gravity field of the moon from the gravity recovery and interior laboratory grail mission spacecraft to spacecraft tracking observations from the gravity recovery and interior laboratory grail have been used to construct a gravitational field of the moon to spherical harmonic degree and order 420 the grail field reveals features not previously resolved including tectonic structures volcanic landforms basin rings crater central peaks and numerous simple craters from degrees 80 through 300 over 98 of the gravitational signature is associated with topography a result that reflects the preservation of crater relief in highly fractured crust the remaining 2 represents fine details of subsurface structure not previously resolved grail elucidates the role of impact bombardment in homogenizing the distribution of shallow density anomalies on terrestrial planetary bodies

geology and petrology of enormous volumes of impact melt on the moon a case study of the orientale basin impact melt sea abstract lunar basin forming impacts produce enormous volumes 10 5 km 3 of impact melt all known basin forming impacts combined may produce 10 8 km 3 of impact melt 1 20th the volume of the lunar crust despite their volumetric importance the geology and petrology of massive deposits of impact melt on the moon have been little studied in part because most basin impact melt deposits are old and have been obscured or buried by subsequent impact cratering and mare infill we investigate the geology and model the petrology of fresh massive impact melt deposits in the relatively young 930 km diameter orientale basin models of impact melt production combined with geologic analyses based on new lola topographic data suggest that most of the impact melt 2 3 produced by the orientale forming impact occurs in a 15 km thick impact melt sheet better described as an impact melt sea 350 km in diameter with a volume of 10 6 km 3 we anticipate that the orientale melt sea has undergone large scale igneous differentiation since terrestrial impact melt sheets such as manicouagan sudbury and morokweng less than a tenth of the thickness and a hundredth of the volume of the orientale melt sea have differentiated we develop a model for the cumulate stratigraphy of the solidified orientale impact melt sea a modeled cumulate stratigraphy occurring below a quench crust and anorthositic fallback breccia with an 8 km thick layer of norite overlying a 4 km layer of pyroxenite and a basal 2 km thick layer of dunite produced by equilibrium crystallization of a homogenized melt sea consistent with vigorous convection in that melt sea is supported by remotely sensed norite excavated by the central peak of maunder crater from 4 km depth generally we predict that very large basin forming impacts including the south pole aitken spa basin forming impact produce melt seas with a cumulate stratigraphy similar to that of the orientale melt sea impact melt differentiation may explain apparently anomalous lithologies excavated in the spa basin interior we note that impact melt differentiates are slow cooled the orientale melt sea took on the order of 10 5 years to solidify and if meteoritic siderophiles fractionate into metal or sulfide layers may not be siderophile enriched therefore impact melt differentiates may pass for pristine highland plutonic rocks in the lunar sample suite these predictions can be tested with current and future mission data

crustal growth associated with anorogenic mid proterozoic anorthosite massifs in northeastern north america abstract mid proterozoic anorthosite massifs north of the grenville front tectonic zone in labrador are believed to have been emplaced in an anorogenic setting chemistry of the adirondack anorthosite mangerite charnockite suite suggests that it is bimodal and was also emplaced anorogenically by inference it is assumed that the intervening massifs of the grenville province are of anorogenic derivation as well geochronologic data indicates that these complexes formed during an interval of 500 m y from 1600 1100 ma with most magma emplaced during the last 300 m y the currently exposed area of the anorthosite fraction of the massifs represents 13 of the area into which they were emplaced if this proportion is continued downward throughout a 35 40 km thick crust its volume yields a computed maximum crustal growth rate of 5 10 km 3 ma per kilometer of magmatic belt if the anorthosites are continued only to 5 km the growth rate becomes 1 2 km 3 ma per kilometer of magmatic belt although considerably less than rates of crustal addition in volcanic arcs the computed rates are substantial and indicate that mid proterozoic anorthositic magmatism made significant local contributions to continental crust during the complicated evolution of northeastern north america

testing the ability of surface arrays to monitor microseismic activity recently there has been much interest in the use of data from surface arrays in conjunction with migration based processing methods for passive seismic monitoring in this study we use an example of this kind of data recorded whilst 18 perforation shots with a variety of positions and propellant amounts were detonated in the subsurface as the perforation shots provide signals with known source positions and origin times the analysis of these data is an invaluable opportunity to test the accuracy and ability of surface arrays to detect and locate seismic sources in the subsurface in all but one case the signals from the perforation shots are not visible in the raw or preprocessed data however clear source images are produced for 12 of the perforation shots showing that arrays of surface sensors are capable of imaging microseismic events even when the signals are not visible in individual traces we find that point source locations are within typically 45 m laterally of the true shot location however the depths are less well constrained 150 m we test the sensitivity of our imaging method to the signal to noise ratio in the data using signals embedded in realistic noise we find that the position of the imaged shot location is quite insensitive to the level of added noise the primary effect of increased noise being to defocus the source image given the migration approach the array geometry and the nature of coherent noise during the experiment signals embedded in noise with ratios 0 1 can be used to successfully image events furthermore comparison of results from data and synthetic signals embedded in noise shows that in this case prestack corrections of traveltimes to account for near surface structure will not enhance event detectability although the perforation shots have a largely isotropic radiation pattern the results presented here show the potential for the use of surface sensors in microseismic monitoring as a viable alternative to classical downhole methods

constraints on the martian lithosphere from gravity and topography data localized spectral admittances of the large martian volcanoes are modeled by assuming that surface and subsurface loads are elastically supported by the lithosphere in order to model the case where the load density differs from that of the crust a new method for calculating gravity anomalies and lithospheric deflections is developed the modeled gravity anomalies depend upon the elastic thickness crustal thickness load density and crustal density and these parameters were exhaustively sampled in order to determine their effect on the misfit between the observed and modeled admittance function we find that the densities of the martian volcanoes are generally well constrained with values of 3200 100 kg m 3 which is considerably greater than those reported previously these higher densities are consistent with those of the martian basaltic meteorites which are believed to originate from the tharsis and elysium volcanic provinces the crustal density is constrained only beneath the elysium rise to be 3270 150 kg m 3 if this value is representative of the northern lowlands then pratt compensation is likely responsible for the approximately 6 km elevation difference between the northern and southern hemispheres the elastic thicknesses of the major martian volcanoes when subsurface loads are ignored are found to be the following elysium rise 56 20 km olympus mons 93 40 km alba patera 66 20 km and ascraeus mons 105 40 km we have also investigated the effects of subsurface loads allowing the bottom load to be located either in the crust as dense intrusive material or in the mantle as less dense material we found that all volcanoes except pavonis are better modeled with the presence of less dense material in the upper mantle which is indicative of either a mantle plume or a depleted mantle composition an active plume beneath the major volcanoes is consistent with recent analyses of cratering statistics on olympus mons and the elysium rise which indicate that some lava flows are as young as 10 30 myr as well as with the crystallization ages of the shergottites of which some are as young as 180 myr

