the macolod corridor a rift crossing the philippine island arc abstract the macolod corridor in southwestern luzon is an approximately 40 km wide zone of still active intense quarternary volcanism which perpendicularly crosses the island in a ne sw direction the tectonic setting of the corridor is still somewhat questionable due to several not yet well understood major structural elements affecting southwestern luzon based on the presently available information we believe that the corridor is a pull apart zone formed by a diffuse system of nw se oriented shearing

behavior of transversely isotropic shale observed in triaxial tests and brazilian disc tests abstract shale rock is widely distributed in nature and must be taken into account in some rock engineering applications in this research three kinds of experiments namely the conventional triaxial compression test reducing confining pressure test and brazilian test were conducted on a type of shale rock specimen with a horizontal bedding plane and a vertical bedding plane collected from lushan city jiangxi province china to further investigate the bedding effect on the mechanical properties of shale rock an acoustic emission ae monitoring system was used to study the fracture process under the conventional triaxial compression test whereas a digital image correlation dic system was employed to monitor the deformation of disk faces during the failure process under the brazilian test another key issue addressed in this research is the failure process and mechanism of shale specimens with horizontal and vertical bedding planes under the reducing confining pressure test the conventional triaxial compression test shows that the bedding plane could easily affect the elasticity modulus and failure pattern and the failure of the bedding plane can lead to stronger energy release and a higher ae count level the reducing confining pressure test shows that the dissipated energy magnitude of unloading path ii reducing confining pressure and increasing axial stress is much larger than that of unloading path i reducing confining pressure and keeping axial strain constant and that continuous energy input and larger energy dissipation led the specimens under unloading path ii to fail faster than those under unloading path i the brazilian test further revealed that the bedding plane has a significant effect on the tensile strength and failure pattern of shale rock

a modified hoek brown failure criterion for anisotropic intact rock abstract the hoek brown criterion parameters c i m i and s are significantly influenced by the strength anisotropy of intact rock in the present study the criterion was modified by incorporating a new parameter k to account for the effect of strength anisotropy thus being able to determine the strength of intact anisotropic rock under loading in different orientations of the plane of anisotropy the range of the parameter k for the rocks tested has been analytically investigated by carrying out triaxial tests in different orientations of the foliation plane the proposed modification was studied for metamorphic rocks gneiss schist marble but could also be applied to other rock types exhibiting inherent anisotropy e g sedimentary as well as igneous rocks the proposed modified criterion is intended for use for prediction of strength of intact rock but can also be extended to rock masses

newly discovered eastern dispersal of the youngest toba tuff volcanic glasses with minor mafic mineral fragments such as biotite and hornblende found in deep sea sediments of the south china sea basin scsb have been clearly identified as eruptive products of the youngest toba tuff ytt northern sumatra indonesia the tephra layer occurs between marine oxygen isotopic event 5 1 79 3 ka and event 4 22 64 1 ka with an interpolated age of 74 0 ka which is in good consistence with previous radiometric dating 73 75 ka and ice core dating 71 5 ka of the ytt the tephra consists predominantly of bubble wall shards with minor elongated vesicles of pumice fragments geochemical characteristics of the tephra such as high total alkali content high 87 sr 86 sr ratio and uniformity of their compositions all suggest that the recovered tephra is of the youngest toba tuff this finding supports an extended dispersal of coarse 63 mm glass shards over 1500 km northeast of the toba caldera a direction opposite to what previously conceived while providing a better documentation of the distribution extent of the toba ash this report points to the need to reestimating the eruptive volume of the ytt and re evaluating its environmental impact q 2000 elsevier science b v all rights reserved

geochemistry of silicic magmas in the macolod corridor sw luzon philippines evidence of distinct mantle derived crustal sources for silicic magmas silicic volcanic deposits 65 wt sio2 which occur as domes lavas and pyroclastic deposits are relatively abundant in the macolod corridor sw luzon philippines at makiling stratovolcano silicic domes occur along the margins of the volcano and are chemically similar to the silicic lavas that comprise part of the volcano pyroclastic flows are associated with the laguna de bay caldera and these are chemically distinct from the domes and lavas at makiling stratovolcano as a whole samples from the laguna de bay caldera contain lower concentrations of mgo and higher concentrations of fe2o3 t than the samples from domes and lavas the laguna de bay samples are more enriched in incompatible trace elements the silicic rocks from the domes makiling volcano and laguna de bay caldera all contain high alkalis and high k2o na2o ratios melting experiments of primitive basalts and andesites demonstrate that it is difficult to produce high k2o na2o silicic magmas by fractional crystallization or partial melting of a low k2o na2o source however recent melting experiments sisson et al contrib mineral petrol 148 635 661 2005 demonstrate that extreme fractional crystallization or partial melting of k rich basalts can produce these silicic magmas our model for the generation of the silicic magmas in the macolod corridor requires partial melting of mantle derived evolved moderate to k rich crystallized calc alkaline magmas that ponded and crystallized in the mid crust major and trace element variations along with oxygen isotopes and ages of the deposits are consistent with this model

s type asteroids ordinary chondrites and space weathering the evidence from galileo s fly bys of gaspra and ida new observations of the s type asteroids gaspra and ida especially by the galileo spacecraft demonstrate that a space weathering process operates which modifies the reflectance spectra of fresh material to be redder straighter and have shallower absorption bands the weathering process appears similar to but less potent than that observed on the moon it operates in the sense that it would tend to convert spectra of ordinary chondrites oc to having the spectral traits of s type asteroids these results appear to resolve the major obstacles of the long standing s type conundrum about the provenance of ordinary chondrite meteorites a wide body of recent research which is reviewed here builds on previous meteoritical evidence to support a new developing consensus that the larger s type asteroids are a diverse assortment of silicaceous assemblages which includes the ordinary chrondite parent bodies recent fairly realistic laboratory simulations of space weathering processes have changed oc spectra to resemble s type spectra j f bell s highly regarded earlier paradigm that oc parent bodies would be found only among sub 10 km main belt asteroids has been tested by an extensive observational survey by r binzel and his proteges the result is that no small main belt analog for the ocs has been found not even the somewhat oc like object boznemcova this article reviews the history of the s type conundrum which set the stage for galileo s historic flybys i review the findings about gaspra and ida including results about their geology their geophysical structure and probable origins and about ida s small moonlet dactyl density constraints on ida set by dactyl s orbit rule out for ida at least the classic view of s types as metallic stripped cores of differentiated precursor asteroids new analysis of the galileo spectral images of ida is presented that provides strong evidence that space weathering occurs on ida and that ida and the koronis family asteroids in general are plausibly oc like in composition after reviewing 1990s developments on the s type conundrum i advocate a new perspective that the ordinary chondrite parent bodies are among the s type asteroids a diverse grouping that also contains other silicaceous and silicate metal assemblages presumably including various stony irons and primitive achondrites represented in meteorite collections gaspra may be such a metal rich assemblage

deformation and strength anisotropy of asan gneiss boryeong shale and yeoncheon schist results of deformability and strength anisotropy on three rock types found in korea are reported the experiments were conducted on rock specimen obtained from the directional coring system the anisotropy ratios of elastic modulus were from 1 7 to 4 0 for rock types in this study the applicability of transversely isotropic model was quantitatively investigated

e type asteroid spectroscopy and compositional modeling 1 we present near infrared spectroscopic observations 0 8 2 5 m of e type asteroids we combine these observations with visible wavelength spectra obtained by other researchers and perform hapke theory mixing model simulations of e type asteroid spectra in order to constrain possible compositions aubrites were originally suggested as the meteorite analog for the e type asteroids because of their similar visible wavelength colors and high albedos the designation e was originally linked with the mineral enstatite common in aubrite meteorites more recently the sulfides troilite and oldhamite have been suggested as possible components of e type asteroids we tested the suggested compositional interpretations of aubrite meteorites and or aubrites enhanced with sulfides we also tested compositions of aubrites mixed with low iron silicate minerals we find that e types can be separated into three groups on the basis of inferred composition nysa like e types are consistent with silicate mineralogy higher in iron than the mineral enstatite angelina like asteroids are consistent with silicate mineralogy including a sulfide such as oldhamite and hungaria like e types are not inconsistent with aubrites our results indicate that some e type asteroids may be composed of materials that are not sampled by meteorites

