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  • Detailed Moho variations under Northeast China inferred from receiver function analyses and their tectonic implications
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-02-11
    Bing Zhang; Jianshe Lei; Xiaohui Yuan; Guangwei Zhang; Jing He; Qiang Xu

    In this study we investigate detailed Moho variations beneath Northeast China by applying the arithmetic mean, back-projected and Fresnel-zone migration imaging methods to a total of 169,602 high-quality P-wave receiver functions from seismograms of 2903 teleseismic events recorded at 127 NECESSArray stations and 321 China Earthquake Administration stations. Our results show that the Moho depth variations are correlated with the surface geology in the study region. The Moho is deeper (~34.0–42.0 km) under the Great Xing'an range, the Lesser Xing'an range, the Zhangguangcai range, and the Changbaishan mountain, whereas it is shallower (~26.0–32.0 km) under the Songliao basin. Our results also reveal obvious Moho variations across the North-South Gravity Lineament. The Moho offsets up to ~5.0 km are clearly observed under the Nenjiang-Balihan, Yilan-Yitong, and Dunhua-Mishan faults, indicating that they are lithospheric-scale faults. A deeper Moho is revealed under the volcanoes, such as the Jingpohu, Wudalianchi, and Changbaishan volcanoes and Abaga and Halaha volcanic groups. In particular, the Moho under the Changbaishan volcano reaches ~40.0 km depth and the observation varies with the teleseismic back-azimuths, suggesting a complicated magma system in the crust. In addition, the Moho under the Songliao basin varies significantly from ~26.0 km depth in the east to ~32.0 km depth in the west, which could be related to the lithosphere extension and thinning. All these results suggest that there exists to a hot and wet mantle upwelling in the big mantle wedge formed by the deep dehydration of the long stagnant Pacific slab in the mantle transition zone under Northeast China.

    更新日期:2020-02-12
  • Two-phase magnetohydrodynamics: Theory and applications to planetesimal cores
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-02-07
    David Bercovici; Elvira Mulyukova

    Core freezing and resultant compositional convection are likely important drivers for dynamo activity in large terrestrial bodies like the Earth. The solidification of compositional mixtures, such as iron and sulfur, generates mush zones of partial melt at the freezing front, which can eject chemically buoyant or heavy liquid that then drives convection. For smaller bodies such as planetesimals in the asteroid belt, conditions for generating a dynamo are harder to achieve. Nevertheless, evidence for magnetization of achondrite meteorites is abundant, suggesting that many planetesimal cores were somehow magnetized. As such small bodies cool rapidly under low gravity they likely spend much of their evolution with a large poorly compacted partial melt mushy zone. The magneto-hydrodynamic behavior of a deformable partial melt zone can induce magnetism via separation of solid and liquid phases, and conversely magnetism can impose extra forces on the phase separation in the mush zone. To this end, we have developed a new two-phase magneto-hydrodynamic theory for deformable mushes and slurries. The model includes the standard effects of Lorentz forces, and the competition between magnetic field stretching and diffusion. There are additional effects at the liquid pore or solid grain scale, which involve the interaction between phases, akin to Darcy or Stokes drag; these include Lorentz drag, as well as pore/grain-scale diffusive exchange of magnetism between solid and fluid phases, and field stretching due to relative motion between phases. Magnetic induction by gravitational phase separation is most significant after extensive mixing of liquid and solid phases, such as induced by vigorous mechanical stirring due to, for example, tidal and elliptic instabilities, or impacts with other bodies, all of which are conceivably common in the asteroid belt, especially in the early solar system. Gravitational phase separation following such events can induce significant magnetism in the liquid and solid phases, and much more rapidly than can magnetization by large-scale circulation. Magnetic field variances can be at first orders of magnitude larger than an imposed background field, during initial gravitational phase separation of the well-mixed slurry. As the phases separate toward the top or bottom, the solid phase compacts, the separation velocity decreases, and the magnetic field variance likewise diminishes. However, solitary waves in the compacting region can cause an additional large magnetic induction in the liquid, taking the form of strongly magnetized wave packets that can be trapped in the solid. Thus, phase separation, segregation and compaction potentially induce large magnetic field anomalies. A linear stability analysis for convection in a porous medium (with a rigid matrix) is also explored. Pore and grain scale effects, such as field stretching due to phase separation, are found to enhance the influence of the magnetic field on convective instability.

    更新日期:2020-02-07
  • Changes in shear-wave splitting at the 2014 Bárðarbunga seismic crisis and dyke intrusion in Iceland compared with earthquakes and other eruptions
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-02-01
    Qiyu Hong; Stuart Crampin; Yuan Gao

    We use shear-wave splitting (SWS) above small earthquakes to monitor stress-variations before the 2014 Bárðarbunga seismic crisis and dyke intrusion in central Iceland. SWS is sensitive to stress-induced variations in the internal geometry of the distributions of stress-aligned fluid-saturated microcracks pervading almost all crustal rocks. This allows stress-accumulation before both impending earthquakes and impending volcanic eruptions to be monitored and potentially the events stress-forecast. We compare the behaviour of SWS before Bárðarbunga with the behaviour before large earthquakes and other volcanic episodes where SWS has been monitored. On the basis of the duration of stress-changes, we classify volcanic episodes into three broad classes. During analysis of SWS before Bárðarbunga, temporal variation in polarizations and another retrospective stress-forecast earthquake were recognized.

