temporal spatial distribution and tectonic implications of the batholiths in the gaoligong tengliang yingjiang area western yunnan constraints from zircon u pb ages and hf isotopes abstract considerable progress has recently been made regarding temporal and spatial distribution of magmatism in the lhasa terrane however the eastward and southeastward correlation of these tibetan magmatic suites in western yunnan and burma remains poorly constrained this paper reports zircon u pb dating and hf isotopic compositions of granites in the gaoligong tengliang yingjiang area west yunnan it reveals three episodes of plutonism and more importantly a southwestward magmatic migration the gaoligong batholiths in the northeast were mainly emplaced during early cretaceous 126 121 ma and comprised predominantly s type granites with negative zircon ehf values ehf 2 12 the tengliang granites situated southwest of the gaoligong belt were emplaced in late cretaceous 68 76 ma and also displayed a strong peraluminous affinity and negative ehf 5 14 indicating a provenance from a proterozoic sedimentary source with little mantle contribution the youngest phase of magmatism 52 66 ma occurred in yingjiang southwestmost of the study area it is composed of s type granites ehf 2 12 in east yingjiang and i type granites ehf 4 6 in west yingjiang near the china burma border the late cretaceous early cenozoic plutons in the tengliang and yingjiang area are thus considered as the northern continuation of the late cretaceous magmatic arc west which comprises i type granites and andesitic rocks and of the belt of predominant s type granites east in burma thailand and malaysia such a chemical polarity of the dual i type and s type granites is strongly reminiscent of the northern american cordillera indicating a cordilleran style continental margin during the late cretaceous early cenozoic while the magmatic arc was related to eastward subduction of the neo tethys beneath the asian continent the s type granites represented the melting products of thickened crust in the hinterland in response to subduction induced decrease in lithospheric strength and compressive plate convergence forces and to a less degree to the collision between burma and sundaland blocks the gaoligong early cretaceous granites which bear strong similarities in lithology geochemistry and emplacement age to those in the northern magmatic belt in the lhasa terrane are also the magmatic expression of crustal thickening this crustal thickening may have stemmed from the collision between the lhasa block and the qiangtang block in late jurassic and early cretaceous the magmatism in western yunnan thus recorded a long term subduction of the neo tethyan plate enhanced by continental collisions at different time

the mechanics of continental extension in western north america implications for the magmatic and structural evolution of the great basin abstract a finite element model of continental extension within a rheologically stratified lithosphere is used to examine the structural and magmatic consequences of extensional collapse of thickened crust within the early tertiary north american cordillera crustal thickening creates a weakness in the upper mantle in the model which focuses strain within the great basin during extension marginal highlands corresponding to the sierra nevada and colorado plateau develop near the edges of the weakened region where abrupt changes in the strength of the lithosphere create large gradients in the amount of strain the great thickness of the crust results in widespread ductile flow in the lower crust within the interior of the great basin favoring the formation of metamorphic core complexes during the early stages of extension ductile flow becomes inhibited as the crust thins and cools possibly contributing to the change in the style of extension from low angle detachment faulting to high angle normal faulting during the middle miocene as the lithosphere cools the strength of the uppermost mantle increases after about 10 m y the upper mantle becomes stronger beneath the great basin than beneath adjacent unextended regions strain then begins to migrate outward from the interior of the great basin onto the marginal highlands and their interior edges begin to collapse and are incorporated into the widening great basin after 40 m y of extension the highest rates of strain are localized at the edges of the great basin in positions corresponding to the walker lane tectonic belt of western nevada and the colorado plateau transition zone the weight of the marginal highlands in the model is partially supported by flexure of the strong layer in the uppermost mantle portions of the uppermost mantle which have been flexed upward cool more rapidly than deeper portions creating periodical variations in the strength of the lithosphere which eventually develop into crustal and lithospheric boudinage with a wavelength similar to that observed in regional gravity studies rapid thinning of the model lithosphere during the first 10 m y of extension results in nearly adiabatic decompression of the lithospheric mantle partial melting of the lower lithospheric mantle is likely during this period if volatile phases or mafic lithologies were present this mechanism may account for widespread silicic magmatism in the great basin during the middle tertiary as the region undergoing extension widens the rate of lithospheric thinning decreases and the mantle beneath the great basin begins to cool this leads to a cessation of melting within the lithosphere and waning of silicic volcanism 15 20 m y after the onset of extension the appearance of predominantly basaltic and bimodal volcanic suites in the great basin during the last 5 10 ma correlates well with the onset of decompression melting in the asthenosphere if the mantle potential temperature is greater than about 1350 c approximately 70 c warmer than typical mantle potential temperature

upper mantle tomography beneath the pacific northwest interior abstract the pacific northwest has undergone extensive tectonic and magmatic construction in the cenozoic and many clues to its history are in a well resolved upper mantle structure we present new p s and v p v s models that benefit from improved algorithms and additional data from recently deployed flexible array experiments in the region of the columbia river basalts western snake river plain and idaho batholith we refine the geometries of previously imaged structures and identify new anomalies beneath the pacific northwest a clear separation is resolved between the wallowa and idaho structures that extends from the base of the crust to the depth extent of these structures the separation follows the precambrian margin of north america possibly indicating separate tectonic histories for the two structures a shallow fast anomaly beneath idaho batholith may be responsible for the observed curvature of the yellowstone track around this batholith and a strong and unusually deep 180 250 km slow anomaly is present east of the apparent juan de fuca slab gap resolving these structures well is important in understanding the origin of the lithospheric fragments in the mantle and key to any reconstruction of the evolution of the pacific northwest farallon kula juan de fuca tectonic system of most relevance understanding the origin of the imaged high velocity mantle structures provides strong constraint on their density that otherwise would be largely unknown which controls the evolution of vertical and horizontal stresses acting at the base of the lithosphere and hence the evolution of topography also resolving the volumes of partially molten upper mantle shapes our understanding on the origin of the abundant volcanism in the pacific northwest interior

is a pyrolitic adiabatic mantle compatible with seismic data in this paper the simplest average physical model of a mantle convecting as a whole i e following an adiabatic temperature gradient with a single composition pyrolite with phase transitions is tested directly against global seismic data instead of against spherically symmetric seismic models constraints from seismic data on average velocities and lower mantle velocity gradients are hard to reconcile with an adiabatic pyrolitic mantle given the current state of knowledge of elastic and anelastic mineral parameters at high pressure and temperature this physical model generally gives a a stronger baseline offset between upper and lower mantle average travel time residuals than allowed by the data and b an insufficient decrease in velocity with depth in the lower mantle above 2500 km we tested 105 upper and 105 lower mantle models that were selected randomly within the mineral parameter uncertainties only 2 lower mantle models and 24 upper mantle models yield whole mantle seismic structures that are compatible with global isc p and s travel times and central frequencies of toroidal and spheroidal fundamental modes with angular order higher than 18 to improve the fit to the seismic data the physical model would require a a lower velocity transition zone composition than dry pyrolite at least around continents and subduction zones as well as b a gradual change in physical state of the lower mantle that decreases the velocity depth gradient e g a superadiabatic temperature gradient

towards a better understanding of the influence of basement heterogeneities and lithospheric coupling on foreland deformation a structural and paleomagnetic study of laramide deformation in the southern bighorn arch wyoming integrated structural anisotropy of magnetic susceptibility ams and paleomagnetic analyses of sedimentary cover rocks along variably oriented major faults and en echelon fold systems in the southern bighorn arch wyoming were undertaken to test kinematic and mechanical models of laramide thick skin deformation the laramide foreland is characterized by an anastomosing network of basement cored arches and associated cover folds that trend overall nw se but in detail are curved range from n s to e w trending and form both right and left stepping en echelon systems development of variably trending laramide arches has been variously attributed to temporal changes in stress directions wrench faulting and localization of deformation related to basement heterogeneities during regional sw ne shortening within the southern bighorn arch widespread but limited layer parallel shortening lps was accommodated mostly by minor faults with conjugate wedge and strike slip geometries early in the deformation history lps directions vary from perpendicular to acute with local fold structural trends consistent with a single shortening episode although internal strain is limited weak ams lineations defined by kinked and rotated phyllosilicates are widely developed and consistently perpendicular to lps directions structurally restored paleomagnetic declinations record only limited non systematic vertical axis rotations indicating that wrenching was not an important component of the deformation field during development of the southern bighorn arch and that curvature of the arch was a primary feature palinspastically restored lps directions are on average wsw ene but display local deflections related to heterogeneities of underlying basement blocks and proximity to major faults some of which were localized along precambrian shear zones and igneous dikes crustal shortening patterns across the laramide foreland are interpreted to reflect deformation partitioning in response to a single far field shortening direction partly related to flat slab subduction along with effects of pre existing basement weaknesses and strain softening during progressive faulting

the physical effects of an intra aggregate structure on soil shrinkage clay and soil containing it have shrinkage curves that are qualitatively different in shape the objective of this work is to qualitatively show with maximum simplicity how a clay shrinkage curve turns into a soil shrinkage curve because of the crack volume the measured shrinkage curve is not the single valued feature of a soil we use a concept of the reference shrinkage curve that is only stipulated by soil shrinkage without cracking single valued and qualitatively similar to an observed shrinkage curve we also use new concepts of an intra aggregate soil structure i a rigid superficial layer of aggregates that loses water during shrinkage and ii lacunar pores micro cracks inside an intra aggregate clay that change in volume during shrinkage then through a series of consecutive steps illustrating each step by a separate graphic presentation we move from a clay shrinkage curve to a soil shrinkage curve with predicted qualitative features that coincide with those experimentally observed in numerous soil shrinkage publications we thereby demonstrate the qualitative physical impact of the intra aggregate structure on soil shrinkage

