metal troilite magnetite assemblage in shock veins of sixiangkou meteorite the first natural occurrence of metal troilite magnetite assemblage composed of fe ni metal and magnetite dendrites and a groundmass of troilite was identified in the shock veins of the sixiangkou l6 chondrite which contain abundant high pressure minerals this assemblage suggests a liquid miscibility among metal fes and iron oxide and subsequently quenching under pressure components of magnetite could be in origin related to chromite that was embedded and dissolved in an fe ni s liquid cr2o3 dissociated from chromite was mainly incorporated into garnet and magnesiowustite in the fine grained matrix of shock veins in which chromium behaves as a lithophile element at the p t conditions experienced by the shock veins the occurrence of metal troilite magnetite assemblage suggests that the shock veins were still under pressure at temperatures from 900 to 950degreesc during solidification of fe ni s or fe ni s o liquid hence indicating a long duration of high pressure in the shock veins copyright c 2002 elsevier science ltd

liquefaction and post liquefaction assessment of lightly cemented sands post liquefaction response of lightly cemented sands during an earthquake may change and become similar to uncemented sands due to bonding breakage in the current study the effect of degree of ce

the distinct morphological and petrological features of shock melt veins in the suizhou l6 chondrite the morphology and petrology of distinct melt veins in the suizhou l6 chondrite have been investigated using scanning electron microscopy electron microprobe analyses and raman spectroscopy synchrotron energy dispersive diffraction and transmission electron microscopy it is found that the melt veins in the suizhou meteorite morphologically are the simplest straightest and thinnest among all shock veins known from meteorites at first glance these veins look like fine fractures but petrologically they are solid melt veins of chondritic composition and consist of fully crystalline materials of two distinct lithological assemblages with no glassy material remaining the suizhou melt veins contain the most abundant high pressure mineral species when compared with all other veins known in chondrites thus these veins in suizhou are classified as shock veins all rock forming and almost all accessory minerals in the suizhou shock veins have been transformed to their high pressure polymorphs and no fragments of the precursor minerals remain in the veins among the 11 high pressure mineral phases identified in the suizhou veins three are new high pressure minerals namely tuite after whitlockite xieite and the cf phase after chromite on the basis of transformation of plagioclase into maskelynite it is estimated that the suizhou meteorite experienced shock pressures andmore shock temperatures up to 22 gpa and 1000 c respectively shearing and friction along shock veins raised the temperature up to 1900 2000 c and the pressure up to 24 gpa within the veins hence phase transition and crystallization of high pressure minerals took place only in the suizhou shock veins fast cooling of the extremely thin shock veins is regarded as the main reason that up to 11 shock induced high pressure mineral phases could be preserved in these veins less

high pressure phases in a shock induced melt vein of the tenham l6 chondrite constraints on shock pressure and duration abstract the microtexture and mineralogy of a 580 m wide melt vein in the tenham l6 chondrite were investigated using field emission scanning electron microscopy and transmission electron microscopy to better understand the shock conditions the melt vein consists of a matrix of silicate plus metal sulfide grains that crystallized from immiscible melts and sub rounded fragments of the host chondrite that have been entrained in the melt and transformed to polycrystalline high pressure silicates the melt vein matrix contains two distinct textures and mineral assemblages corresponding to the vein edge and interior the 30 m wide vein edge consists of vitrified silicate perovskite ringwoodite akimotoite majorite with minor metal sulfide the 520 m wide vein interior consists of majorite magnesiowustite with irregular metal sulfide blebs although these mineral assemblages are distinctly different the pressure stabilities of both assemblages are consistent with crystallization from similar pressure conditions the melt vein edge crystallized at about 23 25 gpa and the vein interior crystallized at about 21 25 gpa this relatively narrow pressure range suggests that the melt vein either crystallized at a constant equilibrium shock pressure of 25 gpa or during a relatively slow pressure release using a finite element heat transfer program to model the thermal history of this melt vein during shock we estimate that the time required to quench this 580 m wide vein was 40 ms because the entire vein contains high pressure minerals that crystallized from the melt the shock pressure duration was at least 40 ms using a synthetic hugoniot for tenham and assuming that the sample experienced a peak shock pressure of 25 gpa near the impact site we estimate that the tenham parent body experienced an impact with collision velocity 2 km s based on a one dimensional planar impact model we estimate that the projectile size was 150 m in thickness

density and bulk sound velocity jumps across the 660 km seismic discontinuity abstract molecular dynamics md simulation with realistic and accurate potential models previously obtained for mg2sio4 polymorphs mgo periclase and mgsio3 polymorphs is used to predict the density and bulk sound velocity jumps in the phase transformation from mg2sio4 spinel to mgsio3 perovskite plus mgo periclase at high temperature and high pressure conditions corresponding to the 660 km seismic discontinuity in the mantle the simulated density and bulk sound velocity jumps are then compared with seismological models reported for the 660 km discontinuity the md simulation for a pyrolite composition 60 vol spinel is found to be compatible with a recent model sf99 shearer and flanagan science 285 1999 1545 within nearly 1 limit for both density and bulk sound velocity jumps the md simulated bulk sound velocity jump for a piclogite composition 40 vol spinel is also consistent with sf99 within 1 while the md density jump for the piclogite lies outside the sf99 data our md computed density and bulk sound velocity jumps either for the pyrolite or the piclogite composition differ substantially from the values by the prem or the ak135 model

melting experiments on the enstatite diopside join at 70 224 kbar including the melting of diopside melting relations on the enstatite diopside en mg2si2o6 di camgsi2o6 join including the compositions of crystalline phases and melts coexisting along the solidi were experimentally determined in the pressure range 70 224 kbar with a split sphere anvil apparatus ussa 2000 melting is peritectic in enstatite rich compositions at 70 124 kbar 1840 2100 c and eutectic at higher pressures while the diopside rich clinopyroxene melts azeotropically at 70 165 kbar and up to 300 c lower temperatures than the eutectic orthopyroxene is replaced with enstatite rich clinopyroxene at 120 kbar and 2090 c first garnet with 17 mol di forms on the solidus at 158 kbar and 2100 c two garnets coexist on the solidus at 165 183 kbar and 2100 c garnet coexists with casio3 perovskite at 183 224 kbar 2100 2230 c and two coexisting perovskites are stable at higher pressures the melting curve of diopside was determined at 80 170 kbar the slope becomes negative at 140 kbar and 2155 c at 170 kbar and 2100 c diopside with 96 di breaks down to garnet with 89 di and casio3 perovskite the new data were used to calculate an improved temperature pressure phase diagram for the cmas system which can be useful for estimating the mineralogy of the earth s upper mantle