space weathering on airless bodies resolving a mystery with lunar samples using new techniques to examine the products of space weathering of lunar soils we demonstrate that nanophase reduced iron npfe0 is produced on the surface of grains by a combination of vapor deposition and irradiation effects the optical properties of soils both measured and modeled are shown to be highly dependent on the cumulative amount of npfe0 which varies with different starting materials and the energetics of different parts of the solar system the measured properties of intermediate albedo asteroids the abundant s type asteroids in particular are shown to directly mimic the effects predicted for small amounts of npfe0 on grains of an ordinary chondrite regolith this measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids

geochemical evidence for initiation of the modern mekong delta in the southwestern south china sea after 8 ma abstract sedimentary records in the southwestern south china sea reflect the evolving erosion and drainage systems that have operated in southeast asia during the neogene analyses of the chemistry and clay mineral composition of sediments from international ocean discovery program iodp site u1433 allow us to examine these processes over the last 17 ma sediment older than 8 ma was deposited relatively slowly sr and nd isotopes indicate a variable provenance with sequences of less and more altered material accompanied by strong changes in the proportion of smectite sediment flux was probably from indochina as well as from a more primitive volcanic source most likely the palawan ophiolite and or luzon sediments younger than 8 ma show a more stable sr and nd isotope character indicating sources close to those seen in the modern mekong river although with some influx from smaller rivers draining the indochina margin especially from 4 to 8 ma our data are consistent with seismic estimates for an onset to the mekong in its present location after 8 ma following an avulsion from the gulf of thailand

pyroxene spectroscopy revisited spectral compositional correlations and relationship to geothermometry the authors wish to thank the various agencies which have provided the necessary support for this project including grants in aid of research from sigma xi the scientific research society to e a c the geological society of america grant 3741 87 to e a c and nasa planetary geology and geophysics grant nagw 642 to m j g

spectral properties and rotational spectral heterogeneity of 433 eros composite spectra of different rotational aspects of the s asteroid 433 eros were assembled from previous studies covering the wavelength range 0 33 2 5 m these data allow us to measure significant attributes of eros s spectrum its mafic mineral absorptions and the degree and nature of compositional heterogeneity of its surface we also evaluated previous s asteroid taxonomies using independent methods and from this test determined that the taxonomy of gaffey et al 1993 provides a sound basis for relating eros to other s asteroids on average eros resembles the s iv asteroids which bear the closest resemblance to ordinary chondrites in mafic mineralogy however eros also exhibits distinct rotational spectral variations comparable to the greatest yet recognized on an s asteroid one side of the asteroid has a shorter wavelength 1 m absorption and a stronger 2 m absorption than the global average and is interpreted to be richer in pyroxene the opposite face has a longer wavelength 1 m absorption and a weaker 2 m absorption and is interpreted to be richer in olivine the pyroxene rich side coincides with a facet like face identified in radar studies and the olivine rich side coincides with a convex shaped face each side of the asteroid exhibits spectral affinities with a different spectral class of s asteroids demonstrating that such subdivisions of s asteroids represent different parts of a compositional continuum high spatial resolution measurement of the mineralogic and elemental compositions and especially the geologic settings of these different materials by the near earth asteroid rendezvous mission will provide a great advance in the understanding of the origin and evolution of a candidate ordinary chondrite parent body

model near infrared optical constants of olivine and pyroxene as a function of iron content the imaginary coefficients of the complex index of refraction of olivine low ca orthopyroxene and high ca clinopyroxene are derived as a function of iron content and wavelength over the spectral region 0 4 to 2 5 m from reflectance spectra of powders and hapke radiative transfer theory reflectance spectra as a function of composition and grain size are computed and compared i find that while spectral effects of variations in these parameters are similar they are distinguishable variations in iron content do not explain all the observed spectral variations in the spectra of the samples investigated

compositional variations of the lunar crust results from radiative transfer modeling of central peak spectra 1 we present model mineralogy of impact crater central peaks combined with crustal thickness and crater central peak depth of origin models to report multiple perspectives of lunar crustal composition with depth here we report the analyses of 55 impact crater central peaks and how their compositions directly relate to the lunar highlands sample suite a radiative transfer model is used to analyze clementine visible plus near infrared spectra to place compositional constraints on these central peak materials central peaks analyzed are dominantly magnesian and plagioclase poor strong compositional similarities to lunar mg suite materials are evident relative to crustal thickness estimates central peak mineralogy becomes more plagioclase rich as the crust thickens relative to the crust mantle boundary the origin of peaks with dominantly mafic mineralogy are confined to the lower crust and primarily within the south pole aitken and procellarum kreep terranes pkt additionally central peaks with anorthositic mineralogy 60 vol plagioclase are transported to the surface from all depths in the crustal column and confined to the feldspathic highlands terrane fht the discovery of mafic and magnesian materials consistent with mg suite rocks of the sample collection in all lunar terranes suggests that the process and sources that give rise to these types of rocks is not unique to the pkt and not necessarily dependent on incompatible elements for formation the identification of ferroan and magnesian anorthositic material near the crust mantle boundary of the fht is also inconsistent with an increasing mafic feldspar ratio and mg with depth in the crust

the geology of gaspra the surface of gaspra can be divided into several facets separated by ridges superimposed on the facets and ridges are two populations of craters type 1 craters are crisply defined and constitute a production function of impact origin type 2 craters are mostly irregular shallow depressions and probably of various origins some of the type 2 craters may have formed by impact and be remnants of a crater population that predates the type 1 population the number of type 1 craters suggests that they started to accumulate 2 107 to 3 108 years ago the freshest craters have a depth diameter ratio of 1 7 as compared with 1 5 typically observed on other bodies the craters appear to have become shallower with age at a rate of 10 6 to 10 7 m year the shallow depth of newly formed craters and the progressive degradation with age are ascribed to downslope movement of poorly coherent surface materials the movement being aided by seismic shaking as a result of impact the surface shows subtle color differences the most prominent differences are observed around craters on ridges where the surface has a stronger 1 m absorption than elsewhere the contrast is not observed around craters on the facets the color differences are attributed to alteration of the materials brought to the surface the unaltered material is estimated to be located at least 50 m below the surface on the facets only on the ridges is unaltered material at a shallow enough depth to be excavated by the observed craters the rate of degradation of craters the rounded form of the ridges the depth of altered material on the facets and the presence of old degraded craters all suggest that gaspra is covered with a regolith a few tens to several tens of meters thick

a synthesis and review of historical eruptions at taal volcano southern luzon philippines abstract the philippines is an area of persistent volcanism being located in one of the most tectonically active regions in the world taal volcano in southern luzon is the second most frequently erupting volcano of the 24 active volcanoes in the philippines a comprehensive and critical review of published and unpublished references describing the 33 known historical eruptions of taal may provide answers to knowledge gaps on past eruptive behavior processes and products that could be utilized for hazard and risk assessment of future eruptions data on the prehistoric eruptions and evolution of taal caldera and subsequent deposits are limited only four caldera forming events were identified based on four mapped ignimbrite deposits from oldest to youngest these are the silicic alitagtag ali and caloocan cal pumice flow deposits the dacitic sambong ignimbrite sam and the basaltic andesitic taal scoria flow renamed scoria pyroclastic flow sfl except for sfl with 14c dating yielding 5380 70 to 6830 80 ky there are no age constraints or estimates of extent for the three older deposits a comprehensive review of the historical eruptions of taal volcano is the central element of this paper and includes all eruptions from ad1572 the first known historic event to ad1977 eruption styles and the interplay between processes and products for each eruption are reinterpreted based on the narrative descriptions from all available accounts a change of classification of eruption styles and eruptive products is undertaken for some events at least nine reported eruptions were deemed uncertain including the ad1605 ad1611 event more likely seismic swarms the ad1634 ad1635 and ad1645 may simply be solfataric or hydrothermal activity events and the ad1790 ad1825 ad1842 ad1873 and ad1903 events that were listed in recent published and unpublished documents but do not provide any details to describe and confirm the eruptions except for listing a default vei of 2 pyroclastic density currents brought devastating impacts to the communities around taal during the ad1749 ad1754 ad1911 and ad1965 eruptions and remain the biggest threat in the case of renewed volcanic activity significant implications for aviation are implied by the narrative of tephra fall dispersal towards manila the central gateway of international aviation operation in the philippines during the ad1754 eruptions the dispersal of tephra in the event of an explosive eruption at taal towards metro manila would have catastrophic effects to transport utilities and business activity potentially generating enormous economic losses hazards from earthquake events associated with future volcanic activity may also have localized impacts occurrences of liquefaction phenomena as a consequence of severe ground shaking are interpreted during the ad1749 ad1754 and ad1911 eruptions more work needs to be done to develop a comprehensive understanding of the hazards and risks associated with an explosive eruption at taal volcano especially related to the older quaternary caldera forming eruptions that produced large volume pyroclastic deposits that are extensively distributed and exposed we acknowledge that there may be additional prehistoric eruptions where the eruptive products have not been preserved recognized or reported events that cannot be verified or do not have sufficient details to confirm the eruption have been downgraded to uncertain eruptions that are confirmed with identified dispersal and emplacement of tephra fall and other eruptive deposits as interpreted from narrated records could provide crucial information that may be utilized in hazard assessment

