deep crustal expressions of exhumed strike slip fault systems shear zone initiation on rheological boundaries abstract the formation of major exhumed strike slip faults represents one of the most important dynamic processes affecting the evolution of the earth s lithosphere detailed models of the potential initiation their properties and architecture of orogen scale exhumed strike slip faults which are often subparallel to mountain ranges are rare the initiation of strike slip faults is at depth where temperature controlled rheological weakening mechanisms play the essential role localizing future strike slip faults in this review study we highlight that in pluton and metamorphic core complex mcc controlled tectonic settings as end members the initiation of strike slip faults occurs by rheological weakening along hot to cold contacts deep within the crust and mantle lithosphere respectively these endmember processes are potential mechanisms for the initiation of orogen scale exhumed strike slip faults at depth result in a specific thermal and structural architecture similar processes guide the overall displacement and ultimately the exhumation at such deep levels these types of exhumed strike slip dominated fault zones expose a wide variety of mylonitic cataclastic and non cohesive fault rocks on the surface which were formed at different structural levels of the crust during various stages of faulting and exhumation exhumation of mylonitic rocks is therefore a common feature of such reverse oblique slip strike slip faults implying major transtensive and or transpressive processes accompany pure strike slip motion during exhumation a major aspect of many exhumed strike slip faults is their lateral thermal gradient induced by the lateral juxtaposition of hot and cold levels of the crust controlling relevant properties of such fault zones and thus the overall fault architecture e g fault core damage zone shear lenses fault rocks and its thermal structure these properties of the overall fault architecture include strength of fault rocks permeability and porosity the hydrological regime as well as the nature and origin of circulating hydrothermal fluids

trace element characteristics ree patterns and partition coefficients of zircons from different geological environments a case study on indian zircons abstract twelve zircon separates from diverse geological settings in peninsular india have been analyzed for their zr hf sc ree th and u contents employing neutron activation techniques the whole rock samples of acid charnockite and a related rock of syenitic composition were also analyzed for these elements after separation of zircons the study reveals that 1 a the zircons exhibit a wide range of variation in elemental abudances and their ratios 2 b their chondritic normalised ree patterns exhibit negative or positive ce and negative eu anomalies in addition to smooth hree enriched patterns without anomalies and 3 c there are significant differences in the ree partition coefficients of zircons from the charnockite and the associated syenite the overall elemental abundances and ree patterns of the zircons could be explained in terms of crystallochemical factors bulk compositional differences of parent melts and paragenetic histories

complexity of the deep san andreas fault zone defined by cascading tremor seismic tremors can be used to distinguish plate boundaries analysis of tremors occurring deep beneath the san andreas fault may identify the boundary between the north american plate and the preserved remnant of a subducted slab

localized shear in the deep lithosphere beneath the san andreas fault system seismic images of the base of the lithosphere across the san andreas fault system california usa yield new constraints on the distribution of deformation in the deep lithosphere beneath this strikeslip plate boundary we show that conversions of shear to compressional waves sp across the base of the lithosphere are systematically weaker on the western side of the plate boundary indicating that the drop in seismic shear wave velocity from lithosphere to asthenosphere is either smaller or occurs over a larger depth range in central and northern california the lithosphere asthenosphere boundary changes character across a distance of 50 km and does so directly beneath the san andreas fault along its simple central segment and beneath the calaveras green valley bartlett springs faults to the north given the absolute velocities of the north america and pacific plates and low viscosities inferred for the asthenosphere these results indicate the juxtaposition of mantle lithospheres with different properties across these faults the spatial correlation between the central san andreas fault and the laterally abrupt change in the velocity structure of the deepest mantle lithosphere points to the accommodation of relative plate motion on a narrow shear zone 50 km in width and a rheology that enables strain localization throughout the thickness of the lithosphere

