Search

We present geochemical data from the first samples of spring fluids from Dorado Outcrop, a basaltic edifice on 23 M.y. old seafloor of the Cocos Plate, eastern Pacific Ocean. These samples were collected from the discharge of a cool hydrothermal system (CHS) on a ridge flank, where typical reaction temperatures in the volcanic crust are low (2–20 °C) and fluid residence times are short. Ridge-flank hydrothermal systems extract 25% of Earth's lithospheric heat, with a global discharge rate equivalent to that of Earth's river discharge to the ocean; CHSs comprise a significant fraction of this global flow. Upper crustal temperatures around Dorado Outcrop are ∼15 °C, the calculated residence time is <3 y, and the composition of discharging fluids is only slightly altered from bottom seawater. Many of the major ions concentrations in spring fluids are indistinguishable from those of bottom seawater; however, concentrations of Rb, Mo, V, U, Mg, phosphate, Si and Li are different. Applying these observed differences to calculated global CHS fluxes results in chemical fluxes for these ions that are ≥15% of riverine fluxes. Fluxes of K and B also may be significant, but better analytical resolution is required to confirm this result. Spring fluids also have ∼50% less dissolved oxygen (DO) than bottom seawater. Calculations of an analytical model suggest that the loss of DO occurs primarily (>80%) within the upper basaltic crust by biotic and/or abiotic consumption. This calculation demonstrates that permeable pathways within the upper crust can support oxic water–rock interactions for millions of years. [ABSTRACT FROM AUTHOR]

Many species of planktonic foraminifera show distinct banding in the intratest distribution of Mg/Ca. This heterogeneity appears biologically controlled and thus poses a challenge to Mg/Ca paleothermometry. The cause of this banding and its relation with chamber formation are poorly constrained and most of what we know about intratest Mg/Ca variability stems from culture studies of tropical, symbiont-bearing foraminifera. Here we present data on the non-spinose, symbiont-barren Neogloboquadrina pachyderma from the subpolar North Atlantic where wintertime mixing removes vertical gradients in temperature and salinity. This allows investigation of biologically controlled Mg/Ca intratest variability under natural conditions. We find that intratest Mg/Ca varies between <0.1 and 7 mmol/mol, even in winter specimens. High Mg/Ca bands occur at the outer edge of the laminae, indicating reduced Mg removal at the end of chamber formation. Our data thus provide new constraints on the timing of the formation of such bands and indicate that their presence is intrinsic to the chamber formation process. Additionally, all specimens are covered with an outer crust consisting of large euhedral crystals. The composition of the crust is similar to the low Mg/Ca bands in the laminar calcite in winter and summer specimens, indicating a tight biological control on crust formation and composition. Nevertheless, despite high intratest variability, the median Mg/Ca of summertime tests is higher than that of wintertime tests. This provides support for Mg/Ca paleothermometry, but to improve the accuracy of paleotemperature estimates biological effects on Mg incorporation need to be better accounted for. [ABSTRACT FROM AUTHOR]

West–east extension is a prominent tectonic feature of southern and central Tibet despite ongoing north–south (N–S) convergence between India and Eurasia. Knowledge of deep structure beneath the N–S trending rifts is key to evaluating models proposed for their origin, including gravitational collapse, oblique convergence along the arcuate plate boundary, and mantle upwelling. We model direct S and Moho-reflected SsPmp phases at teleseismic distances to constrain variations in crustal thickness across the major rifts crossed by a ∼900-km long, W–E broadband array in the Lhasa Terrane. Crustal thicknesses are ∼70–80 km. However, Moho depth decreases by ∼10 km within a horizontal distance of 100 km west of the Yadong–Gulu rift (YGR) and Nyainquentanghla mountains (NQTL). This Moho uplift, taken with deep, extensional focal mechanisms and reduced seismic velocity in the upper mantle, suggests that asthenospheric upwelling has significantly contributed to the pattern of extension across the YGR and NQTL. The ∼100-km separation between surface rift and Moho uplift is likely enabled by partial decoupling across a ductile middle crust. [ABSTRACT FROM AUTHOR]

