the terrestrial alteration of saharan shergottites dar al gani 476 and 489 a case study of weathering in a hot desert environment abstract rare earth element ree and other selected trace and minor element concentrations were determined in various phases of dar al gani 476 and 489 two basaltic shergottites recently found in the libyan sahara whereas merrillite and feldspathic glass compositions do not seem to have been altered since the fall of these meteorites olivine and pyroxenes commonly show light ree enrichments sometimes accompanied by ce anomalies that are attributed to terrestrial alteration sr and ba enrichments are also observed the calcium carbonate that resides in most cracks is essentially devoid of ree but a fine grained amorphous silicate material that fills some veins and pockets has striking light ree enrichments and elevated p sr and ba it is argued that this material likely to be impact melt as well as the notoriously light ree poor olivine and pyroxenes were preferentially affected by a crustal light ree rich contaminant caution is urged when using whole rock or even mineral separate compositional and isotopic data for hot desert meteorites

fault interaction may generate multiple slip vectors on a single fault surface slip vectors of multiple orientations on a single fault surface may be explained by the interaction of crustal scale faults in response to nearby earthquakes field observations of at least five sets of striae on a single planar fault surface can be reproduced in numerical experiments these experimental results suggest that slip vectors having variable orientations may reflect a highly transient local stress state in an otherwise constant regional stress field our results suggest that stress inversion techniques should be applied with caution to areas with complex regional scale fault patterns

a newly recognized type of slickenside striation abstract this note summarizes current views on the origin of slickenside striations and points to the existence of a type of striation not readily explained by established genetic ideas such striations have been seen on fault surfaces in naturally deformed shale and in experimentally deformed paraffin wax they are defined by arrays of shallow slip parallel ridges and grooves of millimetric width and below on any given slip surface the ridges are as common as the grooves and display similar dimensions and profile shapes across any pair of slip surfaces in contact at the end of faulting ridges protruding from one surface fit into or nest with grooves on the other surface the origin of these features is not yet understood

heart mountain wyoming detachment lineations are they in microbreccia or in volcanic tuff the concept of tectonic denudation followed by deposition of lower middle eocene wapiti formation volcanic rocks on the exposed heart mountain detachment has been challenged by hauge his extending allochthon interpretation requires that the wapiti formation be fault emplaced and that lineations in a volcanic tuff overlying the fault north of jim smith peak be fault striae in microbreccia our re examination of the field evidence in minute detail indicates that these lineations were produced by flowage of volcanic rocks on a thin layer of air fall tuff the following lines of evidence indicate that this tuff was deposited on the detachment surface during the brief interval that the denuded surface was exposed 1 field relations indicate that the wapiti volcanic rocks are younger than the detachment and so they could not have been fault emplaced 2 lineations occur only on the upper surface of wapiti formation tuff none were found at the contact of the tuff with the detachment surface 3 the reported direction of translation indicated by the lineations is not consistent many lineations in the tuff indicate north and northeast movement a direction that is consistent with lineations produced by lava flowing from a known vent but inconsistent with a southeast direction of detachment movement 4 the lineations are restricted to the northwestern part of the area covered by the wapiti formation which is also consistent with their derivation as volcanic flow lineations from a known vent if the wapiti had been tectonically emplaced fault striae should occur elsewhere on the detachment surface but none have been observed 5 the lower contact of the tuff with the detachment surface as seen in thin sections is irregular suggesting that it is a depositional rather than a fault contact 6 the contact between the tuff and overlying wapiti as seen in thin sections is also irregular as would be expected if the wapiti volcanic breccia had been deposited on the tuff thin sections of the microbreccia suggest that it is a sedimentary rock not a fault rock 7 a remnant of the tectonic carpet of all carbonate fault breccia lying on the detachment surface unmixed with the overlying wapiti volcanic rock is compatible with the depositional emplacement of the wapiti but is not compatible with wapiti formation being moved many kilometers across the carpet of all carbonate fault breccia and not removing or becoming mixed with it

ce anomalies in the lew85300 eucrite evidence for ree mobilization during antarctic weathering abstract there is abundant evidence for widespread ree mobilization in antarctic eucrites resulting in ce and eu anomalies and lower whole rock ree abundances relative to typical eucrites using secondary ion mass spectrometry sims we investigated the microdistribution of ce anomalies in the antarctic polymict eucrite lew85300 ce anomalies positive and or negative are present in all three of the minerals plagioclase pyroxene and silica analysed the anomalies occur in grains from all four clasts as well as in mineral and lithic fragments from the surrounding matrix thus there appears to be no lithologic association silica which has been heavily shocked and altered exhibits a lree enriched pattern with negative ce and eu anomalies consistent with a derivation of the ree from ca phosphate dissolution trivalent ree are leached from the phosphates with preferential retention of tetravalent ce and redeposited on silica pyroxene is also widely affected by ree mobilization due to an extensive shock induced microcrack network along cleavage planes a tendency for the largest ce anomalies to occur at low lree concentrations suggests that pyroxene itself experienced ree leaching with concomitant ce retention ce anomalies are rare in plagioclase because this mineral lacks an extensive network along which ree can be mobilized the widespread ree mobilization and evidence for other forms of weathering requires that trace element data be used cautiously especially for antarctic eucrites

reverse slip structures at oceanic diverging plate boundaries and their kinematic origin data from tertiary crust of west and south iceland abstract normal faulting predominates within rift zones but reverse fault plane solutions are occasionally found for earthquakes along the mid atlantic ridge furthermore field observations of striae and in situ measurements in places show off rift compression and reverse faulting we analyse eight cases of reverse slip motion observed in the eroded tertiary crust of the borgarfjor ur and hreppar rift jump blocks respectively in west and south iceland these structures were the only ones observed where both striae and marker horizons could be used to deduce the sense of reverse slip motion the vertical displacements are less than 10 m and the motions are of local origin we believe these structures are formed independently from regional compression as they have variable kinematic origins some occur in association with dykes sills or cone sheet without evidence of horizontal shortening across intrusions others are due to local bends of regional steeply dipping normal faults or secondary fractures riedel or secondary fractures reverse slip striations are found at the irregularities of steeply dipping normal faults or at the tips of steeply dipping normal faults uplifted by an underlying propagating dyke striations even conspicuous ones do not necessarily reflect significant amounts of displacement if horizontal compression acts in iceland its magnitude is not sufficient to shorten the rocks and to close the fractures of various tectonic settings the observed examples are explained as local kinematic adjustments to companion structures without regional compressional stress field or shortening and can lead to misinterpretation if not put into the correct context

minor and trace element partitioning between pyroxene and melt in rapidly cooled chondrules we present minor and trace element ree sr y and zr data for pyroxenes and mesostases in four porphyritic chondrules from the semarkona ordinary chondrite apparent partition coefficients for clinoenstatite orthoenstatite pigeonite and augite are compared with experimental and petrologic data from the literature and the effects on apparent partition coefficients of the rapid cooling rates at which chondrules crystallized are evaluated for most elements the effects of cooling at rates of hundreds of degrees per hour cannot be distinguished from variations in equilibrium data resulting from differences in temperature or composition however for lree apparent partition coefficients are significantly higher than comparable equilibrium data and the ratio of hree lree partition coefficients is lower particularly for ca poor pyroxene we attribute this flattening of ree patterns to the effect of rapid cooling apparent partition coefficients of all ree and y in augite are higher than equilibrium data particularly in one chondrule with a high al 2o3 content we suggest that this may be attributed to an increase in the uptake of trivalent trace element cations in the pyroxene crystal structure as a result of charge balanced substitutions with al 31 cations

phosphoran olivine overgrowths implications for multiple impacts to the main group pallasite parent body phosphoran olivine 1 7 wt p2o5 is a metastable phase known from fewer than a dozen meteoritic or terrestrial occurrences we have thoroughly examined phosphoran olivine in the springwater pallasite to characterize its distribution textural relationships and geochemistry phosphoran olivine is abundant in springwater as randomly distributed millimeter scale partial overgrowths on the p free olivine crystals geochemical analyses support the substitution mechanism of p into the tetrahedral si site with octahedral site vacancies for charge balance observed trace element variations on the other hand are not related to p substitution element mapping reveals fine scale oscillatory p zoning in unusual serrate patterns indicating rapid crystal nucleation from a melt as proposed by boesenberg and hewins 2010 and a subsequently variable rate of crystallization the timing of phosphoran olivine formation in springwater is constrained to after the period of macroscopic olivine rounding but before the cooling of the metal matrix because the phosphoran overgrowths overprint specific host grain boundary modifications we suggest that the episode of extremely rapid cooling necessary to crystallize and preserve this rare phase may have been triggered by an additional impact to the parent body

kinematic analyses of brittle roto translational planar and listric faults based on various rotational to translational velocities of the faulted blocks abstract research on rotational roto translational faults have been relatively less than translational faults this is despite perfect translational faults seldom occur in mega scale this work models slickenside lineation patterns on planar and listric fault planes for different ratios of rates of rotation to the uniform speed towards a specific geographic direction v of faulted blocks curves simulated for the planar fault planes are fitted with natural examples of such roto translational faults in our 10 chosen examples the v ratio ranges between 0 2 fault at san miguelito range central mexico and as high as 2 4 fault at hyogoken nambu japan knowing the v ratios from terrains can better interpret its tectonics for example if v and the total time of duration of the deformation are known from some other studies even the total amount of rotation can be estimated the far reaching implication of this study is that as several hydrocarbon reserves and terrains with landslides are related to roto translational faults this work will be a stepping stone in petroleum geosciences e g stability of hydercarbon reserve and engineering geology e g stability of slope

discrepancy between mineral residence time and soil age implications for the interpretation of chemical weathering rates virtually all soil chronosequence studies have equated the degree of mineral weather ing with the soil age which is equal to the time since the cessation of erosion or deposition the primary minerals from the parent material however enter the soil as the weathering front propagates downward and are depleted via chemical weathering the residence time of minerals is thus a function of both the rate of conversion of parent material to soil i e soil production and the minerals susceptibility to chemical weathering reactions we fi nd that mineral residence times are signifi cantly shorter than the soil age by mathematically consid ering the interactions among soil production and chemical weathering we demonstrate that traditional estimates of mineral specifi c chemical weathering rates from soil chronosequences may diverge by several orders of magnitude from the actual weathering rates