    更新日期:2020-02-03
  • Imaging the 2–D crust and upper mantle structure of the Iranian plateau resolved by potential field and seismic data
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-30
    Mojtaba Namvaran; Mohammad Tatar; Seyed–Hani Motavalli–Anbaran

    In this study, the crust and upper mantle density distribution across the Iranian plateau along a ~1500 km profile are investigated using an integrated modeling of potential field data (gravity, geoid and topography) and by assuming local isostatic equilibrium. Our profile is initiated in Arabian platform and running through the main geological structures of Iran including Zagros orogen, Sanandaj – Sirjan Zone (SSZ), Urumieh – Dokhtar Magmatic Arc (UDMA), Central Iran (CI) block, Tabas/Lut blocks, and East Iranian Range (EIR). In the second step, in order to verify the integrated model, the 1–D S–wave absolute velocities for the crust and upper mantle beneath 21 seismic stations which partially covered the density profile are obtained using the joint inversion of P–receiver function (PRF) and surface–wave dispersion data. Our results indicate a thick crust (~60 km) beneath the SSZ and UDMA which thinning toward the east and experienced its minimum value (~40 km) beneath the central Iran, as well as Tabas/Lut blocks. Moreover, a thick lithosphere (>150 km) is observed under the Zagros, SSZ and parts of the UDMA, whereas a thinner lithosphere (~120 km on average in velocity model) is presented under the most of our profile. Both density and velocity models indicate a lithospheric thinning toward the CI block which imply the slab breakoff or lithospheric delamination followed by the upwelling of the asthenosphere in the Neogene. The presence of a relative fast structure in the crust beneath the Tabas block which is coinciding with a shallow high velocity body in the uppermost mantle elucidates a signature of former oceanic crust, which disappeared after the collision of Lut and Afghan continental blocks and E-directed subduction of Neotethys under the Afghan microcontinent either in post-Albian or middle Eocene times.

    更新日期:2020-01-31
  • Shear wave velocity structure of the upper-mantle beneath the northern Zagros collision zone revealed by nonlinear teleseismic tomography and Bayesian Monte-Carlo joint inversion of surface wave dispersion and teleseismic P-wave coda
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-30
    Meysam Mahmoodabadi; Farzam Yaminifard; Mohammad Tatar; Ayoub Kaviani

    The continental collision between the Arabian and Eurasian plates plays an important role in the geodynamical evolution of the Zagros and Iranian plateau. In order to investigate the upper mantle structure across the collision zone, we calculated the absolute and relative shear-wave velocity structure along a dense and long temporary seismic profile in NW Iran. The probabilistic 1-D absolute shear-wave velocity (Vs) depth profiles beneath 23 seismic stations were calculated using a trans-dimensional joint inversion approach of P-wave coda together with the Rayleigh wave phase and group velocity dispersion data. These 1-D models are then interpolated to obtain a 2-D Vs model along the profile. In addition, we used a nonlinear teleseismic tomography method to determine shear wave velocity variations beneath 44 seismic stations. Both the absolute and relative velocity models, obtained by different data sets and methods, show a thick (>150 km) high-velocity anomaly beneath the northern part of the Zagros, which could be the thickened Zagros lithosphere associated with continental shortening. A relatively thin lithosphere (~80 km) and lower S-wave velocity beneath Central Iran may suggest a weakened Iranian mantle lithosphere by upwelling of the hot asthenosphere following slab break-off. The presence of a thickened lithosphere beneath the Zagros implies that the Arabian-Eurasian convergence is accommodated mainly as shortening in the mantle lithosphere beneath the Zagros, rather than underthrusting beneath Central Iran. A narrow low-velocity corridor between the Zagros lithosphere and overriding plate (Central Iran), south of the Sanandaj-Sirjan Zone (SSZ), probably due to delamination of the subducting Arabian lithosphere from the Zagros lower crust, likely prohibits transferring stress from the Zagros lithosphere to Central Iran, causing less deformation in the SSZ which is the edge of the overriding plate.

    更新日期:2020-01-31
  • Fluctuation of the Earth's magnetic field elements in Mexico revealed by archive documents since 1587
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-30
    Avto Goguitchaichvili; Esteban Hernandez; Rafael Garcia; Rubén Cejudo; Gerardo Cifuentes; Miguel Cervantes

    Historical documents, archives and old photographic collections allowed to analyze 877 direct geomagnetic measurement data obtained by sailors (including pirates), United State Coast and Geodetic Survey and National Astronomical Observatory since 1587. The updated catalogue includes 844 values of magnetic declination, 495 of inclination, 467 of the horizontal intensity component (H) and 455 of the vertical intensity component (Z). All data were relocated to Mexico City through the pole conversion method in order to build a reference secular variation curve for Mexico and surrounding area using bootstrap method to mitigate the effect of outliers and estimate the probability of density functions. The directional variation patterns obtained in this investigation were compared to the curves retrieved from Sha.Dif.14k, GUFM1and IGRF-12 models while VADM fluctuations were confronted to similar quality determinations from other localities worldwide as well as archaeomagnetic curves from Mesoamerica.

