strike slip faulting thrusting and related basins in the cenozoic evolution of the southern branch of the bolivian orocline abstract the evolution of the cenozoic deformation of the cordillera oriental and of the contact zone with the altiplano in southern bolivia is well documented in the tupiza nazareno and estarca basins the tectonic evolution started at about 29 ma the period between 29 and about 22 21 ma is marked by development of a pull apart basin related to n s trending left lateral strike slip faulting during this period initial deposition consisted of andesitic lavas and detrital sediments breccias matrix supported red conglomerates sands and silts of the catati and tupiza formation deposited in alluvial fan and flood plain environments from 21 to 20 ma the tectonic setting evolved to n s oriented thrusts which had a dextral component this event caused the tupiza basin to evolve into a full ramp basin and triggered the development of two piggy back basins nazareno and estarca both basins record detrital deposition nazareno formation in an alluvial fan environment at 10 9 ma deformation in this area stopped allowing peneplanation during which time the san juan de oro erosional surface was formed and the fluvial conglomerates of the oploca formation were deposited this segment of the andes was then tectonically transported to the east while uplift due to thrusting continued in the eastern andean front and in the subandean zone

crustal scale block tilting during andean trench parallel extension structural and geo thermochronological insights despite a long history of plate convergence at the western margin of the south american plate that has been ongoing since at least the early paleozoic the southern peruvian fore arc displays little to no evidence of shortening in the light of this observation we assess the deformation history of the southern peruvian fore arc and its geodynamic implications to accomplish this we present a new structural and geo thermochronological data set zircon u pb mica 40ar 39ar apatite and zircon fission track and zircon u th he analyses for samples collected along a 400 km long transect parallel to the trench our results show that the mesoproterozoic gneissic basement was mainly at temperatures 350 c since the neoproterozoic and was later intruded by jurassic volcanic arc plutons along the coast a peculiar apatite fission track age pattern coupled with field observations and a synthesis of available geological maps allows us to identify crustal scale tilted blocks that span the coastal peruvian fore arc these blocks bounded by normal faults that are orthogonal to the trench suggest post 60 ma trench parallel extension that potentially accommodated oroclinal bending in this region block tilting is consistent with the observed and previously described switch in the location of sedimentary sources in the fore arc basin our data set allows us to estimate the cumulative slip on these faults to be less than 2 km and questions the large amount of trench parallel extension suggested to have accommodated this bending

source parameters of the deadly mw 7 6 kashmir earthquake of 8 october 2005 during the last six years national geophysical research institute hyderabad has established a semi permanent seismological network of 5 8 broadband seismographs and 10 20 accelerographs in the kachchh seismic zone gujarat with a prime objective to monitor the continued aftershock activity of the 2001 mw 7 7 bhuj mainshock the reliable and accurate broadband data for the 8 october mw 7 6 2005 kashmir earthquake and its aftershocks from this network as well as hyderabad geoscope station enabled us to estimate the group velocity dispersion characteristics and one dimensional regional shear velocity structure of the peninsular india firstly we measure rayleigh and love wave group velocity dispersion curves in the period range of 8 to 35 sec and invert these curves to estimate the crustal and upper mantle structure below the western part of peninsular india our best model suggests a two layered crust the upper crust is 13 8 km thick with a shear velocity vs of 3 2 km s the corresponding values for the lower crust are 24 9 km and 3 7 km sec the shear velocity for the upper mantle is found to be 4 65 km sec based on this structure we perform a moment tensor mt inversion of the bandpass 0 05 0 02 hz filtered seismograms of the kashmir earthquake the best fit is obtained for a source located at a depth of 30 km with a seismic moment mo of 1 6 1027 dyne cm and a focal mechanism with strike 19 5 dip 42 and rake 167 the long period magnitude ma mw of this earthquake is estimated to be 7 31 an analysis of well developed spn and ssn regional crustal phases from the bandpassed 0 02 0 25 hz seismograms of this earthquake at four stations in kachchh suggests a focal depth of 30 8 km

three dimensional velocity imaging of the kachchh seismic zone gujarat india abstract to understand the causative mechanism of the continued occurrence of earthquakes in kachchh gujarat for the last six years we estimated high resolution three dimensional vp vs and vp vs structures in the aftershock zones of the 2001 mw7 7 bhuj and 2006 mw5 6 gedi earthquakes we used 13 862 p and 13 736 s wave high quality arrival times collected from the seismograms of 2303 aftershocks recorded at 5 18 three component seismograph stations during 2001 06 seismic images revealed a marked spatial variation in the velocities from 20 to 14 in vp from 12 to 13 in vs and from 12 to 12 increase in vp vs in the 0 34 km depth range beneath the bhuj aftershock zone relatively more increase in vp than vs resulting in an increase in vp vs in the crust beneath the seismically active causative fault north wagad fault nwf zone of 2001 bhuj mainshock suggests a rigid mafic crust beneath the region they also delineate an increase of 8 in vp and 14 in vs and a decrease of 4 in vp vs in the almost vertical rupture zone of the 2006 gedi earthquake extending up to 12 km depth this high velocity body associated with the gedi mainshock is inferred to be a gabbroic intrusive the banni region and the wagad uplift are found to be associated with high velocity intrusive bodies inferred to be mafic extending from 5 to 35 km depth which might have intruded during the rifting in early jurassic 160 ma aftershock activity is mainly confined to the zones characterized by high vp high vs and low vp vs ratio which might be representing the strong competent and brittle parts of the fault zone intrusive bodies that could accumulate large strain energy for generating aftershocks for more than six years it is inferred that the crustal stress concentrations associated with the intrusive bodies are contributing significant perturbation to the crustal stress regime to generate the intraplate earthquakes in the kachchh rift zone a few patches of slow vp and vs and high vp vs between 10 to 30 km depth have also been detected on the causative 45 south dipping north wagad fault nwf for the 2001 mainshock which may be attributed to the fluid filled fractured rock matrix interestingly the 2001 bhuj mainshock hypocenter is found to be associated with such a low velocity patch thus it is inferred that the occurrence of 2001 bhuj mainshock might have facilitated by the presence of fluids at hypocentral depth

a model for the thermal and chemical evolution of the moon s interior implications for the onset of mare volcanism crystallization of the lunar magma ocean creates a chemically stratified moon consisting of an anorthositic crust and magma ocean cumulates overlying the primitive lunar interior within the magma ocean cumulates the last liquids to crystallize form dense ilmenite rich cumulates that contain high concentrations of incompatible radioactive elements the underlying olivine orthopyroxene cumulates are also stratified with later crystallized denser more fe rich compositions at the top this paper explores the chemical and thermal consequences of an internal evolution model accounting for the possible role of these sources of chemical buoyancy rayleigh taylor instability causes the dense ilmenite rich cumulate layer and underlying fe rich cumulates to sink toward the center of the moon forming a dense lunar core after this overturn radioactive heating within the ilmenite rich cumulate core heats the overlying mantle causing it to melt in this model the source region for high tio2 mare basalts is a convectively mixed layer above the core mantle boundary which would contain small and variable amounts of admixed ilmenite and kreep this deep high pressure melting as required for the generation of mare basalts occurs after a reasonable time interval to explain the onset of mare basalt volcanism if the content of radioactive elements in the core and the chemical density gradients above the core are sufficiently high but within a range of values that might have been present in the moon regardless of details implied by particular model parameters gravitational overturn driven by the high density of magma ocean fe rich cumulates should concentrate high tio2 mare basalt sources and probably a significant fraction of radioactive heating toward the center of the moon this will have important implications for both the thermal evolution of the moon and for mare basalt genesis

a low seismic wavespeed anomaly beneath northwestern india a seismic signature of the deccan plume abstract seismic tomography of the indian region using p wave arrival times reveals an approximately cylindrical region of lowered seismic velocities in the upper mantle to the north of the gulf of cambay and the present exposure of the deccan flood basalts this anomaly with low velocities interrupts the characteristically high seismic velocities in the lithosphere beneath peninsular india and extends from shallow depth down to a more extensive low velocity zone beneath 200 km the centre of the low velocity anomaly lies just below the earliest alkaline magmatism which has been directly associated with the deccan plume in the northern portion of the cambay graben these magmatic events precede the main deccan flood eruptions by at least 3 myr the lowered seismic wavespeeds link into the ancient narmada lineament and to some extent to the south but here unfortunately the tomographic image runs out of resolution synthetic tests indicate that such a zone of lowered wavespeeds can be recovered with some loss of amplitude towards the south the association of the current seismic anomaly with the deccan traps is intriguing since the cambay graben remains a place of raised heat flow one explanation would be that the seismic anomaly represents the signature of the initial conduit through which plume material forced its way through the lithosphere beneath the cambay rift the zone of lowered seismic velocities beneath the indian lithosphere might then represent the remains of the initial plume head which would need to have moved with india over the 65 myr since the deccan eruptions

source parameters and tectonic implications of aftershocks of the mw 7 6 bhuj earthquake of 26 january 2001 we present and discuss the spatial distribution of more than 1000 aftershocks of the largest continental intraplate earthquake to occur during the modern seismological period the data were recorded on a network of eight portable digital seismographs deployed for 3 weeks starting 17 days after the mainshock we have calculated high quality single event locations based on a 1d velocity model determined for the region for earthquakes with magnitudes between 2 and 5 aftershock locations reveal activity concentrated on a nearly east striking south dipping plane trapezoidal in outline the active zone tapers from about 45 km along strike at the shallow end which is about 5 km deep to no more than 25 km long at a depth of 35 km the total rupture area was about 1300 km 2 we estimate the static stress drop of the mainshock at 16 2 mpa aftershocks extend nearly through the entire crust with concentrations in the lower crust at about 26 km and in the upper crust at about 10 km the fault that ruptured was not mapped at the surface and not known to have been active prior to the 2001 earthquake the aftershock data are consistent with the bhuj earthquake resulting from reactivation in contraction of a fault formed under extension within a failed rift