meso cenozoic tectonic evolution of the se brazilian continental margin petrographic kinematic and dynamic analysis of the onshore araruama lagoon fault system abstract the ararauama lagoon fault system composes one of the most prominent set of lineaments of the se brazilian continental margin it is located onshore in a key tectonic domain where the basement inheritance rule is not followed this fault system is characterized by ene wsw silicified tectonic breccias and cataclasites showing evidences of recurrent tectonic reactivations based on field work microtectonic kinematic and dynamic analysis we reconstructed the paleostresses in the region and propose a sequence of three brittle deformational phases accountable for these reactivations 1 ne sw dextral transcurrence 2 nnw sse dextral oblique extension that evolved to nnw sse pure extension 3 ene wsw dextral oblique extension these phases are reasonably correlated with the tectonic events responsible for the onset and evolution of the se onshore rift basins between the neocretaceous and holocene however based on petrographic studies and supported by regional geological correlations we assume that the origin of this fault system is older related to the early cretaceous south atlantic rifting this study provides significant information about one of the main structural trends of the se brazilian continental margin and the tectonic events that controlled its segmentation since the gondwana rifting and compartmentalization of its onshore sedimentary deposits during the cenozoic

petrogenetic relationships between diogenites and olivine diogenites implications for magmatism on the hed parent body abstract diogenites are orthopyroxenites and harzburgites that are petrogenetically associated with basaltic magmatism linked to the earliest stages of asteroidal melting on the parent body for the howardite eucrite diogenite hed meteorites there are several models proposed for their origin 1 accumulation of orthopyroxene opx chromite chr olivine ol during the crystallization of a magma ocean during the initial stages of asteroidal differentiation 2 accumulation of opx chr ol during the crystallization of compositionally distinct basaltic magmas emplaced into the crust of the hed parent body and 3 the orthopyroxenites formed by the crystallization of basaltic magmas within the hed parent body crust whereas the harzburgites represent the mantle of the hed parent body although ol and opx experienced varying degrees of subsolidus reequilibration 1100 700 c their minor and trace element characteristics appear to partially preserve magmatic signatures that provide insights into distinguishing among different models for the origin of diogenites the opx exhibits a continuous and very systematic variation in incompatible elements such as al ti zr y and yb polymict diogenites i e roda eet 79002 can contain distinct lithologies with both different incompatible element characteristics and different model abundances of ol there appears to be no relationship between the appearance and abundance of ol and the incompatible element characteristics of the opx the ol exhibits a range in mg and systematic variations ni co ni co and mn for examples low ni co appears to be closely associated with the harzburgites and ni and mn exhibit a negative correlation surprisingly incompatible element concentrations in opx are not negatively correlated to ni concentrations in ol the continuous nature of the minor and trace element characteristics of the opx and ol is consistent with the all the diogenite lithologies forming through a single process such as crystallization within a magma ocean or a series of layered intrusions further the range in incompatible element variability in the opx the ni and co systematics in the ol and the association of distinctly different lithologies within polymict diogenites are most consistent with the diogenites representing lithologies from diverse layered intrusions alternatively they may represent crystallization products of a magma ocean much more complex than has been thus far proposed i e multiple mos there are some distinct differences between diogenites and the ol rich achondrite que 93148 that was also analyzed during this study these differences such as ni co in ol estimated conditions of fo2 suggest that que 93148 is closely related to main group pallasites rather than the parent bodies for the hed meteorites

critical porosity and elastic properties of microporous mixed carbonate siliciclastic rocks by integrating elastic property measurements and quantitative mineralogic and petrographic analyses of 45 mixed carbonate siliciclastic samples from two wells drilled in late cretaceous rock of the south provence basin southeast france we can 1 identify and quantify the parameters controlling elastic properties 2 demonstrate that micrite can be considered as a porous medium with a low critical porosity averaging 18 and 3 relate diagenetic transformations pore structure modifications and elastic property changes microporous carbonates with compact anhedral and euhedral microrhombic micrites display a steeper decrease in compressional and shear velocities with increasing porosity than do carbonate rocks with moldic intergranular or intercrystalline macroporosity the low value of critical porosity estimated in micrites 18 as well as the steep slopes of velocity porosity relationships at low porosity is believed to result from a pore network geometry characterized by very flat thin pores bounded by planar faces of micrite crystals cementation of microrhombic micrite steeply increases elastic moduli whereas dissolution processes significantly increase porosity with low variations of elastic moduli thus critical porosity concepts can help describe and model elastic properties of micritic microporous carbonate

generation of abnormal trace element abundances in antarctic eucrites by weathering processes abstract based on rees antarctic eucrites can be divided into two groups those showing normal trace element characteristics e g similar to juvinas and those showing abnormal trace element abundances many antarctic eucrite polymict eucrite and basaltic clast samples show the abnormal trace element abundances with ree patterns exhibiting positive ce anomalies sometimes negative ce anomalies positive eu anomalies and low abundances of the remainder of the rees with the lrees generally being at lower relative abundances than the hrees most samples of crystalline clasts from the polymict eucrites lew85300 lew85302 and lew85303 show the abnormal patterns while the glassy matrixes of these meteorites show normal patterns exterior samples generally show more abnormal patterns larger anomalies greater depletions than interior samples from the same meteorites comparison of all basaltic eucrite literature data combined with our data shows that positive and negative ce anomalies and positive eu anomalies are found in about 61 of antarctic eucrite analyses and are virtually unknown in non antarctic eucrite analyses further positive ce anomalies and positive eu anomalies are commonly associated with antarctic eucrites having low ree concentrations consideration of mineral melt partition coefficients shows that it is unlikely that ce anomalies are magmatic features from the hed parent body cerium anomalies on earth are generally restricted to the weathering zone where the relative ease of oxidizing ce to the 4 state allows for fractionation of ce from the 3 rees we believe the unusual ree patterns of abnormal antarctic eucrites arise from weathering effects generated in or on the antarctic ice our suggested scenario involves formation of melt water and its equilibration with the atmosphere which promotes dissolution of ree rich phosphates and oxidation of ce tetravalent ce can then be fractionated from the trivalent ree in solution the details of the weathering process are unclear and will require detailed chemical and sem investigations of eucrites for their elucidation we predict that rapidly chilled eucrites with glassy rather than crystalline mesostases will be more likely to survive the antarctic environment without alteration of their ree patterns occasional s se and k enrichments are likely due to weathering in the antarctic environment as well but these enrichments are not well correlated with ce anomalies

slickenside and fault surface kinematic indicators on active normal faults of the alpine betic cordilleras granada southern spain abstract twenty four mesoscopic slickenside kinematic indicators are described here for the pliocene quaternary active normal faults of the alpine betic cordilleras granada southern spain the indicators are classified into twelve groups depending on the down or up slope asymmetric orientation of features such as concavities damaged versus sharp grain borders or step edges v shaped markings fractures and trailed material seventeen of the indicators were not previously described in the literature the new kinematic indicators include two types of asymmetric grains a carrot shaped marking six substructures of congruous and incongruous steps trailed fault material a drop shaped figure a v shaped marking three types of synthetic hybrid fractures with congruous steps and two varieties of pluck holes we think that some of these kinematic indicators provide information on the amount of displacement aseismic versus seismic slip rates cataclastic flow frictional wear or surface polishing

identification of shallow water flow sands by vp vs inversion of conventional 3d seismic data shallow water flow swf from overpressured unconsolidated uncemented sands is a high profile hazard in deep water drilling thus accurate predrill seismic prediction of swf sands is an important practical problem laboratory measurements show high seismic compressional to shear velocity vp vs ratios in swf sands thus vp vs anomalies produced by elastic seismic inversion can provide a quantitative identification of swf sands before drilling three 3d common angle aperture prestack time migrated data sets from the garden banks area of the gulf of mexico are inverted simultaneously for vp vs two wells provide constraints high vp vs values are observed in a known swf zone in shell deepwater development s well gb920 1 in kerr mcgee oil gas corporation s well gb877 1 vp vs anomalies match well with independent predrill swf sand predictions based on geologic information and seismic amplitudes high vp vs anomalies 9 are used to identify potential swf sands away from the wells we conclude that

complexities on the acapulcoite lodranite parent body evidence from trace element distributions in silicate minerals the trace element distributions of individual minerals from seven acapulcoites and lodranites have been studied systematic differences are evident between some members of the two groups specifically pyroxenes from the lodranites macalpine hills mac 88177 and lewis cliff lew 88280 exhibit depletions of the rare earth elements ree and other incompatible trace elements ti zr y relative to acapulcoite acapulco allan hills alh a81261 pyroxenes that are consistent with the formation and removal of 15 or more silicate partial melts from these meteorites phosphate ree patterns in these lodranites also support this scenario however other members of the acapulcoite lodranite clan exhibit more complex trace element variations elephant moraine eet 84302 which has been classified as transitional between the acapulcoites and lodranites generally has trace element characteristics similar to the acapulcoites however its plagioclase ree compositions suggest a somewhat greater degree of metamorphism than that experienced by acapulcoites such as acapulco and alha81261 similar and elevated ree abundances in the silicate phases from acapulcoite alha81187 and lodranite graves nunataks gra 95209 suggest that these two meteorites in fact experienced similar thermal histories this probably included some silicate partial melting although little melt appears to have been lost from the samples the observed variations in the trace element abundances of these samples from the acapulcoite lodranite clan emphasize the complex and varied processes that have acted on their parent body the simple bimodal classification of these meteorites based primarily on petrographic criteria which has been used to date appears to be inadequate to describe this diverse group of samples as they represent a range of degrees of partial melting both with and without accompanying melt migration in some instances secondary processes on the parent body such as cryptic metasomatism have further modified sample compositions

slickenside kinematic indicators abstract a new classification of slickenside kinematic indicators is presented based on 61 criteria these slickensides have been subdivided into eleven major groups v or crescentic markings steps fractures trains of inclined planar structures trailed material asymmetric elevations deformed elements mineralogical crystallographic orientations asymmetric plan view features asymmetric cavities and asymmetric folds this classification constitutes a useful tool for geologists interested in the determination of the shear sense in fault surfaces bearing slickensides examples of application of this classification to natural fault surfaces at different scales are presented

sliding behavior and deformation textures of heated illite gouge abstract the run products of a series of triaxial friction experiments on an illite rich gouge have been examined petrographically to study the relationship between textural development and sliding mode the samples show a complete range of textures from ones in which the entire gouge layer is deformed to ones in which the deformation is concentrated along narrow subsidiary shears and the rest of the gouge layer is massive the samples with a pervasively developed deformation fabric slide stably whereas the samples containing shear bands show stick slip motion if the intersection angles between boundary parallel and cross cutting riedel shears are also relatively high these textural differences suggest that localization of shear combined with higher angle riedel shears are somehow involved in stick slip motion the orientation of riedel type shears in natural fault zones may also have potential as a paleoseismological tool