    更新日期:2020-01-31
  • Presenting Meso-Cenozoic seismic sequential stratigraphy of the offshore Indus Basin Pakistan
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-22
    Majid Khan; Yike Liu; Syed Zaheer Ud Din

    Preserved deformed depositional sequences along passive continental margins are important repositories of natural resources as well as key laboratories for understanding rift-drift tectonics. With better post signal processing schemes, interpretation techniques, and potential data, imaging sedimentary basins along these margins has reached unique levels of refinement. This, in turn, has led to considerable improvement in unfolding the complex tectono-sedimentary history since rifting to basin development. In this paper, deep reflection seismic coupled with well data and biostratigraphic information have been used to decipher the third-order depositional sequences of Meso-Cenozoic succession in western parts of the Indian Plate Passive Continental Margin (Offshore Indus Basin) as pioneer research. Based on morpho-tectonic considerations, the depositional sequences are divided into syn-rift, passive margin, and post-rift stages deformed by steeply dipping normal faults. Using the principles of classic sequence stratigraphy, five third-order mappable depositional sequences have been recognized on seismic records that are controlled by regional tectonics and sea-level fluctuations coupled with sedimentation type and rates in the region. The associated system tracts were recognized and mapped based on genetic reflection terminations on seismic profiles and log motifs, and constraint surfaces include sequence boundaries (SBs), maximum flooding surfaces (MFSs) and transgressive surfaces (TSs). The depositional systems encompass lowstand system tracts (LSTs), transgressive system tracts (TSTs), and highstand system tracts (HSTs). The LSTs are composed of shallowing-upward lowstand deltas or terraces prograding in the basin-ward direction while pinches out landward at preceding depositional shoreline breaks. The sand units of TSTs are interpreted as shoreface sands deposited in the shelfal part during rising sea-levels and HSTs are characterized by coarsening and shallowing upward intervals, with both fluvial and laterally prograding deltaic deposits. A hydrocarbon entrapment model is proposed suggesting an interesting petroleum trap. Based on the entire course of this research, valuable recommendations have been made for answering past exploration failures and future efforts. Such studies can be applied to worldwide passive margins dominated by third-order sequences with complex sediments-tectonic interplay.

    更新日期:2020-01-22
  • Detection of high P,T transformational faulting in Fe2SiO4 via in-situ acoustic emission: Relevance to deep-focus earthquakes
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-20
    Timothy Officer; Richard A. Secco

    At transition zone depths in subduction zones, deep-focus earthquakes (300–690 km depth) are thought to be associated with faulting that arises from phase transformations. In order to test the viability of this mechanism experimentally, an investigation was conducted on fayalite at high pressure, P, and high temperature, T, under deviatoric stress in order to initiate transformational faulting. Experiments were performed in a 3000-ton multi-anvil press using an 18/11 octahedral cell with 6 piezoelectric transducers mounted on the rear side of the anvils to monitor acoustic activity in situ. Acoustic emission (AE) signals were collected at a sampling rate of 40 MHz using a triggered system and a data buffer for capturing full waveforms of AE events. The use of multiple transducers distributed in a micro-seismic array allowed for events to be located within the sample based on the arrival time of signals and non-linear least squares inversion techniques. Uncertainty in location estimates were on the order of ~1 mm. The system was tested by comparing the contrasting mechanical properties of quartz beads and AgCl samples. The multi-anvil apparatus constitutes an inherently noisy environment both acoustically and electrically, therefore methods of noise reduction were developed. Results of AE experiments on Fe2SiO4 under high pressure (3.7–9.2 GPa) and high temperature (673–1273 K) conditions in the spinel stability field showed acoustic events that locate within or within 1σ of the sample in five experiments defined by the P,T envelope P = 3.9–8.4 GPa and T = 748–923 K. Optical and scanning electron microscopy of the recovered specimens displayed conjugated faulting associated with transition from fayalite (olivine structure) to ahrensite (spinel structure) and microstructural analysis revealed microstructural morphology identical to that found in similar faulting experiments on Mg2GeO4. This is the first time an olivine→spinel structured transition in a silicate mineral has demonstrated macroscopic faulting and associated microstructures, as well as acoustic activity, under conditions that nominally promote plastic deformation.

    更新日期:2020-01-21
  • Thermodynamic modeling of hydrous-melt–olivine equilibrium using exhaustive variable selection
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-20
    Kenta Ueki; Tatsu Kuwatani; Atsushi Okamoto; Shotaro Akaho; Hikaru Iwamori

    Water in silicate melt influences the phase relations of a hydrous-melt system. Given the importance of water in silicate melts, a quantitative thermodynamic understanding of the non-ideality of hydrous melt is necessary to properly model natural magmatic processes. This paper presents a novel method for quantitative thermodynamic modeling of hydrous-melt–olivine equilibrium. Specifically, a machine learning method, exhaustive variable selection (ES), is used to model the non-ideality of hydrous melts. Using the ES method, we quantitatively validate the predictive capacities of all possible combinations of variables and then adopt the combination with the highest predictive capacity as the optimal model equation. The ES method allows us to obtain the underlying thermodynamic relationship of the hydrous-melt–olivine system, such as the relative importance of different variables to the thermodynamic equilibrium, as well as to construct a robust and generalized model. We show that the combination of a linear term and a squared term of the total water concentration of melt is significant for describing the hydrous-melt–olivine equilibrium. This result is interpreted in terms of the microstructural changes related to the dissociation of water in silicate melt. Calculations using the optimal model reproduce the experimentally determined effects of water on the olivine liquidus and the distribution coefficient for Mg between olivine and hydrous melt. Our study demonstrates that the ES method yields a thermodynamic equilibrium model that captures the essential thermodynamic relationship explaining the high-dimensional and complex experimental data.

