liebermannite kalsi3o8 a new shock metamorphic high pressure mineral from the zagami martian meteorite in this paper we discuss the occurrence of liebermannite ima 2013 128 kalsi 3o 8 a new shock generated high pressure tetragonal hollandite type structure silicate mineral in the zagami basaltic shergottite meteorite liebermannite crystallizes in space group i4 m with z 2 cell dimensions of a 9 15 0 14 1 a c 2 74 0 13 a and a cell volume of 229 19 a 3 for the type material as revealed by synchrotron diffraction in zagami liebermannite likely formed via solid state transformation of primary igneous k feldspar during an impact event that achieved pressures of 20 gpa or more the mineral name is in honor of robert c liebermann a high pressure mineral physicist at stony brook university new york usa

a new martian meteorite from oman mineralogy petrology and shock metamorphism of olivine phyric basaltic shergottite sayh al uhaymir 150 the sayh al uhaymir sau 150 meteorite was found on a gravel plateau 43 3 km south of ghaba oman on october 8 2002 oxygen isotope 17o 2 78 18o 4 74 cre age 1 3 ma and noble gas studies confirm its martian origin sau 150 is classified as an olivine phyric basalt having a porphyritic texture with olivine macrocrysts set in a finer grained matrix of pigeonite and interstitial maskelynite with minor augite spinel ilmenite merrillite pyrrhotite pentlandite and secondary terrestrial calcite and iron oxides the bulk rock composition in particular mg 68 molar mg mg fe 100 fe mn 37 9 and na al 0 22 are characteristic of martian meteorites based on mineral compositions cooling rates determined from crystal morphology and crystal size distribution it is deduced that the parent magma formed in a steady state growth regime magma chamber that cooled at 70 365 c sau 150 is essentially identical to sau 005 094 all representing samples of the same fall that are similar to but distinct from the dag shergottites

high pressure phases in shock induced melt veins of the umbarger l6 chondrite constraints of shock pressure we report a previously undocumented set of high pressure minerals in shock induced melt veins of the umbarger l6 chondrite high pressure minerals were identified with transmission electron microscopy tem using selected area electron diffraction and energy dispersive x ray spectroscopy ringwoodite fa30 akimotoite en11fs89 and augite en42wo33fs25 were found in the silicate matrix of the melt vein representing the crystallization from a silicate melt during the shock pulse ringwoodite fa27 and hollandite structured plagioclase were also found as polycrystalline aggregates in the melt vein representing solid state transformation or melting with subsequent crystallization of entrained host rock fragments in the vein in addition fe2sio4 spinel fa66 fa99 and stishovite crystallized from a feo sio2 rich zone in the melt vein which formed by shock melting of feo sio2 rich material that had been altered and metasomatized before shock based on the pressure stabilities of the high pressure minerals ringwoodite akimotoite and ca clinopyroxene the melt vein crystallized at approximately 18 gpa the fe2sio4 spinel stishovite assemblage in the feo sio2 rich melts is consistent with crystallization of the melt vein matrix at the pressure up to 18 gpa the crystallization pressure of 18 gpa is much lower than the 4590 gpa pressure one would conclude from the s6 shock effects in melt veins stffler et al 1991 and somewhat less than the 25 30 gpa inferred from s5 shock effects schmitt 2000 found in the bulk rock

first principles prediction of fast migration channels of potassium ions in kalsi3o8 hollandite implications for high conductivity anomalies in subduction zones materials sharing the hollandite structure were widely reported as fast ionic conductors however the ionic conductivity of kalsi3o8 hollandite k hollandite which can be formed during the subduction process has not been investigated so far here first principles calculations are used to investigate the potassium ion k transport properties in k hollandite the calculated k migration barrier energy is 0 44 ev at a pressure of 10 gpa an energy quite small to block the k migration in k hollandite channels the calculated ionic conductivity of k hollandite is highly anisotropic and depends on its concentration of k vacancies about 6 k vacancies in k hollandite can lead to a higher conductivity compared to the conductivity of hydrated wadsleyite and ringwoodite in the mantle k vacancies being commonly found in many k hollandite samples with maximum vacancies over 30 the formation of k hollandite during subduction of continental or alkali rich oceanic crust can contribute to the high conductivity anomalies observed in subduction zones

frictional melting processes and the generation of shock veins in terrestrial impact structures evidence from the steen river impact structure alberta canada abstract shock produced melt within crystalline basement rocks of the steen river impact structure sris are observed as thin 1 510 m wide interlocking networks of dark veins which cut across and displace host rock minerals solid state phase transformations such as ferro pargasite to an almandine andradite majorite garnet and amorphization of quartz and feldspar are observed in zones adjacent to comparatively wider 50 500 m sections of the shock veins shock pressure estimates based on the coupled substitution of na ti4 and si4 for divalent cations al3 and cr3 in garnet 14 19 gpa and the pressure required for plagioclase ab62 83 amorphization at elevated temperature 14 20 gpa are not appreciably different from those recorded by deformation effects observed in non veined regions of the bulk rock 14 20 gpa this spatial distribution is the result of an elevated temperature gradient experienced by host rock minerals in contact with larger volumes of impact generated melt and large deviatoric stresses experienced by minerals along vein margins micrometer size equant crystals of almandine pyrope majorite garnet define the shock vein matrix consistent with rapid quench 100 200 ms at 7 5 10 gpa crystallization of the vein occurred during a 0 1 0 15 s shock pressure pulse majoritic garnet formed during shock compression by solid state transformation of pargasite along shock vein margins is observed in tem bright field images as nanometer size gouge particles produced at strain rates in the supersonic field 106 108 these crystals are embedded in vesiculated glass and this texture is interpreted as continued movement and heating along slip planes during pressure release the deformation of high pressure minerals formed during shock compression may be the first evidence of oscillatory slip in natural shock veins which accounts for the production of friction melt via shear when little or no appreciable displacement is observed our observations of the mineralogy chemistry and microtextures of shock veins within crystalline rocks of the sris allow us to propose a model for shock vein formation by shear induced friction melting during shock compression

geologic constraints on the cenozoic antarctica australia pacific relative plate motion circuit in a revised interpretation of the sea floor spreading pattern in the southwest pacific ocean stock and molnar predicted that the modern australia pacific plate boundary through new zealand formed about 35 ma and has accommodated about 800 km of relative motion geologic constraints onshore in new zealand however suggest that the modern plate boundary formed about 23 ma and has accommodated only 500 km of relative motion the 300 km of additional displacement must have been accommodated elsewhere in the antarctica australia pacific plate circuit lithospheric extension between east and west antarctica which formed the transantarctic rift system accounts for at least 138 km of the additional displacement before the modern plate boundary formed in new zealand