lunar highland meteorites and the composition of the lunar crust abstract major minor and trace element data obtained by neutron activation techniques and by spark source mass spectrometry ssms on two lunar meteorites mac88104 and mac88105 are reported both mac samples were also analysed for their contents and isotopic compositions of rare gases additional ssms data were obtained on four lunar highland meteorites previously found in antarctica alha81005 y791197 y82192 and y86032 mac88104 and mac88105 are very similar in chemistry suggesting that they are pieces of a single fall event the bulk chemical composition of mac88104 5 is not very different from the other lunar highland meteorites highly aluminous with relatively low contents of ree and siderophile element concentrations slightly above 1 of a ci chondritic level however mafic element concentrations mg cr mn etc are slightly lower in mac88104 5 than in the other lunar highland meteorites the contents of solar rare gases in the two mac samples are low indicating only a small regolith contribution in agreement with rare petrographically identifiable regolith components the mac samples and also y82192 and y86032 are classified as fragmental breccias with negligible regolith components in contrast to alha81005 and y791197 which are regolith breccias with high solar wind derived rare gas contents there is no correlation among lunar meteorites between peak shock pressures and solar gas contents indicating that peak shock pressures of up to 25 gpa do not lead to gas loss a low 26al activity vogt et al 1990 and high contents of cosmogenic rare gases in mac88104 5 suggest a long exposure 400 000 years in the lunar sub surface k ar ages are in excess of 3 9 by lunar highland meteorites and compositionally similar granulitic rocks from the apollo 16 and 17 landing sites contain about 1 of a ci chondritic component according to siderophile and volatile element contents but independent of the amount of regolith components apparently the major fraction of meteoritic elements in these rocks was not provided by micrometeorites impacting the regolith the abundances of siderophile e g ir and volatile elements may therefore reflect the last spike of accretion of the moon after the formation of the anorthositic crust lunar meteorites of highland origin are chemically different from the bulk of the apollo 16 highland samples in having higher fe mg ratios and lower contents and less fractionated patterns of incompatible and siderophile elements since lunar highland meteorites are associated with at least three but probably four different fall events and since they are not derived from chemically exotic front side terranes they may represent a better sampling of the average chemical composition of the lunar crust than previous estimates based on returned lunar samples and remote sensing data a comparison between an average highland composition derived by taylor 1982 and an estimate based on lunar highland meteorites shows that the taylor composition contains higher concentrations and more fractionated incompatible elements mainly because of a substantial amount of kreep a trace element rich highly fractionated component from the front side of the moon not present at the sites from which the lunar meteorites come

major lunar crustal terranes surface expressions and crust mantle origins in light of global remotely sensed data the igneous crust of the moon can no longer be viewed as a simple globally stratified cumulus structure composed of a flotation upper crust of anorthosite underlain by progressively more mafic rocks and a residual melt kreep sandwich horizon near the base of the lower crust instead global geochemical information derived from clementine multispectral data and lunar prospector gamma ray data reveals at least three distinct provinces whose geochemistry and petrologic history make them geologically unique 1 the procellarum kreep terrane pkt 2 the feldspathic high lands terrane fht and 3 the south pole aitken terrane spat the pkt is a mafic province coincident with the largely resurfaced area in the procellarum imbrium region whose petrogenesis relates to the early differentiation of the moon here some 40 of the th in the moon s crust is concentrated into a region that constitutes only about 10 of the crustal volume this concentration of th average 5 ppm and by implication the other heat producing elements u and k led to a fundamentally different thermal and igneous evolution within this region compared to other parts of the lunar crust lower crustal materials within the pkt likely interacted with underlying mantle materials to produce hybrid magmatism leading to the magnesian suite of lunar rocks and possibly kreep basalt although rare in the apollo sample collection widespread mare volcanic rocks having substantial th enrichment are indicated by the remote data and may reflect further interaction between enriched crustal residues and mantle sources the fht is characterized by a central anorthositic region that constitutes the remnant of an anorthositic craton resulting from early lunar differentiation basin impacts into this region do not excavate significantly more mafic material suggesting a thickness of tens of kilometers of anorthositic crust the feldspathic lunar meteorites may represent samples from the anorthositic central region of the fht ejecta from deep penetrating basin impacts outside of the central anorthositic region however indicate an increasingly mafic composition with depth the spat a mafic anomaly of great magnitude may include material of the upper mantle as well as lower crust thus it is designated a separate terrane whether the spa basin impact simply uncovered lower crust such as we infer for the fht remains to be determined

tectonics and crustal structures related to bhuj earthquake of january 26 2001 based on gravity and magnetic surveys constrained from seismic and seismological studies abstract gravity and magnetic data of the kachchh basin and surrounding regions have delineated major e w and nw se oriented lineaments and faults which are even extending up to plate boundaries in the north arabian sea and western boundary of the indian plate respectively the epicentral zone of bhuj earthquake and its aftershocks is located over the junction of rann of kachchh and median uplifts viz kachchh mainland and wagad uplifts which are separated by thrust faults gravity data with constraints from the results of the seismic studies along a profile suggest that the basement is uplifted towards the north along thrust faults dipping 40 60 south similarly gravity and magnetic modeling along a profile across wagad uplift suggest south dipping 50 60 basement contacts separating rocks of high susceptibility and density towards the north one of these contacts coincides with the fault plane of the bhuj earthquake as inferred from seismological studies and its projection on the surface coincides with the e w oriented north wagad thrust fault a circular gravity high in contact with the fault in northern part of the wagad uplift along with high amplitude magnetic anomaly suggests plug type mafic intrusive in this region several such gravity anomalies are observed over the island belt in the rann of kachchh indicating their association with mafic intrusions the contact of these intrusives with the country rock demarcates shallow crustal inhomogeneities which provides excellent sites for the accumulation of regional stress a regional gravity anomaly map based on the concept of isostasy presents two centers of gravity lows of 11 to 13 mgal 10 5 m s2 representing mass deficiency in the epicentral region their best fit model constrained from the receiver function analysis and seismic refraction studies suggest crustal root of 7 8 km deep crustal inhomogeneity under them for a standard density contrast of 400 kg m3 it is therefore suggested that significant amount of stress get concentrated in this region due to a buoyant crustal root b regional stress due to plate tectonic forces and c mafic intrusives as stress concentrators and the same might be responsible for the frequent and large magnitude earthquakes in this region including the bhuj earthquake of january 26 2001

observation and inversion of surface wave group velocities across central india abstract surface wave group velocities across central india are measured from computer plots of frequency time analysis using multiple filter technique periods range from 5 to 56 sec for fundamental mode rayleigh wave 5 to 16 sec for first higher mode rayleigh wave and 5 to 49 sec for fundamental mode love wave the wave paths from koyna earthquakes to bokaro cross purely through the peninsular plateau the group velocities for these paths are found to be similar to those of surface waves recorded at poona from earthquake which lie to the northeast of bokaro in sub himalayan regions from this it is concluded that the shield structure of the peninsula extends to the sub himalayan regions to northeast of the peninsular plateu with a negligible part of sedimentary layer group velocities of fundamental mode rayleigh and love waves are also obtained for the paths from koyna earthquakes to shillong and are found to be similar to the above mentioned group velocities except at very low periods where group velocities are affected by the small part of each path through thick sedimentary layer of bengal basin northern limit of this basin sedimentary layer has been identified mean and standard deviation of observed group velocity at each period are obtained for each of rayleigh fundamental rayleigh first higher and love fundamental modes the group velocities closely agree with those obtained earlier for the path between new delhi and kodaikanal and are also found to be similar to those observed in some shield regions monte carlo inversion method is applied and crust and upper mantle structure of the indian shield across central india is obtained crustal structure obtained shows a marked resemblance to the results obtained earlier through body wave study

structure and cenozoic kinematics of the eastern cordillera southern bolivia 21 s 1 the eastern cordillera is a main morphotectonic unit of the central andes in southern bolivia it is predominantly composed of ordovician sedimentary rocks as thick as 10 km revision of the ordovician stratigraphy and new structural fieldwork resulted in detailed balanced cross sections improved estimates of crustal shortening and a new kinematic model for the eastern cordillera new estimates of total shortening in the eastern cordillera are up to 95 km 41 44 higher than previous estimates and sufficient to thicken the andean crust to its present state between the eastern foreland and the magmatic arc after initial tertiary uplift at 58 ma first thrusts developed in the middle eocene to early oligocene 40 30 ma exhuming the central part of the eastern cordillera tectonic shortening culminated in late oligocene and early miocene time 25 20 ma when west facing thrust systems developed in the central and western part of the eastern cordillera thrusting terminated in the western part by the end of the early miocene and middle miocene tectonic activity was restricted to minor strike slip faulting in the central part thrusting remained active until the late miocene by 10 ma shortening in the eastern cordillera essentially ceased kinematic fault analyses indicate clockwise rotation of the shortening direction from nne ssw or ne sw in eocene early oligocene time over e w to wnw ese or even nw se in late oligocene to middle miocene time nevertheless wnw ese directed shortening and subvertical extension predominate sinistral oblique motion on many thrusts probably reflects plan view flexural slip in the clockwise rotating southern limb of the bolivian orocline it is proposed that space problems in the oroclinal hinge slowed the rotation there and caused decoupling of the still rotating south limb along ne trending transfer zones

high resolution measurements of absolute thorium abundances on the lunar surface the lunar prospector lp gamma ray spectrometer grs has been used to map the global abundance of thorium on the lunar surface a global map of absolute thorium abundances on a 2 by 2 equal area pixel scale is presented using new detector modeling results and low altitude lp data because thorium is relatively abundant in kreep rich material these data provide fundamental information regarding the locations and importance of terranes that are rich in kreep bearing materials