kibaran a type granitoids and mafic rocks generated by two mantle sources in a late orogenic setting burundi in the mesoproterozoic northeastern kibaran belt of burundi central africa two distinct late kibaran magmatic suites coexist both including a type granitoids they are located along the boundary zone between the kibaran mobile belt western internal domain and the archaean tanzanian craton overlain by mesoproterozoic foreland deposits eastern external domain intense deformation high temperature metamorphism and intrusion of abundant peraluminous anatectic crustal granites occur only in the former domain whereas the mesoproterozoic sedimentary cover of the latter is much less or even nearly undeformed nor metamorphosed the first late kibaran magmatism 350 km long kabanga musongati with an emplacement age of 1275 ma u pb on zircon is mainly composed of mafic and ultramafic layered rocks with subordinate a type acidic differentiates moderately enriched in incompatible elements initial isotopic ratios srlr 0 708 nd 8 indicate an old continental lithospheric mantle origin the emplacement of these late kibaran magmatic rocks was controlled by late lateral shear possibly contemporaneous with the latest intrusions of the kibaran peraluminous synkinematic granites of the western internal domain 1330 1260 ma the second late kibaran magmatism 40 km long gitega makebuko and bukirasazi alignment with an emplacement age of 1249 s ma u pb on zircon is limited in volume it is mainly granitic in composition a type can be strongly enriched in incompatible elements and comprises both syenites and mafic rocks initial isotopic ratios srlr 0 702 na 4 5 to 1 4 point to an oib type asthenospheric lower continental lithospheric mantle origin with only slight contamination by the lower crust during differentiation this group was also intruded during the late lateral shear in both groups liquid lines of descent can be reconstructed although some of the rocks have been strongly albitized this indicates that the granites are produced by differentiation of less evolved magmas and not by crustal anatexis upwelling of the asthenosphere along the tanzanian craton can generate by adiabatic pressure release the oibtype basic melts and provide the heat necessary to melt the continental lithospheric mantle sources this mechanism assigns a major role to a lithosphere scale late kibaran shear event occurring at the end of the regional compressive deformation between two rheologically contrasted domains ascent of the asthenosphere continental lithospheric mantle delamination and late orogenic extensional collapse of the western internal domain are suggested as a possible geodynamic model for the entire northeastern kibaran belt additional work is however necessary to test this model finally our results indicate that in the northeastern kibaran belt the kibaran orogeny ended at 1250 ma despite various reactivation events occurring later e g at 1137 ma

a microstructurally based effective stress for unsaturated soils current alternative choices of stress state variables in unsaturated soils are described and compared with a special focus on the use of an effective stress experimental data on stiffness and shear strength evolution with suction suggest that the proportion of suction contributing to the effective stress is often much smaller than predicted by the term suction times degree of saturation generally used in effective stress expressions of the bishop type it is suggested that effective stress in unsaturated soils should be related to soil microstructure an effective degree of saturation is defined as describing the volume of water partially filling the soil macroporosity this effective degree of saturation defines the proportion of the prevailing suction that actually contributes to the effective stress two alternative expressions piecewise linear and non linear are proposed for the effective degree of saturation they offer a similar performance available data on stiffness and shear strength varia

radial qμ structure of the lower mantle from teleseismic body wave spectra abstract we have measured 150 000 p and 130 000 s wave spectral ratios up to 0 8 hz using recordings of 250 deep focal depth 200 km earthquakes from 890 global and regional network stations we have inverted these data to estimate the attenuation parameters t p and t s for p and s waves and a radial profile of the quality factor q for the lower mantle on average t p increases by about 0 2 s and t s increases by about 0 7 s between epicentral distances of 30 and 97 the relatively strong increase of t s t s 4t p suggests that intrinsic shear attenuation is the cause of the overall trend in our data the increase of t p and t s with distance is smaller than predicted by models prem 12 ql6 11 and qlm9 16 assuming prem values for q in the upper mantle where the data lack resolving power the p and s wave spectra are explained best if q increases from about 360 at prem s 670 km discontinuity to 670 in the lowermost mantle the high values for q can be reconciled with previously determined values by invoking a frequency dependence of q that is proportional to 0 1 data that are separated in pacific and circum pacific subsets have slightly different trends estimates of t p and t s for the pacific data which sample the large low shear velocity province of the pacific are higher than the circum pacific estimates thus it appears that the pacific large low shear velocity province has accompanying low q the difference in q in the lowermost 1000 km of the mantle beneath the pacific and beneath the circum pacific is at most 17 lateral variations of this magnitude are marginally resolvable given the uncertainties of our measurements

anelastic structure of the upper mantle beneath the northern philippine sea we investigated the upper mantle anelastic structure beneath the northern philippine sea region including the izu bonin subduction zone and the shikoku basin we used regional waveform data from 69 events in the pacific and the philippine sea slabs recorded on f net and j array network broadband stations in western japan using the s p phase pair method we obtained differential attenuation factors t which represent the relative whole path q we conducted a tomographic inversion using 978 t values to invert for a fine scale 50 100 km three dimensional anelastic structure the results shows two high q regions qp 1000 which are consistent with the locations of the pacific and the philippine sea slabs also there is a low q qp 110 area extending to the deeper parts 350 400 km of the model just beneath the old spreading center and the kinan seamount chain in the shikoku basin a small depth dependence of the laterally averaged qp was found with values of 266 0 250 km 301 250 400 km and 413 400 500 km 2003 elsevier b v all rights reserved

water content void ratio swell shrink paths of compacted expansive soils this paper addresses the behaviour of compacted expansive soils under swell shrink cycles laboratory cyclic swell shrink tests were conducted on compacted specimens of two expansive soils at surcharge pressures of 6 25 50 00 and 100 00 kpa the void ratio and water content of the specimens at several intermediate stages during swelling until the end of swelling and during shrinkage until the end of shrinkage were determined to trace the water content versus void ratio paths with an increasing number of swell shrink cycles the test results showed that the swell shrink path was reversible once the soil reached an equilibrium stage where the vertical deformations during swelling and shrinkage were the same this usually occurred after about four swell shrink cycles the swelling and shrinkage path of each specimen subjected to full swelling full shrinkage cycles showed an s shaped curve two curvilinear portions and a linear portion however the swelling and shrinkage path occurred as a part of the s shaped curve when the specimen was subjected to full swelling partial shrinkage cycles more than 80 of the total volumetric change and more than 50 of the total vertical deformation occurred in the central linear portion of the s shaped curve the volumetric change was essentially parallel to the saturation line within a degree of saturation range of 50 80 for the equilibrium cycle the primary value of the swell shrink path is to provide information regarding the void ratio change that would occur for a given change in water content for any possible swell shrink pattern it is suggested that these swell shrink paths can be established with a limited number of tests in the laboratory

application of sequence stratigraphic concepts to the upper cretaceous tununk shale member of the mancos shale formation south central utah parasequence styles in shelfal mudstone strata

impacts of matric suction equalization on small strain shear modulus of soils during air drying in this study a weight control bender element system has been developed to investigate the impact of matric suction equalisation on the measurement of small strain shear modulus gmax during an

teleseismic p wave spectra from usarray and implications for upper mantle attenuation and scattering teleseismic p wave amplitude spectra from deep earthquakes recorded by usarray are inverted for maps of upper mantle t for multiple frequency bands within 0 08 2 hz all frequency bands show high t regions in the southwestern u s southern rocky mountains and appalachian margin low t is more common across the cratonic interior inversions with narrower frequency bands yield similar patterns but greater t magnitudes even the two standard deviation t magnitude for the widest band is 2 7 times greater than predicted by global qs tomography or an anelastic olivine thermal model suggesting that much of the t signal is nonthermal in origin nonthermal contributions are further indicated by only a moderate correlation between t and p travel times some geographic variations such as high t in parts of the cratonic interior with high mantle velocities and low heat flow demonstrate that the influence of temperature is regionally overwhelmed transverse spectra are used to investigate the importance of scattering because they would receive no p energy in the absence of 3 d heterogeneity or anisotropy transverse to vertical t z spectral ratios for stations with high t are higher and exhibit steeper increases with frequency compared to t z spectra for low t stations the large magnitude of t estimates and the t z spectra are consistent with major contributions to t from scattering a weak positive correlation between intrinsic attenuation and apparent attenuation due to scattering may contribute to t magnitude and the moderate correlation of t with travel times

qp and qs in the upper mantle beneath the iberian peninsula from recordings of the very deep granada earthquake of april 11 2010 1 granada southern spain is a place of rare and enigmatic very deep focus earthquakes the last one on april 11 2010 with magnitude of 6 3 and depth of 620 km we use regional broadband recordings to estimate qp and qsin the mantle for frequencies between 0 25 and 8 hz computing the spectra of the direct p and s waves with their early p and s coda we use the spectral decay method constraining crustalq to values given in the literature we obtain robust estimates of qp in 6 frequency bands 0 25 0 5 1 2 4 and 8 hz and of qs in 4 bands 0 25 0 5 1 2 hz qp in the mantle ranges from 13 at 0 25 hz to 346 at 8 hz and qs from 59 at 0 25 to 183 at 2 hz the frequency dependence is well fitted by q q0f with equal to 0 6 for qs and 1 0 for qp and q0 equal to 109 for qs and 63 for qp the qp qs ratio is less than 1 these are extreme values within the ranges of mantle q qp qs and values reported in the literature indicating strong scattering attenuation and absence of melt we propose that such values rather than being an exception may approximate the average upper mantle with solid olivine composition and small scale heterogeneity

