chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

influence of offset weak zones on the development of rift basins activation and abandonment during continental extension and breakup 1 we use numerical modelling to investigate reactivation of inherited offset weak zones owz in continental crust and mantle weak zones mwz to form offset rift basins during continental rifting and breakup offset rift basins are basins that are set off offset from the main rift locus of breakup weak zones embedded in a stiff layer are preferentially and rapidly reactivated whereas the same zones are either ignored or slowly reactivated when embedded in pliable layers here stiff implies a nonlinear flow law with a high stress exponent n 10 000 a plastic material and pliable means a low stress exponent n 2 5 as in ductile power law creep of rocks whether offset rift basins form during rifting of a composite lithosphere i e comprising stiff and pliable layers depends on the competition between necking instabilities that develop at the weak zones in the stiff layers and the coupling between the stiff and pliable layers stiff cratonic lithosphere results in early localization of the deformation at the mwz rapid necking and breakup without developing offset rift basins in contrast warm pliable lithosphere develops significant offset basins and has protracted rifting because the mwz is now embedded in a pliable layer we also investigate the influence of owz dip sedimentation and the sensitivity of reactivation to the distance from owz to the mwz and to the size of the mwz a tectonic rifting styles diagram is used to show that the model results agree with natural examples

paleosol sedimentary sequences of the glacis de buenavista central mexico interaction of late quaternary pedogenesis and volcanic sedimentation abstract two sections buenavista and ahuatenco of late quaternary paleosol sedimentary sequences of the glacis de buenavista morelos central mexico were studied and interpreted as a regional record of climatic change and interaction of pedogenesis and volcanic sedimentation buenavista is the deepest section and includes seven pedostratigraphic units with andosol surface unit and luvisol all underlying units types of pedogenesis both types indicate a humid forest environment the divergency being related to differences in pedogenesis duration albeluvisol with a bleached e horizon in unit 5 indicates cooler but still moist conditions in the final late pleistocene whereas strong vertic properties in unit 4 indicate a climate with contrasting seasonal variation of precipitation during the first part of the holocene in the upper part of the ahuatenco section bt horizons of different pedogenetic events form a welded luvisol profile instead of a set of separate paleosols due to less intensive sedimentation material of indurated cm horizons tepetates in the lower part of the ahuatenco section is a mixture of fresh coarse volcanoclastic components and re deposited luvisol clayey material formed by mass movement associated with volcanic events the resulting granulometric composition of these layers is favourable for structural collapse and hydroconsolidation which caused hardening together with subsequent pedogenic illuviation and redoximorphic processes

andosolization of ferrallitic soils in the bambouto mountains west cameroon abstract soils along a toposequence 1500 2260 m on the southern slope of the volcanic bambouto mountains in western cameroon were investigated to elucidate the occurrence and development of andic properties at high altitude 1800 m in the study area the surface layer that has these properties has in the past been interpreted as a weathered volcanic ash layer overlying ferrallitic soils that developed from lava flow deposits and derived pediments physico chemical and mineralogical data demonstrate that the andic properties of the high altitude pedons result from som accumulation favoured by climate and vegetation the andosolization process affecting these profiles involves the formation of organo metallic complexes which is mediated by organic ligands and controlled by the dissolution of gibbsite and iron oxides increasing andosolization with increasing altitude due to som accumulation is well reflected by soil classification names especially by the humic qualifier for the soils below 1800 m a s l and the protoandic subqualifier for the soils at higher altitude all analysed properties show features that are incompatible with derivation of the upper part of the high altitude pedons from volcanic ash in studies of soils from similar settings care should be taken to avoid misinterpretation of surface horizons marked by environmentally conditioned development of organo metallic complexes as ash derived layers

extension and rifting the zeit region gulf of suez abstract a field analysis of faults and fractures in the ras gharib ras gemsa region of the gulf of suez shows that the main late cenozoic extension occurred perpendicular to the rift axis three main types of dip slip normal faults successively developed as the tilt of blocks bounded by antithetic normal faults increased determinations of the amount of extension from structural data are compatible with estimates made using subsidence data through a simplified model of lithospheric stretching the uplift of rift shoulders is related in chronology and volume to the subsidence of the rift the geometry of fault patterns and directions of extension suggests that the late cenozoic total movement corresponds to a counterclockwise rotation of 4 5 of sinai relative to africa with a pole close to cairo

from rifting to active spreading in the lau basin havre trough backarc system sw pacific locking unlocking induced by seamount chain subduction associated with pacific australia plate convergence the lau basin havre trough is an active back arc basin that has been opened since 5 5 ma by rifting and southward propagating oceanic spreading current back arc opening rates decrease from 159 mm yr 1 in the northern lau basin to 15 mm y 1 in the southern havre trough major tectonic changes occur at the transition between havre trough rifting and full oceanic spreading of the eastern lau spreading center elsc where the oblique to trench westward subducting louisville seamount chain lsc sweeps southwards along the tonga trench new swath bathymetry seismic reflection data and limited rock sampling in this area constrain a tectonic and kinematic back arc model that incorporates the effects of lsc subduction the elsc which extends southward to 24 55 s forms a deep rift valley propagating southward through older rifted arc basement present day seismicity and fresh and fractured pillow lavas at 23 42 s are consistent with rift valley neovolcanism conversely the northern havre trough has low seismicity and rifted volcanic basement ridges trending 25 45 oblique to the basin axis consistent with low levels of extensional tectonism and volcanism this latter structural fabric is interpreted as an early stage of rifting that is now locked due to compression on the arc exerted by lsc subduction while in the lau basin such effects have passed as the lsc swept along the tonga trench it is proposed that the lau havre back arc opening is controlled by tectonic constraints exerted at the limits of the system by the lsc subduction which determines the southward migration of the tonga arc pole of rotation and associated lau basin opening a discrete three stage back arc opening evolution is proposed comprising 1 an initial phase of back arc rifting along the whole length of the plate boundary beginning at 6 5 ma 2 a subsequent phase mostly present in the southern part of the back arc domain and still active in the havre trough of transpression and transtension starting at 4 ma in the north as the lsc starts to subduct and sweeps southward along the tonga trench and 3 a renewed opening phase in the northern segment of the back arc domain with rifting and spreading starting at 3 5 ma as subduction of the lsc along the northern tonga trench is progressively completed

hydric properties of high charge halloysitic clay soils from the tropical south pacific region in humid tropical areas the spatial distribution of volcanic ash soils generally follows a weathering sequence in which halloysite rich soils represent an intermediate weathering stage between young soils andosols and strongly weathered soils ferralsols strongly weathered soils rich in crystalline iron oxide and kaolinite are known for their fast and free drainage as well as for their large water retention in micropores caused by micro aggregation they exhibit however low available water here we report on similar properties in halloysitic soils derived from volcanic ash in tongatapu island kingdom of tonga pacific the soils are fine clayey 68 96 clay and contain three dominant constituents humic substances halloysite and iron oxide 6 12 they exhibit a relatively large reserve in alkaline and alkaline earth cations confined to the clay fraction and more specifically to exchangeable and non exchangeable cations associated with high charge clay minerals detected by xrd as smectite whatever the soil layer and the soil organic matter content the soil materials have exceptionally high saturated hydraulic conductivity ranging from 7 to 85 cm h 1 and large water retention 30 40 at low hydric potential 15 000 hpa the water properties show that these soils are strongly micro aggregated we propose that they are caused by specific interactions between halloysite and high surface area iron oxide c 2006 published by elsevier b v

premiers stades d alteration de ponces volcaniques en climat tropical humide montagne pelee martinique abstract the early stages 0 2000 years of soil development on dacito andesitic pyroclasts in the humid tropics were studied in a chronosequence made of three main deposits dated 48 bp 650 bp and 1670 bp respectively which cover the massif of montagne pelee martinique the initial pumices are essentially glassy rich in silicon and aluminium calcium and sodium the nature of secondary products was investigated through particle size fractionation elemental analysis selective dissolution of amorphous products differential thermal analysis xr diffraction and electron microscopy within this period the weathered horizon reached a depth of 30 to 50 cm the median size of particles decreased from approximately 2 mm 48 bp to 0 2 mm 1670 bp the mass of secondary products was estimated to be 1 2 in the youngest soil 48 bp and approximately 10 in the oldest one 1670 bp seventy percent of the secondary products were found in particles finer than 20 m these products are aluminium rich and mainly composed of allophanic products low quantities of clay minerals were detected mainly microspheric halloysite