a deep crustal shear zone exposed in western fiordland new zealand an approximately 180 km long deep crustal shear zone in western fiordland new zealand has been shown to have formed during continental extension between 116 and 100 ma the western fiordland shear zone forms a major tectonic boundary between two sets of gneisses with unrelated deformation histories a detailed study of the northern part of the shear zone has revealed that the shear zone formed at depths of 40 km approximately 12 kbar and 680 c and was originally very gently dipping or subhorizontal prior to subsequent upright folding the current thickness postfolding of the shear zone is 3 4 km abundant asymmetric structures in the shear zone indicate noncoaxial deformation and a top to the ne sense of shear unlike ductile shear zones in metamorphic core complexes from elsewhere in the world there is no evidence that decompression of the shear zone rocks or foot wall rocks occurred during the active life of the shear zone suggesting that displacement along the shear zone by noncoaxial deformation must have been largely horizontal this shear zone provides important evidence for the nature of deep crustal deformation occurring during continental extension

morning precipitation peak over the strait of malacca under a calm condition abstract this paper describes the formation mechanism of morning maximum in the diurnal cycle of precipitation at the strait of malacca under a calm condition with a nonhydrostatic mesoscale numerical model and ship based observational data the morning precipitation peak at the strait is induced by the convergence of two cold outflows that have been produced by the precipitation systems in the previous evening over sumatra and the malay peninsula the outflows converge at the strait of malacca around midnight a new precipitation system is thus generated and reaches its peak in the early morning sensitivity experiments using the numerical model suggest that the timing and position of the morning precipitation peak are affected by the width of the strait in the case of the strait of malacca its width favors the formation of the morning precipitation system around the center of the strait which explains why its diurnal cycle of precipitation can be observed much clearer than those in other coastal ar

shock induced melting recrystallization and exsolution in plagioclase from the martian lherzolitic shergottite grv 99027 plagioclase in the martian lherzolitic shergottite grove mountains grv 99027 was shocked melted and recrystallized the recrystallized plagioclase contains lamellae of pyroxene olivine and minor ilmenite 1 m wide both the pyroxene and the olivine inclusions enclosed in plagioclase and grains neighboring the plagioclase were partially melted into plagioclase melt pools the formation of these lamellar inclusions in plagioclase is attributed to exsolution from recrystallizing melt distinct from other martian meteorites grv 99027 contains no maskelynite but does contain recrystallized plagioclase this shows that the meteorite experienced a slower cooling than maskelynite bearing meteorites we suggest that the parent rock of grv 99027 could have been embedded in hot rocks which facilitated a more protracted cooling history

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

high pressure minerals in shocked meteorites heavily shocked meteorites contain various types of high pressure polymorphs of major minerals olivine pyroxene feldspar and quartz and accessory minerals chromite and ca phosphate these high pressure minerals are micron to submicron sized and occur within and in the vicinity of shock induced melt veins and melt pockets in chondrites and lunar howardite eucrite diogenite hed and martian meteorites their occurrence suggests two types of formation mechanisms 1 solid state high pressure transformation of the host rock minerals into monomineralic polycrystalline aggregates and 2 crystallization of chondritic or monomineralic melts under high pressure based on experimentally determined phase relations their formation pressures are limited to the pressure range up to 25 gpa textural crystallographic and chemical characteristics of high pressure minerals provide clues about the impact events of meteorite parent bodies including their size and mutual collision velocities and about the mineralogy of deep planetary interiors the aim of this article is to review and summarize the findings on natural high pressure minerals in shocked meteorites that have been reported over the past 50 years

abrupt strike slip fault to subduction transition the alpine fault puysegur trench connection new zealand swath bathymetry and other geophysical data collected over the fiordland margin southwest of new zealand are used to investigate the mechanism of transform subduction transition between the alpine fault and the puysegur trench two segments of the pacific australian plate boundary in this region the cenozoic southeast tasman basin which obliquely underthrusts fiordland at the puysegur trench is separated from the cretaceous tasman basin by the resolution ridge system a major lithospheric discontinuity of the downgoing plate interpretation of seafloor morphology shows that the alpine fault extends offshore along the fiordland coast and splits into west and east branches the west branch cuts obliquely across the margin and connects sharply to the puysegur subduction front at the northeastern tip of the resolution ridge system earthquake and seismic reflection data indicate that the west branch is genetically controlled by downgoing plate structures associated with the resolution ridge system hence the west branch is interpreted as the surface trace of the plate boundary segment extending between the alpine fault and the puysegur trench we conclude that the development of the strike slip segment of the plate boundary and its sharp transition to the puysegur subduction are controlled by inherited structures of the australian plate furthermore according to geophysical data presented here a tearing of the downgoing plate can be interpreted beneath the west branch a review of geophysical data along the region of the alpine fault hikurangi trough northeast new zealand shows a progressive transform subduction transition that is accommodated by motion partitioning between the subduction interface and strike slip faults this transition is accounted for by an interplate coupling that progressively increases toward the alpine fault in relation with a gradual thickening of the downgoing crust the comparison between the fiordland and the hikurangi strike slip subduction transitions show that presence of inherited downgoing plate crustal faults properly oriented with respect to the plate motion facilitates a sharp strike slip subduction transition

phase transformations in subducted oceanic crust and buoyancy relationships at depths of 600 800 km in the mantle abstract phase transformations in a representative oceanic crust composition morb have been studied at pressures up to 28 gpa at 1200 c and 1500 c using a multi anvil apparatus the assemblage of majorite casio 3 rich perovskite stishovite which is displayed by the morb composition at pressures above 20 gpa was found to transform further into an assemblage containing a new aluminous phase at pressures above 25 gpa this al phase has a complex composition and is also relatively sodium rich its x ray diffraction pattern is similar to that observed for mgal 2 o 4 calcium ferrite type and is tentatively indexed on the basis of an orthorhombic cell yielding a zero pressure density of 3 87 2 g cm 3 majorite garnet was found to remain as the most abundant phase at the highest pressure studied 28 gpa and does not appear likely to transform to perovskite until pressures exceed 29 30 gpa these results imply that the basaltic crust component of subducted oceanic lithosphere would be 0 1 0 2 g cm 3 less dense than surrounding mantle pyrolite between the depths of 660 800 km thereby confirming an earlier hypothesis of anderson moreover the underlying layer of harzburgite would be 0 05 g cm 3 less dense than pyrolite throughout most of this depth interval these buoyancy relationships contribute to a barrier which impedes and may sometimes prevent the entry of slabs into the lower mantle

hollandite ii phase in kalsi3o8 as a potential host mineral of potassium in the earth s lower mantle abstract high pressure and high temperature experiments on the kalsi3o8 composition were conducted in a laser heated diamond anvil cell at pressures up to 128 gpa which correspond to the lowermost mantle conditions in situ synchrotron x ray diffraction measurements revealed that the hollandite ii phase in kalsi3o8 with a monoclinic symmetry of i2 m was stable over the entire range of mantle conditions and the tunnel structure formed by the double chains of edge sharing si al o6 octahedra which could accommodate a larger cation such as potassium was sustained the si al o6 octahedra in the kalsi3o8 hollandite ii phase showed a similar compression behavior to those in high pressure silicate structures such as rutile type and perovskite type phases and were found to be less compressible than the ko8 polyhedra the kalsi3o8 hollandite ii phase is a potential host mineral for potassium under lower mantle conditions and therefore may have a significant influence on geochemistry if potassium feldspar kalsi3o8 in the earth s crust is transported into the earth s mantle through subduction