Combined U–Pb and Lu–Hf isotope data from zircon populations are widely used to constrain Hadean–Archean crustal evolution. Linear Hf isotope-age arrays are interpreted to reflect the protracted, internal reworking of crust derived from the (depleted) mantle during a short-lived magmatic event, and related 176 Lu/ 177 Hf ratios are used to constrain the composition of the reworked crustal reservoir. Results of this study, however, indicate that Hf isotope-age arrays can also result from complex geodynamic processes and crust–mantle interactions, as shown by U–Pb and Lu–Hf isotope analyses of zircons from well characterized granitoids of the Pietersburg Block (PB), northern Kaapvaal Craton (South Africa). Apart from scarce remnants of Paleoarchean crust, most granitoids of the PB with ages between 2.94 and 2.05 Ga ( n = 32 ) define a straight Hf isotope-age array with low 176 Lu/ 177 Hf of 0.0022, although they show a wide compositional range, were derived from various sources and emplaced successively in different geodynamic settings. The crustal evolution occurred in five stages: (I) predominately mafic crust formation in an intra-oceanic environment (3.4–3.0 Ga); (II) voluminous TTG crust formation in an early accretionary orogen (3.0–2.92 Ga); (III) internal TTG crust reworking and subduction of TTG-derived sediments in an Andean-type setting (2.89–2.75 Ga); (IV) (post-)collisional high-K magmatism from both mantle and crustal sources (2.71–2.67 Ga); and (V) alkaline magmatism in an intra-cratonic environment (2.05–2.03 Ga). The inferred array results from voluminous TTG crust formation during stage II, and involvement of this crust during all subsequent stages by two different processes: (i) internal crust reworking through both partial melting and assimilation at 2.89–2.75 Ga, leading to the formation of biotite granites coeval with minor TTGs, and (ii) subduction of TTG-derived sediments underneath the PB, causing enrichment of the mantle that subsequently became source for high-K granitoids and mafic rocks at 2.68 and 2.05 Ga. Some scatter along the array might have resulted either from significant assimilation of ancient crust, intracrustal Lu/Hf fractionation or melting of heterogeneous mantle sources. Those results show that without any information about the nature and composition of zircon-hosting granitoids, Hf isotope-age data are of limited use to constrain Hadean–Archean magmatogenesis and geodynamics. [ABSTRACT FROM AUTHOR]

Abstract: Subduction is driven by the negative buoyancy of the slab, which depends on both the temperature and composition of the lithospheric plate. In the case of subduction of an oceanic plateau, larger thickness of the lower-density crust and harzburgite layers can locally decrease the negative buoyancy available to drive subduction. However, the ability of a plateau to have an impact on subduction depends on the total buoyancy of the slab, and therefore also depends on size of the plateau and the basalt to eclogite transition, which substantially increases the density of the crust. Using 2-D numerical finite element models of subduction, we investigate the role of eclogitization and oceanic plateau size (thickness and length) in the process of oceanic plateau subduction. Model results show that eclogitization of the crust substantially increases the chances that a plateau will be subducted because the extra buoyancy of larger plateaus is lost through the phase transition. For kinematically driven models, all plateaus are subducted regardless of the thickness or width. Extrapolation of these results to 3-D geometry shows that sufficient slab buoyancy is available to sustain subduction for narrow plateaus with slab widths 6–7 times the plateau width (depending on plateau thickness and length). In dynamically driven models, subduction of oceanic plateaus of various sizes can substantially slow subduction, and large plateaus ( long and thick) can lead to break-off of the slab and underplating of the plateau. [Copyright &y& Elsevier]