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

equatorial rain forest lateritic mantles a geomembrane filter the superimposed weathering layers in equatorial rain forest lateritic mantles from gabon atxca function as interactive compartments forming a dynamic semipermeable geomembrane filter selectivity of the filter is controlled by a progressive downward disappearance of connected macropore pathways created by bioturbation and dissolution the natural balance of root activity translocation dissolution deformation and pore evolution leads to the development of porous and permeable mature open geochemical weathering systems at the expense of the lithosphere these conclusions can be useful in modeling the fate of lateritic soils which cover one third of the emerged area of the world and which are economically important both as metal deposits and agricultural soils

the natural thermoluminescence of meteorites 4 ordinary chondrites at the lewis cliff ice field natural thermoluminescence tl measurements have been made on 302 meteorites from the vicinity of the lewis cliff in the beardmore region of antarctica the data provide information on terrestrial age and unusual radiation and thermal histories which in turn are helpful in identifying fragments of a single fall and in understanding ice sheet movements and the mechanisms by which meteorite concentration occurs at this site the present data with data for induced tl class find location hand specimen descriptions and mineral composition have enabled 70 of the present samples to be assigned to 27 groups of paired meteorites with between 5 and 2 meteorites in each group the distribution of meteorites on the ice the shape of the fields of paired meteorites and trends in the natural tl data indicate that there is a western component to the movement of the ice at this location as well as the previously supposed movement to the north this western vector probably explains the concentration of meteorites along the western edge of the ice tongue meteorites at the northern end of the tongue the lower ice tongue and meteorite moraine to the east have relatively high natural tl and therefore young terrestrial ages while those on the upper tongue show a broad range of ages including a great many large ages details of the meteorite concentration are different on the upper and lower tongue and it might be that these two parts of the ice sheet are unrelated these new natural tl data identify several recent falls and several meteorites which probably had unusually small perihelia immediately prior to capture by the earth

mantle strength of the san andreas fault system and the role of mantle crust feedbacks in lithospheric scale strike slip fault zones upper crustal strength is well constrained from borehole observations and fault rock deformation experiments but mantle strength is less well known using peridotite xenoliths we show that the upper mantle below the san andreas fault system california usa is dry and its maximum resolved shear stress 5 9 mpa is similar to the shear strength of the upper seismogenic portion of the fault these results do not fit with any existing lithospheric strength profile we propose the lithospheric feedback model in which the upper crust and lithospheric mantle act together as an integrated system mantle flow controls displacement and loads the upper crust in contrast the upper crust controls the stress magnitude in the integrated system crustal rupture transiently increases strain rate in the upper mantle below the strike slip fault leading to viscous strain localization the lithospheric feedback model suggests that lithospheric strength is a dynamic property varying in space and time in actively deforming regions

relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks new microstructural data on experimentally deformed wet and dry natural olivine rocks anita bay and aheim dunite together with the other reliable experimental data indicate that the experimental stress recrystallized grain size relationship in olivine rocks is largely independent of water content and temperature and is only slightly dependent on the flow properties of the material the experimental data cover a stress range of 30 300 mpa water contents from 30 ppm to 300 ppm and temperatures in the range 1100 1650 c local melt contents of up to 10 volume cannot be demonstrated to have a significant effect on the stress grain size relationship

the cora lake shear zone athabasca granulite terrane an intraplate response to far field orogenic processes during the amalgamation of laurentia the cora lake shear zone clsz is a 4 6 km wide localized high strain zone that bisects the polydeformed athabasca granulite terrane northern saskatchewan it also coincides with the geophysical trace of the snowbird tectonic zone the clsz represents a major lithotectonic and thermobarometric discontinuity within the exposure of 20 000 km2 of high pressure granulites most rocks have a strong mineral lineation plunging moderately to the southwest the northwestern subdomain hangingwall is characterized by ca 2 6 ga plutonic rocks that contain an early subhorizontal gneissic layering ca 2 57 ga that was overprinted by large amplitude folds and a partitioned but pervasive axial planar dextral shear fabric at ca 1 9 ga thermobarometry suggests metamorphic conditions of 0 9 gpa and 750 c during both of the phases of tectonism the footwall is predominantly underlain by the ca 3 3 3 0 ga chipman tonalite layers of intercalated mafic and felsic granulite and the widespread 1 9 ga chipman