gravitational signatures of lunar floor fractured craters lunar floor fractured craters are impact craters characterized by distinctive shallow floors crossed by important networks of fractures different scenarios have been proposed to explain their formations but recent studies showed that the intrusion of magma at depth below the crater floor is the most plausible explanation the intrusion of dense magma within the light upper most part of the lunar crust should have left a positive signature in the gravity field this study takes advantage of the unprecedented resolution of the lunar gravity field obtained from the nasa s gravity recovery and interior laboratory grail mission in combination with topographic data obtained from the lunar orbiter laser altimeter lola instrument to investigate the gravitational signatures of both normal and floor fractured craters despite the large variability in their gravitational signatures the floor fractured and normal craters in the highlands show significant differences the gravitational anomalies are significantly larger at floor fractured craters the anomaly amplitudes for floor fractured craters are in agreement with synthetic gravity anomalies based on the predicted intrusion shapes from a theoretical flow model our results are consistent with magmatic intrusions intruding a crust characterized by a 12 porosity and where the intrusion has no porosity similar studies have been carried out in the lunar maria and south pole aikten basin although the average gravitational signature of floor fractured craters is larger than at normal craters in these regions they cannot be distinguished statistically due to the small number of craters and the large variability of the anomalies in general a better characterization of the signal due solely to the initial impact crater is needed to isolate the magmatic intrusion signal and characterize the density contrast between the magma and crust

the mineralogical diversity of alkaline igneous rocks critical factors for the transition from miaskitic to agpaitic phase assemblages geochemically the large family of alkaline plutonic rocks both qtz undersaturated and oversaturated compositions can be subdivided into metaluminous na 2 o k 2 o al 2 o 3 types in this paper we discuss two important aspects of the mineralogical evolution of such rocks with respect to their fe mg phases a major mineralogical transition observed is the precipitation of arfvedsonite or aegirine instead of fayalite or magnetite ilmenite the relative stability of these phases is controlled by oxygen fugacity and na activity in the crystallizing melts if na activity in the melt is high enough arfvedsonite aegirine form a common assemblage in peralkaline rocks under both reduced and oxidized conditions major mineralogical differences within this rock group exist with respect to their high field strength element hfse rich minerals most syenitic rocks known as miaskites contain zircon titanite or ilmenite as hfse rich minerals whereas in agpaites complex na k ca ti zr silicates incorporate the hfse similarly only a small group of peralkaline granites are found to lack zircon titanite or ilmenite but instead contain na k ca ti zr silicates here we present a detailed phase petrological analysis of the chemical parameters na 2 o cao k 2 o that influence the transition from miaskitic to agpaitic rocks based on the occurrence of ti and zr minerals several transitional mineral assemblages are identified and two major evolution trends for agpaites are distinguished a high ca trend which is exemplified by the alkaline rocks of the kola province russia and a ca depletion trend which is displayed by the alkaline rocks of the gardar province south greenland both trends show significant na enrichment during magmatic evolution high ca agpaites evolve from nephelinitic parental melts that did not crystallize large amounts of plagioclase in contrast agpaites showing ca depletion originate by extensive fractionation of plagioclase from basaltic parental melts in some peralkaline granites evolutionary trends are observed that culminate in agpaite like hfse mineral associations in the most evolved rocks

imaging hydraulic fractures by microseismic migration for downhole monitoring system abstract it has been a challenge to accurately characterize fracture zones created by hydraulic fracturing from microseismic event locations this is because generally detected events are not complete due to the associated low signal to noise ratio and some fracturing stages may not produce microseismic events even if fractures are well developed as a result spatial distribution of microseismic events may not well represent fractured zones by hydraulic fracturing here we propose a new way to characterize the fractured zones by reverse time migration rtm of microseismic waveforms from some events this is based on the fact that fractures filled with proppants and other fluids can act as strong scatterers for seismic waves therefore for multi stage hydraulic fracturing recorded waveforms from microseismic events induced in a more recent stage may be scattered by fractured zones from previous stages through rtm of microseismic waveforms in the current stage we can determine fractured zones created in previous stages by imaging area of strong scattering we test the feasibility of this method using synthetic models with different configurations of microseismic event locations and borehole sensor positions for a 2d downhole microseismic monitoring system synthetic tests show that with a few events fractured zones can be directly imaged and thus the stimulated reservoir volume srv can be estimated compared to the conventional location based srv estimation method the proposed new method does not depend on the completeness of detected events and only a limited number of detected and located events are necessary for characterizing fracture distribution for simplicity the 2d model is used for illustrating the concept of microseismic rtm for imaging the fracture zone but the method can be adapted to real cases in the future

kinematics of a major fan like structure in the eastern part of the sveconorwegian orogen baltic shield south central sweden abstract the n s trending so called protogine zone in the baltic shield of south central sweden is usually considered to mark a tectonic boundary between the rocks of the transscandinavian igneous belt tib in the east and the sveconorwegian orogen in the west detailed structural mapping in the karlskoga kristinehamn area has shown that an anastomosing network of ductile deformation zones with generally n s strike extends ca 40 km east of the traditional protogine zone furthermore the western boundary of this ductile deformation and the tib is not constrained in the kristinehamn area reconnaissance studies indicate that they both extend westwards towards the so called mylonite zone it is suggested that the eastern limit of the sveconorwegian orogen is located some 40 km east of the present boundary and that the protogine zone concept is obsolete the term sveconorwegian frontal deformation zone sfdz is proposed as a more appropriate alternative in southern sweden south of lake vattern and to correspond to a younger set of oblique ductile deformation zones with reverse and right lateral components of movement in the easternmost part of the orogen farther to the north ductile deformation zones older than the sfdz in the karlskoga kristinehamn area display a fan like geometry in an e w cross section with steep westerly dips in the eastern part of the section vertical dips farther west and moderate easterly dips in the western part of the section kinematic analysis indicates that dip slip movements predominate with a consistent top to the east sense of movement across the entire fan like structure in their present orientation deformation zones are characterized by reverse movements in the eastern part and normal movements in the western part of the structure between kristinehamn and the mylonite zone the main foliation is gently dipping to subhorizontal indicating that the regional structure is strongly asymmetric and that the fan like structure occurs close to the foreland of the orogen deformation zones are spaced to semi penetrative in the eastern part of the fan like structure whereas the deformation is more or less penetrative and the tib rocks are transformed to orthogneisses west of kristinehamn this east to west increase in bulk strain is in accordance with an increase in syn deformational metamorphic grade across the structure younger ductile deformation zones belonging to the sfdz are responsible for a major change in orientation of the older deformation zones in the easternmost part of the structure the fan like structure is best explained by models involving the interference of two separate tectonic events deformation occurred after 1 57 ga and prior to deposition of neoproterozoic and younger cover sedimentary rocks it is not yet clear whether the initial phase of deformation early sveconorwegian or older was related to the build up of an imbricate thrust stack in a compressional regime as favoured here or to regional e w extension the younger deformation phase was related to rotation of these older structures into the compressional late sveconorwegian sfdz