Abstract: Geomorphic and structural features of southern Peru (14–18°S) provide strong evidence for distributed crustal deformation along range-sub-parallel contractile structures. We use in situ produced cosmogenic radionuclides, in conjunction with field and remote mapping, to determine the ages of geomorphic features and find (1) ancient surfaces (>1Ma) preserved as a result of very low surface erosion rates, (2) young (∼30ka) low-relief pediment surfaces developed during recent landscape modifications, (3) active tectonic structures accommodating compressional stresses, and (4) Pleistocene river incision rates of ∼0.3mm/yr consistent with longer-term rates. In this region of southern Peru, the steep western wedge (trench to arc area) of the Andean margin presently maintains the high topography of the Altiplano through a combination of uplift and contractile deformation along steep east-dipping faults and isostatic responses to the focused removal of large amounts of crustal material through canyon incision. [Copyright &y& Elsevier]

Abstract: The magnitude of fault offset, a key parameter of fault geometry and kinematics, provides critical information on the role of the Karakoram fault (KKF) in accommodating deformation of the Tibetan crust. Geologic markers used for estimating the magnitude of offset along the KKF include: (1) geomorphologic features, (2) correlative stratigraphic sequences, (3) ophiolite melange belts, (4) igneous bodies, and (5) regional fault systems. The debated offsets of the KKF range from 40km to as much as 1000km. Conflicting offsets may result from a lack of available offset correlations based on quantitative measurements. The Kunsha granite and the Ayilari granite provide another set of potential markers for estimating the offset along the KKF. U–Pb zircon ages and textural observations provide the basis for correlating these granites. Zircon U–Pb ages show that both the Kunsha granite and the South Ayilari granite crystallized around 50Ma ago, whereas the North Ayilari granite formed mostly around 20Ma ago. Reconstruction of batholiths on two sides of the Namru–Menshi basin, as well as the Yalung–Zangbo suture and the trace of the South Kailas thrust, show the offset along the KKF to be about 52±2km. The chronologic data appear to preclude a 100km offset, based on the correlation between the North Ayilari granite and the Kunsha granite. Our data further disproves the conjecture that the North Ayilari granite is synkinematic granite of the KKF, and thus contradicts a 280–400km ophiolite melange belt offset, since it is based on the an incorrect fault initiation time. We calculate a slip rate of 4.5±0.1mm/yr since 12Ma, which implies that the average long-term slip rate is low. This does not support the lateral extrusion model, which predicts a high slip rate. It does support the concept that the collision between India and Eurasia proceeded by distributed deformation rather than lateral extrusion along faults that bound a rigid Tibet. [Copyright &y& Elsevier]

Abstract: Basalts of the Paraná continental flood basalt (PCFB) province erupted through dominantly Proterozoic continental crust during the Cretaceous. In order to examine the mantle source(s) of this major flood basalt province, we studied Os, Sr, Nd, and Pb isotope systematics, and highly siderophile element (HSE) abundances in tholeiitic basalts that were carefully chosen to show the minimal effects of crustal contamination. These basalts define a precise Re–Os isochron with an age of 131.6±2.3Ma and an initial 187Os/188Os of 0.1295±0.0018 (γ187Os=+2.7±1.4). This initial Os isotopic composition is considerably more radiogenic than estimates of the contemporary Depleted Mantle (DM). The fact that the Re–Os data define a well constrained isochron with an age similar to 40Ar/39Ar age determinations, despite generally low Os concentrations, is consistent with closed-system behavior for the HSE. Neodymium, Sr, and Pb isotopic data suggest that the mantle source of the basalts had been variably hybridized by melts derived from enriched mantle components. To account for the combined Os, Nd, Sr, and Pb isotopic characteristics of these rocks, we propose that the primary melts formed from metasomatized asthenospheric mantle (represented by arc-mantle peridotite) that underwent mixing with two enriched components, EM-I and EM-II. The different enriched components are reflected in minor isotopic differences between basalts from southern and northern portions of the province. The Tristan da Cunha hotspot has been previously suggested to be the cause of the Parana continental flood basalt magmatism. However, present-day Tristan da Cunha lavas have much higher 187Os/188Os isotopic compositions than the source of the PCFB. These data, together with other isotopic and elemental data, preclude making a definitive linkage between the Tristan plume and the PCFB. [Copyright &y& Elsevier]

