the stubenberg meteorite an ll6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field on march 6 2016 at 21 36 51 ut extended areas of upper austria bavaria germany and the southwestern part of the czech republic were illuminated by a very bright bolide this bolide was recorded by instruments in the czech part of the european fireball network and it enabled complex and precise description of this event including prediction of the impact area so far six meteorites totaling 1473 g have been found in the predicted area the first pieces were recovered on march 12 2016 on a field close to the village of stubenberg bavaria stubenberg is a weakly shocked s3 fragmental breccia consisting of abundant highly recrystallized rock fragments embedded in a clastic matrix the texture the large grain size of plagioclase and the homogeneous compositions of olivine fa31 4 and pyroxene fs25 4 clearly indicate that stubenberg is an ll6 chondrite breccia this is consistent with the data on o ti and cr isotopes stubenberg does not contain solar wind implanted noble gases data on the bulk chemistry ir spectroscopy cosmogenic nuclides and organic components also indicate similarities to other metamorphosed ll chondrites noble gas studies reveal that the meteorite has a cosmic ray exposure cre age of 36 3 ma and that most of the cosmogenic gases were produced in a meteoroid with a radius of at least 35 cm this is larger than the size of the meteoroid which entered the earth s atmosphere which is constrained to 20 cm from short lived radionuclide data in combination this might suggest a complex exposure history for stubenberg

dynamic crystallization of chondrule melts of porphyritic and radial pyroxene composition abstract dynamic crystallization experiments in which heterogeneous nucleation is an important variable have been completed on four melts of chondrule composition compositions were chosen to best represent chondrules with porphyritic pyroxene and radial pyroxene textures experimental results show that heterogeneous nucleation is essential for the formation of porphyritic textures without preexisting nuclei too much supercooling is established before crystallization is initiated and the textures are more likely to be dendritic or radial in the near total absence of nuclei radial textures can form at cooling rates as slow as 5 c hr in this study by varying the heterogeneous nucleation conditions and having a melt in which the appropriate phases are stable or metastable analogs to most of the recognized chondrule textures can be produced in a single melt composition olivine inclusions in pyroxene can form readily during an experiment from a starting material which did not initially contain olivine crystals thus care must be taken in the assumption that olivine inclusions in pyroxene represent preexisting crystals

frequency dependent attenuation of shear waves in the crust of the southern kanto area japan the attenuation characteristics of shear waves in the crust of the southern kanto area central japan were estimated using strong motion data including acceleration data recorded in the pre tertiary basement rocks by means of downhole observation the quality factor qs f was determined for a range of discrete frequencies from 0 5 to 16 hz from the analysis of data from 13 local earthquakes with focal depths of less than about 50 km that occurred in the philippine sea plate and in the boundary zone between the lower part of the eurasian plate and the upper part of the philippine sea plate the estimated 1 qs f shows a peaked structure in this frequency range on the assumption that the geometrical spreading exponent is 1 body waves the estimated peak 1 qs f is of the order of 10 2 at 0 8 hz

volcanology history and myths of the lake albano maar colli albani volcano italy abstract the polygenetic albano maar is the most recent centre of the colli albani volcano located just few kilometres to the south east of roma presently the maar hosts a 167 5 m deep crater lake the deepest in europe the maar is to be considered quiescent as phreatic activity is documented throughout the holocene this paper illustrates the close relationships between the activity of the maar and the history of settlement in the roman region as recorded in the geology archaeology history and legends of the area severe fluctuations of the groundwater table and catastrophic overflows of the lake albano from the maar rim had occurred prior to and after the early prehistoric settlements dated in the maar area at the eneolithic times ca iii millennium b c repeated lahars occurred along the northwestern slope of the maar filling in the paleodrainage network and forming a vast plain paleohydraulic analyses on fluvial and lahar deposits originated from the holocene phreatic activity of the albano maar indicate sediment water flows in excess of hundreds of cubic metres per second absolute age determinations of the paleosoil underlying one of the most recent deposits of the lahar succession at 5800 100 yr b p 14 c cal are in perfect agreement with the age of the overlying eneolithic age settlements the last catastrophic overflow is described in the roman literature as a consequence of the anger of poseidon against the romans in 398 b c for their war against the etruscans in 394 b c the romans decided to prevent the repetition of such events by the excavation through the maar crater wall of a 1 5 km long drain tunnel which is still operational keeping the lake 70 m below the lowest point of the maar rim this tunnel drain may be regarded as the first prevention device for volcanic hazard in history and shows an unprecedented development of the engineering technology under the pressure of hazard perception the surprising and still largely unknown results of this study are very important to redefine the hazard of the roman region

metal veins in the kernouve h6 s1 chondrite evidence for pre or syn metamorphic shear deformation abstract kernouve is an h6 chondrite that experienced a very small degree of late stage shock loading s1 however kernouve contains fe ni metal vein like structures whose formation have been attributed to an early impact event to establish the formation conditions of metal veins in kernouve we examined the three dimensional 3d arrangement of metal vein like structures and typical metal grains in two samples of kernouve with x ray microtomography ct at resolutions of 11 m voxel we additionally investigated the 3d structure of the porosity present in kernouve using ct at two different resolutions 3 and 11 m voxel these data and optical microscopy support the hypothesis that kernouve has experienced little post metamorphic shock however the moderate 5 8 vol porosity of kernouve is in the form of intergranular voids rather than cracks which indicates any cracking that may have existed in the relatively brittle silicate grains was annealed we estimate that 70 80 of the primordial porosity in kernouve was removed by impact related compaction moreover we found no collective orientation of metal grains so high metamorphic temperatures following compaction erased any common orientation of metal grains due to compaction we propose that the metal vein structures can be explained as a pre or syn metamorphic shock induced process which we infer was primarily shear deformation with some uniaxial compaction also occurring the coarse metal veins probably formed by accumulation of ductile metal grains along shear zones a process that would have been facilitated by having an already warm h chondrite parent body when shock occurred i e syn metamorphic shock the complexity of shape including numerous tendrils expanding from the primary structure of the veins in kernouve is likely due to the coalescence of metal by metamorphic growth after the shear event the metal veins in kernouve thus appear to record evidence for early shock induced metal mobilization and the maximum shock pressure experienced by kernouve may have been 21 gpa our study suggests that collision induced segregation of metal occurred at an early stage in low gravity planetesimals consistent with the idea that this process could have been important for the differentiation of such objects

a survey of clasts and large chondrules in ordinary chondrites we report the results of a survey of clasts and large 5 mm chondrules macrochondrules within the 833 ordinary chondrites of the natural history museum collection thirty six macrochondrules and 24 clasts were identified and studied macrochondrules have textures and mineral assemblages like normal chondrules and so share a common origin clasts show evidence for fracturing from larger bodies and can be classified as either 1 chemically fractionated if they have major and trace element compositions differing substantially from most chondrules and clasts 2 impact melt clasts if they have microporphyritic textures and signs that indicate they are derived from shock melted chondritic material 3 microporhyritic clasts if they are similar to the last category but lack evidence for derivation through shock melting or 4 indeterminate clasts forming a diverse class that includes all those clasts that do not fit into the other categories

opaque minerals in the matrix of the bishunpur ll3 1 chondrite constraints on the chondrule formation environment abstract the chemistry and mineralogy of a group of opaque mineral assemblages in the matrix of the bishunpur ll3 1 ordinary chondrite provide insight into the nebular environment in which they formed the assemblages consist of a kamacite fe ni core that is rimmed by troilite fes and fayalite fe2sio4 accessory phases in the rims include silica sio2 chromite fecr2o4 whitlockite ca3 po4 2 maricite fenapo4 magnetite fe3o4 and tetrataenite feni we suggest that the metal melted in and equilibrated with an igneous chondrule under high temperature reducing conditions in this environment the molten alloys incorporated varied amounts of si ni p cr and co depending on the oxygen fugacity and temperature of the melt some of the metal was subsequently expelled from the chondrule interiors into the surrounding nebular gas as the temperature dropped the alloy solidified and volatile elements corroded the metal the main reaction products were troilite and fayalite thermodynamic equilibrium calculations are used to constrain the conditions under which these two phases can form simultaneously in the solar nebula kinetic factors are used to place a lower limit on the formation temperature we determine that the metal corroded between 1173 and 1261 k at a total pressure in the range of 10 5 0 to 10 4 1 bars and a dust gas ratio of 302 to 355 x relative to solar composition these conditions are consistent with our model that the metal corroded in a dust rich region of the solar nebula that was cooling after a chondrule formation event