    更新日期:2020-01-21
  • A comparative study of deformation field due to center of dilatation and center of rotation in a viscoelastic half-space model
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-17
    Nishu Verma; Kuldip Singh

    Closed-form analytic expressions for the displacement and stress fields due to two axially symmetric sources, namely, the center of dilatation, and center of rotation in an elastic half-space are obtained using Galerkin vector approach. The correspondence principle of linear viscoelasticity is used to obtain the viscoelastic displacement and stress fields. A comparative study of both these sources has been done graphically. Our analysis revealed that the center of dilatation is more efficient than the center of rotation in generating radial displacement. The results are valid for arbitrary values of the Poisson's ratio and relaxation time.

    更新日期:2020-01-21
  • Upper mantle slab under Alaska: Contribution to anomalous core-phase observations on south-Sandwich to Alaska paths
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-15
    Daniel A. Frost; Barbara Romanowicz; Steve Roecker

    Observations of travel time anomalies of inner core-sensitive PKPdf seismic body waves, as a function of path orientation with respect to the earth's rotation axis, have been interpreted as evidence of anisotropy in the inner core. Paths from earthquakes in the South Sandwich Islands to stations in Alaska show strongly anomalous travel times, with a large spread that is not compatible with simple models of anisotropy. Here we assess the impact of strong velocity heterogeneity under Alaska on the travel times, directions of arrival and amplitudes of PKPdf. We use 3D ray-tracing and 2.5D waveform modelling through a new, high-resolution tomography model of the upper mantle beneath Alaska. We find that the structure beneath Alaska, notably the subducting slab, is reflected in the patterns of these PKPdf observations, and this can be replicated by our model. We also find similar patterns in observed teleseismic P waves that can likewise be explained by our slab model. We conclude that at least 2 s of the travel time anomaly often attributed to inner core anisotropy is due to slab effects in the upper mantle beneath Alaska.

    更新日期:2020-01-15
  • Source parameters of the 1926 and 1927 Jersey earthquakes from historical, instrumental, and macroseismic data
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-15
    D. Amorèse; J. Benjumea; M. Cara

    English Channel Islands are located off Normandy coast of France within an intraplate area not associated with high seismicity rate and active tectonics. However, in July 1926 a damaging and well-documented earthquake occurred there, followed by a strongly felt event in February 1927. In this paper, we reprocess macroseismic observations, analog seismograms and bulletin data in order to re-appraise the location and magnitude of these two earthquakes. We find that the macroseismic epicentre of the 1926 Jersey earthquake is shifted to the East when compared with the location offshore South of Jersey given in both the French database SisFrance and the recent French catalog FCAT-17. Arrival-times from published data, together with our own onset-time readings, are processed in order to obtain probabilistic hypocentral locations. The maximum-likelihood instrumental epicentre of the 1926 event is located about 15 km East of Jersey Island (49.20°N, 1.82°W). This epicentre is well constrained within a 10 km radius area. The location of the 1927 epicentre is slightly south of Jersey, at a location similar to that of SisFrance, but this latter epicentre is less constrained as fewer observations are available (the Probability Density Function for the 1927 epicentre is relatively “diluted”). Focal depth remains very poorly determined for both the 1926 and 1927 events. Analysis of historical seismograms is also performed in order to determine both surface-wave and moment magnitudes, MS and MW. We find MS = 5.6 ± 0.2 for the 1926 event and Ms. = 5.0 for the 1927 event. Waveform fitting of some of the highest quality seismograms of the 1926 event gives us MW in the range [5.0, 5.5], depending on the chosen focal depth and focal mechanism. The 1927 Jersey earthquake is expected with an intensity magnitude MI about 0.6 smaller.

    更新日期:2020-01-15
  • One-dimensional seismic velocity model of the sub-basin of Chalco, Mexico
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-08
    Filiberto Vergara-Huerta; Jorge Aguirre-González

    In this work, a one-dimensional (1-D) seismic velocity model is proposed for the central portion of the sub-basin of Chalco, located in the southeast (SE) sector of the basin of Mexico. The seismic model was integrated from spectral analysis of the seismic ambient vibrations (microtremors or seismic noise) records, through the methodologies of Modified Spatial Autocorrelation (MSPAC) and H/V spectral ratios. The one-dimensional (1-D) seismic model is the result of the simultaneous inversion of the H/V ratios and the phase-velocity dispersion curves, corresponding with Rayleigh waves and contained in the vertical component of the microtremor records. The scheme used in the inversion process was Monte Carlo. Which allowed us to establish a best fit model configured by four representative lithological units, congruent with the amplitude and dominant periods identified in this sector of the basin of Mexico.