faults shear zones in the earth s mantle abstract geodetic data support a short term continental deformation localized in faults bounding lithospheric blocks whether major faults observed at the surface affect the lithospheric mantle and if so how strain is distributed are major issues for understanding the mechanical behavior of lithospheric plates a variety of evidence from direct observations of deformed peridotites in orogenic massifs ophiolites and mantle xenoliths to seismic reflectors and seismic anisotropy beneath major fault zones consistently supports prolongation of major faults into the lithospheric mantle this review highlights that many aspects of the lithospheric mantle deformation remain however poorly understood coupling between deformation in frictional faults in the uppermost crust and localized shearing in the ductile crust and mantle is required to explain the post seismic deformation but mantle viscosities deduced from geodetic data and extrapolated from laboratory experiments are only reconciled if temperatures in the shallow lithospheric mantle are high 800 c at the moho seismic anisotropy especially shear wave splitting provides strong evidence for coherent deformation over domains several tens of km wide in the lithospheric mantle beneath major transcurrent faults yet it cannot detect narrow strain localization zones or shallowly dipping faults seismic profiling images shallow dipping seismic reflectors in the lithospheric mantle interpreted as the continuation of normal or less frequently inverse faults in the mantle however the nature of these reflectors is poorly understood there is a large discrepancy between the scale at which deformation processes are studied a few kilometers at most due to the limited size of continuous mantle exposures at the earth s surface and the scale inferred for strain localization in the mantle from geophysical observations tens of kilometers combining data on deformation microstructures and crystal preferred orientations in naturally deformed peridotites and seismologic observations allows nevertheless discussing strain localization processes that may play a role on the development of mantle shear zones

deformation in the lower crust of the san andreas fault system in northern california a continuous seismic velocity and reflectivity cross section of the san andreas fault system in northern california shows offsets in the lower crust and the mohorovicic discontinuity near the san andreas and maacama strike slip faults these faults may cut through the crust to the upper mantle in a zone less than 10 kilometers wide the northern california continental margin to the eastern edge of the coast ranges is underlain by a high velocity lowermost crustal layer that may have been emplaced within 2 million years following the removal of the gorda plate slab the rapid emplacement and structure within this layer are difficult to reconcile with existing tectonic models

mantle flow beneath a continental strike slip fault postseismic deformation after the 1999 hector mine earthquake two recent large earthquakes in the mojave desert california the magnitude 7 3 1992 landers and magnitude 7 1 1999 hector mine earthquakes have each been followed by elevated crustal strain rates over periods of months and years geodetic data collected after the hector mine earthquake exhibit a temporally decaying horizontal velocity field and a quadrant uplift pattern opposite to that expected for localized shear beneath the earthquake rupture we interpret the origin of this accelerated crustal deformation to be vigorous flow in the upper mantle in response to the stress changes generated by the earthquake our results suggest that transient flow in the upper mantle is a fundamental component of the earthquake cycle and that the lower crust is a coherent stress guide coupling the upper crust with the upper mantle

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

x ray computed tomography imaging a not so nondestructive technique x ray computed tomography has become a popular means for examining the interiors of meteorites and has been advocated for routine curation and for the examination of samples returned by missions here we report the results of a blind test that indicate that ct imaging deposits a considerable radiation dose in a meteorite and seriously compromises its natural radiation record ten vials of the bruderheim l6 chondrite were placed in ct imager and exposed to radiation levels typical for meteorite studies half were retained as controls their thermoluminescence tl properties were then measured in a blind test five of the samples had tl data unaltered from their original 10 cps while five had very strong signals 20 000 cps it was therefore very clear which samples had been in the ct scanner for comparison the natural tl signal from antarctic meteorites is 5000 50 000 cps using the methods developed for antarctic meteorites the apparent dose absorbed by the five test samples was calculated to be 83 5 krad comparable with the highest doses observed in antarctic meteorites and freshly fallen meteorites while these results do not preclude the use of ct scanners when scientifically justified it should be remembered that the record of radiation exposure to ionizing radiations for the sample will be destroyed and that tl or the related optically stimulated luminescence are the primary modern techniques for radiation dosimetry this is particularly important with irreplaceable samples such as meteorite main masses returned samples and samples destined for archive