post shock annealing of miller range 99301 ll6 implications for impact heating of ordinary chondrites mil 99301 is an ll chondrite that has experienced successive episodes of thermal metamorphism shock metamorphism and annealing the first recognizable petrogenetic episode resulted in thermal metamorphism of the rock to petrologic type 6 as indicated by homogeneous olivine compositions significant textural recrystallization and the presence of coarse grains of plagioclase metallic fe ni and troilite the source of heat for this thermal episode is not identified the rock also experienced shock metamorphism to shock stage s4 as indicated by extensive silicate darkening caused by the dispersion within silicate grains of thin chromite melt veins and trails of metallic fe ni and troilite blebs polycrystalline troilite myrmekitic plessite a relatively high occurrence abundance oa of metallic cu 3 6 the presence of numerous chromite plagioclase assemblages and coarse grains of low ca clinopyroxene with polysynthetic twinning the shock event responsible for these effects must have occurred after the epoch of thermal metamorphism to type 6 levels otherwise the polycrystallinity of the troilite would have disappeared and the low ca clinopyroxene would have transformed into orthopyroxene despite abundant evidence of strong shock olivine and plagioclase in mil 99301 exhibit sharp optical extinction consistent with shock stage s1 and characteristic of an unshocked rock this implies that an episode of post shock annealing healed the damaged olivine and plagioclase crystal lattices and thereby changed undulose extinction into sharp extinction the rock was probably annealed to metamorphic levels approximating petrologic type 4 more significant heating would have transformed the low ca clinopyroxene into orthopyroxene it is not plausible that an episode of annealing occurring after the epoch of thermal metamorphism could have been caused by the decay of 26al because this isotope would have decayed away by that time impact heating is a more plausible source of post metamorphic annealing of rocks in the vicinity of impact craters on low density high porosity asteroids with rubble pile structures

revised model calculations for the thermal histories of ordinary chondrite parent bodies recent measurements of ordinary chondrite physical and thermal properties along with new geothermometry studies have provided the necessary parameters for updating a previously proposed model miyamoto et al 1981 for the thermal evolution and internal structure of ordinary chondrite parent bodies model calculations assumed a heat source term derived from the decay of 26al justification is provided differences from the previous model include varying the thermal diffusivity parameter with increasing temperature and decreasing porosity using variable physical and thermal parameters to provide end member models and incorporating a shortened thermal history of 60 ma obtained from new pb pb chronology of phosphates rather than 100 ma times of isotopic closure in chondrite phosphates overlap the thermal model estimates and postmetamorphic cooling rates from the model approximately coincide in both trend and magnitude with metallographic and fission track cooling rate data model calculations attempt to match peak metamorphic conditions in the central portions of these bodies and yield accretion ages between 1 4 to 3 1 ma after calcium aluminum inclusion cai formation model calculations also predict that both the h and the l chondrite parent asteroids consisted of 80 equilibrated and 20 unequilibrated chondritic material and that their original radii ranged from 80 to 95 km

stones from mohave county arizona multiple falls in the franconia strewn field one of the most productive and well sampled dense collection areas for meteorites on earth is the franconia strewn field in mohave county arizona which since 2002 has yielded hundreds of meteorites in an ellipsoidal area approximately 5 16 km across based on petrographic mineral chemical and terrestrial age data we conclude that among 14 meteorites examined there are at least 6 and possibly 8 distinct meteorites represented which fell over a period of approximately 0 20 kyr ago these include equilibrated h chondrites such as franconia h5 and buck mountains bm 001 h6 h3 6 breccias such as buck mountains wash and bm 004 and l6 chondrites such as bm 002 and bm 003 which may be paired palo verde mine and bm 005 to confidently pair such meteorites often requires thorough petrographic examination mineral chemical analyses and terrestrial ages we estimate that 50 10 of the larger specimens in this area are paired yielding a relatively high value of approximately 2 3 2 9 distinct meteorites km 2 the meteorite flux estimated for franconia area is higher than the flux inferred from contemporary fireball data for larger masses we suggest that one large h3 6 meteoroid fell in the area most likely that of buck mountains wash approximately 4 kyr ago which produced an elliptical strewn field with masses generally increasing toward one end and which raised the meteorite productivity in the recovery area

repeating earthquake activities associated with the philippine sea plate subduction in the kanto district central japan a new plate configuration revealed by interplate aseismic slips abstract we detect repeating earthquakes associated with the philippine sea plate subduction to reveal the plate configuration in the kanto district we find 140 repeating earthquake groups with 428 events by waveform similarity analysis most repeating earthquakes in the eastern part of the kanto district occur with a regular time interval they have thrust type focal mechanisms and are distributed near the upper surface of the philippine sea plate these observations indicate that the repeating earthquakes there occur as a repetition of ruptures on the isolated patches distributed on the plate boundary owing to the concentration of stress caused by aseismic slips in the surrounding areas this shows that the distributions of repeating earthquakes suggest the aseismic slips in the surrounding areas of small patches we determine spatial distributions of repeating earthquakes in the eastern part of the kanto district and find that they correspond to the upper boundary of the philippine sea plate that is the upper boundary of the oceanic crust layer of the philippine sea plate the plate geometry around choshi is newly constrained by repeating earthquake data and a rather flat geometry in the eastern part of the kanto district is revealed the obtained geometry suggests uplift of the philippine sea plate due to the collision with the pacific plate beneath choshi repeating earthquakes in the western part of the kanto district have extremely shorter recurrence times and their focal mechanisms are not of the thrust types these repeating earthquakes are classified as burst type activity and likely to occur on the preexistent fault planes which are distributed around the collision zone between the philippine sea plate and the inland plate the variation among the repeating earthquake activities in the kanto district indicates that regular repetition of repeating earthquakes is possible only on the plate boundary with a smooth and simple geometry

large silica rich igneous textured inclusions in the buzzard coulee chondrite condensates differentiates or impact melts we studied three large 2 4 mm diameter igneous textured inclusions in the buzzard coulee h4 chondrite using microanalytical techniques olm sem empa sims to better elucidate the origins of igneous inclusions in ordinary chondrites the inclusions are clasts that come in two varieties 1 white inclusions bz 1 and bz 2 represent a nearly holocrystalline assemblage of low ca and high ca pyroxene 63 66 area and cristobalite 33 36 and 2 tan inclusion bz 3 is glass rich approximately 60 with low ca and high ca pyroxene phenocrysts the bulk compositions of the inclusions determined by modal reconstruction are all sio2 rich approximately 67 wt for bz 1 and bz 2 approximately 62 for bz 3 but bz 3 is enriched in incompatible elements e g ree approximately 4 5 ci abundances whereas bz 2 and bz 1 are depleted in those elements that are most incompatible in pyroxene e g la ho approximately 0 15 0 4 ci abundances these bulk compositions do not resemble what one would expect for partial or complete shock melting of a chondritic precursor and show no evidence for overall volatility control we infer that the inclusions originated through igneous differentiation and feo reduction with bz 3 forming as an andesitic partial melt approximately 30 40 partial melting of an h chondrite precursor and bz 1 and bz 2 forming as pyroxene cristobalite cumulates from an si rich melt we suggest that both types of melts experienced a period of transit through a cold low pressure space environment in which cooling feo reduction and interaction with a vapor occurred melts may have been lofted into space by excavation or splashing during collisions or by pyroclastic volcanism our results indicate intriguing similarities between the inclusions in buzzard coulee and the silicates in some iron iie type and stony iron iva type meteorites suggesting a genetic relationship

contribution of early impact events to metal silicate separation thermal annealing and volatile redistribution evidence in the pultusk h chondrite three dimensional x ray tomographic reconstructions and petrologic studies reveal voluminous accumulations of metal in pultusk h chondrite at the contact of these accumulations the chondritic rock is enriched in troilite the rock contains plagioclase rich bands with textures suggesting crystallization from melt unusually large phosphates are associated with the plagioclase and consist of assemblages of merrillite and fluorapatite and chlorapatite the metal accumulations were formed by impact melting rapid segregation of metal sulfide melt and the incorporation of this melt into the fractured crater basement the impact most likely occurred in the early evolution of the h chondrite parent body when post impact heat overlapped with radiogenic heat this enabled slow cooling and separation of the metallic melt into metal rich and sulfide rich fractions this led to recrystallization of chondritic rock in contact with the metal accumulations and the crystallization of shock melts phosphorus was liberated from the metal and subsumed by the silicate shock melt owing to oxidative conditions upon slow cooling the melt was also a host for volatiles upon further cooling phosphorus reacted with silicates leading to the formation of merrillite while volatiles partitioned into the residual halogen rich dry fluid in the late stages the fluid altered merrillite to patchy cl f apatite the above sequence of alterations demonstrates that impact during the early evolution of chondritic parent bodies might have contributed to local metal segregation and silicate melting in addition postshock conditions supported secondary processes compositional textural equilibration redistribution of volatiles and fluid alterations

shock compaction heating and collisional processes in the production of type 3 ordinary chondrites lessons from the nearly unique l3 chondrite melt breccia northwest africa 8709