the pyroxene pallasites vermillion and yamato 8451 not quite a couple two pallasites vermillion and yamato y 8451 have been studied to obtain petrologic trace element and o isotopic data both meteorites contain low ca and high ca pyroxenes 2 by volume and have been dubbed pyroxene pallasites pyroxene occurs as large individual grains as inclusions in olivine and in other pyroxene and as grains along the edges of olivine symplectic overgrowths sometimes found in main group and eagle station pallasites are not seen in the pyroxene pallasites olivine compositions are fa10 12 similar to those of main group pallasites siderophile trace element data show that metal in the two meteorites have significantly differing compositions that are for many elements outside the range of the main group and eagle station pallasites these compositions also differ from those of iab and iiiab iron meteorites rare earth element ree patterns in merrillite are similar to those seen in other pallasites indicating formation by subsolidus reaction between metal and silicate with the merrillite inheriting its pattern from the surrounding silicates the o isotopic compositions of vermillion and y 8451 are similar but differ from main group or eagle station pallasites as well as other achondrite and primitive achondrite groups although vermillion and y 8451 have similar mineralogy pyroxene compositions ree patterns and o isotopic compositions there is sufficient evidence to resist formally grouping these two meteorites this evidence includes the texture of vermillion siderophile trace element data and the presence of cohenite in vermillion

fe mg fe mn relations of meteorites and primary heterogeneity of primitive achondrite parent bodies abstract we examine fe mg mn relations of meteorites as represented on plots of molar fe mg ratio vs molar fe mn ratio and use them to consider whether it is meaningful to classify achondrites as primitive or evolved first we demonstrate that fe mg fe mn plots can be used to identify some of the major processes that have affected meteorite parent bodies during both the nebular condensation and accretion and the planetary igneous stages of their evolution examination of compositions of chondrites on this diagram reveals distinct patterns that result from three nebular processes 1 volatility controlled mn mg fractionation 2 metal silicate fractionation under highly reducing conditions and 3 subsequent oxidation leading to variations in feo mgo ratio ordinary chondrites ocs show a characteristic pattern that records all three of these processes and suggests that the latter two are coupled examination of the compositions of achondrites on this diagram shows that all of those that have been classified as primitive lodranites acapulcoites winonaites iab silicate inclusions brachinites and ureilites are easily distinguished from those that have been classified as evolved sncs heds and lunar basalts the mn mg ratios of the former are chondritic while those of the latter are superchondritic hence they plot in two graphically distinct regions of the fe mg fe mn diagram a simple melting calculation reveals that this distinction results principally because the former are residues and the latter are melts or cumulate products of melts rather than because the latter are more evolved additionally however some of the groups classified as primitive achondrites show fe mg fe mn patterns similar to that of ocs constant but distinct mno mgo ratios over large ranges of feo mgo ratio we argue that these trends reflect primary heterogeneity resulting from the same nebular processes as those that affected ocs and therefore preserve evidence that more of the materials that accreted to form planetesimals experienced these processes than is apparent from known chondrites this evidence is preserved principally because these meteorites are residues in contrast groups commonly classified as evolved achondrites show fe mg fe mn patterns that reflect only igneous processing and any evidence for primary heterogeneity of their parent bodies has been obliterated again this is principally because these meteorites represent melts rather than beause they are more evolved usage of the terms primitive and evolved to describe achondrites should be clearly defined

the aljibes half graben active extension at the boundary between the trans mexican volcanic belt and the basin and range province mexico the aljibes half graben is located 140 km west northwest of mexico city and is characterized by several parallel 10 km long south dipping and east striking normal faults late miocene basalt flows with 40 ar 39 ar ages of 7 7 0 1 ma and 7 1 0 5 ma are displaced along these faults with reference to this basalt the composite throw and heave of the half graben are 480 m and 270 m respectively and the relative extension is 5 whereas the vertical slip rate along the faults of the aljibes half graben after the deposition of the basalt is 0 07 mm yr the aljibes half graben is located at the northern margin of the trans mexican volcanic belt and perpendicularly intersects northstriking normal faults of the basin and range province the relative sequence of activity of the two stress fields and fault systems cannot be resolved in the study area and the two systems may have been active simultaneously we explain this structural configuration by horizontal migration of the boundary between the two stress provinces with time which requires intermittent permutations between the intermediate and least principal stresses 2 and 3 this is supported by the low stress ratio 2 3 1 3 obtained from modeling the stress tensor associated with the slip along the faults of the aljibes half graben the orientations of the fault planes and slip vectors of the aljibes half graben are practically identical to those of the nearby acambay graben and the venta de bravo fault which caused the acambay earthquake of november 19 1912 m s 6 9 and the maravatio earthquake of february 22 1979 m b 5 3 furthermore the aljibes half graben forms the extrapolated western continuation of the northern master fault of the mezquital graben which ruptured partly in the cardonal earthquake of march 26 1976 m b 5 3 this suggests the aljibes half graben may also be seismically active although no historical earthquake is known to have occurred along this structure further evidence for the likely seismic activity of the aljibes half graben are two east to eastnortheast trending epicenter alignments between the aljibes halfgraben and the mezquital graben and structural indication for stickslip behavior based on the structure of the aljibes half graben we believe the maximum credible earthquake that may occur along the faults of the aljibes half graben is on the order of 2 10 27 dyne cm m 0 6 10 25 dyne cm and 7 5 m w 6 5

vp vs ratio versus differential stress and rock consolidation a comparison between rock models and time lapse avo data the compressional to shear wave velocity ratio vp vs is an important parameter in seismic amplitude versus offset avo analysis and this parameter plays a key role especially for lithology and fluid prediction methods the p wave velocity is a key parameter in traditional pressure prediction methods because overpressure often results in a velocity reduction however for avo based pore pressure prediction methods one expects that the vp vs ratio also is a key parameter the hertz mindlin geomechanical model predicts a constant vp vs ratio as the differential stress changes in a dry package of identical spheres ultrasonic core measurements show increased vp vs ratios as the differential stress decreases especially for unconsolidated wet sands thus one is likely to assume that the vp vs ratio is dependent on rock consolidation by combining the hertz mindlin model with the gassmann model we show how to obtain a sim ple rock physics framework including both the differential stress and

neogene extensional collapse in the western mediterranean betic rif alpine orogenic belt implications for the genesis of the gilbraltar arc and magmatic activity the betic rif orogenic belt crops out in the western mediterranean and constitutes the westernmost part of the alpine edifice the building up of this belt by compressional nappe tectonics occured during a series of alpine deformational episodes subsequent neogene extension resulted from the collapse of the previous compressional edifice through major extensional detachment systems this episode was accompanied by cafe alkaline to shoshonitic and lamproitic volcanism tectonic denudation of metamorphic core complexes and emplacement of peridotite bodies as a final consequence of the evolution of detachment systems furthermore we relate the generation of the gibraltar arc and the opening of the alboran sea to this major extensional event finally two main stages of tectonic denudation of these detachment systems are defined 1 nevado filabride stage with ex humation of metamorphic core complexes and 2 ronda beni boussera stage with a more advanced degree of denudation leading to the exhumation of upper mantle peridotites which may be tentatively termed mantle core complexes

the relationship between slickenside surfaces in fine grained quartz and the seismic cycle abstract well polished or reflective fault surfaces with or without linear striae indicating the sliding direction are commonly referred to as slickensides this study examines the development of slickensides which are now exposed along the surface trace of a large seismically active normal fault zone in dixie valley nevada u s a geologic and mineralogic constraints indicate the slickenside surfaces formed at depths of less than 2 km and temperatures less than 270 c the slickenside surface material is composed of greater than 98 quartz with less than 2 kaolinite and iron oxide transmission electron microscope tem observations reveal that the slickenside surface material has an extremely fine yet variable grain size 0 01 1 m and an unusual nonequilibrium texture characterized by irregular grain boundaries and low dislocation density angular fragments in the cataclasite to either side of the slickensides provide clear evidence of cataclasis crystallographic preferred orientation in the slickenside surface material indicates that non brittle continuous deformation occurred within 0 1 10 mm of the fault surfaces in many areas non brittle continuous deformation must have alternated with cataclasis because some fragments in the cataclasite have strong preferred orientations we suggest that in the dixie valley slickensides continuous deformation and the development of crystallographic preferred orientations occurred at relatively low strain rates during the interseismic period while cataclasis occurred at higher strain rates associated with seismic events the wide range of strain rates occurring within a fault zone during the earthquake cycle may be an essential element in the formation of fine grained glassy slickensides both at dixie valley nevada and many other areas

pressure solution structures in a granite abstract syntectonic two mica granites in northwest spain have suffered regional late variscan shear deformation the deformed corcoesto granite shows a marked planar and linear fabric resulting from ductile behaviour and contains quartz veins at about 60 to the foliation offsets of these quartz veins along shear planes are commonly contrary to the general sense of shear and thus provide evidence for pressure solution processes

the petrophysical basis for shallow water flow prediction using multicomponent seismic data physical properties of shallow water flow swf sands differ from most reservoir and seal rocks studied for petroleum purposes these materials exist near the transition zone between rocks and sediments our investigations the subject of this article suggest that physical properties of swf sands are amenable to a prediction methodology that uses high resolution multicomponent seismic data swf sands are a primary hazard to deepwater drilling operations in the gulf of mexico they have the potential to result in well failures and significant discharges of subsurface fluids into the ocean however at present most operators make only a modest attempt to identify swf before drilling they drill through these hazards and mitigate any resulting damage at significant expense if one is encountered this is not rare according to a report from fugro geoservices approximately 70 of all deepwater wells have experienced swf a method for predrill delineation of sands that are close to failure and thus likely to exhibit swf would be advantageous in selecting optimal drilling locations and in developing cost effective well plans the current method of identifying swf involves predrill hazard studies utilizing conventional and high resolution seismic data to identify zones that might produce swf however the high incidence of swf mitigation events in deepwater wells shows that existing techniques do not provide adequate resolution or accuracy at present no robust seismic method exists for accurately identifying and characterizing swf operators do not have the option to avoid the hazard instead of mitigating the problem after it has started a new method is required that will permit operators to identify the hazard before the well is drilled using seismic data for accurate understanding of the physical properties and deformational behavior of swf sands is essential to characterization prediction and interpretation of these stratigraphic units to date very few core and