petrogenesis of metaluminous a type granitoids in the tengchong lianghe tin belt of southwestern china evidences from zircon u pb ages and hf o isotopes and whole rock sr nd isotopes abstract the tengchong lianghe tin belt is the most importantpart of the tin metallogenic belt in southwest china s sanjiang metallogenic province in this district two a type granite plutons that are spatially associated with the tin deposits have recently been discovered these granitoids are dominated by biotite granites with weakly peraluminous to metaluminous compositions high sio2 contents 73 3 76 2 wt and high alkali contents k2o na2o 8 3 9 17 wt trace element spider diagrams show that these granitoids are also clearly enriched with the large ion lithophile elements rb th u and k but are markedly depleted in ba and sr they are significantly depleted in the high field strength elements nb and ti but are enriched with zr and hf these rocks have relatively high zircon saturation temperatures 774 833 c high zr nb ce y contents 272 416 ppm and 10 000 ga al ratios almost 2 7 that are typical of a type granites they also have high total rare earth element ree contents 174 404 ppm and relatively flat chondrite normalized ree patterns with significantly negative eu anomalies la icp ms zircon u pb dating results indicate that the emplacement of these two granite plutons occurred during the early tertiary 52 7 0 3 53 0 0 4 ma and the late cretaceous 73 3 0 5 73 3 0 5 ma periods respectively isotopic compositions show that the granitoids have highly variable 87sr 86sr i ratios 0 7182 0 7457 relatively constant low end t values 11 2 to 12 4 and ancient nd and hf model ages 1 56 1 88 ga suggesting that they were derived from the partial melting of the paleoproterozoic continental crust their zircon 18o values 6 6 8 5 and ehf values from 8 6 to 11 3 also suggest that these granitoids mainly originated from the middle lower continental crust consisting of mafic and metasedimentary rocks such geochemical characteristics indicate that these two a type granite plutons were generated by the partial melting of paleoproterozoic mafic and the metasedimentary basement of the tengchong block in a post collisional or syn collisional extensional setting of the neo tethy anorogenic zone during the late cretaceous early cenozoic the late cretaceous granitoids were probably associated with the subduction of the neo tethyan plate under the post collisional extension of the western burma and tengchong microplates collision during the jurassic early cretaceous the early tertiary granitoids might be the syn collisional product of stretching relaxation during the middle and late main collisional period 55 41 ma between india and asia

frequency dependence of q in earth s upper mantle inferred from continuous spectra of body waves q0 f f0 a and applied a grid search to determine the best fit a and q0 the inferred frequency dependence 0 2 a 0 4 in most regions is consistent with laboratory data on solid olivine but not on partially molten olivine rich rocks except those data for deep events close agreement between seismological and laboratory observations on frequency dependence of q suggests that physical mechanisms of seismic wave attenuation are common and therefore laboratory data can be used to infer the physical state of earth s upper mantle from seismic wave attenuation index terms 5144 physical properties of rocks wave attenuation 7218 seismology lithosphere and upper mantle 8162 tectonophysics rheology mantle citation shito a s karato and j park 2004 frequency dependence of q in earth s upper mantle inferred from continuous spectra of body waves geophys res lett 31 l12603

an upper mantle seismic discontinuity beneath the galapagos archipelago and its implications for studies of the lithosphere asthenosphere boundary an upper mantle seismic discontinuity the gutenberg or g discontinuity at which shear wave velocity decreases with depth has been mapped from s to p conversions in radial receiver functions recorded across the galapagos archipelago the mean depth of the discontinuity is 91 8 km beneath the southeastern archipelago and 72 5 km beneath surrounding regions the discontinuity appears deeper beneath the portion of the nazca plate that we infer passed over the galapagos mantle plume than elsewhere in the region we equate the depth of the g discontinuity to the maximum depth extent of anhydrous melting which forms an overlying layer of dehydrated and depleted mantle we attribute areas of shallow discontinuity depth to the formation of the dehydrated layer near the galapagos spreading center and areas of greater discontinuity depth to its modification over a mantle plume with an excess temperature of 115 30 c the g discontinuity lies within a high seismic velocity anomaly that we conclude forms by partial dehydration and a gradual but steady increase in seismic velocity with decreasing depth after upwelling mantle first encounters the solidus for volatile bearing mantle material at the depth of the solidus for anhydrous mantle material removal of remaining water creates a sharp decrease in velocity with depth this discontinuity may also mark a site of melt accumulation results from seismic imaging the compositions of galapagos lavas and rare earth element concentrations across the archipelago require that mantle upwelling and partial melting occur over a broad region within the dehydrated and depleted layer we conclude that the g discontinuity beneath the archipelago does not mark the boundary between rigid lithosphere and convecting asthenosphere

frequency dependence of seismic wave attenuation in the upper mantle beneath the australian region summary the differential attenuation for upper mantle paths beneath northern australia has been estimated using spectral ratio methods both in a narrow frequency band near 0 6 hz to obtain stable estimates for subsequent inversion and also over a broad frequency band up to 3 6 hz to look at the frequency dependence of attenuation the frequency dependence of the differential attenuation between p and s wave arrivals is estimated using a spectral ratio technique based on a power law relationship between q and frequency this approach isolates the intrinsic q rather than any scattering component by exploiting nearly 2000 paths crossing the australian region which provide a good coverage of the mantle the geographical variation of the frequency dependence of attenuation for body waves can be mapped the differential attenuation t sp between p and s waves in the 0 6 hz band varies between close to zero for paths wholly within the shield lithosphere to nearly 4 for paths with a long asthenospheric component a measure of frequency dependence is obtained by fitting the spectral ratio information as a function of frequency using a single power law relation for the average dependence of the whole path the estimates of power law exponents show a strong correlation with qualitative measures of attenuation based on the relative frequency content of p and s there is a weak frequency dependence in the northwestern part of australia especially in the shallow part of the upper mantle where q is very high in the eastern part of australia there is a complex structure in attenuation with a mixture of styles of frequency dependence with exponents approaching 1 for the most attenuative paths

seismic attenuation beneath northeastern japan constraints on mantle dynamics and arc magmatism we apply a three step approach to estimate three dimensional 3 d p wave attenuation qp 1 structure beneath northeastern japan first corner frequencies of earthquakes are determined using the spectral ratio method for s coda waves then whole path attenuation terms t and site amplification factors are simultaneously estimated by a joint inversion the set of t is finally inverted for 3 d attenuation structure the results show that the mantle wedge has low attenuation in the fore arc and high attenuation in the back arc a depth profile of qp 1 in the back arc mantle is explained by attenuation expected for a two dimensional 2 d thermal model with qp qs 2 and grain sizes of 1 and 3 cm however an inclined high attenuation zone observed in the back arc mantle wedge which is interpreted as an upwelling flow shows higher attenuation than that calculated from the 2 d thermal model the higher seismic attenuation is probably caused by the concentration of partial melt in the upwelling flow a combined interpretation of seismic attenuation and velocity structures further suggests that the degree of partial melt in the upwelling flow varies along the arc and that volcanoes are clustered transverse to the arc below which the upwelling flow contains a higher degree of melt these observations indicate that magmatism is controlled by a mantle wedge process that depends strongly on spatial variations in the degree of partial melt in the upwelling flow our results further imply the breakdown of hydrous minerals in a hydrous layer above the pacific plate at a depth of 120 km

mesozoic extensional structures of the fangshan tectonic dome and their subsequent reworking during collisional accretion of the north china block the fangshan area sw of beijing lies at the junction of the nne trending taihang mountain range and the southeastern portion of the yanshan intraplate orogenic belt and has undergone at least five stages of deformation mid to late triassic extensional deformation d 1 is represented by the formation of the fangshan tectonic dome during se directed extensional tectonics this deformation was later modified by nnw directed thrusting in the late triassic d 2 and wnw directed thrusting in the late jurassic d 3 these d 1 d 3 structures were deformed by the arcuate beiling syncline d 4 which formed during the intrusion of the 133 128 ma fangshan pluton d 5 deformation is represented by cretaceous to quaternary nne striking high angle normal faults the ages of these events demonstrate that the principal ene trending tectonic framework of the yanshan intraplate orogenic belt was established mainly in the mid to late triassic the indosinian event the jurassic to cretaceous yanshanian deformation with thick skinned thrusting was associated with intrusion of numerous plutons and strongly modified the older structures the tectonic evolution of the fangshan tectonic dome was linked genetically with the collision of the north china block and the siberian craton and the later collision of the north and south china blocks

cretaceous cenozoic tectonic events in the western myanmar burma assam region correlation of late mesozoic mafic and ophiolitic rocks suggests that in the late lower cretaceous a northeasterly facing mafic arc was emplaced onto southeast borneo western sumatra western myanmar burma then 1100 km south of its present position the mogok belt of myanmar and the denqen bangong co ophiolite zone in tibet all then situated on the southwestern margin of asia reversal in tectonic polarity and eastward subduction generated a late cretaceous magmatic arc in western myanmar and sumatra and its continuation through the mogok belt into the gandise batholith of tibet magmatism interrupted in the latest cretaceous probably resumed in the western myanmar tibet and sumatra arc segments in the early palaeogene it was again interrupted in the mid eocene when an east vergent ophiolite nappe overrode the indo burman ranges deforming lower eocene turbidites derived from the magmatic arc to the east following renewed northward and eastward subduction of ocean floor in the latest eocene india collided with northern myanmar and with tibet along a suture south of the jurassic triassic flysch and adjacent yarlung ophiolite in the mogok segment of the late cretaceous arc crust thickened in the early cretaceous orogeny underwent extension to form a metamorphic core complex as myanmar west of the sagaing fault moved northward more than half of this northward movement preceded the well documented 450 km of post early miocene dextral displacement on the sagaing fault and related spreading in the andaman sea generation of late cretaceous to early eocene i and s type granites in and east of the mogok belt was related either to crustal shortening or more probably to subsequent extension in the mogok belt

