsula radiocarbon dating of deposits associated with the landslides has revealed at least two phases of increased landslide activity during the late glacial chronozone and holocene epoch the main landslide phase presumably took place at some time between the late glacial and atlantic chronozones minor reactivation of landslide toes occurred during the subatlantic chronozone and some of them have been active up to recent times the first major landslide phase was possibly triggered by an earthquake whereas late holocene activity can be attributed both to seismic and hydroclimatic factors

the downward continuation of magsat crustal anomaly field over southeast asia a general method for the local downward continuation at ground level of geopotentials measured by low orbiting satellites at different altitudes is proposed such a continuation is the inverse solution of the external dirichlet problem the stability of the solution with respect to the altitude and the distribution of data points is discussed principal component analysis is shown to perform well and leads to a stable solution the method proposed has the advantage of being directly applicable to measured data points which are not evenly spaced and at different altitude as an illustration it is applied to magsat data over southeast asia two independent maps of the vertical component of the anomaly field at a constant altitude near ground level are derived for dawn descending orbits and dusk ascending orbits data separately the two maps reveal similar anomalies and confirm the correlation of the magsat derived anomaly field with the mosaic structure of the continental crust in southeast asia stable continental blocks are associated with positive anomalies and intervening collision belts correspond to well defined negative anomalies a very prominent low is observed above the himalaya and extends over the tibet plateau confirming an anomalous crustal and thermal structure of the plateau

injection veins of crushing originated pseudotachylyte and fault gouge formed during seismic faulting this paper describes the injection veins of crushing originated pseudotachylyte and fault gouge formed along the iida matsukawa fault in granitic cataclasite southern nagano prefecture central japan the pseudotachylyte which shows a dense and aphanitic appearances and fault gouge occur as simple veins fault vein along the main fault plane and as complex network veins injection vein in the neighboring cataclasite locally the injection veins of pseudotachylyte and fault gouge can be traced back to the fault veins powder x ray diffraction patterns and petrological analysis indicate that both of the pseudotachylyte and fault gouge consist entirely of fine grained angular clasts and that the pseudotachylytes and fault gouges have a similar x ray diffraction patterns with that of the host granite the similarity of chemical compositions and distribution patterns of grain size also show that the injection veins of pseudotachylyte and fault gouge have the same source material as that of fault veins field occurrences and petrological characteristics strongly suggest that the injection veins of pseudotachylyte and fault gouge formed during seismic faulting by a rapid intrusion and fluidization of crushed fine grained materials generated in the shear zone in a gas solid fluid system

surface traces and related deformation structures of the southern sanyi fault taiwan as deduced from field mapping electrical resistivity tomography and shallow drilling abstract the southern sanyi fault extends across a highly urbanized area in central west taiwan it is within 1 2 km from and generally parallels the northern chelungpu fault which last ruptured in 1999 mw 7 6 chi chi earthquake and caused about 2400 fatalities several questions thus arise is the sanyi fault likewise active what is its geometry and extent and should it be zoned or otherwise designated to mitigate risk through restrictions on development or engineering design we address these questions by mapping river exposed outcrops by interpreting nine near surface geophysical surveys electrical resistivity tomography ert and by compiling and assessing existing shallow borehole data outcrops in the dajia river show that the sanyi fault is mainly a low angle thrust that juxtaposes poorly lithified sandstone over alluvial gravels fault branches are common both in the hanging wall and footwall to the south the fault is not marked by a break in topography and its trace has not been clearly mapped within the alluvial plain in part motivating the current effort here the ert surveys identify the hanging wall sandstone by a relatively low resistivity of

fluidization and melting of fault gouge during seismic slip identification in the nojima fault zone and implications for focal earthquake mechanisms 1 the record of physical processes that occur during seismic slip events is well preserved in fault rocks from the active nojima fault in japan the fault rocks formed at about 3 km depth and comprise thin alternating layers of very fine gouge and pseudotachylyte derived from granite each layer is thinner than a few millimeters and corresponds to one seismic slip event the very thin slip zone width suggests that some mechanisms of slip weakening operated and our studies of the fault rocks suggest that fluidization and melting of gouge were particularly important fluidized and nonfluidized gouges were distinguished using the detection probability of fragmented counterparts method it is known from granular material science that the phase transition from a grain friction regime to fluidization of granular materials can occur only by a very small decrease in volume fraction of solid grains once fluidization occurs the frictional resistance decreases abruptly to nearly zero even before thermal pressurization reaches its extreme state when fault gouge is melted frictional resistance is governed by the viscosity of melt which depends mainly on temperature chemical composition h2o concentration and the volume fraction of unmelted grains for each pseudotachylyte layer we estimated the temperature of melt using various temperature indices and measured volume fraction of unmelted grains we synthesized these data to reconstruct the change in viscosity during seismic slip events the melt viscosity is very high 107 9 pas during initial melting due to the combined effect of low temperature 750 800 c and large volume fraction of solid grains thus seismic slip is inevitably restrained instantaneously once this mechanical barrier is overcome the viscosity reduces continuously and dramatically as slip increases at 1000 c the viscosity reduces to 104pas and eventually to 10pas at 1280 c thus stress drops almost completely and rupturing tends to run away