analysis and interpretation of the heterogeneous rupture process application of the empirical green s function method and nonlinear inversion technique to large earthquakes abstract heterogeneous rupture processes were revealed using an empirical green s function egf method and a nonlinear inversion technique three events the 1980 east izu peninsula earthquake the 1983 japan sea earthquake and the 1987 east chiba earthquake are studied kernel events used as empirical green s functions were selected among the foreshocks and aftershocks the dimension and orientation of the fault plane were evaluated from the aftershock distribution and main shock fault plane solution a moment ratio between the main shock and the kernel event was estimated in order to identify the number of subfaults strong motion waveforms recorded at near distances were inverted to estimate moment release rupture time and rise time at each subfault with the stress drop calculated from the moment release and rise time distributions of these faulting parameters can be related to the aftershock distribution and geological structures general features are that the moment release was large where the aftershock activity was low that the irregular rupture propagations detected here were related to geological structures such as a ridge junction seamount chains and other tectonic plate boundaries and that stress drop distributions show some relation to the pattern of aftershocks an exception is the small moment release at the bending corner of the 1983 japan sea earthquake where the aftershock activity was low with this method it is possible to extract not only the detailed source history but also information on geophysical structures

a unique high mn fe microgabbro in the parnallee ll3 ordinary chondrite nebular mixture or planetary differentiate from a previously unrecognized planetary body the study of planetary materials in chondritic meteorites constrains the compositional diversity of materials in different nebular environments and provides information on the degree of differentiation of early planetary bodies we studied a unique microgabbro fragment from the parnallee ll3 unequilibrated ordinary chondrite the fragment which was originally identified by its ophitic to sub ophitic texture exhibits features characteristic of lunar and terrestrial tholeiitic basalts extreme compositional zoning in clinopyroxene wo 10 en 65 fs 25 to wo 15 en 2fs 83 a multiply saturated major element composition similar to mid ocean ridge basalt with 3 1 wt na 2o and 0 15 wt k 2o and uniformly enriched rare earth elements c 10 c1 a high bulkmno feo ratio 0 064 distinguishes the microgabbro from other basaltic rocks and suggests the precursor material formed or reached equilibrium in a reducing environment however the absence of fe metal and the extreme enrichment of feo up to 40 wt in late crystallizing pyroxferroite requires the last crystallization event to have occurred in a relatively oxidizing environment we suggest the microgabbro formed by partial melting in a planetary body after removal of metallic fe examination of possible planetary source materials such as alkali rich eucritic material a volatile depleted c1 carbonaceous chondrite or h group chondrite shows that multiple stage fractionation is required to produce a melt with the feo mgo ratio of the microgabbro from these materials the increasing number of planetary igneous fragments observed in unequilibrated ordinary chondrites uoc suggests the picture of uoc as primitive assemblages of unprocessed material is overly simplistic

the origin of sulfide rimmed metal grains in ordinary chondrites abstract we report results from an experimental study of sulfide chemistry during metamorphism on ordinary chondrite parent bodies artificial ll chondrite material composed of silicate iron metal and sulfide grains was placed in sealed evacuated silica tubes and heated to either 500 c or 900 c these temperatures are representative peak metamorphic temperatures experienced by type 3 and type 6 ordinary chondrites respectively rapid sulfur mobilization occurs during heating and results in the formation of sulfide rims around the metal grains and sulfur loss from the original sulfide crystals the newly formed sulfide rims have two distinct layers that incorporate nearby silicate grains we also observe narrow sulfide trails that follow silicate grain boundaries and connect separate sulfide rimmed metal grains the morphologies of the sulfide rims suggest that vapor transport is the main mechanism for sulfur mobilization sulfur loss is observed along cracks and crystal boundaries of the initial sulfide grains after extensive reaction patches of iron metal appear at the outer edges of the sulfide crystals and large pore spaces form throughout the original sulfides the experimental metal sulfide assemblages resemble those found in low metamorphic grade ordinary chondrites this suggests metamorphism is mainly responsible for the observed metal sulfide textures in these chondrites

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

crystal chemistry of trioctahedral micas in the top sequences of the colli albani volcano roman region central italy abstract trioctahedral mica crystals are frequently found in the volcanoclastic products emplaced during the final stages of the activity of the colli albani volcano roman region central italy in the youngest phreatomagmatic deposits mica is found either as a minor mineral phase in holocrystalline ejecta scoriae and coherent pyroclastics or as loose phenocryst in incoherent pyroclastics based on optical and electron microscope investigations as well as crystal chemical and structural data the micas selected for this study were divided into two groups the first one encompassing brownish fe rich crystals type a phlogopites hereafter referred as t a with 0 68 from a petrological point of view the textural and chemical variations of t a phlogopites are compatible with fractional crystallization processes taking place within the magma chamber t b phlogopites show evidence of a ti oxy substitution mechanism thus suggesting high fo2 conditions textural and paragenetic features observed in t b phlogopite bearing rock samples indicate a genesis by thermal metamorphism of a siliceous dolomitic limestone with the input of a variable amount of a potassic magma possibly the same from which the t a phlogopites formed with the exception of one sample for which a different parental magma is suggested indeed there is an almost continuous spectrum of crystal chemical and structural parameters starting from t b and evolving towards t a phlogopites the t a phlogopites displays complex apparently meaningless relationships in their crystal chemical parameters thus indicating interplay of several substitution mechanisms they possibly formed in polybaric conditions since their cell volumes differ but the total size of the cations hosted in the octahedral sheet is the same

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

the role of the 1999 chamoli earthquake in the formation of ground cracks abstract the moderate magnitude chamoli earthquake that occurred in the garhwal higher himalaya in the early hours of march 29 1999 caused intense damage to the ground and mountain slopes of the alaknanda mandakini river valley and adjoining region a systematic survey of this induced damage was conducted immediately after the earthquake occurred prominent shallow cracks of significant length negligible width and indeterminate vertical extent conspicuously tensile in nature with little or no slip across the crack planes were observed in the ground at several places along the surveyed route these cracks had formed in the dynamic phase of the chamoli earthquake process that is in the period of time during which the earthquake generated seismic waves were passing through the geographic region of interest however we use the theory of earthquake induced static or long time stress changes to visualize such cracks at some selected sites where ground damage was relatively more intense and varied to suggest lower bound estimates of the dynamic stress contributions of the main shock for their formation based on the results of our analysis we conclude that just prior to the earthquake occurrence under the influence of the local ambient stress field the ground at these sites was already near failure in tension to this in its dynamic phase the chamoli earthquake induced stress perturbations having across the planes of the cracks i shear components which were nearly equal and opposite to similar components of the ambient stress field and ii normal tensile components necessary for triggering tensile failure of the ground the 3 or minimum principal stress component of the resultant perturbed failure stress field thus became sufficiently tensile while the transverse stresses became sufficiently insignificant this facilitated formation of major tensile cracks in the ground there our static estimates of the tensile stress changes at the different sites are in essence estimates of the minimal triggering stress perturbations that was provided by the chamoli earthquake in the dynamic state for the formation of the tensile cracks there

shock experiments with the h6 chondrite kernouve pressure calibration of microscopic shock effects shock recovery experiments were carried out on samples of the h6 chondrite kernouve at shock pressures of 10 15 20 25 30 35 45 and 60 gpa and preheating temperatures of 293 k low temperature experiments and 920 k high temperature experiments using a calculated equation of state of kernouve pressure pulse durations of 0 3 to 1 2 s were estimated the shocked samples were investigated by optical microscopy to calibrate the various shock effects in olivine orthopyroxene oligoclase and troilite the following pressure calibration is proposed for silicates 1 undulatory extinction of olivine gpa 2 weak mosaicism of olivine from 10 15 gpa to 20 25 gpa 3 onset of strong mosaicism of olivine at 20 25 gpa 4 transformation of oligoclase to diaplectic glass completed at 25 30 gpa low temperature experiments and at 20 25 gpa high temperature experiments 5 onset of weak mosaicism in orthopyroxene at 30 35 gpa low temperature experiments and at 25 30 gpa high temperature experiments and 6 recrystallization or melting of olivine starting at 45 60 gpa low temperature experiments and at 35 45 gpa high temperature experiments and completed above 45 60 gpa in the high temperature experiments troilite displays distinct differences between the samples shocked at low and high temperatures in the low temperature experiments the following effects can be observed in troilite 1 undulatory extinction up to 25 gpa 2 twinning up to 45 gpa 3 partial recrystallization from 30 to 60 gpa and 4 complete recrystallization 35 gpa whereas in the high temperature experiments troilite shows 1 complete recrystallization from 10 up to 45 gpa and 2 melting and crystallization above 45 gpa localized shock induced melting is observed in samples shocked to pressures 15 gpa in the high temperature experiments and 30 gpa for the low temperature experiments in the form of feni metal and troilite melt injections and intergrowths and as pockets and veins of whole rock melt obviously the onset and abundance of shock induced localized melting strongly depends on the initial temperature of the sample

seismotectonics beneath the tokyo metropolitan area japan effect of slab slab contact and overlap on seismicity 1 we first determine the configuration of the upper surface of the pacific pac slab beneath kanto japan from the distribution of interplate earthquakes relocated by an appropriate 1 d velocity model then traveltime tomography is carried out to estimate three dimensional seismic velocity structures around kanto using 735 520 p wave and 444 049 s wave arrival times from 6508 local earthquakes the obtained results suggest that the philippine sea phs slab is subducting to depths of 130 140 km without a gap even to the northwest of the izu collision zone we subsequently define the lateral extent of the contact zone between the bottom of the phs slab and the upper surface of the pac slab phs pac interface and reveal that the slab contact zone underlies a wider area beneath kanto in harmony with the kanto plain the downdip limit of interplate thrust type earthquakes on the pac slab is deepened by 30 km locally under the slab contact zone this deepening is probably caused by a lower temperature environment in the pac slab resulting from the overlap with the phs slab subducting above and consequent thermal shielding by the phs slab from the hot mantle wedge we detect an extremely low velocity anomaly in the easternmost portion of the phs slab which is probably attributable to serpentinization of mantle peridotite interplate earthquakes are almost absent along the phs pac interface overlain by the serpentinized mantle in the phs slab suggesting that ductile deformation takes place along the interface because of low viscosity of the serpentine