mineral weathering and elemental transport during hillslope evolution at the susquehanna shale hills critical zone observatory located in the uplands of the valley and ridge physiographic province of pennsylvania the susquehanna shale hills critical zone observatory ssho is a tectonically quiescent first order catchment developed on shales of the silurian rose hill formation we used soil cores augered at the highest point of the watershed and along a subsurface water flowline on a planar hillslope to investigate mineral transformations and physical chemical weathering fluxes about 25 m of bedrock was also drilled to estimate parent composition depletion of carbonate at tens of meters of depth in bedrock may delineate a deep carbonate weathering front overlying this extending from 6 m below the bedrock soil interface up into the soil is the feldspar dissolution front in the soils depletion profiles for k mg si fe and al relative to the bedrock define the illite and chlorite reaction fronts when combined with a cosmogenic nuclide derived erosion rate on watershed sediments these depletion profiles are consistent with dissolution rates that are several orders of magnitudes slower for chlorite 1 5 10 17 mol m 2 s 1 and illite 2 9 10 17 mol m 2 s 1 than observed in the laboratory mineral reactions result in formation of vermiculite hydroxy interlayered vermiculite and minor kaolinite during weathering exchangeable divalent cations are replaced by al as soil ph decreases the losses of mg and k in the soils occur largely as solute fluxes in contrast losses of al and fe are mostly as downslope transport of fine particles physical erosion of bulk soils also occurs results from a steady state model demonstrate that physical erosion accounts for about half of the total denudation at the ridgetop and midslope positions chemical weathering losses of mg na and k are higher in the upslope positions likely because of the higher degree of chemical undersaturation in porewaters chemical weathering slows down in the valley floor and al and si even show net accumulation the simplest model for the hillslope that is consistent with all observations is a steady state clay weathering limited system where soil production rates decrease with increasing soil thickness

slip vector analysis with high resolution t lidar scanning abstract a palaeostress analysis of an active bedrock normal fault scarp based on kinematic indicators is reconstructed using terrestrial laser scanning tls for this purpose three key elements are necessary for a defined region i the orientation of the fault plane ii the orientation of the slickenside lineation or other kinematic indicators and iii the sense of motion of the hanging wall the paper specifies a workflow in order to obtain stress data from point cloud data using terrestrial laser scanning tls in an active tectonic environment the entire analysis was performed on a continuous limestone bedrock normal fault scarp on the island of crete greece at four different locations along the wnw ese striking spili fault at each location we collected data with the terrestrial light detection and ranging system t lidar we then validated the calculated three dimensional stress results at three of the locations by comparison with conventional methods using data obtained manually with a compass clinometer numerous kinematic indicators for normal faulting were discovered on the fault plane surface using t lidar data when comparing all reconstructed stress data obtained from t lidar to that obtained through manual compass measurements the degree of fault plane orientation divergence is 005 03 for dip direction and dip the degree of slickenside lineation divergence is 003 03 for dip direction and dip therefore the percentage threshold error of the individual vector angle at each investigation site is lower than 3 for the dip direction and dip for planes and lower than 6 for the strike the maximum mean variation of the complete calculated stress tensors is 005 03

experimentally produced slickenside lineations in pyrophyllitic clay abstract during shearing of pyrophyllitic clay fault planes bearing slickenlines were generated on previously initiated c and c planes these slickenlines have excess lengths with respect to the measured slip displacement on the fault plane and are of the ridge in groove type with the hangingwall nesting into the footwall and vice versa these features cannot be explained in terms of either frictional asperity ploughing or dissolution reprecipitation but are produced during the development of a complex ductile shear zone that contains the fault plane this initial shear zone nucleates from localized shear bands that link up to form a throughgoing shear plane the nucleation and propagation of the fault post dates the formation of the shear plane and depends on the development of a zone of highly oriented layer silicates within the pyrophyllitic clay the fault is confined to this zone the lineations observed on the fault surfaces are produced while the material behaves plastically prior to the brittle faulting with increasing shear strain the brittle ductile transition is crossed and sliding continues under brittle conditions along the former shear zone

a petrologic and isotopic study of lodranites evidence for early formation as partial melt residues from heterogeneous precursors abstract we have conducted petrologic chemical and isotopic studies of lodranites in an attempt to constrain their genesis lodran gibson y 791491 y 791493 y 74357 y 8002 y 75274 mac 88177 lew 88280 eet 84302 fro 90011 and que 93148 are classified as lodranites lodranites and acapulcoites are indistinguishable on the basis of oxygen isotopic compositions but are distinct in average grain sizes of their mafic silicates with lodranites being significantly coarser grained lodranites exhibit a diverse range of petrologic and mineralogic features they range widely in mafic silicate compositions fa3 13 plagioclase 0 11 4 vol fe ni metal 0 5 20 vol and troilite 0 2 5 3 vol contents and shock levels s1 s4 they appear to have experienced high peak temperatures and rapid cooling in the temperature range recorded by metallographic cooling rates i e 700 350 c the only dated lodranite gibson cooled to ar closure temperatures at 4 49 0 01 ga lodranites formed from chemically and isotopically heterogeneous precursors in which the mineral and oxygen isotopic compositions were correlated heating of their parent body to temperatures between 1050 1200 c resulted in formation of fe ni fes and basaltic partial melts depletions of troilite and or plagioclase in most lodranites testify to the removal of some of these partial melts although melt migration was complex lodranites appear to have experienced a complex cooling history of slow cooling at high temperatures followed by rapid cooling at intermediate temperatures possibly related to breakup of the parent body lodranites were liberated from their parent body during 1 3 impact events with most having cosmic ray exposure ages of 5 5 7 ma the acapulcoites are samples from the same parent body but were heated to lower temperatures and thus experienced lower degrees of partial melting

contrasting styles of superposed deformation in the southernmost andes brittle fault arrays regional structural patterns and marine multichannel seismic reflection profiles across the magallanes basin near 53 s latitude show contrasting styles of superposed extensional contractional and transtensional deformation below the northeastern end of a ne sw transect of the basin seismic reflection profiles show deepening levels of pre late jurassic basement and upper jurassic to lower cretaceous volcanic horizons toward the southwest this trend is associated with apparent normal fault offsets that may be attributed to a widespread late jurassic early cretaceous extensional event contrastingly below the southwestern end of magallanes basin subsurface depths of basement and volcanic horizons shallow to the southwest integration of seismic reflection data with published seismic refraction data geologic mapping and satellite gravity anomaly data suggest that this shallowing trend is controlled structurally by craton vergent basement involved contractional deformation this style of shortening contrasts with thin skinned styles of thrusting in the northern and central parts of the basin on tierra del fuego structural relationships stratigraphic data and previously published metamorphic data indicate that basement involved contraction occurred during latest cretaceous to early tertiary time overprinting all contractional structures steep tertiary strike slip and oblique slip faults in the central and southern parts of the magallanes basin display oblique normal mostly down to the southwest offsets across wnw ese trending segments of the south american scotia transform plate boundary on the south american continent newly discovered features along the plate boundary segment include sediment filled grabens and half grabens up to 7 km wide that occur between subparallel fault splays in the magallanes fault zone kinematic analyses of fault slip data indicate that sinistral transtensional motion occurred within this fault zone between the eastern arm of the straits of magellan and central tierra del fuego together these data indicate that 1 the southernmost andes were under compression during rapid cooling and exhumation of unique high pressure 8 kbars basement rocks now exposed in the darwin metamorphic complex dmc near 55 s latitude and 2 final exhumation of basement rocks in the dmc occurred during a shift away from compression toward transtension during late tertiary crustal relaxation we suggest that preexisting structural anisotropies formed during basement involved contractional deformation and the initiation of seafloor spreading south of south america during the oligocene controlled late tertiary sinistral transtensional patterns in the magallanes fault zone

morphology and topology of dolostone lithons in the regional carboneras fault zone southern spain abstract dolostones in a neogene strike slip fault zone are described two main types of structural features are recognised i background deformation in the form of a network of bedding perpendicular and hybrid conjugate fractures barren fractures and bedding parallel stylolites ii fault related features include breccias and cataclasites orthorhombic rock lithons are generated from the intersection of fracture sets with bedding and or joints lithon size and morphology change across the dolostone fault block gradually producing a tetragonal or isometric shape the lithons are 1 2 cm in dimension only 20 outside this range and have an average cross sectional aspect ratio of 1 6 irrespective of size or structural position topology is analysed using nodes and branches ranging from isolated i node and i i branch to connected y and x nodes and i c to c c branches respectively the quantitative description of the geometrical and topological analysis of the dolostone lithons suggest that they become more connected and interact within the dolostone fault blocks assessing the change in topology and lithons connectivity have important implications for subsurface reservoirs and aquifers hosted in dolostone fault zones

methods for quantitatively determining fault slip using fault separation abstract fault slip and fault separation are generally not equal to each other however they are geometrically related the fault slip s is a vector with a magnitude a direction and a sense of the movement in this paper a series of approaches are introduced to estimate quantitatively the magnitude and direction of the fault slip using fault separations for calculation the known factors are the pitch of slip lineations the pitch of a cutoff the dip separation smd or the strike separation smh for one marker the two main purposes of this work include 1 to analyze the relationship between fault slip and fault separation when slickenside lineations of a fault are known 2 to estimate the slip direction when the parameters smd or smh and for two non parallel markers at a place e g a point are known we tested the approaches using an example from a mainly strike slip fault in east quantoxhead united kingdom and another example from the jordan field ector county texas also we estimated the relative errors of apparent heave of the normal faults from the sierra de san miguelito central mexico

seismic velocities of unconsolidated sands part 2 influence of sorting and compaction induced porosity variation unaccounted for porosity variation in unconsolidated sediments can cloud the interpretation of the sediment s seismic velocities for factors such as fluid content and pressure however an understanding of the effects of porosity variation on the velocities can permit the remote characterization of porosity with seismic methods we present the results of a series of measurements designed to isolate the effects of sorting and compaction induced porosity variation on the seismic velocities and their pressure dependences in clean unconsolidated sands we prepared a set of texturally similar sand and glass bead samples with controlled grain size distributions to cover an initial porosity range from 0 26 to 0 44 we measured the compressional and shear wave velocities and porosity of dry samples over a series of hydrostatic pressure cycles from 0 1 to 20 mpa over this rangeof porosities the velocities of the dry samples at a given pressure vary by 15 however the water saturated compressional wave ve