determining an age for the inararo tuff eruption of mt pinatubo based on correlation with a distal ash layer in core md97 2142 south china sea abstract the largest known eruption of mt pinatubo in the late quaternary was the inararo tuff formation itf eruption roughly estimated as five times larger than the 1991 eruption the precise age of the itf eruption has been uncertain here a correlative of the itf eruption layer d is identified in marine sediments and an age obtained tephras were identified in core md97 2142 of leg ii of the images iii cruise in northern offshore of palawan southeastern south china sea 12 41 33 n 119 27 90 e on the basis of the geochemical and isotopic fingerprints layer d can be correlated with the itf eruption of the modern pinatubo eruption sequence by means of the md97 2142 specmap chronology layer d was dated at around 81 2 ka this estimated age of the itf eruption and tephra layer d coincides with an anomalously high so4 2 spike occurring within the 5 millennia from 79 to 84 ka in the gisp2 ice core record

near at eros imaging and spectral results eros is a very elongated 34 kilometers by 11 kilometers by 11 kilometers asteroid most of the surface of which is saturated with craters smaller than 1 kilometer in diameter the largest crater is 5 5 kilometers across but there is a 10 kilometer saddle like depression with attributes of a large degraded crater surface lineations both grooves and ridges are prominent on eros some probably exploit planes of weakness produced by collisions on eros and or its parent body ejecta blocks 30 to 100 meters across are abundant but not uniformly distributed over the surface albedo variations are restricted to the inner walls of certain craters and may be related to downslope movement of regolith on scales of 200 meters to 1 kilometer eros is more bland in terms of color variations than gaspra or ida spectra 800 to 2500 nanometers are consistent with an ordinary chondrite composition for which the measured mean density of 2 67 0 1 grams per cubic centimeter implies internal porosities ranging from about 10 to 30 percent

widespread seagrass meadows during the early miocene burdigalian in southwestern australia paralleled modern seagrass distributions abstract the trealla limestone which forms a veneer of foraminiferal rich limestone and covers over 4000 km2 of the tectonically stable southern carnarvon platform contains the oldest evidence for seagrass meadows known in western australia it belongs to lower tf1 letter stage based on larger benthic foraminifers of the burdigalian within interval 19 16 ma and is the only miocene unit on the platform the trealla limestone here is coeval to the deeper water lower part of the much thicker trealla limestone in the exmouth sub basin to the northwest a seagrass meadow depositional environment is indicated by most of the studied microfacies based on comparisons with modern sediment composition and foraminiferal assemblages found in innermost shelf seagrass banks between 23 s and 32 s on the present western australian coast some levels in the trealla limestone on the platform e g with abundant miliolid foraminifers and absence of coral debris probably were deposited in and around dense seagrass meadows similar to those present today in the metahaline 40 55 ppt salinity reaches of shark bay whereas other levels e g coral floatstone were deposited under normal marine conditions based on comparisons with modern carbonate sediment and biota in the region the biogenic composition of the trealla limestone on the platform suggests winter minimum sea surface temperatures within the range of 17 22 c the nullabor limestone in the eucla basin at 10 further south on the southern australian margin is similar at least in part in composition and age to the trealla limestone on the southern carnarvon platform both may have been deposited during a burdigalian sea level rise and during part of the miocene climate optimum recognized elsewhere sediment composition and foraminiferal assemblages including epiphytic types found in the trealla and nullabor limestones are similar to those in the modern seagrass banks of the region this suggests that seagrasses similar to the extensive posidonia and amphibolus stands which are dominant today between 25 s and 35 s along the western australian coast were widespread during the burdigalian

effect of layer orientation on the failure of layered sandstone under brazilian test conditions abstract the experimental research in this paper focuses at macro scale on the effect of the layer orientation on failure strength and fractures induced by the brazilian tensile test for one particular sandstone sandstone from modave in the south of belgium the variation in the strength the applied energy and the failure pattern are examined as a function of the inclination angle between the layer plane and the loading direction for each sample the length of fractures parallel to the layers as well as corresponding to other directions is measured for the layered sandstone in this study the transition angle range is determined whereby the relative importance of both types of fractures switches

significance of slab derived partial melts and aqueous fluids for the genesis of tholeiitic and calc alkaline island arc basalts evidence from mt arayat philippines abstract mt arayat an inactive stratovolcano is located behind the volcanic front of the bataan segment of the taiwan luzon arc in the central valley of luzon the philippines volcanism in this arc segment results from subduction of south china sea basin crust along the manila trench eruption products of mt arayat comprise pyroclastics and porphyritic basalt and andesite lavas of high k calc alkaline affinity compared to typical oceanic island arc volcanics the basalts display slightly elevated abundances of ta and nb relative to zr and hf and of ta nb zr hf and light rare earth elements lree s relative to y and heavy rare earths hree s their ree distribution suggests mixing between high hree low lree hree and low hree high lree hree components the latter suggesting the presence of residual garnet in the source region of mt arayat basalts enrichment of lree s relative to hree s is typical of calc alkaline and high k calc alkaline island arc basalts but is usually missing or small in island arc tholeiites lree enrichment is often attributed to a metasomatizing aqueous fluid generated during dehydration of the subducted slab for this model to be applicable extremely low abundances in the fluid of agents like f oh and or co2 3 which form hard complexes with the ree s are a prerequisite due to the temperature dependence of the eu 3 eu 2 redox potential divalent eu predominates in aqueous fluids of low complex forming capacity in the subduction zone environment whereas the other ree s with the possible exception of yb are still trivalent a lree enriched aqueous fluid generated by slab dehydration should therfore display a positive eu anomaly however lree enriched island arc basalts generally do not show positive eu anomalies implying that this lree enrichment is unlikely to result from ree transfer by an aqueous fluid instead a model is favoured which assumes contributions from both slab derived aqueous fluids and partial melts in the source region for island arc tholeiites the mantle wedge is only affected by a lile enriched aqueous fluid whereas the source region for calc alkaline and high k calc alkaline basalts is additionally metasomatized by small volumes of melt generated by small degrees of partial melting of the subducted slab with garnet as a residual phase these lree enriched partial melts may react with the depleted peridotite of the mantle wedge to produce domains of refertilized garnet peridotite subsequent partial melting produces calc alkaline melts whose trace element compositions display signatures of both depleted peridotite and more fertile garnet peridotite

a spectral analysis of ordinary chondrites s type asteroids and their component minerals genetic implications three salient features of visible and infrared reflectance spectra of ordinary chondrites ocs and s type asteroids are 1 albedo at 0 56 m 2 continuum slope and 3 depth of the electronic absorption band due to octahedrally coordinated fe2 in olivine and pyroxene these quantities were numerically extracted from the spectra of 23 ocs representing all metamorphic grades and 39 s type asteroids to be plotted in a three dimensional coordinate system the spectral characteristics of three ocs which were comminuted melted recrystallized and recomminuted are also presented in the same format the results show that although laboratory simulation of melt alteration in an asteroidal regolith does alter oc spectra the spectral parameters of these altered meteorites do not change enough to leave the parametric region defined by unaltered oc spectra when the region containing the 39 s asteroid spectra is compared with that of the altered and unaltered ocs it is found that not one of the ocs falls within the s asteroid region the differences may be largely attributed to spectral differences between the respective metallic components the range of s asteroid parameters is then compared with potential pure end member components most likely to result from magmatic differentiation of a chondritic protoasteroid olivine orthopyroxene clinopyroxene and fe ni meteorite metal alternatively represented by the m asteroids it is found that the s asteroid array is consistent with random mixtures of the differentiated components except for a notable dominance of the spectral characteristics of the opaque metallic component these results suggest that the m asteroids may form a composition continuum with the s asteroids we discuss a scenario consistent with this analysis and with the bell et al theory of the geological structure of the asteroid belt ordinary chondritic protoasteroids of all sizes were probably the dominant primary condensates in the inner portion of the main asteroid belt these were later heated by electromagnetic induction or by 26al nuclide decay as a result the smaller ones were subjected to various degrees of metamorphism while the larger ones were subjected to large scale magmatic differentiation petrological domains of the s asteroids beneath a mixed regolith may be large and supply achondrites irons and stony irons to earth rather than well mixed breccias of these components the smaller oc protoasteroids may still be abundant in the asteroid belt but if small enough to escape differentiation may also be small enough to escape earth based identification