shergottites dhofar 019 sau 005 shergotty and zagami 40ar 39ar chronology and trapped martian atmospheric and interior argon we report a high resolution 40ar 39ar study of mineral separates and whole rock samples of olivine phyric dhofar 019 sayh al uhaymir sau 005 and basaltic shergotty zagami shergottites excess argon is present in all samples the highest 40ar 36ar trapped ratios are found for argon in pyroxene melt inclusions 1500 maskelynite 1200 impact glass 1800 of shergotty and impact glass of sau 005 1200 a high 40ar 36ar trapped componentusually uniquely ascribed to martian atmosphere can also originate from the martian interior indicating a heterogeneous martian mantle composition as additional explanation of variable high 40ar 36ar trapped ratios in shocked shergottites we suggest argon implantation from a transient atmosphere during impact induced degassing the best 40ar 39ar age estimate for dhofar 019 is 642 72 ma maskelynite sau 005 samples are between 700900 ma old relatively high 40ar 39ar ages of melt inclusions within dhofar 019 1086 252 ma and sau 005 olivine 885 66 ma could date entrapment of a magmatic liquid during early olivine crystallization or reflect unrecognized excess 40ar components the youngest 40ar 39ar age of shergotty separates maskelynite is 370 ma that of zagami is 200 ma the 40ar 39ar chronology of dhofar 019 and sau 005 indicate 1 ga ages apparent ages uncorrected for trapped e g martian atmosphere mantle argon components approach 4 5 ga but are not caused by inherited 40ar because excess 40ar is supported by 36artrapped young ages obtained by 40ar 39ar and other chronometers argue for primary rather than secondary events the cosmic ray exposure ages calculated from cosmogenic argon are 15 7 0 7 ma dhofar 019 1 0 1 6 ma sau 005 2 1 2 5 ma shergotty and 2 2 3 0 ma zagami

joint hypocentre determination of intermediate depth earthquakes in fiordland new zealand abstract relocation of well observed intermediate depth earthquakes in the fiordland region by the method of joint hypocentre determination has revealed some fine structure in the benioff zone the earthquakes occur in three groups the central group is the largest and occupies a planar volume less than 15 km thick striking n40 e and dipping at 80 the deepest events in the region at depths of 150 km occur at the northeast end of this group the two smaller groups lie to the northeast and to the south of the main group the focal mechanism of the majority of the main group is that of thrust faulting we suggest that the main group lies within a section of indian plate lithosphere which has been broken off and rotated into its observed position and that the northern edge of the unbroken subducted indian plate is indicated by the southern group we suggest that the small northeastern group has quite a different tectonic origin and is similar to a group of earthquakes further north which are at a similar distance from and presumably related to the alpine fault use has also been made of the travel time information which is a by product of the joint hypocentre method to construct upper mantle velocity models for p and s waves in the south island the features of this model are a high velocity region in the vicinity of the benioff zone and a subcrustal zone of high seismic velocities running east west across the center of the south island in an otherwise normal mantle

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

shock temperatures in anorthite glass temperatures of caal 2si 2o 8 anorthite glass shocked to pressures between 48 and 117 gpa have been measured in the range from 2500 to 5600 k using optical pyrometry techniques the pressure dependence of the shock temperatures deviates significantly from predictions based on a single high pressure phase either a variable specific heat or the existence of three phase transitions at pressures of about 55 85 and 100 gpa and with transition energies of about 0 5 mj kg 1 each 1 5 mj kg 1 total can explain the shock temperature data the proposed phase transition at 100 gpa can possibly be identified with the stishovite melting transition theoretical models of the time dependence of the thermal radiation from the shocked anorthite based on the geometry of the experiment and the absorptive properties of the shocked material yield good agreement with observations indicating that it is not necessary to invoke intrinsic time dependences to explain the data in many cases observed time dependences were used to calculate absorption coefficients of the shocked material of from about 2 mm 1 to greater than 24 mm 1 an increasing function of shock pressure the assumption that the shocked material radiates as a black body is supported by the theoretical model and by the close agreement between measured and calculated black body spectral radiance as a function of wavelength

first discovery of stishovite in an iron meteorite the first occurrence of stishovite in an iron meteorite muonionalusta group iva is reported the mineral occurs intimately mixed with amorphous silica forming tabular grains up to 3 mm wide with a hexagonal outline it was identified using x ray diffraction and raman microspectroscopy the unit cell parameters of stishovite are a 4 165 3 a and c 2 661 6 a and its chemical composition is nearly pure sio2 raman spectra show relatively sharp bands at 231 and 754 cm 1 and a broad band with an asymmetric shape and a maximum around 500 cm 1 the rare grains are found within troilite nodules together with chromite daubreelite and schreibersite from their composition and morphology and by comparisons with silica inclusions in e g the gibeon iva iron we conclude that these rare grains represent pseudomorphs after tridymite the presence of stishovite in muonionalusta is suggested to reflect shock metamorphic conditions in the iva parent asteroid during a cosmic impact event

sayh al uhaymir 094 a new martian meteorite from the oman desert sayhal uhaymir sau 094 is a 223 3 g partially crusted strongly to very strongly shocked melanocratic olivine porphyric rock of the shergottite group showing a microgabbroic texture the rock consists of pyroxene 52 0 58 2 vol dominantly prismatic pigeonite en60 68fs20 27wo7 9 associated with minor augite en46 49fs15 16wo28 31 brown shock oxidized olivine fo65 69 22 1 31 completely isotropic interstitial plagioclase glass maskelynite an50 64or0 3 0 9 8 6 13 0 chromite and titanian magnesian chromite 0 9 1 0 traces of ilmenite ilm80 86 pyrrhotite fe92 100 0 1 0 2 merrillite 0 1 and pockets 4 8 6 7 consisting of green basaltic to basaltic andesitic shock glass that is partially devitrified into a brown to black product along boundaries with the primary minerals the average maximum dimensions of minerals are olivine 1 5 mm pyroxene 0 3 mm and maskelynite 0 3 mm primary melt inclusions in olivine and chromite are common and account for 0 1 0 6 of the rock x ray tomography revealed that the specimen contains 0 4 vol of shock melt associated vesicles up to 3 mm in size which show a preferred orientation fluidization of the maskelynite melting and recrystallization of pyroxene olivine and pyrrhotite indicate shock stage s6 minor terrestrial weathering resulted in calcite veining and minor oxidation of sulfides the meteorite is interpreted as paired with sau 005 008 051 the modal composition is similar to dar al gani 476 489 670 735 876 with the exception that neither mesostasis nor titanomagnetite nor apatite are present and that all phases show little zonation the restricted mineral composition predominance of chromite among the oxides and abundance of olivine indicate affinities to the lherzolitic shergottites