    更新日期:2020-01-08
  • Application of wavelets for specifying tsunami from tide: A comprehensive study on the 1945 Makran tide gauge records
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-07
    Ahmad Ala Amjadi; Mohammad Mokhtari

    In tide gauge records, the separation of tidal from non-tidal contents is in general done by specialists after applying high pass or bandpass filtering techniques. However, there is always a tradeoff between losing some valuable contents of the signal while trying to remove the tide. In this manuscript, we deal with two significant tide gauge records of the 1945 Makran tsunami. The importance of these data is well known for researchers since these are the only valid tide gauge data for any evaluation of tsunami in the western Makran region. Wavelet decomposition technique was applied as a tool by us to minimize the influence of tidal contents on these data. Several parameters were set and applied to several types of wavelets in various temporal series and frequency ranges. The goal was to find the most appropriate wavelet parameter and type, to distinguish tsunami data from tidal contents. Our results show that the application of wavelets in comparison to conventional methods yields to lesser RMS errors before the arrival of the tsunami wave and therefore produces minor data loss after applying. Moreover, after applying suitable wavelets to data, we have noticed a sudden decrease in the sea level before the arrival of tsunami waves, which is consistent with eyewitness reports. The result of our work is beneficial for further evaluation of tsunami modeling in western Makran. The procedure introduced can be applied at any tide gauge data for tidal analysis with wavelet decomposition techniques.

    更新日期:2020-01-07
  • P-wave upper-mantle tomography of the Tanlu fault zone in eastern China
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-11-18
    Jianshe Lei; Dapeng Zhao; Xiwei Xu; Mofei Du; Qi Mi; Mingwen Lu

    The Tanlu fault zone is the most significant active fault in eastern China, which generated the great 1668 Tancheng earthquake (M 8.5). It is still unclear whether or not there is a link between the great earthquake generation and the upper-mantle structure. To address this issue, we study P-wave upper-mantle tomography beneath eastern China using 44,047 teleseismic P-wave arrival times. Our results show that at depths <150 km, high-velocity (high-V) anomalies appear west of the Tanlu fault zone, whereas low-velocity (low-V) anomalies are visible east of the fault zone. Strong lateral heterogeneities are revealed along the fault zone. At depths of 230–470 km, northwest of the Tanlu fault zone, there are obvious low-V anomalies that may reflect hot and wet mantle upwelling, whereas to the east high-V anomalies are visible, which may reflect the detached Eurasian lithosphere (downwelling). In the mantle transition zone (MTZ), both high-V and low-V anomalies are revealed, and the widespread high-V anomalies may reflect the stagnant Pacific slab. Beneath the hypocenter of the 1668 Tancheng earthquake, intermittent low-V anomalies are revealed in the upper mantle down to the MTZ depth, which may reflect hot and wet mantle upwelling flow. Integrating the present results with previous findings, we deem that the Tancheng earthquake was affected by fluids from the hot and wet mantle upwelling associated with the lithospheric delamination. Complicated mantle convection, including both upwelling and downwelling flows, may occur under the Tanlu fault zone in the big mantle wedge above the stagnant Pacific slab in the MTZ.

    更新日期:2020-01-04
  • Calcium carbonate at high pressures and high temperatures: A first-principles investigation
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-11-19
    Samuel S.M. Santos; Michel L. Marcondes; João F. Justo; Lucy V.C. Assali

    We present a theoretical investigation, within the density functional theory and the quasi-harmonic approximation framework, on the stability properties of calcium carbonate (CaCO3) at the thermodynamic conditions of the Earth's lower mantle. We initially explored the structural properties of a low-pressure phase (aragonite) using three different approximations for the exchange-correlation potential, and find that all properties are better described, when compared to recent experimental data, by using the one that takes into account the van der Waals interactions. We used this approximation to compute the free energy of this mineral in several crystalline phases, and explored the respective thermodynamic properties at high temperatures and high pressures. The results on phase stability, thermal expansivity, specific heat, bulk modulus, and mass density were compared to available experimental data. Then, we built the phase diagram for this mineral and discussed its impact on the Earth's mantle properties.

    更新日期:2020-01-04
  • High-pressure, high-temperature phase stability of iron-poor dolomite and the structures of dolomite-IIIc and dolomite-V
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-11-21
    Jannes Binck; Stella Chariton; Michal Stekiel; Lkhamsuren Bayarjargal; Wolfgang Morgenroth; Victor Milman; Leonid Dubrovinsky; Björn Winkler

    The stability of Fe-poor dolomite, CaMg0.98Fe0.02(CO3)2, was studied by Raman spectroscopy and single-crystal X-ray diffraction at high pressures (P < 60 GPa) and high temperatures (T < 2300 K). Density functional theory calculations were employed to complement the experimental study. Between 40 and 60 GPa and 1800–2300 K, we observed the formation of a high P,T phase, “dolomite-V”, which, after quenching to ambient temperature, remained stable down to 12 GPa. The dolomite-V phase crystallizes in the space group C2/c with Z = 4 formula units. The structure of the high pressure polymorph “dolomite-IIIc” was solved, which crystallizes in the space group P1¯ with Z = 8 formula units. The combined experimental and theoretical findings show that at high pressures and low to moderate temperatures Dol-IIIc is formed, while at high pressures and high temperatures Dol-V becomes stable. Assuming that thermodynamic equilibrium is obtained at high-pressure, high-temperature conditions, the current study extends our understanding of the phase stability of Fe-poor dolomite polymorphs at upper and lower mantle conditions.