dynamic cyrstallization of chondrule melts of porphyritic olivine composition textures experimental and natural abstract melts of the same composition as has been defined for porphyritic olivine chondrules have been crystallized under controlled cooling conditions dynamic crystallization the full range of textures observed in such chondrules has been duplicated in the experimentally produced analogs the primary controlling factor in producing this range of textuures is the heterogeneous nucleation behavior in general if nuclei are present when cooling begins growth starts immediately at low degrees of supercooling and porphyritic textures result the shapes of the phenocyrsts depend on the growth rate which in turn depends on the cooling rate with high nucleation densities and modest to low cooling rates the textures are microporphyritic with generally equant euhedral phenocrysts as the nucleatio density decreases the phenocrysts become larger and as the cooling rate increases they become increasingly skeletal if nuclei are not present when cooling begins growth is delayed until subcritical sized embryos graduate to supercritical nuclei growth usually begins at some significant degree of supercooling depending on the cooling rate and how long it takes the embryos to become nuclei the shapes of the crystals depend on the degree of supercooling when growth is initiated and on the subsequent cooling rate the resulting textures vary from plate dendrites barred olivine chondrules to randomly oriented elongated skeletal crystals as the degree of supercooling and cooling rates decreases the results of a matrix of experiments set limits on the maximum melting temperatures of chondrule forming materials and the subsequent cooling rates based primarily on crystal shape the porphyritic textures develop best for this composition at melting temperatures less than 1590 c and cooling rates near 100 c hr and definitely less than 1000 c hr at cooling rates significantly less than 100 c hr the phenocrysts are generally larger than observed in chondrules and as cooling rates approach 1000 c hr they become more skeletal barred olivine chondrule textures form best from materials melted at higher temperatures and cooling rates in the range 1000 to 3000 c hr

investigation of the h7 ordinary chondrite watson 012 implications for recognition and classification of type 7 meteorites abstract despite the fact that the number of officially classified meteorites is now over 45 000 we lack a clearly defined sequence of samples from a single parent body that records the entire range in metamorphic temperatures from pristine primitive meteorites up to the temperatures required for extensive silicate partial melting here we conduct a detailed analysis of watson 012 an h7 ordinary chondrite to generate some clarity on the textural and chemical changes associated with equilibrium based silicate partial melting in chondritic meteorites to do this we compare the textures in the meteorite with those preserved in metamorphic contact aureoles on earth the most distinctive texture generated by the partial melting that affected watson 012 is an extensively interconnected plagioclase network which is clearly observable with a petrographic microscope enlarged metal troilite grains are encapsulated at widenings in this plagioclase network and this is clearly visible in reflected light together with these features we define a series of other characteristics that can be used to more clearly classify chondritic meteorites as being of petrologic type 7 to provide comprehensive evidence of silicate partial melting and strengthen the case for using simple petrographic observations to classify similar meteorites we use high resolution x ray computed tomography to demonstrate that the plagioclase network has a high degree of interconnectedness and crystallised as large cm scale skeletal crystals within an olivine orthopyroxene clinopyroxene framework essentially pseudomorphing a melt network back scattered electron imaging and element mapping are used to show that some of the clino and orthopyroxene in watson 012 also crystallised from silicate melt and the order of crystallisation was orthopyroxene clinopyroxene plagioclase x ray diffraction data supported by bulk geochemistry are used to show that plagioclase and ortho and clinopyroxene were added to the watson 012 sample by through flowing basaltic melt along with the absence of glass and granophyre this interconnected network of coarse grained skeletal plagioclase indicates that the sample cooled slowly at depth within the parent body the evidence of melt flux indicates that watson 012 formed in the presence of a gravitational gradient and thus at significant distance from the centre of the h chondrite parent body the gravitational gradient at the centre would be zero our interpretation is that incipient silicate partial melting in watson 012 occurred when a region of radiogenically heated h6 material located at considerable depth possibly at 15 20 km from surface was heated by an additional ca 200 300 c in association with a large shock event due to insulation at depth within an already hot parent body the post shock temperature equilibrated and remained above the solidus long enough for widespread equilibrium based silicate partial melting and for melt to migrate although the observed melting may have been facilitated by additional heating from an impact event this is not an example of instantaneous shock melting which produces thermal disequilibrium at short length scales and distinctly different textures a small number of h l and ll chondrites have been previously classified as being of petrologic type 7 with our new criteria to support that classification these represent our best opportunity to explore the transition from high temperature sub solidus metamorphism through the onset of silicate partial melting in three different parent bodies

interaction between two subducting plates under tokyo and its possible effects on seismic hazards 1 underneath metropolitan tokyo the philippine sea plate phs subducts to the north on top of the westward subducting pacific plate pac new relatively high resolution tomography images the phs as a well defined subduction zone under western kanto plain as pac shoals under eastern kanto the phs lithosphere is being thrusted into an increasingly tighter space of the pac eurasian mantle wedge as a result zones of enhanced seismicity appear under eastern kanto at the top of phs internal to phs and also at its contact with pac these zones are located at depths greater than the causative fault of the disastrous 1923 great tokyo megathrust earthquake in the vicinity of several well located historical damaging m6 and m7 earthquakes thus a rather unique interaction between subducting plates under tokyo may account for additional seismic hazards in metropolitan tokyo

dynamic versus static stress triggering and friction parameters inferences from the november 23 1980 irpinia earthquake this paper concentrates on the problem of fault interaction and earthquake triggering through the 1980 irpinia italy sequence more specifically this paper deals with the problem of the triggering of the second subevent by the mainshock the interaction between the two segments is modeled through a dynamic coulomb failure function the aims of this paper are first to discriminate between the dynamic and the static stress effects on the triggering if these effects exist second to estimate the fault strength relative to the initial state of stress third to determine the parameters of a slip dependent friction law that lead to the observed delay of 20 s numerical simulations show that the critical slip dc may range from 0 03 m up to 1 7 m and that the initial slope of the friction law 0 must be lower than 0 04 m 1 we show that the relative magnitude of the fault strength and the initial state of stress govern the existence and value of a dc lower threshold under which the fault always ruptures before 13 s a close to failure fault is not consistent with a critical slip dc less than 0 8 m whereas small values of dc typically 0 03 m imply a far from failure fault general results concern the effect of a dynamic stress pulse we show that an event can be triggered by a transient stress pulse and that in this case the event can have an initiation duration much longer than the pulse duration we show that it is possible to explain both the triggering and the time delay only with the effect of the transient stress pulse this may explain aftershock triggering even in regions of negative coulomb failure function or long distance triggering of earthquakes by propagating waves

widespread evidence for high temperature formation of pentlandite in chondrites abstract by investigating the compositional and textural evolution of sulfides within a wide range of relatively pristine aqueously altered and thermally metamorphosed chondrites we constrain the equilibration temperatures of sulfide minerals and compare them to the metamorphic history of their host meteorite sulfides in mighei like carbonaceous chondrites are complex as they equilibrated mostly between 100 and 135 c but some may have equilibrated at temperatures up to 600 c this is consistent with some cm chondrite sulfides forming at high temperature during chondrule cooling and others during low temperature aqueous alteration and or annealing karoonda like carbonaceous chondrite sulfides equilibrated between 500 and 230 c which is consistent with formation during cooling and annealing after thermal metamorphism sulfides in the ll chondrites equilibrated between 600 and 230 c and are consistent with formation during chondrule cooling for semarkona ll3 00 and during cooling after thermal metamorphism for the equilibrated samples types 4 6 sulfides in the rumuruti like r chondrites equilibrated between 600 and 500 c and are consistent with formation after thermal metamorphism the sulfides within the brachinite equilibrated between 600 and 400 c consistent with formation during cooling after thermal metamorphism contrary to the assertion that pentlandite is solely the product of low temperature aqueous alteration in many chondrite groups this study suggests that most sulfides in chondrites are formed at or upon cooling from high temperature the evaluation of a single mineral system within samples that retain petrographic context is vital to the interpretation of formation and alteration processes recorded by small extraterrestrial samples such as those that have been returned by the spacecraft missions stardust and hayabusa and will be returned by osiris rex and hayabusa2