tropical western pacific warm pool and maritime continent precipitation rates and their contrasting relationships with the walker circulation 1 the cenozoic reorganization of islands in the maritime continent region of the tropical western pacific may have increased the amount of land surface area changed the distribution of sea surface temperature sst and consequently provided a necessary condition for the onset of the walker circulation precipitation rates over the maritime continent measured with the tropical rainfall measurement mission trmm satellite and generated from the climate prediction center merged analysis of precipitation cmap correlate positively with a variety of measures of the walker circulation s strength surface easterlies and high level westerlies over the western pacific and hence with la nina conditions similarly measured precipitation rates over the western pacific warm pool correlate positively with the strength of tropical zonal circulation shifted to the east and thus a weakened walker circulation and stronger el nino like conditions areas of high precipitation rates correlate with areas of ascent in the atmosphere and with high sst condensation associated with precipitation over the warm pool provides about twice the amount of latent heating as that over the maritime continent largely because the surface area of the warm pool is about 1 9 times larger than that of the maritime continent these results support the conjecture that tectonic expansion and reorganization of the maritime continent may have led to a strengthening of the walker circulation and may be related to a change in tropical pacific climate from a permanent and zonally uniform el nino like state in pre ice age time to the present day el nino southern oscillation enso state

the mid cenozoic challenger rift system of western new zealand and its implications for the age of alpine fault inception analysis of the structure and sedimentary geology of western new zealand has identified a middle eocene to early miocene continental rift system 1 200 km long and 100 200 km wide named here the challenger rift system four phases of rift development occurred 1 infra rift subsidence 2 active axial trough subsidence 3 expanded rift subsidence involving collapse of the rift shoulders and 4 incipient sea floor spreading the spatial and temporal distribution of these phases identifies a north island and a south island rift segment and shows that rifting propagated toward the center of the rift from both ends the northern segment shows a simple pattern of rifting that is comparable with vink9s model of rift propagation the southern segment with locked zones and rift nucleation segments is comparable to courtillot9s model of rift propagation the sea floor spreading history of the southwest pacific shows that the northern rift segment probably linked with a sea floor spreading center in the norfolk basin and the southern segment linked with the southeast indian ridge this is corroborated by the good correlation between the ages of sea floor magnetic anomaly lineations that are aligned with the rift and the biostratigraphic ages of rifting the probable continuity of the rift system in its early development precludes pre miocene transcurrent displacement on the alpine fault an early miocene 23 m y b p age of alpine fault inception is indicated by the age and pattern of rift disruption attributed to compression that originated at the australia pacific plate boundary the modern australia and pacific plates were not discrete entities therefore until the early miocene

shock induced deformation of shergottites shock pressures and perturbations of magmatic ages on mars shergottites and chassignites practiced major deformation effects whose nature magnitude and relevance were controversially evaluated and disputatively debated our studies of many shocked shergottites present contrary to numerous previous reports ample evidence for pervasive shock induced melting amounting of at least 23 vol of the shergottite consisting of maskelynite and pyrrhotite partial melting of pyroxene titanomagnetite ilmenite and finding of several high pressure polymorphs and pressure induced dissociation reactions our results cast considerable doubt on using the refractive index ri or cathodoluminescence cl spectra of maskelynite in estimating the magnitudes of peak shock pressure in both shergottites and ordinary chondrites ri of maskelynite was set after quenching of the feldspar liquid before decompression to maskelynite glass followed by glass relaxation after decompression at the closure temperature of relaxation the ri procedure widely practiced in the past 38 years revealed unrealistic very high pressure estimates discrepant with the high pressure mineral inventory in shocked shergottites and ordinary chondrites and with results obtained by robust laboratory static experiments shergottites contain the silica high pressure polymorphs the scrutinyite structured polymorph seifertite a monoclinic ultra dense polymorph of silica with zro2 structure stishovite a dense liquidus assemblage consisting of stishovite na hexa aluminosilicate na cas and both k lingunite and ca lingunite applying individual high pressure silica polymorphs alone like stishovite to estimate the equilibrium shock pressure is inadequate due to the considerable shift of their nominal upper pressure bounds intrinsically induced by spatially variable absorptions of minor oxides like al2o3 na2o feo mgo and tio2 this practice revealed variable pressure estimates even within the same shergottite subjected to the same peak shock pressure occurrence of na cas stishovite lack of the naalsio4 ca ferrite structured polymorph or jadeite indicates that the peak shock pressures barely exceeded 22 gpa we present convincing and ample evidence refuting the claim that the shock induced high pressure inventory in shergottites and ordinary chondrites are disequilibrium assemblages resulted from local pressure spikes in excess of 80 gpa and during the decompression stage such scenario calls for a series of incomplete and quenched retrograde reactions starting with the crystallization of mg silicate perovskite magnesiowustite if the claimed peak shock pressure was in excess of 80 gpa this would be followed by replacement of this pair by majorite pyrope ss magnesiowustite or akimotoite magnesiowustite below 23 gpa and 2000 degrees c polycrystalline ringwoodite above 16 gpa respectively and finally replacement by polycrystalline olivine below 16 gpa such incomplete retrograde reactions were never encountered in any shergottite chassignite or shocked ordinary chondrite so far olivine ringwoodite phase transformation in the l6 y 791384 commences with the coherent mechanism producing ringwoodite lamellae with their 111 planes parallel to the 100 of olivine followed by the incoherent mechanism due to build up of strain in the parental olivine this is in accord with the olivine ringwoodite settings produced in static laboratory experiments in a multi anvil device olivine ringwoodite phase transitions were also encountered in comparable settings in the shergottite nwa 1068 application of experimentally obtained kinetic parameters of the olivine ringwoodite phase transitions reveals possible duration of the natural dynamic events up to few seconds thus unambiguously refuting the claimed disequilibrium decompression mechanism the shock induced pervasive melting of labradorite pyrrhotite titanomagnetite ilmenite and partial melting of clinopyroxene strongly suggests shock induced partial to complete resetting of the ar ar rb sr sm nd re os u pb and lu hf radiometric systems this also casts considerable doubt on the radiometric ages shorter than 575 ma reported in the past 38 years to allegedly be the igneous crystallization ages these short ages probably resulted from partial or total shock induced age resetting c 2012 elsevier ltd all rights reserved