    更新日期:2020-01-04
  • Upper mantle tomography of the Western Junggar: Implications for its geodynamic evolution
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-11-26
    Yuanyuan Hua; Yixian Xu; Dapeng Zhao; Rong Huang; Xiaohuan Jiang

    A high-resolution 3-D P-wave velocity model of the upper mantle beneath the Western Junggar is determined by inverting a large number of relative travel-time residuals of teleseismic events. Our results reveal a prominent high-velocity (high-V) anomaly beneath the western Junggar basin and a low-velocity (low-V) anomaly beneath the Darbut belt. The NE-SW striking high-V anomaly at depths of 50–200 km beneath the western Junggar basin dips toward the northwest, which represents a fossil oceanic slab. The low-V anomaly may reflect an intraoceanic arc-related terrain that has experienced strong metasomatism by hot upwelling asthenosphere in the late Paleozoic, resulting in adakitic intrusions and concentration of porphyry CuAu deposits in the Darbut belt. These results shed new light on the geodynamic evolution of the Western Junggar and formation mechanisms of the adakites and porphyry CuAu deposits.

    更新日期:2020-01-04
  • Regional variation of coda wave attenuation in Northeast India: An understanding of the physical state of the medium
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-11-25
    Rabin Das; Sagarika Mukhopadhyay

    In this study an attempt has been made to estimate spatial variation in attenuation characterisitics in Northeast India using coda Q. The entire study region is divided into three sub-regions for this purpose. Estimated average frequency dependency of coda wave attenuation for 30 s window length are Qc(f) = 135 ± 7f0.99±0.03, Qc(f) = 109 ± 7f1.10±0.03 and Qc(f) = 90 ± 2f1.04±0.02 for Shillong Plateau, Mikir hills and surrounding River valley, and Indo-Burma Ranges respectively. It is observed that Q0 is greater for the Shillong Plateau than the other sub-regions. This indicates lower attenuation due to more rigid high-density material present in this area than the other sub-regions. The depth variations of the Qc, Q0 and n values were also examined. It is observed that the rate of increase of Q0 with depth is not uniform for all the sub-regions. Indo-Burma Ranges has the smallest Q0 and the largest n values at all depth levels among the three sub-regions. These results indicate that central part of Indo-Burma Ranges is the most attenuative, seismically active and heterogeneous in nature. However, this region has smaller Qc values than the other two sub-regions for all window lengths up to the 6 Hz. This means at lower frequencies the subsurface beneath this area is more attenuative compared to the other two sub-regions. Similar trends are observed at 8, 10 and 12 Hz, up to 45 s window lengths. For window lengths ≥55 s, central part of Indo-Burma Ranges has higher Qc values at 10 and 12 Hz compared to Shillong plateau. Qc values are lower for Shillong Plateau compared to the other two regions for window length ≥ 55 s at 10 and 12 Hz, which corresponds to depth levels ≥90 km. Such a complicated variation in Qc values is a manifestation of complex nature of tectonic regime in Northeast India.

    更新日期:2020-01-04
  • JULOC: A local 3-D high-resolution crustal model in South China for forecasting geoneutrino measurements at JUNO
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-12-06
    Ruohan Gao; Zhiwei Li; Ran Han; Andong Wang; Yufeng Li; Yufei Xi; Jingao Liu; Xin Mao; Yao Sun; Ya Xu

    Geothermal energy is one of the keys for understanding the mechanisms driving the plate tectonics and mantle dynamics. The surface heat flux, as measured in boreholes, provides limited insights into the relative contributions of primordial versus radiogenic sources of the interior heat budget. Geoneutrino, electron antineutrino that is produced from the radioactive decay of the heat producing elements, is a unique probe to obtain direct information about the amount and distribution of heat producing elements in the crust and mantle. Cosmochemical, geochemical, and geodynamic compositional models of the Bulk Silicate Earth (BSE) individually predict different mantle neutrino fluxes, and therefore may be distinguished by the direct measurement of geoneutrinos. Due to low counting statistics, the results from geoneutrino measurements at several sites are inadequate to resolve the geoneutrino flux. However, the JUNO detector, currently under construction in South China, is expected to provide an exciting opportunity to obtain a highly reliable statistical measurement, which will produce sufficient data to address several vital questions of geological importance. However, the detector cannot separate the mantle contribution from the crust contribution. To test different compositional models of the mantle, an accurate a-priori estimation of the crust geoneutrino flux based on a three-dimensional (3-D) crustal model is important. This paper presents a 3-D crustal model over a surface area of 10° × 10° grid surrounding the JUNO detector and a depth down to the Moho discontinuity, based on the geological, geophysical and geochemical properties. This model provides a distinction of the thickness of the different crustal layers together with the corresponding Th and U abundances. We also present our predicted local contribution to the total geoneutrino flux and the corresponding radiogenic heat. Compared to previous studies where the surface layer is subdivided into a few geologic units and each of them is considered to have the same geochemical property, our method has provided an effective approach to reduce the uncertainty of geoneutrino flux prediction by constructing the composition of the surface layer through cell by cell which are independent to each other.