influence of temperature on brittle creep in sandstones the characterization of time dependent brittle creep promoted by chemically active pore fluids is fundamental to our understanding of the long term evolution and dynamics of the earth s crust here we report results from a study of the influence of temperature on both short term strength and time dependent brittle creep in three sandstones under triaxial stress conditions we show that an increase in temperature from 20 degrees to 75 degrees c significantly enhances stress corrosion cracking in all three sandstones leading to 1 a systematic reduction in strength during constant strain rate experiments and 2 an increase by several orders of magnitude in brittle creep strain rates during stress stepping creep experiments we also show that a conventional creep experiment performed at 75 degrees c exhibits a qualitatively similar three stage brittle creep curve as that observed at ambient temperature extrapolation of our results suggests that temperature is likely to be the dominant influence on the evolution of creep strain rate with depth in the shallow crust citation heap m j p baud and p g meredith 2009 influence of temperature on brittle creep in sandstones geophys res lett 36 l19305 doi 10 1029 2009gl039373

geology of 243 ida abstract the surface of 243 ida is dominated by the effects of impacts no complex crater morphologies are observed a complete range of crater degradation states is present which also reveals optical maturation of the surface darkening and reddening of materials with increasing exposure age regions of bright material associated with the freshest craters might be ballistically emplaced deposits or the result of seismic disturbance of loosely bound surface materials diameter depth ratios for fresh craters on ida are 1 6 5 similar to gaspra results but greater than the 1 5 ratios common on other rocky bodies contributing causes include rim degradation by whole body ringing relatively thin ejecta blankets around crater rims or an extended strength gradient in near surface materials due to low gravitational self packing grooves probably represent expressions in surface debris of reactivated fractures in the deeper interior isolated positive relief features as large as 150 m are probably ejecta blocks related to large impacts evidence for the presence of debris on the surface includes resolved ejecta blocks mass wasting scars contrasts in color and albedo of fresh crater materials and albedo streaks oriented down local slopes color data indicate relatively uniform calcium abundance in pyroxenes and constant pyroxene olivine ratio a large relatively blue unit across the northern polar area is probably related to regolith processes involving ejecta from azzurra rather than representing internal compositional heterogeneity a small number of bluer brighter craters are randomly distributed across the surface unlike on gaspra where these features are concentrated along ridges this implies that debris on ida is less mobile and or consistently thicker than on gaspra estimates of the average depth of mobile materials derived from chute depths 20 60 m grooves 30 m and shallowing of the largest degraded craters 20 50 m minimum 100 m maximum suggest a thickness of potentially mobile materials of 50 m and a typical thickness for the debris layer of 50 100 m

anisotropy of elastic moduli p wave velocities and thermal conductivities of asan gneiss boryeong shale and yeoncheon schist in korea abstract this paper presents the anisotropic characteristics of the elastic moduli p wave velocities and thermal conductivities of three types of anisotropic rocks i e asan gneiss boryeong shale and yeoncheon schist occurring in korea the experiments were conducted on rock samples that show clear evidence of transverse isotropy cylindrical core samples with different anisotropy angles were prepared by coring at 15 degree intervals from the transversely isotropic plane using the laboratory directional coring system established for this study elastic moduli p wave velocities and thermal conductivities were determined along the sample axis for different anisotropy angles the anisotropy ratio is defined as the ratio of the properties parallel to the transversely isotropic plane to those perpendicular to the plane and the anisotropy ratios for the thermal conductivities k 90 k 0 of asan gneiss boryeong shale and yeoncheon schist were 1 4 2 1 and 2 5 respectively the p wave velocity anisotropy ratios v p 90 v p 0 for asan gneiss boryeong shale and yeoncheon schist were 1 2 1 5 and 2 3 respectively the elastic moduli p wave velocities and thermal conductivities that were obtained were compared with theoretical predictions by mean prediction error mpe the correlations between the measured properties were evidently correlated with some minor scatter in the data the degree of anisotropy measured in this study suggests that ignoring anisotropy in rock properties may mislead to erroneous results the application of tensorial transformation evaluations revealed that the three types of rocks chosen for this study can be modeled effectively by a transversely isotropic model

space weathering from mercury to the asteroid belt the variety of evidence bearing on the nature of space weathering is reviewed the effects of space weathering include spectral darkening reddening and subdued absorption bands and the distinctive magnetic electron spin resonance caused by single domain metallic iron particles ever since the apollo missions two paradigms have dominated the thinking of the planetary science community concerning space weathering 1 the optical effects are caused by impact vitrified glass in agglutinates and 2 the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind however studies carried out since the apollo program showed that both of these paradigms are invalid a hypothesis first suggested by the author and his colleagues 26 years ago but not generally accepted at that time now appears to be essentially correct both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor deposited coatings on soil particle surfaces and inside agglutinates the vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith the iron is reduced by a physical process the selective loss of oxygen that occurs during deposition of the vapor and does not require heating melting or a reducing environment a mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the moon mercury and an s asteroid

recent enrichment in the source region of arc magmas from luzon island philippines sr and nd isotopic evidence luzon the philippines is wedged between east and west directed subducting slabs westward subduction has resulted in pre miocene igneous rocks from northern luzon characterized by 87 sr 86 sr and 143 nd 144 nd ratios typical of intra oceanic arcs where sediment involvement is minor in addition pliocene to holocene volcanic eruptions of sr and nd isotopic signatures similar to those of the pre miocene rocks have developed along the bicol arc in southern luzon these rocks are also associated with the westward subduction in contrast pliocene to holocene volcanoes have been generated by eastward subduction along the western coast of central luzon the bataan arc in the north and the mindoro arc in the south and are significantly higher in radiogenic sr and lower in radiogenic nd than the rocks discussed above the pre miocene and bicol arc isotopic characteristics appear to reflect the mixing of small amounts of products from the philippine sea crust with the mantle wedge magmas erupted along the bataan and mindoro arcs may reflect that larger amounts of sediment are available for subduction in the south china sea rocks containing the highest radiogenic sr and lowest radiogenic nd values so far noted in philippine igneous rocks occur in the mindoro arc and may have been contaminated by slivers of the continental mindoro north palawan terrane which apparently had been carried down to mantle depths after the collision of this terrane and the arc in the miocene these interpretations imply that nd and by inference other rare earth elements can migrate from the subducted slab to the mantle wedge thus variable nd isotopic ratios in island arc magmas e g sunda and lesser antilles arcs may not be a primary feature of the mantle wedge but a consequence of variations in the release of nd from the subducted slab

enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands a sink for atmospheric co2 atmospheric co2 and global climate are closely coupled since 800 ka co2 concentrations have been up to 50 higher during interglacial compared to glacial periods because of its dependence on temperature humidity and erosion rates chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition cooler and drier conditions and lower non glacial erosion rates suppressed in situ chemical weathering rates during glacial periods however using systematic variations in major element geochemistry sr nd isotopes and clay mineral records from ocean drilling program sites 1143 and 1144 in the south china sea spanning the last 1 1 ma we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials we attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for 9 of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial interglacial variation of 80 ppmv as a result if similar magnitudes can be identified in other tropical shelf slope systems the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric co2 during cold stages of the quaternary this in turn would have caused an intensification of glacial cycles

radiative transfer modeling of lunar highlands spectral classes and relationship to lunar samples 1 tompkins and pieters 1999 identified eleven spectral classes present on the surface of the moon here we model these spectral classes to determine the compositions that define them we do this by mathematically matching spectral classes to radiative transfer computed spectra using spectral shape contrast and excursion parameters as defining characteristics model spectra are based upon known mineralogies mafic mineral mg s molar mg mg fe 100 and maturities we compare these compositional results to a compilation of 100 apollo samples to determine plausible representative samples for these spectra results indicate that unique mineralogic solutions for several spectral classes can be determined unambiguously however classes previously interpreted to be pyroxene rich are compositionally ambiguous results suggest these ambiguous mineral assemblages are not random but correlate with variations in absolute reflectance these data further suggest absolute reflectance is a compositionally diagnostic spectral parameter that should be used in conjunction with relative reflectance analysis to constrain mineralogy although absolute reflectance for the eleven spectral classes is not available to constrain their composition we detail mineral chemical i e mg and absolute reflectance variations of matching model relative reflectance spectra to narrow the possibilities this information is used in a pilot study of bullialdus crater for which clementine absolute reflectance is known results indicate bullialdus s central peak consists of tompkins and pieters spectral classes an agn and n bullialdus s spectra that match class n are roughly consistent with previous compositional interpretations however matches to classes an and agn indicate more mafic assemblages typical of mg suite norite gabbronorite rocks

