Earth and Planetary Science Letters最新文献

The cross-equatorial southwesterly winds from the eastern equatorial Pacific direct moisture toward the Pacific coast of northwestern South America, where subsequent orographic lifting creates the wettest regions in the world. The Choco low-level jet is emblematic of broader westerly winds in this region and is projected to weaken by the end of the 21st century, but climate models show considerable disagreement about the extent of weakening. Using contemporary observations, we demonstrate that the configuration of westerly winds in the eastern equatorial Pacific is reflected by hydrogen isotopes in precipitation ($\delta D_p$) in western Ecuador. As westerly winds strengthen, $\delta D_p$ increases from greater transport of $\delta D_{vapor}$ enriched in deuterium from the Eastern Pacific Warm Pool. We apply this framework to a new record of reconstructed $\delta D_p$ using leaf waxes in ocean sediments off the coast of Ecuador (ODP1239, $0°{40.32}^{\prime }S,82°{4.86}^{\prime }$ W) that span the Plio-Pleistocene. Low $\delta D_p$ in the early Pliocene indicates weak westerly water vapor transport in a warmer climate state, which is attributed to a low sea surface temperature gradient between the cold tongue and off-equatorial regions in the eastern equatorial Pacific. Near 3 Ma, westerly water vapor transport weakens, possibly as a result of shifts in the Intertropical Convergence Zone forced by high latitude Northern Hemisphere cooling. In complementary isotope-enabled climate simulations, a weak Choco jet and westerly water vapor transport in the early Pliocene are matched by a decrease in $\delta D_p$ and hydroclimate changes in western Ecuador. Precipitation from the Choco jet can cause deadly landslides and weakened westerly winds in the early Pliocene implies a southward shift of these hazards along the Pacific coast of northwestern South America in the future.

Vertical crustal movements associated with large earthquakes excite various kinds of atmospheric waves. They propagate upward and often disturb ionosphere. Here, I report a case for the 2024 January 1 M_w7.5 earthquake that occurred in the northern tip of the Noto Peninsula, Central Japan, using a dense network of multi-GNSS receivers. A rectangular-shaped positive anomaly of ionospheric total electron content emerged ∼9 min after the mainshock. The initial sharp peak was composed of two acoustic wave pulses excited at the two ends of the fault spanning ∼100 km. It was followed by a series of smaller-amplitude broad peaks, the largest of which was possibly excited by a slow fault rupture near the NE edge of the fault ∼8 min after the mainshock. These signatures become large where the wavefronts overlap with those of medium-scale traveling ionospheric disturbances, suggesting possible enhancement of the coseismic signals by downward displacements of high electron density regions in the ionosphere.

The Short-Wave Infrared Spectrometer (SWIR) in the Mars Surface Composition Detector (MarSCoDe) package onboard the Zhurong rover revealed the presence of hydrated phases. However, the exact types of phases are ambiguous and should be further constrained using laboratory spectroscopic studies. Therefore, we build a spectral dataset of binary mixtures by mixing pyroxene and potential hydrated phases (allophane and gypsum) in the laboratory to match the SWIR spectra and calculate the hydrated phase content. We find that the primary hydrated phase may be allophane according to the spectral similarity between the laboratory dataset and SWIR spectra. The relative abundance of pyroxene (∼82 wt%) and allophane (∼18 wt%) is determined using the models built by the integrated band depth (IBD) of binary mixture spectra. When the content of pyroxene is normalized to its content in Martian soil (∼30 wt%), the content of allophane is ∼7 wt%. The allophane may come from short-term fluid-rock interactions under cold climate involving ice and snow melt, and the content of allophane (∼7 wt%) represents a low-moderate degree of weathering at the Tianwen-1 landing site. We propose possible geological evolution scenarios of the Tianwen-1 landing site, i.e., the process of rapid aqueous alteration of volcanic materials under low-temperature conditions due to environmental changes, to explain the geomorphic features and widespread allophane observed by the Zhurong rover.

The stability of minerals that can hold water is important for understanding the distribution and transportation of water in the Earth's deep interior. Water distribution in the lower mantle depends on the stability of water-bearing minerals in the subducting slab because minerals in the surrounding lower mantle have low water solubility. Recent studies have reported that pure SiO₂ high-pressure phases can hold large amounts of water (>3 wt%) however, their experimental results are contradictory regarding stability. In this study, the stability of hydrous SiO₂ stishovite in a water-saturated system was investigated at pressures of 10–30 GPa and temperatures reaching 1300 °C by in situ X-ray observation using a multi-anvil apparatus. The experiments revealed that the unit-cell volume of stishovite was significantly greater than that of anhydrous stishovite (by 3.8 % at the maximum) below 700 °C in the studied range of pressure, suggesting a high water content in stishovite (up to 5.4 wt% H₂O). However, the excess volume decreased rapidly at higher temperatures and the volume was approximately identical to anhydrous stishovite above 800 °C. Time-resolved measurements at constant temperatures of 450 and 500 °C, where water-induced excessive volume was observed, showed that the unit-cell volume shrank with time. This indicates that the dissolution of water in stishovite is a metastable phenomenon. These results indicate that SiO₂ stishovite in crustal materials subducting into the lower mantle is unlikely to retain >1 wt% of water as a stable phase.