natural cati2o4 structured fecr2o4 polymorph in the suizhou meteorite and its significance in mantle mineralogy abstract the first natural occurrence of a high pressure polymorph of chromite has been discovered in the shock metamorphosed suizhou meteorite the composition of this high pressure polymorph is identical to that of the precursor chromite the raman spectrum of this polymorph is distinct from that of chromite synchrotron x ray diffraction analysis revealed that this polymorph has an orthorhombic cati2o4 type structure the cell parameters are a 9 462 6 a b 9 562 9 a c 2 916 1 a v 263 8 4 a3 z 4 space group bbmm and the density 5 63 g cm3 the numbers in parentheses are standard deviations on the last significant digits this polymorph is 11 5 denser than chromite the p t conditions for the phase transformation from chromite to the cati2o4 structured polymorph are estimated at 20 23 gpa and 1800 to 2000 c respectively this dense cati2o4 structured fecr2o4 phase could be a host phase for cr al fe mg and mn and other metallic elements in the deep earth

the role of volatiles in the transition zone phase relations in the system mgo sio2 with low volatile contents of h2o f2 and cl2 were experimentally investigated at 100 234 kbar pressures and 850 2050 c temperatures using a split sphere anvil apparatus ussa 2000 superphase b mg10si3o14 oh f 4 was observed at 160 234 kbar fluorous phase b mg12si4o19f2 at 178 kbar and hydrous phase f mg4si7o16 oh 4 also at 178 kbar at lower pressures the volatiles were present in phase a mg7si2o8 oh f 6 phase c mg 7 x si 2 x o 9 x oh f 4 and phase e mg 2 x si 1 x o 4 x y oh f 2y with the exception of the fluorous phase b all these phases can coexist with stishovite at pressures above 130 kbar in a purely hydrous system the dehydration temperatures of the assemblage superphase b stishovite increase from 1200 c at 160 kbar to 1400 c at 234 kbar dehydration produces beta phase mg2sio4 possibly containing up to 7 wt of structural h2o about 3 wt of h2o in beta phase expands the stability of the assemblage beta phase stishovite at the expense of ilmenite by 30 kbar in more complex compositions the volatile solidus is below 1350 c thus at the temperatures which are much lower than the expected mantle temperatures at the relevant depths consequently most of the mantle is in a partially molten state the volatile bearing phases can only be present in the colder subducted slabs but not in the rest of the transition zone 400 670 km hydrous beta phase and stishovite are the most likely constituents of the slabs incongruent melting of the hydrous beta phase coexisting with stishovite producing garnet and melt could be the cause of deep focus earthquakes evidence for a mineralogically and chemically stratified upper mantle is reviewed and its structure is discussed in the context of the present results

garnet and pyroxenes in the mantle a test of the majorite fractionation hypothesis experimental data are reported for the compositions of garnets and pyroxenes that coexist with liquid in the system cao mgo al2o3 sio2 cmas at 80 160 kbar all experiments were run using the uniaxial split sphere apparatus at stony brook our data have permitted a refinement of gasparik s 1990a thermodynamic analysis of garnets and pyroxenes that occur at arid below the solidus our results should provide precise estimates of the temperature pressure conditions at which peridotite and garnet xenoliths equilibrated in the mantle an examination is also made of the composition of garnet that crystallizes as a liquidus phase it is demonstrated to be a function of both composition and pressure pressure has the effect of changing the composition of garnet from pyropic at around 80 kilobars to pyroxene like majorite at pressures in excess of 140 kbar changes that mirror those seen for garnets in the subsolidus failure to consider the effects of pressure on the composition of liquidus garnet can result in an erroneous test of the hypothesis that garnet fractionation occurred in early earth history it is shown that primitive mantle peridotite could have formed as a liquid by 35 majorite garnet fractionation from a cv chondrite like allende at 200 260 kbar these results support the hypothesis that extensive or possibly total melting occurred during the growth of the earth by accretion of planetesimals e g davies 1985 abe and matsui 1985 stevenson 1987 wetherill 1990 and that majorite fractionation could have occurred during this time ohtani and sawamoto 1987 removal of majorite to the lower mantle during the crystallization of a magma ocean is a successful way of explaining differences in mgo sio2 and cao al2o3 between mantle peridotite and chondrite

shock induced p t conditions and formation mechanism of akimotoite pyroxene glass assemblages in the grove mountains grv 052082 l6 meteorite akimotoite mg fe sio 3 ilmenite was encountered in shock induced melt veins of grove mountains grv 052082 a highly equilibrated low iron ordinary chondritic meteorite l6 coexistence of ringwoodite majorite and majorite pyrope solid solution indicates the shock pressure at 18 23 gpa and temperature of 2000 2300 c during the natural dynamic event most low ca pyroxene clasts entrained in the melt veins have been partially or entirely transformed into akimotoite pyroxene glass assemblages which contain micrometer sized areas with various brightness in the backscattered electron images different from the chemically homogeneous grains in the host rock fs 20 5 21 3 the transmission electron microscopy study of a focused ion beam fib slice from the heterogeneous areas shows that the assemblages are composed of feo depleted and heterogeneous akimotoite fs 6 19 crystals 100 nm up to 400 nm in size scattered in feo enriched and relatively homogeneous pyroxene glass fs 31 39 all analyses of the akimotoite pyroxene glass assemblages plot on a fractionation line in feo mgo diagram with the host rock pyroxene at the middle between the compositions of feo depleted akimotoite and the feo enriched pyroxene glass these observations are different from previous reports of almost identical compositions of akimotoite bridgmanite mg fe sio 3 perovskite or pyroxene glass to the host rock pyroxene chen et al 2004 ferroir et al 2008 ohtani et al 2004 tomioka and fujino 1997 which is consistent with solid state transformation from pyroxene to akimotoite and preexisting bridgmanite that could be vitrified the observed fractionation trend and the granular shapes of akimotoite suggest crystallization from liquid produced by shock melting of the host rock pyroxene and the pyroxene glass matrix was probably quenched from the residual melt however this interpretation is inconsistent with the static experiments that expect crystallization of majorite mg fe sio 3 garnet instead of akimotoite from pyroxene liquid sawamoto 1987 our discovery raises the issue on formation mechanisms of the high pressure polymorphs of pyroxene and places additional constraints on the post shock high pressure and high temperature conditions of asteroids