imaging of small scale features on 433 eros from near evidence for a complex regolith on 25 october 2000 the near earth asteroid rendevous near shoemaker spacecraft executed a low altitude flyover of asteroid 433 eros making it possible to image the surface at a resolution of about 1 meter per pixel the images reveal an evolved surface distinguished by an abundance of ejecta blocks a dearth of small craters and smooth material infilling some topographic lows the subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter sized blocks

geologic map of the northern hemisphere of vesta based on dawn framing camera fc images abstract the dawn framing camera fc has imaged the northern hemisphere of the asteroid 4 vesta at high spatial resolution and coverage this study represents the first investigation of the overall geology of the northern hemisphere 22 90 n quadrangles av 1 2 3 4 and 5 using these unique dawn mission observations we have compiled a morphologic map and performed crater size frequency distribution csfd measurements to date the geologic units the hemisphere is characterized by a heavily cratered surface with a few highly subdued basins up to 200 km in diameter the most widespread unit is a plateau cratered highland unit similar to although of lower elevation than the equatorial vestalia terra plateau large scale troughs and ridges have regionally affected the surface between 180 e and 270 e these tectonic features are well developed and related to the south pole veneneia impact saturnalia fossae trough unit elsewhere on the hemisphere they are rare and subdued saturnalia fossae cratered unit in these pre rheasilvia units we observed an unexpectedly high frequency of impact craters up to 10 km in diameter whose formation could in part be related to the rheasilvia basin forming event the rheasilvia impact has potentially affected the northern hemisphere also with s n small scale lineations but without covering it with an ejecta blanket post rheasilvia impact craters are small

ejecta blocks on 243 ida and on other asteroids abstract seventeen positive relief features 45 150 m across are identified as probable blocks in galileo high resolution images of ida their presence provides direct evidence for regolith retention on asteroids the spatial distribution maximum size and integrated volume of the blocks are consistent with those of blocks associated with craters on the earth the moon phobos and deimos the concordance suggests that the features are impact ejecta fragments and that cratering mechanics on ida an object of average diameter 32 km are similar to those applying on previously studied rocky bodies the blocks that lie within or near the rims of craters lascaux and mammoth were likely mobilized in the low velocity tail portion of the excavation flow that formed those craters a few blocks located near smaller craters may have migrated some distance away from their source possibly by impact induced spallation hopping rolling and or sliding some blocks on ida could be surviving fragments from the koronis parent body accreted after its breakup the lifetime of 102 m sized boulders against collisional disruption is estimated to be in the 108 109year range consistent with ages considered for the largest and oldest craters on ida extrapolation of successful ejecta scaling laws to other asteroids suggests that blocks 15 and 70 m across could be present on dactyl and gaspra respectively in both cases too small to be identified in available galileo images blocks 100 m in size could be present on 433 eros and km sized megablocks on 4 vesta

optical maturation of asteroid surfaces abstract analysis of laboratory experiments simulating space weathering optical effects on atmosphereless planetary bodies reveals that the time needed to alter the spectrum of an ordinary chondrite meteorite to resemble the overall spectral shape and slope of an s type asteroid is about 10 5 yr the time required to reduce the visible albedo of samples to 0 05 is 10 6 yr since both these timescales are much less than the average collisional lifetime of asteroids larger than several kilometers in size numerous low albedo asteroids having reddish spectra with subdued absorption bands should be observed instead of an s type dominated population this is not the case because asteroid surfaces cannot be considered as undisturbed unlike laboratory samples we have estimated the number of collisions occurring in the time of 10 5 yr between asteroids and projectiles of various sizes and show that impact activated motions of regolith particles counteract the progress of optical maturation of asteroid surfaces we suppose that the maturation level of asteroid surfaces may be a compromise resulting from a competition between impact resurfacing and solar wind darkening and that after reaching some steady state after a relatively short time 7 10 5 yr thereafter depends only slightly on time spectroscopic analysis using relatively invariant spectral parameters such as band centers and band area ratios can determine whether the surface of an s asteroid has chondritic composition or not in this sense the bodies with the ordinary chondrite composition cannot be masked among s asteroids differences in the environment of the main asteroid belt versus that at 1 au and the physical difference between the moon and main belt asteroids i e size can account for the lack of lunar type weathering on main belt asteroids

experimental investigation of the effect of temperature on the mechanical behavior of tournemire shale this paper is devoted to the experimental investigation of the effect of temperature on the mechanical behavior of a typical anisotropic clayey rock the tournemire shale hydrostatic and conventional triaxial compression tests are first performed under room temperature for two principal loading orientations respectively parallel and perpendicular to the bedding planes the obtained results confirm an anisotropic mechanical behavior observed by the previous works further hydrostatic and triaxial compression tests with different confining pressures are carried out under different temperatures up to 250 c with the increase of temperature there is a significant decrease of young s modulus and the compression failure strength but an increase of the overall deformability of material the temperature change also affects the anisotropic response related to the deformation of bedding planes

importance of space weathering simulation products in compositional modeling of asteroids 349 dembowska and 446 aeternitas as examples based on recent progress in simulating space weathering on asteroids using pulse laser irradiation onto olivine and orthopyroxene samples detailed analyses of two of the a and r type asteroid reflectance spectra have been performed using reflectance spectra of laser treated samples the visible near infrared spectrum of olivine is more altered than that of pyroxene at the same pulse laser energy suggesting that olivine weathers more rapidly than orthopyroxene in space the same trend can be detected from reflectance spectra of the asteroids where the more olivine an asteroid has the redder its 1 m band continuum can become comparison of the 1 m band continuum slope and the 2 1 m band area ratio between the asteroids and olivine and pyroxene samples including the laser treated ones suggests that asteroids may be limited in the degree of space weathering they can exhibit possibly due to the short life of their surface regolith their pyroxenes may also have a limited chemical composition range fitting the visible continuum shape and other parts of the spectra especially the 2 m part has been impossible with any combination of common rock forming minerals such as silicates and metallic irons however this study shows for the first time excellent fits of reflectance spectra of an a asteroid aeternitas and an r asteroid dembowska including their visible spectral curves band depths and shapes and overall continuum shapes our results provide estimates that aeternitas consists of 2 fresh olivine 93 space weathered olivine 1 space weathered orthopyroxene and 4 chromite and that dembowska consists of 1 fresh olivine 55 space weathered olivine and 44 space weathered orthopyroxene these results suggest that space weathering effects maybe important to the interpretation of asteroid reflectance spectra even those with deep silicate absorption bands modified gaussian model deconvolutions of the laser irradiated olivine samples show that their identity as olivine remained the most recent submicroscopic mineralogical analyses have revealed that the laser irradiated olivine samples contain nanophase iron particles similar to those in space weathered lunar samples

regoliths on small bodies in the solar system a regolith is defined as a layer or mantle of loose incoherent rocky material of whatever origin that nearly everywhere forms the surface of the land and rests on coherent bedrock the regoliths on many planetary bodies are the result of continual impacts which transform coherent surfaces into fragmental debris the present investigation is concerned with the special case of regolith formation and evolution on small objects such as asteroids and meteorite parent bodies first order models of regolith evolution on asteroidal surfaces are constructed on the basis of data provided by studies of lunar samples and meteorites it appears that regolith formation proceeds by deposition of discrete layers of the widely spread ejecta primarily from the larger impacts moderate size 100 300 km diameter asteroids are covered by modest regoliths of the order of one km in depth small rocky asteroids develop negligible regoliths

anatomy of a partially differentiated asteroid a near sighted view of acapulcoites and lodranites with the insertion of the near spacecraft into orbit around the asteroid 433 eros a new stage of asteroid exploration has begun with the return of spatially resolved mineralogical geological and chemical information from specific asteroids in this paper we outline the features of a partially differentiated asteroid using the acapulcoite and lodranite meteorites as a guide such a body would likely contain a variety of lithologies including chondritic rocks largely unaltered by melting residues of partial melts and basaltic and fe ni fes rocks crystallized from the partial melts the presence or nature of the regolith remains largely unconstrained mineralogical and isotopic heterogeneities preserved in these rocks suggest spatial separation of these rock types by distances in excess of 200 m spacecraft based remote sensing instrumentation should detect substantial spectral heterogeneity most prominently manifested in the band area ratio and chemical heterogeneity observation of these various lithologies in situ would provide important new constraints on the processes involved during the earliest differentiation of asteroids