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

high pressure phase relations in the system caal4si2o11 naal3si3o11 with implication for na rich cas phase in shocked martian meteorites abstract high pressure phase relations in the system naal 3 si 3 o 11 caal 4 si 2 o 11 were examined at 13 23 gpa and 1600 1900 c using a multianvil apparatus a ca aluminosilicate with caal 4 si 2 o 11 composition designated cas phase is stable above about 13 gpa at 1600 c in the system naal 3 si 3 o 11 caal 4 si 2 o 11 the cas phase dissolving naal 3 si 3 o 11 component coexists with jadeite corundum and stishovite below 22 gpa above which the cas phase coexists with na rich calcium ferrite corundum and stishovite at 1600 c the solubility of naal 3 si 3 o 11 component in the cas solid solution increases with increasing pressure up to about 50 mol at about 22 gpa above which the solubility decreases with pressure the maximum solubility of naal 3 si 3 o 11 component in the cas phase increases with temperature up to around 70 mol at 1900 c at 22 gpa the dissociation of naalsi 2 o 6 jadeite to naalsio 4 calcium ferrite plus stishovite occurs at about 22 gpa lattice parameters of the cas phase with the hexagonal ba ferrite structure change with increase of the naal 3 si 3 o 11 component a axis decreases and c axis slightly increases resulting in decrease of molar volume enthalpies of the cas solid solutions were measured by high temperature drop solution calorimetry techniques the results show that enthalpy of hypothetical naal 3 si 3 o 11 cas phase is much higher than the mixture of naalsi 2 o 6 jadeite corundum and stishovite and is close to that of the mixture of naalsio 4 calcium ferrite corundum and stishovite when we adopt the na ca ratio of 75 25 of the natural na rich cas phase in a shocked martian meteorite zagami the phase relations determined above suggest that the natural cas phase crystallized from melt at pressure around 22 gpa and temperature close to or higher than 2000 2200 c the inferred p t conditions are consistent with those estimated using other high pressure minerals in the shocked meteorite

mode of crustal shortening adjacent to the alpine fault new zealand the late cenozoic episode of crustal shortening in the south island new zealand which has caused present day uplift rates of greater than 10 mm yr and has formed the southern alps may have also caused clockwise rotation of the alpine fault by up to 20 in contrast to the northern end of the alpine fault which appears to have remained fixed relative to the australian plate increasing westward movement of the fault trace has occurred southward along the fault this westward movement may exceed 100 km where the fault crosses the coastline in northern fiordland most shortening adjacent to the southern end of the alpine fault has occurred within australian plate continental crust which has been thrust beneath pacific plate continental crust this zone of continental underthrusting merges with the fiordland subduction zone further south where australian plate oceanic crust is being subducted gravity modelling of the continental collision zone beneath the southern alps indicates that the leading edge of underthrust australian plate crust may be close to a relatively sharp 10 km change in moho depth inward dipping thrust faults on both plates mark the outer limits of the collision zone which is over 300 km wide near the southern end of the alpine fault the probable increase in crustal thickness due to the late cenozoic shortening suggests that the amount of crustal thickening is similar in size to the amount of eroded crust

anatomy of black veins in zagami clues to the formation of high pressure phases abstract black melt veins in the martian basaltic meteorite zagami were investigated using analytical transmission electron microscopy with the goal to constrain the mechanisms and ptt conditions that result in the formation of high pressure phases therein our study reveals the existence of a number of high pressure minerals stishovite k and na ca rich hollandites akimotoite silicate ilmenite as well as amorphous grains of silicate perovskite composition crystals of a ferro magnesian silicate titanite with a low ca content have been identified for the first time the veins formed by rapid shear melting and solidified in extremely short times as a consequence the vein melt could not homogeneously mix and it partially preserves the chemical heterogeneity of precursor minerals accounting for the large diversity of high pressure minerals most of the tiny phases directly crystallized from the melt under high pressure at very high temperatures silicate perovskite probably amorphized upon decompression and evolved at its grain boundaries by solid state diffusion toward the lower pressure assemblage wustite stishovite not only do these observations help to understand the formation of high pressure phases in shock events but they also provide clues to the mineralogical complexity that can be expected in planetary mantles

role of tectonic denudation in warping and uplift of low angle normal faults large displacement on a low angle normal fault results in isostatic uplift of the lower plate in response to tectonic denudation simple models of the denudation process predict warping of the lower plate into a broad antiform or antiform synform pair with axes perpendicular to the direction of extension the amount of warping is strongly influenced by initial fault geometry surface topography the amount of extension and the distribution of extension within the upper plate late stage processes that augment antiform growth include one sided denudation of the antiform reverse faulting due to concave upward flexure and wholesale detachment and reverse drag folding of the antiform antiformal uplifts now exhumed by erosion form mountain ranges in the southwestern united states where conditions were favorable for warping during mid tertiary crustal extension four major structural domains are apparent in transects across these uplifts and adjacent areas 1 unextended area 2 synformal upper plate 3 antiformal uplift and 4 wedge shaped upper plate each domain is separated from adjacent domains by the traces of a master low angle normal fault

western fiordland orthogneiss early cretaceous arc magmatism and granulite facies metamorphism new zealand u pb isotopic analyses of zircons from a distinctive suite of previously undated granulite facies metaplutonic rocks here termed the western fiordland orthogneiss wfo in fiordland southwest new zealand indicate synkinematic magmatic emplacement between 120 and 130 ma ago these rocks were previously interpreted as possibly being of precambrian age initial pb and sr ratios are consistent with arc subduction related magmagenesis with little or no involvement of ancient continental crust subsequent high pressure 12 kb metamorphism of the wfo may reflect a major collision event involving crustal thickening by overthrusting of a 15 km thick sequence metamorphism ceased 116 ma ago based on206pb 238u ages of zircon from a retrogressed granulite u pb isotopic analysis of apatite along with previously published rb sr mineral ages indicate that final uplift and cooling to 300 400 c was largely completed by 90 ma the average uplift rate during this period is inferred to have been in excess of 1 mm yr unmetamorphosed gabbronorites of the darran complex in eastern fiordland inferred by some investigators to be the granulite protolith yield concordant u pb zircon ages of 137 1 ma u pb ages of apatite and previously published k ar mineral ages indicate that these rocks experienced a rapid and simple cooling history lasting only a few million years the high grade wfo and unmetamorphosed darran complex are now separated by a profound structural break however the ages and similarities in initial pb and sr isotopic ratios suggest that both suites are products of the same early cretaceous cycle of subduction related magmatism the timing of early cretaceous magmatism and metamorphism collision and resultant crustal thickening and subsequent great uplift and erosion in fiordland has important implications for terrane accretion and the evolution of relative plate motions along the new zealand segment of the gondwana margin

shock experiments up to 30 gpa and their consequences on microstructures and magnetic properties in pyrrhotite 1 shock experiments with pressures ranging from 3 to 30 gpa have been conducted on a mixed assemblage of hexagonal and monoclinic pyrrhotite all samples were studied with respect to their particular shock induced microstructures and magnetic properties at high and low temperatures up to 8 gpa microstructures in shocked pyrrhotite are characterized by mechanical deformation producing a damage of the crystal structure at pressures of 20 gpa and upward amorphization and mechanical twinning are the dominant structural features induced by shock within the lower pressure range coercivity saturation isothermal remanent magnetization and coercivity of remanence increase with shock pressures in agreement with more single domain sd like behavior simultaneously the peak of hexagonal pyrrhotite decreases and the 34 k transition of monoclinic pyrrhotite broadens and is depressed magnetic hardening is triggered by grain size reduction but also by the formation of sd within discrete multidomain grains planar deformation features subdivide such multidomain grains into lath shaped domains with average sizes lying in the sd range the planar deformation features disappear at 20 gpa and irregular nanometer sized amorphous domains occur instead pressure release from 30 gpa finally triggers partial melting of pyrrhotite the sharp interfaces between molten and crystalline pyrrhotite document a rapid change of thermal conditions within molten pyrrhotite quenched iron crystals occur the presence of native iron strongly influences the magnetic properties depending on the particular amount in the studied sample and likely affects the magnetic properties of impact lithologies on earth and extraterrestrial material