shear modulus and q of forsterite and dunite near partial melting from forced oscillation experiments an apparatus designed to determine the complex shear modulus of rock samples by forced torsion oscillations at high temperature and in the seismic frequency band 0 003 30 hz is briefly described measurements were performed on natural dunite from aheim norway up to 1400 c and on polycrystalline forsterite up to 1500 c at 1 atm pressure the two materials were chosen to study by comparison the effect of melt on the elasticity and anelasticity of mantle rocks between 1000 and 1200 c the absolute values of the shear modulus g are almost equal for both materials above 1200 c g for natural dunite decreases progressively with temperature and at 1400 c and 1 hz reaches 13 of its value at 1100 c in contrast g of pure forsterite depends little on temperature for petrological reasons supported by simultaneous measurements of the electric resistivity there is strong evidence that the decrease of g in dunite above 1200 c is due to melt from the lower melting components of the dunite based on different models estimates of the melt fraction are made at high temperature in both materials q 1 is characterized by a monotonic decrease with frequency according to with 0 25 an apparent activation energy of 38 5 kcal mol 1 for forsterite and 48 8 kcal mol 1 for dunite was found with no significant change in the regime of partial melting from this it is concluded that q 1 even at partial melting is dominated by solid state high temperature background absorption there is no indication from these experiments for a constant q band at low seismic frequencies or an increase of q proportional to frequency as suggested by some seismologists the present results are in good qualitative agreement with those for young s modulus obtained previously by strain retardation experiments

seismic attenuation tomography of the tonga fiji region using phase pair methods the anelastic structure of the region surrounding the tonga slab and lau back arc spreading center in the southwest pacific is studied using data from 12 broadband island stations and 30 ocean bottom seismographs two differential attenuation methods determine t over the frequency band 0 1 to 3 5 hz for earthquakes in the tonga slab the s p method measures the difference in spectral decay between p and s waves arriving at the same station the p p method measures the difference in spectral decay for p waves with different paths through the upper mantle eight hundred sixty phase pairs are used to invert for two dimensional 1 q structure using a nonnegative least squares algorithm a grid search method determines the q q ratio most compatible with both the s p and p p differential measurements the highest attenuation q 90 is found within the upper 100 km beneath the active portions of the lau basin extending westward to the lau ridge these regions probably delineate the source region for the back arc spreading center magmas expected to be within the upper 100 km based on petrological considerations the high attenuation regions also correlate well with zones of low p wave velocity determined by regional velocity tomography somewhat lower attenuation is found beneath the fiji plateau than beneath the lau basin the entire back arc is characterized by a gradual decrease in attenuation to a depth of 300 to 400 km the slab is imaged as a region of low attenuation q 900 material a q q ratio of 1 75 provides the best fit between the s p and p p data sets upon inversion spectral stacking shows no frequency dependence within the frequency band analyzed

three dimensional laramide deformation of the colorado plateau competing stresses from the sevier thrust belt and the flat farallon slab 1 kinematic analysis of laramide basement cored uplifts on the northern colorado plateau indicate that four of the uplifts were constructed by northeast directed shortening while at least two were constructed by southeast directed shortening available timing data suggest that all of the uplifts rose at approximately the same time 72 50 ma this paper proposes that the different shortening directions are a predictable result of deformation in a three dimensional stress field where the magnitude of 2 approaches that of 1 the concept is supported by both angelier stereographic analysis and elastic modeling tectonically 1 is may have been the result of coupling between the horizontally subducting farallon slab and the north american plate the elevated values of 2 are attributed to far field stresses generated by the topographically high sevier thrust belt which wraps around the western edge of the colorado plateau and was active at the time of deformation in the plateau

multistage multidirectional tertiary shortening and compression in north central new mexico the nature of laramide deformation in the southern rocky mountains remains highly debated advocates of north south strike slip faulting favor transpression and northward displacement of the colorado plateau whereas advocates of east west shortening by thrust faulting contest evidence for large right lateral displacements minor faults n 2552 were measured to determine the laramide to holocene structural evolution of north central new mexico multimodal slickenline and ideal 1 orientations as well as consistent crosscutting relationships indicate multiphase multidirectional faulting the oldest set of thrust and strike slip faults indicates east northeast to east trending shortening and compression the faults cut rocks as young as the upper paleocene lower eocene diamond tail formation strike slip faults from a second phase of northeast to north northeast trending shortening and compression cut the eocene galisteo formation but do not cut the 27 ma galisteo dike elsewhere later north striking strike slip faults cut 24 ma igneous units indicating north northeast to north trending shortening and compression of mid tertiary age subsequent north striking normal faults related to rio grande rifting commonly reactivate the mid tertiary strike slip fault planes these results show the validity of both strike slip and thrust hypotheses in north central new mexico although neither is adequate in exclusion of the other early laramide east west thrusting probably formed the north trending laramide arches of the region later counterclockwise rotation of regional shortening and compression directions may have caused transpression opening some late laramide axial basins and causing limited northward displacement of the colorado plateau subsequent mid tertiary strike slip deformation may be a missing link between paleogene laramide shortening and neogene rio grande rifting

the tidal history of iapetus spin dynamics in the light of a refined dissipation model 1 we study the tidal history of an icy moon basing our approach on a dissipation model which combines viscoelasticity with anelasticity and takes into account the microphysics of attenuation we apply this approach to iapetus the most remote large icy moon in the saturnian system different authors provide very different estimates for iapetus s despinning timescale by several orders of magnitude one reason for these differences is the choice of the dissipation model used for computing the spin evolution as laboratory data on viscoelastic properties of planetary ices are sparse many studies relied on dissipation models that turned out to be inconsistent with experiment a pure water ice composition generally assumed in the previous studies of the kind yields despinning times of the order of 3 7 gyr for most initial conditions we demonstrate that through accounting for the complexity of the material like second phase impurities one arrives at despinning times as short as 0 9 gyr a more exact estimate will remain unavailable until we learn more about the influence of impurities on ice dissipation by including the triaxial shape caused torque we encounter a chaotic behavior at the final stage of despinning with the possibility of entrapments in the intermediate resonances the duration of these entrapments turns out to be sensitive to the dissipation model no long entrapments have been found for iapetus described with our laboratory based dissipation model

dynamic models for metamorphic core complex formation and scaling the role of unchannelized collapse of thickened continental crust abstract metamorphic core complexes at collisions between cratons and softer terranes such as in the northern north american cordillera share a set of characteristic features including spatial and temporal association of ductile mid crustal deformation with brittle normal faulting spatial coincidence with prior crustal thickening characteristic spatial scaling and limited duration and extent of deformation these properties are reproduced in numerical solutions for gravity driven collapse of a viscous crustal region under conditions where vertical stress is continuous through thickened lithosphere rigid deformable conditions such solutions allow inversion for effective mechanical properties and crustal geometry from direct observations of aspect ratio and exhumation velocity in the northern rockies core complex geometry is consistent with a twofold decrease in viscosity of the thickened cordilleran crustal welt

detailed facies analysis of the upper cretaceous tununk shale member henry mountains region utah implications for mudstone depositional models in epicontinental seas abstract lower middle turonian strata of the tununk shale member of the greater mancos shale were deposited along the western margin of the cretaceous western interior seaway during the greenhorn second order sea level cycle in order to examine depositional controls on facies development in this mudstone rich succession this study delineates temporal and spatial relationships in a process sedimentologic based approach the 3 dimensional expression of mudstone facies associations and their stratal architecture is assessed through a fully integrative physical and biologic characterization as exposed in outcrops in south central utah sedimentologic characteristics from the millimeter to kilometer scale are documented in order to fully address the complex nature of sediment transport mechanisms observed in this shelf muddy environment the resulting facies model developed from this characterization consists of a stack of four lithofacies packages including 1 carbonate bearing silty and sandy mudstone cssm 2 silt bearing calcareous mudstone scm 3 carbonate bearing silty mudstone to muddy siltstone cms and 4 non calcareous silty and sandy mudstone ssm spatial and temporal variations in lithofacies type and sedimentary facies characteristics indicate that the depositional environments of the tununk shale shifted in response to the 2nd order greenhorn transgressive regressive sea level cycle during this eustatic event the tununk shows a characteristic vertical shift from distal middle shelf to outer shelf cssm to scm facies then from outer shelf to inner shelf environment scm to cms and to ssm facies shifting depositional environments as well as changes in dominant paleocurrent direction throughout this succession indicate multiple source areas and transport mechanisms i e longshore currents offshore directed underflows storm reworking this study provides a rare documentation of the greenhorn cycle as exposed across the entire shelf setting high resolution mapping of genetically related packages facilitate the development of process based depositional models that can be utilized for lateral correlations into the equivalent foredeep strata of the cretaceous interior

crust and mantle structure across the basin and range colorado plateau boundary at 37 n latitude and implications for cenozoic extensional mechanism we present new evidence on the seismic velocity and density of the crust and upper mantle along a 200 km long transect across the eastern basin and range and western colorado plateau at 37 n latitude receiver functions computed from the p waveforms recorded with 10 portable broadband stations deployed along the transect were used to estimate crustal thickness variations the crust is 30 35 km thick within the eastern basin and range and increases over a distance of 100 km at the western edge of the colorado plateau reaching a maximum of approximately 45 km east of the hurricane fault the timing of crustal multiples within the reciever functions were used to estimate the v p v s of the crust along the profile and we found that the western colorado plateau crust is characterized by a high poisson s ratio 0 28 0 29 indicative of a crust with an average mafic composition we estimated the upper mantle lid thickness along our profile based on teleseismic p wave travel times and constraints provided by gravity data our data and available geophysical constraints are most consistent with a lithosphere that thickens from an average thickness of 60 km beneath the basin and range to 100 km beneath the western colorado plateau although the basin and range lithosphere may have significant thickness variations the thick strong mafic crust and thicker mantle lid under the colorado plateau can account for the relative geologic stability and subdued magmatism of the plateau during laramide compression and cenozoic extension compared to surrounding regions the crustal and lithospheric thinning across the tectonic boundary occurs over a short distance 100 km suggesting it is a geologically young feature produced by a predominantly mechanical response to late cenozoic extension our new lithosphere model at 37 n latitude is consistent with the existence in early cenozoic time of a flat subducted slab at 100 km depth and a relict sevier laramide 50 60 km thick crustal welt and 60 100 pure shear extension values of 1 6 2 0 during the late cenozoic