    更新日期:2020-01-04
  • Comparisons between measurements and predictions of Rayleigh wave amplification across the contiguous United States
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-12-02
    Celia L. Eddy; Göran Ekström

    We present local surface-wave-amplification maps spanning the contiguous United States for Rayleigh waves between 35 s and 125 s using data recorded on the USArray between 2006 and 2015. We isolate the effect of local structure from those of the earthquake and propagation using a previously developed method based on ratios of amplitudes measured at adjacent stations. To assess the ability of our technique to resolve surface-wave amplification, we perform a parallel synthetic-tomography experiment. We determine amplification from a large dataset of SPECFEM synthetic seismograms calculated for USArray stations and compare the measurements with direct predictions of local amplification. Correlations between synthetic and predicted amplification are high, with correlation coefficients ranging from 0.77 at 40 s to 0.95 at 100 s, indicating that we are able to resolve well local variations in amplification, particularly at long periods. The remaining differences between synthetic and directly predicted amplification maps suggest the influence of finite-frequency effects on surface-wave amplitudes. Observed Rayleigh wave amplification factors reflect local elastic structure in the region surrounding each station and could be used as a complementary constraint to image the structure of the Earth's crust and upper mantle.

    更新日期:2020-01-04
  • Examination of the repeatability of two Ms6.4 Menyuan earthquakes in Qilian-Haiyuan fault zone (NE Tibetan Plateau) based on source parameters
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-12-02
    Xiaohui He; Yipeng Zhang; Xuzhang Shen; Wenjun Zheng; Peizhen Zhang; Dongli Zhang

    Repeating earthquakes are key evidence for understanding earthquake recurrence and help improve long-term seismic risk assessment. In 1986 and 2016, two Ms6.4 earthquakes occurred in Menyuan region, near the middle segment of Qilian-Haiyuan fault zone, NE Tibetan Plateau. Long period waveforms of the two events at teleseismic stations show high degree of similarity, however, previous solutions on earthquake location and focal mechanism show remarkable discrepancies, especially for the 1986 event, as well the ruptured faults also remain ambiguous. In this study, we determined the source parameters of these two earthquakes, including the relative location, focal depth, focal mechanism, source duration and rupture directivity. The results show that two earthquakes are thrust events in shallow crust and are located within 15 km, and the 2016 earthquake ruptured down-dip for ~6 km along the southwest dipping plane. Combing the source parameters, geological data and deep seismic-reflection profiles, we infer that these two earthquakes occurred on the same secondary fault of Lenglong Ling fault (the middle segment of Qilian-Haiyuan fault), but they ruptured on different sections of the fault. Although the two events are probably not repeating earthquakes of Qilian-Haiyuan fault zone, the seismic risk of ~M6 thrust earthquake on these secondary faults and even larger strike-slip earthquake on Lenglong Ling fault are not negligible based on the source parameters and ten-year GPS observations.

    更新日期:2020-01-04
  • Constraints on S-wave velocity structures of the lithosphere in mainland China from broadband ambient noise tomography
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-12-14
    Jie Peng; Jinli Huang; Zhikun Liu; Kang Xing

    In this study, a 3-D S-wave velocity model of the lithosphere in mainland China down to 150 km depth was determined from ambient noise data. First, we collected 2-year continuous waveforms recorded by 1031 broadband stations of the China Regional Seismic Network and NECESSArray. Then, by applying the procedures of noise cross-correlation and time-frequency domain phase-weighted stacking, we obtained the interstation empirical Green's functions of Rayleigh waves. We measured the group and phase velocity dispersions at periods of 5–125 s from the EGFs and inverted both group and phase velocities for the S-wave velocity model. Our model revealed that the lithospheric thickness in the northern Songliao basin is ~70–110 km. A weak high-velocity anomaly that is discontinuous in the vertical direction was detected beneath the southern Songliao basin, which may indicate that the lithosphere is delaminated in this area. The model also revealed that deep (>150 km) high-velocity lithospheric roots exist beneath the Ordos and Sichuan basins. The lithospheric thicknesses in eastern parts of the Northeast China Block, the North China Craton, and the South China Block are only 60–100 km, which may be the result of a series of deep processes caused by the subduction of the Pacific plate to the Eurasian plate that produced strong lithospheric thinning in eastern China. The lithospheric thickness within the Tanlu fault belt is generally thinner than that in the adjacent areas of the fault belt, and the S-wave velocity of the mantle lithosphere beneath the fault belt is also lower than that beneath the adjacent areas, indicating that the Tanlu fault belt is a deep fault belt cutting through the lithosphere.

    更新日期:2020-01-04
  • Deformation of two welded half-spaces caused by a centre of rotation source
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-12-18
    Nishu Verma; Kuldip Singh

    Closed-form analytic expressions for Papkovich-Neuber displacement potentials, displacements, and stresses due to the centre of rotation source in an elastic half-space overlying an elastic half-space are obtained. The elastic results are valid for different values of Poisson's ratio and a change in the rigidity of the two half-spaces. Further, the correspondence principle of linear viscoelasticity is used to obtain the corresponding solutions in an elastic half-space overlying a viscoelastic half-space. The viscoelastic results are valid for different values of relaxation time and a change in the rigidity of the two half-spaces. The variation of the displacements and stresses with the epicentral distance as well as with the relaxation time are studied. The magnitude of displacement and normal stress components assume a maximum value for the Maxwell model and minimum value for the Kelvin model whereas the shear stresses assume a minimum value for the Maxwell model and maximum value for the Kelvin model.