geology and u pb geochronology of the kipawa syenite complex a thrust related alkaline pluton and adjacent rocks in the grenville province of western quebec the kipawa syenite complex a thin folded sheet of amphibole syenite quartz syenite and minor nepheline syenite lies along a west vergent thrust separating a lower slice comprising the kikwissi granodiorite and biotite tonalite dated at 2717 15 11 ma and unconformably overlying metasedimentary rocks from an overlying slice containing the red pine chute orthogneiss an alkali granite gneiss and the mattawa quartzite the syenite complex dated at 1033 3 ma lies within the lower slice but has metasomatically altered the overlying slice texturally guided u pb spot analyses on partially metasomatised zircons from the alkali granite gneiss yield a cluster of 207pb 206pb ages at 1389 8 ma interpreted as the time of igneous crystallization and four ages overlapping the time of syenite emplacement interpreted as in situ metasomatic growth the highest structural slice comprises garnet amphibolite separated from lower slices by the allochthon boundary thrust metamorphic grade increases upward from

local vertical seismic profiling vsp elastic reverse time migration and migration resolution salt flank imaging with transmitted p to s waves to avoid the defocusing effects of propagating waves through salt and overburden with an inaccurate overburden velocity model we introduce a vertical seismic profiling vsp local elastic reverse time migration rtm method for salt flank imaging by transmitted p to s waves this method back projects the transmitted ps waves using a local velocity model around the well until they are in phase with the back projected pp waves at the salt boundaries the merits of this method are that it does not require the complex overburden and salt body velocities and it automatically accounts for source side statics in addition the method accounts for kinematic and dynamic effects including anisotropy absorption and all other unknown rock effects outside of this lo cal subsalt velocity model numerical tests on an elastic salt model and offset 2d vsp data in the gulf of mexico using a finite difference time domain staggered grid rtm scheme partly demonstrate the effectiveness of this method over interferometry

the source scanning algorithm mapping the distribution of seismic sources in time and space summary we introduce a new method which we call the source scanning algorithm ssa for imaging the distribution of seismic sources in both time and space using trial locations and origin times the method calculates the brightness function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times the spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness the greatest advantages of this method are that 1 it exploits waveform information both arrival times and relative amplitudes without the need to calculate highfrequency synthetic seismograms and 2 it requires neither pre assembled phase picking data nor any a priori assumptions about the source geometry a series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval finally we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip ets sequence in the northern cascadia subduction zone

seismic imaging using microseismic events results from the san andreas fault system at safod 1 we have developed a new passive seismic imaging approach that consists of two steps first the hypocenter of the microseismic event is precisely located second this event is treated as a pseudo active seismic source and the reflections within the recorded wavefield are processed by using a directional migration algorithm in order to construct a high resolution image of the illuminated subsurface region in this paper we demonstrate the application of our approach to a number of microseismic events recorded by a borehole array in the san andreas fault observatory at depth main hole results obtained were high resolution 3 d images of different se nw oriented reflectors related to the san andreas fault saf system in the close vicinity of the borehole to support our approach we compared our findings with other active and passive seismic images and analyzed the correlation with borehole lithology we revealed a predominantly satisfactory agreement for both juxtapositions furthermore the stacked image of several microearthquakes provides a spatial characterization of the complex internal structure of the saf with much higher resolution than can be obtained from surface seismic reflection data

the lunar mascons revisited the entire spectra of the surface topography and gravity field of lunar mascons are well presented by the high resolution clementine data the negative correlation between the topography and gravitational potential of the mascons suggests that they are dynamically supported both elastic support and viscous decay models are examined for the elastic support models the spectral characteristics and the lateral variations of the thickness of the elastic layer are determined on the basis of the thin spherical shell flexure formulation and using only the antivarying harmonics of the topography and potential an elastic layer thickness of about 50 km is required to support imbrium serenitatis and nectaris mascons about 35 km for crisium mascon and about 30 km for smythii and humorum mascons a layer of about 20 km thickness can support orientale mascon the strength envelopes of the upper 100 km of the moon within 4 3 gyr ago show that the elastic layer was not thick enough to support the mascons in the early history they decayed through viscous deformation of the lunar interior a lower limit of 6 1024 pa s is estimated for the lunar viscosity within 3 6 3 gyr ago we also determine the thicknesses of the crust and mare flows of the mascon basins on the basis of the assumption that the basins were isostatically compensated prior to the mascon formation the crust beneath the mascon basins is about 30 40 km except for crisium and orientale where the crust is about 20 km the mare flows of about 3 6 km are obtained for almost all of the mascon basins the topography and gravitational potential of aitken basin shows that the basin is compensated at 52 54 km depth the mantle beneath the basin has rebounded upward by about 20 30 km and is overlain by about 20 25 km of a mixture of the excavated crustal and mantle material the lack of a mascon and pervasive mare flows in the basin brings into question the current models of the mascon formation

density and lithospheric structure at tyrrhena patera mars from gravity and topography data the tyrrhena patera highland volcano mars is associated with a relatively well localized gravity anomaly and we have carried out a localized admittance analysis in the region to constrain the density of the volcanic load the load thickness and the elastic thickness at the time of load emplacement the employed admittance model considers loading of an initially spherical surface and surface as well as subsurface loading is taken into account our results indicate that the gravity and topography data available at tyrrhena patera is consistent with the absence of subsurface loading but the presence of a small subsurface load cannot be ruled out we obtain minimum load densities of 2960 kg m 3 minimum load thicknesses of 5 km and minimum load volumes of 0 6 106 km3 photogeological evidence suggests that pyroclastic deposits make up at most 30 of this volume such that the bulk of tyrrhena patera is likely composed of competent basalt best fitting model parameters are a load density of 3343 kg m 3 a load thickness of 10 8 km and a load volume of 1 7 106 km3 these relatively large load densities indicate that lava compositions are comparable to those at other martian volcanoes and densities are comparable to those of the martian meteorites the elastic thickness in the region is constrained to be smaller than 27 5 km at the time of loading indicating surface heat flows in excess of 24 mw m 2