comparison of truly undrained and constant volume direct simple shear tests the paper describes a chamber for the norwegian geotechnical institute s direct simple shear device that enables undrained tests with pore pressure measurements to be run the results of undrained

cyclic loading response of loose air pluviated fraser river sand for validation of numerical models simulating centrifuge tests cyclic loading response of loose fraser river sand was investigated as input to numerical simulation of centrifuge physical models using constant volume direct simple shear tests conducted with a

the breakdown of diopside to ca rich majorite and glass in a shocked h chondrite fine grained assemblages of majorite and glassy grains are for the first time identified in a shock induced melt vein in an h chondritic meteorite the bulk chemical composition of these aggregates is similar to that of diopside camgsi2o6 in the host rock both majorite and glassy grains are ca rich and their formulae can be approximated as mg0 65fe0 09ca0 26 sio3 and mg0 23fe0 05ca0 72 sio3 respectively these ca rich assemblages are dissociation products of the host diopside and were produced at 18 24 gpa by a shock event the casio3 rich glass is inferred to have crystallized in a perovskite structure but was vitrified during the pressure release

a shock produced mg fe sio3 glass in the suizhou meteorite ovoid grains consisting of glass of stoichiometric mg fe sio3 composition that is intimately associated with majorite were identified in the shock veins of the suizhou meteorite the glass is surrounded by a thick rim of polycrystalline majorite and is identical in composition to the parental low ca pyroxene and majorite these ovoid grains are surrounded by a fine grained matrix composed of majorite pyrope garnet ringwoodite magnesiowstite metal and troilite this study strongly suggests that some precursor pyroxene grains inside the shock veins were transformed to perovskite within the pyroxene due to a relatively low temperature while at the rim region pyroxene grains transformed to majorite due to a higher temperature after pressure release perovskite vitrified at post shock temperature the existence of vitrified perovskite indicates that the peak pressure in the shock veins exceeds 23 gpa the post shock temperature in the meteorite could have been above 477 c this study indicates that the occurrence of high pressure minerals in the shock veins could not be used as a ubiquitous criterion for evaluating the shock stage of meteorites

petrogenesis of miller range 07273 a new type of anomalous melt breccia implications for impact effects on the h chondrite asteroid miller range 07273 is a chondritic melt breccia that contains clasts of equilibrated ordinary chondrite set in a fine grained 3 gpa possibly to 15 19 gpa and temperature 1350 c possibly to 2000 c the higher pressures and temperatures would have involved back reaction of high pressure polymorphs to pyroxene and olivine upon cooling silicates outside of melt matrix have compositions that were relatively unchanged owing to brief heating duration

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

sh velocity and compositional models near the 660 km discontinuity beneath south america and northeast asia 1 we constrain sh wave velocity structures near the 660 km discontinuity beneath south america and northeast asia using triplicated phases near the discontinuity recorded in the epicentral distance range of 10 35 for three deep events we then explore mineralogical and compositional models appropriate for explaining the inferred seismic structures between the two regions sh velocity structures near the 660 km discontinuity are found to be different in the two regions beneath south america the velocity gradient above the 660 km discontinuity is larger than that of preliminary earth reference model prem while the velocity jump across the discontinuity is the same as prem beneath northeast asia the velocity gradient above the 660 km discontinuity is the same as that of prem while the velocity jump across the discontinuity is larger than prem both regions are characterized by a large velocity gradient extending about 80 km deep below the 660 km discontinuity the different velocity structures require different mineralogical models in the transition zone in the two regions the larger velocity gradient above the 660 km discontinuity beneath south america requires existence of the ilmenite phase in the bottom of transition zone while that beneath northeast asia can be explained by the temperature and pressure dependence of elastic properties of the major mantle mineral assemblages the observed large velocity gradients in the top of the lower mantle can be explained by gradual transformation of garnet to perovskite persisting to greater depths the velocity jump across the 660 km discontinuity beneath south america in the presence of the ilmenite phase in the bottom of the transition zone requires a bulk composition of more garnet than the pyrolite model while a larger velocity jump across the discontinuity beneath northeast asia requires a larger fraction of garnet transforming to perovskite across the discontinuity than what is required for explaining prem these different mineralogical models can be caused by different mantle temperature or composition especially the aluminum content in mantle composition the presence of garnet 80 km below the 660 km discontinuity in the two regions may be explained by a uniform composition in the lower mantle with an aluminum content of 3 4 the existence of ilmenite in the bottom of the transition zone beneath south america and the absence of ilmenite beneath northeast asia can be explained by either a difference in mantle temperature of about 100 c with that beneath south america being lower between the two regions assuming a uniform mantle composition or alternatively a difference in aluminum content of about 1 with that beneath south america being lower between the two regions without invoking a temperature difference between the two regions we also discuss conditions of mantle composition and temperature that double discontinuities may occur near the 660 km depth as well as the depth separation and velocity jumps of the double discontinuities for the inferred mantle temperature and composition beneath south america and northeast asia the maximum separation of the double discontinuities is 20 km and cannot be resolved by the sh wave data