relationships among physical properties as indicators of high temperature deformation or post shock thermal annealing in ordinary chondrites collisions and attendant shock compaction must have been important for the accretion and lithification of planetesimals including the parent bodies of chondrites but the conditions under which these occurred are not well constrained a simple model for the compaction of chondrites predicts that shock intensity as recorded by shock stage should be related to porosity and grain fabric to test this model we studied sixteen ordinary chondrites of different groups h l ll using x ray computed microtomography ct to measure porosity and metal fabric ideal gas pycnometry and 3d laser scanning to determine porosity and optical microscopy om to determine shock stage these included a subsample of six chondrites previously studied using transmission electron microscopy tem to characterize microstructures in olivine combining with previous data results support the simple model in general but not for chondrites with low shock porosity foliation low spf chondrites these include kernouve h6 portales valley h6 7 butsura h6 park l6 gro 85209 l6 estacado h6 mil 99301 ll6 spade h6 and queen s mercy h6 among others the data for these meteorites are best explained by high ambient heat during or after shock low spf chondrites tend to have older 40ar 39ar ages 4435 4526 ma than other non low spf type 6 chondrites in this study we conclude that the h l and ll asteroids all were shock compacted at an early stage while warm with collisions occurring during metamorphic heating of the parent bodies results ultimately bear on whether chondrite parent bodies have internal structures more akin to a metamorphosed onion shell or metamorphosed rubble pile and on the nature of accretion and lithification processes for planetesimals

lithification of gas rich chondrite regolith breccias by grain boundary and localized shock melting we studied the fine grained matrices 150 m of 14 gas rich ordinary chondrite regolith breccias in an attempt to decipher the nature of the lithification process that converted loose regolith material into consolidated breccias we find that there is a continuous gradation in matrix textures from nearly completely clastic class a to highly cemented class c breccias in which the remaining clasts are completely surrounded by interstitial shock melted material we conclude that this interstitial material formed by shock melting in the porous regolith in general the abundances of solar wind implanted 4he and 20ne are inversely correlated with the abundance of interstitial shock melted feldspathic material chondrites with the highest abundance of interstitial melted material class c experienced the highest shock pressures and temperatures and suffered the most extensive degassing it is this interstitial feldspathic melt that lithifies and cements the breccias together those breccias with very little interstitial melt class a are the most porous and least consolidated

deformation and thermal histories of ordinary chondrites evidence for post deformation annealing and syn metamorphic shock abstract we show that olivine microstructures in seven metamorphosed ordinary chondrites of different groups studied with optical and transmission electron microscopy can be used to evaluate the post deformation cooling setting of the meteorites and to discriminate between collisions affecting cold and warm parent bodies the l6 chondrites park shock stage s1 bruderheim s4 leedey s4 and morrow county s5 were affected by variable shock deformation followed by relatively rapid cooling and probably cooled as fragments liberated by impact in near surface settings in contrast kernouve h6 s1 portales valley h6 7 s1 and mil 99301 ll6 s1 appear to have cooled slowly after shock probably by deep burial in warm materials in these chondrites post deformation annealing lowered apparent optical strain levels in olivine additionally kernouve morrow county park mil 99301 and possibly portales valley show evidence for having been deformed at an elevated temperature 800 1000 c the high temperatures for morrow county can be explained by dynamic heating during intense shock but kernouve park and mil 99301 were probably shocked while the h l and ll parent bodies were warm during early endogenically driven thermal metamorphism thus whereas the s4 and s5 chondrites experienced purely shock induced heating and cooling all the s1 chondrites examined show evidence for static heating consistent with either syn metamorphic shock kernouve mil 99301 park post deformation burial in warm materials kernouve mil 99301 portales valley or both the results show the pitfalls in relying on optical shock classification alone to infer an absence of shock and to construct cooling stratigraphy models for parent bodies moreover they provide support for the idea that secondary metamorphic and tertiary shock processes overlapped in time shortly after the accretion of chondritic planetesimals and that impacts into warm asteroidal bodies were common

foreshocks and pre events associated with the nucleation of large earthquakes we propose a theoretical model which can explain the occurrence of foreshocks and pre events associated with the nucleation of large earthquakes we consider a broad weak zone with a locally strong part asperity on a fault plane in a two dimensional framework and examine the transition process from quasistatic nucleation to high speed rupture propagation through numerical simulations the dynamic rupture of the asperity occurs in three different manners as aseismic slip foreshock or pre event depending on the peak stress of the asperity in all cases the rupture of the asperity accelerates the nucleation of main rupture

cause of m 7 intraslab earthquakes beneath the tokyo metropolitan area japan possible evidence for a vertical tear at the easternmost portion of the philippine sea slab 1 we perform travel time tomography beneath kanto japan to obtain detailed structures of the wedge shaped serpentinized mantle previously observed in the philippine sea slab the results suggest that the western boundary of the serpentinized mantle serpentine boundary is subvertical and p and s wave velocities vary by 15 20 across it over the short distance of 10 km two intraslab earthquakes in 1921 m7 0 and 1987 east off chiba earthquake m6 7 are inferred to have occurred along the serpentine boundary accompanied by right lateral movement based on analyses of focal mechanisms and aftershock distribution a subvertical earthquake cluster penetrating the entire philippine sea slab is observed along the serpentine boundary and four earthquakes in the cluster have strike slip focal mechanisms similar to that of the 1987 earthquake focal mechanisms obtained for past large earthquakes and present day microearthquakes suggest a concentration of right lateral deformation along the mechanically weak serpentine boundary the philippine sea slab may have been torn in two along this boundary with the eastern portion being left behind relative to subduction of the western portion assuming that one of the large aftershocks m7 1 of the 1923 kanto earthquake m7 9 which occurred off the boso peninsula ruptured the same asperity as did the 1987 earthquake the slip deficit accumulated along the serpentine boundary during the 64 year interval is consistent with the fault slip of the 1987 earthquake interaction between the seismic slip along the plate interface and the serpentine boundary can explain the series of m7 class earthquakes before and after the 1923 kanto earthquake

mesoscale and microscale shock effects in the ll6 s4 chondrites saint severin and elbert a tale of two breccias

interplate coupling in the kanto district central japan deduced from geodetic data inversion and its tectonic implications abstract interplate coupling between the philippine sea phs the north american nam and the pacific pac plates in the kanto district central japan has been investigated through the inversion analysis of geodetic data using akaike s bayesian information criterion abic the data used for the analysis are annual rates of level changes 1972 1985 and horizontal length changes 1973 1990 which presumably represent average crustal movements during the interseismic period disregarding effects of steady plate subduction we may ascribe the observed crustal movements to the effects of locking or faulting on some parts of the plate boundaries in our model the effect of locking is represented by back slip on the plate boundary and that of faulting by forward slip the results of the inversion analysis show the existence of a strongly coupled area on the southwestern shallower part of the nam phs plate boundary which almost coincides with the faulting area of the 1923 kanto earthquake m 7 9 and a notable faulting area on the northeastern deeper part of the phs pac plate boundary in the southwestern strongly coupled area the rate of back slip reaches 3 5 cm yr and its direction is oriented n33 w which is almost opposite to the direction of fault slip s29 e at the time of the 1923 event this suggests that tectonic stress accumulation for the next large event is effectively proceeding there and its recurrence time is roughly estimated as 245 years the strongly coupled region is also recognized as corresponding to a recent seismic gap the inverted forward slip distribution on the phs pac plate boundary which has the average rate of 1 9 cm yr and the average direction of n56 e may be explained by aseismic northeastward slip in relation to the process to form a peculiar configuration of downward bend of the phs plate beneath the kanto district

mega chondrules and large igneous textured clasts in julesberg l3 and other ordinary chondrites vapor fractionation shock melting and chondrule formation abstract a petrographic microprobe study of large metal poor igneous textured objects in julesberg l3 and other ordinary chondrites suggests that they can be classified into two petrographic types mega chondrules and large lithic clasts and into two chemical types na poor and na rich mega chondrules show textural evidence of having solidified as freely floating melt droplets whereas lithic clasts formed by the fragmentation of larger objects possibly still larger mega chondrules barred olivine or barred olivine pyroxene textures are most common for mega chondrules whereas a variety of textures occur in large lithic clasts the two petrographic types cannot be distinguished on the basis of modal bulk or phase compositions sodium poor objects are characterized by 1 plagioclase or glass with mainly bytownite composition an70 90 typical 2 subchondritic na al ratios and typically subchondritic volatile element na k and mn abundances and 3 bulk chemical trends that resemble those expected for vapor fractionation processes some na poor objects may have formed by the melting of precursors that formed as condensates or vaporization residues others may have formed by the melting of precursors that formed by fractional condensation or fractional vaporization following vapor fractionation na poor objects or their precursors appear to have reequilibrated at lower temperatures which raised the bulk na content of the objects but not to the levels seen in na rich objects enrichments of fe2 na k and p on the margins of some na poor objects suggest that they partly reacted with volatile rich surroundings both before and after brecciation sodium rich objects are characterized by 1 plagioclase or glass with oligoclase or albite composition an2 25 2 roughly chondritic na al ratios and volatile element na k mn abundances and 3 bulk chemical trends similar to those shown by melt pocket glasses in ordinary chondrites sodium rich melt objects could have formed by the shock melting of chondritic precursors feldspathic compositions for some na rich melt objects can be explained by preferential shock melting of feldspar or feldspathic glass in chondritic target materials literature data imply that the same two chemical populations of objects na poor and na rich occur among smaller normal sized chondrules in type 3 ordinary chondrites suggesting that the same processes that affected large melt objects also affected chondrules