a look inside the san andreas fault at parkfield through vertical seismic profiling the san andreas fault observatory at depth pilot hole is located on the southwestern side of the parkfield san andreas fault this observatory includes a vertical seismic profiling vsp array vsp seismograms from nearby microearthquakes contain signals between the p and s waves these signals may be p and s waves scattered by the local geologic structure the collected scattering points form planar surfaces that we interpret as the san andreas fault and four other secondary faults the scattering process includes conversions between p and s waves the strengths of which suggest large contrasts in material properties possibly indicating the presence of cracks or fluids

passive seismic tomography using induced seismicity at a petroleum field in oman a borehole network consisting of five monitoring wells monitored the induced seismicity at a producing petroleum field for about 11 months nearly 5400 microseismic events were analyzed and used to image the reservoir based on a new double difference dd seismic tomography the dd tomography method simultaneously solved for event locations and vp vs and vp vs models using absolute and differential p s and s p arrival times microseismicity in the field was caused primarily by compaction of the reservoir in and above the gas bearing formation and was distributed along the two major northeast southwest faults in the field the model resolution analysis based on the checkerboard test and the resolution matrix showed that the central part of the model was resolved relatively well for the depth range of 0 7 to 1 1 km clear velocity contrasts were imaged across most parts of the two northeast southwest faults the vp vs ratio estimates from the tomographic inversion were low 1 75 in the shallow

primary and secondary niobium mineral deposits associated with carbonatites abstract this work reviews the character and origin of primary and supergene economic deposits of niobium associated with carbonatites the brazilian supergene deposits account for about 92 of the total worldwide production of nb with the primary st honore carbonatite and other sources accounting for only for 7 and 1 respectively the emphasis of the review is upon the styles of nb mineralization and the geological factors which lead to economic concentrations of nb bearing minerals primary economic deposits of nb are associated principally with carbonatites found in diverse types of plutonic alkaline rock complexes primary magmas are principally those of the melilitite nephelinite and aillikite clans although many primary niobium deposits are associated with carbonatites ijolites and syenites in the same alkaline complexes can also contain significant nb mineralization in the form of niobian titanite and diverse nb zr silicates marianoite wohlerite these potential sources of nb have not as yet been explored or exploited primary nb deposits can be regarded as large tonnage low grade typically

gaussian beam migration just as synthetic seismic data can be created by expressing the wave field radiating from a seismic source as a set of gaussian beams recorded data can be downward continued by expressing the recorded wave field as a set of gaussian beams emerging at the earth s surface in both cases the gaussian beam description of the seismic wave propagation can be advantageous when there are lateral variations in the seismic velocities gaussian beam downward continuation enables wave equation calculation of seismic propagation while it retains the interpretive raypath description of this propagation this paper describes a zero offset depth migration method that employs gaussian beam downward continuation of the recorded wave field the gaussian beam migration method has advantages for imaging complex structures like finite difference migration it is especially compatible with lateral variations in velocity but gaussian beam migration can image steeply dipping reflectors and will not produce unwanted reflectio

possible mantle origin of olivine around lunar impact basins detected by selene the composition structure and evolution of the moon s mantle is poorly constrained a global survey of the moon s surface using the spectral profiler onboard the lunar explorer selene kaguya identifies a number of exposures of olivine in concentric regions around lunar craters with a possible mantle origin

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

the effect of titanite and other hfse rich mineral ti bearing andradite zircon eudialyte fractionation on the geochemical evolution of silicate melts abstract we present trace element data for hfse rich minerals titanite eudialyte ti bearing andradite zircon from plutonic rocks of the eocene tamazeght complex high atlas mountains morocco in most lithologies significant amounts of titanite are present and as such titanite fractionation played a major role in the evolution of the hfse budget of the whole complex by combining our data with published titanite melt partition coefficients we explore the effects of titanite fractionation on the evolution of geochemical parameters zr hf nb ta la lu and th u ratios during differentiation of silicate melts in detail based upon this we further discuss the genetic relationships between the various rock types present in the tamazeght complex and show that the above mentioned element ratios can potentially be useful for distinguishing geochemically distinct melt reservoirs within a given plutonic rock suite zircon eudialyte and ti bearing andradite are generally rare or are restricted to localized rock units despite their scarcity each of them can have a significant effect upon the hfse budget in their evolving magmas here we derive first estimations of eudialyte melt partition coefficients for ree application of these data to eudialyte bearing rocks of the ilimaussaq complex south greenland and comparing the results to published estimations for the parental melts of these rocks yields consistent results and demonstrates the reliability of our estimations

modification of a rare earth element deposit by low temperature partial melting during metamorphic overprinting norra karr alkaline complex southern sweden abstract rare earth elements play a crucial role in modern technologies and are necessary for a transition to a green economy potentially economic deposits of these elements are typically hosted in minerals such as monazite bastnasite and eudialyte a complex na ca fe zr silicate mineral with cl making these prime targets for geological research globally rare earth mineral deposits commonly show evidence of polyphase development and mineralisation processes which need to be better understood to improve exploration strategies the norra karr alkaline complex sweden contains a globally significant deposit of rare earth elements hosted in the mineral eudialyte in this study we focussed on eudialyte crystals in undeformed cross cutting pegmatoid veins from norra karr in order to determine their age we refined an established micromilling method to enable sampling of minerals rich in rare earth elements for precise analysis of major and trace elements nd isotope ratios and sm nd geochronology down to a scale of

measurements of the elastic thickness under ancient lunar terrain abstract the part of a planet s gravity that is coherent with its topography provides information about the deflection of its crust after loading and hence the resistance of its lithosphere to bending at the time the load was emplaced we used observed line of sight accelerations from lunar prospector together with the accelerations we would have expected if anomalies in the gravity field were only caused by topography to estimate the admittance and coherence between topography and gravity over several regions of the lunar nearside we then compared our estimates to what we would expect if the lithosphere behaved as a floating elastic plate or shell assuming a linear relationship between topography and gravity we found in the region surrounding the southern highland crater clavius that the data can be modeled using a thin plate with t e 12 5 km and uncorrelated loads at the surface and base of the upper crust a spherical shell model with surface loading is less satisfactory to fit the admittance adequately requires topography with wavelengths over 400 km to be formed when t e 1 km and the remainder when t e 7 5 km by contrast the apparent lack of compensation around the youngest giant impact basins requires a plate with t e 80 km or a shell with t e 25 km our results indicate the thickness of the lunar lithosphere increased from 12 km in the pre nectarian to 25 km in the nectarian