the role of pedogenesis in palaeosols of mexico basin and its implication in the paleoenvironmental reconstruction abstract most of the paleoenvironmental information for the basin of mexico comes from sedimentary proxies which unfortunately are incomplete for the terminal pleistocene and the holocene in this paper we present a temporal and spatial reconstruction of past soil cover in the south and north of the basin of mexico during the mis 2 and 1 marine isotope stage 2 and 1 palaeosol profiles were selected from three locations cuicuilco copilco and avon in the south basin and compared with soils studied in the teotihuacan valley pachuca and texcoco at north of the basin the results show that the pleistocene soil cover is more homogeneous dominated by the presence of luvisol type soils with secondary carbonates dated to around 20 000 cal yr bp during the holocene the soil distribution changes with andosols developing in the south while vertisols and calcisols form in the north the new soil distribution reflects differing climate conditions during the holocene conditions which characterize the basin today the andosol cover in south basin however represents the result of short term pedogenesis andosols are considered high quality soils that were attractive to settlers and were a factor in the development of sedentary villages

styles of lithospheric extension controlled by underplated mafic bodies abstract the role of underplated mafic bodies upmb in the localization of deformation is examined using a two dimensional thermo mechanical finite element model rheological heterogeneity brought about by the upmb is linked with the following two main physical effects the upmb material is assumed to have 1 an anomalous high temperature and 2 a mafic crustal rock composition that is intrinsically weaker than the mantle the thermal effect will disappear rather quickly but the rock composition can have an effect at any stage of extension we show that the upmb has a strong influence on the style of lithospheric extension which depends on the thermal condition of the uppermost mantle at the time when the upmb is emplaced since the strength contrast between the weakened and non weakened regions is the most important factor the upmb works more efficiently on the localization of deformation for a colder uppermost mantle dependence of the localization of deformation on the temperature and thickness of the upmb i e more significant localization for the upmb with higher temperature and greater thickness also depends on the thermal condition of the uppermost mantle however the width of the upmb has a strong influence on the localization for any thermal condition of the uppermost mantle a greater amount of thinning is distributed into a narrower weakened region such a model behaviour implies that various styles of lithospheric extension including inward or outward migration of deformation and asymmetric extension can be simply obtained by considering the emplacement of the upmb which also plays an important role in controlling the onset of continental break up

the subsurface structure of the aira caldera and its vicinity in southern kyushu japan abstract southern kyushu japan includes a chain of large and small calderas and active volcanoes and the greatest part of it is covered with thick pyroclastic ejecta the regional and local structures of this area are discussed from the standpoint of physical volcanology with consideration of all available data the regional structure of this area is examined in the light of gravity and geomagnetic anomalies two layers of the earth s uppermost crust are defined by spectrum analysis of the gravity anomalies these two layers are identical with the two identified by seismicwave velocities the bouguer gravity anomalies are relatively high and rather monotonous over outcrops of the mesozoic basement and the granite but are relatively low and perturbed over calderas and caldera like structures two low gravity anomalies in kagoshima bay are remarkable one is circular with its center on the aira caldera the other is elongated between the satsuma and oosumi peninsulas the southern end of the latter anomaly is occupied by the ata caldera discussion of the gravity anomalies of the aira caldera suggests that the subsurface basement has a funnel shape and is overlain by fallback the sub bottom geology of the caldera suggests that it is formed by a few smaller depressions though the distribution of the overall gravity anomalies is parallel with its shape the southern part of kagoshima bay is characterized by a graben like topography and low gravity anomalies and moreover by several calderas the middle part between the aira and ata calderas may have a graben like structure a profile crossing the bay through sakurajima volcano is modeled on the basis of results from drilling and gravity surveys the basement has a graben like structure and is filled with coarse and low density deposits and the structure continues northwards to the aira caldera with a funnel shape a comparison of this area with the taupo rotorua depression in new zealand and lake toba in indonesia leads the authors to the conclusion that such major volcanic depressions may have been formed by amalgamation of a series of caldera like structures which were formed by multiple violent explosions accompanied by ejection of a tremendous amount of pyroclastic material

coexistence of allophane gibbsite kaolinite and hydroxy al interlayered 2 1 clay minerals in a perudic andosol allophane and halloysite are the most common secondary aluminosilicate minerals in andosols developed in pyroclasts in humid tropical areas we studied the composition and the charge properties of the clays extracted from the weathered b horizon of a perhydrated andosol developed in andesitic ash in guadeloupe french west indies by selective dissolution x ray diffraction xrd thermal analysis and characterization of ion exchange properties the bw horizon contained weatherable minerals and exhibited an allophane content of 25 its clay fraction contained gibbsite allophane kaolinite and hydroxy al interlayered 2 1 clay minerals the occurrence of gibbsite allophane and kaolinite was linked with intense leaching of silica after oxalate dissolution of allophane the cation exchange capacity cec was 11 8 cmol c kg 1 clay i e a typical value for low activity clays subsequent citrate treatment completely dissolved gibbsite but partly extracted al interlayers from the hydroxy al interlayered phase this extraction led to a 5 6 fold increase of the cation exchange capacity 62 3 cmol c kg 1 clay and a 2 3 fold increase in k selectivity the 2 1 clay minerals involved a combination or continuum of high charge beidellite and vermiculite from our data we believe that the 2 1 clay minerals first acted as a sink for aluminium and might have expressed an anti gibbsitic effect after substantial al interlayering of 2 1 clay minerals mimicking low activity clay gibbsite might have formed in a second stage c 2003 elsevier science b v all rights reserved

halloysite neoformation during the weathering of nephelinitic rocks under humid tropical conditions at mt etinde cameroon abstract mt etinde eruptions are dated at 0 65 ma it is located on the sw oceanic border of mt cameroon and is composed essentially of nephenilitic rocks the weathering of nephelinites has resulted in the formation of a 150 cm deep andic cambisol humic consisting of three horizons ah bw c mineral weathering was studied in detail in two profiles one p 1 developed from unaltered nephelinite nephelinite u and the other p 2 formed from hydrothermally altered nephelinite nephelinite h emphasis was on the impact of hydrothermal alterations on weathering profiles to characterise the signature of halloysite in nephelinitic regoliths and to discuss the evolution of mt etinde soils on the quaternary nephelinitic parent rocks the mineralogy of nephelinite u consists predominantly of clinopyroxene nepheline leucite hauyne titanomagnetite perovskite apatite and sphene nephelinite h differs from nephelinite u by phillipsite calcite occurrence the main weathering products are halloysites 1 nm and 0 7 nm and minor occurrence of gibbsite and hematite sem micromorphological examination coupled with microprobe analyses showed halloysites resulting from in situ alterations of feldspathoids phillipsites and clinopyroxenes 1 nm hydrated halloysite neoformation characterises the alteromorphs of the saprolite while 1 nm and 0 7 nm halloysite coexist in the bw and the ah horizons of both soils during weathering these halloysites had a chemical dependence with parent mineral as follows ce rich halloysite characterises alteromorph after phillipsite fe rich halloysite alteromorph after clinopyroxene ca rich halloysite alteromorph after hauyne and k rich halloysite alteromorph after leucite ce rich halloysite is a tracer of the hydrothermal impact in soils profile the si al ratio is also characteristic of the parent mineral therefore the availability of si is the only factor that controlled the formation of 1 nm halloysite at the base of the saprolite while the presence of 1 nm and 0 7 halloysite in the upper part of the saprolite the bw horizon and the ah horizon suggesting only time controls of the evolution of the profiles by both kinetic wet dry seasons and thermodynamic si bearing factors gibbsite occurs only in the nephelinite h soil its presence is due to the hydrothermal alteration which favoured the development of an intense microporosity allowing the elimination of silica the study highlighted the influence of past hydrothermal activity on the recent weathering process in the humid tropical area

tracing recent environmental changes and pedogenesis using geochemistry and micromorphology of alluvial soils sabie sand river basin south africa abstract three pedons on the alluvial terraces of the sabie sand river basin within kruger national park south africa were studied to improve our understanding of recent environmental changes and assess degree of chemical weathering and pedogenesis in the area using geochemical and micromorphology proxies particle size distributions were obtained using malvern mastersizer soil geochemistry was determined by xrf and thin sections by routine laboratory procedures the soils are predominantly sandy 94 sand in all samples the mean phi values of the soils had little variation suggesting that reworking of sediments upwards in individual profiles produced a more uniform pedogenesis rather than coming from different physical sources calcification is the dominant pedogenic process in these alluvial soils the chemical index of alteration cia proved a more suitable index than chemical index of weathering ciw for evaluating weathering in the terraces the micromass and b fabrics are mostly granostriated and partly brown mosaic speckled miseca values for the degree of soil development range from 4 to 9 which mean weakly to moderately developed soils coarse secondary calcite nodules and coatings are responsible for cementation as observed in pedon 2 which suggests calcium carbonate precipitation from periodical flooding and evaporating groundwater events the features and diagnostic properties of the soils on the alluvial terraces along the sabie sand river provide evidence for land surface impacts of recent environmental changes in this internationally important conservation area precise dating of calcium carbonate precipitates is however needed to put the observed evidence into a wider geochronological perspective