the mesozoic la mula island coahuila mexico granitic rocks at potrero de la mula and sierra del fuste coahuila mexico are the only known exposures of a late triassic pluton that by the late jurassic stood as a topographically high area until it was inundated by the cretaceous sea the principal igneous rock at potrero de la mula is a two feldspar biotite hornblende i type granite that is cut by comagmatic dikes of six ages and by several shear zones a rb sr age of 213 14 m y and an initial ratio of 0 705 0004 were obtained from nine whole rock samples a shallow depth of emplacement is inferred from textural and mineralogical evidence mineralogy chemistry and isotopes suggest emplacement above a subduction zone which is consistent with the hypothesis that a late paleozoic earliest mesozoic convergent plate boundary existed in northern mexico after being unroofed the pluton contributed sediment to the adjoining sabinas gulf until the mid neocomian by the hauterivian the pluton supported a deeply weathered terrain of moderate relief flanked on its northeastern side by lagoonal environments oballos member padilla formation farther south uplift by faulting along the northern flank of the coahuila island produced a clastic wedge the finer grained paralic components of which la mula formation prograded northeastward and eventually covered la mula island subsequent deposits at potrero de la mula beginning with gypsum reflect gradually deepening water and include the la virgen cupido la pena and tamaulipas formations

phase relations in the system kalsi3o8 naalsi3o8 at high pressure high temperature conditions and their implication for the petrogenesis of lingunite abstract multi anvil experiments have been made with the composition k0 2na0 8 alsi3o8 at 14 25 gpa and 1400 2400 c these experiments suggest that at subsolidus conditions the stable phase assemblages are hollandite i jadeite stishovite at pressures up to 20 gpa hollandite ii jadeite stishovite at pressures between 20 and 24 gpa and hollandite ii calcium ferrite type naalsio4 stishovite at pressures 24 gpa where hollandite i and hollandite ii are distinguished by their chemical compositions and phase diagram topology the maximum naalsi3o8 in hollandite occurs at 22 gpa and its fraction is positively correlated to temperature attaining a value of 51 mol at 2200 c at supersolidus conditions the solidus and liquidus phases around 14 gpa are hollandite i and jadeite respectively at 22 gpa however the solidus phase is jadeite while the liquidus phase is either stishovite or hollandite ii with a very low fraction of naalsi3o8 these experimental results therefore suggest that lingunite with the hollandite structure and 90 mol naalsi3o8 found in some meteorites is a disequilibrium product it is similarly proposed that the phase with the structure of jadeite but the composition of plagioclase found along with lingunite is also a disequilibrium phase

a model for the layered upper mantle abstract numerical modeling of mantle convection by liu 1994 science 264 1904 1907 favors a two layer convection if the results are reinterpreted for the correct phase relations in mg fe 2sio4 the resulting chemical isolation of the upper and lower mantle suggests a highly differentiated and layered upper mantle to account for the discrepancy between the observed compositions of mantle xenoliths and the cosmic abundances of elements it is shown that a layered upper mantle with a hidden reservoir can have a structure consistent with the observed seismic velocity profiles and an average bulk composition corresponding to the cosmic abundances the evolution of the upper mantle and the origin of komatiites are discussed in the context of the proposed model

postcyclic reconsolidation strains in low plastic fraser river silt due to dissipation of excess pore water pressures the postcyclic reconsolidation response of low plastic fraser river silt was examined using laboratory direct simple shear testing specimens of undisturbed and reconstituted natural low plastic fraser river silt and reconstituted quartz powder initially subjected to constant volume cyclic loading under different cyclic stress ratios csrs and then reconsolidated to their initial effective stresses vo were specifically investigated the volumetric strains during postcyclic reconsolidation ev ps were noted to generally increase with the maximum cyclic excess pore water pressure umax and maximum cyclic shear strain experienced by the specimens during cyclic loading the values of ev ps and maximum cyclic excess pore water pressure ratio ru max were observed to form a coherent relationship regardless of overconsolidation effects particle fabric and initial precyclic void ratio of the soil the specimens with high ru max suffered significantly higher postcyclic reconsolidation st

phase relations in the camgsi 2 o 6 kalsi 3 o 8 join at 6 and 3 5 gpa as a model for formation of some potassium bearing deep seated mineral assemblages the join camgsi2o6 kalsi3o8 has been studied at 6 gpa 890 1 500 c and 3 5 gpa 1 000 1 100 c k rich melts in the join produce assemblages cpx grt cpx opx cpx san and cpx grt san at 1 100 1 300 c at nsansystem 90 mol this explains a scarcity of san in mantle cpx rich assemblages and its association with high k aluminosilicate melt inclusions in diamonds in absence of san kcpx is the only host for potassium the k jadeite content in kcpx systematically increases with decreasing temperature and reaches 10 12 mol near the solidus however kcpx coexists with san at nsansystem 70 mol and 4 gpa to cpx san at p 4 gpa similar sequence of assemblages is observed in some eclogitic xenoliths from kimberlites and grt cpx rocks of the kokchetav complex northern kazakhstan

estimating shock pressures based on high pressure minerals in shock induced melt veins of l chondrites here we report the transmission electron microscopy tem observations of the mineral assemblages and textures in shock induced melt veins from seven l chondrites of shock stages ranging from s3 to s6 the mineral assemblages combined with phase equilibrium data are used to constrain the crystallization pressures which can be used to constrain shock pressure in some cases thick melt veins in the tenhaml6 chondrite contain majorite and magnesiowstite in the center and ringwoodite akimotoite vitrified silicate perovskite and majorite in the edge of the vein indicating crystallization pressure of 25 gpa however very thin melt veins 5 30 m wide in tenham contain glass olivine clinopyroxene and ringwoodite suggesting crystallization during transient low pressure excursions as the shock pressure equilibrated to a continuum level melt veins of umbarger include ringwoodite akimotoite and clinopyroxene in the vein matrix and fe2sio4 spinel and stishovite in sio2 feo rich melt indicating a crystallization pressure of 18 gpa the silicate melt veins in roy contain majorite plus ringwoodite indicating pressure of 20 gpa melt veins of ramsdorf and nakhon pathon contain olivine and clinoenstatite indicating pressure of less than 15 gpa melt veins of kunashak and la lande include albite and olivine indicating crystallization at less than 2 5 gpa based upon the assemblages observed crystallization of shock veins can occur before during or after pressure release when the assemblage consists of high pressure minerals and that assemblage is constant across a larger melt vein or pocket the crystallization pressure represents the equilibrium shock pressure

