Physics of the Earth and Planetary Interiors最新文献

We report systematic first-principles results of structural properties and compression behavior based on density functional theory (DFT) and an exchange-correlation functional for solids, of Al-bearing garnets of general compositions in the pyrope-almandine-grossular solid solution system. The combination of DFT and a simple solid solution model is able to produce a compositional dependence of the compression curve consistent with trends observed in experimental studies. Using end-member properties extrapolated from our computations and perturbing an extant thermodynamic model we observe only marginal effects on the bulk sound velocity of pyrolite and MORB along relevant geothermal paths. However, this could hide important effects on the elemental partitioning between garnet and other major phases which should be further investigated both experimentally and computationally. We also present simulations of the effect of combined Fe and Ca substitutions for Mg on the elastic tensor of Al-bearing garnets, our simplified modeling shows only partial agreement with the trends observed in experiments. Therefore, further computational investigations, especially of the effect of Fe-Mg substitution on the tensor, are needed.

Singhbhum Craton (SC) hosted eight different dyke swarm events, which are collectively known as the Newer Dolerite Dykes. These have been correlated with different cratons and supercontinents based on age, geochemistry, and paleomagnetic data. However, our understanding of stress conditions during and after the dyke intrusions and the magma chamber dynamics is limited due to lack of information. In this study, we have investigated magma dynamics and crustal extension for different dyke swarm events in the SC to explore the magma chamber dynamics during the supercontinent breakup and at other cratons around the globe. Further, we have also quantified post-intrusion response to the far-field stress in different dyke swarms of the SC. For a comprehensive understanding of the magma dynamics and deformation history of the dyke swarms, we investigated dykes associated structures and estimated the magma pressure relative to the principal stresses. We used dyke wall attitude data to explore the paleostress conditions during the dyke intrusion, fault-slip data for post-emplacement deformation, and field structures with dyke thickness data to understand magma dynamics and crustal extension.

Paleostress analysis in four dyke swarms indicates relatively higher magma pressure in the Pipilia dyke swarm compared to Ghatgaon, Keonjhar, and Kaptipada dyke swarms. This is further supported by the fact that Pipilia dykes are thicker than the other three dyke swarms. Post-emplacement deformation is evident from the fault-slip observations, tectonic fractures, and veins cross-cutting dykes and host rock. Fault-slip observations suggest an extensional tectonic event followed by a compressive one. The extensional stress regime, active during the intrusion of Pipilia dyke swarm, overprints the Ghatgaon dyke swarm, while the far-field stress from the Singhbhum Shear Zone affects all the analyzed dykes and the host rock. These observations are in agreement with the thinned lithosphere of SC. We estimate that the Ghatgaon swarm caused the maximum average crustal extension/dilation of 9.65%, while the Keonjhar swarm led to the least average extension of 1.58%. We suggest that the Pipila dyke swarm event may have dilated a part of the Columbia supercontinent by ∼8.5% as the dilations for other regions in the supercontinents are not known.

The earthquake, which occurred in Yogyakarta, Indonesia, on May 26, 2006, at 22:53:58 UTC with Mw ∼6.4, was one of the most destructive earthquakes in Indonesia. The earthquake caused thousands of fatalities, tens of thousands of injuries, and hundreds of thousands of house damages in the Yogyakarta area and its surroundings at a loss of billions of dollars. Previous studies from seismic tomography and satellite radar imaging hypothesized that the earthquake was caused by activating a so far unknown fault east of the Opak Fault. Although, in the beginning, the Opak fault was suspected to be the source of the Yogyakarta earthquake in 2006. This assumption was made because the damage was maximum in the Bantul area west of the Opak Fault. This study demonstrates that our seismic tomography achieved a higher resolution than the previous study and could resolve a failed complex fault system. We utilized more aftershocks (2170 events) and smaller grid sizes for seismic tomography inversion. Four focal mechanisms from aftershocks for Mw ≥ 4.5 were also conducted to support structure interpretation in the study area. Our results successfully delineate the Opak Fault and the second fault, namely the Ngalang Fault, parallel to the eastern part of the fault at a depth of 9 km. Two faults could be indicated by the velocity contrast of Vp, Vp/Vs ratio, and Vs from a horizontal section tomogram. Our focal mechanisms also support seismic tomography, revealing two fault planes in our study area. The results show that the two faults are connected by the Oyo Fault, which is ruptured in the opposite direction compared to the two faults.