faulting and extension rate over the last 20 000 years in the offshore whakatane graben new zealand continental shelf oblique rifting in the offshore taupo volcanic zone new zealand is expressed in widely distributed active normal faulting in the 20 km wide whakatane graben active faults are identified along seafloor scarps and displacements of the post last glacial transgressive ravinement surface 400 faults we derive an extension rate at seismogenic depths 6 10 km across the graben of 13 6 mm yr by summing surface measurements assuming an average crustal fault dip of 45 15o and correcting for the discrepancies between surface and deep crustal extension estimates structural and kinematic data implies an extension direction 20o oblique to the rift axis resulting in up to 4 6 2 1 mm yr of dextral motion parallel to the rift axis the strike slip motion is accommodated by dip slip displacements on oblique faults in the centre of the graben and oblique slip faulting along the rift margins pure dip slip in the graben centre represents 50 of the total slip with the rangitaiki fault accommodating 25 of the total extension in the graben

earthquake histories and holocene acceleration of fault displacement rates displacement rates for normal and reverse faults n 57 are generally higher when averaged for the holocene 10 ka than for the late quaternary 300 ka and longer time scales holocene acceleration of displacement rates could be attributed to geological processes that produce increases of tectonic tempo we propose an alternative model in which the observed rate changes arise from variability in earthquake slip and or recurrence coupled with a sampling bias toward those faults that are best represented at the earth s surface and that accrued displacement fastest during the holocene this model is consistent with displacement rates measured over time intervals of as long as 300 ka for 129 faults from the taupo rift new zealand departures of earthquake parameters and associated displacement rates from their long term 300 ka averages are attributed to fault interactions and occur on time intervals inversely related to these long term displacement rates and to regional strain rates

slope gradient controls soil thickness and chemical weathering in subtropical brazil understanding rates and timescales of regional soilscape evolution through a combination of field data and modeling

color variations of the quaternary red clay in southern china and its paleoclimatic implications abstract the red clay and red weathering crust are widely distributed in southern china to study the possible relationship between soil color and paleoclimatic environment three color parameters lightness l redness a and yellowness b of twelve quaternary red clay qrc profiles in southern china were measured using a colorimeter colors of the qrc profiles vary vertically a and b generally increase downward and l decreases downwards colors of the qrc also show spatial variation a and b generally increase towards the equator whereas l increases away from it both a and b are positively significantly correlated with clay

the dynamic history of the trans mexican volcanic belt and the mexico subduction zone abstract the trans mexican volcanic belt tmvb is a 1000 km long neogene continental arc showing a large variation in composition and volcanic style and an intra arc extensional tectonics it overlies the rivera and cocos slabs which display marked changes in geometry geophysical studies indicate that lithospheric mantle is very thin or absent beneath the forearc and arc the fluids from the slab are released in a 40 to 100 km wide belt beneath the frontal part of the arc and the lower crust beneath the arc is partially molten east of 101 w the tmvb is built on a precambrian to paleozoic crust with thickness of 50 55 km west of 101 w the tmvb is underlain by jurassic to cenozoic marine and continental arcs with a 35 40 km thick crust the evolution of the tmvb occurred in four stages 1 from 20 to 10 ma the initial andesitic arc moved inland showing progressively drier melting and eventually slab melting suggesting flattening of the subducted slab 2 since 11 ma a pulse of mafic volcanism migrated from west to east reaching the gulf of mexico by 7 ma this mafic lavas marks the lateral propagation of a slab tear triggered by cessation of subduction beneath baja california 3 thereafter the volcanic front started moving trenchward with a marked phase of silicic volcanism between 7 5 and 3 ma local emplacement of small volume intraplate like basalts since 5 ma and development of extensional faulting these features are related to slab rollback enhancing asthenophere flux into the mantle wedge and promoting partial melting of the crust 4 the modern arc consists of a frontal belt dominated by flux and slab melting and a rear belt characterized by more differentiated rocks or by mafic lavas with little or no evidence of subduction fluids but higher asthenosphere fingerprint

reconstructing the geological and structural history of an active geothermal field a case study from new zealand abstract the utilisation of geothermal systems benefits from an understanding of the host rock geology locations and controls of permeability pathways and the nature and timing of magmatic sources providing thermal energy kawerau geothermal field in the central taupo volcanic zone tvz of new zealand is currently developed for electricity generation and direct uses of high temperature steam to 200 mw electrical output the kawerau geothermal system is hosted in a sequence of volcanic lithologies tuffs lavas and intrusive bodies and sediments that overlie faulted mesozoic metasedimentary greywacke basement identification of lithologies in the volcanic sedimentary sequence is challenging due to the levels of hydrothermal alteration and lithological similarities a combination of detailed petrological investigations consideration of the emplacement processes and greater certainty of crystallisation or eruption ages through u pb age determinations on zircons is used to reconstruct the depositional and faulting evolution of the rocks hosting the currently active hydrothermal system the oldest event inferred is faulting of the greywacke along northwest southeast orientated dominantly strike slip structures to generate half grabens that were filled with sediments incorporating two dated ignimbrites 2 38 0 05 and 2 17 0 05 ma a 1 46 0 01 ma ignimbrite was deposited relatively evenly across the field implying that any topographic relief was subdued at that time subsequent deposition of ignimbrites occurred in episodes around 1 0 0 55 0 6 and 0 32 ma interspersed with thin sedimentary sequences that accumulated at average rates of 0 06 mm yr 1 andesite lavas from a buried composite cone occur as a conformable package between units dated at 1 0 and 0 6 ma bodies of coherent rhyolite occur at multiple stratigraphic levels two magma types with associated tuffs were emplaced as domes and sills at 0 36 0 03 ma and a third type at 0 138 0 007 ma as dikes and domes that are exposed at surface the andesitic putauaki composite cone southwest of the field first erupted around 8 ka but earlier hydrothermal eruption breccias imply that magma was intruded to shallow depths as early as 16 ka age data and associated correlations show that post 1 5 ma normal faulting has accompanied episodic subsidence of the kawerau area with fault movement focused between northeast southwest structures associated with the geometry of the modern tvz and the reactivated northwest southeast structures associated with most displacement in the area prior to 1 5 ma contrasts between emplacement of coherent rhyolite as sills at 0 36 ma and a dike at 0 138 ma reflect a shift in orientation of the principal stress axes in response to initiation of the modern tvz rifting regime most volcanic rocks at kawerau are distally sourced from elsewhere in the tvz but form local marker horizons that delineate topographic relief within the field and additionally constrain past subsidence rates current rates of subsidence and thermal output at kawerau are geologically recent features associated with latest quaternary rifting processes

distinct silicon and germanium pathways in the soil plant system evidence from banana and horsetail plants strongly impact the continental silicon cycle by taking up si and precipitating opal phytoliths which are recycled into the soil studying ge incorporation a chemical analog of si relative to si may provide a useful tracer of si pathways however ge uptake and transport through plants and the impact on ge si of phytoliths remain poorly understood here we report ge uptake and accumulation and ge si fractionation in all plant parts and solutions from 1 hydroponic banana 2 in situ sampled banana and 3 horsetails we further combine these data with delta si 29 from banana plants our data reconcile opposite conclusions drawn from previous studies on ge uptake and pathways no discrimination of ge occurred at the root solution interface banana and horsetails were shown to accumulate ge in roots a previous study provided evidence of low ge si ratios in root phytoliths which contrasts with high bulk ge si ratios in roots we report here this suggests that ge is organically trapped in roots consequently shoots display lower ge si ratios without fractionation between shoot parts since ge would follow transpiration stream as silicon and is not discriminated between shoot parts this contrasts with the two step discrimination against heavy si isotopes at the root solution interface and then within the shoots the soil composition clays versus fe oxides has a leading role on the ge si signatures of plants which may in turn impact on the si and ge fluxes to the global ocean