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

the case for old basaltic shergottites abstract the crystallization age of shergottites is currently not agreed upon although mineral 87 rb 87 sr 147 sm 143 nd 176 lu 176 hf and u pb isochrons all give very young ages typically in the range of 160 180 ma 207 pb 206 pb data support a much older crystallization age at 4 1 ga which is consistent with published whole rock 87 rb 87 sr data on basaltic shergottites different isotopic systems present different complexities but crater counting chronology which shows that a substantial fraction of the martian surface was resurfaced during the late heavy bombardment is in favor of an old martian lithosphere with ages in accordance with pb pb and rb sr isotopic data a 4 1 ga pb pb age of shergottites also agrees with the 142 nd and 182 w anomalies found in these rocks and concur with the presence of an actively convecting mantle during the first 500 myr of the planet s history we here present new sm nd lu hf and pb pb mineral isochrons for the basaltic shergottites shergotty and los angeles complementing our previous results on zagami bouvier a blichert toft j vervoort j d and albarede f 2005 the age of snc meteorites and the antiquity of the martian surface earth planet sci lett 240 221 233 the internal 147 sm 143 nd and 176 lu 176 hf isochrons give young ages of respectively 172 40 mswd 2 0 and 188 91 mswd 3 1 for shergotty and 181 13 mswd 0 14 and 159 42 mswd 0 01 for los angeles in contrast the pb isotope compositions of the leached whole rock fragments and maskelynite separates of shergotty and los angeles fall on the whole rock isochron previously established for zagami and other shergottite samples and collectively yield a pb pb age of 4050 70 ma for the crystallization of the basaltic shergottite suite the contrast between the 170 ma ages of internal isochrons and the 4 1 ga age supported by pb pb and 87 rb 87 sr on whole rocks simply reflects that the younger age dates the perturbation of a suite of rocks of noachian age the internal rb sr sm nd lu hf and u pb errorchrons are heavily biased by the presence of disseminated phosphate minerals and inclusions for which d h ratios d 4600 indicate strong interaction with martian subsurface waters in contrast baddeleyite occasionally present in sncs and also having extremely young u pb ages reflect resetting under the shock conditions that prevailed either during shergottite extraction from the planet or from impacts associated with a major break up event of planetesimals in the main asteroid belt we finally also re examine 39 ar 40 ar data on snc meteorites and suggest that they as well support old crystallization ages

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

shock events in the solar system the message from minerals in terrestrial planets and asteroids impacts are central to the origin and evolution of planets of the solar system the shapes of craters which can reach up to 1 000 km in diameter on the moon provide critical information on the large scale dynamics of the impact and related shock minerals formed at high pressure and temperature found in shocked terrestrial rocks and meteorites give additional and complementary insights on the shock process at a smaller scale typically from a few micrometers to a few millimeters local flaws in rocks such as voids and mineral interfaces are the preferential sites for the formation of high pressure melts and minerals calculations based on the physics of shocks and the thermodynamics and kinetics of mineral transformations provide orders of magnitude for the duration transient pressure and prevailing temperature conditions of shock events case studies on shocked terrestrial and extraterrestrial materials illustrate the links between these parameters and impact duration many of the high pressure min

a new natural high pressure na ca hexaluminosilicate caxna1 x al3 xsi3 xo11 in shocked martian meteorites a ca na hexaluminosilicate whose ca end member was previously synthesized in numerous high pressure experiments has been identified by raman spectroscopy in heavily shocked martian meteorites this mineral has a structural formula close to caxna1 x al3 xsi3 xo11 and is similar to the calcium aluminum silicate phase previously synthesized in high pressure experiments performed on anorthite and rocks of basaltic composition this new mineral occurs in shock melt pockets in two distinct settings and is intimately intergrown with sio2 stishovite the first setting encountered in zagami consists of idiomorphic equant crystals overgrown by acicular stishovite that crystallized from a melt of labradorite composition the second setting contains the na ca hexaluminosilicate phase intergrown with stishovite and hollandite and was formed during partial melting at high pressures the mineralogical association na ca hexaluminosilicate stishovite was observed in shock melt pockets which have distinct bulk compositions in seven martian shergottites this new mineral represents after majorite the second natural occurrence of a silicate mineral with silicon in both four and six coordination the assemblage stishovite na ca hexalummosilicate sets constraints on the pressure and temperature conditions that prevailed during shock in some of the studied meteorites the na ca hexaluminosilicate mineral is a potential carrier of al and na during subduction of oceanic crust in the lower mantle of the earth c 2003 elsevier b v all rights reserved

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

input of river derived sediment to the new zealand continental shelf i mass abstract the input of river borne sediments to the new zealand continental shelf has been calculated for all the major rivers and basins in new zealand south island yields 284 40 106 tonnes per year of sediment from a land area of 152 977 km2 and north island yields 105 9 4 106 tonnes per year from a land area of 114 621 km2 particularly high discharges are noted off the west coast of south island and east coast of north island and result in higher offshore sedimentation there the data are compatible with measured sedimentation rates on the new zealand continental shelf the specific sediment yield from south island is amongst the highest previously recorded

two distinct assemblages of high pressure liquidus phases in shock veins of the sixiangkou meteorite shock produced complex veins including earlier and later veins are identified in the sixiangkou l6 chondrite the early vein is intersected by the late vein and consists of coarse grained aggregates of ringwoodite majorite and lingunite and fragments of olivine pyroxene plagioclase metal and troilite as well as a fine grained matrix of garnet ringwoodite metal and troilite the late vein mainly consists of a fine grained matrix of garnet magnesiowustite metal and troilite as well as a small amount of coarse grained aggregates the amount of fine grained matrix suggests that the late vein was nearly completely melted whereas the early vein underwent partial melting both fine grained assemblages of garnet plus ringwoodite in the early vein and garnet plus magnesiowustite in the late vein are liquidus phases crystallized from shock induced melt based on our understanding of the liquidus assemblages the late vein experienced a higher pressure and temperature than the early vein