mineralogy and genesis of planosols under a semi arid climate borborema plateau ne brazil abstract planosols such as those found on the borborema plateau ne brazil form an important class of moderately weathered soils that support subsistence agriculture in underdeveloped regions of africa asia and south america despite its socioeconomic importance the genesis of this soil class has not yet been fully elucidated this study was conducted with the aim of improving knowledge about the genesis of planosols under a semi arid climate three planosol profiles on the borborema plateau in ne brazil were collected classified and described morphologically and the main physical and chemical attributes the pedogenetic forms of iron oxides and the mineralogical compositions of the sand silt and clay fractions were determined the results indicate that a parent materials richer in feldspar and biotite favor the formation of planosols with a higher clay content b the dissolution of primary minerals and the formation of clay minerals known as the argillation process are fundamental for the genesis of bt horizons c depth drainage deficiency leads to hydromorphism an associated gray color and the formation of mottles and d monosialitization and bisialitization processes kaolinite formation and the formation of 2 1 clay minerals respectively prevail in planosols located within landscape positions that have good and poor drainage respectively in addition the present study shows that planosols under a semi arid climate can have a clay fraction consisting predominantly of kaolinite and mineralogical alteration pathways similar to those described in soils under an analogous climate and geology in northwest africa this refutes classical theories that soils with 2 1 clay minerals prevail in warmer and drier regions this study thus provides greater knowledge about the attributes of planosols in dry and poor regions and can be used as a reference in studies on the sustainable use and management of such soils

an experimentally based model for the origin of tonalitic and trondhjemitic melts abstract the results of melting experiments have been used to establish equations relating melt composition to temperature t pressure p and water content of the source y h2o for tonalitic and trondhjemitic melts produced by partial melting of average archean tholeiite aat a normative classification diagram for these rocks has been translated into a t p y h2o diagram showing the required conditions of partial melting tonalites form at high temperatures low pressures and high water contents while trondhjemites form at lower temperatures higher pressures and lower water contents as pressure increases the k content increases but the melts never achieve the composition of a granodiorite or granite a method for estimating the conditions for the formation of natural tonalites and trondhjemites is proposed the method has been successfully tested against other experimental studies and natural rocks where the temperature pressure conditions have been constrained by traditional geochemical methods

initial scalar magnetic anomaly map from magsat a scalar magnetic anomaly map between 50 geographic latitude was derived from magsat data acquired during the november 1979 to june 1980 mission lifetime separation of anomaly fields from core and external fields was accomplished utilizing techniques developed for pogo data mayhew 1979 langel et al 1980 comparison with a similar map from pogo data shows that the basic anomaly patterns are essentially reproducible except in a few regions such as the atlantic and pacific at latitudes south of 15 increased resolution due to a lower measurement altitude is evident in the magsat map

an equivalent layer magnetization model for the united states derived from satellite altitude magnetic anomalies long wavelength 500 km magnetic anomalies measured by the pogo series satellites at altitudes 400 700 km over the united states and adjacent areas are inverted to an equivalent layer magnetization model based on an equal area dipole source array at the earth s surface minimum source spacing giving a stable solution and a physically meaningful magnetization distribution is 300 km but a scheme is presented for effectively sampling the distribution on a grid twice as fine the model in effect expresses lateral variation in the vertical integral of magnetization and is a starting point for models of lateral variation in the form of the magnetization depth curve in the magnetic crust the magnetization model contours correlate with large scale tectonic features and in the western part of the country probably reflect curie isotherm undulations