the effect of lower crustal flow on continental extension and passive margin formation the great variety of styles of continental extension may reflect different crustal thickness and thermal states of continental lithosphere during the initiation of rifting to investigate how these and other factors affect rifting and the development of passive continental margins we develop a simplified model of lithospheric extension we consider the evolution of extensional deformation for a three layer model lithosphere bounded laterally by much stronger lithosphere the cold part of the crust and mantle are treated as thin brittle plastic layers the lower crust is approximated as a thin viscous channel each brittle plastic layer can extend in only one location determined by the strength of the layer shear of the lower crust and buoyancy forces related to both crustal thickness variations and thermally induced density differences the lower crust flows in response to crustal thickness variations and is sheared when the loci of extension for the two brittle plastic layers are horizontally offset a situation we term shear decoupling as in previous studies we see three distinct patterns or modes of extensional deformation that occur under different sets of model parameters the core complex mode the wide rift mode and the narrow rift mode shear decoupling occurs only in cases with a crustal rheology at the weak end of the spectrum of laboratory estimated values we are aware of no observations that require that the upper crust and upper mantle strain at laterally displaced positions we show that for large magnitudes of extension there can be transitions between modes as inferred for some highly extended continental areas predicted patterns of crustal thickness and heat flow for some models are similar to observations at several rifted continental margins including very wide and asymmetric margins

use of soils and palaeosols on volcanic materials to establish the duration of soil formation at different chronological scales abstract in this paper we present an overview of the mexican volcanic palaeosol sequences as a valuable tool to establish the duration of soil formation at different chronological scales we have selected four study cases which cover time intervals from decennial centennial to millennial pedogenesis the first case corresponds to the soils in el chichon volcano where the short interval between the eruptions gives the opportunity to study the soil formation in periods less than 500 years in this interval the transformation from regosol to andosol is observable in el nevado de toluca pedogenesis of longer duration 4000 to 6000 y characterizes a vitric andosol stage in this area the transformation of andosol to luvisol is also shown in periods longer than 10 000 years the third study case corresponds to the tlaxcala palaeosol sequence where pedogenesis in intervals from 10 000 to 100 000 years is observable in this case no andosols are present and a complete set of luvisols showing different properties is found this differentiation is not only related to the duration of the pedogenesis but also to the climatic conditions which lead to changes in specific properties clay content weathering of the primary minerals fed content in this way these soils are valuable for palaeoenvironmental reconstruction the fourth case is related to faster pedogenesis in the volcanic regions of mexico where highly developed luvisols are found formed in intervals less than 15 000 y in this case the influence of a pre weathered volcanic material as a source of clay allows the rapid transformation

oblique back arc rifting of taupo volcanic zone new zealand taupo volcanic zone tvz is a back arc rift innorth island new zealand its geometry andkinematics are investigated using shaded reliefimages field examination of faults and offset streamchannels the results show that tvz trends nne is 250 km long by hikurangi margin in the north island of new zealand 20 km wide and consists of fivesegments extension is principally manifest as steeplydipping 60 90 normal faults parallel to tvz these in the last 300 kyr have experienced acomponent of dextral shear tvz is therefore anoblique back arc rift the dextral shear is 37 of thetotal displacement which for previously estimatedspreadingrates 7mm yr correspondsto 2 6mm yr thisvalueissimilartopreviousestimatesofthedextralshear from the back arc to the forearc domains in thenorthisland distributeddextralshearacrosstvzthussuggests that strain partitioning across the plateboundary at latitudes of tvz is less significant thanpreviously thought

normal fault growth and linkage in the whakatane graben new zealand during the last 1 3 myr determination of fault growth rates and fault network evolution at time scales from 104 106 years has been hampered by a lack of a well constrained stratigraphic succession that provides a high fidelity record of fault development over these time periods here we show how seismic reflection data of different spatial resolutions can be used to constrain the linkage history and displacement rate variations of a single major fault we present data collected in the offshore whakatane graben bay of plenty new zealand where intense normal faulting occurs as a result of active back extension the focus of our study is the rangitaiki fault a linked segmented normal fault which is the dominant active structure in the graben the total linked fault length is c 20 km long and has a displacement of up to 830 130 m in the top 1 5 km of sediments the fault has been actively growing for the last 1 34 0 51 ma and has developed from isolated fault segments to a fully linked fault system initially the dominant process of fault growth was tip propagation with an average and maximum displacement rates of 0 52 0 18 mm yr 1 and 0 72 0 23 mm yr 1 respectively interaction and linkage became more significant as the fault segments grew towards each other resulting in the fault network becoming fully linked between 300 and 18 ka following fault segment linkages the average displacement rate of the fault network increased by almost three fold to 1 41 0 31 mm yr 1 while the maximum displacement rate increased to 2 72 0 61 mm yr 1 this is the first time that the growth rate of unlinked fault segments has been resolved and has been shown to be slower than in the subsequent linked fault system

seismic velocity structure of the central taupo volcanic zone new zealand from local earthquake tomography abstract the 3 d distribution of p wave velocity vp and the p wave s wave velocity ratio vp vs are derived for the crust in the central taupo volcanic zone tvz new zealand by tomographic inversion of p and s wave arrival time data from local earthquakes resolution in the seismogenic mid crust 4 6 km is good but poorer above and below these depths the 3 d velocity model has several vp anomalies as large as 5 in the mid lower crust 4 10 km and more than 10 in the upper crust 0 4 km the model achieves a 55 reduction in data variance from an initial 1 d model young caldera structures okataina rotorua and reporoa are characterised by low vp anomalies at a depth of about 4 km and these coincide with large negative residual gravity anomalies we attribute these anomalies to large volumes of low vp low density volcaniclastic sediments that have filled these caldera collapse structures although there are no vp anomalies which suggest the presence of molten or semi molten magma beneath the tvz a large high vp anomaly of more than 15 and a high vp vs anomaly are observed coincident with a diorite pluton beneath the ngatamariki geothermal field however vp anomalies cannot be seen beneath the largest geothermal fields waimangu waiotapu and reporoa and consequently if such anomalies exist they must be below the resolution of our data a prominent vp contrast of 5 10 occurs at a depth of about 6 km beneath the boundary between the taupo reporoa depression and the taupo fault belt tfb coincident with the eastern limit of the seismic activity beneath the tfb we interpret this velocity contrast as being caused by the presence of extensive non molten intrusives beneath the taupo reporoa depression we suggest that the high velocity material beneath the taupo reporoa depression is isolated from regional extension in the tvz and from the resulting faulting and seismicity which occurs preferentially within the weaker material of the tfb we are unable to determine whether greywacke which forms the basement beneath the eastern most part of the tvz continues further west or is replaced by a volcanic rock such as andesite which has similar vp and density vp vs anomalies are much smaller than vp anomalies and generally have little spatial relationship to the vp pattern there is a widespread decrease in vp vs from 1 76 to 1 70 1 73 between 4 and 6 km depth over much of the study area and vp vs is high southwest of the okataina caldera where vp is low hypocentres calculated using the 3 d velocity model differ little from those obtained using a 1 d model with station terms however some groups of earthquakes are more tightly clustered following relocation there is a slight decrease in the estimated thickness of the seismogenic zone with 73 of hypocentres between 4 and 7 km depth and a slight increase in the depth of the brittle ductile transition from 6 to 6 5 km

quantification of weathering processes in an acid brown soil developed from tuff beaujolais france the petrographical and mineralogical composition of tuff in the studied area was determined by optical microscopy x ray analysis bulk chemical analysis and mean chemical composition of each mineral obtained from the electron microprobe the tuff stones sampled on the surface and in the pits of soil are usually surrounded by a bleached rind from the results of chemical weathering mass balance isovolumetric calculations the chemical and mineralogical transformation are quantified during the formation of this weathered rind this tuff from the upper visean was composed of about 45 5 phenocrysts quartz andesine albite and biotite and about 55 5 devitrified groundmass spherolites quartz k feldspar albite andesine and biotite this series was a broad monotonous series although some facies diversity occurred i e colour and density of plagioclase phenocrysts evidence of fluidality a local heterogeneity in the tuff mineralogy and a variation in its chemical composition k2o cao na2o and loss on ignition have been induced by devitrification of the groundmass and hydrothermal alteration the contact metamorphism seemed to have caused the groundmass devitrification and recrystallization of biotite phenocrysts as small biotite crystals 0 1 mm hydrothermal alteration has led to biotite chloritization transformation of plagioclase albite and andesine into white mica and k feldspar and a few veins quartz chlorite epidote in the montagne des aiguillettes tuff weathering appeared as a thin bleached rind around all stones the weathering gradient inside rinds corresponded to a progressive dissolution of tuff minerals quartz k feldspar white mica biotite albite apatite andesine the weathering processes were characterized by a strong dissolution of plagioclases and apatite increase of voids by about 12 and to a lesser extent by the transformation of micas biotite into hydroxy interlayered vermiculite hiv and mica hiv mixed layer minerals and by kaolinite ka precipitation the results of the petrographical study were consistent with the calculated mass balance the weight losses were about 18 and corresponded to a strong exportation of cao na2o sr p2o5 al2o3 and sio2 74 62 51 42 17 and 25 respectively and an increase in the water content eighty two percent of andesine 41 of apatite 40 of albite and biotite 3 were dissolved the increase in the total water content corresponded to the formation of hydrated weathered minerals 2 6 of hiv and 4 3 of ka