melt composition control of zr hf fractionation in magmatic processes zircon zrsio4 and hafnon hfsio4 solubilities in water saturated granitic melts have been determined as a function of melt composition at 800 and 1035 c at 200 mpa the solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt moreover the molar ratio of zircon and hafnon solubility is a function of melt composition although the solubilities are nearly identical in peralkaline melts zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts accordingly calculated partition coefficients of zr and hf between zircon and melt are nearly equal for the peralkaline melts whereas for metaluminous and peraluminous melts dhf dzr for zircon is 0 5 to 0 2 consequently zircon fractionation will strongly decrease zr hf in some granites whereas it has little effect on the zr hf ratio in alkaline melts or similar depolymerized melt compositions the ratio of the molar solubilities of zircon and hafnon for a given melt composition temperature and pressure is proportional to the hf zr activity coefficient ratio in the melt the data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts however it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached for most ferromagnesian minerals in equilibrium with a depolymerized melt dhf dzr typical values of dhf dzr range from 1 5 to 2 5 for clinopyroxene amphibole and titanite because of the change in the hf zr activity ratio in the melt the relative fractionation of zr and hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite it is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in zr hf whereas fractional crystallization of depolymerized melts tends to increase zr hf there is no need to invoke fluid metasomatism to explain these effects results demonstrate that for ions with identical charge and nearly identical radius crystal chemistry does not alone determine relative compatibilities rather the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice

farside deep moonquakes and deep interior of the moon 1 an effort to find farside deep moonquakes among the recently discovered nests of deep moonquakes has identified about 30 nests that are likely to be on the farside although only a few of them are locatable with currently available data and those few provide little new information about the deep interior of the moon the inferred distribution of the rest of these nests indicates that either the region of the moon s deep interior within about 40 degrees from the antipode of the moon is nearly aseismic or alternatively the very deep interior of the moon severely attenuates or deflects seismic waves since this has important bearing on the origin and evolution of the moon future missions to the moon need to be oriented toward resolving this uncertainty some limited data favor the attenuation deflection hypotheses

fractionation of geochemical twins zr hf nb ta and y ho and hree enrichment during magmatic and metamorphic processes in peralkaline nepheline syenites from norra karr sweden abstract the 1 49 ga norra karr complex sweden consists of deformed and metamorphosed peralkaline nepheline syenites that contain eudialyte group minerals as the major host of high field strength elements and rare earth elements earlier studies revealed the presence of distinct generations of eudialyte group minerals and clinopyroxene of magmatic and metamorphic origin here we present the trace element characteristics of the different generations of rock forming minerals the trace element chemistry of eudialyte group minerals mimic whole rock compositions and display well developed negative eu anomalies and strong sr and ba depletions in chondrite normalized diagrams they imply that the norra karr rocks developed by intense fractional crystallization from an alkali basaltic parental magma our data further illustrate that eudialyte group minerals do not strongly fractionate the geochemical twins zr hf y ho and nb ta during magmatic processes the transition from a magmatic to metamorphic environment is marked in egm by a drop in y ho and nb ta the exceptional enrichment of heavy rare earth elements in late metamorphic eudialyte may result from residual enrichment light rare earth elements and nb were preferentially mobilized to form local secondary light rare earth rich rinkite group mineral assemblages while the heavy ree stayed behind and formed heavy ree rich eudialyte magmatic clinopyroxene shows a clear preference for hf over zr while on a subunit scale a negative correlation of the total ree in cpx and in egm is noticed both indicate that early cpx fractionation would not only increase zr hf of the evolving melt but also affect the ree deportment in major hfse hosts

measurement and analysis of lunar basin depths from clementine altimetry altimetric profiles from the clementine lidar are used to calculate the depths of 29 large craters and basins on the moon plotting the depths of the best preserved structures together with values for simple and complex craters measured in pre clementine studies reveals an inflection in the depth diameter d d curve in addition to the one revealed by pre clementine data this inflection occurs in the diameter range that corresponds to the morphologic transition from complex crater to basin the best empirical power law fit for basin depths is log10 d 0 41 log10 d 0 57 this relationship is characterized by a lower slope than that for complex craters demonstrating that this morphologic transition corresponds to a further decrease in the depth of an impact structure relative to its diameter with increasing size qualitative consideration of possible causes for the second inflection leads to the conclusion that it is most likely a consequence of a short term modification mechanism that influences fundamental crater morphology such as the increasing influence of gravity with diameter thicknesses of maria in the major basins are calculated by assuming that their unfilled depths would follow thed drelation results are compared with previous estimates and yield thicknesses that are generally greater than those determined by studies of flooded craters and less than those obtained from analysis of gravity

the origin of lunar mascon basins high resolution gravity data from the gravity recovery and interior laboratory spacecraft have clarified the origin of lunar mass concentrations mascons free air gravity anomalies over lunar impact basins display bull s eye patterns consisting of a central positive mascon anomaly a surrounding negative collar and a positive outer annulus we show that this pattern results from impact basin excavation and collapse followed by isostatic adjustment and cooling and contraction of a voluminous melt pool we used a hydrocode to simulate the impact and a self consistent finite element model to simulate the subsequent viscoelastic relaxation and cooling the primary parameters controlling the modeled gravity signatures of mascon basins are the impactor energy the lunar thermal gradient at the time of impact the crustal thickness and the extent of volcanic fill

three dimensional passive seismic waveform imaging around the safod site california using the generalized radon transform 1 we apply a three dimensional 3d generalized radon transform grt to scattered p waves from 575 local earthquakes recorded at 68 temporary network stations for passive source imaging of near vertical structures close to the san andreas fault observatory at depth safod site the grt image profiles through or close by the safod site reveal near vertical reflectors close to the fault zone as well as in the granite to the southwest and the franciscan melange to the northeast of the main fault although slightly lower in resolution these structures are generally similar to features in 2d images produced with steep dip prestack seismic migration of data from active source seismic reflection and refraction surveys our grt images however also reveal several vertical reflectors to the northeast of the saf that do not appear in the migration images but which are consistent with local geology these results suggest that in a seismically active area inverse scattering of earthquake data for instance with the grt can be a viable and in 3d economic alternative to an active source survey

density and porosity of the lunar crust from gravity and topography 1 newly obtained gravity and topography data of the moon combined with a lithospheric flexure model that considers both surface and subsurface loading are used to place constraints on the density of the upper crust from a localized spectral admittance analysis subsurface loads are found to be relatively unimportant in the highlands and when subsurface loads are neglected the best fitting bulk densities for a number of highland regions are found to vary from 2590 to 2870 kg m 3 with a mean value of 2691 kg m 3 crustal rock densities estimated from geochemical considerations and global iron and titanium abundances imply somewhat greater densities which we interpret as porosity affecting the gravity derived bulk density estimates the average porosity in the upper few kilometers of crust is calculated to be about 7 7 which is consistent with porosity estimates of impact fractured meteorites and terrestrial impact craters