the case for an imbrium origin of the apollo thorium rich impact melt breccias abstract mafic th rich impact melt breccias most of which are identified with the composition known as low k fra mauro lkfm are the most common rock type in the nonmare regoliths of the apollo lunar landing sites the origin of mafic impact melt breccias bears on many lunar problems the nature of the late meteoroid bombardment cataclysm the spatial distribution of kreep both near the surface and at depth the ages of the major basins and the composition of the early crust of the nearside lunar highlands thus it is crucial that the origin of mafic impact melt breccias be accurately understood because of both intra and intersite differences in compositions of mafic impact melt breccia samples apparent differences in crystallization age and differences in siderophile element ratios previous studies have argued that either 1 most mafic impact melt breccias are the products of several large craters local to the site at which they were found but that some are of basin origin or that 2 they are all from the imbrium apollos 14 and 15 nectaris apollo 16 and serenitatis apollo 17 basins here we reconsider the hypothesis that virtually all of the th rich mafic impact melt breccias from the apollo missions are products of the imbrium impact ejecta deposit modeling based on modern crater scaling indicates that the imbrium event produced ejecta deposits that average hundreds of meters thick or more at all apollo highland sites which is thicker than some previous estimates substantial amounts of imbrium ejecta should have been sampled at every apollo highland site we suggest that the mafic impact melt breccias may be the principal form of those ejecta the imbrium projectile impacted into th rich material that we regard as part of a unique mafic lunar geochemical province we call the high th oval region based on the surface distribution of th only basins within the high th oval region excavated th rich material the th concentrations of the highlands as observed by the apollo orbiting ray experiments are consistent with the estimates from ejecta modeling of the younger basin forming impacts only imbrium was large enough to produce the copious amount of melt required by the ubiquitous presence of mafic impact melt breccias in the apollo sampled regolith the high th oval region still may have been molten or hot at shallow depths 4 ga ago when the imbrium projectile struck we reason that compositional heterogeneity of ejected melt breccia is to be expected under these circumstances we argue that siderophile element fingerprints of mafic impact melt breccias are not inconsistent with production of all common types by a single projectile we suggest that the narrow range of ages of 3 7 4 0 ga for all successfully dated mafic impact melt breccias may reflect a single event whose age is difficult to measure precisely rather than a number of discrete impact events closely spaced in time such that reported age variations among mafic impact melt breccias reflect the ability to measure 40ar 39ar ages with greater precision than the accuracy with which measured portions of mafic impact melt breccias have recorded the time of their formation

a continent wide map of 1 hz lg coda q variation across eurasia and its relation to lithospheric evolution 1 we present new maps of lg coda q qo and its frequency dependence at 1 hz that cover virtually all of eurasia qo is relatively high up to 650 or more in the east european siberian indian and kazakh platforms but is surprisingly low 300 500 in the arabian platform and western portion of the siberian platform as well as in great britain and the northwestern portion of mainland europe it is generally low throughout the tethysides orogenic belt but there too it displays substantial regional variations 150 400 most qo anomalies appear to be related to the tectonic history of the eurasian crust the four regions with lowest values coincide with four of eurasia s most active concentrations of earthquake activity observed eurasian qo values are consistent with a previously determined empirical plot of global values in which qo in any region is proportional to the time elapsed since the most recent episode of tectonic or orogenic activity there comparisons of the new qo map with maps of rayleigh wave velocity temperature subducted lithosphere and seismicity lead us to infer that lg coda wave attenuation is most easily explained by energy lost in moving fluids through permeable rock or in being scattered from fluid enhanced zones the fluids are likely to have originated by hydrothermal release from subducting lithosphere or other upper mantle heat sources anomalies in qo and other lithospheric properties in some cases extend well outside the tethysides belt and other regions where upper mantle heat sources are known to occur possible explanations include earlier episodes of subduction activity crustal deformation due to collision of the afro arabian and indian plates or broader than expected back arc activity beneath eurasia

concentrations of radioactive elements in lunar materials as an aid to interpreting data obtained remotely on the distribution of radioactive elements on the lunar surface average concentrations of k u and th as well as al fe and ti in different types of lunar rocks and soils are tabulated the u th ratio in representative samples of lunar rocks and regolith is constant at 0 27 k th ratios are more variable because k and th are carried by different mineral phases in nonmare regoliths at the apollo sites the main carriers of radioactive elements are mafic i e 6 8 fe impact melt breccias created at the time of basin formation and products derived therefrom

mantle derived spinel lherzolite xenoliths from the deccan volcanic province india implications for the thermal structure of the lithosphere underlying the deccan traps abstract petrography mineral and host rock chemistry of the mantle derived spinel lherzolite xenoliths in the nephelinites of kutch a late variant of the deccan traps province india are reported the xenoliths register equilibration temperatures between 920 70 c and 1060 50 c and an ascent time between 19 and 168 days representing a palaeogeotherm of minimum heat flow between 60 and 70 mw m 2 the xenoliths possibly came from the oceanic lithosphere under the deccan field following the cretaceous eocene fragmentation of gondwanaland

group velocity dispersion characteristics and one dimensional regional shear velocity structure of the eastern indian craton abstract in the past three years a semi permanent network of fifteen 3 component broadband seismographs has become operational in the eastern indian shield region occupying the archean 2 5 3 6 ga singhbhum odisha craton soc and the proterozoic 1 0 2 5 ga chotanagpur granitic gneissic terrane cggt the reliable and accurate broadband data for the recent 2015 nepal earthquake sequence from 10 broadband stations of this network enabled us to estimate the group velocity dispersion characteristics and one dimensional regional shear velocity structure of the region first we measure fundamental mode rayleigh and love wave group velocity dispersion curves in the period range of 7 70 s and then invert these curves to estimate the crustal and upper mantle structure below the eastern indian craton eic we observe that group velocities of rayleigh and love waves in soc are relatively high in comparison to those of cggt this could be attributed to a relatively mafic rich crust mantle structure in soc resulting from two episodes of magmatism associated with the 1 6 ga dalma and 117 ma rajmahal volcanisms the best model for the eic from the present study is found to be a two layered crust with a 14 km thick upper crust uc of average shear velocity vs of 3 0 km s and a 26 km thick lower crust lc of average vs of 3 6 km s the present study detects a sharp drop in vs 2 to 3 at 120 260 km depths underlying the eic representing the probable seismic lithosphere asthenosphere boundary lab at 120 km depth such sharp fall in vs below the lab indicates a partially molten layer further a geothermal gradient extrapolated from the surface heat flow shows that such a gradient would intercept the wet basalt solidus at 88 103 km depths suggesting a 88 103 km thick thermal lithosphere below the eic this could also signal the presence of small amounts of partial melts thus this 2 3 drop in vs could be attributed to the presence of partial melts in the upper mantle related to the earlier volcanic episodes viz back arc volcanism associated with the archean proterozoic subduction 1 6 ga dalma volcanism and 117 ma rajmahal volcanism the main result of our modeling provides evidences for the absence of keel or thick lithosphere below the eic

apollo 14 mare basalts petrology and geochemistry of clasts from consortium breccia 14321 eleven mare basalt clasts have been extracted from polymict lunar breccia 14321 for a combined petrologic and geochemical study by our consortium ten of these clasts are high al low ti mare basalts similar to those discovered previously at apollo 14 the other is a highly evolved tridymite ferrobasalt with low al and intermediate ti contents a high al ilmenite ferrobasalt from lunar breccia 14305 is the most evolved high al basalt described from the apollo 14 site the major and trace element characteristics of the basalts studied here allow them to be grouped into five compositional types that range from lree depleted to lree enriched some of these types may be related by varying percents of partial melting of the same source but at least two separate sources that differ by a factor of two in incompatible trace element concentrations are required the 14321 type basalts and vitrophyres have steep chondritenormalized hree slopes and may have formed by assimilation of intermediate k fra mauro kreep which is presumed to represent a partial melt of the lower crust the age of these basalts 3 9 aeons suggests that mare volcanism played an important role in the evolution of the early lunar crust

geochemistry petrology and cooling history of 14161 7373 a plutonic lunar sample with textural evidence of granitic fraction separation by silicate liquid immiscibility we report new findings related to sample 14161 7373 the first analyzed lunar intrusive rock to show textural evidence for the formation of granitic material by silicate liquid immiscibility sli and geochemical evidence for separation of that material at least on a small scale from mafic residua ion microprobe analyses of rare earth element ree concentrations in silicates record the compositional evolution of this late stage assemblage for a sample whose bulk assemblage that of whitlockite monzogabbro has ree concentrations at 5 6 kreep levels the silicates have only moderately high ree concentrations the calculated ree concentrations of melt in equilibrium with pigeonite after re integration of pigeonite host and augite lamellae is approximately 2 high k kreep the high bulk ree concentrations of the assemblage are the result of a high proportion of whitlockite probably an excess i e the assemblage is a whitlockite cumulate variations in silicate ree concentrations reflect the co crystallization of whitlockite which we interpret to have begun crystallizing prior to the onset of late stage immiscibility of the felsic melt fraction calculated cooling rates based on a quantitative model of pyroxene exsolution reveal a two stage thermal history which involved initial crystallization at a minimum depth of 700 800 m during which the primary augite and pigeonite grains unmixed to form the observed host lamella pairs unusual compositional profiles close to the host lamella interface are consistent with a second stage of mild reheating followed by rapid cooling at a depth of 30 m most likely in an ejecta blanket the shallow depth of origin indicated for 14161 7373 is consistent with other studies of evolved lunar intrusive rocks supporting the interpretation that lunar qmd and granite as found among the apollo samples are late stage differentiates of high level intrusions and are not related to differentiation of deep crustal kreep reservoirs

lunar surface geochemistry global concentrations of th k and feo as derived from lunar prospector and clementine data abstract accurate estimates of global concentrations of th k and feo have an important bearing on understanding the bulk chemistry and geologic evolution of the moon we present empirical ground truth calibrations transformations for lunar prospector gamma ray spectrometer data k and th and a modified algorithm for deriving feo concentrations from clementine spectral reflectance data that incorporates an adjustment for tio 2 content the average composition of soil samples for individual landing sites is used as ground truth for remotely sensed data among the apollo and luna sites apollo 12 and 14 provide controls for the incompatible element rich compositions apollo 16 and luna 20 provide controls for the feldspathic and incompatible element poor compositions and apollo 11 15 and 17 and luna 16 and 24 provide controls for fe rich compositions in addition to these apollo and luna sample data we include the composition of the feldspathic lunar meteorites as a proxy for the northern farside highlands to extend the range of the calibration points thus providing an additional anorthositic end member composition these empirical ground truth calibrations for lunar prospector th and k provide self consistency between the existing derived data and lunar sample data clementine spectral reflectance data are used to construct a tio 2 sensitive feo calibration that yields higher feo concentrations in areas of high fe low ti mare basalt rich surfaces than previous feo algorithms the data set so derived is consistent with known sample compositions and regolith mixing relationships