eros shape topography and slope processes stereogrammetric measurement of the shape of eros using images obtained by near s multispectral imager provides a survey of the major topographic features and slope processes on this asteroid this curved asteroid has radii ranging from 3 1 to 17 7 km and a volume of 2535 20 km3 the center of figure is within 52 m of the center of mass provided by the navigation team this minimal difference suggests that there are only modest variations in density or porosity within the asteroid three large depressions 10 8 and 5 3 km across represent different stages of degradation of large impact craters slopes on horizontal scales of 300 m are nearly all less than 35 although locally scarps are much steeper the area distribution of slopes is similar to those on ida phobos and deimos regions that have slopes greater than 25 have distinct brighter markings and have fewer large ejecta blocks than do flatter areas the albedo patterns that suggest downslope transport of regolith have sharper boundaries than those on phobos deimos and gaspra the morphology of the albedo patterns their lack of discrete sources and their concentration on steeper slopes suggest transport mechanisms different from those on the previously well observed small bodies perhaps due to a reduced relative effectiveness of impact gardening on eros regolith is also transported in talus cones and in connected sinuous paths extending as much as 2 km with some evident as relatively darker material talus material in at least one area is a discrete superposed unit a feature not resolved on other small bodies flat floored craters that apparently contain ponded material also suggest discrete units that are not well mixed by impacts

the geochemistry and tectonic setting of the northern section of the luzon arc the philippines and taiwan abstract the luzon arc consists of a 1200 km chain of stratovolcanoes and volcanic necks stretching from mindoro 13 n to the coastal range of taiwan 24 n this study is concerned with three of the five major segments along the arc the northern luzon babuyan and taiwan segments the late tertiary to quaternary volcanics of these segments are primarily andesitic but range in composition from basalt to rhyolite and are typical arc volcanics porphyritic plagioclase textures primarily calc alkaline with a few tholeiitic volcanic centers low tio 2 concentrations and low high field strength element hfse to large ion lithophile element lile ratios there is a large range in k 2 o and other liles from low k tholeiites to high k calc alkaline suites calayan island and mt tabungon volcanic substratum of mt cagua volcanics in the babuyan segment and most rocks from the taiwan coastal range are low k tholeiites e g nearly flat ree patterns low lree and lile concentrations and low th u ratios the dominant calc alkaline series ranges from medium k to high k rocks the high k calc alkaline rocks are mainly young and are found on batan and lutao islands when the low k tholeiitic and medium and high k calc alkaline rocks are associated in the same region the low k rocks are usually older there is a general relationship between k 2 o and other lile concentrations and k ar radiometric dates to some extent 87 sr 86 sr ratios also increase with time throughout the arc there is a correlation between latitude and 87 sr 86 sr and a positive correlation between 87 sr 86 sr and la sm cn an increase in both these geochemical parameters has been associated with an increase in the input of continental crustal material in other arc regions the lowest 87 sr 86 sr ratios found along the entire luzon arc the samples from baguio are equivalent to those found in samples from mid tertiary plutons from northern luzon and the bicol arc both groups of rocks are associated with westward subduction along the philippine trench where presumably deep oceanic sediments with little or no continental crustal component have been subducted the absence of continental crust below the arc in the northern luzon and babuyan segments has been suggested by several groups of researchers this together with the fact that metasomatized ultramafic nodules probably of mantle origin in disequilibrium with their batan host lavas but with similar 87 sr 86 sr and la sm cn ratios to the host rocks suggests that upper level assimilation afc processes does not appear to be the major influence on the geochemical signatures a collision zone between the upper crustal block of eastern china and taiwan and the manila trench has been recorded in the northern section of the arc taiwan sediments have also been shown to decrease in thickness along the south china sea basin nearly parallel to the manila trench from north to south the sediment source region is most probably taiwan and perhaps eastern china this latitudinal in variation sediment thickness may explain the crustal signature related to both geochemical and age parameters we suggest that this crustal input has taken place via subduction of sediment rich in a crustal component

odd partnerships among middle eocene bartonian nummulites examples from the transylvanian romania and dorog hungary basins abstract nummulites assemblages recovered from the middle eocene of the transylvanian basin romania and dorog basin hungary were studied in order to infer the paleoecological structuring of the assemblages the studied material consists mostly of a and b generation tests of nummulites perforatus in both basins however specimens of nummulites beaumonti and of nummulites striatus were sporadically recorded in the transylvanian and dorog basin respectively the co occurrence of two different nummulites taxa which show a striking size difference in protoconch and adult test suggests that the small sized nummulites beaumonti and nummulites striatus were the odd partners of the large sized nummulites perforatus during the bartonian middle eocene the co occurrence of these closely related species might reflect their different life strategies growth rate and or the use of different reproduction seasons the association of the same large partner with two distinct small sized partners in two different but connected basins is due to the wider paleogeographic distribution and more abundant occurrence of the larger partner n perforatus as compared to n beaumonti and n striatus the smaller sized partners

a double island arc between taiwan and luzon consequence of ridge subduction analysis of geomorphological geochronological geochemical and geophysical features in the segment of the taiwan luzon arc between taiwan and luzon the bashi segment allows the recognition of a double arc structure the two volcanic chains are separated by 50 km just north of luzon 18 n and converge near 20 n islets in the western chain are older and largely composed of volcanic rocks of miocene to pliocene age they all show low relief lateritic platforms and wave cut terraces and are covered by massive recrystallized limestone in contrast all active volcanoes in this segment of the taiwan luzon arc belong to the eastern chain where most islets are quaternary in age the volcanoes have well developed cone shapes and well preserved deposits of near vent facies magmas of the eastern chain have higher ksi la n la yb n and lowerend than their counterparts at the same latitude in the western chain therefore the magmas erupted in the eastern chain were derived from more enriched mantle sources than the magmas erupted in the western chain moreover the available seismological data seem to suggest an abrupt increase of the dip angle from 30 at 18 n to 80 at 20 n thus the double arc structure is located in the region where the benioff zone suddenly changes in analogy with the lesser antilles arc we propose a geodynamic model in which the double arc in the bashi strait is the tectonic manifestation of the subduction of the aseismic scarborough seamount chain the extinct mid ocean ridge of the south china sea before that ridge reached the manila trench the western chain was the volcanic front when the ridge reached the subduction zone at 5 4 ma its buoyancy temporarily interrupted the subduction thus causing a time gap in magmatic activity furthermore this ridge arc collision was probably also responsible for regional uplift causing extensive sub aerial weathering and erosion as well as massive reef formation in the western chain when subduction started again the dip angle became shallower in response to the extra buoyancy of the downgoing ridge if the depth of magma generation remained constant the shallower dip angle would have naturally led to an eastward shift of the volcanic front thus producing the younger eastern chain moreover we speculate that the abrupt change of the dip angle may have torn the downgoing slab thus allowing more enriched continental lithospheric material to invade the mantle wedge from the northwest thus imprinting a geochemically more enriched signature on the magmas of the eastern chain

space weathering on eros constraints from albedo and spectral measurements of psyche crater we present combined multi spectral imager msi 0 95 m and near infrared spectrometer nis 0 8 2 4 m observations of psyche crater on s type asteroid 433 eros obtained by the near earth asteroid rendezvous near shoemaker spacecraft at 5 3 km in diameter psyche is one of the largest craters on eros which exhibit distinctive brightness patterns consistent with downslope motion of dark regolith material overlying a substrate of brighter material at spatial scales of 620 m spectrum psyche crater wall materials exhibit albedo contrasts of 32 40 at 0 946 m associated spectral variations occur at a much lower level of 4 8 2 4 we report results of scattering model and lunar analogy investigations into several possible causes for these albedo and spectral trends grain size differences olivine pyroxene and troilite variations and optical surface maturation we find that the albedo contrasts in psyche crater are not consistent with a cause due solely to variations in grain size olivine pyroxene or lunar like optical maturation a grain size change sufficient to explain the observed albedo contrasts would result in strong color variations that are not observed olivine and pyroxene variations would produce strong band correlated variations that are not observed a simple lunar like optical maturation effect would produce strong reddening that is not observed the contrasts and associated spectral variation trends are most consistent with a combination of enhanced troilite a dark spectrally neutral component simulating optical effects of shock and lunar like optical maturation these results suggest that space weathering processes may affect the spectral properties of eros materials causing surface exposures to differ optically from subsurface bedrock however there are significant spectral differences between eros proposed analog meteorites ordinary chondrites and or primitive achondrites and eros freshest exposures of subsurface bright materials after accounting for all differences in the measurement units of our reflectance comparisons we have found that the bright materials on eros have reflectance values at 0 946 m consistent with meteorites but spectral continua that are much redder than meteorites from 1 5 to 2 4 m most importantly we calculate that average eros surface materials are 30 40 darker than meteorites