At a late stage of its accretion, the Earth experienced high-energy planetary impacts. Following each collision, the metal core of the impactor sank into molten silicate magma oceans. The efficiency of chemical equilibration between these silicates and the metal core controlled the composition of the Earth interior and left a signature on geochemical and isotopic data. These data constrain the timing, pressure and temperature of Earth formation, but their interpretation strongly depends on the efficiency of metal-silicate mixing and equilibration. We investigate the role of planetary rotation on the dynamics of the sinking metal and on its chemical equilibration using laboratory experiments of particle clouds settling in a rotating fluid. Our clouds initially sink as spherical turbulent thermals, but after a critical depth, rotation becomes important and they transition to a vortical columnar flow aligned with the rotation axis. Applied to Earth formation, our results predict that rotation strongly affects the fall of metal in the magma ocean for impactors smaller than 459 km in radius on a proto-Earth that rotates twice faster than today. On a proto-Earth spinning 5 times faster than today, rotation is important for any impactor smaller than the Earth itself. In contrast with a thermal that grows in all directions, the vortical column grows vertically but keeps a constant horizontal extent. The slower dilution in vortical columns reduces chemical equilibration compared to previous estimates that neglect planetary rotation. We find that rotation significantly affects the degree of equilibration for highly siderophile elements with partition coefficients larger than ${10}^3$. In this case, for a planet spinning twice faster than today, the degree of equilibration decreases by up to a factor 2 compared to previous estimates that neglect the effect of rotation. Finally, the ultimate fate of iron drops is to be detrained from the vortical column as an iron rain, reconciling the traditional iron rain scenario with the model of turbulent thermal.

The combination of ultrasonic technique with synchrotron X-ray diffraction and radiography in a multi-anvil apparatus was utilized to measure the elastic wave velocities of sodium aluminosilicate glass and melt with the partially depolymerized composition of Na₃AlSi₃O₉ (NAS). The measurements were conducted at pressure and temperature of up to 7.3 GPa and at ambient temperature for glass and up to 4.3 GPa and 2120 K for melt, respectively. The compressional wave velocity (V_P) of the NAS glass remained mostly constant up to 4 GPa; subsequently, it increased with increasing pressure. Additionally, the NAS glass exhibited a minimum shear wave velocity (V_S) at 4–5 GPa. Alternatively, the V_P of the NAS melt was smaller than that of the NAS glass, showing a velocity minimum at ∼2 GPa. The negative pressure dependence of V_P of the NAS melt is completely different from the depolymerized diopside (Di) melt, which shows a monotonic increase in V_P with pressure. The contrasting behavior of the NAS and Di melts is caused by the difference in their structure, characterized by their degree of polymerization. Natural magma found in the interior of the Earth, such as basalt, has a partially depolymerized composition. This study indicates that the magma can exhibit elastic properties with negative pressure dependence, similar to the NAS melt.

The rock and rock-ice mixtures of the core-enveloping spherical shells comprising terrestrial body interiors have thermally determined viscosities well described by an Arrhenius dependence. Accordingly, the implied viscosity contrasts determined from the activation energies (E) characterizing such bodies can reach values exceeding ${10}^{40}$, for a temperature range that spans the conditions found from the lower mantle to the surface. In this study, we first explore the impact of implementing a cut-off to limit viscosity magnitude in cold regions. Using a spherical annulus geometry, we investigate the influence of core radius, surface temperature, and convective vigour on stagnant lid formation resulting from the extreme thermally induced viscosity contrasts. We demonstrate that the cut-off viscosity must be increased with decreasing curvature factor, $f$ ($=r_{\text{in}}/r_{\text{out}}$, where $r_{\text{in}}$ and $r_{\text{out}}$ are the inner and outer radii of the annulus, respectively), if the solutions are to be not only computationally manageable but physically valid. We find that for statistically-steady systems, the mean temperature decreases with core size, and that a viscosity contrast of at least ${10}^7$ is required for stagnant lid formation as $f$ decreases below 0.5. Inverting the results from over 80 calculations featuring stagnant lids (from a total of approximately 180 calculations), we apply an energy balance model for heat flow across the thermal boundary layers and find that the non-dimensionalized temperature in the Approximately Isothermal Layer (AIL) in the convecting region under a stagnant lid is well predicted by $T_{\mathrm{AIL}}^{\prime }=\frac{1}{2}\left(-\left(2T_{\text{out}}^{\prime }+\gamma \right)+\sqrt{{\gamma }^2+4\gamma \left(1+T_{\text{out}}^{\prime }\right)}\right)$ where $\gamma$ is a function of E and $f$, and $T_{\text{out}}^{\prime }$ is the non-dimensionalized surface temperature. Moreover, the normalized (i.e., non-dimensional) thickness of the stagnant lid, $L^{\prime }$, can be obtained from a measurement of the non-dimensional surface heat flux once <