global distribution of lunar composition new results from lunar prospector 1 maps of thorium th feo the ratio of epithermal to thermal neutrons e t and fast neutrons fn from lunar prospector were studied to determine their global distribution on the moon these distributions are compared to that of the 750 nm lunar albedo from clementine to aid in their interpretation all distributions were parameterized using a spherical harmonic expansion out to order l 30 resultant harmonic coefficients generally decrease with increasing l value as a power law in l for all five variables the axes of all dipole components l 1 cluster closely about a centroid given by 14 1 latitude and 16 4 west longitude this location is very close to the symmetry axes of their quadrupole components l 2 which cluster about a centroid given by 24 6 latitude and 25 1 west longitude both centroids are near the center of a suggested procellarum basin given by whitaker 1981 at 23 latitude and 15 west longitude this suggestion is strengthened by a sharp decrease of the intensities of all three variables at 50 from the centroids which is close to the boundary of the putative procellarum basin the coincidence of the global concentration of heat producing elements through th and mare deposits on the lunar surface through feo t e and fn with the circular outline of a putative procellarum basin suggests that the events that were responsible for producing oceanus procellarum perhaps a single giant impact must figure importantly in shaping the global distribution of surface composition a second apparently older circular structure having its center near 5 latitude and 65 east longitude and a radius of 50 is also hinted at in the data

the apollo 15 yellow impact glasses chemistry petrology and exotic origin the apollo 15 yellow impact glasses are characterized by moderate tio2 4 8 and high abundances of the large ion lithophile elements e g k p hf th ree since the chemistry of these glasses cannot be duplicated by any combination of local components presently known to occur at the apollo 15 landing site these yellow glasses seem to be exotic to that area chemical and petrologic constraints suggest that these samples were produced by impact melting of an immature mare regolith developed upon an unusual variety of mare basalt we speculate that the target basalts were the youngest lava flows known to exist on the moon i e eratosthenian age lavas in oceanus procellarum and mare imbrium specific tests are proposed for evaluating this provocative hypothesis

thermal models of the middle america trench at the nicoya peninsula costa rica 1 we present thermal models of the 24 ma cocos plate subducting under the caribbean plate at the nicoya peninsula costa rica our modeling incorporates the effect of hydrothermal cooling of the seafloor and the absence of an accretionary prism initial geotherms of the incoming plate representing different effective cooling depths of hydrothermal circulation affect the thermal structure and temperatures along the main subduction thrust excluding the deforming prism results in a higher heat flow immediately landward of the trench than previous models and therefore significant frictional heating is not required conductive plate cooling over predicts heat flow across the frontal forearc with no or very low frictional heating models with hydrothermal cooling to depths of 2 km under predicts the heat flow comparisons with recently determined hypocenter locations indicate that the updip limit of seismicity is consistent with temperatures between 100 150 c but there are large along strike variations in both the seismicity and thermal regime

were the deccan flood basalts derived in part from ancient oceanic crust within the indian continental lithosphere abstract deep mantle plumes supposedly incorporate deeply subducted eclogitized oceanic crust and continental flood basalts cfbs are now thought by some to be derived from such eclogite bearing peridotite plumes eclogite peridotite mixtures have much lower solidi and produce much greater melt fractions for a given temperature than peridotite fe rich eclogite or pyroxenite bearing sources have been inferred for many cfbs however plumes with considerable amounts of eclogite should have difficulty in upwelling owing to the high density of eclogite besides cfbs are always located along pre existing lithospheric structures suture zones edges of thick cratons and commonly associated with lithospheric rifting and continental breakup india s major late mesozoic cfb the deccan traps erupted through rift zones and a new continental margin that had developed along ancient suture zones traversing the subcontinent many deccan basalts are too fe rich to have been in equilibrium with a peridotite mantle source and have commonly been considered to be significantly fractionated derivatives of picritic liquids however it is possible to view them as relatively less evolved liquids derived from a source with extra fertility i e an fe rich source a new non plume plate tectonic model for icelandic hotspot volcanism involves melting of a shallowly recycled slab of eclogitized iapetus oceanic crust formerly trapped along the caledonian suture the model explains the geochemical petrological characteristics of icelandic basalts and is consistent with passive upper mantle upwelling under iceland inferred from recent seismic tomography based on the petrological and geochemical features of the deccan flood basalts of the type section in the western ghats i propose that old eclogitized oceanic crust trapped in the ancient indian suture zones could have produced voluminous basaltic melts during the deccan event

the titanium contents of lunar mare basalts lunar mare basalt sample data suggest that there is a bimodal distribution of tio2 concentrations using a refined technique for remote determination of tio2 we find that the maria actually vary continuously from low to high values the reason for the discrepancy is that the nine lunar sample return missions were not situated near intermediate basalt regions moreover maria with 2 4 wt tio2 are most abundant and abundance decreases with increasing tio2 maria surfaces with tio2 5 wt constitute only 20 of the maria although impact mixing of basalts with differing ti concentrations may smear out the distribution and decrease the abundance of high ti basalts the distribution of basalt ti contents probably reflects both the relative abundances of ilmenite free and ilmenite bearing mantle sources this distribution is consistent with models of the formation of mare source regions as cumulates from the lunar magma ocean

exhumation history of the southern altiplano plateau southern bolivia constrained by apatite fission track thermochronology 1 although the structural geometry of the cenozoic altiplano puna plateau in the central andes is well defined the temporal evolution of this contractile deformation is poorly constrained to address this shortcoming we used apatite fission track thermochronology aft to quantify the cooling and exhumation history along a transect at 21 s in southern bolivia through the deformed intermontane altiplano basin the doubly vergent thrust belt of the eastern cordillera and the inner foreland thrust belt east of the plateau interandean zone thermal history modeling combined with published balanced cross sections and stratigraphic data constrain exhumation histories exhumation started during the late eocene 40 36 ma in the central eastern cordillera possibly due to bivergent thrusting and cretaceous rift structure inversion during the early oligocene 33 27 ma exhumation spread across the study area as the current boundary thrusts of the eastern cordillera were activated the inner west vergent thrust system became active in irregular order until circa 20 ma whereas the east vergent interandean thrust belt formed by eastward propagating deformation since circa 30 ma plateau exhumation continued at 0 2 mm yr until shortening terminated by 11 7 ma shortening within the plateau since circa 30 ma did not evolve by lateral accretion of thrust wedges the propagating deformation style is spatially confined to the foreland thrust belt which initiated coeval to plateau deformation interandean zone but propagated mainly after circa 10 ma subandean zone early oligocene plateau wide tectonically driven exhumation suggests that subduction related processes had already thermally weakened the continental lithosphere prior to the 27 25 ma onset of volcanic activity

crustal and lithospheric thinning beneath the seismogenic kachchh rift zone gujarat india its implications toward the generation of the 2001 bhuj earthquake sequence a high resolution passive seismic experiment in the kachchh rift zone of the western india has produced an excellent dataset of several thousands teleseismic events from this network 500 good teleseismic events recorded at 14 mobile broadband sites are used to estimate receiver functions for the 30 310 back azimuth ranges which show a positive phase at 4 5 6 1 s delay time and a strong negative phase at 8 0 11 0 s these phases have been modeled by a velocity increase at moho i e 34 43 km and a velocity decrease at 62 92 km depth the estimation of crustal and lithospheric thicknesses using the inversion of stacked radial receiver functions led to the delineation of a marked thinning of 3 7 km in crustal thickness and 6 14 km in lithospheric thickness beneath the central rift zone relative to the surrounding un rifted parts of the kachchh rift zone on an average the kachchh region is characterized by a thin lithosphere of 75 9 5 9 km the marked velocity decrease associated with the lithosphere asthenoshere boundary lab observed over an area of 120 km 80 km and the isotropic study of xenoliths from kachchh provides evidence for local asthenospheric updoming with pockets of partial melts of co2 rich lherzolite beneath the kachchh seismic zone that might have caused by rifting episode at 88 ma and the associated deccan thermal plume interaction at 65 ma episodes thus the coincidence of the area of the major aftershock activity and the moho as well as asthenospheric upwarping beneath the central kachchh rift zone suggests that these pockets of co2 rich lherzolite partial melts could perhaps provide a high input of volatiles containing co2 into the lower crust which might contribute significantly in the seismo genesis of continued aftershock activity in the region it is also inferred that large stresses in the denser and stronger lower crust at 14 34 km depths induced by ongoing banni upliftment crustal intrusive marked lateral variation in crustal thickness and related sub crustal thermal anomaly play a key role in nucleating the lower crustal earthquakes beneath the kachchh seismic zone

mapping the feo and tio2 content of the lunar surface with multispectral imagery the derivation of quantitative elemental concentrations from multispectral imaging of the moon has long been a goal of lunar remote sensing concentration maps at the spatial resolutions available from the recent clementine mission would provide a revolutionary new tool for understanding the origin and evolution of the lunar crust lucey et al 1995 presented a method for extracting the concentration of fe from multispectral imaging of the moon this paper examines and quantifies important aspects ofthat technique left unexamined by lucey et al which had the potential to severely limit its utility these aspects include the effects of maturity grain size mineralogy shading due to topography and the presence of glass we also present a new algorithm for derivation of tio2 from multispectral imaging of both mare and highland units we find that both techniques are only weakly sensitive to maturity and that they have about 1 wt accuracy based on examination of the spectral properties and compositions of resolved lunar sampling stations presented by blewett et al 1997 we also discuss these findings in the context of two contrasting views of the effect of composition on lunar spectral properties presented by pieters and coworkers and hapke and coworkers we find the view of hapke and coworkers to be more consistent with our observations using a global mosaic of clementine multispectral data and these element derivation algorithms we find that the global modal abundance of feo is 4 5 wt 1 wt and the global modal abundance of tio2 is 0 45 wt 1 wt