Abstract: Subduction zones play a fundamental role in the geochemical cycle of carbon, and related arc volcanism is believed to exert primary control on atmospheric CO2 concentrations over geological time. Arc volcanism may have been particularly important in the most recent Greenhouse of the late Cretaceous, where it has been hypothesized that the subduction of the carbonate-rich Tethys contributed to overall higher volcanic CO2 outgassing rates and thus a warmer climate. To test this hypothesis, the decarbonation efficiencies of modern subduction zones were calculated through a geochemical database that compared subaerial arc CO2 fluxes with the subducting crust and sediment geochemistry. The modern data are used to postulate a CO2 recycling and degassing scenario for arc volcanism related to the closure of the Tethys. Our analysis indicates that the thermal structure of subduction zones controls the extent and depth of slab decarbonation, while the sediment geochemistry (e.g. the amount of carbonate sediment) may be of secondary importance. The calculated decarbonation efficiency of modern arcs ranges from 18 to 70%. Our calculations support recent models predicting carbon recycling through infiltration-driven decarbonation, and limited by water availability at sub-arc depths. This analysis allows us to make inferences about the potential volcanic CO2 flux from subduction of the Tethys during the Cretaceous, suggesting between an 8 and 222% increase over modern CO2 outgassing. We suggest that the primary reason for the increase in CO2 outgassing in the Cretaceous is contamination of arc magmas by platform carbonates in the overlying crust and increased decarbonation efficiency. [Copyright &y& Elsevier]

Abstract: The rate of earthquake occurrence varies by many orders of magnitude in a given region due to variations in the stress state of the crust. Our focus here is on variations in seismicity rate triggered by transient aseismic processes such as fluid flow, fault creep or magma intrusion. While these processes have been shown to trigger earthquakes, converting observed seismicity variations into estimates of stress rate variations has been challenging. Essentially aftershock sequences often obscure changes in the background seismicity rate resulting from aseismic processes. Two common approaches for estimating the time dependence of the underlying driving mechanisms are the stochastic Epidemic Type Aftershock Sequence model (ETAS) [Ogata, Y., (1988), Statistical models for earthquake occurrences and residual analysis for point processes, J. Am. Stat. Assoc., 83, 9–27.] and a physical approach based on the rate- and state-model of fault friction [Dieterich, J., (1994), A constitutive law for rate of earthquake production and its application to earthquake clustering, J. Geophys. Res., 99, 2601–2618.]. The models have different strengths that could be combined to allow more quantitative studies of earthquake triggering. To accomplish this, we identify the parameters that relate to one another in the two models and examine their dependence on stressing rate. A particular conflict arises because the rate–state model predicts that aftershock productivity scales with stressing rate while the ETAS model assumes that it is time independent. To resolve this issue, we estimate triggering parameters for 4 earthquake swarms contemporaneous with geodetically observed deformation transients in various tectonic environments. We find that stressing rate transients increase the background seismicity rate without affecting aftershock productivity. We then specify a combined model for seismicity rate variations that will allow future studies to invert seismicity catalogs for variations in aseismic stressing rates. [Copyright &y& Elsevier]