microscopic features of quartz and clay particles from fault gouges and infilled fractures in granite discriminating between active and inactive faulting abstract to assist in identifying faults that have a significant potential for displacement at or near the ground surface we carried out in depth investigations on fault gouges and a fracture infilled with clay clay vein in the kojaku granite on the tsuruga peninsula central japan we sampled several fault gouges at different stages of evolutions and clay rich infilling of a fracture with no evidence of offset based on our field observations gouge in an active fault is characterized by 1 stacked layers of different colors made up of comminuted fragments and clays and 2 injection of the fragments and clays from the gouge into the surrounding rocks indicating an accumulation of seismic induced shearing our thin section observations and x ray diffraction analyses show that all our samples are similar in the degree of fragmentation and mineral composition and because of this our study became focused mainly on microscopic features using laser diffraction particle size analysis scanning electron microscopy sem and transmission electron microscopy tem we identified the mineralogical and textural characteristics of the samples in order to improve our ability to discriminate between active and inactive faulting particle size distribution analysis showed that the gouge in the active fault contains the greatest abundance of finer particles due to multiple slip events which contrasts with the clay rich infilling of a fracture sem examination of the quartz particles showed that the gouge in the active fault contains more particles that have retained sharp and smooth crystal surfaces formed by fracturing than do either the gouges in minor faults that show no evidence of recent shear or the clay rich infilling of a fracture in contrast tem observations of very fine clay minerals approximately

episodic mineralization of hydrothermal illite in the soultz sous forets granite upper rhine graben france episodic and localized illite mineralization is documented in the hydrothermally altered soultz sous forets granite upper rhine graben france separated grain size fractions of altered granite and argillite vein samples contain mixtures of 2m1 and 1m trans vacant illite varieties the platy pseudohexagonal 2m1 illite phases dominate the vein fillings whereas the 1m illite occurs largely as a fibrous pore filling variety which is particularly abundant in the granite matrix multiple phases of fluid injections into the granite body have resulted in different illite assemblages each sample containing a mixture of polytype generations formed during different crystal growth events on the basis of mineralogical and k ar isotopic constraints the ages of these vein mineralizing events are determined by plotting the k ar values of the various grain size fractions against polytype abundance and the fitted volume weighted crystallite thickness distributions the results suggest a permian age for the formation of the studied argillite veins characterized by successive injections of hydrothermal fluids secondary episodes of illite crystallization occurred during jurassic and cretaceous or even younger times in both the veins and the granite matrix there are indications that the polytype structure and composition of illite were strongly influenced by variations in fluid chemistry and the degree of fluid rock interaction as the granite was progressively sealed during post variscan episodic hydrothermal activity

coeval potassic and sodic calc alkaline series in the post collisional hercynian tanncherfi intrusive complex northeastern morocco geochemical isotopic and geochronological evidence abstract the post collisional late hercynian tanncherfi intrusive complex tic is part of a widespread intrusive episode in the moroccan meseta the complex contains a wide range of rock types from monzogabbros to monzogranites two distinct magmatic series are recognized 1 a potassic shoshonitic series consisting of monzogabbros quartz monzonites and monzogranites and 2 a sodic granodioritic series represented by quartz monzodiorites and granodiorites all the tanncherfi plutonic rocks display similar spider diagram profiles with lile and lree enrichment and nb ta ti depletion which are typical of subduction related magmas combined major trace element compositions and sr nd isotopic results indicate that the two series have been derived from a lile and lree enriched continental lithospheric mantle source under different partial melting and or depth conditions intrusion of the tanncherfi rocks was not temporally related to subduction and the enrichment of their source is likely to be linked to preceding subduction events the two series evolved by fractional crystallization of clinopyroxene plagioclase hornblende biotite k feldspar and accessories fe ti oxide minerals titanite apatite and zircon for the potassic series while the sodic series combined fractional crystallization with assimilation of felsic magmas with lower sr isotopic ratio than the more mafic term of the series the quartz monzodiorite the intrusion of the potassic magmas 344 6 ma marks a major change in the tectonic regime of eastern meseta these magmas intruded during post thickening uplift and extension both probably favored by convective thinning of the lithosphere this model provides a reasonable mechanism for the genesis of other hercynian intrusive complexes in morocco