paleoseismology of the 1912 acambay earthquake and the acambay tixmadeje fault trans mexican volcanic belt the acambay graben is a major intra arc basin of the trans mexican volcanic belt trenching studies at four sites along the acambay tixmadeje fault reveal evidence for the 1912 acambay earthquake and at least four late pleistocene and holocene ground rupturing earthquakes with similar displacements to the 1912 event evidence for multiple events was recognized by a combination of upward terminating faults fissure fills erosionally truncated fissures colluvial wedge fills and downward increasing separation of stratigraphic units sites along the central part of the ese wnw trending rangefront fault indicates large dip slip separations across a multi event scarp in holocene colluvium with a penultimate event that occurred since 5230 calibrated years before present cal yr b p on the huapango plain near the eastern end of the 1912 rupture where slip was oblique the penultimate earthquake occurred after 4700 cal yr b p and there is evidence for at least four more earthquakes in the last 34 000 cal yr b p three dimensional excavation of lacustrine and channel deposits at las lomas yields a left normal slip vector of s40 5 e with 105 10 cm of slip for the last three events there this slip vector is consistent with nne oriented extension across the graben the amount and style of slip documented for prehistoric ruptures are also consistent with the 1912 rupture with a mean of 60 cm event of dip slip on the rangefront and a mean of 35 cm event of oblique slip on the n48 w trending huapango plain assuming these values represent a characteristic behavior yields an average recurrence interval of 3600 years for the last four large earthquakes since 11 570 cal yr b p and a slip rate of 0 17 mm yr across the rangefront empirical earthquake parameters calculated from our paleoseismic data support instrumental measures indicating that the 1912 acambay earthquake was of m 6 8 7 0 the 1912 event is representative of ground rupturing earthquakes on the acambay tixmadeje fault and demonstrates that large seismic events m 7 can be generated by faults in the trans mexican volcanic belt and in other intra arc settings

distribution of quaternary deformation in the central main ethiopian rift east africa 1 the main ethiopian rift mer is a narrow continental rift characterized by an along axis variation in rift evolution with early stages in the south evolving to incipient breakup in the north although distribution and style of quaternary volcanotectonic deformation is well known in the northern rift sector knowledge of these characteristics is comparatively less constrained southward in this paper we present the results of a field structural study carried out to better constrain the time space distribution of faulting in the central sector of the mer central mer the new field structural data coupled with new 14c radiometric dating of faulted rocks suggest a localization of faulting at both rift margins of the central mer where radiometric dating of faulted material has allowed establishing a late pleistocene holocene activity of border faults conversely in rift faulting wonji fault belt wfb is subordinate highlighting a major difference with the northern sector of the mer where deformation is essentially accommodated in the axial zone this is consistent with an along axis variation in rift evolution showing the central mer less evolved than the northern rift sector inversion of cumulative fault slip data reveals a variation in the extension direction between the rift margins n105 110 e and the rift floor n90 95 e which accords well with the current nubia somalia plate kinematics the variation in extension direction across the rift could manifest a slip partitioning between the boundary faults and in rift wfb faults

systematic variation in the depths of slabs beneath arc volcanoes summary the depths to the tops of the zones of intermediate depth seismicity beneath arc volcanoes are determined using the hypocentral locations of engdahl et al these depths are constant to within a few kilometres within individual arc segments but differ by tens of kilometres from one arc segment to another the range in depths is from 65 km to 130 km inconsistent with the common belief that the volcanoes directly overlie the places where the slabs reach a critical depth that is roughly constant for all arcs the depth to the top of the intermediate depth seismicity beneath volcanoes correlates neither with age of the descending ocean floor nor with the thermal parameter of the slab this depth does however exhibit an inverse correlation with the descent speed of the subducting plate which is the controlling factor both for the thermal structure of the wedge of mantle above the slab and for the temperature at the top of the slab we interpret this result as indicating that the location of arc volcanoes is controlled by a process that depends critically upon the temperature at the top of the slab or in the wedge of mantle immediately below the volcanic arc

volcanic soils of iceland abstract the parent materials of all icelandic soils are volcanic in origin and most of the soils are classified as andosols iceland has the largest area of andosols in europe and may have 5 of all andosols in the world a new classification scheme based on the world reference base world reference base for soil resources world soil resources reports 84 fao rome is used to provide an overview of icelandic volcanic soils the data were acquired as part of a recently initiated effort to build a database for icelandic soils but are also partly based on data from the eu cost 622 action a literature review and unpublished icelandic research the main soil types in iceland are histosols histic andosols gleyic andosols brown andosols vitrisols and leptosols in the icelandic language a single term is used to refer to each soil type this system reflects the dominant influence of eolian deposition and drainage conditions on the formation of histosols and andosols the parent materials of icelandic soils are mixtures of tephra layers and eolian sediments consisting mostly of volcanic glass the steady flux of eolian sediments from unstable sandy deserts constantly recharges the surface with basaltic tephra materials the histosols 20 c have appreciable amounts of andic materials because of the eolian deposition the andosols histic gleyic and brown andosols show characteristic properties of soils dominated by andic materials with allophane contents of up to 30 ferrihydrite commonly accounts for 5 15 of the soil the contents of both allophane and ferrihydrite generally decrease with increasing organic c content of soil horizons as organic matter inhibits allophane formation and iron tends to become reduced and lost in poorly drained locations the vitrisols are soils of desert surfaces with low organic content but they usually meet criteria for andic materials with 30 glass and al 1 2fe o 0 4 cryoturbation is intense in iceland resulting in a range of geomorphic surface features the cryoturbation is related to both climatic factors and the andic soil properties including high water retention and rapid hydraulic conductivity

history of basin formation and tectonic evolution at the termination of a large transcurrent fault system deformation mode of central kyushu japana abstract the central part of the kyushu island is a locus of active arc volcanism associated with subduction of the philippine sea plate being located at a bend in the boundary between the philippine sea and eurasian plates a complicated lateral displacement has generated half grabens a zone of strike slip and rhomboidal basins filled with volcanic material in central kyushu initial northward subduction in latest miocene time activated the n s trending kokura tagawa tectonic line ktl as a left lateral slip fault that bounds the western margin of the area of volcano tectonic depression the hohi volcanic zone which was initially formed about 6 ma ago the depocenter which is now called kuju basin in the hohi volcanic zone was at the corner of the ktl and the e w trending median tectonic line mtl relative convergence direction of the philippine sea plate shifted counterclockwise at about 1 5 ma and active motion on the ktl declined at the same time west northwestward subduction enhanced right slip on the mtl geologic gravimetric and seismic data indicate that the mtl has shifted its active trace northward in central kyushu as far as 10 km as a result the depocenter adjacent to the transcurrent fault migrated northeastward in the hohi volcanic zone specifically from kuju basin pliocene via shonai basin early quaternary to beppu bay basin late quaternary the latest depocenter of the beppu bay is surrounded by active faults that clearly delineate a rhomboidal basin on the mtl central kyushu exemplifies the basin forming history and tectonic evolution at the termination of a large transcurrent fault system

ferrihydrite and allophane in four andepts from hawaii and implications for their classification abstract the mineralogy and composition of the waimea kukaiau akaka and hilo soils on the island of hawaii were studied using methods which included moessbauer spectroscopy and chemical dissolution the hilo soil which experiences 3000 mm year rainfall and the akaka soil 3800 mm year rainfall both contain large amounts about 25 of iron oxides of short range order together with other iron oxides gibbsite and allophane the iron oxides of short range order have characteristics similar to those of the reactive mineral ferrihydrite which is known to occur in a wide range of soils these characteristics however in two respects x ray diffraction and acid oxalate solubility do not rule out the presence or admixture of the much less known feroxyhite another closely related iron oxide of short range order most samples from these two soils dry irreversibly to give hard aggregates a property probably related to the presence of the iron oxides of shortrange order both the hilo and the akaka soils are classified as hydrandepts in the current usda soil taxonomy in the new proposed order of andisols these two soils would become hydrudands it is desirable to recognise the presence of short range order iron oxides in these soils the kukaiau soil currently classified as a dystrandept which occurs in a lower rainfall zone 1500 mm year contains about 25 allophane and lesser amounts of ferrihydrite other iron oxides and gibbsite the waimea soil occurs in the lowest rainfall zone 1000 mm year and the dominant mineral is halloysite but some allophane ferrihydrite and hematite are also present this soil is currently classified as a eutrandept under the andisol proposal the kukaiau and waimea soils would be a hapludand and a haplustand respectively quartz mica and other layer silicates were present in all four of the soils suggesting that there have been additions of eolian material