lunar multiring basins and the cratering process abstract numerous studies of the lunar gravity field have concluded that the lunar moho is substantially uplifted beneath the young multiring basins this uplift is presumably due to the excavation of large quantities of crustal material during the cratering process and subsequent rebound of the impact basin floor using a new dual layered crustal thickness model of the moon the excavation cavities of some nearside multiring basins grimaldi and larger and younger than tranquillitatis were reconstructed by restoring the uplifted moho to its preimpact location the farside south pole aitken spa basin was also considered due to its importance in deciphering lunar evolution restoring the moho to its preimpact position beneath these basins resulted in a roughly parabolic depression from which the depth and diameter of the excavation cavity could be determined using these reconstructed excavation cavities the basin forming process was investigated excavation cavity diameters were generally found to be on the small side of most previous estimates for orientale the modeled excavation cavity lies within the inner rook ring additionally with the exception of the three largest basins serenitatis imbrium and south pole aitken the depth diameter ratios of the excavation cavities were found to be 0 115 0 005 a value consistent with theoretical and experimental results for impact craters orders of magnitude smaller in size the three largest basins however appear to have significantly shallower depths of excavation compared to this trend it is possible that this may reflect a different physical process of crater formation e g nonproportional scaling special impact conditions or postimpact modification processes the crustal thickness model also shows that each basin is surrounded by an annulus of thickened crust we interpret this thickened crust as representing thick basin ejecta deposits and we show that the radial variation in the thickness of these deposits is consistent with scaling laws obtained from small scale experimental studies if multiring basins ever possessed a terraced main crater rim this terraced zone may be presently unrecognizable at the surface due to the emplacement of ejecta deposits that exceed a few kilometers in thickness exterior to the excavation cavity rim we also show that the interiors of many basins were superisostatic before mare volcanism commenced those basins that were closest to approaching a premare isostatic state lie close to or within an anomalous geochemical province rich in heat producing elements

bulk and mush melt evolution in agpaitic intrusions insights from compositional zoning in eudialyte ilimaussaq complex south greenland

initial observations from the lunar orbiter laser altimeter lola as of june 19 2010 the lunar orbiter laser altimeter an instrument on the lunar reconnaissance orbiter has collected over 2 0 10 9 measurements of elevation that collectively represent the highest resolution global model of lunar topography yet produced these altimetric observations have been used to improve the lunar geodetic grid to 10 m radial and 100 m spatial accuracy with respect to the moon s center of mass lola has also provided the highest resolution global maps yet produced of slopes roughness and the 1064 nm reflectance of the lunar surface regional topography of the lunar polar regions allows precise characterization of present and past illumination conditions lola s initial global data sets as well as the first high resolution digital elevation models dems of polar topography are described herein

comparison of surface and borehole locations of induced seismicity monitoring of induced microseismic events has become an important tool in hydraulic fracture diagnostics and understanding fractured reservoirs in general we compare microseismic event and their uncertainties using data sets obtained with surface and downhole arrays of receivers we first model the uncertainties to understand the effect of different acquisition geometries on location accuracy for a vertical array of receivers in a single monitoring borehole we find that the largest part of the final location uncertainty is related to estimation of the backazimuth this is followed by uncertainty in the vertical position and radial distance from the receivers for surface monitoring the largest uncertainty lies in the vertical position due to the use of only a single phase usually p wave in the estimation of the event location in surface monitoring results lateral positions are estimated robustly and are not sensitive to the velocity model in this case study we compare event location solutions from two catalogues of microseismic events one from a downhole array and the second from a surface array of 1c geophone our results show that origin time can be reliably used to find matching events between the downhole and surface catalogues the locations of the corresponding events display a systematic shift consistent with a poorly calibrated velocity model for downhole dataset for this case study locations derived from surface monitoring have less scatter in both vertical and horizontal directions

long period long duration seismic events during hydraulic fracture stimulation of a shale gas reservoir we report here a series of long period and long duration lpld seismic events observed during hydraulic fracturing in a shale gas reservoir these unusual events 10 100 s in duration are observed most clearly in the frequency band of 10 80 hz and are remarkably similar in appearance to tectonic tremor sequences first observed in subduction zones these complex but coherent wave trains have finite moveouts obtained from cross correlation the moveout direction of the events confirms that they originate in the reservoir from the area where the fracturing is going on clear p and s wave arrivals cannot be resolved within the lpld episodes but in some cases small micro earthquakes occur in the sequences whether these micro earthquakes are causal or coincidental is not known it has also been observed that in three contiguous frac stages all lpld events appear to come from two distinct places along one of two hypothetical fracture planes interestingly the stages which have the largest number of lpld

the density and porosity of lunar rocks 1 accurate lunar rock densities are necessary for constructing gravity models of the moon s crust and lithosphere most apollo era density measurements have errors of 2 5 or more and few include porosity measurements we report new density and porosity measurements using the bead method and helium pycnometry for 6 apollo samples and 7 lunar meteorites with typical grain density uncertainties of 10 30 kg m 3 0 3 0 9 and porosity uncertainties of 1 3 comparison between igneous grain densities and normative mineral densities show that these uncertainties are realistic and that the helium fully penetrates the pore space basalt grain densities are a strong function of composition varying over at least 3270 kg m 3 high aluminum basalt to 3460 kg m 3 high titanium basalt feldspathic highland crust has a bulk density of 2200 2600 kg m 3 and porosity of 10 20 impact basin ejecta has a bulk density of 2350 2600 kg m 3 and porosity of 20

isostasy of the moon from high resolution gravity and topography data implication for its thermal history 1 the lunar prospector line of sight acceleration data after terrain correction have been inverted to the high resolution bouguer gravity anomalies of the lunar nearside lithospheric thicknesses of the early moon were investigated by comparing the gravity anomalies of craters and impact basins of various dimensions the lithosphere was already thick enough to support craters with diameters up to 300 km in the pre nectarian and nectarian periods degree of isostatic compensation of larger impact basins suggested lithospheric thickness of 20 60 km at that time which depended more on localities rather than age differences