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

transmission electron microscopy characterization of dislocations and slip systems in k lingunite implications for the seismic anisotropy of subducted crust in order to estimate the seismic anisotropy of subducted crust polycrystalline samples of kalsi3o8 klingunite 25 of the total subducted transformed sediments have been synthesized and deformed under the temperature and pressure conditions of the subducted slabs transmission electron microscopy tem characterizations of the recovered samples reveal that the microstructures are clearly dominated by 0 0 1 glide involving screw dislocations for this reason only 100 could be identified as glide planes the question of 0 0 1 slip on 110 remains open few 1 2 111 dislocations were observed gliding on 110 planes which implies that 1 2 111 110 is a harder slip system than those involving 0 0 1 slip the occurrence of sub grain boundaries suggests that diffusion and climb might be active under these conditions

shock induced transition of naalsi3o8 feldspar into a hollandite structure in a l6 chondrite natural naalsi3o8 hollandite was found in the tenham chondrite it occurs as aggregates of extremely fine grains of several tens of nanometers the hollandite phase seems to have formed from host feldspar in a solid state reaction during the shock event it is very sensitive to electron beam irradiation and easily becomes amorphous similar to mgsio3 perovskite contained in the same chondrite the existence of crystalline silicate perovskite and hollandite in tenham indicates that the peak pressure and the post shock temperature were much lower than previously believed

a back arc basin formed within continental lithosphere the central volcanic region of new zealand abstract the central volcanic region is an area of quaternary volcanism and tensional tectonics within the north island of new zealand that appears to be a direct continuation of a young oceanic back arc basin the havre trough into the continental structure of new zealand volcanism is predominantly rhyolitic yet the region possesses many of the geophysical characteristics often associated with oceanic back arc basins upper mantle seismic velocities are low pn and sn velocities of 7 4 and 3 95 km s respectively the crust is anomalously thin for its continental setting and the heat flow almost all of which is expressed in the discharge of hot water through geothermal systems is about 700 mw m2 i e some twelve times greater than normal continental heat flow in order to account for such a high heat flow a large scale mass transfer of heat is required it is proposed therefore that the central volcanic region represents a site of active back arc spreading within a continental lithosphere

tropical rainfall measuring mission observation and regional model study of precipitation diurnal cycle in the new guinean region 1 the diurnal cycle of precipitation in the new guinean region is studied on the basis of satellite observations from tropical rainfall measuring mission trmm precipitation radar pr measurements and regional atmospheric model simulations the study focuses on the effects of both the land sea breeze and the orographic forcing on the diurnal evolution of precipitation during the rainy season january march in the region the 7 year trmm pr data composite reveals several distinct features of the precipitation diurnal cycle in the region precipitation bands develop in the inland coastal region in the late morning to early afternoon and migrate inland from both northeast and southwest sides of the new guinean island following the inland penetration of the sea breeze fronts a separate convective rainband develops over the central mountain ridge in the early afternoon as a result of the development of the upslope winds due to the elevated surface warming over the mountain in the morning hours this mountain ridge rainband intensifies and becomes the dominant rainband as the coastal rainbands associated with the sea breeze fronts weaken during the late afternoon and the early evening in the midnight to the early morning the rainband over the mountaintop weakens as downslope winds develop and splits into two rainbands propagating away from the mountain ridge one to the north and one to the south and weakens over the lowland some distance away from the coasts meanwhile a coastal rainband develops offshore on each side of the island in the late evening to midnight and remains strong through early morning before it migrates offshore as a result the rainfall rate peaks in the late afternoon to early evening in most land areas except for in the lowland regions between the coastlines and the mountain where the rainfall rate peaks during the midnight while the rainfall rate peaks in the late evening to early morning in most coastal regions offshore the distribution of the diurnal amplitude shows two maxima one over the mountains and the other in the coastal regions offshore convective rainfall rate peaks in the late afternoon while stratiform rainfall rate peaks in the midnight to early morning the latter dominates the large diurnal amplitude over the mountain areas in the early morning the above broad features are simulated reasonably well in a control experiment with a high resolution regional atmospheric model a sensitivity experiment with the terrain removed is conducted to elucidate the role of orographic forcing in the diurnal evolution of both the local circulation and rainfall patterns the results show that the orographic forcing affects the diurnal precipitation through three major processes first the orography increases the moisture convergence at low levels by blocking and deflecting the mean flow second the upslope winds help initiate convection in the afternoon at the mountaintop finally the deep convection over the mountain acts as a source of propagating gravity waves which help initiate rainbands in the coastal regions offshore in the late evening to early morning implication of the results is discussed

zagami product of a two stage magmatic history abstract large specimens of the zagami shergottite show highly varied grain sizes and mineral abundances on a cm scale and preferred alignment of pyroxene laths we document the presence of whitlockite and of melt veins and pockets of shock origin pyroxene crystals have homogeneous mg rich pigeonite and augite cores overgrown by fe rich zoned pyroxene mostly pigeonite rims amphibole bearing magmatic melt inclusions occur exclusively in the cores we conclude that zagami experienced a twostage crystallization history the first stage occurred in a deep seated slowly cooling magma chamber there the homogeneous mg rich cores of the pyroxenes crystallized during relatively slow cooling the deep seated origin of the cores is also indicated by the presence of amphibole within them which requires pressures of formation equivalent to crystallization at depths 7 5 km on mars modest abundance of homogeneous mg rich cores 15 20 indicates that crystal settling did not play a significant role in this part of the magma chamber during the second stage the mg rich pyroxenes were entrained into a magma that either intruded to the near surface and cooled in a relatively thin dike or sill or extruded to the surface and crystallized in a lava flow 10 m thick again without indications for crystal settling this scenario is suggested by estimates of cooling rates of 0 1 0 5 c h based on sizes of the plagioclase maskelynite crystals and of 0 02 c h based on the width of pyroxene exsolution lamellae brearley 1991 irregular shapes of the mg rich cores result from resorption and possible solid state diffusion and the shapes and sizes of the pyroxenes after crystallization of fe rich pigeonite rims onto the cores were strongly controlled by the shapes and sizes of the cores the finer grained areas of the rock inherited smaller and more numerous mg rich pyroxene cores from the first stage than did the coarser grained areas crystallization of both augite and pigeonite cores at depth but mostly pigeonite rims in the nearsurface environment may be the result of a phase boundary shift and expansion of the pigeonite stability field at lower pressures the estimated depth of the magma chamber for zagami of 7 5 km and thickness of the putative lava flow of 10 m are consistent with calculations and observations of volcanic constructs and flows in the tharsis region of mars

boundary layer evolution and regional scale diurnal circulations over the and mexican plateau data collected in a measurement campaign in february and march 1997 showed that the mexico basin also called the valley of mexico located atop the mexican plateau fails to develop the strong nocturnal inversions usually associated with basins and does not exhibit diurnally reversing valley wind systems data analyses two and three dimensional numerical simulations with the regional atmospheric modeling system rams and a lagrangian particle dispersion model are used to interpret these observations and to examine the effects of topography and regional diurnal circulations on boundary layer evolution over the mexico basin and its surroundings during fair weather periods in the winter dry season we show that the boundary layer evolution in and above the basin is driven primarily by regional diurnal circulations that develop between the air above the mexican plateau and the generally cooler surrounding coastal areas a convective boundary layer cbl grows explosively over the plateau in the late morning to reach elevations of 2250 m agl 4500 m msl by noon and a strong baroclinic zone forms on the edges of the plateau separating the warm cbl air from its cooler surroundings in early afternoon the rates of heating and cbl growth are slowed as cool air leaks onto the plateau and into the basin through passes and over low lying plateau edges the flow onto the plateau is retarded however by the strongly rising branch of a plain plateau circulation at the plateau edges especially where mountains or steep slopes are present an unusually rapid and deep cooling of the air above the plateau begins in late afternoon and early evening when the surface energy budget reverses the cbl decays and air accelerates onto the plateau through the baroclinic zone flow convergence near the basin floor and the associated rising motions over the basin and plateau produce cooling in 3 hours that is equivalent to half the daytime heating while the air that converges onto the plateau comes from elevations at and above the plateau it is air that was modified earlier in the day by a cool moist coastal inflow carried up the plateau slopes by the plain plateau circulation