energy evolution characteristics of hard rock during triaxial failure with different loading and unloading paths abstract triaxial compression tests were conducted on fine to medium grained granite specimens with initial confining pressures of 10 20 40 and 60 mpa under various loading and unloading stress paths the energy evolution characteristics of granite specimens from a quarry in miluo city china were studied in the triaxial deformation and failure process of the rocks the results show that the time history curves of the total strain energy elastic strain energy and dissipative strain energy exhibit significant stage features in particular the ratio of the dissipative strain energy to the total strain energy can be used to describe the deformation and degree of damage to rock specimens during the triaxial loading and unloading processes under the same initial confining pressure the maximum values of the total strain energy elastic strain energy and dissipative strain energy occur in the conventional triaxial compressive testing of group i and the minimum values occur in test group ii with constant axial stress and decreasing confining pressure the total strain energy elastic strain energy and circumferential strain energy all increase as the initial confining pressure increases whereas the dissipative strain energy does not during the process of unloading the confining pressure the increase of the circumferential strain is considerably larger than that of the axial strain under unloading conditions rock bursts may occur more easily for hard rocks than under conventional triaxial loading conditions especially under the conditions of test group iii with increasing axial stress and decreasing confining pressure the micro difference in the granite micro cracks was identified using a scanning electron microscope sem combined with an energy dispersive spectrometer eds shear failure characteristics were observed in a conventional triaxial test and the combined tension and shear failure was identified through unloading confining pressure tests the tensile failure characteristics of the granite in group iii are more pronounced than those of group ii this indicates that the triaxial failure of rock results from the development of micro extension cracks and volumetric expansion in the granite specimen under unloading confining pressure tests

extraction of magnetic anomalies of crustal origin from magsat data over the area of the japanese islands three component data along the magsat paths in the area of 110 e 170 e and 8 n 68 n were fitted by polynomial series of the coordinates of the satellite position along the path the coefficients decrease sharply up to the sixth degree and become almost constant the fields represented by the sixth degree polynomials were subtracted from the data to remove the core and the external fields for the altitude correction a rectangular harmonic analysis was applied to the residuals thus obtained by employing local cartesian coordinates the residual fields were expanded into double fourier series of the maximum order of n m 3 over areas of 4000 4000 km and 2000 2000 km and anomaly fields were computed for the satellite altitude it was revealed that 1 an intense positive anomaly of the vertical component ran along the kuril trench 2 the japan sea was covered with a negative vertical anomaly in the northeastern part and with a positive in the southwestern part 3 there was a pair of positive and negative vertical anomalies covering the area from northern korea to the east china sea suggesting the existence of an extremely localized magnetization like a dipole near the surface in the southwestern tip of the korean peninsula

spatial distribution and characteristics of fracture zones near a long lived active fault a field based study for understanding changes in underground environment caused by long term fault activities abstract fracture zone development has a substantial impact on long term changes in the underground environment because fracture zones are potential major groundwater flowpaths as well as a locus for mechanical disturbance by fracturing to understand fracture zone development we surveyed the spatial distribution and characteristics of fracture zones in areas around the atotsugawa fault a long lived active fault in central japan within 500 m of the atotsugawa fault trace the number of exposed fracture zones increases sharply and most fracture zones greater than 2 m width are concentrated the width of the clay rich fault gouge in the majority of fracture zones is less than 1 m fracture zones greater than 2 m width along the atotsugawa fault are composed mainly of a zone with numerous fractures and breccia and are considered to act as a major conduit controlling regional groundwater flow based on rock features and deformation fabrics at meso and microscopic scales once fracture zones had formed epigenetic deformation was concentrated in the older fracture zones fracture zones formed by fracturing along hydrothermal veins or fracturing and weathering that accompanied displacement along joints schistosities or lithological boundaries are sparsely but widely distributed in the study area though most of their width are less than 2 m the existence of unfavorable hydraulic characteristics needs to be studied by engineered methods for the purpose of site selection and design of underground facilities

improved compound support system for coal mine tunnels in densely faulted zones a case study of china s huainan coal field abstract when tunnelling in densely faulted zones of coal mines serious deformation often occurs due to adverse geological conditions such as extremely broken and weak rock mass high tectonic stress fissure water to investigate a more efficient support strategy for tunnels passing through densely faulted zones a tunnel in china s huainan mining area is taken as an experimental site to study an improved support method some key factors associated with the stability of tunnels in the densely faulted zone are analysed based on the analysis of failure characteristics of a previously excavated tunnel a detailed procedure for the improved support method is proposed in which a long pipe pre grouting method together with a new kind of grouting cable are applied finally the improved support strategy is implemented in the experimental tunnel the monitoring results suggest that serious deformation is avoided and the improved compound support method is feasible for tunnels in densely faulted zones