Abstract: Direct measurement of a contact area using pressure-sensitive film was performed for artificially generated granite tensile fractures, with different shear displacements of 2, 3, and 5 mm and at various normal stresses of up to approximately 100 MPa, to clarify the relationship between anisotropic flow and normal stress in a rock fracture with shear displacement. Aperture distributions with contact areas were then numerically generated using fracture surface geometry data, and anisotropic flow was evaluated through a bi-directional flow simulation. The directional distributions of contacting asperities in the fracture plane were clearly observed for every given condition and the contacting asperities tended to align in the direction perpendicular to shear displacement. Generally, the contact area increased and the anisotropic distribution was enhanced with increasing normal stress. However, the contact areas for ≥3 mm shear displacement were less stress dependent. Anisotropic flow with higher permeability in the perpendicular direction was always observed for aperture distributions with an anisotropic distribution of the contacting asperities. Flow paths created in the aperture distributions seemed less tortuous in the perpendicular direction due to the distribution of the contacting asperities. The anisotropic flow was enhanced with increasing normal stress to the fracture, and was more evident for the smaller shear displacements of 2 mm due to the high sensitivity of the contact area to the normal stress. The results suggested that the anisotropic flow was likely for a wide range of normal stresses (and correspondingly, at varying depths in the Earth''s crust), at which anisotropic flow was enhanced with increasing normal stress based on the stress dependence of the contact area. In addition, the stress dependent anisotropic flow is expected for much higher normal stresses because complete fracture closure with 100% contact area may be unexpected under the crustal stress conditions at depths of several to ten thousand meters. [Copyright &y& Elsevier]

Abstract: This experimental study examines the solubility of rutile in silicate melts and presents a model for rutile saturation as a function of temperature, pressure and melt composition. Rutile saturation experiments were carried out in the system SiO2–TiO2–Al2O3–MgO–CaO–Na2O–K2O at 1 bar to 35 kbar and 1150 to 1450 °C on model rhyodacite (∼69 wt.% SiO2) and haplobasalt (∼54 wt.% SiO2) base melt compositions. At rutile saturation, the concentration of TiO2 in the model rhyodacite base melt increases at 1 bar from 3.27±0.03 wt.% at 1150 °C to 13.88±0.04 wt.% at 1450 °C. At 1350 °C it decreases from 8.89±0.08 wt.% at 1 bar to 2.06±0.13 wt.% at 35 kbar. Rutile solubility is significantly higher in the haplobasalt base melt at a given pressure and temperature. The concentration of TiO2 in rutile-saturated haplobasalt increases at 1 bar from 20.9±0.3 wt.% at 1300 °C to 39.0±0.3 wt.% at 1450 °C. At 1350 °C it decreases from 25.8±0.3 wt.% at 1 bar to 15.67±0.16 wt.% at 15 kbar. Results from these experiments were combined with data from the literature to formulate a model for rutile saturation in silicate melts. Application of this model to partial melting of MORB-type eclogite indicates that beneath volcanic arcs low-degree, hydrous partial melts of rutile-bearing subducted oceanic crust contain only ∼600 ppm TiO2. Therefore, rutile will remain as a residual phase in the eclogite and the amount of TiO2 that will be transferred to the mantle wedge will be small because so little TiO2 is dissolved in the melt. Partial melting of recycled oceanic crust in an upwelling mantle plume can exhaust rutile from the residual solid at moderate degrees of partial melting (∼22%). The retention of rutile in subducted oceanic lithosphere during dehydration and/or partial melting, combined with exhaustion of rutile during partial melting of eclogite in mantle plumes suggests that HFSE enrichments in recycled crust that were established during subduction may be detectible in OIB. [Copyright &y& Elsevier]

Abstract: Hydrogenous ferromanganese crust deposits on seafloor and volcanic seamounts are archives of past isotopic compositions of the ocean. Isotopic compositions of long-life radiogenic isotopes that are dissolved in the ocean such as Nd and Pb, are mixtures of different erosion products (continents, volcanics arcs, ridges etc…) transported by oceanic currents or winds. Isotopic studies on Mn crusts are thus potential paleogeographic and paleoceanographic tracers. However, global paleogeography can drastically evolve over the period of growth of crust, as well as the latitude, longitude and water depth of the Mn crust. Thus each crust sampled a succession of geographic sites related to its spatial evolution through time. For this reason, valid information about the past ocean isotopic composition can only be extracted from Mn crust under the condition that the successive paleogeographic and paleodepth positions can be reconstructed for each Mn crust. We followed this approach for six hydrogenous Mn crusts from the Pacific Ocean that have recorded Pb and Nd isotopic signals for the past 80 Myr. The evolution of the isotopic data was considered within a proper geodynamical framework that takes into account the paleopositions of the Pacific plate and surrounding continents, of the hot spots and ridges as well as the paths of the six crusts. The differences and similarities between the Pb and Nd revealed by our analysis emphasize their complementarity as paleoceanographic tracers. The Nd isotopes are strongly influenced by the exchange between Indian and Pacific waters, specifically by the progressive closure of the Indonesian Gateway. The closed central Pacific characteristics are defined from the extrapolation of the isotopic trend. This highlights the important role played by erosion of volcanic arcs in the Nd isotopic value of seawater. Our approach also stresses the influence of local volcanic activity (ridges or active hot spot) for lead isotopes. [Copyright &y& Elsevier]