thermochronological constraints on the multiphase exhumation history of the ivrea verbano zone of the southern alps abstract the ivrea verbano zone of the western southern alps nw italy exposes a well preserved tilted section across the lower continental crust making it a key region for studying deep crustal and exhumation processes this paper refines the cooling and exhumation history of the ivrea verbano zone using k ar dating of mica and illite rich fault gouges as well as zircon fission track and u th he thermochronology the adjacent strona ceneri zone sesia lanzo zone and lower penninic nappes are included in the study to derive a broader picture of the low temperature history of the area in the strona profile of the ivrea verbano unit the biotite k ar zircon fission track and u th he geochronometers show well preserved but unusually wide partial retention zones the youngest ages representing the formerly deepest position are situated along the insubric line the main foliation of the ivrea verbano zone is vertical the exhumation of the ivrea verbano zone which section has a horizontal position on the surface now took place in three steps during jurassic time the ivrea verbano zone was exhumed to a shallow to mid crustal position by continental scale extension in this displacement the pogallo line probably played a dominant role the studied section occupied an oblique position with a calculated angle of ca 15 to 23 in the jurassic later the ivrea verbano zone experienced a minor cooling event in the late eocene 38 ma zircon fission track ages that was probably related to thrusting and erosion the final exhumation towards the surface took place in the mid miocene as documented by the ca 14 ma zircon u th he ages and a 12 8 ma k ar fault gouge age the magnitude and the high rate of final exhumation suggest orogen parallel extension as a driving force which is widespread in the alps in the lower to middle miocene and is most probably connected to orogenic collapse

microscopic evidence of stishovite generated in low pressure shock experiments on porous sandstone constraints on its genesis it has been almost exactly half a century since the first synthesis of stishovite in shock experiments on quartz was reported but its formation conditions during shock is still under debate here we present direct transmission electron microscopic observation of stishovite within material recovered from high explosive shock experiments on porous sandstone shocked at 7 5 and 12 5 gpa our observations allow for new conclusions on the genesis of stishovite in a close to nature environment the formation of stishovite in short time shock experiments proves that its crystallization is ultrafast 1 s crystals were found only embedded in amorphous veins indicating homogeneous nucleation crystallization from melt rather than from glass can be concluded from the observation of roundish defect free crystals up to 150 nm in diameter embedded in nondensified glass the formation of stishovite at 7 5 gpa is in accordance with the phase diagram of silica if rapid undercooling is present that becomes only possible by the existence of small hot spots in an otherwise cold material which is supported by transient heat calculation the absence of coesite at 7 5 gpa suggests kinetic hindrance of its crystallization from melt and thus smaller critical cooling rates compared to stishovite where critical cooling rates are estimated to be as large as 1011 k s 1 while the amorphous veins containing stishovite represent unambiguously hot spots no associated pressure amplification could be verified within these veins the rapid liquidus crystallization of stishovite only in hot spots generated in porous material is an alternative formation mechanism to the widely accepted theory of solid solid transition from quartz to stishovite and might represent the more general mechanism occurring in nature for low shock pressure events

vertical moisture transport above the mixed layer around the mountains in western sumatra 1 a remarkable increase in moisture frequently occurred in august afternoon radio soundings in 2001 in the layer up to 1000 m above the mixed layer ml near the mountains of western sumatra indonesia this moisture enhancement was also apparent in the monthly mean diurnal cycle the mixing ratio is not vertically uniform in this layer suggesting that turbulent mixing cannot be a major mechanism of the vertical moisture transport a climatological numerical study using a cloud resolving model suggests that thermally induced upslope winds converge over the mountain summits during daytime forming a moist air band along the mountain range ambient winds above the mountain range then advect the moist air into the surroundings moisturizing the air above the ml over the leeward terrain this mechanism is important for producing diurnal mesoscale precipitation systems over a wide area of the indian ocean as documented by previous studies analyzing trmm and gms observational data

eclogitic minerals in a shocked basaltic meteorite analytical transmission electron microscopy atem was used to characterize mineral parageneses occurring in melt veins of shock origin in the martian meteorite zagami we discovered a new ultra high pressure eclogite facies mineral assemblage consisting of omphacite stishovite and kalsi3o8 hollandite these tiny 200 300 nm high pressure minerals are embedded in silicate glass which forms the groundmass of the shock veins the microtexture of the veins and zoning of the clinopyroxene indicate the formation of minerals by crystallization from a high pressure melt using calibration data from shock and multi anvil experiments we infer that frictional melting occurred in veins at minimum temperatures of 2400 2500 c and at a pressure of ca 30 gpa subsequently the high pressure phases crystallized during decompression in the pressure interval from 25 5 gpa

multigenetic gravity couple across a modern convergent margin inheritance from cretaceous asymmetric extension summary profiles of the pronounced gravity couple associated with the puysegur margin in new zealand suggest that the crust of the fiordland block which occupies the leading edge of the overriding pacific plate thins rapidly trenchwards and is domed upwards the crust beneath parts of central western fiordland appears to be anomalously thin 10 km and causes a major 180 mgal positive anomaly in the forearc region the density contrast caused by subduction of the australia plate to upper mantle depths contributes little to this positive bouguer anomaly the radical crustal thinning cannot have originated chiefly by differential uplift coupled with erosion in response to late cenozoic convergence as proposed earlier by others the amount of crustal thinning required is not consistent with the limited volume of sediment in surrounding basins moreover the timing of thinning is chiefly cretaceous not late cenozoic an alternative hypothesis of tectonic denudation is invoked that attributes the crustal structure of fiordland to cretaceous early tertiary asymmetric continental extension and consequent crustal thinning because the present crustal structure retains inherited geometry from cretaceous tectonism the observed positive gravity anomaly over fiordland is not due solely to the modern plate convergence but reflects the earlier extension and hence the gravity couple is multigenetic

natural high pressure polymorph of merrillite in the shock veins of the suizhou meteorite abstract a new high pressure polymorph of merrillite with the structure of trigonal ca 3 po 4 2 was found in the shock produced veins of the suizhou meteorite where it coexists with ringwoodite majorite naalsi 3 o 8 hollandite and majorite pyrope garnet the crystallographic nature of this natural ca 3 po 4 2 phase was characterized by raman spectroscopy and x ray diffraction and all data compare favorably to the same data obtained from ca 3 po 4 2 synthesized at 14 gpa and 1400 c the cell parameters of this new high pressure mineral are a 5 258 1 angstroms and c 18 727 3 angstroms space group r 3m and density 3 447 g cm 3 where the number in parentheses are standard deviations in the last significant digits the natural occurrence of the ca 3 po 4 2 phase together with other high pressure minerals constrains the pressure of the shock veins at about 23 gpa the suizhou meteorite provides the first naturally occurring example of ca 3 po 4 2 polymorph