spade an h chondrite impact melt breccia that experienced post shock annealing the low modal abundances of relict chondrules 1 8 vol and of coarse i e 200 m size isolated mafic silicate grains 1 8 vol in spade relative to mean h6 chondrites 11 4 and 9 8 vol respectively show spade to be a rock that has experienced a significant degree of melting various petrographic features e g chromite plagioclase assemblages chromite veinlets silicate darkening indicate that melting was caused by shock plagioclase was melted during the shock event and flowed so that it partially to completely surrounded nearby mafic silicate grains during crystallization plagioclase developed igneous zoning low ca pyroxene that crystallized from the melt or equilibrated with the melt at high temperatures acquired relatively high amounts of cao metallic fe ni cooled rapidly below the fe ni solvus and transformed into martensite subsequent reheating of the rock caused transformation of martensite into abundant duplex plessite ambiguities exist in the shock stage assignment of spade the extensive silicate darkening the occurrence of chromite plagioclase assemblages and the impact melted characteristics of spade are consistent with shock stage s6 low shock stage s2 is indicated by the undulose extinction and lack of planar fractures in olivine this suggests that spade reached a maximum prior shock level equivalent to stage s6 and then experienced post shock annealing probably to stage s1 these events were followed by a less intense impact that produced the undulose extinction in the olivine characteristic of shock stage s2 annealing could have occurred if spade were emplaced near impact melts beneath the crater floor or deposited in close proximity to hot debris within an ejecta blanket spade firmly establishes the case for post shock annealing this may have been a common process on oc asteroids

shock and annealing in the amphibole and mica bearing r chondrites mil 11207 r6 and lap 04840 r6 contain hornblende and phlogopite mil 07440 r6 contains accessory titan phlogopite and no hornblende all three meteorites have been shocked mil 11207 contains extensive sulfide veins pyroxene that formed from dehydrated hornblende and an extensive network of plagioclase glass mil 07440 contains chromite plagioclase assemblages chromite veinlets and blebs pincer shaped plagioclase patches but no sulfide veins lap 04840 contains olivine grains with chromite bleb laden cores and opaque free rims rare grains of pyroxene that formed from dehydrated hornblende and no sulfide veins these meteorites appear to have been heated to maximum temperatures of approximately 700 900 c under conditions of moderately high ph2o perhaps 250 500 bars all three samples underwent postshock annealing during this process olivine crystal lattices healed giving the rocks the appearance of shock stage s1 and diffusion of fe and s from thin sulfide veins to coarse sulfide grains caused the veins to disappear in mil 07440 and lap 04840 this latter process apparently also occurred in most s1 s2 ordinary chondrites of high petrologic type the pressure temperature conditions responsible for forming the amphibole and mica in these rocks may have been present at depths of a few tens of kilometers as suggested in the literature a giant impact or a series of smaller impacts would then have been required to excavate the hornblende and biotite bearing rocks and bring them closer to the surface it was in that latter location where the samples were shocked deposited in a hot ejecta blanket of low thermal diffusivity and annealed

shock and thermal history of northwest africa 4859 an annealed impact melt breccia of ll chondrite parentage containing unusual igneous features and pentlandite abstract northwest africa 4859 nwa 4859 is a meteorite of ll chondrite parentage that shows unusual igneous features and contains widely distributed pentlandite the most obvious unusual feature is a high proportion of large 3 cm diameter igneous textured enclaves lites interpreted as shock melts that were intruded into an ll chondrite host one such lite appears to have been produced by whole rock melting of ll chondrite initial rapid partial crystallization and subsequent slow cooling of the residual melt in the host to produce a differentiated object other unusual features include mm sized overgrowth objects fine grained plagioclase rich bands and coarse troilite 7 mm across grains all these features are interpreted as having crystallized from melts produced by a single transient shock event followed by slow cooling a subsequent shock event of moderate s3 intensity produced veining and transformed some of the pyroxene into the clinoenstatite polytype pentlandite together with associated troilite in nwa 4859 probably formed by the breakdown of a monosulfide precursor phase at low temperature 230 c following the second shock event nwa 4859 is interpreted to be an unusual impact melt breccia that contains shock melt which crystallized in different forms at depth within the parent body

chromite plagioclase assemblages as a new shock indicator implications for the shock and thermal histories of ordinary chondrites abstract chromite in ordinary chondrites oc can be used as a shock indicator a survey of 76 equilibrated h l and ll chondrites shows that unshocked chromite grains occur in equant subhedral and rounded morphologies surrounded by silicate or intergrown with metallic fe ni and or troilite some unmelted chromite grains are fractured or crushed during whole rock brecciation others are transected by opaque veins the veins form when impacts cause localized heating of metal troilite intergrowths above the fe fes eutectic 988 c mobilization of metal troilite melts and penetration of the melt into fractures in chromite grains chromite plagioclase assemblages occur in nearly every shock stage s3 s6 oc the assemblages range in size from 20 300 m and consist of 0 2 20 m size euhedral subhedral anhedral and rounded chromite grains surrounded by plagioclase or glass of plagioclase composition plagioclase has a low impedance to shock compression heat from shock melted plagioclase caused adjacent chromite grains to melt chromite grains crystallized from this melt those chromite grains in the assemblages that are completely surrounded by plagioclase are generally richer in al 2 o 3 than unmelted matrix chromite grains in the same meteorite chromite veinlets typically 0 5 2 m thick and 10 300 m long occur typically in the vicinity of chromite plagioclase assemblages the veinlets formed from chromite plagioclase melts that were injected into fractures in neighboring silicate grains chromite crystallized in the fractures and the residual plagioclase rich melt continued to flow eventually pooling to form plagioclase rich melt pockets chromite rich chondrules consisting mainly of olivine plagioclase normative mesostasis and 5 15 vol chromite occur in many shocked oc and oc regolith breccias but they are absent from primitive type 3 oc they may have formed by impact melting chromite plagioclase and adjacent mafic silicates during higher energy shock events the melt was jetted from the impact site and formed droplets due to surface tension crystallization of these droplets may have commenced in flight prior to landing on the parent body surface chromite plagioclase assemblages and chromite veinlets occur in 25 out of 25 shock stage s1 oc of petrologic type 5 and 6 that i examined although these rocks contain unstrained olivine with sharp optical extinction most possess other shock indicators such as extensive silicate darkening numerous occurrences of metallic cu polycrystalline troilite and opaque veins it seems likely that these rocks were shocked to levels at least as high as shock stage s3 and then annealed by heat generated during the shock event during annealing the olivine crystal lattices healed but other shock indicators survived published ar ar age data for some s1 oc indicate that many shock and annealing events occurred very early in the history of the parent asteroids the common occurrence of shocked and annealed oc is consistent with collisions being a major mechanism responsible for metamorphosing oc

orogens and slabs vs their direction of subduction abstract subduction zones appear primarily controlled by the polarity of their direction i e w directed or e to nne directed probably due to the westward drift of the lithosphere relative to the asthenosphere the decollement planes behave differently in the two end members in the w directed subduction zone the decollement of the plate to the east is warped and subducted whereas in the e to nne directed it is ramping upward at the surface there are w directed subduction zones that work also in absence of active convergence like the carpathians or the apennines w directed subduction zones have shorter life 30 40 ma than e or ne directed subduction zones even longer than 100 ma the different decollements in the two end members of subduction should control different ptt paths and therefore generate variable metamorphic assemblages in the associated accretionary wedges and orogens these asymmetries also determine different topographic and structural evolutions that are marked by low topography and a fast eastward migrating structural wave along w directed subduction zones whereas the topography and the structure are rapidly growing upward and expanding laterally along the opposite subduction zones the magmatic pair calc alkaline and alkaline tholeiitic volcanic products of the island arc and the back arc basin characterise the w directed subduction zones magmatic rocks associated with e or ne directed subduction zones have higher abundances of incompatible elements and mainly consist of calc alkaline shoshonitic suites with large volumes of batholithic intrusions and porphyry copper ore deposits the subduction zones surrounding the adriatic plate in the central mediterranean confirm the differences among subduction zones as primarily controlled by the geographic polarity of the main direction of the slab the western margin of the adriatic plate contemporaneously overridden and underthrust europe toward the west to generate respectively the alps and the apennines while the eastern margin subducted under the dinarides hellenides these belts confirm the characters of the end members of subduction zones as a function of their geographic polarity similarly to the pacific subduction zones