geochemical comparison between minettes and kersantites from the western european hercynian orogen trace element and pbsrnd isotope constraints on their origin trace element and isotopic characteristics of late carboniferous to early permian minettes and kersantites have been determined these lamprophyres have been sampled throughout the western european hercynian orogen from brittany to the west to schwarzwald to the east in spite of sharp petrological differences reflected by mineralogy and major element geochemistry minettes and kersantites exhibit close identity with respect to trace element and isotopic features these features comprise enrichment in incompatible elements highcs rb and lowce pb ratios ta and ti relative depletion high abundance in transition elements and highni mg ratios pb isotope ratios are undistinguishable from those measured on hercynian continental crust initial143nd 144nd ratios are between0 5120 ei 5 and0 5122 ei 1 for minettes and kersantites whereas initial87sr 86sr ratios vary between 0 7055 0 710 for minettes and 0 707 0 708 for kersantites no simple mixing relations are visible on rbsr and smnd isochron diagrams the exceptional homogeneity of these geochemical characteristics along a 1000 km traverse does not allow for an hypothesis of enrichment through upper level assimilation and thus leads to propose that these rocks originated through melting of a mantle enriched by recycling of crustal material

low to high velocity frictional properties of the clay rich gouges from the slipping zone of the 1963 vaiont slide northern italy the final slip of about 450 m at about 30 m s of the 1963 vaiont landslide italy was preceded by 3 year long creeping phase which was localized in centimeter thick clay rich layers 60 70 smectites 20 30 calcite and quartz here we investigate the frictional properties of the clay rich layers under similar deformation conditions as during the landslide 1 5 mpa normal stress 2 10 7 to 1 31 m s slip rate and displacements up to 34 m experiments were performed at room humidity and wet conditions with biaxial torsion and rotary shear apparatus the clay rich gouge was velocity independent to velocity weakening in both room humidity and wet conditions in room humidity experiments the coefficient of friction decreased from 0 47 at v 0 70 m s full lubrication results from the formation of a continuous water film in the gouge the vaiont landslide occurred under wet to saturated conditions the unstable behavior of the landslide is explained by the velocity weakening behavior of the vaiont clay rich gouges the formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero even without invoking the activation of thermal pressurization this explains the extraordinary high velocity achieved by the slide during the final collapse

fracturing mode analysis and relative age dating of faults by surface textures of quartz grains from fault gouges abstract surface textures of quartz grains taken from about 250 samples of fault gouges in faults ranging in length from several metres to several tens of metres with the faults extending several tens to several hundreds of kilometres in length are examined by means of the scanning electron microscope and are categorized into four groups from i to iv based on the smoothness of the surface degree of undulation and development of cavities as mentioned in a previous paper based on surface features of quartz grains from faults the geological age of movement of which is known the groups i to iv are tentatively related to the age of formation of quartz grains and the period of formation of surface textures this correlation makes it clear that quartz grain surface textures are an important clue to dating a relative age of faulting river patterns striations granular fracture surfaces and dimple like textures are observed to appear on less corroded surfaces of quartz grains from fault gouges fractographic analysis of these surfaces of quartz grains should be a clue to revealing the mode of fracture of the fault movement which released the quartz grains into the fault gouge

fault rock injections record paleo earthquakes fault rocks such as pseudotachylyte melt or granular gouge are sometimes injected into cracks off a fault surface the width to height ratio of the injection veins is a direct measure of the shear strain in the wall rock required to accommodate the injection so the aspect ratios preserve a record of the overpressure opening the cracks and injecting melt or fluidized granular material from the fault zone we measured the aspect ratios for 201 pseudotachylyte injections and 29 granular injections they have aspect ratios of 0 2 0 177 0 025 and 0 227 0 077 respectively within 99 confidence these are significantly proportionally wider than the aspect ratios of ordinary dikes from 10 4 to 10 3 the injection aspect ratios exceed the usual limit of elastic strain in the wallrock 1 so we infer that the injection veins were accommodated by permanent deformation by microcracking and slip on foliation surfaces in the host rock which is difficult to detect observationally the fully elastic model therefore offers an upper bound on the stress required to open these injection veins 10 8 210 10 pa with higher pressures in stiffer host rock lithologies these overpressures cannot be achieved by expansion of the fault rock fluids during melting or gouge fluidization mechanisms as the pressure along the fault is limited to 10 7