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

simultaneous microseismic event localization and source mechanism determination abstractmicroseismic monitoring has become a tool of choice for the development and optimization of oil and gas production from unconventional reservoirs the primary objective of micro seismic monitoring includes localization of micro seismic events and characterization of their source mechanisms most seismic events are of a nonexplosive nature and thus there are waveform polarity differences among receivers specifically double couple sources represented a challenge for migration based localization techniques we developed and applied a new migration type location technique combined with source mechanism inversion that allowed for constructive interference of signal in seismic waveforms the procedure included constructing image functions by stacking the amplitudes with compensated polarity changes the compensation weights were calculated by using moment tensor inversion this method did not require any picking of arrivals at individual receivers but it required receivers to be distributed i

wavelet transform mapping of effective elastic thickness and plate loading validation using synthetic data and application to the study of southern african tectonics 1 we present a new wavelet transform method to map spatial variations in effective elastic thickness te and plate loading ratio f the method assumes a model of thin plate flexural isostasy to describe the mechanical response of the lithosphere to vertical loading in this model the rheological properties of the lithosphere are aggregated into the effective elastic thickness te of an equivalent thin plate overlying an inviscid fluid a number of methods have been developed to map spatial variations in te in an attempt to assess regional patterns of flexural strength our new method first obtains local coherence and local admittance through wavelet cross spectral analysis of surface topography and bouguer gravity anomaly wavelet coherence is used to obtain the local characteristic wavelength which is a function of both te and the degree of relative loading f of the plate by subsurface loads and surface loads loading is the combined effect of erosion sedimentation intrusion faulting and metamorphism wavelet admittance in a normalized form is used to resolve this f te ambiguity and maps are made of the spatial variations in te and f we carry out extensive tests of the wavelet method on simulated topography and bouguer gravity anomaly data that we generate through finite difference simulations of flexural isostasy with spectrally realistic loads and simple spatial variations in te these tests demonstrate that the wavelet inversion method is reasonably robust to uncertainties in loading and in crustal thickness and is able to recover te to within 25 50 of its correct value we apply the wavelet method to southern africa and recover estimates of te principally in the range 25 50 km in good agreement with existing estimates from forward modeling and fourier coherence analyses we find that our te estimates often exceed estimates of crustal thickness pointing to a strong upper mantle in parts of southern africa

the lunar crust global structure and signature of major basins new lunar gravity and topography data from the clementine mission provide a global bouguer anomaly map corrected for the gravitational attraction of mare fill in mascon basins most of the gravity signal remaining after corrections for the attraction of topography and mare fill can be attributed to variations in depth to the lunar moho and therefore crustal thickness the large range of global crustal thickness 20 120 km is indicative of major spatial variations in melting of the lunar exterior and or significant impact related redistribution the 61 km average crustal thickness constrained by a depth to moho measured during the apollo 12 and 14 missions is preferentially distributed toward the farside accounting for much of the offset in center of figure from the center of mass while the average farside thickness is 12 km greater than the nearside the distribution is nonuniform with dramatic thinning beneath the farside south pole aitken basin with the global crustal thickness map as a constraint regional inversions of gravity and topography resolve the crustal structure of major mascon basins to half wavelengths of 150 km in order to yield crustal thickness maps with the maximum horizontal resolution permitted by the data the downward continuation of the bouguer gravity is stabilized by a three dimensional minimum slope and curvature algorithm both mare and non mare basins are characterized by a central upwarped moho that is surrounded by rings of thickened crust lying mainly within the basin rims the inferred relief at this density interface suggests a deep structural component to the surficial features of multiring lunar impact basins for large 300 km diameter basins moho relief appears uncorrelated with diameter but is negatively correlated with basin age in several cases it appears that the multiring structures were out of isostatic equilibrium prior to mare emplacement suggesting that the lithosphere was strong enough to maintain their state of stress to the present

density and lithospheric thickness of the tharsis province from mex mars and mro gravity data 1 radio science tracking of mars express mars experiment and mars reconnaissance orbiter produced high resolution martian gravity data applying localized spectral analysis on the new gravity data sets we study the surface density and lithospheric elastic thickness in the tharsis province the gravity signal is predicted with geophysical models either including bottom loading top bottom model or taking into account the loading history top top model volcanic shields are mainly composed of high density lava but their construction could have begun with lower density lava with the exception of ascraeus mons which has a top of lower density buoyant bottom loading may have been present in the form of a mantle plume under olympus mons the elastic thickness was much larger at olympus mons than at other volcanoes suggesting large spatial variations of heat flux during the hesperian alternatively small elastic thicknesses could be artifacts reflecting the presence of very localized high density crustal intrusions beneath the volcanoes thaumasia highlands were probably supported by a mantle plume at the time of formation in valles marineris top bottom models predict low densities and large elastic thicknesses in conflict with the basaltic rock composition and hesperian age of the valley dense mafic dikes underlie the western part of the valley the top top model serves to test another scenario in which the trough is formed with sedimentary infilling removed much later by erosion the elastic thickness increasing in between at the large volcanoes the relation between gravity and topography is anisotropic probably because of density variations

excavation of the lunar mantle by basin forming impact events on the moon abstract global maps of crustal thickness on the moon derived from gravity measurements obtained by nasa s gravity recovery and interior laboratory grail mission have shown that the lunar crust is thinner than previously thought hyperspectral data obtained by the kaguya mission have also documented areas rich in olivine that have been interpreted as material excavated from the mantle by some of the largest lunar impact events numerical simulations were performed with the isale 2d hydrocode to investigate the conditions under which mantle material may have been excavated during large impact events and where such material should be found the results show that excavation of the mantle could have occurred during formation of the several largest impact basins on the nearside hemisphere as well as the moscoviense basin on the farside hemisphere even though large areas in the central portions of these basins were later covered by mare basaltic lava flows surficial lunar mantle deposits are predicted in areas external to these maria our results support the interpretation that the high olivine abundances detected by the kaguya spacecraft could indeed be derived from the lunar mantle

images of a lower crustal oceanic slab direct evidence for tectonic accretion in the archean western superior province the archean western superior province in canada is the type area for proposed archean plate tectonics seismic images from this region provide direct evidence for assembly of the craton by terrane accretion and for a large slab of remnant oceanic crust preserved at the base of the crust this slab with inferred garnet amphibolite composition adds a critical piece of evidence to previous suggestions that archean subduction was at a shallow angle and that some neoarchean tonalite trondhjemite granodiorite suites distinct from most modern day suprasubduction magmas are melts primarily derived directly from subducted slabs

focal mechanism determination using high frequency waveform matching and its application to small magnitude induced earthquakes s u m m a r y we present a new method using high frequency full waveform information to determine the focal mechanisms of small local earthquakes monitored by a sparse surface network during the waveform inversion we maximize both the phase and amplitude matching between the observed andmodelled waveforms in addition we use the polarities of the firstp wave arrivals and the average s p amplitude ratios to better constrain the matching an objective function is constructed to include all four criteria an optimized grid search method is used to search over all possible ranges of source parameters strike dip and rake to speed up the algorithm a library of green s functions is pre calculated for each of the moment tensor components and possible earthquake locations optimizations in filtering and cross correlation are performed to further speed the grid search algorithm the new method is tested on a five station surface network used for monitoring induced seismicity at a petroleum field the synthetic test showed that our method is robust and efficient to determine the focal mechanism when using only the vertical component of seismograms in the frequency range of 3 9 hz the application to dozens of induced seismic events showed satisfactory waveform matching between modelled and observed seismograms the majority of the events have a strike direction parallel with the major ne sw faults in the region the normal faulting mechanism is dominant which suggests the vertical stress is larger than the horizontal stress