Abstract: We analyzed teleseismic waveforms recorded by 44 stations in the Fujian and Taiwan provinces of China and obtained 5344 high quality receiver functions. The crustal thickness (H) and average crustal V P /V S ratio (k) beneath every station were estimated using the H–k stacking method. Crustal thicknesses near the Fujian Province range from 28.3 to 32.8 km with an average of 31.1 km, and the corresponding V P /V S ratios vary from 1.70 to 1.84 with a mean of 1.76. From inland to offshore of the Fujian Province, the crustal thicknesses decrease and Poisson''s ratios increase. These may indicate decreasing SiO2 and increasing calc-alkaline contents in the crust. The discontinuity structures such as the Moho, subducting slab, the 410- and 660-km discontinuities (hereafter we call them the 410 and the 660) are also studied using common converted point (CCP) stacking of receiver functions. Along two NW–SE lines of central and northern Taiwan, the CCP stacking results show a western dipping structure at depths above 50 km, suggesting that the Philippine Sea plate is probably subducting beneath the Eurasian continent plate near the central and northern Taiwan. The CCP stacking results show sharp and flat 410- and 660-km discontinuities, and the transition zone thickness (TZT) is the same as that of ambient mantle beneath Fujian and Taiwan Strait, but thickens in the east of Taiwan. These results suggest that (1) the subducting Eurasian continent plate is confined to the depths above 410 km beneath Fujian and Taiwan Strait; and (2) the South China Sea slab may reach the transition zone beneath the east of Taiwan. [Copyright &y& Elsevier]

At many cold vent sites authigenic carbonates precipitate due to the release of carbonate alkalinity during the anaerobic oxidation of methane. Carbonate precipitation often induces the formation of massive crusts at the sediment surface or within surface sediments. The range of physical and biogeochemical conditions allowing for the formation of carbonate crusts is largely unknown so that the significance of these widespread manifestations of fluid flow is unclear. Here, we use numerical modeling to investigate the conditions that induce carbonate crust formation in the sediment and the effect of crust formation on sediment porosity and fluid flow rate. Starting with the conditions prevailing at a previously investigated reference site located on Hydrate Ridge, off Oregon, several parameters are systematically varied in a number of numerical experiments. These parameters include coefficients of bioturbation and bioirrigation, sedimentation rate, fluid flow velocity, methane concentration in the ascending vent fluids, and pH and saturation state at the sediment–water interface. The simulations show that carbonate crusts in the sediments only form if the fluids contain sufficient dissolved methane (>50 mM) and if bioturbation coefficients are low (<0.05 cm2 a−1). Moreover, high sedimentation rates (>50 cm ka−1) inhibit crust formation. Bioirrigation induces a downward displacement of the precipitation zone and accelerates the formation of a solid crust. Crusts only form over a rather narrow range of upward fluid flow velocities (20–60 cm a−1), which is somewhat enlarged (up to 90 cm a−1) if the overlying bottom waters are supersaturated with respect to calcite. At higher flow rates, methane is rapidly exported into the water column so that methane oxidation and carbonate precipitation cannot proceed within the surface sediment. The formation of a several centimeters thick carbonate crust in surface sediments is typically completed after a few hundred years (100–500 a). Crust formation reduces the supply of methane to surface sediments which imposes a strong resistance against diffusive and advective methane transport. Therefore, rates of anaerobic methane oxidation and sulfide production are diminished and thus the density and metabolism of chemosynthetic biological communities is limited by crust formation. Due to the moderate flow rates and the slow diffusive transport, only very little methane escapes into the bottom water overlying carbonate-encrusted vent areas. [Copyright &y& Elsevier]