    更新日期:2020-01-04
  • Possible H2O storage in the crystal structure of CaSiO3 perovskite
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-12-23
    H. Chen; K. Leinenweber; V. Prakapenka; C. Prescher; Y. Meng; H. Bechtel; M. Kunz; S.-H. Shim

    The lower mantle is believed to contain much less hydrogen (or H2O) because of the low storage capacity of the dominant mineral phases, such as bridgmanite and ferropericlase. However, possible hydrogen storage in the third most abundant mineral in the region, CaSiO3 perovskite (Ca-Pv), is not well unknown. We have synthesized Ca-Pv from different starting materials with varying H2O contents at 19–120 GPa and 1400–2200 K in laser-heated diamond-anvil cell. While cubic perovskite structure is stable at the mantle-related pressures-temperatures (P−T) in anhydrous systems, we found non-cubic diffraction peak splitting in Ca-Pv even at high temperatures when it is synthesized from hydrous starting materials. In-situ high-pressure infrared spectroscopy showed OH vibration possibly from Ca-Pv. The unit-cell volume of hydrothermally synthesized Ca-Pv is systematically smaller than that of anhydrous Ca-Pv at high pressures. These observations suggest possible H2O storage in Ca-Pv at mantle-related P−T conditions. We also found the formation of separate δ–AlOOH and Ca-Pv phases from Al-bearing CaSiO3 glass starting materials in an H2O medium at 60 GPa and 1400 K. Ca-Pv still showed non-cubic peak splitting at high temperatures in this experiment. Therefore, it is possible that hydrous phases may coexist together with hydrous Ca-Pv in the lower mantle.

    更新日期:2020-01-04
  • Identification of paleomagnetic remanence carriers in ca. 3.47 Ga dacite from the Duffer Formation, the Pilbara Craton
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2020-01-03
    Yoichi Usui; Masafumi Saitoh; Kenichiro Tani; Manabu Nishizawa; Takazo Shibuya; Chie Kato; Tomoyo Okumura; Teruhiko Kashiwabara

    The ca. 3.47 Ga Duffer Formation has been considered to carry one of the oldest paleomagnetic records. Yet, the lack of rock magnetic data limits the interpretation of the nature of the remanence. We conducted a rock magnetic and paleomagnetic investigation on columnar dacite of the Duffer Formation. The main magnetic minerals are phenocrysts of titanomagnetite and magnetite, and secondary hematite in groundmass. Detailed thermal demagnetization revealed more complex natural remanence than previously estimated, consisting of four components with typical unblocking temperature of 200 − 350, 200 − 500, 590, and 690 °C. Combined with alternating field demagnetization and rock magnetic data, they are attributed to titanomagnetite, coarse-grained magnetite, fine-grained magnetite, and hematite, respectively. The comparison of unblocking temperature and coercivity suggest that the previously proposed secondary component is carried by fine-grained magnetite as well as hematite, while the putative primary component is carried by coarse-grained magnetite and titanomagnetite. Microscopic observations showed that coarse-grained magnetite and titanomagnetite are primary crystals, although this does not necessarily indicate they preserve primary remanence. The remanence directions of all components revealed higher scatter than the previous studies, suggesting the need for caution in interpretation. The low unblocking temperature of tittanomagnetite suggests that if their remanence is truly primary, the rocks must have kept below ∼ 250 °C for ∼3.47 billion years.

    更新日期:2020-01-04
  • Extremely young melt infiltration of the sub-continental lithospheric mantle
    Phys. Earth Planet. Inter. (IF 2.615) Pub Date : 2019-10-23
    Simon Turner; Michael Turner; Bernard Bourdon; Kari Cooper; Don Porcelli

    It has long been inferred that mantle metasomatism and the incompatible element enrichment of the continents both require movement of melts formed by very low degree melting of the mantle. Yet establishing the presence of these melts and whether this process is on-going and continuous, or spatially and temporally restricted, has proved difficult. Here we report large U-Th-Ra disequilibria in metasomatised, mantle xenoliths erupted in very young lavas from the Newer Volcanics Province in southeastern Australia. The 226Ra-230Th disequilibria appear to require reappraisal of previous estimates for the age of eruption that now seems unlikely to be more than a few kyr at most. We propose that infiltration of carbonatitic melts/fluids, combined with crystallization of pargasite, can account for the first order U-series disequilibria observations. Irrespective of the exact details of the complex processes responsible, the half-lives of the nuclides require that some of the chemical and isotopic disturbance was extremely young (« 8 kyr) and potentially on-going at the time of incorporation into the alkali basalts that transported the xenoliths to the surface. This provides evidence for the presence and possibly continuing migration of small melt fractions (~0.02%) in the upper convecting mantle that may contribute to the seismic low velocity zone. By implication, it appears that the asthenosphere must lie close to its solidus, at least in this region. Pressure-temperature estimates indicate that the small degree melts identified could infiltrate as far as 25 km upwards into the sub-continental lithospheric mantle leading to strong incompatible element enrichment and the recent timing of this event this urges a reappraisal of the meaning of 300–500 Ma Nd model ages in mantle xenoliths from this region. In principle, the resultant metasomatised mantle could provide a component for some ocean island basalts, should the sub-continental lithospheric mantle be returned to the asthenosphere by convective removal at some later time.

    更新日期:2020-01-04
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