new perspectives on geological strain rates calculated from both naturally deformed and actively deforming rocks abstract a value of 10 14 s 1 is commonly cited as an average geological strain rate this value was first suggested for finite strain across an orogen but based on more limited information than the combined geophysical geological and experimental data now available on active and ancient rock deformation thus it is timely to review the data constraining strain rates in the continents and to consider the quantifiable range of crustal strain rates here where resolution allows both spatial and temporal strain rate variations are explored this review supports that a strain rate of 10 14 1 s 1 arises from geological estimates of bulk finite strains microstructural arguments combining laboratory derived piezometers and viscous flow laws however imply local rates that are orders of magnitude faster geodetic rates in contrast are typically 10 15 s 1 in actively deforming areas about an order of magnitude slower than the bulk rates estimated from geological observations this difference in estimated strain rates may arise from either low spatial resolution or the fact that surface velocity fields can not capture strain localisation in the mid to lower crust integration of geological and geodetic rates also shows that strain rates can vary in both space and time over both single and multiple earthquake cycles overall time averaged geological strain rates are likely slower than the strain rates in faults and shear zones that traverse the crust or lithosphere

cerium anomalies in lateritic profiles the ree geochemistry and mineralogy have been studied in four lateritic profiles one derived from a syenite akongo sw cameroon the others being developed on a gneissic basement and located along a soil toposequence goyoum e cameroon there is a fractionation between lree and hree in the lateritic samples during weathering the weathered residual products being enriched in lree from la to eu and depleted in hree from gd to lu sampled waters are enriched in hree in relation to the syenite host rock a positive ce anomaly has been found systematically at the top of the saprolite beneath a zone of iron oxide accumulation in the laterite up to 2000 ppm ce may be present in the akongo profile cerianite ceo2 is present as very fine coatings in non ferruginous clayey domains primary ree bearing accessory minerals are weathered at the bottom of the profile specifically allanite and apatite are transformed into florencite and rhabdophane but these phases have no ce anomaly all the data are interpreted as the result of the following processes 1 1 ree leaching in a reducing environment 2 2 oxidation of ce3 to ce4 in an oxidizing environment 3 3 deposition of cerium as cerianite whereas the other ree remain in solution

earthquake cycle simulations with rate and state friction and power law viscoelasticity abstract we simulate earthquake cycles with rate and state fault friction and off fault power law viscoelasticity for the classic 2d antiplane shear problem of a vertical strike slip plate boundary fault we investigate the interaction between fault slip and bulk viscous flow with experimentally based flow laws for quartz diorite and olivine for the crust and mantle respectively simulations using three linear geotherms dt dz 20 25 and 30 k km produce different deformation styles at depth ranging from significant interseismic fault creep to purely bulk viscous flow however they have almost identical earthquake recurrence interval nucleation depth and down dip coseismic slip limit despite these similarities variations in the predicted surface deformation might permit discrimination of the deformation mechanism using geodetic observations additionally in the 25 and 30 k km simulations the crust drags the mantle the 20 k km simulation also predicts this except within 10 km of the fault where the reverse occurs however basal tractions play a minor role in the overall force balance of the lithosphere at least for the flow laws used in our study therefore the depth integrated stress on the fault is balanced primarily by shear stress on vertical fault parallel planes because strain rates are higher directly below the fault than far from it stresses are also higher thus the upper crust far from the fault bears a substantial part of the tectonic load resulting in unrealistically high stresses in the real earth this might lead to distributed plastic deformation or formation of subparallel faults alternatively fault pore pressures in excess of hydrostatic and or weakening mechanisms such as grain size reduction and thermo mechanical coupling could lower the strength of the ductile fault root in the lower crust and concomitantly off fault upper crustal stresses

alkaline rocks from continental brazil abstract the present literature review on brazilian alkaline rocks stresses mainly the petrographic and geologic aspects at least eight different rock associations are represented agewise four groups are found among southern brazilian outcrops an older one about 240 m y only that is still poorly known the massifs clustered around jacupiranga about 130 m y old a few occurrences 100 110 m y old tunas itapirapua and the youngest and most important one with an age spread from about 80 m y to about 53 m y recent research shows a clear tectonic control both on local and on regional scales of alkaline occurrences in southern brazil alkaline magmatism was set off by pre drift and drift activity and is at its onset geologically related to basaltic activity emplacement of many massifs is also locally controlled by old lineaments e g in the minas gerais goias belt as is emphasized by geophysical data on a petrographic and chronologic basis several alkaline provinces are distinguished in southern brazil preliminary data on the cambrian precambrian rocks from southern bahia state a province with undersaturated syenites and litchfieldites and from cratonic areas in northern brazil are also presented