upper mantle sh and p velocity structures and compositional models beneath southern africa abstract we constrain sh and p wave velocity structures in the upper mantle beneath southern africa using triplicated phases recorded in the epicentral distance range of 11 28 for one shallow event we then explore thermal and compositional models appropriate for explaining the inferred seismic structures in the region both sh and p wave data suggest presence of a low velocity zone with velocity reductions of at least 5 for s waves and 2 for p waves beneath a 150 km thick high velocity lithospheric lid seismic observations also suggest that the p s ratio is larger 1 88 in the transition zone than in the lithospheric lid 1 70 the inferred p wave velocity jump across the 660 km discontinuity is small

high pressure phase relations in the composition of albite naalsi3o8 constrained by an ab initio and quasi harmonic debye model and their implications abstract phase relations in the composition of albite naalsi3o8 at pressures up to 40 gpa were constrained by a theoretical method that combines the ab initio calculation and quasi harmonic debye model first the p t dependence of the thermodynamic potentials of the individual phase stishovite sio2 st the calcium ferrite type naalsio4 cf jadeite naalsi2o6 jd or the hypothetical hollandite structured naalsi3o8 na holl was derived our results are generally in consistent agreement with available experimental data and previous theoretical predictions second the gibbs free energy of the hypothetical na holl phase was compared with that of the phase assemblage jd st js or cf 2st cs our results show that the na holl phase is not a thermodynamically stable phase over the studied p t conditions of 0 40 gpa and 100 600 k which rules it out as a possible intermediate phase along the transition path from the js phase assemblage to cs phase assemblage our calculations have predicted that the js phase assemblage transforms into the cs phase assemblage at about 33 6 gpa at 0 k and the clayperon slope of this phase transition is about 0 014 gpa k this study implies that lingunite na holl found in some meteorites is not possibly a thermodynamically stable high p phase and the cf phase probably plays an important role in maintaining the sodium budget and hosting the large ion lithophile elements in the deep interior of the earth

an experimental study of grain scale microstructure evolution during the olivine wadsleyite phase transition under nominally dry conditions abstract the grain scale microstructure evolution during the phase transformation of olivine to wadsleyite was investigated using a multi anvil high pressure apparatus we identified three stages in the microstructure evolution during olivine to wadsleyite phase transformation 1 nucleation of wadsleyite along potential nucleation sites e g grain boundaries and grain corners inside of grains dislocations stacking faults 2 development of an interconnected network of fine grained wadsleyite along grain boundaries 3 growth of wadsleyite into olivine our observations suggest that at low over pressures 3 gpa intra crystalline nucleation makes a significant contribution to the volume fraction transformed the rheological properties of a sample undergoing the phase transformation are controlled by the grain size and the connectivity of newly formed grains based on the model of grain size evolution involving both nucleation and growth we show that the initial grain size of wadsleyite is controlled by the competition between nucleation rate and growth rate when phase transformation takes place near the equilibrium boundary at relatively higher temperatures 1200 k but mostly by critical size for nucleation when phase transformation takes place away from the equilibrium boundary at relatively low temperatures

melting of garnet peridotite to 13 gpa and the early history of the upper mantle by analogy with the evolution of the moon it has been suggested that the earth may have had a magma ocean or liquid outer layer before 3 800 myr ago 1 its presence would have had profound implications for the primary stratification of the mantle into upper mantle transition zone and lower mantle2 3 an essential constraint on this hypothesis is a knowledge of the high pressure melting characteristics of mantle material generally assumed to be peridotite in the upper mantle we recently described4 the first melting experiments on mantle peridotite to 14 gpa using spinel iherzolite klb 1 from kilbourne hole new mexico we showed that partial melts close to the solidus at 5 7 gpa are komatiitic in composition and that the solidus and liquidus converge at high pressures here we report further melting experiments on garnet iherzolite phn1611 from thaba putsoa lesotho we confirm the convergence of the solidus and liquidus and we show a negative dt dp slope for the liquidus above 7 gpa these observations are briefly discussed in terms of their importance to the petrological evolution of the upper mantle and the presence of a magma ocean in the early archaean

phase transition processes of olivine in the shocked martian meteorite tissint clues to origin of ringwoodite bridgmanite and magnesiowustite bearing assemblages abstract tissint is a heavily shocked olivine phyric shergottite we investigated and documented several phase transformations and dissociation phenomena of olivine adjacent to and in many shock induced melt pockets of tissint olivine grains entrained in the melt pockets dissociated to equigranular magnesiowustite bridgmanite latter now vitrified with approaching to the boundaries between the melt pockets and host rocks of tissint some olivine grains entrained in the melt pockets are incompletely dissociated spherulitic magnesiowustite bridgmanite assemblages occur in the incompletely dissociated olivine several residual olivine domains are retained at the center of spherulitic texture with further approaching to the boundaries between the melt pockets and host rocks some olivine grains entrained in the melt pockets are segmented with a cellular like texture presumably induced by defect arrangement many fine grained magnesiowustite occurs around the individual cells of the segmented olivine grains considering the temperature gradient in the melt pockets and the arrangement of dissociation and segmentation textures olivine dissociation reaction was presumably initiated by the segmentation of olivine subsequently followed by magnesiowustite crystallization around the individual cells of the segmented olivine and by bridgmanite formation subsequently spherulitic magnesiowustite bridgmanite assemblages occur around residual olivine domain and finally olivine completely dissociates to equigranular magnesiowustite bridgmanite assemblage olivine grains adjacent to the melt pockets transform to randomly oriented polycrystalline ringwoodite assemblages in rare case ahrensite occurs in the more iron rich portions of the olivine grains with increasing distance from the melt pockets sets of ringwoodite lamellae occur in increasing abundance into the interior of the olivine grains the lamellae consist of almost crystallographically oriented polycrystalline ringwoodite assemblages the phase transitions from olivine to ringwoodite were presumably promoted by interface controlled incoherent mechanism the ringwoodite would be metastable phase which formed in the stability field where olivine dissociates into magnesiowustite bridgmanite