the formation and alteration of the renazzo like carbonaceous chondrites iii toward understanding the genesis of ferromagnesian chondrules to better understand the formation conditions of ferromagnesian chondrules from the renazzo like carbonaceous cr chondrites a systematic study of 210 chondrules from 15 cr chondrites was conducted the texture and composition of silicate and opaque minerals from each observed feo rich type ii chondrule and a representative number of feo poor type i chondrules were studied to build a substantial and self consistent data set the average abundances and standard deviations of cr2o3 in feo rich olivine phenocrysts are consistent with previous work that the cr chondrites are among the least thermally altered samples from the early solar system type ii chondrules from the cr chondrites formed under highly variable conditions e g precursor composition redox conditions cooling rate with each chondrule recording a distinct igneous history the opaque minerals within type ii chondrules are consistent with formation during chondrule melting and cooling starting as s and ni rich liquids at 988 1350 c then cooling to form monosulfide solid solution mss that crystallized around olivine pyroxene phenocrysts during cooling fe ni metal crystallized from the s and ni rich liquid and upon further cooling mss decomposed into pentlandite and pyrrhotite with pentlandite exsolving from mss at 400 600 c the composition texture and inferred formation temperature of pentlandite within chondrules studied here is inconsistent with formation via aqueous alteration however some opaque minerals fe ni metal versus magnetite and panethite present in type ii chondrules are a proxy for the degree of whole rock aqueous alteration the texture and composition of sulfide bearing opaque minerals in graves nunataks 06100 and grosvenor mountains 03116 suggest that they are the most thermally altered cr chondrites

characteristic silent earthquakes in the eastern part of the boso peninsula central japan 1 analysis of global positioning system gps data shows transient crustal deformation in the boso peninsula central japan for about fifty days from october 2002 the southeastward horizontal displacements detected suggest the occurrence of interplate aseismic slip between the philippine sea plate and the north american plate six years after a similar event in 1996 we estimate an area of aseismic slip with moment magnitude mw 6 6 centered off the boso peninsula adjacent to associated seismic activity slip evolution of the 2002 aeismic slip started on october 4 and migrated from north to south for about ten days followed by gradual subsidence and restarting of slip which lasted until december 2 propagating more southward similarities in focal area and slip process between the 1996 and the 2002 events suggest the boso aseismic slips as characteristic silent earthquakes together with the repetitive occurrence of seismic swarm in a similar region every six to seven years a more tightly coupled southern area that did not release enough energy in the 1996 event may have caused the differences in magnitude central slip area and duration between the 1996 and the 2002 events if the hypothesized recurrence interval for strain accumulation is true based on swarm seismicity

detection of the subducting crust of oceanic plates beneath the kanto district japan abstract low velocity crustal layers on the top of the subducting slabs beneath the kanto district central japan were detected by a travel time inversion using 40 763 p wave arrival times from 3038 local earthquakes recorded by a local network of 41 seismic stations the inversion covered 188 228 110 km volume of the target region and the model was parameterized by 47 57 18 rectilinear blocks measuring 4 0 km per side horizontally and 4 10 km varying thickness in depth a prominent e w directed low velocity band of about 25 km width appeared in the central kanto region at a depth of 30 km moving north or northwestward gradually with depth this band can be traced to the depth of about 60 km at a depth of 60 km a slightly lower amplitude nearly n s directed low velocity band was observed at the east coast of the kanto region moving westward with depth these low velocity bands are thin layers attached to the top of the inclined thick layers with relatively high velocity in the kanto district the philippine sea phs plate subducts under the eurasian eur plate and the pacific pac plate also underthrusts beneath both the eur and phs plates some authors already suggested low velocity anomalies near the surface of those descending plates in this region mainly from the analyses of later phases and focal mechanisms of local earthquakes the shapes of the low velocity bands are similar to the depth distribution of the upper boundary of the phs and pac plates proposed by other authors the thrust earthquakes that occur at the boundaries between the eur and phs plates and between the phs and pac plates are almost located in the low velocity layers described above we conclude that these low velocity layers are the crusts that exist at the top of the subducting phs and pac plates while high velocity layers are subducting slabs themselves for the phs plate low density crust of the izu bonin arc is probably stacking at the range from 139 25 e to 139 55 e at 35 55 n which is observed as a thick low velocity region to the south of the range and in a steep inclination to the north of it this is also recognized from the gravity anomaly

volcanoes and human history abstract the study of volcanic hazards leads inevitably to questions of how past cultures have lived in volcanically active regions of the world here we summarize linkages between volcanological archaeological and anthropological studies of historic and prehistoric volcanic eruptions with the goal of evaluating the impact of past eruptions on human populations to better prepare for future events we use examples from papers collected in this volume to illustrate ways in which volcanological studies aid archaeological investigations by providing basic stratigraphic markers and information about the nature and timing of specific volcanic events we then turn to archaeological perspectives which provide physical evidence of the direct impacts of volcanic eruptions such as site abandonment and human migration as well as indirect impacts on local cultures as reflected in human artifacts finally we review anthropological studies of societal responses to past and recent volcanic eruptions we pay particular attention to both the psychological impact of catastrophic events and records of these impacts encoded within oral traditions taken together these studies record drastic short term eruption impacts but adaptation to volcanic activity over the longer term largely through strategies of adaptive land use

a planetary h group pebble in the barwell l6 unshocked chondritic meteorite abstract one stone of the barwell l6 shower contains an igneous inclusion with the oxygen isotopic signature of h group chondrites the inclusion is composed dominantly of olivine with a composition fo 75 5 identical with that of its host other phases are only partially equilibrated with the host the inclusion has a fractionated rare earth element pattern showing depletion in the heavy rare earth elements and a positive eu anomaly it is depleted in siderophile elements inclusion and host have ar ar ages 4 44 and 4 51 ga respectively and 129 xe r i ratios identical within experimental error we conclude that melting occurred very early on an h group chondritic body two objects from a single meteorite have different oxygen isotopic ratios but identical 129 xe r 127 i ratios which may indicate that the i xe systematics reflect chronological differences in closure to xe rather than isotopically heterogeneous iodine the inclusion and its host cooled to xe closure temperature contemporaneously with chondrules from unequilibrated ordinary chondrites

magnitude and location of historical earthquakes in japan and implications for the 1855 ansei edo earthquake 1 japan meteorological agency jma intensity assignments ijma are used to derive intensity attenuation models suitable for estimating the location and an intensity magnitude mjma for historical earthquakes in japan the intensity for shallow crustal earthquakes on honshu is equal to 1 89 1 42mjma 0 00887 h 1 66log h where mjma is the jma magnitude h 2 h2 1 2 and and h are epicentral distance and focal depth km respectively four earthquakes located near the japan trench were used to develop a subducting plate intensity attenuation model where intensity is equal to 8 33 2 19mjma 0 00550 h 1 14 log h the ijma assignments for the mjma7 9 great 1923 kanto earthquake on the philippine sea eurasian plate interface are consistent with the subducting plate model using the subducting plate model and 226 ijma iv vi assignments the location of the intensity center is 25 km north of the epicenter mjma is 7 7 and mjma is 7 3 8 0 at the 1 confidence level intensity assignments and reported aftershock activity for the enigmatic 11 november 1855 ansei edo earthquake are consistent with an mjma 7 2 philippine sea eurasian interplate source or philippine sea intraslab source at about 30 km depth if the 1855 earthquake was a philippine sea eurasian interplate event the intensity center was adjacent to and downdip of the rupture area of the great 1923 kanto earthquake suggesting that the 1855 and 1923 events ruptured adjoining sections of the philippine sea eurasian plate interface

subducting oceanic crusts of the philippine sea and pacific plates and weak zone normal compression in the kanto district japan summary oceanic crusts subducting into the mantle were detected by analyses of mantle earthquakes in the kanto district central japan earthquakes in a depth range of 30 80 km in the southwestern ibaraki prefecture were relocated by a modified method of joint hypocentre determination we obtained a good distribution map of hypocentres and focal mechanisms a boundary layer between the eurasian and philippine sea plates was found where thrust earthquakes with p axes in the nw se direction and of which low angle nodal planes dip northward occurred in a layer with a thickness of about 4 km the p wave velocity in this layer is estimated to be less than about 7 0kms l another boundary layer between the philippine sea and pacific plates exists about 15 km beneath the above boundary layer thrust earthquakes with p axes in the ew direction and of which low angle nodal planes dip westward occurred in this layer that also has a thickness of about 4km furthermore normal faulting earthquakes of which the p axes are almost perpendicular to the boundary layers were found immediately outside the boundary layers combining these results we can conclude that the boundary layers are oceanic crusts that exist at the top of the subducting philippine sea and pacific plates weak zone normal compression was proposed to result from the existence of low velocity oceanic crusts at plate boundaries this hypothesis can be explained because only stress caused by relative motion of the two plates is consumed inside the weak oceanic crust the remnant stress after subtracting the above stress from the tectonic one applied at the plate boundary is the stress of which the p axis is normal to the plate boundary