tertiary arc rifting in northern luzon philippines the north luzon terrane nlt comprising the section of luzon north of the philippine fault is one of the largest arc terranes in the philippine archipelago numerous features suggest that the nlt is a late oligocene to early miocene analogue for the processes in the modern intra arc rift zone at the northern end of the mariana trough first the nlt has bifurcating magmatic arcs sharing similar magmatic histories these include the northern sierra madre nsm and cordillera central cc magmatic arcs which are separated by the cagayan basin but which are linked in the caraballo range to the south the rock record indicates that the nsm cc and caraballo ranges were active arcs in late eocene to late oligocene time second seismic reflection and well data indicate that the cagayan basin formed by extensional faulting in late oligocene to early miocene time third alkalic arc magmatism recognized to be a precursor of intra arc rifting in modern settings occurred at the juncture of the nsm and cc arcs in late oligocene to early miocene time fourth oceanic crust represented by the itogon ophiolite formed at the southwestern end of the cagayan basin in late oligocene to early miocene time major and trace element chemistry show that the itogon sheeted dikes have tholeiitic arc and backarc basin basalt affinities the rock record and geophysical offshore data suggest that the nlt was developing in an island arc system above the subducting west philippine plate in late eocene time rifting occurred in the island arc from late oligocene to early miocene time but did not mature into backarc spreading most likely because of the collision of the benham rise a basaltic rise in the west philippine basin with the nlt the arc rifting in the nlt may be another manifestation of the extensional tectonism that affected most of southeast asia in late oligocene to early miocene time during which the south china and southeast sulu basins formed subsequent to arc rifting the history of the nlt has been linked to the subduction of the south china plate along the manila trench the structural history of the cagayan basin and magmatic history of the southern cc suggest that the subduction in the manila trench at the latitude of the nlt began about 15 ma

meteorite and asteroid reflectance spectroscopy clues to early solar system processes although earth has a magnetic shield that protects it from energetic ions and a cushioning atmosphere that catches the tons of small particles i mm that bombard it daily solid material from extraterrestrial sources nevertheless reaches the surface of earth many times a year dodd 1 98 1 when the largest of these bodies impact the surface with great velocity they release immense energy usually form a crater and often disrupt the terrestrial biosphere fortunately such events occur relatively infrequently although individual impacts are currently unpredictable beyond a statistical accounting shoemaker et al 1979 grieve 1 982 cosmic material between the size of small dust particles and the larger crater forming bodies is slowed by the terrestrial atmosphere upon entry the outermost portion of these objects is melted and ablated during passage forming a fusion crust which protects the interior and they land

failure of transversely isotropic rock under brazilian test conditions abstract the behavior of transversely isotropic rock material was studied under brazilian test conditions for nine different rocks two sandstones one shale two slates one schist and three gneiss both the variation of the strength and the final fracture patterns induced by testing were examined as a function of the inclination angle of the weak planes the combination of the observations for both parameters illustrated clearly the complexity of the failure of such rocks which was summarized by assuming four different trends the four trends for the variation of the strength as a function of the inclination angles range from little or no variation trend 1 i e isotropic behavior for strength to a sharp decrease of the strength from very small angles onwards followed by a leveling off trend 4 trend 2 is characterized by a constant value between 0 and about 45 followed by a linear decrease while trend 3 corresponds to a decrease of the strength over the entire interval but a rather systematic decrease approximating a linear variation different variations were observed among these four trends in terms of the relative lengths of the respective fractures along the weak planes and in any other direction for the rocks investigated there is a cross over from dominant fractures in directions other than the weak planes to dominant fractures along the weak planes for the four trends there are systematic changes in the position of this cross over point i e on average at about an inclination angle of 75 for trend 1 and at about 15 for trend 4 for inclination angles larger than the cross over point the rock specimens failed primarily by splitting between both loading lines

bathyal records of enhanced silicate erosion and weathering on the exposed luzon shelf during glacial lowstands and their significance for atmospheric co2 sink abstract we present a new high resolution multiproxy data set of mass accumulation rates sr nd isotopes as well as major and trace elements for the siliciclastic sediment fraction from international marine global change study core md06 3052 located on the continental slope of the western philippine sea we integrate our new data with published grain sizes and sea surface temperatures from the same core as well as with equatorial pacific sea level and east asian summer monsoon precipitation in order to constrain at high resolution changes in physical erosion and chemical weathering intensities on luzon and sediment source to sink processes we assess the potential significance of chemical weathering of arc silicates in regulating global atmospheric co2 since 156 kyr bp sr nd isotopes show that the siliciclastic sediments were dominantly sourced from volcanic rocks exposed on luzon 68 100 with a lesser contribution from asian dust 0 32 different indices indicate that stronger physical erosion and chemical weathering occurred during marine isotope stage mis 6 130 156 kyr bp as well as in the latter stage of mis 3 and mis 2 14 40 kyr bp the large sea level lowstands and associated significant exposure of continental shelf in the western philippine sea during these two cold periods should favor physical erosion and chemical weathering of unconsolidated sediments on the exposed shelf furthermore we notice the relatively good coherence between chemical weathering intensities on luzon and global atmospheric co2 concentrations over these cold intervals we suggest that strengthening of chemical weathering of silicates on luzon and other tropical arcs within 20 of the equator during the quaternary glacial sea level lowstands may significantly contribute to the lowering of atmospheric co2 concentrations during ice ages we estimate that a significant fraction up to 16 i e 8 ppmv of all atmospheric co2 ultimately sequestered by silicate weathering may be processed through an area corresponding to only 1 of the exorheic drainage area worldwide

the basaltic to trachydacitic upper diliman tuff in manila petrogenesis and comparison with deposits from taal and laguna calderas abstract the basaltic to trachydacitic 50 65 wt sio2 upper diliman tuff is the youngest deposit of a sequence of tuffaceous deposits in metro manila the deposit is located north of taal caldera and northwest of laguna caldera which are both within the southwest luzon volcanic field chemical variations in the pumice fragments within the upper diliman tuff include medium k basalt to basaltic andesite high k basaltic andesite to andesite and trachyandesite to trachydacite magma mixing mingling is ubiquitous and is shown by banding textures in some pumice fragments considerable range in groundmass glass composition 54 to 65 wt sio2 in a single pumice fragment and zoning in plagioclase phenocrysts simple binary mixing modeling and polytopic vector analysis were used to further evaluate magma mixing trace element variations are inconsistent with the medium k and high k magmas being related by crystal fractionation the medium k basalts represent hotter intrusions which induced small degrees of partial melting in older crystallized medium k basaltic material within the crust to produce the high k magmas all melts likely differentiated in the crust but the emplaced and new basaltic intrusions originated from the mantle wedge and were generated by subduction zone processes the volcanic source vent for the upper diliman tuff has not been identified in comparisons with the deposits from adjacent taal and laguna calderas it is chemically distinct with respect to both major and trace element concentrations

coupled organic synthesis and mineral alteration on meteorite parent bodies the hypothesis that the soluble fraction of the organic compounds present in carbonaceous chondrite meteorites was formed during aqueous alteration of the parent body was tested with masstransfer reaction path calculations in these calculations we start with likely compositions of the original parent body and asteroidal fluids that are far from thermodynamic equilibrium and metastable and stable equilibrium constraints are imposed as the total gibbs free energy of the parent body environment is minimized the results of these calculations suggest that the classes of soluble organic compounds present in carbonaceous chondrite meteorites could have formed during relatively low temperature aqueous alteration of the meteorite parent body or bodies the main controls on the potential for synthesis and transformation of organic compounds were the oxidation state of the rock fluid system the bulk composition of that system and the temperatures that were achieved during the alteration event or events it also appears that the alteration mineral assemblages were influenced by the presence of soluble organic compounds and reaction among them