effective stress response of clay to undrained cyclic loading the effective stress response of a natural marine clay to slow undrained symmetrical cyclic reversal in shear stress is presented the effects of cyclic principal stress difference amplitude cyclic principal effective stress ratio amplitude initial direction of loading and step increase in cyclic stress level on the clay stress strain response are studied under stress conditions of the triaxial test characteristic behaviour patterns are identified in terms of effective stresses key words clay cyclic loading effective stress hysteretic work loading direction step loading

assessment of the liquefaction susceptibility of fine grained soils observations from recent earthquakes and the results of cyclic tests indicate that the chinese criteria are not reliable for determining the liquefaction susceptibility of fine grained soils fine grained soils that liquefied during the 1994 northridge 1999 kocaeli and 1999 chi chi earthquakes often did not meet the clay size criterion of the chinese criteria cyclic testing of a wide range of soils found to liquefy in adapazari during the kocaeli earthquake confirmed that these fine grained soils were susceptible to liquefaction it is not the amount of clay size particles in the soil rather it is the amount and type of clay minerals in the soil that best indicate liquefaction susceptibility thus plasticity index pi is a better indicator of liquefaction susceptibility loose soils with pi 0 85 were susceptible to liquefaction and loose soils with 12 0 8 were systematically more resistant to liquefaction soils with pi 18 tested at low effective confining stresses

host rock solid state transformation in a shock induced melt vein of tenham l6 chondrite abstract the host rock fragments entrained in a 580 m wide melt vein of the tenham l6 chondrite were investigated using field emission scanning electron microscopy fesem and transmission electron microscopy tem to better understand the solid state transformation mechanisms and the shock conditions the melt vein consists of a matrix of silicate plus metal sulfide that crystallized from immiscible melts and sub rounded host rock fragments that have been entrained in the melt and transformed to polycrystalline high pressure silicates by solid state transformation mechanisms these high pressure phases include ringwoodite low ca majorite clinoenstatite hollandite structured plagioclase and ca rich majorite the ca rich majorite occurs as a symplectitic intergrowth with a ca poor amorphous silicate phase in a 200 m diameter chondrule in the vein this intergrowth seems to be the result of a disproportionate breakdown of a ca rich clinopyroxene precursor into ca rich majorite and femg sio 3 perovskite which subsequently vitrified upon pressure release the tem observations suggest that most solid state transformations in the tenham are reconstructive the transformation of olivine to polycrystalline ringwoodite appears to involve incoherent intracrystalline nucleation and interface controlled growth lamellae in partially transformed olivine are not continuous coherent lamellae but rather lamellae of polycrystalline ringwoodite which is inconsistent with a coherent lamellar transformation mechanism growth rate calculations based on published kinetic data suggest that the time required to grow 1 m ringwoodite crystal is 100 ms at 1600 k suggesting that the minimum shock pulse of approximately 100 ms

effects of sample disturbance and consolidation procedures on measured shear strength of soft marine norwegian clays after many decades of research the issue of sample disturbance is still important as regards to determining reliable and representative soil parameters for foundation design in soft clays parallel laboratory tests have been carried out on high quality block samples and ordinary piston tube samples from 12 deposits of soft norwegian marine clays undrained triaxial and direct simple shear dss tests on samples reconsolidated to the in situ effective stresses show that sample disturbance has a significant effect on the measured stress strain strength behaviour the more disturbed the sample the lower the shear stress at small strains and the higher the shear stress at large strains breakdown of the clay structure including cementation bonds is the assumed cause of lower shear resistance at small strains whereas at large strains the shear resistance is governed mainly by the water content which for soft clay samples reconsolidated to the in situ effective stresses will be lower and the strength t

the nature of maskelynite in shocked meteorites not diaplectic glass but a glass quenched from shock induced dense melt at high pressures abstract maskelynite an important constituent of shocked meteorites once thought to be diaplectic plagioclase glass formed by shock induced solid state transformation our systematic investigation of shocked l chondrites and snc meteorites indicates that maskelynite does not contain inherited fractures or cleavage and shock induced fractures we found no evidence for models calling for melting that initiated in pdfs and affected the whole crystals maskelynite grains are smooth and display radiating cracks emerging from their surfaces into neighboring pyroxene this is indicative of shock induced melting and quenching of the dense melt at high pressure thus erasing the inherited and shock induced fractures this was followed by relaxation of the dense plagioclase glass which induced the expansion cracks in pyroxene and olivine enrichment in potassium deviation from stoichiometry degradation of igneous zoning the presence of offshoots of maskelynite in pyroxene the lack of vesiculation in the melt pockets melt veins and molten mesostasis are clear evidence for melting and quenching under high pressure our investigations present unequivocal evidence that maskelynite in meteorites is not diaplectic plagioclase glass formed by solid state transformation but a dense quenched glass the duration of the shock pulse in natural events can be several orders of magnitude longer than in shock experiments since kinetic effects are crucial factors in promoting phase transitions vitrification and melting experimentally induced solid state vitrification of plagioclase produced in dynamic experiments is inadequate for calibration of peak shock pressures in maskelynite bearing natural samples

phase relations in the transition zone phase relations in the systems mgo al2o3 sio2 and cao mgo sio2 have been investigated experimentally at 166 226 kbar pressures and 1350 2500 c temperatures with a split sphere anvil apparatus ussa 2000 mgsio3 ilmenite is stable to lower pressures 175 kbar than found previously casio3 perovskite forms at p bar 15t c 151 000 three new high pressure phases are reported a phase with the diopsidic composition the cm phase a high pressure polymorph of al2o3 and superphase b with the tentative composition mg10si3o14 oh f 4 the invariant point for coexisting majorite mg4si4o12 perovskite mgsio3 beta phase mg2sio4 and liquid has been located at 224 kbar 2430 c with the eutectic melt composition on the enstatite forsterite join at 40 44 wt of forsterite the melting temperature of mgsio3 perovskite at 225 kbar is predicted to be 2600 c the new data made possible the calculation of a temperature pressure phase diagram for the system cao mgo al2o3 sio2 cmas in the pressure range 0 280 kbar the mineralogy of the earth s mantle and the possible mechanisms for producing large seismic velocity gradients in the transition zone are discussed on the basis of the derived phase relations