calibrating one dimensional velocity model for downhole microseismic monitoring using station pair differential arrival times based on the differential evolution method abstract for microseismic monitoring in order to obtain accurate microseismic locations a good estimation of the velocity model for the region covering the monitoring stations and microseismic sources is crucial perforation shots are generally used to estimate a velocity model suitable for microseismic location however the origin times of the perforation shots are generally not accurate to mitigate the effect of inaccurate origin times of perforation shots on calibrating the velocity model we propose to search for a velocity model fitting for station pair differential arrival times instead of absolute arrival times from perforation shots another advantage of using station pair differential arrival times is that waveform cross correlation can be used to estimate more accurate differential times because of waveform similarity among stations for perforation shots due to high nonlinearity of the objective function for estimating one dimensional velocity model the differential evolution de method for solving high dimensional global optimization problems is utilized in the optimization compared to the grid search method the de method is much more efficient synthetic tests based on a downhole microseismic monitoring system show the effectiveness of the proposed method to recover the velocity model we also test our de based method by using perforation shots for a real microseismic monitoring project compared to the well sonic velocity model station pair differential arrival times are better fitted and perforation shots are also more accurately relocated with the calibrated velocity model

abrupt onset of the little ice age triggered by volcanism and sustained by sea ice ocean feedbacks 1 northern hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes however the causes of superposed century scale cold summer anomalies of which the little ice age lia is the most extreme remain debated largely because the natural forcings are either weak or in the case of volcanism short lived here we present precisely dated records of ice cap growth from arctic canada and iceland showing that lia summer cold and ice growth began abruptly between 1275 and 1300 ad followed by a substantial intensification 1430 1455 ad intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium a transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times and that cold summers can be maintained by sea ice ocean feedbacks long after volcanic aerosols are removed our results suggest that the onset of the lia can be linked to an unusual 50 year long episode with four large sulfur rich explosive eruptions each with global sulfate loading 60 tg the persistence of cold summers is best explained by consequent sea ice ocean feedbacks during a hemispheric summer insolation minimum large changes in solar irradiance are not required

petroleum reservoir characterization using downhole microseismic monitoring imaging of microseismic data is the process by which we use information about the source locations timing and mechanisms of the induced seismic events to make inferences about the structure of a petroleum reservoir or the changes that accompany injections into or production from the reservoir a few key projects were instrumental in the development of downhole microseismic imaging most recent microseismic projects involve imaging hydraulic fracture stimulations which has grown into a widespread fracture diagnostic technology this growth in the application of the technology is attributed to the success of imaging the fracture complexity of the barnett shale in the fort worth basin texas and the commercial value of the information obtained to improvecompletions and ultimately production in the field the use of commercial imaging in the barnett is traced back to earlier investigations to prove the technology with the cotton valley imaging project and earlier experiments at the m site in the piceance

ancient selenophysical structure of the grimaldi basin constraints from grail gravity and lola topography abstract the grimaldi impact basin is located near the western limb of the moon and lies to the southwest of the oceanus procellarum a clearly visible positive gravity anomaly exists in its low lying inner wall implying a subsurface mass concentration beneath the crater exploration of this basin could extend our meaningful and fundamental understanding of giant impact processes as well as the structure of mare basins craters limited by the low resolution of previous gravity field models it was once impossible to explore the structure beneath grimaldi the recent high resolution gravity data from the gravity recovery and interior laboratory mission make it possible to break through this barrier prior to our investigation of the selenophysical structure around crater grimaldi we developed a flexure model that includes surface and subsurface loads a localized admittance analysis was performed by combining high resolution gravity data with the high resolution topography data obtained from lunar orbiter laser altimeter within 2 std error constraints we estimated the best fit parameters over grimaldi as well as two other places in its neighborhood all the predicted admittances show a goodness of fit with their corresponding observations the large load ratio 9 2 found at the grimaldi is an indirect mirror of the dominant subsurface load consistent with its large positive gravity anomaly in its low lying floor not only the crustal thickness of 48 km but also the crustal density of 2500 kg m 3 found around grimaldi shows a great accordance with the recent results of grail given the best fit parameters of f bc and c the elastic thickness te is found to be around 28 km over grimaldi taking into account the best fit values in its neighborhood a regional elastic thickness of 30 km could be roughly concluded around grimaldi which is completely in the previous ranges 20

location for direct access to subglacial lake ellsworth an assessment of geophysical data and modeling ellsworth is 14 7 km 3 1 km with an area of 28 9 km 2 lake depth increases downlake from 52 m to 156 m with a water body volume of 1 37 km 3 the ice thickness suggests an unusual thermodynamic characteristic with the critical pressure boundary intersecting the lake numerical modeling of water circulation has allowed accretion of basal ice to be estimated we collate this physiographic and modeling information to confirm that lake ellsworth is ideal for direct access and propose an optimal drill site the likelihood of dissolved gas exchange between the lake and the borehole is also assessed citation woodward j a m smith n ross m thoma h f j corr e c king m a king k grosfeld m tranter and m j siegert 2010 location for direct access to subglacial lake ellsworth an assessment of geophysical data and modeling geophys res lett 37 l11501 doi 10 1029 2010gl042884

focal mechanism determination of induced microearthquakes in an oil field using full waveforms from shallow and deep seismic networks a new relatively high frequency full waveform matching method was used to study the focal mechanisms of small local earthquakes induced in an oil field which are monitored by a sparse near surface network and a deep borehole network the determined source properties are helpful for understanding the local stress regime in this field during the waveform inversion we maximize both the phase and amplitude matching between the observed and modeled waveforms we also use the polarities of the first p wave arrivals and the average s p amplitude ratios to better constrain the matching an objective function is constructed to include all four criteria for different hypocenters and source types comprehensive synthetic tests showed that our method is robust enough to determine the focal mechanisms under the current array geometries even when there is considerable velocity inaccuracy the application to several tens of induced microseismic events showed satisfactory waveform matching between modeled and obs

distinguishing magmatic and metamorphic processes in peralkaline rocks of the norra karr complex southern sweden using textural and compositional variations of clinopyroxene and eudialyte group minerals