global elemental maps of the moon the lunar prospector gamma ray spectrometer lunar prospector gamma ray spectrometer spectra along with counting rate maps of thorium potassium and iron delineate large compositional variations over the lunar surface thorium and potassium are highly concentrated in and around the nearside western maria and less so in the south pole aitken basin counting rate maps of iron gamma rays show a surface iron distribution that is in general agreement with other measurements from clementine and the lunar prospector neutron detectors

peculiarities of surface wave propagation across central eurasia abstract the recent installation of six broadband digital iris ida seismic stations in the ussr has provided new opportunities for studying surface wave propagation across eurasia group velocities of fundamental rayleigh and love modes between epicenters and these stations were determined for 35 events that occurred since april 1989 to the middle of july 1990 near eurasia differential phase velocities were found for the same arrivals along paths between several pairs of stations group and phase velocities were obtained in the period range from 15 to 300 sec frequency time polarization analysis was used for studying polarization properties of surface waves in some cases significant anomalies in the particle motion for periods up to 100 sec were observed they are attributed to surface wave refraction and scattering due to lateral inhomogeneities at the boundaries and inside the eurasia continent

geochronology and petrogenesis of apollo 14 very high potassium mare basalts rb sr k ar and sm nd isotopic studies were undertaken for two apollo 14 very high potassium vhk mare basaltic clasts from breccias 14305 and 14168 the samples are distinctly more radiogenic than other lunar mare basalts rb sr data for the whole rock and mineral separates determine internal isochrons corresponding to essentially identical ages of 3 83 0 08 b y and 3 82 0 12 b y for samples 14305 and 14168 respectively for 87rb 0 0139 b y 1 their corresponding initial 87sr 86sr ratios are indistinguishable and are 0 6995 0 0005 and 0 6997 0 0004 respectively the 39ar 40ar age spectra for the two samples are very similar and give identical plateau ages of 3 85 0 02 b y for 14305 and 3 85 0 05 b y for 14168 the identical rb sr and k ar isotopic results for the two rocks indicate that they could be derived from the same flow the sm nd isotopic data of whole rock and mineral separates for the two vhk basalts define an internal isochron age of 3 94 0 16 b y for 147sm 0 00654 b y 1 and an initial 143nd 144nd of 0 50673 21 the averaged model age relative to the chondritic initial 143nd 144nd of 0 505893 for the basalts is 4 56 0 04 b y the concordance of rb sr k ar and sm nd ages strongly suggests that vhk basalts crystallized from a melt 3 85 b y ago the rb sr and sm nd isotopic data indicate that vhk basalts show very large rb sr fractionation but no significant sm nd fractionation at the time of crystallization the source material for these basalts had a rb sr ratio similar to those of apollo 14 high a1 mare basalts and a nearly chondritic sm nd ratio extreme enrichments of rb sr and k la during the formation of vhk basalts can be adequately explained by an assimilation model that involves basalt granite interaction k rb rich components of granitic wall rocks in highland crust were selectively introduced into ascending hot high a1 mare basaltic magma upon contact a similar crustal assimilation process has been frequently observed in terrestrial mantle derived magma that ascended through the continental crust

mixing levels the apennine front soil component and compositional trends in the apollo 15 soils variations in concentrations of lithophile elements in samples of apollo 15 soil can be explained in terms of only four chemical components three components are represented by extrusive rock types found at the apollo 15 site mare basalt kreep basalt and the pyroclastic green glass associated with breccia 15426 the fourth component the highlands component can be represented by soil from the apennine front particularly the soil obtained from the 55 57 cm depth interval of station 2 core 15007 8 among samples of apennine front soil this one appears to be the least contaminated by mare materials and may be our most typical sample of the apennine front highlands although soil fron the apennine front is itself a complex mixture of many types of highlands rocks it behaves as a single component with respect to mixing with the other three rock type components the various subcomponents of the apennine front soil e g melt rock and anorthositic norite that have been used in some mixing models are not required as discrete components in order to explain the compositional variation among samples of apollo 15 soil most of this compositional variation results from mare highlands mixing i e apennine front soil with mare basalt kreep basalt which probably derives from local possibly unexposed sources is also a variable component of the soil and is most prevalent in the soil from stations lm 6 and 9

lithospheric mantle deformation beneath the indian cratons abstract the nature of deformation of the deep continental roots beneath the archean early proterozoic terrains opens the question whether these ancient terrains have had stable roots since the precambrian or whether recent plate motions have deformed them in view of this we make an attempt to study the thermal structure beneath the cratonic regions of the indian shield which vary in lithospheric thickness from 65 km in the singhbhum craton to 148 km in the archean dharwars the average depth of 104 km to the top of the underlying asthenosphere is consistent with other termination methods and is in fact less than half the 200 400 km depth found in other stable areas of the earth similarly the average reduced heat flow of about 35 mw m2 and moho temperature of about 550 c range 400 730 c for the indian cratons are also much higher than their counterparts elsewhere our study indicates a large scale deformation of the cratonic mantle lithosphere beneath the indian shield since the mesoproterozoic c

sediment accumulation on top of the andean orogenic wedge oligocene to late miocene basins of the eastern cordillera southern bolivia a large volume of tertiary synorogenic sediment accumulated on top of the eastern cordillera of southern bolivia as the andean orogenic wedge was shortened thickened and uplifted oligocene to upper miocene strata were deposited in five basins that were separated by active north trending fold thrust structures of the then frontal part of the orogenic wedge these coarse grained deposits recorded accumulation in the most proximal sector of the andean foreland basin system the wedge top depozone analyses of depositional systems sediment dispersal patterns and clast provenance of 0 6 2 3 km thick oligocene to upper miocene wedge top successions demonstrate that faultpropagation and fault bend folds commonly isolated individual basins while serving as primary sediment sources growth strata which formed by progressive fold limb rotation indicate thrust fault displacement and related folding concurrent with deposition alluvial fans defined most basin margins whereas braided streams or small lakes occupied basin axes diagnostic stratigraphic units confined to individual basins suggest that streams were rarely able to cut across growing folds to connect adjacent basins growth strata and crosscutting and onlapping relationships between contractional structures and wedge top strata delineate the chronology of fold thrust deformation in the eastern cordillera five new 40 ar 39 ar dates and previously published k ar dates ranging from 30 to 8 ma define an oligocene phase of west vergent backthrusting followed by primarily east vergent thrusting during miocene time timing of displacement on two east vergent thrusts is determined by 40 ar 39 ar ages of tuffs within adjacent growth strata sequences of the tupiza formation conglomerate 16 14 0 06 ma and oploca formation 13 33 0 15 ma 15 7 2 4 ma these ages combined with basin depositional histories demonstrate synchronous and out of sequence thrust displacement during miocene shortening upper crustal contractional deformation and wedge top deposition terminated in the eastern cordillera during late miocene time as the thrust front propagated eastward into the subandean zone continued thrust front migration produced the present day configuration in which eastern cordillera wedge top basins originally developed above the toe of the orogenic wedge at relatively low elevations are now 250 km west of the active thrust front and at 3 km elevation the modern wedge top depozone overlies the active frontal part of the orogenic wedge and consists of strata in thrustbounded subandean zone basins and sediment overlying blind structures beneath the westernmost chaco plain in general wedge top deposits become highly susceptible to erosional recycling as the orogenic wedge propagates forward and the wedge surface is uplifted nevertheless eastern cordillera wedge top deposits have been preserved for 10 30 m y in southern bolivia such long term preservation may reflect the inability of drainage systems to remove sediment mass from this low precipitation region of the central andes retention of sediment mass within the orogenic belt may promote critical thrust wedge conditions in which propagation of the thrust front is favored

late permian middle jurassic lithospheric thinning in peru and bolivia and its bearing on andean age tectonics abstract integrated studies and revisions of sedimentary basins and associated magmatism in peru and bolivia 8 22 s show that this part of western gondwana underwent rifting during the late permian middle jurassic interval rifting started in central peru in the late permian and propagated southwards into bolivia until the liassic dogger along an axis that coincides with the present eastern cordillera southwest of this region lithospheric thinning developed in the early jurassic and culminated in the middle jurassic producing considerable subsidence in the arequipa basin of southern peru this 110 ma long interval of lithospheric thinning ended 160 ma with the onset of malm earliest cretaceous partial rift inversion in the eastern cordillera area the lithospheric heterogeneities inherited from these processes are likely to have largely influenced the distribution and features of younger compressional and or transpressional deformations in particular the altiplano plateau corresponds to a paleotectonic domain of normal lithospheric thickness that was bounded by two elongated areas underlain by thinned lithosphere the high eastern cordillera of peru and bolivia results from late oligocene neogene intense inversion of the easternmost thinned area

the procellarum kreep terrane implications for mare volcanism and lunar evolution geophysical remote sensing and sample data demonstrate that the procellarum and imbrium regions of the moon make up a unique geochemical crustal province here dubbed the procellarum kreep terrane geochemical studies of imbrium s ejecta and the crustal structure of the imbrium and serenitatis basins both suggest that a large portion of the lunar crust in this locale is composed of a material similar in composition to apollo 15 kreep basalt kreep basalt has about 300 times more uranium and thorium than chondrites so this implies that a large portion of moon s heat producing elements is located within this single crustal province the spatial distribution of mare volcanism closely parallels the confines of the procellarum kreep terrane and this suggests a causal relationship between the two phenomena we have modeled the moon s thermal evolution using a simple thermal conduction model and show that as a result of the high abundance of heat producing elements that are found in the procellarum kreep terrane partial melting of the underlying mantle is an inevitable outcome specifically by placing a 10 km kreep basalt layer at the base of the crust there our model predicts that mare volcanism should span most of the moon s history and that the depth of melting should increase with time to a maximum depth of about 600 km we suggest that the 500 km seismic discontinuity that is observed in the apollo seismic data may represent this maximum depth of melting our model also predicts that the kreep basalt layer should remain partially molten for a few billion years thus the imbrium impact event most likely excavated into a partially molten kreep basalt magma chamber we postulate that the kreep basalt composition is a by product of mixing urkreep with shallow partial melts of the underlying mantle since mg suite rocks are likely derived from crystallizing kreep basalt the provenance of these plutonic rocks is likely to be unique to this region of the moon