crystal chemistry of ca bearing majorite single crystals of ca bearing majorite a garnet with composition cao 49mg2sl mgsi sipi2 have been synthesized at 18 2 gpa and 2050 0c this sample is the first silicate garnet to display ordering on both octahedral and dodecahedral sites behavior that may increase the compositional flexibility of garnet affect element partitioning at high pressure and stabilize the garnet structure in the transition zone and upper portion of the lower mantle the garnet is tetragonal space group 14 a z 8 a 11 5816 9 c 11 5288 13 a v 1546 39 29 a3 and like mgsio majorite displays twinning by twofold rotation about 110

dating phosphates of the strongly shocked suizhou chondrite impacts on undifferentiated asteroidal bodies provide invaluable information for understanding the solar system evolution nevertheless dating early and small scale impact events is technically challenging uranium lead u pb systematics of u bearing phases within shock induced melt veins smvs of chondrites may be significantly disturbed by localized heating thus providing opportunities to date these impact events as one of the major u hosts in chondrites apatite in the suizhou l6 chondrite has been compositionally and structurally modified to varying degrees by shock metamorphism apatite grains in the host remained largely intact during the impact and have recorded the initial thermal cooling time similar to 4550 ma on their parent body apatite grains in regions less than 100 mu m bordering the smvs or in relatively cold regions within the smvs were partly decomposed to tuite driven by the localized transient heating within the smvs their u pb systematics were disrupted to varying extents apatite in regions close to the center of the smvs has been completely transformed to tuite which yields an age of 4481 30 ma 2 sigma providing an upper limit to the impact event this study clearly demonstrates that by integrating in situ u pb isotope analysis with detailed microstructural and compositional analysis of phosphates it is possible to deduce the timing of early and small scale celestial impact events and hence create a more comprehensive understanding of the impact history of the solar system

shock and thermal history of martian meteorite allan hills 84001 from transmission electron microscopy microstructures in the allan hills 84001 meteorite were studied using optical and electron microscopy putting emphasis on shock effects which are widespread some orthopyroxene exhibits only 100 slip but more typical grains suffered extensive slip microfracturing and frequently contain 100 clino inversion lamellae in fracture zones shock deformation of orthopyroxene has produced all three effects in profusion together with intergranular pockets of orthopyroxene glass and intragranular glass lamellae which were apparently created by shearing on low index planes usually 100 or 110 both types of plane are loci that pseudo planar fractures tend to follow thus the glass lamellae which have not been observed in other meteorites probably formed by frictional heating during the sliding of microscale corrugated surfaces one over another leading to local melting we infer that the orthopyroxene glass and the fracture zones both formed from shear stresses created by strong shock ubiquitous undeformed micrometer and submicrometer euhedral chromites in orthopyroxene and plagioclase glasses and carbonate probably crystallized after shock heating and fracture zone formation nanocrystals of eskolaite cr2o3 coating silica glass grains are probably also a result of shock induced thermal decomposition of chromite iron sulfides pyrite and pyrrhotite were identified tended to be associated with plagioclase glass a carbonate disk showing no evidence for shock deformation had a substructure of elongated slightly misoriented subcells in the exterior interior regions had more eqiaxed subcells both microstructures probably formed during growth but the conditions are undetermined chemical composition varied on a micron scale but the rim of the disk was more ferroan oxide precipitates and voids were widely distributed as in fracture filling carbonates if the fracture zones and opx glass are the result of strong shock as we deduce it is very unlikely that pores could have filled by carbonate long after the fracture zones formed we infer that the carbonate like the phosphate olivine pyrrhotite eskolaite and many euhedral submicrometer chromites crystallized during the final stages of the impact that created the fracture zones and glasses with compositions of plagioclase silica and orthopyroxene

tuite γ ca3 po4 2 formed by chlorapatite decomposition in a shock vein of the suizhou l6 chondrite tuite ca3 po4 2 was first discovered as the high pressure phase of whitlockite in shock veins of the suizhou l6 meteorite this study reports the finding of tuite in a shock vein of the same suizhou chondrite as a product of decomposition of chlorapatite where it coexists with coarse grained ringwoodite majorite lingunite fine grained majorite pyrope solid solution and magnesiowustite moreover we also successfully synthesized tuite with a multianvil apparatus from chlorapatite at 15 gpa and 1573 k over 24 h both natural and synthetic tuite crystals were examined by means of optical microscopy scanning electron microscope electron microprobe analysis x ray diffraction and raman spectroscopy our results suggest that the na2o mgo and cl contents in natural tuite may serve as good indicators for distinguishing the precursor phosphate mineral chlorapatite or whitlockite

description of new shock induced phases in the shergotty zagami nakhla and chassigny meteorites the shergottite nakhlite and chassignite snc meteorites shergotty zagami nakhla and chassigny have been studied by analytical transmission electron microscopy new phases characteristic of strong shock conditions have been discovered calcium rich majorites in shergottty wadsleyite with anomalously elevated iron content in chassigny and impact melts in shergotty zagami and nakhla cristobalites and polymorphs observed in shergotty and zagami may also be related to shock and are interpreted as back transformation products of post stishovite silica polymorphs shocks corresponding to pressure and temperature conditions characteristic of the earth s transition zone and lower mantle have occurred in those meteorites moreover impact melts indicate high temperature conditions in localized areas on the other hand no massive impact melting is observed in those meteorites consistent with previous descriptions these observations provide evidence of highly heterogeneous shock conditions at the scale of few micrometers in these meteorites strongly heterogeneous conditions such as those suggested by the present study may help to explain the preservation in martian meteorites of phases practically unaffected by shock being very close to strongly shock metamorphized minerals