robust determination of earthquake source parameters and mantle attenuation 1 an improved inversion technique is needed to effectively separate the frequency dependence of the source from the intrinsic attenuation of the medium we developed a cluster event method cem in which clusters of nearby events instead of individual events pair with stations to form the basis for measurements ofq value and corner frequency fc we assume that the raypaths from one cluster to a station share an identical q while each event in the same cluster is allowed for only one fcin the inversion process this approach largely reduces the degrees of freedom to achieve a robust inversion we use an optimization algorithm of simulated annealing to solve the nonlinear inverse problem the cem was applied to events at 70 150 km depths in the japan subduction zone recorded by f net we show that the method proposed here leads to better constraints on both source parameters and attenuation the resultantq s in the mantle wedge increase from lower than 300 beneath the arc and back arc to greater than 600 in the fore arc region thefc s satisfy a self similar scaling relationship with seismic moment ofm0 fc 3 with a best fit stress drop of 21 9 6 9 mpa in madariaga s form this contrasts to the stress drop of 1 4 1 1 mpa for a global data set composed of prior measurements for crustal events the results of this study agree with results from previous studies except with an upward deviation due to higher corner frequencies and stress drops

southwestward weakening of wyoming lithosphere during the laramide orogeny the mechanism of laramide deformation in the central rocky mountains remains enigmatic it is generally agreed that the deformation resulted from low angle subduction of the farallon plate beneath the north american plate during the latest cretaceous early eocene however recent studies have suggested the importance of slab removal or slab rollback in causing this deformation here we infer wyoming lithosphere structure and surface deformation pattern by conducting 2 d flexural subsidence modeling in order to provide constraints on the mechanism of laramide deformation we assume that wyoming lithosphere behaved as an infinite elastic plate subject to tectonic loading of mountain ranges and conduct 2 d flexural subsidence modeling to major laramide basins to document lithospheric stiffness and mountain load height our results show that the stiffness of wyoming lithosphere varied slightly in each basin during the 30 myr duration of the laramide deformation and decreased from northeastern wyoming te 32 46 km to southwestern wyoming te 6 9 km our results also imply that the increase of equivalent load height of major laramide ranges accelerated during the early eocene we propose that the bending stresses induced by the topographic load of the sevier fold and thrust belt combined with crust mantle decoupling initiated by the overthickened sevier hinterland and the end loads due to the low angle subduction at the western edge of the thick wyoming craton have caused the southwestward decrease of lithospheric stiffness in wyoming moreover we attribute the accelerated load height gain during the early eocene to both dynamic and isostatic effects associated with slab rollback

a depositional model for offshore deposits of the lower blue gate member mancos shale uinta basin utah usa depositional models that use heterogeneity in mud dominated successions to distinguish and diagnose environments within the offshore realm are still in their infancy despite significant recent advances in understanding the complex and dynamic processes of mud deposition six cored intervals of the main body of the mancos shale the lower blue gate member uinta basin were examined sedimentologically stratigraphically and geochemically in order to evaluate facies heterogeneity and depositional mechanisms unique sedimentological and geochemical features are used to identify three offshore environments of deposition the prodelta the mudbelt and the sediment starved shelf prodelta deposits consist of interlaminated siltstone and sandstone and exhibit variable and stressed trace fossil assemblages and indicators of high sedimentation rates the prodelta was dominated by river fed hyperpycnal flow mudbelt deposits consist of interlaminated siltstone and sandstone and are characterized by higher bioturbation indices and more diverse trace fossil assemblages ripples scours truncations and normally graded laminations are abundant in prodelta and mudbelt deposits indicating dynamic current conditions mudbelt sediment dispersal was achieved by both combined flow above storm wave base and current enhanced and wave enhanced sediment gravity flows below storm wave base sediment starved shelf deposits are dominantly siltstone to claystone with the highest calcite and organic content bioturbation is limited to absent sediment starved shelf deposits were the result of a combination of shelfal currents and hypopycnal settling of sediment despite representing the smallest volume sediment starved shelf deposits are the most prospective for shale hydrocarbon resource development due to elevated organic and carbonate content sediment starved shelf deposits are found in either retrogradational to aggradational parasequence sets or early distal aggradational to progradational parasequence sets bounding the maximum flooding surface an improved framework classification of offshore mudstone depositional processes based on diagnostic sedimentary criteria advances our predictive ability in complex and dynamic mud dominated environments and informs resource prospectivity

the influence of soil structure and stress history on the soil water characteristics of a compacted till the soil water characteristic defines the relationship between the soil suction and gravimetric water content w or the volumetric water content or the degree of saturation s theoretical and

tectonic evolution of a laramide transverse structural zone sweetwater arch south central wyoming structural anisotropy of magnetic susceptibility ams and paleomagnetic data record patterns of layer parallel shortening lps vertical axis rotation and regional fault fold evolution across the sweetwater arch a major west to wnw trending basement cored laramide uplift in wyoming the southern arch flank is bounded by a wnw striking reverse fault zone that imbricated basement and cover rocks the northern flank is bounded by a west striking fault zone with a component of strike slip and nw trending en echelon folds and the eastern plunge transitions into an area of multiple trending faults and folds synorogenic strata record major arch uplift from maastrichtian to early eocene time followed by arch collapse lps with development of systematic minor fault sets and ams lineations preceded large scale folding lps directions estimated from both minor fault and ams data were oriented wsw along the northern flank subparallel to laramide regional shortening but were refracted to the ssw along the southern flank and to the west along the eastern arch plunge additional minor faults developed along steep fold limbs during continued shortening with directions remaining ssw along the southern flank but becoming more variable along the eastern plunge where an increasingly heterogeneous stress field developed as additional faults were activated along basement heterogeneities vertical axis rotation was limited along the arch flanks whereas the eastern plunge underwent counterclockwise rotation deflections in shortening directions were partly related to basement heterogeneities including weak supracrustal belts on the arch flanks a strong granitic core and local reactivation of precambrian shear zones

is there seismic attenuation in the mantle article history the small scale heterogeneity of the mantle is mostly due to the mixing of petrological heterogeneities by a smooth but chaotic convection and should consist in a laminated structure marble cake with a power spectrums k varying as 1 k w herekis the wavenumber of the anomalies this distribution of heterogeneities during convective stirring with negligible diffusion called batchelor regime is documented by fluid dynamic experiments and corresponds to what can be inferred from geochemistry and seismic tomography this laminated structure imposes density seismic velocity and potentially anisotropic heterogeneities with similar 1 kspectra a seismic wave of wavenumberk 0 crossing such a medium is partly reflected by the heterogeneities and we show that the scattered energy is proportional tok 0 s 2k 0 t he reduction of energy for the propagating wave appears therefore equivalent to aq uality factor 1 q k 0 s 2k 0 w ith the specif ic 1 kspectrum of the mantle the resulting apparent attenuation should therefore be frequency independent we show that the total contribution of 6 9 rms density velocity and anisotropy would explain the observed s and p attenuation of the mantle although these values are large they are not unreasonable and we discuss how they depend on the range of frequencies over which the attenuation is explained if such a level of heterogeneity were present most of the attenuation of the earth would be due to small scale scattering by laminations not by intrinsic dissipation intrinsic dissipation must certainly exist but might correspond to a larger yet unobservedq this provocative result would explain the very weak frequency dependence of the attenuation and the fact that bulk attenuation seems negligible two observations that have been difficult to explain for 50 years

model for the prediction of shear strength with respect to soil suction experimental studies on unsaturated soils are generally costly time consuming and difficult to conduct shear strength data from the research literature suggests that there is a nonlinear increas

attenuation of broadband p and s waves in tonga observations of frequency dependent q teleseismic broadband recordings of intermediate and deep focus earthquakes are used to quantify both compression q and shear q wave attenuation within the lau backarc basin a spectral ratio method is employed to measure differential attenuation t between the depth phases ss pp and sp and the direct s and p phases over the frequency band 0 05 and 0 5 hz we use a stacking algorithm to combine the spectra of several phase pairs from a single event having similar azimuth and range to obtain more robust t measurements these estimates are then used to compute the average q above the focal depth q and q are measured directly from the ss s and pp p phase pairs respectively however the interpretation of t measured from sp p requires assumptions about the ratio q q we find an empirical ratio of q q 1 93 for this region and use it to compute q and q from the q sp observations

early cretaceous intra arc ductile strain in triassic jurassic and cretaceous continental margin arc rocks peninsular ranges california the cuyamaca laguna mountain shear zone clmsz lies along the axis of the peninsular ranges batholith separating it into an eastern and western plutonic zones the shear zone involves triassic jurassic and early cretaceous plutonic units which intruded the triassic julian schist and transects the eastern edge of a cryptic lithospheric boundary separating oceanic crust on the west from continental crust on the east the julian schist crops out on either side of the cryptic lithospheric boundary and is interpreted to represent an overlap sequence this structural stratigraphic relationship indicates that the contrasting lithospheric types must have been juxtaposed prior to approximately the triassic time and as a result the clmsz probably developed in an intra arc setting at least two periods of deformation produced the polygenetic clmsz structures that formed during d1 include s1 and l1 in triassic jurassic and early cretaceous orthogneisses s1 a pervasive nw striking and ne dipping mylonitic gneissosity obliterates nearly all traces of an older magmatic fabric l1 plunges steeply to the ne lies within the plane of s1 and is locally a well developed stretching lineation d1 structures can be traced from the 115 ma oriflamme canyon protomylonite into the adjacent julian schist and are represented by a well developed s c mylonitic structures indicative of ne sw contraction d1 structures in the oriflamme canyon protomylonite and in the 118 ma pine valley granodiorite developed while these plutons were incompletely solidified hence d1 probably occurred between 118 and 115 ma and had culminated in the 105 my emplacement of the las bancas tonalite normal convergence 125 to 115 ma between the north american and farallon plates is coincident with d1 and the syntectonic emplacement of the pine valley granodiorite and the oriflamme canyon protomylonite this relationship suggests that the mechanically weak thermally and melt softened cryptic lithospheric interface between oceanic and continental lithosphere may have yielded during the normal convergence event resulting in the concentration of strain into the clmsz during arc magmatism such a conclusion underscores the possibility of using intra arc structures to deduce convergence patterns as elegantly argued in several recent papers a 12 km long normal sense shear zone transects d1 structures and formed during d2 mesoscopic structure associated with the normal sense shear zone includes s2 l2 and c2 d2 structures are the record of ne sw extension between 105 and 94 ma they may be related to the vertical loading of the clmsz by the hanging wall block of the westward verging santa rosa and borrego springs mylonite belts or they may represent an early local response to magmatically and structurally overthickened gravitationally unstable crust in the latter interpretation d2 structures are the harbingers of tertiary aged gravity driven collapse of the sw cordilleran margin