a petrologic chemical and isotopic study of monument draw and comparison with other acapulcoites evidence for formation by incipient partial melting abstract we have conducted petrologic chemical and isotopic studies of acapulcoites acapulco monument draw yamato 74063 alh a77081 alh a81261 alh a81315 alh 78230 alh a81187 and alh 84190 in an attempt to constrain their genesis acapulcoites have distinctly different oxygen isotopic compositions than silicate inclusions in iab and iiicd irons winonaites and ureilites and thus formed on a different parent body oxygen isotopic compositions which are slightly heterogeneous within the group overlap with lodranites indicating a likely origin on a common parent body these groups can be distinguished on the basis of mafic silicate grain size all acapulcoites have mafic silicate compositions intermediate between e and h chondrites roughly chondritic mineralogies achondritic equigranular textures micrometer to centimeter sized veins of fe ni fes which cross cut silicate phases rapid metallographic cooling rates at 600 400 c 103 105 c myr and trapped noble gas abundances comparable to type 3 4 ordinary chondrites they exhibit variable mafic silicate zoning abundance of fe ni fes veins ree abundances and patterns and possibly cosmic ray exposure ages 5 7 ma momument draw and yamato 74063 retain rare relict chondrules phosphates are associated with fe ni fes veins or form separate veins in monument draw and acapulco heating and cooling of acapulcoites occurred very early in the history of the solar system as evidenced by the 39ar 40ar ages of 4 51 ga these ages appear distinctly younger than the likely formation time for acapulco of 4 557 ga but are older than analogous 39ar 40ar ages for most chondrites acapulcoites formed from a precursor chondrite which differs from known chondrites in mineral and oxygen isotopic compositions heating to 950 1000 c resulted in melting at the fe ni fes cotectic but silicates did not melt silicate textures resulted from extensive solid state recrystallization heating was by noncollisional sources e g 26al electromagnetic induction despite uncertainties owing to a lack of data acapulcoites may have experienced a three stage thermal history of slow cooling at high temperature rapid cooling at intermediate temperatures and slow cooling at low temperatures possibly resulting from breakup and gravitational reassembly of the parent body the complex thermal history is also reflected in disequilibrium ree abundances one or at most two impact events 7 ma and possibly 5 ma ago are consistent with the cosmic ray exposure ages of all four acapulcoites for which cosmogenic noble gas data exist

trace element distributions within ordinary chondrite chondrules implications for chondrule formation conditions and precursors the concentrations of thirty six lithophile elements in the major silicate phases of chondrules have been determined by ion microprobe two types of porphyritic chondrule olivines normal and incompatible rich have been identified the incompatible rich olivines which have forsterite contents that are greater than fo98 appear to have formed under highly reducing conditions the olivine and low ca pyroxene grains in porphyritic chondrules have relatively unfractionated l chondrite normalized ree abundances compared to expectations from equilibrium distribution coefficients this is consistent with porphyritic chondrules having formed at cooling rates of the order of 1000 c h or faster the alkali metal na k rb and cs to al ratios in chondrule glasses vary by two orders of magnitude the lower values possibly being the result of volatile loss from chondrules no correlation was found between alkali metal depletions in chondrule glasses and enrichments in the surrounding rims but any such correlation may have been destroyed by the diffusive redistribution of these elements in rims that is likely to occur even under mild metamorphic conditions the refractory lithophiles with the exception of mg are all highly incompatible in silicate melts and are as a result concentrated in the chondrule glasses the refractory lithophiles in the glass are in most cases unfractionated from one another suggesting that neither vapor phase nor crystal liquid fractionation played a major role in the formation of chondrules or their precursors based largely on the observation that the refractory lithophiles are concentrated in the chondrule glasses it is suggested that previously reported correlations between these elements in bulk chondrule analyses are due to chondrules themselves as opposed to refractory condensates having been their own immediate precursors a simple monte carlo simulation using the compositions of the major chondrule silicate phases reported here supports this hypothesis it is argued that the upper limit of about one observed in the atomic na al ratios of chondule glasses is not due to an albitic precursor but simply reflects that for na to be incorporated into the structure of the melt it must take part in the coupled substitution naalo2 sio2

calcite dissolution rates in texturally diverse calcareous rocks the injection of reactive fluids into carbonate reservoirs during enhanced recovery operations can induce important changes in rock permeability however reliably predicting these changes requires accurate knowledge of calcite reaction rates while numerous studies have examined calcium carbonate dissolution rates most have focused on pure calcite crystals rather than actual rocks in this study two types of flow through experiments were carried out to determine the calcite dissolution rates in texturally diverse calcareous rocks the first type of experiment had a duration of 3 days while the second type ran for 3 months our experiments show that rocks with differing textures and roughness samples included coarse grained oolitic limestone fine grained solnhofen limestone marble and calcite spar do in fact dissolve by different mechanisms however despite these differences bulk reaction rates were found to be remarkably similar with a relative standard deviation of 20 and consistent with previously reported reaction rates for calcite thus our results suggest that textural differences between rock types are unlikely to have an important impact on overall reaction rates in fractured carbonate reservoirs water rock interaction often changes the porosity and permeability of rocks and soils as a result mineral reactions in porous media often impact many natural and industrial processes such as diagenesis in sedimentary basins carbon sequestration in geological formations matter kelemen 2009 and enhanced hydrocarbon recovery from subsurface reservoirs emberley et al 2005 qajar et al 2013 although all rock types have the potential to be changed by water rock interaction carbonate rocks are particularly susceptible to alteration especially during enhanced recovery techniques that employ carbon dioxide injection while this process reduces oil viscosity and causes swelling of the oil phase kovscek cakici 2005 the elevated co2 concentrations also increase the acidity of reservoir brines emberley et al 2004 leading to mineral dissolution and reprecipitation which can either enhance or reduce permeability e g mohamed et al 2012 qajar et al 2013 in addition reactions involving carbonate minerals can affect other oil production techniques such as water based enhanced oil recovery also known as smart water rezaeidoust et al 2009 fathi et al 2011 in the smart water method it has been suggested that grain dissolution due to chemical disequilibrium between the injected water and displaced brine may cause oil droplets to detach from the carbonate surface hiorth et al 2010 thus mineral reactions in carbonate rocks can affect the recovery levels from subsurface reservoirs although accurately predicting the impact of reacting fluids on permeability evolution remains a critical challenge luquot gouze 2009 luquot et al 2013 nogues et al 2013 varloteaux et al 2013 mineral reactions in carbonate formations are often concentrated along naturally occurring fractures cracks and joints that act as conduits for fluid flow reaction rates along these preferential flow paths are influenced by numerous factors including flow rates fluid composition and the surface area of the mineral fluid interface lasaga 1998 in the case of calcite dissolution is often described by the following reactions plummer et al 1978 chou et al 1989 caco3 h k1 ca2 hco3 1 caco3 h2co3 k2 ca2 2hco3 2 caco3 k3 ca2 co2 3 3 these three dissolution mechanisms can be incorporated into an overall rate equation of the form pokrovsky et al 2005 jcalcite k1 ah k2 ah2co3 k3 aca2 aco2 3 4 where jcalcite is the reaction rate in mol cm 22 s k1 k2 and k3 are rate coefficients and ah ah2co3 aca2 and aco2 3 are the activities of h carbonic acid ca2 and carbonate respectively according from agar s m geiger s eds fundamental controls on fluid flow in carbonates geological society london special publications 406 http dx doi org 10 1144 sp406 14 the geological society of london 2014 publishing disclaimer www geolsoc org uk pub ethics by guest on july 23 2014 http sp lyellcollection org downloaded from

vesta as the howardite eucrite and diogenite parent body implications for the size of a core and for large scale differentiation if vesta is the parent body of the howardite eucrite and diogenite hed meteorites then geo chemical and petrologic constraints for the meteorites may be used in conjunction with astronomical constraints for the size and mass of vesta to 1 determine the size of a possible metal core in vesta and 2 model the igneous differentiation and internal structure of vesta the density of vesta and petrologic models for hed meteorites together suggest that the amount of metal in the parent body is 25 mass with a best estimate of 5 assuming no porosity for a porosity of up to 5 in the silicate fraction of the asteroid the permissible metal content is 30 these results suggest that any metal core in the hed parent body and vesta is not unusually large a variety of geochemical and other data for hed meteorites are consistent with the idea that they originated in a magma ocean it appears that diogenites formed by crystal accumulation in a magma ocean cumulate pile and that most noncumulate eucrites excepting such eucrites as bouvante and statinem formed by subsequent crystallization of the residual melts modelling results suggest that the hed parent body is enriched in rare earth elements by a factor of 2 5 3 5 relative to ci chondrites and that it has approximately chondritic mg si and al sc ratios stokes settling calculations for a vesta wide nonturbulent magma ocean suggest that early crystallizing magnesian olivine orthopyroxene and pigeonite would have settled relatively quickly permitting fractional crystallization to occur but that later crystallizing phases would have settled or floated an order of magnitude more slowly allowing instead a closer approach to equilibrium crystallization for the more evolved eucritic melts this would have inhibited the formation of a plagioclase flotation crust on vesta plausible models for the interior of vesta which are consistent with the data for hed meteorites and vesta include a metal core 130 km radius an olivine rich mantle 65 220 km thick a lower crustal unit 12 43 km thick composed of pyroxenite from which diogenites were derived and an upper crustal unit 23 42 km thick from which eucrites originated the present shape of vesta with 60 km difference in the maximum and minimum radius suggests that all of the crustal materials and possibly some of the underlying olivine from the mantle could have been locally excavated or exposed by impact cratering

morphologically ductile criteria for the sense of movement on slickensides from an extensional detachment fault in southern spain abstract new criteria for the sense of movement on slickenside surfaces displaying evidence for mesoscopic ductility are described in the neogene jaloche extensional detachment fault in southern spain this detachment develops spectacular slickensides and fault gouges and four of the criteria for the sense of movement observed along the highly polished slip surfaces are new to the literature they are 1 synthetic secondary fractures with hangingwall drag effects in the form of roll over microsynclines 2 metre scale oval shaped asymmetric culmination and depression features 3 microthrusts verging towards the direction of motion of the opposite block and dragging overthrusting previous planar elements on the fault surface and 4 flakes of fault surface material trailed and plastered in the direction of the missing block the geometry and microstructure of these features reveal that they deformed in a morphologically ductile manner by the coupled processes of cataclastic flow and shear localization probably during aseismic sliding during transient seismic pulses deformation occurred along shiny polished slickenside fault planes occasionally bearing jigsaw implosion breccias fluids under high pressure present initially may have promoted distributed cracking whereas the process of dilatancy hardening may have served to facilitate cataclastic flow in the deformation history