characterization of a weathering sequence of soils derived from volcanic ash in cameroon taxonomic mineralogical and agronomic implications the characteristics of eight pedons developed in quaternary basaltic pyroclasts in western cameroon under humid tropical conditions are reported the soil weathering sequence consists of an andept tropept udalf udult association andic properties physico chemical characteristics and weathering stage clearly distinguish the taxonomic units the total reserve in bases trb and the clay content measured after adequate h2o dispersion with na resins both appear to be suitable weathering indices clay mineralogy of non andic soils shows direct relationships between interstratified halloysite smectite content cec of the clay fraction and weathering stage the weathering stage of the investigated soils is reflected not only in their components and classification but also in their nutrient status and banana crop performance

continental rifting and initial sea floor spreading in the woodlark basin our understanding of the processes by which continents rift and sea floor spreading initiates is derived primarily from studies either of old passive margins and oceanic crust or of young regions of intra continental extension where spreading has not yet started it has been thought that continental rifting ceases when sea floor spreading begins1 2 that oceanic fracture zones develop from transfer or transform faults within continental rifts3 4 and that linear magnetic anomalies correlate with the onset of sea floor spreading during times of magnetic reversals5 6 here we present a marine geophysical survey of one of the few active examples of continental rifting and spreading initiation the western woodlark basin papuan peninsula region of new guinea which shows that in detail these assumptions do not hold the data confirm models of the rifting to spreading transition that invoke both ridge propagation and nucleation of discrete spreading cells7 10 and provide an unambiguous example of a spreading centre reorienting by synchronous jumping rather than propagation

a revised age for the kawakawa oruanui tephra a key marker for the last glacial maximum in new zealand abstract the kawakawa oruanui tephra kot is a key chronostratigraphic marker in terrestrial and marine deposits of the new zealand nz sector of the southwest pacific erupted early during the last glacial maximum lgm the wide distribution of the kot enables inter regional alignment of proxy records and facilitates comparison between nz climatic variations and those from well dated records elsewhere we present 22 new radiocarbon ages for the kot from sites and materials considered optimal for dating and apply bayesian statistical methods via oxcal4 1 7 that incorporate stratigraphic information to develop a new age probability model for kot the revised calibrated age 2 standard deviations for the eruption of the kot is 25 360 160 cal yr bp the age revision provides a basis for refining marine reservoir ages for the lgm in the southwest pacific

buried palaeosols of the nevado de toluca an alternative record of late quaternary environmental change in central mexico buried palaeosols of central mexico not previously analysed from a palaeopedological standpoint have helped to develop a reliable regional model of late quaternary climatic change this paper focuses upon morphological and micromorphological properties particle size distribution and extractable fe al and si of seven palaeosols named pt1 pt7 in the vicinity of the nevado de toluca volcano the characteristics of andic cambisol pt1 similar to those of modern soils in semi arid environments indicate a drier climate in the first half of the holocene humic andosols pt2 pt4 are analogous to modern volcanic soils of humid forest environments they show evidence that a moist palaeoclimate prevailed during marine oxygen isotope stages ois 2 and 3 luvisols pt5 and pt6 which are assumed to have formed at the end of marine ois 5 to marine ois 4 also indicate humid conditions we attribute the differences between andosols pt2 pt4 and luvisols pt5 pt7 to variations in the duration in the pedogenesis rather than to changes in palaeoclimate micromorphological features of andosol to luvisol transition confirm that these soils form an evolutionary sequence being for the most part consistent with lacustrine records the palaeosol properties do not reflect the episodes of drier climate during the last glacial maximum however as shown by diatom and palynological data from lake sediments mesoclimate variations and or incompleteness of soil memory reflecting mostly periods of humid pedogenesis probably provide the reason for this disagreement copyright 2001 john wiley sons ltd

mineralogic evidence for subglacial volcanism in the sisyphi montes region of mars abstract here we examine the mineral assemblages detected on possible glaciovolcanic edifices in the sisyphi planum region of mars a high latitude region in the southern highlands nestled between the argyre and hellas impact basins minerals were identified utilizing visible near infrared spectra from the compact reconnaissance imaging spectrometer for mars crism analysis of eleven crism images located on the volcanic edifices revealed three distinct spectral classes in the region which are interpreted to be gypsum dominated smectite zeolite iron oxide dominated possibly palagonite and polyhydrated sulfate dominated material while sulfates can form under a variety of alteration conditions palagonite like mineral assemblages require low temperature and high water to rock hydrothermal conditions typically found in subglacial or subaqueous volcanic eruptions the possible palagonite detections on the volcanic edifices the geomorphology of the region and the analogous terrestrial mineralogy of subglacial eruptions strongly suggests the formation of these minerals during subglacial eruptions or associated hydrothermal systems this implies that thick water ice sheets were present in this region in the late noachian or early hesperian and that the subglacial hydrothermal systems could have supported habitable environments with excellent biosignature preservation potential

variations of δ30si and ge si with weathering and biogenic input in tropical basaltic ash soils under monoculture in soils silicon released by mineral weathering can be retrieved from soil solution through clay formation si adsorption onto secondary oxides and plant uptake thereby impacting the si isotopic signature and ge si ratio of dissolved si dsi exported to rivers here we use these proxies to study the contribution of biogenic si bsi in a soil plant system involving basaltic ash soils differing in weathering degree under intensive banana cropping delta si 30 and ge si ratios were determined in bulk soils 2 mm sand 50 2000 mu m silt 2 50 mu m amorphous si asi 2 50 mu m and clay 2 mu m fractions delta si 30 by mc icp ms nu plasma in medium resolution operating in dry plasma with mg doping delta si 30 vs nbs28 0 12 parts per thousand 2 sigma sd ge si computed after determination of ge and si concentrations by hr icp ms and icp aes respectively components of the asi fraction were quantified by microscopic counting phytoliths diatoms ashes compared to fresh ash delta si 30 0 38 parts per thousand ge si 2 21 mu mol mol 1 soil clay fractions 2 mu m were enriched in light si isotopes and ge with increasing weathering degree delta si 30 decreased from 1 19 to 2 37 parts per thousand and ge si increased from 4 10 to 5 25 mu mol mol 1 sand and silt fractions displayed delta si 30 values close to fresh ash 0 33 parts per thousand or higher due to saharian dust quartz deposition whose contribution was evaluated by isotopic mass balance calculation si isotopic signatures of bulk soils 2 mm were strongly governed by the relative proportions of primary and secondary minerals the bulk soil si isotopic budget could be closed indicating that all the phases involved were identified microscopic counting highlighted a surface accumulation of banana phytoliths and a stable phytolith pool from previous forested vegetation delta si 30 and ge si values of clay fractions in poorly developed volcanic soils isotopically heavier and ge depleted in surface horizons support the occurrence of a dsi source from banana phytolith dissolution available for si sequestration in clay sized secondary minerals clay minerals formation and si adsorption onto fe oxide in the soil plant system delta si 30 and ge si are thus highly relevant to trace weathering and input of dsi from phytoliths in secondary minerals although not quantifying the net input of bsi to dsi c 2009 elsevier ltd all rights reserved

andosol to luvisol evolution in central mexico timing mechanisms and environmental setting abstract surface and buried andosols and buried luvisols of the nevado de toluca late quaternary tephra paleosol sequence central mexico were studied to show whether these soils present an evolutionary sequence and to determine the pedogenic mechanisms and environmental factors involved in the evolutionary process micromorphological observations and mineralogical composition of fine sand and clay fractions were used to detect type and succession of soil forming process some of the buried andosols defined as intergrade andosols have a predominantly blocky structure humus depleted areas redoximorphic features and thin clay coatings in ah horizons clay fractions of buried andosols contain halloysite besides amorphous components whereas in modern andosols allophane is dominant luvisols have micro areas with granular structure and abundant phytoliths in the groundmass of bt horizons assumed to be the relict andosol features luvisol clay fractions are dominated by halloysite and kaolinite primary minerals show micromorphological weathering features in all studied soils being stronger in luvisols however even in luvisols sand fractions consist mostly of unstable volcanic silicates we hypothesise that the studied profiles form an evolutionary sequence andosols intergrade andosols luvisols the soil transformation is supposed to be linked to progressive crystallisation of 1 1 clay minerals comparing the nevado de toluca paleosol properties with the existing data on volcanic soil climo and chronesequences and assessing the regional paleopedological and lacustrine records of quaternary paleoclimates we concluded that wet dry climatic oscillations took place during the formation of the studied paleosols rapid crystallisation of 1 1 minerals occurred during dry phases which speeded up the andosol to luvisol transformation and made it independent from the primary mineral weathering status the andosol to luvisol transformation accelerated by climatic fluctuations is thought to be a common soil evolutionary pathway in the subtropical and tropical regions of recent volcanism which suffered contrasting precipitation oscillations in the quaternary