upper mantle q structure beneath old seafloor in the western pacific the pacific lithosphere anisotropy and thickness experiment ocean bottom seismometer array south of the shatsky rise allows imaging the attenuation structure of the upper mantle in the oldest parts of the pacific ocean the array consisted of eight seismometers with a lateral extent of 200 km by 600 km intermediate and deep focus earthquake sources in the mariana and izu bonin subduction zones provide paths that probe different depths beneath the seafloor acceleration spectra from the vertical component of p waves are inverted for the attenuation operator and corner frequency pn propagation indicates very high qp values in the lithosphere of order 1000 while path average qp values in the upper mantle are on the order of 400 the variety of source epicentral distances and depths enables us to deduce the vertical qp 1 structure of the upper mantle using the amplitude spectra directly in a weighted least squares problem that accounts for the effects of triplications in the traveltime curves we invert for qp 1 as a function of depth we demonstrate that qp is frequency dependent and adopt a power law dependence with coefficient 0 27 we resolve three distinct layers using a reference frequency of 1 hz with qp on the order of 145 at depths 100 250 km qp on the order of 350 at depths 250 410 km and very high qp with attenuation indistinguishable from zero for depths below 410 km the p waves have a component of scattering and thus qp 1 represents the maximum intrinsic attenuation beneath normal undisturbed oceanic lithosphere

late cretaceous early eocene laramide uplift exhumation and basin subsidence in wyoming crustal responses to flat slab subduction low angle subduction of the farallon oceanic plate during the late cretaceous early eocene is generally considered as the main driver forming the high rocky mountains in wyoming and nearby areas how the deformation was transferred from mantle to upper crust over the great duration of deformation 40 myr is still debated here we reconstruct basin subsidence and compile paleoelevation thermochronology and provenance data to assess the timing magnitude and rates of rock uplift during the laramide deformation we reconstruct rock uplift as the sum of surface uplift and erosion constrained by combining paleoelevation and exhumation with regional stratigraphic thickness and chronostratigraphic information the amount and rate of rock uplift of individual laramide ranges was less than 2 4 4 8 km 0 21 0 32 mm yr during the early maastrichtian paleocene stage 1 and increased to more than 3 km 0 38 0 60 mm yr during the late paleocene early eocene stage 2 our quantitative constraints reveal a two stage development of the laramide deformation in wyoming and an increase of rock uplift during stage 2 associated with enhanced intermontane basin subsidence exhumation and uplift during stage 1 is consistent with eastward migration of cordilleran deformation associated with low angle subduction whereas the change in exhumation during stage 2 seems to follow a southwestward trend which requires an alternative explanation we here suggest that the increase of rock uplift rate during the late paleocene early eocene and the southwestward younging trend of uplift may be a response to the rollback and associated retreating delamination of the farallon oceanic slab

crustal structure in the elko carlin region nevada during eocene gold mineralization ruby east humboldt metamorphic core complex as a guide to the deep crust the deep crustal rocks exposed in the ruby east humboldt metamorphic core complex northeastern nevada provide a guide for reconstructing eocene crustal structure 50 km to the west near the carlin trend of gold deposits the deep crustal rocks in the footwall of a west dipping normal sense shear system may have underlain the pinon and adobe ranges about 50 km to the west before tertiary extension close to or under part of the carlin trend eocene lakes formed on the hanging wall of the fault system during an early phase of extension and may have been linked to a fluid reservoir for hydrothermal circulation the magnitude and timing of paleogene extension remain indistinct but dikes and tilt axes in the upper crust indicate that spreading was east west to northwest southeast perpendicular to a paleozoic and mesozoic orogen that the spreading overprinted high geothermal gradients associated with eocene or older crustal thinning may have contributed to hydrothermal circulation in the upper crust late eocene eruptions upper crustal dike intrusion and gold mineralization approximately coincided temporally with deep intrusion of eocene sills of granite and quartz diorite and shallower intrusion of the harrison pass pluton into the core complex rocks stacked mesozoic nappes of metamorphosed paleozoic and precambrian rocks in the core complex lay at least 13 to 20 km deep in eocene time on the basis of geobarometry studies in the northern part of the complex the presently exposed rocks had been even deeper in the late mesozoic to 30 km depths before losing part of their cover by eocene time nappes in the core plunge northward beneath the originally thicker mesozoic tectonic cover in the north part of the core complex mesozoic nappes and tectonic wedging likely occupied the thickened midlevel crustal section between the deep crustal core complex intrusions and nappes and the overlying upper crust these structures as well as the subsequent large displacement cenozoic extensional faulting and flow in the deep crust would be expected to blur the expression of any regional structural roots that could correlate with mineral belts structural mismatch of the mineralized upper crust and the tectonically complex middle crust suggests that the carlin trend relates not to subjacent deeply penetrating rooted structures but to favorable upper crustal host rocks aligned within a relatively coherent regional block of upper crust

tectonic framework for late cretaceous to eocene quartz gold vein mineralization from the caborca orogenic gold belt in northwestern mexico

role of crustal thickening and extensional collapse in the tectonic evolution of the sevier laramide orogeny western united states the effects of crustal thickening and extensional collapse of continental crust combined with variations in plate convergence forces provide a coherent explanation for evolution of the cretaceous early tertiary sevier laramide orogeny crustal thickening of the sevier laramide hinterland region was triggered by the combination of compressive plate convergence forces and subduction induced conductive heating of the crust eastward progradation of the locus of sevier laramide deformation through time reflects the progressive widening of the region of crustal thickening the region of maximum crustal thickening migrated outward until about 80 to 75 ma when it encountered excessively strong lithosphere of the colorado plateau the locus of deformation was then transmitted laterally across both a hinterland that had attained maximum crustal thickness and the rigid colorado plateau into the laramide rocky mountain foreland an episode of vigorous extensional collapse of orogenically thickened crust affected the southern cordillera between about 75 and 35 ma early tertiary waning of plate convergence rates and continued subduction induced conductive heating of thickened crust allowed extensional collapse along the southern cordillera region to drive the colorado plateau block northward the result was the late laramide phase of rocky mountain foreland deformation because of this compressive deformation in the central and southern laramide rocky mountain region continued through eocene time rather than ceasing at 56 ma as it did in the northern cordillera

the period and q of the chandler wobble summary we have extended our calculation of the theoretical period of the chandler wobble to account for the non hydrostatic portion of the earth s equatorial bulge and the effect of the fluid core upon the lengthening of the period due to the pole tide we find the theoretical period of a realistic perfectly elastic earth with an equilibrium pole tide to be 426 7 sidereal days which is 8 5 day shorter than the observed period of 435 2 day using rayleigh s principle for a rotating earth we exploit this discrepancy together with the observed chandler q to place constraints on the frequency dependence of mantle anelasticity if q in the mantle varies with frequency u as u between 30 s and 14 months and if q in the lower mantle is of order 225 at 30 s we find that 0 04 5 a 5 0 1 1 if instead q in the lower mantle is of order 350 near 200 s we find that 0 11 5 a 0 19 in all cases these limits arise from exceeding the 68 per cent confidence limits of 2 6 day in the observed period since slight departures from an equilibrium pole tide affect the q much more strongly than the period we believe these limits to be robust

insights from scs s measurements on deep mantle attenuation abstract we apply a recently developed method based on the instantaneous frequency to analyze broadband seismic data recorded by the transportable usarray we measure in the frequency band 0 018 0 2 hz about 700 high quality differential scs s anelastic delay times t scs s sampling the mantle below central america and below alaska that we compare to elastic delay times t scs s obtained by cross correlating the s and scs signals we confirm that the instantaneous frequency matching method is more robust than the classical spectral ratio method by a series of careful analyses of the effects of signal to noise ratio source mechanism characteristics and possible phase interferences on measurements of differential anelastic delay times we demonstrate that in order to obtain accurate values of t scs s the seismic records must be rigorously selected in spite of the limited number of data that satisfy our quality criteria we recover using an additional stacking procedure a clear dependence of t scs s on the epicentral distance in the two regions the absence of correlation between the obtained anelastic and elastic delay times indicates a complex compositional thermal origin of the attenuation structure or effects of scattering by small scale structure in accordance with possible presence of subducted material the regional 1 d inversions of our measurements indicate a non uniform lower mantle attenuation structure a zone with high attenuation in the mid lower mantle q 250 and a low attenuation layer at its base q 450 a comparison of our results with low frequency normal model q models is consistent with frequency dependent attenuation with q and 0 1 0 2 i e less attenuation at higher frequencies although possible effects of lateral variations in q in the deep mantle add some uncertainty to these values

effects of wetting drying and stress ratio on anisotropic stiffness of an unsaturated soil at very small strains the very small strain shear modulus of soil g0 is affected by many factors including soil properties current stress state stress history and matric suction very little research has been condu