the origin of ridge in groove slickenside striae and associated steps in an s c mylonite abstract a three dimensional study of an s c mylonite reveals that the s surfaces anastomose around porphyro clasts and c surfaces are not truly planar but curvi planar with the linear generator parallel to the movement direction it is suggested that it may be common for shear surfaces at all scales to take this form in the material studied surfaces exposed by parting primarily along c surfaces which are a product of ductile deformation and are penetrative have all the characteristics of classic slickensides on the slickensides striae of the ridge in groove type and steps of both congruous and incongruous types are developed the ridge in groove shape of the striae is directly related to the curvi planar shape of the c surfaces incongruous steps are smooth they are the result of parting along s surfaces congruous steps are rough first order congruous steps are formed by fracturing between individual c surfaces whereas second order congruous steps form by breaking off the tips of the dihedra between s and c surfaces thus the smoothness roughness technique can be used to determine the sense of shear in strongly deformed rocks where the angle between s and c surfaces is too small to be recognized in the field this may prove to be a useful shear sense indicator

seismic images and rock properties of the very shallow structure of campi flegrei caldera southern italy in september 2001 an extensive active seismic investigation serapis experiment was carried out in the gulfs of naples and pozzuoli with the aim of investigating and reconstructing the shallow crustal structure of the campi flegrei caldera and possibly identifying its feeding system at depth the present study provides a joint analysis of the very shallow seismic reflection data and tomographic images based on the serapis dataset this is achieved by reflection seismic sections obtained by the 3d data gathering and through refined p velocity images of the shallowest layer of pozzuoli gulf z 3 500 m s correlates with units made up of agglomerate tuffs and interbedded lava which form the southern edge of the caldera which was probably formed following the two large ignimbritic eruptions that marked the evolutionary history of the area under study the upper part of the anomaly that tends to split into two parallel arcs is correlated with dikes volcanic mounds and hydrothermal alteration zones noted in previous shallow reflection seismic analyses the depth of the transition between the upper and lower parts of the anomaly is characterized by an abrupt vp increase on the one dimensional 1d profiles extracted from the 3d tomographic model and by the presence of a strong reflector located at about 0 6 0 7 s two way time twt on common mid point gathers the move out velocity analysis and stack of the p p and p s reflections at the layer bottom allowed to estimate relatively high vp vs values 3 7 0 9 this hypothesis has been tested by a theoretical rock physical modeling of the vp vs ratio as a function of porosity suggesting that the shallow layer is likely formed by incoherent water saturated volcanic and marine sediments that filled pozzuoli bay during the post caldera activity

partial melting and melt migration in the acapulcoite lodranite parent body we review petrologic evidence that the acapulcoites and lodranites formed by 1 vol to probably 20 vol whole rock partial melting of a chondritic precursor material at low degrees of partial melting only fe ni fes cotectic melting occurred migration distances for partial melts were short resulting in the formation of acapulcoites with essentially chondritic troilite and plagioclase contents but achondritic textures at high degrees of partial melting both fe ni fes and basaltic plagioclase pyroxene partial melts formed and the melts may have migrated out of the source rock the partial melt residues which are more or less depleted in fe ni fes and plagioclase are the lodranites melt migration was complex most acapulcoites which experienced relatively low degrees of partial melting lost little if any of the partial melt one acapulcoite lew 86220 represents a unique case in which fe ni fes and basaltic partial melts appear to have migrated from a lodranite source region into a cooler acapulcoite region where they were trapped in cases of the relatively high degrees of partial melting experienced by lodranites melts may have been partly selectively or totally removed from the rocks and fe ni fes and or basaltic partial melts may have been removed to different degrees and may in fact have been trapped on occasion in greater than chondritic proportions we model vein and dike formation and melt migration by calculating the excess pressures and vein and dike sizes for varying degrees of partial melting our calculations are broadly consistent with observations indicating that melt migration is inefficient at low degrees of partial melting and extremely efficient at high degrees of partial melting although the size of the acapulcoite lodranite parent body and the volatile contents of the chondritic precursor rocks are poorly constrained the lack of basaltic rocks in the world s meteorite collections complementary to the lodranites suggests that basaltic partial melts may have been accelerated off the body by explosive volcanism of the type envisioned by wilson and keil 1991 and ejected into space the diversity of rocks from the acapulcoite lodranite parent body may provide a basis for better understanding the diverse range of spectral subtypes recognized among the s type asteroids

using a mathematical model of a weathering clast to explore the effects of curvature on weathering abstract for the first time we show that rind thicknesses developed on surfaces of a clast with different values of curvature can be used to estimate the duration of clast weathering to obtain an analytical expression for the velocity of the curvilinear weathering front on a clast of arbitrary shape we approximate our previous multi mineral reactive diffusion model and explore a simplified 2 d model numerically and analytically our analysis documents that with increasing curvature of the weathering front the mathematical description of weathering advance is equivalent to that derived for advection as the dominant solute transport mechanism even for the case where transport is occurring by diffusion only specifically for a curvilinear weathering front with constant curvature k

mantle core complexes and neogene extensional detachment tectonics in the western betic cordilleras spain an alternative model for the emplacement of the ronda peridotite abstract an alternative model for the emplacement of the ronda peridotite betic alpine orogenic belt southern spain is proposed involving mantle uprising during a major neogene extensional event the development of a detachment system and its further evolution by isostatic rebound and upward arching would have triggered the tectonic denudation of these ultramafic bodies forming what may be termed mantle core complexes mantle core complexes would represent a final step in the core complex forming processes once a complete separation of the upper and lower blocks has been achieved in a detachment system marking probably the transition from an intracontinental to a proto oceanic rift environment

application of an integrated workflow for shallow hazard characterization using a 3d high resolution survey offshore azerbaijan abstract a methodology has been developed for quantitative prediction of shallow hazard zones based on 3d high resolution 3dhr seismic and shallow log data the main goal of the integrated workflow is to produce an optimal structural image conduct an avo feasibility study and if applicable identify avo trends within the depositional sequences of the shallow overburden at the azeri field offshore azerbaijan shallow near surface geologic engineering hazards and features are not always visible on seismic volumes typically processed for reservoir targets the 3d high resolution seismic data provide good definition of shallow stratigraphy indication of buried mudflows and landslides and good fault delineation avo feasibility from rock property analysis was affected by uncertainties arising from lack of or poor log data quality with limited amounts of log data increasing the uncertainties the use of trends based on data provided offered some initial understanding of shallow seismic sensitivity in d

high resolution 3d laser scanner measurements of a strike slip fault quantify its morphological anisotropy at all scales 1 the surface roughness of a recently exhumed strike slip fault plane has been measured by three independent 3d portable laser scanners digital elevation models of several fault surface areas from 1 m2 to 600 m2 have been measured at a resolution ranging from 5 mm to 80 mm out of plane height fluctuations are described by non gaussian distribution with exponential long range tails statistical scaling analyses show that the striated fault surface exhibits self affine scaling invariance with a small but significant directional morphological anisotropy that can be described by two scaling roughness exponents h1 0 7 in the direction of slip and h2 0 8 perpendicular to the direction of slip

scales of structural heterogeneity within neotectonic normal fault zones in the aegean region abstract structural heterogeneities within neotectonic normal fault zones in the aegean region are important controls on the geomorphic expression of their uplifted footwall blocks contrasting fault rocks and slip plane phenomena corrugations comb fractures slip parallel fractures and pluck holes are responsible for mesoscopic inhomogeneities within fault scarps along strike disruptions in the continuity of fault scarps step over zones step up zones step down zones footwall cross faults and hangingwall cross faults are products of perturbations in slip plane geometry or intersections with transverse faults large scale variations in range front morphology reflect contrasting patterns of deformation within fault zones some major fault zones and many minor fault zones are characterized by a migration of the active slip plane towards the hangingwall resulting in a distributed network of high angle faults and a range front which is stepped in profile the presence of a localized mass of uneroded bedrock hangingwall salients protruding from the hangingwall of some major fault zones results in intense deformation along a principal slip plane and a range front which is ramp like in profile as a consequence of structural heterogeneities within neotectonic normal fault zones fault scarps and range fronts in the aegean region are subject to a temporally and spatially variable pattern of degradation

limestone weathering rates accelerated by micron scale grain detachment the weathering of carbonate rocks plays a critical role in the evolution of landscapes the erosion of buildings and monuments and the global scale shifting of carbon from the atmosphere to the ocean chemical dissolution is often assumed to govern the rates of weathering of carbonate rocks although some studies have suggested that mechanical erosion could also play an important role quantifying the rates of the different processes has proved challenging in part due to the high degree of variability encountered across different scales in both field and laboratory conditions to constrain the rates and mechanisms controlling long term limestone weathering we analyze a lidar scan of the western wall a roman period edifice located in jerusalem we find that extreme erosion rates in fine grained micritic limestone blocks are as much as two orders of magnitude higher than the average rates estimated for coarse grained limestone blocks at the same site atomic force microscope imaging of dissolving micritic limestone suggests that these elevated reaction rates are likely to be the result of rapid dissolution along micron scale grain boundaries followed by mechanical detachment of tiny particles from the surface our analysis indicates that such grain detachment could be the dominant erosional mode for fine grained carbonate rocks in many regions on earth

pore pressure detection sensitivities tested with time lapse seismic data in an exploration context pore pressure prediction from seismic data relies on the fact that seismic velocities depend on pore pressure conventional velocity analysis is a tool that may form the basis for obtaining interval velocities for this purpose however velocity analysis is inaccurate and in this paper we focus on the possibilities and limitations of using velocity analysis for pore pressure prediction a time lapse seismic data set from a segment that has undergone a pore pressure increase of 5 to 7 mpa between the two surveys is analyzed for velocity changes using detailed velocity analysis a synthetic time lapse survey is used to test the sensitivity of the velocity analysis with respect to noise the analysis shows that the pore pressure increase cannot be detected by conventional velocity analysis because the uncertainty is much greater than the expected velocity change for a reservoir of the given thickness and burial depth finally by applying amplitude variation with offset avo analysis to the same data we demonstrate that seismic amplitude analysis may yield more precise information about velocity changes than velocity analysis