crater ejecta scaling laws fundamental forms based on dimensional analysis a model of crater ejecta is constructed using dimensional analysis and a recently developed theory of energy and momentum coupling in cratering events general relations are derived that provide a rationale for scaling laboratory measurements of ejecta to larger events specific expressions are presented for ejection velocities and ejecta blanket profiles in two limiting regimes of crater formation the so called gravity and strength regimes in the gravity regime ejecta velocities at geometrically similar launch points within craters vary as the square root of the product of crater radius and gravity this relation implies geometric similarity of ejecta blankets that is the thickness of an ejecta blanket as a function of distance from the crater center is the same for all sizes of craters if the thickness and range are expressed in terms of crater radii in the strength regime ejecta velocities are independent of crater size consequently ejecta blankets are not geometrically similar in this regime for points away from the crater rim the expressions for ejecta velocities and thickness take the form of power laws the exponents in these power laws are functions of an exponent that appears in crater radius scaling relations thus experimental studies of the dependence of crater radius on impact conditions determine scaling relations for ejecta predicted ejection velocities and ejecta blanket profiles based on measured values of are compared to existing measurements of velocities and debris profiles

very high potassium vhk basalt complications in mare basalt petrogenesis apollo 14 vhk very high potassium basalt is a newly discovered variety of low ti high al mare basalt characterized by unusually high concentrations of k rb and ba and high ratios of these elements to other incompatible elements that exceed normal lunar values potassium feldspar and k si rich glass are ubiquitous and widespread components of these basalts other phases include magnesian olivine fo 60 73 fe rich olivine fo 31 50 pigeonite plagioclase an 79 95 ilmenite cr ulv spinel fe metal and troilite vhk basalts have low initial 87sr 86sr ratios with rb sr ratios estimated to be 15 higher than their source this rb sr fractionation occurred at their time of formation 3 75 aeons hypotheses involving volatile nonvolatile fractionations or long term enrichment of the source regions in k are inconsistent with the high ba la ratios and low initial 87sr 86sr ratios of vhk basalt the most plausible origin for these rocks is partial assimilation of lunar granite by a normal low ti high al mare basalt assimilation occurs by diffusion controlled exchange of alkalis and ba between two melts trace element compositions of the granitic melt are controlled in part by refractory accessory phases in the granite significant geochemical interaction between the lunar crust and mare basalts is implied

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

surface heat flow and probable evolution of deccan volcanism abstract in the light of surface heat flow observations as well as other related geological and geophysical data the origin of the deccan basalts has been examined the indian lithosphere after its detachment from gondwanaland apparently traversed a rising plume at la reunion which virtually bored through the lithosphere to emerge as the deccan trap volcanism on the surface subsequent volcanic and plutonic activity appears to have continued not only up to the oligocene as is indicated by the alkaline magmatic activity observed near the junction of the three prominent features the west coast faults the narmada son tapti lineament and the cambay graben but also up to the mio pliocene as indicated by the heat flow and gravity data over the cambay graben the dyke swarms and sills which are mostly post trappean evolved from the lithosphere after the indian plate moved away from the hot spot

a possible origin of intraplate earthquakes in the kachchh rift zone india since the 2001 mw7 7 bhuj earthquake abstract we herein use the joint inversion of p receiver functions and fundamental mode group velocity dispersion data 9 70 s of rayleigh and love waves to estimate crustal and lithospheric thicknesses at twenty three component mobile broadband stations in kachchh gujarat modeled moho depths range from 35 to 43 km while lithospheric thicknesses vary from 64 to 106 km the main result of our modelling is the delineation of a marked crustal 2 4 km as well as lithospheric 10 20 km thinning and a 2 6 drop in vs across the lithosphere asthenosphere boundary lab within the samkhiali graben associated with gravity high underlying the central kachchh rift zone krz where 95 of the continued aftershock activity took place since 2001 such a large drop in vs could be attributed to the presence of carbonatite melts in the upper mantle our modeling reveals a 4 km crustal thinning below the central krz and a 4 km crustal thickening below the surrounding riftless regions this kind of crustal structure is inferred to induce large flexural deviatoric stresses 50 100 mpa in the upper crust thereby these stresses in the presence of regional plate tectonic stresses can bring the samkhiali graben below the central krz near to the critical stress level while stress transfer meteoric water in the upper crust and metamorphic fluid as well volatile co2 flows in the lower crust provide the required triggering effect to the critically stressed graben structure down to 35 km depth for generating continued aftershock activity in the kachchh rift zone since 2001 we also propose that the deeper circulation of volatile co2 through the inferred conduit related to the 65 ma deccan plume activity extending from lower crust down to asthenosphere plays a key role in the generation of uninterrupted occurrence of earthquakes in the kachchh rift zone gujarat india

discussion sediment accumulation on top of the andean orogenic wedge oligocene to late miocene basins of the eastern cordillera southern boliviadiscussion in the tupiza area of southern bolivia cenozoic strata are outstandingly exposed in five north trending basins because they could yield important information on the local andean tectonic development these basins were independently studied by herail et al 1996 1 by a german group

a serenitatis origin for the imbrian grooves and south pole aitken thorium anomaly the northwest corner of the moon s south pole aitken spa basin contains a high abundance of thorium and a unique imbrian aged geomorphologic unit that consists of grooves and mounds referred to here as the imbrian grooves because the location of these features are almost antipodal to the imbrium basin where high thorium ejecta and seismic energy are expected to have converged an imbrium origin for these units has long seemed certain by modeling the deposition of impact ejecta on the moon we have investigated whether the convergence of imbrium s ejecta at its antipode could be the origin of both the imbrian grooves and spa thorium anomaly as a result of the moon s rotation our results show that ejecta from this basin should converge more than 12 west of its antipode both the imbrian grooves and thorium anomaly within spa however reside slightly to the east of imbrium s antipode in an attempt to reconcile this disparity the effects of a putative oblique imbrium impact have been qualitatively investigated while this model can distribute ejecta in the general vicinity of the imbrian grooves the planform of our modeled antipodal ejecta is distinctly different from that which is observed as an alternative explanation for the origin of these features we find that the modeled distribution of ejecta from an oblique serenitatis impact is surprisingly similar to the planform of the imbrian grooves with the exception that it is offset directly to the east this eastward offset is likely to be an artifact of our not being able to properly include the effects of the moon s rotation in our oblique impact models we conclude that the imbrium grooves and spa thorium anomaly are most consistent with having an origin from the convergence of ejecta antipodal to the serenitatis basin if this conclusion can be substantiated once quantitative ejecta scaling relations for oblique impacts are determined then this implies that 1 the serenitatis target contained a high abundance of thorium and 2 the convergence of seismic energy at the antipodes of either the imbrium or serenitatis basin was not sufficient to cause substantial surface modification extrapolating this result to mercury suggests that the hilly and lineated terrain antipodal to the caloris basin was formed by the convergence of ejecta and not seismic waves

the great lunar hot spot and the composition and origin of the apollo mafic lkfm impact melt breccias thorium rich mafic impact melt breccias from the apollo 14 17 missions that is those breccias identified with the composition known as lkfm are regarded largely as products of basin forming impacts that penetrated the feldspathic crust and sampled underlying mafic material and magma ocean residuum carrying the compositional signature of kreep potassium rare earth elements phosphorous despite considerable compositional variation among such breccias compositions of all of them correspond to mixtures of only four components 1 a norite with composition generally similar to that of apollo 15 basalt mean abundance 58 range 30 95 2 fo 90 dunite mean 13 range 1 27 3 feldspathic upper crust mean 29 range 4 50 and feni metal 0 1 1 7 petrographic evidence has shown that much of the feldspathic component but none of the kreep component is clastic this observation and the high proportion of kreep norite component in the breccias suggest that the melt zone of the impact or impacts forming the breccias contained little feldspathic material but consisted predominantly of material with the average composition of kreep norite the dunite component probably derives ultimately from the upper mantle these conclusions support the hypothesis that the breccias were not formed in typical feldspathic crust but instead by one or more impacts into what is designated here the great lunar hot spot that is the anomalous th rich terrane in the imbrium procellarum area identified by the apollo and lunar prospector gamma ray spectrometers the lkfm composition is a special product of the great lunar hot spot and is not the average composition of the lower crust in typical feldspathic highlands similarly mg suite and alkali suite plutonic rocks of the apollo collection are likely all differentiation products of the hot spot not of plutons that might occur in typical feldspathic crust