using short term postseismic displacements to infer the ambient deformation conditions of the upper mantle 1 to interpret short term postseismic surface displacements in the context of key ambient conditions e g temperature pressure background strain rate water content creep mechanism we combined steady state and transient flow into a single constitutive relation that can explain the response of a viscoelastic material to a change in stress the flow law is then used to investigate mantle deformation beneath the eastern california shear zone following the 1999 m7 1 hector mine earthquake the flow law parameters are determined using finite element models of relaxation processes constrained by surface displacement time series recorded by 55 continuous gps stations for 7 years following the earthquake results suggest that postseismic flow following the hector mine earthquake occurs below a depth of 50 km and is controlled by dislocation creep of wet olivine diffusion creep models can also explain the data but require a grain size 3 5 mm that is smaller than the inferred grain size 10 20 mm based on the mantle conditions at these depths in addition laboratory flow laws predict dislocation creep would dominate at the stress grain size conditions that provide the best fit to diffusion creep models model results suggest a transient creep phase that lasts 1 year and has a viscosity 10 times lower than subsequent steady state flow in general agreement with laboratory observations the postseismic response is best explained as occurring within a relatively hot upper mantle e g 1200 1300 c at 50 km depth with a long term background mantle strain rate of 0 1 0 2 mstrain yr consistent with the observed surface strain rate long term background shear stresses at the top of the mantle are 4 mpa then decrease with depth to a minimum of 0 1 0 2 mpa at 70 km depth before increasing slowly with depth due to the pressure dependence of viscosity these conditions correspond to a background viscosity of 10 21 pa s within a thin mantle lid that decreases to 5 10 19 pa s within the underlying asthenosphere this study shows the utility of using short term postseismic observations to infer long term mantle conditions that are not readily observable by other means

deformation mechanism maps for feldspar rocks abstract deformation mechanism maps for feldspar rocks were constructed based on recently published constitutive laws for dislocation and grain boundary diffusion creep of wet and dry plagioclase aggregates the maps display constant temperature contours in stress grain size space for strain rates ranging from 10 16 to 10 12 s 1 two fields of dominance of grain boundary diffusion controlled creep and dislocation creep are separated by a strongly grain size sensitive transition zone for wet rocks diffusion controlled creep dominates below a grain size of about 0 1 1 mm depending on temperature stress strain rate and feldspar composition plagioclase aggregates containing up to 0 3 wt water as often found in natural feldspars are more than 2 orders of magnitude weaker than dry rocks the strength of water bearing feldspar rocks is moderately dependent on composition and water fugacity for a grain size range of about 10 50 m commonly observed in natural ultramylonites the deformation maps predict that diffusion controlled creep is dominant at greenschist to granulite facies conditions low viscosity estimates of 10 18 10 19 pa s from modeling postseismic stress relaxation and channel flow of the continental lower crust can only be reconciled with laboratory experiments assuming dislocation creep at high temperatures 900 c or at lower temperatures diffusion creep of fine grained rocks possibly localized in abundant high strain shear zones for similar thermodynamic conditions and grain size lower crustal rocks are predicted to be less than order of magnitude weaker than upper mantle rocks

the effect of dynamic recrystallization on olivine fabric and seismic anisotropy insight from a ductile shear zone oman ophiolite abstract subhorizontal mantle structures subparallel to the moho are rotated into nw se subvertical orientations across a shear zone in a sinistral sense of shear within the northern fizh mantle section of the oman ophiolite dynamic recrystallization resulted in grain size reduction of olivine and the development of porphyroclastic texture mean olivine grain size stabilized at 0 7 mm within the shear zone center this may reflect the steady state grain size of dynamically recrystallized olivine as determined by the deviatoric stress which in this case was as low as 10 mpa crystal preferred orientation cpo patterns of olivine are consistently 100 fiber or partial fiber texture indicating that olivine slip systems did not change during shearing dynamic recrystallization causes a weakening of olivine fabric intensity toward the shear zone center but this weakening is counterbalanced by cpo strengthening due to dislocation glide this process resulted in an abrupt decrease in seismic anisotropy at the center of the shear zone in contrast to a gradual decrease in olivine fabric intensity and mean grain size the measured seismic anisotropy patterns did not change in ways that would be significantly measurable by seismological observations despite the development of the shear zone dispersion of both p and s waves in the shear zone may be of little effect with respect to the overall seismic anisotropy this is not only because the shear zone occurs substantially in a narrow region but also because the seismic anisotropy is weaker in the shear zone than the high t structure region it suggests that a record of simple systematic seismic anisotropy observed in the upper mantle may indicate a simplified mantle flow structure as localized structures may be obscured in the region of the observation