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

earthquakes and rock deformation in crustal fault zones the physical origin of earthquakes lies ultimately in the geological structure of fault zones and the deformation processes that occur therein in response to tectonic stress although the possibility now exists that the nucleation regions for large earthquakes at depths of 10 km may shortly become directly accessible by deep drilling our present knowledge of fault structure and the shallow earthquake source is derived largely from a variety of indirect sources these include seismological studies surface studies of fault zones and earthquake ruptures geodetic information on modes of fault slip geophysical constraints on fault zone structure and rheology and information garnered from materials science and experi mental rock deformation studies of fault zone structure and the rock products of faulting provide complementary information on deformation processes at depth in fault zones although descriptions of fault rocks are widespread in the geological literature e g spry 1969 higgins 1971 it is only in the past decade that they have begun to be interpreted in the context of the physical conditions and processes prevalent in seismically active fault zones at different crustal depths sibs on 1977 watts williams 1979 anderson et a11983 wise et ai 1984 such interpretations are still at an early stage but the deformation textures and structural associations of fault rocks have already been shown to have the potential to yield information on such diverse topics as shear stress levels power dissipation and seismic efficiency during earthquake faulting on fluid pressure levels and episodic fluid flow accompanying

morphotectonics of a high plateau on the northwestern flank of the continental rift of southeastern brazil abstract integration of landform and structural analysis allowed the identification of late pleistocene holocene pulses of tectonic activity in the campos do jordao plateau with ages and regimes similar to the ones from the continental rift fault reactivation along precambrian shear zones give rise to a series of conspicuous morphotectonic features determine the formation of stream piracy phenomena and divide the plateau into smaller blocks recognition of these tectonic pulses as well as of their effects in landform development particularly clear on the campos de sao francisco at the highest area of the se edge of the plateau show that besides the climate related quaternary environmental changes significant neotectonic instability should be considered in the geomorphic evolution of the campos do jordao plateau

petrology of unique achondrite queen alexandra range 93148 a piece of the pallasite howardite eucrite diogenite parent body abstract queen alexandra range que 93148 is a small 1 1 g olivine rich achondrite mg 86 that contains variable amounts of orthopyroxene mg 87 and kamacite 6 7 wt ni with minor augite olivine in que 93148 contains an unusual suite of inclusions 1 5 100 m sized lamellae with a cao and cr2o3 rich 10 and 22 wt respectively composition that may represent a submicrometer scale intergrowth of chromite and pyroxene s 2 75 500 m sized lamellar symplectites composed of chromite and two pyroxenes with minor metal 3 15 20 m sized irregularly shaped symplectites composed of chromite and pyroxene s 4 100 150 m sized elliptical inclusions composed of chromite two pyroxenes metal troilite and rare whitlockite type 1 2 and 3 inclusions probably formed by exsolution from the host olivine during slow cooling whereas type 4 more likely resulted from early entrapment of silicate and metallic melts followed by closed system oxidation queen alexandra range 93148 can be distinguished from most other olivine rich achondrites ureilites winonaites lodranites acapulcoites brachinites eagle station type pallasites and pyroxene pallasites as well as from mesosiderites by some or all of the following properties o isotopic composition fe mn mg relations of olivine cao and cr2o3 contents of olivine orthopyroxene compositions molar cr cr al ratios of chromite metal composition texture and the presence of the inclusions in terms of many of these properties it shows an affinity to main group pallasites nevertheless it cannot be identified as belonging to this group meteorite que 93148 appears to be a unique achondrite possibly it should be considered to be a pyroxene pallasite that is genetically related to main group pallasites alternatively it may be derived from the mantle of the pallasite howardite eucrite diogenite parent body

kinematic indicators on active normal faults in western turkey quaternary normal fault zones in western turkey comprise multiple slip planes and zone parallel layers of fault breccia they also contain several little known kinematic indicators that are probably typical of many formed at shallow levels in extending terrains the recent exhumation by contractors of about 2000 m2 of slip planes in a sse dipping fault zone separating quaternary colluvium from bedrock carbonates at yavansu 7 km se of kusadasi permits an unusually complete inventory of the indicators to be compiled the most spectacular indicators are metre scale 69 w pitching corrugations in slip planes and recemented breccia sheets underlying them corrugations characterized by sinusoidal profiles normal to their long axes and less commonly culminations and depression along their axes possibly developed as a result of upwards propagating slip planes seeking undemanding pathways through heterogeneous fault precursor breccias that formed in advance of tip lines parallel to corrugation long axes are those of gutters flat floored sleep sided channels a few centimetres wide probably related to the abrasion of subslip plane breccia sheets centimetre scale tool tracks scored in the uppermost subslip plane breccia sheet by resistant colluvial clasts are irregular at their proximal ends but distally they swing into alignment with corrugation axes frictional wear striae centimetres long but only a few millimetres wide and pitching 78 w are superimposed on the other slip parallel lineations comb fractures nearly perpendicular to slip planes define an intersection lineation which is normal to corrugation axes fault plane solutions of earthquakes on sse dipping active faults in the west anatolian extensional province indicate that mainly normal combined with minor dextral slip is the dominant mode a conclusion in accord with the sense of slip inferred from the indicators exposed on the yavansu slip planes

tectonic evolution of the intra uplift vigodi gugriana khirasra netra fault system in the seismically active kachchh rift basin india implications for the western continental margin of the indian plate abstract the e w striking kachchh rift basin krb at the western continental margin of indian plate is located in the northern part of gujarat state india krb has undergone polyphase deformation owing to changing stress field since late triassic we establish the kinematic framework along the nw striking intra uplift vigodi gugriana khirasra netra fault system vgknfs located at the western part of the krb the vgknfs consists of 0 25 50 km long sub parallel striated reactivated dip slip faults a total of 1150 fault slip data consisting of fault planes and striations attitude were recorded from 66 sites including a single site with systematic joints slip sense of faults was determined by documenting kinematic indicators paleostress analysis was carried out using win tensor t tecto faultkin and sg2ps to compare and validate the results the chi square statistical analysis was undertaken to evaluate how relevant are paleostress analysis results to the present day compressional stress field geophysical investigations were conducted at selected sites using ground penetrating radar gpr to understand the shallow subsurface geometry and trace the continuity of faults buried below patchy alluvial cover 15 17 m long 2d gpr cross sections were recorded across faults using monostatic antenna of 200 mhz frequency two major deformation events d1 and d2 are determined in the present study the extension event d1 shows w and nw nnw extension during late triassic to late cretaceous it occurred during the rift phase of krb in response of the break up of gondwanaland the latest event d2 shows nne ne compression from late cretaceous up to the present it is interpreted to have developed during post rift inversion phase induced by collision of the indian plate with the eurasian plate at 55 ma

an analogue of dominance of tectonic over climatic forcing in intermontane coal bearing basins padul se spain abstract a multiproxy study based on sedimentology mineralogy magnetic susceptibility organic geochemistry and fossil content allowed to establish the sedimentary evolution of palustrine basins and to study the interplay between tectonic and climatic forcings in the sedimentation and facies arrangement that can be extrapolated to other coal bearing basins the reinterpretation of the data from 18 cores allowed to determine the facies distribution and to model the sedimentary evolution of the padul basin with the longest continuous continental quaternary record in the southwestern mediterranean region the padul basin sediment record and facies successions provide an outstanding example of tectonically and environmentally controlled sedimentation the sedimentary characteristics of the cores and thickness distribution revealed that recent tectonics was a more important forcing than other processes e g climate the influence of recent tectonics was determinant in facies arrangement that is to say that the activity of a rotated fault produced a differential subsidence causing more than 100 m of palustrine deposits to stack on the basis of the sedimentological record combined with data on the mineralogy fossil content magnetic susceptibility and total organic carbon three main sedimentary units were identified linked to diverse subsidence rates and paleoenvironmental oscillations the magnetic susceptibility was likely to have been controlled by the organic matter content toc values linked to oxic anoxic conditions in the lower part of the record unit a 107 0 68 7 m shallow lacustrine conditions were dominant with an important influx associated with considerable runoff from active alluvial fans linked to a higher subsidence rate unit b 68 7 37 6 m had a transitional character with a considerable decrease in the influence of the alluvial fan system the lake recharge through overland flow markedly diminished and pre existing groundwater recharge was dominant a sudden change to peaty materials indicated that surface runoff was directly diverted to the recently excavated durcal river gorge thereby precluding the basin from becoming a swampy environment with stagnant waters unit c upper 37 6 m was almost exclusively fed by bicarbonate groundwater and subsurface runoff through the highly permeable coarse alluvial fan deposits within these main sedimentary units minor mud peat shallowing upward sequences were identified

crustal scale fluid circulation and co seismic shallow comb veining along the longest normal fault of the central apennines italy the extensional val roveto fault which is the longest exhumed potentially seismogenic structure of central apennines italy is examined to constrain earthquake related fluid circulation and fluid sources within shallow carbonate hosted faults the study focuses on fault related comb and slip parallel veins that are calcite filled and cut through the principal surface of the val roveto fault we observe multiple crack and seal events characterized by several veining episodes probably related to different slip increments along the fault plane we show that vein calcite precipitated in late pleistocene time below the present day outcrop level at a maximum depth of similar to 350 m and temperatures between 32 and 64 degrees c from meteoric derived fluids modified by reactions with crustal rocks and with a mantle contribution up to similar to 39 the observed warm temperatures are not compatible with a shallow similar to 350 m precipitation depth which in this region is dominated by circulation of cold meteoric water and or shallow groundwater based on structural geochemical data we propose that deep seated crust mantle derived warm fluids were squeezed upward during earthquakes and were hence responsible for calcite precipitation at shallow depths in co seismic comb and slip parallel fractures as comb and slip parallel veins are rather common particularly along seismogenic extensional faults we suggest that further studies are necessary to test whether these veins are often of co seismic origin if so they may become a unique and irreplaceable tool to unravel the seismic history of hazardous active faults

queen alexandra range 93148 a new type of pyroxene pallasite trace elements including the rare earth elements were measured in olivine and orthopyroxene from queen alexandra range que 93148 and in olivine from two main group pallasites springwater and mount vernon although que 93148 was originally classified as a lodranite a variety of data including oxygen isotopic compositions goodrich and righter 2000 preclude a genetic relationship with the acapulcoites lodranites incompatible trace element e g ti zr distributions in orthopyroxene do indicate large amounts of melting and are consistent with the ultramafic assemblage observed in this meteorite trace element abundances in olivine are consistent with suggestions that que 93148 may be related to the main group pallasites goodrich and righter 2000 although there are some inconsistencies its trace element distributions are most like those of the pyroxene pallasites suggesting that it may have formed in a similar manner que 93148 may represent a new type of pyroxene pallasite with links to the main group pallasites

minor element zoning and trace element geochemistry of pallasites i report here on an ion probe study of minor element spatial distributions and trace element concentrations in six pallasites pallasite olivines exhibit ubiquitous minor element zoning that is independent of grain size morphology and adjacent phases ca cr ti v and ni concentrations decrease from center to rim by factors of up to 10 while mn is generally unzoned or increases slightly at the very edge of some olivine grains the maximum concentrations of these elements at the center of olivine vary from grain to grain within the same meteorite and among the pallasites studied these zoning profiles are consistent with thermal diffusion during rapid cooling the inferred cooling rates at high temperature regimes are orders of magnitude faster than the low temperature metallographic cooling rates similar to0 5 to 2degreesc ma this suggests that pallasites like mesosiderites have experienced rather complicated thermal histories i e cooling rapidly at high temperatures and slowly at low temperatures