f phlogopites in the alban hills volcanic district central italy indications regarding the role of volatiles in magmatic crystallisation abstract a systematic analysis of micas contained in effusive pyroclastic and hypabyssal rocks of the alban hills volcanic district ahvd central italy was made in order to characterise minerals of pyroclastic units for tephrostratigraphy and to obtain as much information as possible on the activity of volatiles in this magmatic system the phlogopite shows a large range of f contents between 0 50 and 7 50 wt that make it possible to discriminate different ahvd lithologies in particular micas of lava groundmass are characterised by extremely high f up to 7 50 wt and ba up to 9 70 wt contents seldom or never found in other magmatic ultrapotassic rocks moreover the micas of pyroclastics ultramafic cumulates and holocrystalline inclusions made up of leucite clinopyroxene and phlogopite hereafter italites show mg mg fe values between 0 65 and 0 90 that are not correlated with f contents the variations in f contents observed in the ahvd micas do not appear to be due to a temperature effect or pressure changes but they may be due to variations in the h 2 o and co 2 activities in the magma chamber they make it possible to differentiate three crystallisation environments in the ahvd magmatic system the first one had elevated co 2 activity and formed the italites near the carbonate contact these rocks represent at least those enriched in clinopyroxene without skarn minerals the hypabyssal crystallisation of the ahvd magmas at the periphery of magma chamber the second one characterised by a higher water activity is represented by the micas of the ultramafic cumulates and pyroclastic scorias and is located in the inner part of magma chamber the third environment the groundmass of the lavas it is not related with the previous ones and is characterised by the absence of water and by a high f activity in general our results suggest that the compositional variations observed in the micas al si ti ba reflect different h 2 o activities inversely correlated with f activity in the magma chamber

inversion for the rupture details of the 1987 east chiba earthquake japan using a fault model based on the distribution of relocated aftershocks the rupture of the 1987 east chiba earthquake was investigated using an empirical green s function method and a nonlinear inversion technique in order to discuss what happened on the fault plane in more detail we relocated the aftershocks as well as the main shock relocations were done using a joint hypocenter method in order to increase the accuracy of the relative locations based on this aftershock distribution we propose a double fault model the main fault strikes n11 w with nearly vertical dip a subsidiary fault is perpendicular to the main fault the results of a source inversion using strong motion waveforms are as follows 1 moment release was large both in the deep northern area of the main fault and on the subsidiary fault where aftershock activity was weak 2 rupture propagated on both main and subsidiary faults simultaneously and rupture velocity decreased at the depth of around 35 km near the upper boundary of the philippine sea plate and 3 stress drop was high on the lower northern corner of the main fault where the rupture terminated and on the deep southern area of main fault where the rupture initiated a negative correlation was found between moment release during the main shock and that during the aftershock sequence but they did not compensate each other quantitatively this suggests the existence of a heterogeneous strain distribution in the fault area either before the main shock or after its aftershock sequence

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

mineralogy and texture of fe ni sulfides in ci1 chondrites clues to the extent of aqueous alteration on the ci1 parent body to better understand the role of aqueous alteration on the ci1 parent body we have analyzed the texture composition and mineral associations of iron nickel sulfides in four of the five known ci1 chondrites the most commonly occurring sulfide present in the ci1 chondrites is the iron deficient fe ni sulfide pyrrhotite fe ni 1 xs that has a composition close to that of stoichiometric troilite fes three of the ci1s alais ivuna and tonk also contain pentlandite fe ni 9s8 although pentlandite is a rare phase in ivuna cubanite cufe2s3 was found in both alais and ivuna in this study although it has also been reported in orgueil macdougall and kerridge 1977 the pyrrhotite grains in all four chondrites form hexagonal rectangular or irregular shapes and show no evidence of ni or co zoning the pyrrhotite grains in orgueil and ivuna are in general smaller and show more corrosions or embayments than those in alais or tonk we suggest that the precursor sulfide present in the ci1 chondrites was troilite which during brecciation and oxidation on the parent body at a temperature of 100 c or less converted the troilite to magnetite and pyrrhotite with pentlandite inclusions subsequently continued alteration on the parent body removed pentlandite partially from alais tonk and ivuna completely from orgueil leaving behind pyrrhotite with spaces corrosions where the pentlandite had been ni derived from the pentlandite was incorporated into ferrihydrite onto the surface of which the ni na sulfate ni bloedite formed based on the size and abundant corrosions within pyrrhotite grains combined with observations from other authors we conclude that orgueil and ivuna have undergone a greater degree of alteration than alais and tonk further work is needed to assess the conditions under which pentlandite would be dissolved preferentially to pyrrhotite as the study of terrestrial literature indicates that the latter mineral is preferentially removed

geometry and relative motion of the philippine sea plate and pacific plate beneath the kanto tokai district japan the recent acquisition of high density and improved seismic data by the kanto tokai k t observational network of the national research institute of earth science and disaster prevention requires the revision of conventional plate configuration models for the k t district we propose a new interpretation of the configuration and relative motion of the philippine sea phs plate pacific pac plate and eurasian eur plate on the basis of the distribution of hypocenters velocity structure and focal mechanisms in the k t district the new model for the configuration of the phs and pac slabs clearly delineates the phs slab subducting northwestward beneath the k t district from the sagami and suruga troughs and the pac slab subducting westward beneath the phs slab from the japan trench the thickness of the descending phs slab is estimated to be 30 5 km the proposed configuration of the phs slab is significantly different from those obtained by other researchers including our own previous study the new model is fully consistent with global plate motion data the new model leads to an interpretation of the tectonic processes taking place beneath the k t district for the sagami trough wing of the phs slab the northeastern portion of the slab is dipping northwestward in direct contact with the upper surface of the pac slab the southwestern portion carrying the izu peninsula has been bent upward because of its buoyancy producing the observed contorted shape for the suruga trough wing the dip direction of the phs slab gradually changes from northwestward at the eastern portion to northward at the western portion the new model also indicates the presence of offset within the phs slab between the sagami and suruga trough wings this area is characterized by a low level of seismic activity the absence of a high velocity structure and the presence of quaternary volcanoes it seems reasonable to speculate that the distribution of quaternary volcanic edifice construction is controlled by the location of the offset within the phs slab in view of this new model the tectonic processes of large earthquakes which occurred recently in the studied area are also reexamined

earthquake of 1987 off chiba central japan and possible triggering of eastern tokyo earthquake of 1988 abstract a moderate earthquake m 6 7 occurred off eastern chiba central japan on december 17 1987 as a consequence of the internal deformation of the philippine sea plate this event helped in clarifying the geometry of the easternmost part of the philippine sea plate as well as the mode of earthquake occurrence in this region three months later another moderate earthquake m 6 0 took plate beneath eastern tokyo this event was generated at the slab slab collision zone at about 90 km depth and is considered to be triggered by the former earthquake a similar phenomenon was observed for the izu m 6 7 of june 29 1980 and the mid chiba m 6 1 of september 25 1980 earthquake pair and the off ibaraki m 7 0 of july 23 1982 and the southern ibaraki m 6 0 of february 27 1983 earthquake pair these are the only three earthquake pairs of m 6 which occurred in the tokyo metropolitan area since 1974 thus over these 15 years all m 6 interplate earthquakes in this specific region are preceded by nearby m 7 earthquakes this suggests that m 7 shallow events enhance stress in the deeper plate collision zone beneath the tokyo metropolitan area and trigger m 6 interplate events

scaling relations of earthquakes that occurred in the upper part of the philippine sea plate beneath the kanto region japan estimated by means of borehole recordings acceleration source spectra of sh waves for 94 interplate and 74 intraplate earthquakes with a moment range of m 0 10 13 10 18 n m are investigated using 634 strong motion records obtained at 27 borehole and 7 surface hard rock stations installed in the kanto region central japan different scaling relations control the estimated acceleration source spectra for interplate and intraplate events the estimated acceleration source spectra of interplate events are similar to the spectra expected from the barrier model and those of intraplate events show a characteristic bump around the corner frequency the amplitude of acceleration source spectrum of interplate events is on the whole larger than that of intraplate events for the same seismic moment seismic moment m 0 corner frequency f c and seismic energy e are evaluated from the estimated acceleration source spectrum for each earthquake the seismic moment m 0 is nearly proportional to f c 3 the ratio of seismic energy to seismic moment is e m 0 1 15 12 9 10 5 for all events without a significant difference between interplate and intraplate earthquakes this means that the estimated velocity source spectra for interplate and intraplate events with the same seismic moment are nearly identical the dependence of apparent stress a e m 0 on seismic moment is weak and depends on tectonic setting apparent stress drop 2 a is almost proportional to the brune9s stress drop

the flash melting of chondrules an experimental investigation into the melting history and physical nature of chondrule precursors abstract constraints placed on chondrule formation have largely been generated from experiments which use a long duration below liquidus isothermal melting minutes to hours rather than a short duration above liquidus flash melting event seconds to minutes in this paper we examine how a short duration superliquidus heat pulse can produce chondrule textures by incompletely melting material with a type of flash melting we show that the maximum temperature limit of chondrule formation was approximately 2100 c almost 400 c higher than previously constrained previous experiments also have not studied the effect of variations in precursor grain size on the formation of chondrule textures for this reason we simultaneously investigate the effect of variations in the grain size of a starting composition on the formation of chondrule textures we show how mgo rich type ia chondrules and other fine grained chondrules could only have been formed from the incomplete melting of a rather uniformly grain sized precursor of less than 63 m because fine grained mgo rich chondrules have the some of the highest chondrule liquidus temperatures we proposed that these types of textures define a minimum melting temperature for chondrule formation