frictional properties and sliding stability of the san andreas fault from deep drill core the strength of tectonic faults and the processes that control earthquake rupture remain central questions in fault mechanics and earthquake science we report on the frictional strength and constitutive properties of intact samples across the main creeping strand of the san andreas fault saf california united states recovered by deep drilling we find that the fault is extremely weak friction coefficient 0 10 and exhibits both velocity strengthening frictional behavior and anomalously low rates of frictional healing consistent with aseismic creep in contrast wall rock to the northeast shows velocity weakening frictional behavior and positive healing rates consistent with observed repeating earthquakes on nearby fault strands we also document a sharp increase in strength to values of 0 40 over 1 m distance at the boundary between the fault and adjacent wall rock the friction values for the saf are sufficiently low to explain its apparent weakness as inferred from heat flow and stress orientation data our results may also indicate that the shear strength of the saf should remain approximately constant at 10 mpa in the upper 5 8 km rather than increasing linearly with depth as is commonly assumed taken together our data explain why the main strand of the saf in central california is weak extremely localized and exhibits aseismic creep while nearby fault strands host repeating earthquakes

mobilization and re distribution of major and trace elements during extreme weathering of basalt in hainan island south china major trace and organic elements of a laterite profile developed on neogene basalts in northern hainan island south china were reported in this paper the aim of which was to investigate element mobilization and re distribution during extreme weathering the results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution organic matter om can significantly improve the transport of insoluble elements among all the elements th is the least mobile as for the general conservative elements during incipient chemical weathering such as fe ti zr hf nb and ta the removals are up to 20 40 in the upper profile however these elements behave as conservatively as th in the lower profile in the middle profile oxic environment occurs accompanied with significant om decomposition the mn and ce transferred downward are readily oxidized into insoluble mn iv and ce iv and precipitate in the oxic front important om decomposition decreases the capacity of transfer of insoluble elements in aqueous solution consequently al significantly precipitates in the oxic front and rees with the exception of ce precipitate largely in the omdepleted layers co and u are also concentrated in the oxic front in association with mn and ce respectively however cr shows a negative correlation with mn because its response to redox condition changes is reversed from that of mn mn oxides hydroxides fe oxides hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for rees except for ce in the profile rees with high concentrations in the profile seem closely associated with mn oxides hydroxides remarkable highly correlated ce and gd anomalies are observed in the profile ce anomalies are caused by ce precipitation in the oxic environment and successive decomposition of organic matter gd anomalies are likely to have resulted from lower stability constants of gd om complexes compared to those of neighboring rees the overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re distribution of the elements during extreme weathering

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

rare earth element mobility during conversion of nepheline syenite into lateritic bauxite at passa quatro minais gerais brazil abstract in a lateritic bauxite formed by weathering of nepheline syenite at passa quatro minas gerais state brazil bauxites on the hill tops directly develop from the syenite bed rock while downslope a kaolinitic layer occurs between bauxite and synetie a petrological investigation was performed on undisturbed weathered rock samples collected from a representative upslope pit the undisturbed weathered rocks were chemically analysed for major trace elements including ree and zr mass balance calculations were applied and the behaviour of the ree in the passa quatro weathering system was established compared to ree reference chondrite and to ree reference parent rock in the lateritic bauxite the results suggest that the first stages of weathering induce a volumetric change of 50 i e collapse with respect to the parent rock and remove ree with a slightly larger loss of the lree except ce compared to the hree in the upper layers where bauxite is more mature a net mass gain in ree is observed relative to the underlying layers this gain takes place during the reduction of the upper layer during the downward progression of the weathering front very significant ree losses occurs during the bauxitization processes throughout the upslope profile in addition the downslope kaolinitic system is demonstrated to be depleted in ree in the same proportions as the upslope bauxite we proposed that the ree exported in solution from the whole weathering mantle have enriched neighbouring watershed sediments