defect microdynamics in minerals and solid state mechanisms of seismic wave attenuation and velocity dispersion in the mantle the propagation of seismic waves in the earth s mantle can be significantly affected by relaxation processes causing attenuation and velocity dispersion reduction this paper reviews the solid state mechanisms of relaxation processes based on the theory of defect microdynamics in solids together with some experimental observations on defects in minerals particularly in olivine for a given mechanism to have a significant effect on seismic wave propagation both the density and the mobility of the defects must be in an appropriate range the examination of the densities and geometry and mobilities of defects in olivine shows that dislocation and or grain boundary mechanisms can have a significant effect on seismic wave propagation although wide distributions of geometrical factors such as spacing of pinning points and of mobilities are required to explain all available data point defect mechanisms however are unlikely to be important because their densities are too small and or their mobilities are too large since the dislocation density and or grain size are determined in most cases by the long term tectonic stress seismic wave attenuation and velocity dispersion reduction involving these defects are likely to depend on the magnitude of the tectonic stress as well as the temperature theoretical considerations suggest a wide range of dependence of seismic wave attentuation and velocity dispersion on the long term tectonic stress this is particularly the case for dislocation mechanisms and warrants careful experimental investigation dislocations and or grain boundaries cause anelastic behavior relaxation peaks when they are pinned or blocked at some points pinning or blocking becomes ineffective at high temperatures and or low frequencies causing a transition to viscoelastic behavior both laboratory and seismological observations of internal friction are dominated by the high temperature background where internal friction increases monotonically with temperature which can be interpreted as a gradual transition to viscoelastic behavior or to a wide distribution of relaxation times however in most experimental studies to date the dislocation densities or the grain sizes were not well controlled making it difficult to identify the attenuation mechanisms and preventing any quantitative applications to earth the need for better characterization of defect microstructures in experimental specimens is emphasized

the role of mantle delamination in widespread late cretaceous extension and magmatism in the cordilleran orogen western united states extension during plate convergence and mountain building is widely recognized yet the causes of synconvergent extension remain controversial here we propose that delamination of lithospheric mantle aided by decoupling of the crust from the mantle via a reduction in the viscosity of the lower crust through heating incursion of fl uids and partial melting explains many enigmatic yet prevalent aspects of the metamorphic magmatic and kinematic history of the sevier laramide orogen of the western united states during the late cretaceous extension heating anatexis magmatism and perhaps rock uplift were widespread during a restricted time interval in the late cretaceous 75 67 ma along the axis of maximum crustal thickening within the mojave sector of the sevier orogen and to a lesser extent within the interior of the idaho utah wyoming sector to the north similar processes may have been active in the peninsular range sierran western mojave and salinian segments of the mesozoic cordilleran arc these processes are viewed as predictable consequences of the thermal rheological and dynamic state of the overlying crust following delamination of mantle lithosphere beneath isostatically compensated mountain belts the proposed delamination would have occurred immediately prior to eastward propagation of lowangle subduction of the farallon plate during the inception of the laramide orogeny following delamination extension and anatexis of the north american crust were aided locally by egress of slab derived fl uids from the low angle farallon slab we suggest that lithospheric delamination may have aided in the shallowing of the slab to achieve lowangle subduction geometry delamination has been proposed to be common in areas of thickened continental lithosphere in the terminal phase or late in orogenesis the late cretaceous delamination event proposed here for the sevier laramide orogen occurred during protracted plate convergence and was synchronous with and followed by continued shortening in the external part of the orogen

shear wave attenuation and dispersion in melt bearing olivine polycrystals 2 microstructural interpretation and seismological implications 1 the torsional forced oscillation tests of melt bearing olivine aggregates reported by jackson et al 2004 consistently show a peak in attenuation that is absent from melt free aggregates tested under similar conditions and grain sizes characterization by sem shows that the melt resides in triple junction tubules and larger pockets as previously described tem imaging and eds analysis reveals that olivine olivine grain boundaries are characterized by a region 1 nm wide which is structurally and chemically distinct from olivine grain interiors from the possible mechanisms that can produce an anelastic attenuation peak melt squirt can be eliminated for our samples and experimental conditions we attribute the observed attenuation peak to elastically accommodated grain boundary sliding requiring that the grain boundaries are weak relative to olivine grain interiors but have a significantly higher viscosity than bulk melt while the nanometer scale grain boundary structure in the melt bearing aggregates is essentially the same as for melt free aggregates studied previously elastically accommodated sliding in the latter is apparently inhibited by tight three grain edge intersections the exponentially increasing high temperature background attenuation in both types of aggregate is attributed to diffusionally accommodated grain boundary sliding extrapolation to mantle grain sizes shows that the broad peak may be responsible for nearly frequency independent attenuation in partially molten regions of the upper mantle

layer parallel shortening across the sevier fold thrust belt and laramide foreland of wyoming spatial and temporal evolution of a complex geodynamic system abstract varying patterns of layer parallel shortening lps and vertical axis rotations from the thin skin sevier fold thrust belt to the thick skin laramide foreland of wyoming are quantified from integrated structural anisotropy of magnetic susceptibility ams and paleomagnetic analyses within the sevier belt widespread early lps was accommodated by spaced cleavage fracture sets minor folds and minor faults lps directions are subperpendicular to structural trends of systematically curved thrust sheets of the wyoming salient reflecting a combination of primary dispersion and secondary rotation during thrusting within the laramide foreland limited lps was accommodated mostly by minor faults with conjugate wedge and strike slip geometries lps directions in gentler fold limbs vary from perpendicular to acute with structural trends of variably oriented anastomosing basement cored arches steep forelimbs display more complex relations including younger fault sets that developed during evolving stress states and localized vertical axis rotations although internal strain is limited weak ams lineations defined by kinked and rotated phyllosilicates are widely developed and consistently oriented perpendicular to measured lps directions palinspastically restored lps directions corrected for paleomagnetically determined vertical axis rotations vary on average from w e in the sevier belt to wsw ene in the laramide foreland in detail lps directions display deflections related to primary sedimentary wedge geometry and basement fabrics lps in the sevier belt is interpreted to partly reflect stress transmitted from the hinterland through the growing orogenic wedge and topographic stress along the front of the wedge lps in the laramide foreland is interpreted to partly reflect basal traction during flat slab subduction beneath thick cratonic lithosphere with spatial temporal variations in stress trajectories related to basement heterogeneities and evolving fault systems evidence for significant late n s laramide shortening as proposed by multi stage shortening models is not observed

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

intracontinental orogeny enhanced by far field extension and local weak crust the accommodation of intraplate stresses in preexisting weak regions of plate interiors is here investigated using thin viscous sheet numerical models the intraplate stresses are governed by multicomponent and multidirectional stresses originating at plate boundaries the modeled scenarios mimic plate boundary conditions during the intraplate alice springs orogeny aso central australia and include 1 a northwest southeast zone of weak lithosphere within strong continental blocks to the north and southand 2 a principal south directed stress condition at the northern boundary that causes minor clockwise rotation of the northern block alternative tectonic environments are investigated in additional models that include 1 secondary compressional or extensional stresses acting at the eastern boundary representing the temporally variable stress conditions during the tasmanides orogeny and 2 an eastern wedge shaped zone of rheologically weak lithosphere mirroring rift fill of the irindina subbasin our results highlight that a low angle between major crustal features e g orogenic elongation and preexisting regional structures and the principal transmitted stresses is highly relevant in the concentration of elevated levels of differential stress and subsequent localization of deformation in plate interiors secondary stresses orthogonal to the principal acting stresses may introduce effects that explain the episodic orogenic activity in the case of the aso the combination of secondary extensional stresses at the eastern boundary of australia and weak lithosphere of the preexisting irindina subbasin strongly influences the observed spatial strain intensity localization and kinematics of deformation during the aso

tessera terrain on venus a survey of the global distribution characteristics and relation to surrounding units from magellan data the tessera terrain on venus comprised of areas of high radar backscatter complex deformation patterns relative to other units and topography standing higher than surrounding plains covers 35 33 106 km2 about 8 of the surface of venus and is nonrandomly distributed being preferentially located at equatorial and higher northern latitudes with a distinct paucity below about 30 s individual tessera occurrences range in area from the lower limits of our measurements about 200 km2 up to the largest tessera ovda with an area of about 8 6 106 km2 or about 2 of the surface area of venus the size frequency distribution of tessera patches is strongly unimodal and skewed toward smaller sizes reflecting the great abundance of small tessera fragments modes of occurrence include 1 large clusters e g aphrodite terra and ishtar terra 2 arc like segments which may extend for thousands of kilometers and are either concave inward toward the major tessera cluster development or away from it 3 areas where tesserae are rare or absent which occur both as low lying plains e g guinevere planitia and as elevated regions e g atla regio tessera terrain has a bimodal elevation frequency distribution with the main peak at about 0 1 km and an additional peak at about 3 km above mean planetary radius in terms of number of occurrences however tesserae do not display a correlation with elevation at the global scale since small tessera patches commonly occupy low lying regions although tessera exhibit a range of gravity signatures many occurrences are interpreted to represent relatively shallow crustal levels of compensation tessera boundaries include type i sinuous embayed dominated by adjacent lava plains embaying tessera massifs 73 of total tesserae boundaries and type ii linear tectonic only a small percentage of the length of all boundary types show no lava embayment and could be interpreted as tectonically active for long periods subsequent to initial tessera formation occurrence of broad slopes of post tessera embayed plains away from tessera boundaries suggests that regional tilting occurred subsequent to final tessera deformation in some places several lines of evidence suggest the possibility that a widespread tessera like basement comprising at least 55 of the surface of venus is buried under a cover of lava plains a few hundred meters to as much as 2 4 km thick a wide variety of deformational structures and patterns is observed within the tessera including those representing extension compression shear and transpression in some cases the apparently complex patterns can be resolved into single event kinematic interpretations involving noncoaxial deformation e g itzpapalotl while in other cases polyphase deformation is more likely e g central ovda and thetis where relations can be determined stratigraphically earliest deformation within the tessera is primarily related to crustal shortening and compression phase i followed by pervasive extensional deformation commonly oriented normal to the strike of phase i features generally along the same principal stress direction phase ii evidence also exists for the contemporaneous formation of these distinctive deformation patterns lava plains within and adjacent to the tessera embay both of these fabrics but sometimes overlap in time with phase ii extensional deformation and with regional tilting tessera terrain as a geologic unit occupies the lowest portion of the stratigraphic column in all areas that we have observed an observation consistent with many other mapping studies we see no evidence for transitional stages between tessera and volcanic rises and or lowlands that might represent a long term sequence of upwelling or downwelling followed by crustal deformation and tessera formation no impact craters deformed by phase i deformation have yet been observed on tessera suggesting that phase i tessera deformation sufficiently intense to eradicate earlier impact craters ceased relatively abruptly somewhat before 300 500 m y ago however the starting time and thus duration of tessera formation is unknown on the basis of the very small number of on tessera craters deformed by phase ii extensional deformation this period probably did not last more than several tens of millions of years after the cessation of phase i little observable deformation of the tessera terrain appears to have taken place in the last several hundred million years during which time the vast volcanic plains were emplaced although tilting of early plains along some tessera margins is observed building on the global synthesis presented here future analyses of individual tessera occurrences will provide the detailed descriptions kinematic interpretations and strain histories necessary to assess and distinguish between the several catastrophic and uniformitarian models for tessera formation