geology and eruptive history of unzen volcano shimabara peninsula kyushu sw japan abstract during the past 500 thousand years unzen volcano an active composite volcano in the southwest japan arc has erupted lavas and pyroclastic materials of andesite to dacite composition and has developed a volcanotectonic graben the volcano can be divided into the older and the younger unzen volcanoes the exposed rocks of the older unzen volcano are composed of thick lava flows and pyroclastic deposits dated around 200 300 ka drill cores recovered from the basal part of the older unzen volcano are dated at 400 500 ka the volcanic rocks of the older unzen exceed 120 km3 in volume the younger unzen volcano is composed of lava domes and pyroclastic deposits mostly younger than 100 ka this younger volcanic edifice comprises nodake myokendake fugendake and mayuyama volcanoes nodake myokendake and fugendake volcanoes are 100 70 ka 30 20 ka and

properties of the guin ungrouped iron meteorite the origin of guin and of group iie irons abstract guin is an ungrouped iron meteorite containing 45 g g ga and 186 g g ge it is a coarse octahedrite with an unusually high ni content 92 5 mg g its metal composition is generally similar to irons in groups iab and iiicd but its closest relative is the cruz del aire ungrouped iron guin contains 6 3 vol silicate inclusions that are petrologically and compositionally similar to those in iie irons the largest inclusion 2 4 cm consists primarily of a shock melted plagioclase rich matrix surrounding large 1 15 mm partly melted augite grains the oxygen isotopic composition of the inclusion 18 o 5 29 17 o 3 87 is near the ll chondrite field the guin inclusion is similar in bulk composition to selected melt pocket glasses in ordinary chondrites produced in situ by preferential melting of plagioclase by shock compression we suggest that the guin assemblage formed by impact melting on a chondritic parent body silicate inclusions in iie irons share many petrologic and compositional but not oxygen isotopic characteristics with the guin inclusions suggesting that iie irons also formed by impact melting of chondritic materials individual iie irons were probably derived from separate cratering events

evidence from the northern red sea on the transition from continental to oceanic rifting abstract the northern red sea is an active rift in the last stages of continental rifting which is beginning to undergo the transition to oceanic seafloor spreading the rift can be divided into two distinct regions the marginal areas consist of a series of bathymetric terraces and as indicated by geophysical data are underlain by a series of rotated fault blocks the axial depression which forms the axis of deep water is a continuous region 10 to 25 km wide near the center of the sea which is characterized by high heat flow a large gravity minimum and very deformed sediments both regions are divided along strike into segments roughly 60 km long by cross trending transfer zones the presently active tectonics are characterized by the concentration of extension and deformation in the axial depression and by the emplacement of a number of large intrusions the intrusions occur at distinct sites located at the intersection of transfer zones with the faults bounding the rotated blocks in the marginal areas and at deeps located in the axial depression halfway between transfer zones although extension is becoming concentrated in the axial depression geophysical data imply that at least the upper few kilometers of the crust in that region consists of non magnetic continental type material and that this ca apace has been ruptured by large intrusions only at the deeps a wide range of crustal seismic velocities has been observed in the northern red sea including velocities normally associated with oceanic crust the velocity variations appear spatially related to corresponding large variations in basement rock type observed on shore in the eastern desert of egypt the northern red sea is in an intermediate stage between a continental rift valley and a young ocean basin and delineation of its structure and tectonics allows a model to be developed for the evolution of a rifted continental margin rifting starts in a series of linked half grabens 50 60 km long and formed over detachment surfaces which probably penetrate no deeper than the mid or lower crust this style of rifting can accommodate at least the amcunt of extension represented by the gulf of suez 35 km at some greater amount of extension the rift acquires a more symmetric shape probably through the development of antithetically faulted blocks in the hanging wall extension in this stage is still distributed throughout the rift and is accommodated in the upper crust by rotation of fault blocks at the stage represented by the northern red sea extension becomes concentrated in an axial depression and begins to be partially accommodated by large intrusions which form deeps the position of the deeps is controlled by the transfer zones established in the earliest stages of rifting with further extension the deeps serve as nucleation points that develop into small discrete cells of seafloor spreading these cells grow and coalesce to form a continuous mid ocean ridge spreading center such as is found in the southern red sea

geochemical variations of core sediments of pichavaram lagoon southeast coast of tamil nadu india a provenance and paleoenvironmental study the present study aims to identify the natural and anthropogenic imprints left by the accumulation of elements and to determine identify the current level of enrichment of major oxides in the pichavaram mangrove sediments pichavaram mangrove is a dynamic intertidal environment lying in between the vellar and coleroon estuaries in the cauvery delta along the east coast of india in the present study results of texture studies reveal highly variable depositional environment in upper and lower portion of core 1 and middle portion of core 2 in both the cores decrease in grain size is observed in the upper portion which may suggest that the sediments in the upper portion were deposited at low energy condition mn al mg al ca al ti al p al and k al ratios are found to be low in the both the core samples ti elemental ratio is lower in both core samples indicating that ti concentrations in marine sediments are the best indicators of lithogenous material flux to the marine environment the concentration of various elements in the core can be summarized as si al fe mn mg ca ti p k the pia values of core 1 indicate that the sediments were derived from predominant weathering up to 40 cm and the remaining sediments derived from unweathered matrices plagioclase index of alteration pia values of most of the downcore samples of core 2 are found to be more than 40 suggesting the predominance of weathering activity low pia values are observed at the depth of 54 70 cm indicating the moderately weathered nature of the sediments in the study area positive correlation between fe and mg and their negative relationship with silica indicates the presence of ferromagnesian debris in top of the sediments major oxide geochemistry indicates a heterogeneous and moderately weathered to unweathered source for the sediments of the present study area

rapid evolution of subduction related continental intraarc rifts the taupo rift new zealand the evolution of the continental intra arc taupo rift in the north island new zealand is rapid significantly faster than comparative intra continental rifts such as the african rifts based on our faulting data and published geological geophysical and borehole data we show that activity in the 2 ma taupo rift has rapidly and asymmetrically narrowed via inward and eastward migration of faulting at rates of ca 30 km my 1 and 15 km my 1 respectively and has propagated southwards along its axis 70 km in 350 kyr the loci of voluminous volcanic eruptions and active faulting are correlated in time and space suggesting that a controlling factor in the rapid rift narrowing is the presence of large shallow heterogeneities in the crust such as large rhyolitic magma bodies generated by subduction processes which weaken the crust and localize deformation eastward migration of faulting also follows the eastward migration of the volcanic arc which may be related to rollback of the pacific crust slab at the hikurangi subduction zone southward propagation of the rift is linked with southward migration of the hikurangi plateau chatham rise subduction point and occurs episodically aided by stress changes associated with voluminous local volcanism the large magma supply during early continental intra arc rift stages explains faster evolution from tectonic to magmatic than intracontinental rifts however the fast changes in magma supply from the subduction zone can also lead to evolution reversals more evolved magmatic stages reverting to less evolved tectonic stages rift cessation and thus failed continental break up

weathering sequence of soils from volcanic ash involving allophane and halloysite new zealand abstract the clay minerals in a series of soils from rhyolitic ash having the same stratigraphy but different leaching environments were estimated quantitatively by oxalate dissolution infrared spectroscopy differential thermal analysis electron microscopy and x ray diffraction three soils were studied in detail these were the kereone soil mean annual rainfall 1200 mm the ohaupo soil 1400 mm and the mairoa soil 2600 mm the kereone soil contained halloysite as the predominant clay mineral whereas the mairoa soil was mainly allophanic the ohaupo soil contained considerable amounts of both allophane and halloysite thus the allophane content of the soils increased as rainfall increased reflecting a sequence of increased l leaching the si concentration in soil solution decreased as rainfall increased also reflecting increasing leaching of the soils at mairoa si is rapidly removed and allophane al si 2 1 with monomeric silicate is formed whereas at kereone less leaching occurs si levels are higher and halloysite al si 1 1 with polymeric silicate is formed at intermediate sites either allophane or halloysite may form the often reported situation of younger allophanic beds overlying older 10 000 year halloysitic beds may not be due to allophane weathering to halloysite but may result from lower temperature and drier climate during the last glacial maximum between 10 000 and 26 000 years before present bp a new weathering scheme for volcanic ash in new zealand is presented