analytical dual energy microtomography a new method for obtaining three dimensional mineral phase images and its application to hayabusa samples abstract we developed a novel technique called analytical dual energy microtomography that uses the linear attenuation coefficients lacs of minerals at two different x ray energies to nondestructively obtain three dimensional 3d images of mineral distribution in materials such as rock specimens the two energies are above and below the absorption edge energy of an abundant element which we call the index element the chemical compositions of minerals forming solid solution series can also be measured the optimal size of a sample is of the order of the inverse of the lac values at the x ray energies used we used synchrotron based microtomography with an effective spatial resolution of 200 nm to apply this method to small particles 30 180 m collected from the surface of asteroid 25143 itokawa by the hayabusa mission of the japan aerospace exploration agency jaxa a 3d distribution of the minerals was successively obtained by imaging the samples at x ray energies of 7 and 8 kev using fe as the index element the k absorption edge of fe is 7 11 kev the optimal sample size in this case is of the order of 50 m the chemical compositions of the minerals including the fe mg ratios of ferromagnesian minerals and the na ca ratios of plagioclase were measured this new method is potentially applicable to other small samples such as cosmic dust lunar regolith cometary dust recovered by the stardust mission of the national aeronautics and space administration nasa and samples from extraterrestrial bodies those from future sample return missions such as the jaxa hayabusa2 mission and the nasa osiris rex mission although limitations exist for unequilibrated samples further this technique is generally suited for studying materials in multicomponent systems with multiple phases across several research fields

thermoluminescence and the shock and reheating history of meteorites iv the induced tl properties of type 4 6 ordinary chondrites abstract the induced thermoluminescence tl properties of 121 equilibrated ordinary chondrites have been measured the samples were 74 h and 47 l chondrites of which 33 h and 32 l were from antarctica the distribution of tl sensitivities for non antarctic l chondrites differs from that of non antarctic h chondrites consistent with a greater proportion of the former class suffering post metamorphic shock data on the effect of laboratory annealing on tl sensitivity and step wise ar release measurements enable the meteorites to be sorted into three shock related temperature groups

shear wave splitting beneath western united states in relation to plate tectonics we have examined shear wave splitting in teleseismic shear waves from 26 broadband stations in the western united states fast polarization directions and delay times t show spatial variations that are coherent within geologic provinces stations located near the san andreas fault show clear evidence for fault parallel anisotropy in the crust and upper mantle 115 125 km thickness this can be explained by the finite strain associated with the relative plate motion between the north american and pacific plates the lateral extent of this strain field is probably narrow to the west because stations 55 km west of the san andreas fault do not show fault parallel anisotropy in southern california station lac located 80 km east of the san andreas fault shows large fault parallel anisotropy this suggests that the pacific north american plate boundary in the mantle might be displaced to the east in southern california a deeper e w oriented fast direction of anisotropy underlies the fault parallel anisotropic layer in the vicinity of the san andreas fault an e w fast feature is also present beneath the western basin and range and the foothills of the sierra nevada although local variations are present the magnitude of delay times suggests that this feature resides in the asthenosphere we interpret this feature as the asthenospheric flow in the slabless window left behind the farallon plate the flow induced anisotropy may partially be frozen in at shallow depths station orv is located near the southern edge of the gorda slab where no anisotropy is detected the absence of anisotropy at this location could therefore mark a boundary between farallon associated flow and regions where e w oriented asthenospheric flow did not occur the lack of evidence for ne sw fast orientation within the walker lane shear belt of western nevada suggests that this crustal feature does not extend into the mantle or that is not as well developed as that beneath the san andreas fault stations located over the young subducting gorda plate mark a change in the fast direction to nearly ne sw this direction aligns well with the maximum compressive stress direction in the overlying north american plate and the ne sw directed internal shearing of the gorda plate the anisotropic thicknesses calculated from delay times suggest roughly double that expected for purely lithospheric contributions this implies that the anisotropic thickness may include some of the asthenosphere alternatively using a higher anisotropy of 8 can bring thicknesses in line with other measures of lithospheric thicknesses the correspondence between the fast directions and the present plate tectonic deformations suggest that mapping upper mantle deformation through seismic anisotropy is a viable method and that asthenospheric flow may be a significant contributor to seismic anisotropy