p wave attenuation in the pacific slab beneath northeastern japan revealed by the spectral ratio of intraslab earthquakes abstract we investigate p wave attenuation q p 1 in the pacific slab beneath northeastern ne japan adopting for the first time the spectral ratio technique for intraslab earthquakes when seismograms of two earthquakes are recorded at a station and their ray paths to the station are largely overlapped station dependent amplification and structural effects on the overlapped rays can be canceled out from the ratio of the spectral amplitudes of the seismograms therefore adopting the spectral ratio technique for intraslab earthquakes has a great advantage for the precise evaluation of q p 1 in the slab because the structural effects above the slab including the high attenuation mantle wedge are removed for estimating the intraslab q p 1 we determined corner frequency of the intraslab earthquakes using the s coda wave spectral ratio as the first step then we evaluated the inter event path attenuation t from the ratio of the spectral amplitudes of p waves the obtained result shows that p wave attenuation in the pacific slab marks q p 1 of 0 0015 q p of 670 at depths of 50 250 km this indicates that the p wave attenuation in the pacific slab is weaker than that in the mantle wedge the relatively high q p 1 is correlated with the distributions of intraslab earthquakes suggesting that the p wave amplitude is more attenuated around active seismicity zones in the slab therefore our observations likely indicate the presence of fractures hydrous minerals and dehydrated fluid around seismogenic zones in the slab at intermediate depths

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

fracture network of the ferron sandstone member of the mancos shale east central utah usa abstract the fracture network at the outcrop of the ferron sandstone member of the mancos shale was studied to gain an understanding of the tectonic history of the region and to contribute data to studies of gas and water transmissivity related to the occurrence and production of coal bed methane about 1900 fracture readings were made at 40 coal outcrops and 62 sandstone outcrops in the area from willow springs wash in the south to farnham dome in the north of the study area in east central utah two sets of regional vertical to nearly vertical systematic face cleats were identified in ferron coals a northwest striking set trends at a mean azimuth of 321 and a northeast striking set has a mean azimuth of 55 cleats were observed in all coal outcrops examined and are closely spaced and commonly coated with thin films of iron oxide two sets of regional systematic joint sets in sandstone were also identified and have mean azimuths of 321 and 34 the joints of each set are planar long and extend vertically to nearly vertically through multiple beds the northeast striking set is more prevalent than the northwest striking set in some places joints of the northeast striking set occur in closely spaced clusters or joint zones flanked by unjointed rock both sets are mineralized with iron oxide and calcite and the northwest striking set is commonly tightly cemented which allowed the northeast striking set to propagate across it all cleats and joints of these sets are interpreted as opening mode mode i fractures abutting relations indicate that the northwest striking cleats and joints formed first and were later overprinted by the northeast striking cleats and joints burial curves constructed for the ferron indicate rapid initial burial after deposition the ferron reached a depth of 3000 ft 1000 m within 5 2 million years m y and this is considered a minimum depth and time for development of cleats and joints the sevier orogeny produced southeast directed compressional stress at this time and is thought to be the likely mechanism for the northwest striking systematic cleats and joints the onset of the laramide orogeny occurred at about 75 ma within 13 7 m y of burial and is thought to be the probable mechanism for development of the northeast striking systematic cleats and joints uplift of the ferron in the late tertiary contributed to development of butt cleats and secondary cross joints and probably enhanced previously formed fracture sets using a study of the younger blackhawk formation as an analogy the fracture pattern of the ferron in the subsurface is probably similar to that at the surface at least as far west as the paradise fault and joe s valley graben farther to the west on the wasatch plateau the orientations of ferron fractures may diverge from those measured at the outcrop

thermal modelling of the laramide orogeny testing the flat slab subduction hypothesis abstract the laramide orogeny is the late cretaceous to palaeocene 80 55 ma orogenic event that gave rise to the rocky mountain fold and thrust belt in canada the laramide block uplifts in the usa and the sierra madre oriental fold and thrust belt in mexico the leading model for driving laramide orogenesis in the usa is flat slab subduction whereby stress coupling of a subhorizontal oceanic slab to the upper plate transmitted stresses eastwards producing basement cored block uplifts and arc magmatism in the foreland the thermal models presented here indicate that arc magma generation at significant distances inboard of the trench 600 km during flat slab subduction is problematic this conclusion is consistent with the coincidence of volcanic gaps and flat slab subduction at modern convergent margins lawsonite eclogite xenoliths erupted through the colorado plateau in oligocene time are inferred to originate from the subducted farallon slab and indicate that the laramide flat slab subduction zone was characterised by a cold thermal regime thermal modelling indicates that this regime can be produced by flat slab subduction of old 50 myr oceanic lithosphere at high convergence rates in the canadian and mexican portions of the laramide orogen the coeval development of a magmatic arc within 300 km of the trench refutes the existence of flat slab subduction in these regions it is proposed that subduction of an oceanic plateau aseismic ridge may have overcome the negative buoyancy inherent in old oceanic lithosphere and resulted in a spatially restricted zone of flat slab subduction in the usa these findings cast doubt on the flat slab model as a primary means of driving laramide orogenesis along its entire length and instead point to the need for an alternative mechanism for cordilleran wide laramide orogenesis

nazca south america interactions and the late eocene late oligocene flat slab episode in the central andes 1 the most prominent features of the andean range are the altiplano and puna plateaus which were constructed by crustal shortening and uplift over the past 45 myr the early construction of these plateaus may have controlled subsequent growth of the orogen proposed models have suggested that an abrupt acceleration in relative motion between the nazca plate and the south american plate at 30 ma may have led to compression of the continent however the major plate motion change occurred at 25 23 ma and paleomagnetic rotations and crustal shortening of the andean forearc require that the arica bend formed prior to about 25 ma inferred history of flat slab subduction along the altiplano section of the andean margin and the structure of the adjacent south american cratonic shield combine to suggest an alternate scenario based partly upon geodynamic models of oceanic continental plate interactions in subduction zones we propose that central andean tectonism may have been controlled by two distinct regimes of subduction 1 oblique subduction along the central andean margin during the late eocene and oligocene accompanied by downdip alignment with the center of the amazonian shield flat slab activity in this phase of orogenesis may have been caused by a combination of cratonic root enhanced tectonics and oceanic plateau subduction and 2 an abrupt transition to trench normal subduction after 25 ma toward the more distal sao francisco craton was accompanied by a return to normal angle subduction similar interactions are hypothesized to have occurred during the laramide orogeny in western north america

on the anelastic contribution to the temperature dependence of lower mantle seismic velocities abstract there is little agreement regarding the importance of anelastic contributions to the temperature dependence of seismic wave velocities some studies consider the anelastic contribution to be negligible whereas others argue that it may be as important as the purely elastic contribution in order to evaluate these claims we review physically plausible models for mantle relaxation processes and construct a model of activation enthalpy based on solid state physics as well as on recent experimental results we then deduce self consistent 1 d q profiles and evaluate the anelastic contribution to the temperature dependence of v s and v p physically plausible values of activation enthalpies yield anelastic contributions that increase with depth and account for at least 20 of the velocity temperature derivatives at 2600 km we show that anelasticity may significantly moderate temperature variations in hot slow velocity zones this suggests that inferred lateral changes in temperature as well as arguments regarding the presence of chemical heterogeneity and or temperature induced phase transformations are likely to be significantly affected by anelastic effects in the mantle we also compute values of the dimensionless parameters r s p r s and r s we find that anelasticity can either increase or decrease r s p but the magnitude of the correction of the order of 15 is smaller than the uncertainty in the elastic value anelasticity cannot change the sign of r s and r s but it can decrease their values by as much as 50 however given current uncertainties in seismic and mineral data the effects of anelasticity on the dimensionless parameters do not bring any quantitative constraints on lateral variations of temperature chemical composition and or mineral phase

dissipation at tidal and seismic frequencies in a melt free moon 1 we calculate viscoelastic dissipation in the moon using a rheological extended burgers model based on laboratory deformation of melt free polycrystalline olivine lunar temperature structures are calculated assuming steady state conduction with variable internal heat production and core heat flux successful models can reproduce the dissipation factor q measured at both tidal and seismic frequencies and the tidal love numbers h2 and k2 without requiring any mantle melting however the frequency dependence of our modelqat tidal periods has the opposite sign to that observed using the apparently unrelaxed nature of the core mantle boundary cmb the best fit models require mantle grain sizes of 1 cm and cmb temperatures of 1700 k if melt or volatiles are present the lunar temperature structure must be colder than our melt free models we estimate a present day mantle heat production rate of 9 10 nwm 3 suggesting that roughly half of the moon s radiogenic elements are in the crust