andisols of madeira island portugal characteristics and classification abstract this paper reports the morphological physical chemical and mineralogical features of seven pedons selected to represent the major types of udands occurring in madeira island all of these pedons showed similar high contents of organic matter 60 g kg 1 of c and often more to depths of more than 40 cm despite this similarity only three pedons had the colour requirements of fulvudands the others had colour values too high to meet the criterion this was attributed to the high amounts of hematite masking the dark brown colour of organic colloids as testified by their variable total reserve in bases trb and their variable contents of allophane andisols of madeira have reached different stages of weathering the most weathered ones are very acid alic and very rich in total fe 2 o 3 they qualify as non allophanic andisols it is suggested that the pyroclastic parent materials of these highly weathered andisols had been altered prior to the present pedogenetic cycle such a hypothesis would explain their mineralogy characterized by high lithogenic hematite and low weatherable minerals contents in such non allophanic andisols the andic soil properties are probably due mainly to al humus complexes accompanied by some ferrihydrite

middle late pleistocene tephrostratigraphy of the eastern bay of plenty new zealand abstract up to fifty tephras ranging in age from ca 500 to 50 ka are recorded in a terrestrial sequence of loess and paleosols in the eastern bay of plenty north island new zealand tephra correlations are based on the distinctive physical characteristics of the airfall beds and confirmed by microprobe analysis of glass shards the deposits are divided into six subgroups with their boundaries marked by either major tephras or significant changes in the paleo climate indicator deposits such as loess and paleosols age control on these tephras has been provided by fitting the paleoclimatic data seen in the field to the specmap oxygen isotope curve with correlations to a few well dated tephras and ignimbrites providing key time planes within this record

balancing the plate motion budget in the south island new zealand using gps geological and seismological data summary the landmass of new zealand exists as a consequence of transpressional collision between the australian and pacific plates providing an excellent opportunity to quantify the kinematics of deformation at this type of tectonic boundary we interpret gps geological and seismological data describing the active deformation in the south island new zealand by using an elastic rotating block approach that automatically balances the pacific australia relative plate motion budget the data in new zealand are fit to within uncertainty when inverted simultaneously for angular velocities of rotating tectonic blocks and the degree of coupling on faults bounding the blocks we find that most of the plate motion budget has been accounted for in previous geological studies although we suggest that the porter s pass amberley fault zone in north canterbury and a zone of faults in the foothills of the southern alps may have slip rates about twice that of the geological estimates up to 5 mm yr 1 of active deformation on faults distributed within the southern alps 100 km to the east of the alpine fault is possible the role of tectonic block rotations in partitioning plate boundary deformation is less pronounced in the south island compared to the north island vertical axis rotation rates of tectonic blocks in the south island are similar to that of the pacific plate suggesting that edge forces dominate the block kinematics there the southward migrating chatham rise exerts a major influence on the evolution of the new zealand plate boundary we discuss a model for the development of the marlborough fault system and hikurangi subduction zone in the context of this migration

geochemical fingerprinting and source discrimination of agricultural soils at continental scale 2108 agricultural soil samples ap horizon 0 20 cm were collected in europe 33 countries area 5 6 million km2 as part of the recently completed gemas geochemical mapping of agricultural and grazing land soil soil mapping project gemas soil data have been used to provide a general view of element origin and mobility with a main focus on source parent material and source rocks at the continental scale either by reference to average crustal abundances or to normalized patterns of element mobility during weathering processes the survey area covers a large territory with diverse types of soil parent materials with distinct geological history and a wide range of climate zones and landscapes to normalize the chemical composition of european agricultural soil mean values and standard deviation of the selected elements have been compared to model compositions of the upper continental crust ucc and mean european river suspended sediment some elements are enriched relative to the ucc al p pb zr whereas others such as mg na and sr are depleted the concept of the ucc extended normalization pattern has been applied to selected elements the mean values of rb k y ti al si zr ce and fe are very similar to the values from the ucc model even when standard deviations indicate slight enrichment or depletion zirconium has the best fit to the ucc model using both mean value and standard deviation lead and cr are enriched in european soil when compared to the ucc model but their standard deviation values span a large particularly towards very low values which can be interpreted as a lithological effect gemas soil data have been normalized to al and na taking into account the main lithologies of the ucc in order to discriminate provenance sources additionally sodium normalization highlights variations related to the soluble and insoluble behavior of some elements e g k rb versus ti al si v y zr ba and la respectively their reactivity e g fe mn zn and association with carbonates e g ca and sr maps of europe showing the spatial distribution of normalized compositions and element ratios reveal difficulties with the use of classical element ratios because of the large lithological differences in compositions of soil parent material the ratio maps and color composite images extracted from the gemas data can help to discriminate the main lithologies in europe at the regional scale but need to be used with caution due to the complexity of superimposed processes responsible for the soil chemical composition

spatiotemporal evolution of a marine caldera forming eruption generating a low aspect ratio pyroclastic flow 7 3 ka kikai caldera japan implication from near vent eruptive deposits abstract the vei 7 7 3 ka caldera forming eruption of the kikai caldera occurred in a shallow sea and caused devastating damage to the prehistoric human settlements of southern kyushu japan this holocene activity at this volcano records eruptions with compositional range of 56 to 74 wt in sio2 spanning with the climactic eruption in this study stratigraphy component and lithology of the pyroclastic deposits were analyzed at near vent islands satsuma iwo jima and take shima in order to reconstruct this eruption stratigraphic sections are characterized by plinian pumice fall deposits unit a intraplinian flow deposits unit b climactic pyroclastic flow deposits units c1 c3 and co ignimbrite ash fall deposits unit d in total the estimated magma volume in the system was 70 80 km3 dre and the eruption therefore represents the evacuation of a major silicic magmatic system the plinian stage phase 1 is subdivided into an initial small phase and a second large one the column height in the second phase was estimated to be 40 43 km the total tephra volume of this stage was estimated to be 40 km3 the magma discharge rate has been calculated from the column height data to be 2 108 kg s the eruption duration is also estimated to be a minimum of approximately 28 h collapse of the column phase 2 produced unit b which consists of multiple thin lithic rich or pumice rich layers or pods including welded pumice fall layers the deposits are characterized by stratified or cross stratified facies and display various degree of welding these sedimentary characteristics indicate that during the plinian column collapse high temperature turbulent density currents were generated where dense pyroclasts were well segregated resulting in the lithic rich layers or pods phase 3 is characterized by units c1 c3 unit c1 shows non welded stratified facies which consist of lithic and crystals including quenched juvenile materials as a minor constituent unit c2 displays welded stratified facies which consist of lithic rich layers and pumice rich layers these two subunits occur only in topographic lows in satsuma iwo jima unit c3 is thickest and poorly sorted non welded massive deposit which includes fragments of welded tuff from underlying units in proximal regions these facts indicate that multiple pyroclastic density currents produced units c1 and c2 in the near vent area and were followed by the main sustained current producing unit c3 a low aspect ratio ignimbrite distributed over a wide area of southern kyushu across the sea varying extents of magma water interactions started during phase 2 continuing during the early stages of phase 3 and diminished during the climactic c3 ignimbrite stage in addition collapse of the caldera may have started before unit c deposition based on the evidence of a fault overlain by unit c on the caldera rim the collapse may have initiated water access to the magma the source appears to have been biased toward the western side of the caldera the holocene evolution of the kikai volcano records the existence of a large silicic magma system at depths of about 7 km that coexisted with or was regularly recharged with mafic magma

tectonics of an arc arc junction an example from kyushu island at the junction of the southwest japan arc and the ryukyu arc abstract three distinctive geologic events occurred synchronously during the last 6 m y on kyushu island lying at the junction of the southwest japan arc and the ryukyu arc these events included 1 dextral fault displacement along a 100 km section of the median tectonic line 2 formation of a rectangular volcano tectonic depression 70 km long and 40 km wide and 3 approximately 30 of counterclockwise crustal rotation we propose an integrated tectonic model that explains these three tectonic features in terms of subduction of the philippine sea plate which resumed at around 6 ma after a halt of more than 5 m y oblique subduction of the philippine sea plate beneath the southwest japan arc detached a fore arc sliver that was displaced along a dextral fault the median tectonic line north of the nankai trough a volcano tectonic depression the hohi volcanic zone was formed by the pull apart structure on the western margin of the median tectonic line by contrast normal subduction of the philippine sea plate under the ryukyu arc caused back arc spreading observed as crustal extension in the northern okinawa trough the crustal extension caused the counterclockwise rotation for the northernmost ryukyu arc including southern kyushu