high pressure polymorphs of magnesian orthopyroxene from a shock vein in the yamato 000047 lherzolitic shergottite abstract we found a simple thin shock vein less than or equal to about 60 m in width and 1 8 mm in length in the poikilitic area in the yamato y 000047 lherzolitic shergottite the shock vein occurs only in magnesian ca poor clinopyroxene which may have transformed from orthopyroxene during the pressure increase at the shock event the shock vein consists of mg0 8 fe0 2 sio3 pyroxene polymorphs such as columnar akimotoite two kinds of pyroxene glasses dendritic akimotoite and framboidal pyroxene glass in the order from the periphery to the center the compositions and textures suggest that columnar akimotoite in the periphery of the shock vein crystallized from solid state phase transition of clinopyoroxene during the cooling of the vein and the remains in the shock vein solidified from shock produced melt the glass includes two kinds of massive glass in the vein and framboidal glass in the vein center the framboidal glass is the most magnesian and may have been vitrified from perovskite crystallized from high pressure melt produced at high temperature 3000 c and high pressure 23 40 gpa dendritic akimotoites in the vein center metastably crystallized from residual shock melt the formation sequences of the constituent phases in the shock vein happen in the following order columnar akimotoites rim glass center glass framboidal glass and dendritic akimotoites the increase of the raman intensity of 660 670 cm 1 in the order of rim glass center glass and framboidal glass suggests that the formation of the pyroxene chain proceeds faster in the vein center than in the vein rim due to its slower cooling the finding of the shock vein consisting merely of high pressure polymorphs of pyroxene akimotoite and framboidal glass vitrified perovskite is the first reported among all martian meteorites

paleogeographic evolution of early deep water gulf of mexico and margins jurassic to middle cretaceous comanchean the paleobathymetric configuration of the early gulf of mexico is inferred from 1 cretaceous carbonate shelf margins interpreted from seismic profiles and other stratigraphic data 2 distribution of jurassic and cretaceous platform and basinal facies and 3 hindcasting of subsidence history in the central basin substantial paleogeographic ambiguity results from uncertainty about 1 kinematics and timing of late triassic to jurassic extensional opening of the gulf basin which probably involved major strike slip faulting 2 the magnitude of subsequent compressive deformation on the western and southern basin margins and 3 possible accretion of allochthonous terranes the initial sub sea level topographic depression created by crustal extension is manifested by the distribution of callovian pre marine salt and oxfordian basinal marine facies late jurassic sea floor spreading split the main salt body and created a central deep water 1 km trough from the oxfordian to early neocomian ramp like platform margins generally underwent net retreat except in the northern gulf where major clastic progradation took place carbonate platform margins with sufficient paleorelief for geometric expression on seismic profiles developed early in the cretaceous these cretaceous carbonate margins exhibit a variety of architectural styles including 1 in the northwestern gulf two cycles of progradation coahuilan and comanchean terminated by drowning events 2 in the southwestern gulf a single cycle of progradation 3 continuous aggradation along the florida and campeche escarpments paleobathymetric relief across cretaceous carbonate margins ranges from high and steep to low relief to ramplike the close of comanchean drowning event greatly and permanently reduced the extent of circum gulf carbonate platforms and especially rimmed margins locations of cretaceous carbonate margins were influenced by basement hinge zones and paleohighs developed on attenuated continental crust by the distribution of salt and by clastic progradation eustacy is commonly invoked to explain behavior and architecture of carbonate margins in the gulf but other paleoenvironmental variables such as nutrient abundance are probably important as well

regional stratigraphy and distribution of epigenetic stratabound celestine fluorite barite and pb zn deposits in the mvt province of northeastern mexico northeastern mexico hosts numerous epigenetic stratabound carbonate hosted low temperature hydrothermal deposits of celestine fluorite barite and zinc lead which formed by replacement of mesozoic evaporites or carbonate rocks such deposits can be permissively catalogued as mississippi valley type mvt deposits the deposits studied in the state of coahuila are associated with granitic and metasedimentary basement highs horsts marginal or central to the mesozoic sabinas basin these horsts controlled the stratigraphy of the mesozoic basins and subsequently influenced the laramide structural pattern the sabinas basin consists of 6 000 m thick jurassic to cretaceous siliciclastic carbonate and evaporitic series the mvt deposits are mostly in barremian and in aptian albian to cenomanian formations and likely formed from basinal brines that were mobilized during the laramide orogeny although earlier diagenetic replacement of evaporite layers barite and celestine deposits and lining of paleokarstic cavities in reef carbonates zn pb deposits is observed fluid inclusion microthermometry and isotopic studies suggest ore formation due to mixing of basinal brines and meteoric water homogenization temperatures of fluid inclusions range from 45 c to 210 c salinities range from 0 to 26 wt nacl equiv and some inclusions contain hydrocarbons or bitumen sulfur isotope data suggest that most of the sulfur in barite and celestine is derived from barremian to cenomanian evaporites regional geology and a compilation of metallogenic features define the new mvt province of northeastern mexico which comprises most of the state of coahuila and portions of the neighboring states of nuevo leon durango and perhaps extends into zacatecas and southern texas this province exhibits a regional metal zonation with celestine deposits to the south fluorite deposits to the north and barite and zn pb deposits mostly in the central part

liquefaction susceptibility criteria for silts and clays new liquefaction susceptibility criteria for saturated silts and clays are presented that are based on the mechanics of their stress strain behavior and which provide improved guidance for selecting engineering procedures for estimating potential strains and strength loss during seismic loading monotonic and cyclic undrained loading test data for silts and clays show that they transition over a fairly narrow range of plasticity indices pi from soils that behave more fundamentally like sands sand like behavior to soils that behave more fundamentally like clays clay like behavior with the distinction having a direct correspondence to the type of engineering procedures that are best suited to evaluating their seismic behavior it is recommended that the term liquefaction be reserved for describing the development of significant strains or strength loss in fine grained soils exhibiting sand like behavior whereas the term cyclic softening failure be used to describe similar phenomena in fine grained soils exhibiting clay like behavior for practical purposes clay like behavior can be expected for fine grained soils that have pi 7 although a slightly lower transition point for soils with a cl ml classification perhaps pi 5 or 6 would be equally consistent with the available data issues related to the practical application of these criteria are discussed