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

acapulco and lodran like achondrites petrology geochemistry chronology and origin we have performed petrologic and geochemical studies of five primitive achondrites alha81187 and alha81261 acapulco like eet 84302 transitional but acapulco like and lew 88280 and mac 88177 lodran like we have also performed 39ar 40ar chronology on alha81187 alha81261 and eet 84302 lew 88280 and mac 88177 contain more ferroan olivines orthopyroxenes clinopyroxenes and chromites than do the acapulco like achondrites plagioclase is present in only alha81187 alha81261 and eet 84302 its composition does not track that of the mafic silicates eet 84302 with the most calcic plagioclase contains olivine and pyroxene with an mg intermediate between alha81187 and alha81261 similarly spinels in eet 84302 have the same mg as those in alha81187 while pyroxenes in the former are more ferroan than in the latter acapulco like achondrites have sm sc ratios between 0 8 1 5 times h chondrites and na sc ratios are between 0 81 0 times h chondrites indicating that silicate partial melts have not been lost from these rocks siderophile and chalcophile elements are fractionated and show a trend of increasing ir ni ratios with decreasing se co ratios this variation is consistent with fractionation by partial melting in the fe ni s system eet 84302 is very depleted in se and troilite is a accessory phase indicating essentially total loss of the low temperature fe ni s melt in contrast the lodran like achondrites are depleted in the highly incompatible lithophile elements relative to more compatible elements sm sc ratios are 0 2 0 7 times and na sc ratios are 0 04 0 18 times h chondrites these data are consistent with a model for formation of the lodran like achondrites as partial melting residues however the low ir ni and high se co ratios in two lodran like achondrites suggest the metal troilite in these rocks is dominated by the low melting fraction in the fe ni s system this metal troilite was added to the silicates after partial melting depleted them in a basaltic fraction the ar ar release spectra yield good plateau ages of 4 507 0 024 ga alha81187 4 511 0 007 ga alha81261 and 4 519 0 017 ga eet 84302 in good agreement with previously determined ar ar ages for other acapulco like achondrites together the ar ar ages demonstrate that metamorphism on the acapulco lodran parent body occurred 4 51 0 02 ga ago roughly 50 ma after its formation the geochemical and petrologic evidence on the acapulco and lodran like achondrites suggest that heating on the parent body was localized and heterogeneous in space and time the parent body was probably not subjected to parent body wide magmatism in contrast to the case for 4 vesta and the hed meteorites

quantifying micron scale grain detachment during weathering experiments on limestone weathering in carbonate rocks is often assumed to be governed by chemical dissolution nevertheless chemical processes can be coupled to mechanical mechanisms with small grains undergoing partial dissolution along grain boundaries followed by detachment from the rock surface crucially this process can even extend down to the micron scale although chemo mechanical detachment could be critical for the understanding of carbonate weathering at the global scale the role it plays has not been directly quantified to calculate the contribution of grain detachment to surface retreat rates and to determine the impact of the flow regime we carried out a series of flow through weathering experiments on micritic limestone using atomic force microscopy we obtained high resolution in situ data of surface topography for reacting rock surfaces in all the experiments both grain detachment and chemical dissolution were observed under the laminar flow conditions we explored we found no clear correlation between flow rate and the size of detached grains or between the flow rate and the frequency of grain detachment events importantly our results establish that grain detachment contributes significantly to the overall surface retreat on average accelerating mass loss by 38 in addition to speeding up weathering this micron scale mechanism could also influence the evolution of porosity in aquifers and hydrocarbon reservoirs and provide a natural flux of colloids that could transport heavy metals or radionuclides in groundwater

pedogenic slickensides indicators of strain and deformation processes in redbed sequences of the appalachian foreland pedogenic slickensides are convex concave slip surfaces that form during expansion contraction in expansive clay soils such as vertisols in the central appalachians they occur near the tops of fining upward cycles in paleozoic redbeds such as the bloomsburg catskill and mauch chunk formations pedogenic slickensides are found in association with other pedogenic or paleosol features such as clay skinned peds in situ calcareous nodules and root impressions repeated movements along these shear planes during pedogenesis produce strongly aligned clay particles adjacent to pedogenic slickensides as a result they are preserved as discrete fractures throughout diagenesis compaction and superimposed tectonic deformation during whole rock deformation pedogenic slickensides segregate penetratively deformed rocks into independent foliated packets and serve as discontinuities that are followed by later structural features because the original morphology of pedogenic slickensides is known they can be used as crude strain markers

geometry and kinematics of a landslide surface in tertiary clays from the duero basin spain abstract the penalba roto translational landslide is one of the large landslides that can be observed in the central area of the duero basin spain its present morphology is a semicircular shaped depression in which more than 6 m of vertical movement have been measured the erosion of the banks of the duero river affecting the slope of the penalba hill has incised vertical cliffs where a slip surface outcrops and can be observed currently the incision level of the duero river is located 22 m below this surface the slip surface on the translational zone within a large roto translational landslide developed within the duenas facies in a single bed with a high pi 39 0 47 8 and lower carbonate contents would have behaved as low shear strength surfaces r 18 21 8 at penalba the slip surface and the deformation structures related to it have been exceptionally well preserved the structures observed are similar to those usually described in shear zones of tectonic origin an s c fabric related to progressive simple shear and c planes called extensional crenulation cleavage these similarities suggest that analogous kinematic processes would have taken place in completely different geodynamic environments in the present work we have adopted a structural geological kinematic approach to explain the development of the features in this roto translational landslide

the dissolution kinetics of major sedimentary carbonate minerals abstract among the most important set of chemical reactions occurring under near earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals these minerals comprise about 20 of phanerozoic sedimentary rocks calcite and to a significantly lesser extent dolomite are the major carbonate minerals in sedimentary rocks in modern sediments aragonite and high magnesian calcites dominate in shallow water environments however calcite is by far the most abundant carbonate mineral in deep sea sediments an understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel co 2 on climate diagenesis of sediments and sedimentary rocks it also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs and the preservation of buildings and monuments constructed from limestone and marble in this paper we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions we will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments such complex topics are clearly worthy of review papers on their own merits calcite has been by far the most studied mineral over a wide range of conditions and solution compositions in recent years there has been a substantial shift in emphasis from measuring changes in solution composition to determine batch reaction rates to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy afm however there remain major challenges in integrating these two very different approaches a general theory of surface dissolution mechanisms currently lacking although see lasaga and luttge science 291 2001 2400 is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components studies of aragonite high magnesian calcites magnesite and dolomite dissolution kinetics are much more limited in number and scope than those for calcite and provide at best a rather rudimentary understanding of how these minerals are likely to behave in natural systems although the influences of a limited number of reaction inhibitors have been studied probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of foreign ions and organic matter on the near equilibrium dissolution kinetics of carbonate minerals

the role of bedding in the evolution of meso and microstructural fabrics in fault zones abstract to investigate the role of bedding in the evolution of meso and microstructural fabrics in fault zones detailed microscopic mineralogical and geochemical analyses were conducted on bedding oblique and bedding parallel faults that cut a folded neogene siliceous mudstone that contains opal ct smectite and illite an analysis of asymmetric structures in the fault gouges indicates that the secondary fractures associated with each fault exhibit contrasting characteristics those of the bedding oblique fault are r 1 shears whereas those of the bedding parallel fault are reactivated s foliation the bedding oblique fault shows the pervasive development of s foliation lacks opal ct and has low sio 2 tio 2 ratios only in gouge whereas the bedding parallel fault exhibits these characteristics in both gouge and wall rocks the development of s foliation and the lack of silica can result from local ductile deformation involving the sliding of phyllosilicates coupled with pressure solution of opal ct although such deformation can occur in gouge the above results indicate that it may occur preferentially along bedding planes preceding the formation of a gouge slip surface thus in sedimentary rocks that contain phyllosilicates and soluble minerals bedding can influence the rheological evolution of meso and microstructural fabrics in fault zones

pore scale heterogeneous reaction rates on a dissolving limestone surface abstract the rate at which limestone dissolves determines the resistance of buildings and monuments to weathering the efficiency of carbon capture in deep geological reservoirs and the processes by which soils rocks and landscapes form and evolve however the normalized rates of mineral dissolution measured in laboratory experiments are often found to be far greater than those measured in field settings here we use atomic force microscopy afm measurements to demonstrate experimentally that the rate of calcite dissolution within micron size pores at the surface of a limestone sample is much lower than the rate of dissolution in the surrounding calcite surface in addition we use numerical simulations to show that this difference cannot be explained using a simple diffusion surface reaction model we suggest that the observed heterogeneous reaction rates could instead be due to the elevated density of reactive high curvature features on the polished surface surrounding the pore these high curvature features can strongly affect local interfacial free energy making such surfaces more prone to dissolution as a result polished surfaces should be more reactive than pore surfaces that have effectively been smoothed during prolonged contact with natural fluids as rate experiments routinely use polished and powdered samples the results may help to explain the widely reported discrepancy between lab and field based dissolution rates

nanograin formation and reaction induced fracturing due to decarbonation implications for the microstructures of fault mirrors abstract principal slip zones often contain highly reflective surfaces referred to as fault mirrors shown to consist of a nanogranular coating there is currently no consensus on how the nanograins form or why they survive weathering on a geological time scale to simplify the complex system of a natural fault zone where slip and heat generation are inherently coupled we investigated the effect of elevated temperatures on carbonate rock surfaces as well as their resistance to water exposure this allows us to isolate the role of the decarbonation process in the formation of nanograins we used cleaved crystals of iceland spar calcite manually polished dolomite protolith as well as natural dolomite fault mirror surfaces the samples were heated to 200 800 c in a 5 h heating cycle followed by slow cooling 12 h to room temperature subsequently we imaged the samples using scanning electron microscopy and atomic force microscopy nanograin formation on all sample surfaces was pervasive at and above 600 c the foiana fault mirror samples were initially coated with aligned naturally formed nanograins but display a non directional nanogranular coating after heating the nanograins that were formed by heating rapidly recrystallized to bladed hydroxides upon exposure to deionized water whereas the nanograins on unheated fault mirror samples remained unchanged in water this shows that the nanograins formed by heating alone are different from those formed in fault zones and calls for a better characterization of nanograins and their formation mechanisms furthermore we find a characteristic star shaped crack pattern associated with reacted regions of the carbonate surfaces the existence of this pattern implies that the mechanical stresses set up by the decarbonation reaction can be sufficiently large to drive fracturing in these systems we propose that this mechanism may contribute to grain size reduction in fault zones