basaltic magmatism on the moon a perspective from volcanic picritic glass beads abstract it is widely accepted that basaltic magmas are products of partial fusion of periodotite within planetary mantles as such they provide valuable insights into the composition structure and processes of planetary interiors those compositions which approach primary melt compositions provide the most direct information about planetary interiors and serve as a starting point to understand basaltic evolution within the collection of lunar samples returned by the apollo and luna missions are homogeneous picritic glass beads of volcanic origin these picritic glasses are our closest approximations to primary magmas as such these glass beads provide a unique perspective concerning the origin of mare basalts the characteristics of the lunar interior and processes in the early differentiation of the moon we have obtained trace element data for these picritic glasses using sims techniques these data and literature isotopic and experimental data on the picritic glasses are placed within the framework of mare basaltic magmatism the volcanic glasses are very diverse in their trace element characteristics for example they have a wide range of ree pattern shapes and concentrations like the crystalline mare basalts all picritic glasses have a negative eu anomaly unlike the crystalline mare basalts there is little correlation between the size of the eu anomaly and overall ree concentrations trace element differences among the various glasses suggests that a kreep component was incorporated into their mantle source this implies large scale mixing of the lunar magma ocean derived cumulate pile subtle differences among glasses suggest that local mixing of sources may also have been an important process preservation of subtle chemical differences in the picritic glasses and crystalline basalts may be interpreted as indicating that they were produced by small to moderate degrees of partial melting and that the lunar mantle did not experience extensive melting during episodes of mare volcanism several lines of evidence are consistent with the view that the picritic glasses were derived from mantle sources that were compositionally distinct from the sources for crystalline mare basalts these are parallel but no common liquid lines of descent chemical differences between picritic glasses and the more primitive crystalline mare basalts experimental studies indicating that the picritic glasses are multiply saturated at depths greater than that of the mare basalts differences in lead isotopic data and the mode of eruption i e fire fountaining for glass beads these data also provide circumstantial evidence that suggests that the picritic glasses were derived from a source somewhat more volatile rich than that of the mare basalts several petrogenetic models are suggested by the trace element characteristics of the picritic glasses 1 1 partial melting of heterogeneous lunar mantle at depths greater than 300 km to produce the parental magmas picritic for both the mare basalts and picritic glasses picritic magmas represented by glass beads were erupted to the surface with small degrees of fractional crystallization while mare basalts were produced by larger degrees of fractional crystallization 15 30 of similar but not identical picritic magmas 2 2 picritic magmas represented by the glass beads were generated at depths greater than 400 km in a volatile enriched relative to the mare basalt source heterogeneous mantle while mare basalts are fractional crystallization products of picritic magmas generated at depths of less than 400 km 3 3 the picritic magmas represented by the glass beads represent polybaric melting that initiated at depths of at least 1000 km a primitive mantle component or less processed cumulate mantle components may have been involved in the generation of the picritic glasses in any of these models

the materials of the lunar procellarum kreep terrane a synthesis of data from geomorphological mapping remote sensing and sample analyses major features of the moon s procellarum kreep terrane include subdued relief and extensive resurfacing with mare basalt consistent with high concentrations of th and other heat producing elements at depth we relate the chemistry of sampled materials to the geomorphology th surface concentrations determined by the lunar prospector 2 pixels and feo and tio2 concentrations derived from clementine ultraviolet visible spectral data on the basis of geologic maps each pixel was classified as mare terra or mixed near the periphery of the terrane terra pixel compositions are relatively feldspathic in the interior they mainly represent imbrium basin rim or ejecta deposits and are mainly incompatible trace element rich norites and presumably represent materials from a thick section tens of kilometers of the pre imbrium crust of the terrane excavated by the imbrium event although imbrium ejecta are the principal source of surface terra materials the imbrium event did not create the th rich procellarum kreep terrane broad continuous expanses of mare pixels are observed with little interruption from protruding terra or terra penetrating craters the mare basalt dominated regoliths of these areas have a wide range of tio2 concentrations 18 leading to the conclusion that the high th concentrations are in the mare basalts and are not present in the regoliths as terra derived materials volcanic glasses and impact glasses of mare basalt composition collected from the procellarum kreep terrane support this conclusion

upper mantle shear velocity structure below northwestern india based on group velocity dispersion abstract we derive a well resolved 1d model of shear wave velocity v s through both linear and nonlinear joint inversions of rayleigh and love wave group velocity dispersion data our best model from the deterministic approach suggests a two layered crust over a half space the upper crust is 13 8 km thick with a shear velocity of 3 22 km s for the lower crust they are 24 9 km and 3 62 km s respectively finally we use a global optimization method very fast simulated annealing to estimate shear wave velocity multiple models give acceptable fits to the observed data a common feature of these models is a low velocity zone lvz with its upper boundary at 60 70 km depth at this depth the temperature depth profile of kachchh cuts the wet peridotite geotherm resulting in increased water content due to partial melting and thus the decreased shear velocity this lvz extends down to a depth of 120 130 km where the temperature depth profile of kachchh cuts the dry peridotite geotherm that leads to a sharp decrease in water content thereby a sharp increase in shear velocity the maximum v s perturbation of 3 in the upper mantle can be explained by the presence of 100 150 k excess temperature beneath northwestern india at 70 120 km depth relative to the adjacent mantle along with the presence of 1 penny shaped melt inclusions probably co 2 rich carbonatite melts in the upper mantle this is likely related to the imprints of the initial deccan reunion plume head that might have moved with india since the deccan volcanism at 65 ma

apollo 14 aluminous mare basalts and their possible relationship to kreep thirty six aluminous mare basalt fragments from breccia 14321 and other apollo 14 basalts are statistically divided into two broad groups comprising five subgroups using la sm and yb data major element compositions petrographic characteristics and mineral compositions are similar for the five groups however there is an eight fold increase in ree abundances from group 5 to group 1 with group 1 having a ree pattern similar to kreep groups 1 to 3 may be related by partial melting of a source similar to that proposed by unruh et al 1984 for feldspathic basalt 12038 however groups 4 and 5 cannot be as closely matched by larger degrees of partial melting of this source groups 1 to 4 could also be produced by assimilation of a kreep component by a magma similar in composition to group 5 such a magma can be produced by partial melting of an olivine orthopyroxene source that crystallized from a magma with chondritic relative ree abundances

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

the imbrium impact event and the thorium distribution at the lunar highlands surface late in the moon s heavy bombardment period the impact that formed the imbrium basin excavated and melted a tremendous volume of material that was subsequently distributed over most of the moon s surface the apollo orbiting ray experiments metzger et al 1977 show that the imbrium projectile struck in a th rich area called the high th oval region here and regarded as a unique lunar geochemical province imbrium primary ejecta were thus probably rich in th it is shown here using ejecta deposit modeling that the distribution of th in the highlands surface along the ground tracks of the ray spectrometers is consistent with the distribution expected for imbrium ejecta deposits deep basins other than imbrium appear to have excavated regions of lower crust that were mafic and fe bearing but not th rich the possibility that the surface th distribution arises mainly from imbrium ejecta has implications for the nature of the moon s igneous differentiation and the nature of the proposed cataclysm or late bombardment with large meteoroids

deep seismic sounding studies in the north cambay and sanchor basins india summary deep seismic sounding dss studies have been carried out in the north cambay and sanchor sedimentary basins in western india along three lines covering about 350km seismic refraction and wide angle reflection data pertinent to the sedimentary basin as well as the deep crustal section have been recorded from 41 shot points using a 60 channel dfs v digital recording system with 200 m geophone spacing and 4 ms data sampling extensive modelling and interpretation of a large number of seismic record sections reveal four sub basins in the sedimentary section along these lines maximum depth to the granitic proterozoic basement p wave velocity 5 9 6 0 km s 1 is about 5000 m in the north sanchor and the patan sub basins and about 5600 m in the south sanchor sub basin the deepest part of the sedimentary basin is delineated within the gandhinagar sub basin where the basement depth reaches 7700 m the deccan traps p wave velocity 4 3 4 8 km s 1 form the base of the tertiary sediments almost in the entire study area except the extreme northern part there is also some indication of the presence of sub trappean mesozoic sediments along this profile within the sedimentary basin two horst features one near diyodar the diyodar ridge and the other northwest of mehsana the unhawa ridge are indicated by the seismic data consistent with the tectonics of the region the thickness of the upper crust in this region does not exceed 15 km p wave velocity reaching 6 3km s 1 a prominent low velocity zone velocity 5 5 km s 1 occurs in the depth range from 10 5 to 12 5 km the lower crust consists of two layers of velocities 6 6 6 9 km s 1 and 7 3 7 4 km s 1 the discontinuity between them occurring at 23 25 km depth the moho discontinuity pm velocity 8 0 km s 1 lies at a depth of 31 33 km the high velocity 7 3 7 4 km s 1 lower crustal layer represents underplating of the crust due to mantle upwelling and rifting with large scale extrusion of the deccan volcanics the large thickness of the tertiary sediments in the cambay basin and a relatively thin crust in the region suggest further rifting during the tertiary

characterization of the causative fault system for the 2001 bhuj earthquake of mw 7 7 abstract precise hypocenters erh m w 2 0 5 3 delineate a east west trending blind thrust dipping 45 towards south named as north wagad fault nwf about 25 km north of kachchh main land fault kmf as the causative fault for the 2001 bhuj earthquake of m w 7 7 the aftershock zone involves a crustal volume of 60 40 35 km 3 lying between kmf and nwf the waveform inversion of 45 aftershocks of m 3 0 5 3 suggest that the e w trending south dipping reverse faulting mainly characterizes the aftershock zone however some reverse faulting along nw se as well as ne sw planes and some strike slip faulting along nw se trending vertical plane are also noticed the estimated p axes point on an average towards n s while t axes orient in e w agreeing well with the prevailing regional plate tectonic stress directions the estimated velocity model from one dimensional inversion of 8000 p and 5000 s travel times from 600 aftershocks deciphers a detailed crustal structure of the region upper 0 6 km on an average suggests a low velocity zone characterizing the jurassic and younger sediments the depth range 6 42 km is characterized on an average by larger values of v p 6 31 to 6 98 km s with an average of 6 71 km s v s 3 64 to 4 05 km s with an average of 3 85 km s and v p v s 1 69 to 1 81 with an average of 1 75 the high crustal velocities can be attributed to the existence of a high velocity mafic intrusive rift pillow structure beneath the region probably emplaced during the rifting time this brittle competent high velocity zone beneath the epicentral area in response to the compression due to the northward movement of the indian plate could induce sufficient local stress perturbation for generating large intraplate earthquakes of m w 7 5 in the lower crust further within the overall higher velocity depth range a layer characterized by large values of v p 6 98 km s v s 3 854 km s and v p v s 1 81 is found in the depth range of 20 5 30 km which is inferred to be fractured and saturated high crack density and probably fluid filled presence of numerous fractures in this layer is confirmed by a high b value 0 75 1 1 in this layer this layer might have facilitated the nucleation process of the 2001 bhuj earthquake the major rupture and 47 of the aftershocks have occurred within this layer

lunar prospector overview lunar prospector is providing a global map of the composition of the moon and analyzing the moon s gravity and magnetic fields it has been in a polar orbit around the moon since 16 january 1998 neutron flux data show that there is abundant h and hence probably abundant water ice in the lunar polar regions gamma ray and neutron data reveal the distribution of fe ti and other major and trace elements on the moon the data delineate the global distributions of a key trace element rich component of lunar materials called kreep and of the major rock types magnetic mapping shows that the lunar magnetic fields are strong antipodal to mare imbrium and mare serenitatis and has discovered the smallest known magnetosphere magnetosheath and bow shock complex in the solar system gravity mapping has delineated seven new gravity anomalies and shown that the moon has a small fe rich core of about 300 km radius