multiple ophiolite generation preserved in the northern philippines and the growth of an island arc complex abstract although all oceanic arcs grow through the addition of subduction generated magmas the geology of the northern philippines demonstrates that a major contribution to arc crustal growth can come from repeated episodic intra arc back arc and or fore arc oceanic crust generation with subsequent preservation of the basic ultrabasic units in the arc complex at least five episodes of oceanic crust generation are represented in the northern philippines by preserved ophiolitic sequences and recent intra arc seafloor spreading each episode is distinct in age as confirmed by modern dating techniques with the ages ranging from pre jurassic to quaternary although the philippines is widely regarded as an amalgamation of allochthonous terranes a review of the available data shows that there is currently no compelling evidence that these ophiolites are of exotic origin and that they have been tectonically accreted to the philippine arc complex rather the evidence suggests that most and possibly all of the ophiolites were generated as back arc fore arc or intra arc crust within the philippine arc complex hence there is a close spatial association of several ophiolitic terranes of diverse ages spanning 150 myr that formed as part of the arc complex such an association may have arisen from episodic generation of oceanic crust during periods of local extension in a suprasubduction zone setting which has experienced changing and possibly overlapping subduction from the east and west sides in the current reference frame disruption of the ophiolitic basement terranes has been and continues to be effected primarily by wrench faulting this style of arc growth has implications for the paleotectonic interpretation of ancient ophiolite arc terranes in continents and the petrologic evolution of island arcs

a 2 ma record of explosive volcanism in southwestern luzon implications for the timing of subducted slab steepening 1 new chemical and isotopic analyses of the tephra layers plus deep sea tephrostratigraphic record from two cores from either side of luzon island philippines have allowed the identification of two periods of explosive volcanic activity originating from the macolod corridor in the southwestern part of the luzon the first period extended from prior to 1355 ka to 1977 ka and the second period extended from 478 ka to the present separated by a period of relative quiescence the time intervals between large explosive eruption events in each period were 31 15 ka and 156 52 ka respectively combined with published chronological and geochemical data from onshore volcanic deposits the tephrostratigraphic record shows that the locus of large explosive eruptions has migrated southwestward from the northeastern section to the middle and southwestern sections of the macolod corridor the period of relative quiescence is characterized by monogenetic volcanism in the central section of the corridor the migration of active volcanism across the southwestern part of luzon during the quaternary is used to infer the evolution of the subducting south china sea crust the period of relative quiescence represents a period of adjustment of the subducted slab by steepening which began around 1355 ka or shortly thereafter and finished at around 478 ka

a large spectral survey of small lunar craters implications for the composition of the lunar mantle a global spectral survey of 4506 immature craters with diameters 1 km was carried out using near ir data from the kaguya spectral profiler to characterize the composition of the lunar megaregolith on the basis of band minima and radiative transfer mixing models small crater spectra fall into three groups 1 mare basalts with strong absorptions at relatively long wavelengths indicating high ratios of high to low ca pyroxene 2 norites containing about 50 plagioclase and with pyroxene assemblages dominated by low ca pyroxene that occur within the south pole aitken basin spa near apollo 14 and other locations near imbrium basin and three major cryptomaria deposits and 3 noritic anorthosites occurring within the feldspathic highlands terrane containing about 20 wt pyroxene with a pyroxene assemblage containing exclusively very low ca pyroxene very few pure anorthosites are present in this survey and there are no occurrences of pyroxene poor olivine rich assemblages models of the composition of basin ejecta incorporate large amounts of mantle material and the spectral results require that that the sampled mantle is orthopyroxenite basin depth diameter ratios used in the models required to match the measured composition are consistent with prior estimates for the largest basins the composition found in the spa and imbrium regions are consistent with mafic impact melt breccias or basaltic impact melts of basin origin for spa we model this composition and find it requires an extremely low impact angle while this is consistent with prior work on an oblique impact for the spa event a more robust solution invokes the production of norite in impact melt seas

the barringer award address presented 1996 july 25 berlin germany impact experiments related to the evolution of planetary regoliths impact induced comminution of planetary surfaces is pervasive throughout the solar system and occurs on submillimeter to global scales resulting in comminution products that range from fine grained surface soils to massive polymict ejecta deposits to collisionally fragmented objects within this wide range of comminution products we define regoliths in a narrow sense as materials that were processed by repetitive impacts to dimensional scales comparable to or smaller than that of component minerals of the progenitor rock s in this paper we summarize a wide variety of impact experiments and other observations that were primarily intended to understand the evolution of regoliths on lunar basalt flows and we discuss some of their implications for asteroidal surfaces cratering experiments in both rock and noncohesive materials combined with photogeologic observations of the lunar surface demonstrate that craters 500 m in diameter contribute most to the excavation of local bedrock for subsequent processing by micrometeorites the overall excavation rate and thus growth rate of the debris layer decreases with time because the increasingly thicker fragmental layer will prevent progressively larger projectiles from reaching bedrock typical growth rates for a 5 m thick lunar soil layer are initially 3 ga ago a few mm ma and slowed to 1 mm ma at present the coarse grained crater ejecta are efficiently comminuted by collisional fragmentation processes and the mean residence time of a 1 kg rock is typically 10 ma the actual comminution of either lithic or monomineralic detritus is highly mineral specific with feldspar and mesostasis comminuting preferentially over pyroxene and olivine thus resulting in mechanically fractionated fines especially at grain sizes 20 m such fractionated fines also participate preferentially in the shock melting of lunar soils thus giving rise to agglutinate melts as a consequence agglutinate melts are systematically enriched in feldspar components relative to the bulk composition of their respective host soil s compositionally homogeneous impact derived glass beads in lunar soils seem to result from micrometeorite impacts on rock surfaces reflecting lithic regolith components and associated mineral mixtures cumulatively experimental and observational evidence from lunar mare soils suggests that regoliths derive substantially from the comminution of local bedrock the addition of foreign exotic components is not necessary to explain the modal and chemical compositions of diverse grain size fractions from typical lunar soils regoliths on asteroids are qualitatively different from those of the moon the modest impact velocities in the asteroid belt some 5 km s 1 are barely sufficient to produce impact melts also substantially more crater mass is being displaced on low gravity asteroids compared to the moon collisional processing of surface boulders should therefore be more prominent in producing comminuted asteroid surfaces these processes combine into asteroidal surface deposits that have suffered modest levels of shock metamorphism compared to the moon impact melting does not seem to be a significant process under these conditions however the role of cometary particles encountering asteroid surfaces at presumably higher velocities has not been addressed in the past unfortunately the asteroidal surface processes that seemingly modify the spectral properties of ordinary chondrites to match telescopically obtained spectra of s type asteroids remain poorly understood at present despite the extensive experimental and theoretical insights summarized in this report and our fairly mature understanding of lunar surface processes and regolith evolution

experimental and theoretical study of the anisotropic properties of shale abstract the effect of bedding plane orientations on shear strength and failure mechanisms of shale is investigated with an emphasis on the shear parameters of the bedding planes this study is based on direct shear tests conducted on directional shale samples obtained from formations which exhibit well developed stratification the tested cylindrical specimens were prepared by coring at 30 intervals from the direction of the bedding planes the results indicate that the anisotropy of the shear strength of shale can be readily observed due to the anisotropic effects of bedding plane orientation and normal stress the shear parameters such as strength cohesion and internal friction angle reach their maximum and the minimum values at 60 and 0 respectively where is the angle between the bedding planes and the coring orientation which is also the direction of normal stress during the laboratory tests it is demonstrated that the bedding planes are weak not only with regards to cementing strength but also with regards to friction three different shear failure modes were built up depending on the shearing angle 1 sliding failure across the bedding planes 2 sliding failure along the bedding planes and 3 sliding failure across the bedding planes combined with tensile splitting along the bedding planes an expression of the shear stress concentration factor of the direct shear model is derived to evaluate the anisotropy of shear strength

galileo photometry of asteroid 243 ida galileo imaging observations over phase angles 19 5 to 109 8 are combined with near opposition earth based data to derive the photometric properties of ida to first order these properties are uniform over the surface and well modeled at 0 55 m by hapke parameters 0 0 22 h 0 020 b0 1 5 g 0 33 and 18 with corresponding geometric albedop 0 21 0 030 01and bond albedoab 0 081 0 0170 008 ida s photometric properties are more similar to those of average s asteroids p helfenstein and j veverka 1989 asteroids ii univ of arizona press tucson than are those of 951 gaspra two primary color units are identified on ida terrain a exhibits a spectrum with relatively shallower 1 m absorption and a relatively steeper red spectral slope than average ida while terrain b has a deeper 1 m absorption and a less steep red slope the average photometric properties of ida and terrain a are similar while those of terrain b differ mostly in having a slightly higher value of 0 0 22 versus 0 21 suggesting that terrain b consists of slightly brighter more transparent regolith particles galileo observations of ida s satellite dactyl over phase angles 19 5 to 47 6 suggest photometric characteristics similar to those of ida the major difference being dactyl s slightly lower albedo 0 20 compared to 0 21