A volcanic edifice generates a compressive stress field in the upper crust which affects magma transport. As a central cone builds up, primitive magmas can no longer erupt through the focal area and stall at depth. Within a vertical column terminating below the Earth’s surface, magma is overpressured with respect to the surroundings and may feed a horizontally propagating dyke. We define three regimes for magma transport as a function of magma buoyancy, edifice size and density stratification in the upper crust: (1) eruption through the summit, (2) storage beneath the edifice, (3) horizontal propagation to feed a distal eruptive vent. We study the dynamics of horizontal dyke propagation away from the focal area of a volcanic field. Large horizontal propagation distances can only be achieved if an edifice prevents eruption through the focal area and if magma is negatively buoyant at shallow depth. With no edifice, a horizontal dyke is always tallest at the injection point, implying that, if it is able to breach the surface, it only does so in the focal area. With an edifice, at small distances from the axis, confining stresses due to the edifice load act to impede vertical propagation. In this case, a horizontal dyke does not grow vertically at the injection point and develops a hump at some distance from the focal area, which accounts for distal eruptive centers. During propagation, this hump may be far removed from the dyke tip and migrates at a different velocity. All else being equal, a decreasing supply rate or a decreasing magma viscosity generate eruptive centers at increasing distances from the focal area. This is consistent with the distribution of erupted products in many volcanic fields, such that, with increasing distance from the focal area, magma compositions are less and less evolved. [Copyright &y& Elsevier]

Teleseismic images suggest that the Tarim plate plunges ∼45°S, down to ∼300 km depth, beneath NW Tibet. The 410 km discontinuity shallows by ∼10 km under the plateau, implying ∼100°C cooler upper mantle. The deepest Moho on record (∼90 km) lies under W Qiangtang. It rises abruptly by ∼20 and ∼10 km beneath the Altyn Tagh Fault and Bangong Suture, respectively. Vp/Vs ratios are normal, except in the Yecheng flexural basin and deep under the south Karakax volcanics (∼1.92). W Kunlun’s Neogene tectonics are simply accounted for by oblique subduction of lithospheric mantle beneath an upward-extruding thrust wedge of the Tarim crust. [Copyright &y& Elsevier]

The seismic determinations of the crustal thickness and mantle velocities are key parameters for most geophysical and geochemical lunar studies. We determine a new seismic model of the Moon after a complete independent reprocessing of the Apollo lunar seismic data with determination of arrival times of about 60 natural and artificial lunar quakes, as well as travel times of converted phases at the crust–mantle interface below the Apollo 12 landing site. On the near side in the Procellarum KREEP Terrane, the only major discontinuity compatible with the crust–mantle boundary is located around 30 km deep. In this terrane, seismic constraints on the crust and mantle lead to a 30 km thick anorthositic crust and a pyroxenite cold mantle, with a bulk composition of 6.4% Al2O3, 4.9% CaO and 13.3% FeO. Mantle temperatures are in accordance with profiles obtained from the observed electrical conductivity and exclude a liquid Fe core, while being compatible with a Fe–S liquid core. Our Moon model might be explained by a mixture of a primitive Earth with tholeiitic crust and depleted upper mantle, together with a chondritic enstatitic parent body for the impactor planet. It provides mixture coefficients comparable to those obtained by impact simulation as well as an estimate of bulk U of about 28 ppb, in accordance with the U budget in a 40 km mean thick crust, 700 km thick depleted mantle and a lower undepleted primitive mantle. [Copyright &y& Elsevier]