lunar iron and titanium abundance algorithms based on final processing of clementine ultraviolet visible images the clementine mission to the moon returned global imaging data collected by the ultraviolet visible uvvis camera this data set is now in a final state of calibration and a five band multispectral digital image model dim of the lunar surface will soon be available to the science community we have used observations of the lunar sample return sites and stations extracted from the final dim in conjunction with compositional information for returned lunar soils to revise our previously published algorithms for the spectral determination of the feo and tio2 content of the lunar surface the algorithms successfully normalize the effects of space weathering so that composition may be determined without regard to a surface s state of maturity these algorithms permit anyone with access to the standard archived dim to construct high spatial resolution maps of feo and tio2 abundance such maps will be of great utility in a variety of lunar geologic studies

seismological evidence of the hales discontinuity in northeast india the crust and upper mantle shear wave velocity structure beneath the northeast india is estimated by joint inversion of rayleigh wave group velocity and receiver function calculated from teleseismic earthquakes data recorded at nine broadband seismic stations the assam valley and the shillong mikir plateau are the two important tectonic blocks in the northeast india which are surrounded by the himalayan collision zone in the north indo burma subduction zone in the east and by the bengal basin in the south the joint inversion followed by forward modeling reveal crustal thicknesses of 30 34 km beneath the shillong plateau 36 km beneath the mikir hills and 38 40 km beneath the assam valley with an average shear wave velocity vs of 3 4 3 5 km s the estimated low upper mantle shear wave velocity vsn 4 2 4 3 km s may be due to the rock composition or grain size or increased temperature and partial melt 1 in the upper mantle or an effect of all also we report for the first time the existence of the hales discontinuity at depths 56 74 km with vs 4 4 4 6 km s variable depth of the hales discontinuity may be explained by the geotherm and or addition of cr3 and fe2 in the spinel garnet system

the 2001 bhuj earthquake tomographic evidence for fluids at the hypocenter and its implications for rupture nucleation 1 the january 26 2001 bhuj earthquake mw 7 6 is one of the most catastrophic indian earthquakes we have investigated the 3 d seismic velocity and poisson s ratio structures of the bhuj source area to understand the probable cause of triggering the earthquake we used 1948 p and 1865 s wave high quality arrival times from 331 aftershocks recorded at a temporary seismic network significant variations up to 5 in velocity and 10 in poisson s ratio are revealed in the aftershock area the mainshock is located in a distinctive zone characterized by high vp low vs and high poisson s ratio in the depth range of 20 to 30 km and extending 15 to 30 km laterally this feature is very similar to that of the 1995 kobe earthquake zhao et al 1996 the anomaly may be due to a fluid filled fractured rock matrix which might have contributed to the initiation of the bhuj earthquake

clementine images of the lunar sample return stations refinement of feo and tio2 mapping techniques clementine uvvis images of the lunar sample return sites have been processed and used to produce refined calibrations for the iron and titanium determination algorithms of lucey et al 1995 1996 the high spatial resolution of the clementine data permits individual sampling stations to be resolved at the apollo 15 16 and 17 landing sites we find an excellent linear correlation between the spectral fe and ti parameters and the average feo and tio 2 contents of soils sampled at each site or station this correlation demonstrates that these techniques can confidently be applied to other areas of the moon the luna 24 site does not fit the ti relation found for other sites suggesting that either its sample is nonrepresentative or the reported landing coordinates are incorrect

remote sensing of lunar pyroclastic mantling deposits abstract mantling deposits on the moon are considered to be pyroclastic units emplaced on the lunar surface as a result of explosive fire fountaining these pyroclastic units are characterized as having low albedos having smooth fine textured surfaces and consisting in part of homogeneous febearing volcanic glass and partially crystallized spheres mantling units exhibit low returns on depolarized 3 8 cm radar maps indicating an absence of surface scatterers in the 1 to 50 cm size range a number of reflectance spectra from several regional pyroclastic deposits are presented for the first time these data support a previous interpretation that mantling units have a unique spectral signature which is indicative of the presence of a significant fe bearing volcanic glass component the rima bode region is discussed as an example of an area in which several types of remote sensing data including 3 8 cm radar spectral reflectance and multispectral vidicon data were used to reconstruct the geologic events surrounding the emplacement of a regional pyroclastic mantling deposit the recognition of numerous varieties of volcanic glass samples especially relatively high albedo e g green yellow glasses suggests the existence of additional unrecognized mantling deposits with albedos higher than those studied to date on the basis of the remote sensing data summarized and presented five new areas have been identified which may represent higher albedo regional pyroclastic deposits

comparison of the upper mantle shear wave velocity structure of the indian shield and the tibetan plateau and tectonic implications summary travel times and waveforms of long period sh waves recorded at distances of 10 30 and some ss waveforms are used to constrain the upper mantle velocities down to a depth of 400km beneath both the indian shield and the tibetan plateau the shear velocity in the uppermost mantle beneath both the indian shield and the tibetan plateau is high and close to 4 7 km s 1 the indian shield has a fairly thick high velocity lid and the mean velocity between 40 and 250 km is between 4 58 and 4 68 km s 1 in contrast s wave travel times and waveforms of s waves as well as a few for ss show that the mean velocity between 70 and 250km beneath the central and northern part of the tibetan plateau is slower by 4 per cent or more than that beneath the indian shield and probably is between 4 4 and 4 5km s 1 no large differences in the structure of the two areas below 250 km are required to explain both the arrival times and the waveforms of sh phases crossing tibet or the indian shield these results show that the structure of tibet is not that of a shield and imply that the indian plate is not underthrusting the whole of the tibetan plateau at the present time

stratigraphy of the lunar highland crust depths of burial of lunar samples from cooling rate studies current models of lunar crustal stratigraphy are based primarily on models of impact cratering coupled with what is known about the distribution of rock types in the ejecta blankets associated with the large multiring basins these models postulate an upper crust rich in the ferroan anorthosite component underlain by a more mafic noritic lower crust spudis 1993 we attempted to test these models by determining the depth at which various lunar plutonic rocks formed despite intense brecciation and shock many lunar highland samples retain vestiges of a prior magmatic history for example pyroxene samples preserve a record of their thermal history in such phenomena as cation ordering and exsolution textures by computer simulation of the growth of exsolution lamellae in augite and pigeonite we deduced cooling rates and from these estimated a depth of burial on the basis of a simple model for the thermal evolution of the lunar crust despite the fairly large uncertainties in the calculations it is clear that the ferroan anorthosite samples we studied formed at a depth between 10 and 20 km whereas some members of highland magnesian and alkali suites formed as cumulates in magma chambers intruded into the uppermost layers of the crust as yet there is no evidence to indicate that crystalline rocks from the lower half of the lunar crust are present in the samples returned by the apollo missions most samples derived from the lower crust appear to be impact melts oflow k fra mauro noritic composition

bayesian inference gibbs sampler and uncertainty estimation in geophysical inversion the posterior probability density function ppd m d obs of earth model m where d obs are the measured data describes the solution of a geophysical inverse problem when a bayesian inference model is used to describe the problem in many applications the ppd is neither analytically tractable nor easily approximated and simple analytic expressions for the mean and variance of the ppd are not available since the complete description of the ppd is impossible in the highly multi dimensional model space of many geophysical applications several measures such as the highest posterior density regions marginal ppd and several orders of moments are often used to describe the solutions calculation of such quantities requires evaluation of multidimensional integrals a faster alternative to enumeration and blind monte carlo integration is importance sampling which may be useful in several applications thus how to draw samples of m from the ppd becomes an important aspect of geophysical inversion such that importance sampling can be used in the evaluation of these multi dimensional integrals importance sampling can be carried out most efficiently by a gibbs sampler gs we also introduce a method which we called parallel gibbs sampler pgs based on genetic algorithms ga and show numerically that the results from the two samplers are nearly identical we first investigate the performance of enumeration and several sampling based techniques such as a gs pgs and several multiple maximum a posteriori map algorithms for a simple geophysical problem of inversion of resistivity sounding data several non linear optimization methods based on simulated annealing sa ga and some of their variants can be devised which can be made to reach very close to the maximum of the ppd such map estimation algorithms also sample different points in the model space by repeating these map inversions several times it is possible to sample adequately the most significant portion s of the ppd and all these models can be used to construct the marginal ppd mean covariance etc we observe that the gs and pgs results are identical and indistinguishable from the enumeration scheme multiple map algorithms slightly underestimate the posterior variances although the correlation values obtained by all the methods agree very well multiple map estimation required 0 3 of the computational effort of enumeration and 40 of the effort of a gs or pgs for this problem next we apply gs to the inversion of a marine seismic data set to quantify uncertainties in the derived model given the prior distribution determined from several common midpoint gathers

a systematic error in estimating surface wave group velocity dispersion curves and a procedure for its correction abstract a systematic error is known to occur in estimating surface wave group velocity dispersion when the multiple filter analysis technique is applied the error comes from the fall off of the amplitude spectra at long periods we propose a method for correcting this error it consists of using a centroid frequency of the filtered spectrum instead of the central frequency of the gaussian window the method is especially useful when the group velocity curve is obtained from stacking of individual frequency time diagrams we apply this technique to two data sets the first one consists of nine seismograms of coastal subduction zone earthquakes recorded by a broadband station located in mexico city this data set has been previously used to estimate an average crustal structure of southern mexico the second data set consists of broadband seismograms recorded in india and has been used to determine an average structure of the indian peninsular region our results show that in the first case the systematic error is negligible this is due to the relatively low decay rate of the spectral amplitudes at long periods however in the case of the indian data the systematic error of the multiple filter analysis cannot be neglected since it changes significantly the measured dispersion curves and leads to errors in the estimated crustal structure our tests show that the proposed method successfully corrects a major part of the systematic error