computed tomographic analysis of meteorite inclusions the discovery of isotopic anomalies in the calcium and aluminum rich inclusions of the allende meteorite has improved our knowledge of the origin of the solar system inability to find more inclusions without destroying the meteorite has hampered further study by using a fourth generation computed tomographic scanner with modifications to the software only the interior of heterogeneous materials such as allende can be nondestructively probed the regions of material with high and low atomic numbers are displayed quickly the object can then be cut to obtain for analysis just the areas of interest

three dimensional observation of carbonaceous chondrites by synchrotron radiation x ray ct quantitative analysis and developments for the future sample return missions abstract carbonaceous chondrites were observed by synchrotron radiation x ray computed tomography sr ct three dimensionally we analyzed the chemical composition of the components of the carbonaceous chondrites such as chondrules matrix and iron inclusions from the linear attenuation coefficient lac of x rays histograms of the lac were used for the analysis of chemical composition of the internal material and we could find a clear relation of the compositions between the chondrules and matrix we also analyzed the size distribution of low fe inclusions chondrules using image processing of ct images cumulative size distribution of chondrules shows power law distribution and slopes of the distribution changed for different chondrite classes results of these analyses show that the chondrule and matrix would have formed from the same precursor and were incorporated into the parent bodies without large scale mixing in the solar nebula the method will also provide important information for the analysis of future sample return missions our examinations demonstrate great potential of the quantitative determination of chondrite class nondestructively by sr ct

the natural thermoluminescence of meteorites i twenty three antarctic meteorites of known 26al content the level of thermoluminescence tl naturally present in 23 antarctic chondrites of known 26al content has been measured as a means of exploring their thermal and radiation history antarctic meteorites tend to have lower natural tl than non antarctic meteorites presumably because of their generally longer terrestrial ages seventeen of the meteorites lie on a band of increasing natural tl and 26al activity meteorites with 26al of 45 60 dpm kg have natural tl values normalized to the high temperature tl of 2 4 whereas those with 26al values of 30 45 dpm kg have normalized natural tl values of 1 2 and alha 76008 with an 26al content of 11 dpm kg has a tl value of 0 87 0 01 this suggests that the half life for tl decay is comparable to that of 26al the six meteorites not lying on the tl 26al trend have much lower tl than others of comparable 26al for two of them rkpa 79001 and rkpa 80202 which are tentatively paired the low natural tl probably reflects a recent severe shock while another alha 77294 has previously been measured in this lab and had tl consistent with the tl 26al trend the remaining three alha 78006 alha 77296 and alha 77297 of which the last two are probably paired have suffered a recent reheating such as would be expected from orbits of unusually small perihelia

rheological evolution of a pseudotachylyte bearing deep crustal shear zone in the western canadian shield abstract crustal scale continental strike slip fault systems are typically thought to be thermally segregated into an upper seismogenic expression and a lower zone of ductile deformation likely extending into the lower crust the ability of the lower crust to sustain stress is fundamental to understanding the mechanical behavior of the lithosphere yet significant debate exists regarding the strength of the ductile crust the cora lake shear zone in the western churchill province of the canadian shield is a 4 7 km wide zone of granulite to upper amphibolite facies mylonite which hosts synkinematic pseudotachylyte suggesting a locally strong lower crust kilometer scale mapping suggests that the shear zone localized at a major lithological and terrane boundary with the pseudotachylyte network centered within the ca 1 km wide more intensely deformed finer grained ultramylonitic core in this contribution we use optical petrography and electron backscatter diffraction to describe microstructure across a transect of the cora lake shear zone by combining these observations with grain size piezometry experimental flow laws and regional pressure temperature paths we conclude that stress amplification from a relatively common type of km scale lithological heterogeneity and cooling history is the most reasonable explanation for the deep crustal pseudotachylyte