direct esr dating of fault gouge using clay minerals and the assessment of fault activity abstract the esr dating method has been applied to the fault gouge of the nojima fault the outcrop of which arose due to the southern hyogo prefecture earthquake on january 17th 1995 and to the fault gouge of the median tectonic line mtl which is a major active fault in japan without considering the resetting of esr signals the esr ages obtained for clay minerals in the fault gouges are considered to indicate the age of the beginning of the fault movements at the outcrop assuming no radon loss and the general values of water content and ray efficiency the esr ages of the fault gouges of the nojima fault and mtl are estimated as 0 55 1 16 and 6 76 9 28 ma respectively the esr age of the nojima fault is consistent with the age of the beginning of the rokko movements in the kinki districts estimated geologically on the other hand the esr age obtained from the mtl is younger than the k ar age about 11 ma which is presumably overestimated due to the existence of the source minerals in the k ar dating sample since it is geologically known that the mtl at the outcrop had moved until the late pleistocene holocene the fault movement of the mtl at this outcrop probably began at 6 76 9 28 ma b p after the intrusion of the felsitic dyke 12 16 ma which is the source rock of the fault gouge into the fault boundary the esr dating of clay minerals in the fault gouge may be effective for assessing fault activity if no quaternary deposit exists at the outcrop the younger the esr age of the fault gouge is the higher the fault activity is if not indurated and the freshest clay gouge can be collected at the outcrop the esr age of the most recent movement may be obtained from the clay gouge

sliding mechanical properties of fault gouge studied from ring shear test based microscopic morphology characterization abstract fault activity is a factor causing geological disasters and controlling their spatial distribution the information on fault activity can be recorded by the microstructure of the fault gouge sliding surface which provides an approach to study the macroscopic mechanical behavior of faults in this study the ring shear test was used to simulate the shear sliding behavior of a fault gouge under different stress states and water contents and the microstructure of the shear sliding surface was quantitatively analyzed using scanning electron microscopy sem the results revealed an evident relationship between the microstructure and macroscopic mechanical properties of the fault gouge the microstructure represented by sliding scratches was primarily created by the movement of coarse particles such as sand and quartz an index of the sliding scratch ratio was proposed to characterize the microstructure the sliding scratch ratio is negatively correlated with water content and normal stress and a multivariate model of sliding scratch ratio was established with water content normal stress and coarse particle contents allying the model to natural scratches of the fault gouge reveals that the observed sliding scratches were formed during slope sliding which proves the influence of fault on the occurrence of the studied landslide influenced by the gully land consolidation projects in the loess plateau of china the groundwater level may increase and then weaken the shear strength of fault gouge reducing the stability of slopes crossed by fault zone therefore more attention should be paid to potential geological disasters induced by faults in gully filled areas

structural and isotopic constraints on fluid flow regimes and fluid pathways during upper crustal deformation an example from the taemas area of the lachlan orogen se australia 1 structural and stable isotope studies of calcite veins and host rocks in a 1000 m thick devonian limestone sequence in the taemas area of the lachlan orogen in se australia indicate that externally derived fluids migrated through the sequence over a protracted interval during folding and associated reverse faulting at temperatures of 200 c the evolution of fluid pathways was governed by growth of fold related and fault related fracture networks at transiently supralithostatic fluid pressures the internal structures of veins indicate growth during repeated cycles of permeability enhancement and sealing systematic increase in 18o of vein calcite upward through the limestone sequence and the presence of an o isotope alteration front in the vein system is related to buffering of fluid compositions by fluid rock reaction during upward migration of overpressured low 18o fluids repeated switching of fractures between high permeability and low permeability states promoted episodic flow and changes in flow paths during progressive deformation a lack of significant migration of the isotopic front during the flow history is consistent with fluid rock interaction being associated with numerous separate pulses of fluid ascending through the percolation network irregular variations in fluid 18o with time during vein growth are interpreted to be driven by repeated changes in reactive path lengths reaction rates and flow rates in a discontinuous flow regime systematic upward changes in vein 18o over an area of 20 km2 requires that on a time averaged basis most of the vein system was hydraulically well connected to the external fluid reservoir and that growth of the fracture network occurred by fluid driven invasion percolation processes repeated failure and sealing events in the fracture system are interpreted to have been driven by episodic migration of fluid pressure waves up through the fracture network possibly in response to deeper level fault rupture events repeatedly breaching an overpressured fluid reservoir