The ca. 565 Ma Ediacaran geodynamo was highly unusual, producing an ultralow field 10 times weaker than present-day value of 8 x 10²² A m². A ∼5 times rise in field strength is seen in time-averaged single crystal paleointensity data of ca. 532 Ma Early Cambrian anorthosites of Oklahoma (USA). The field increase could record the onset of inner core nucleation predicted by thermal evolution and numerical dynamo models. Here, we examine the renewal of the geodynamo through zircon U-Pb geochronology and single crystal paleointensity studies of plagioclase from the Chatham-Grenville syenite intrusion in the Grenville Province (Canada). U-Pb data indicate a ca. 544 Ma age and Thellier single crystal paleointensity data yield field strengths of 2.3 ± 0.6 x 10²² A m². The new single crystal paleointensity data further support an increase in field intensity near the Ediacaran-Cambrian transition, consistent with latent heat of crystallization and release of light elements providing new energy sources to power the geodynamo upon the onset of inner core nucleation. Moreover, our new results suggest that plagioclase from syenites can yield valuable records of the geodynamo.

The lunar magma ocean (LMO) hypothesis predicts that the uppermost mantle (∼60–100 km) is composed of ilmenite-bearing cumulate (IBC), which may have sunk deeply due to gravitational instability. However, the extent to which this process restructured the lunar mantle and influenced mare volcanism remains unclear. Here, we approach this issue by examining pyroxenes in Chang'E-5 (CE5) basalts and petrological modeling. We show that the low Mg# and negative anomalies in Ti and Ta of CE5 basalts cannot be produced by extensive fractionation of peridotite-derived low-Ti basalts, but were most likely formed through partial melting of a shallow (< 100 km) IBC pyroxenite source. This model is also applicable to the ∼3.0 Ga lunar basaltic meteorites. The increasing involvement of IBC sources in young lunar magmas, also revealed by the remote-sensing data, implies an inefficient gravitational restructuring process during the late LMO stage and provides new insights into the thermochemical state of the lunar interior.

Aragonite (CaCO₃) is a stable calcium carbonate phase under high pressure conditions. However, its formation in (sub)surface environments, where calcite is the stable polymorph, is widespread. Regardless of its origin, aragonite is expected to undergo transformation into calcite under moderate pressures and temperatures. However, this transformation does not always take place, which results in the presence of abundant aragonitic relics in the geological record. Traditionally, this preservation has been explained by the presence of chemical inhibitors that prevent the conversion of aragonite to calcite. While it is widely accepted that magnesium (Mg) plays a key role in the polymorphic selection of CaCO₃, the influence of other ions has also been suggested. This work evaluates the effect that different concentrations of sulfate (SO₄²⁻) in the fluid has on the progress of the aragonite-to-calcite transformation at 220 °C. Our results show that, upon reaction with deionized water or sulfate-poor solutions ([SO₄²⁻]_aq < 0.1 mM), aragonite single crystals are extensively replaced by calcite aggregates (crystal size > 15 µm) through an interface coupled dissolution-precipitation reaction. The replacement starts at the aragonite crystal surfaces and advances inwards thanks to the development of an extensive network of fractures. Contrarily, when the solution bears higher concentrations of sulfate ([SO₄²⁻]_aq > 0.1 mM), only a thin layer of smaller crystals of calcite (< 10 µm) form on the aragonite substrates, without any further transformation taking place. We interpret that these smaller crystals exert too little crystallization pressure and fail to promote the development of a network of fractures. In the absence of this network, the aragonite-calcite transformation cannot take place. The transformation does not occur neither when the experiments are conducted with deionized water and fragments of gypsum or anhydrite together with the aragonite grains. The results of this study shed light on the influence of dissolved sulfate in the kinetics of the fluid-driven transformation of aragonite into calcite. These results are useful to understand the preservation of aragonite in a variety of current geological settings and provide valuable insights for better understanding the diagenesis of sedimentary carbonates.

The mechanical state (i.e., creeping or locked) of fault zone systems implies future seismic hazards. The Anninghe-Daliangshan fault zone in southeastern Tibet serves as the central curved segment of the most seismically active fault system in mainland China, which has produced a remarkable sequence of historical large earthquakes. To better understand its deformation modes and seismic-aseismic slip partitioning, we built a high-resolution earthquake catalog along the Anninghe fault (ANHF) zone and the Daliangshan fault (DLSF) zone utilizing a dense seismic array deployed between 2017 and 2022. The machine-learning based workflow produces ∼16,000 events with various behaviors and patterns located within the two fault zones. We then systematically evaluated and compared the spatiotemporal seismic patterns, seismic slip rate, statistical properties (b-value, C_V value, and nearest neighbor distance distribution), as well as geodetic measurements. Our results infer that the lower seismogenic crust (16–30 km; brittle) of the northern DLSF zone is creeping and releasing elastic strain with abundant microearthquakes; and the northern ANHF behaves similarly. Moving toward the south, the ANHF transits to a locked state, characterized by sparse seismicity, significantly low seismic energy release and a low b-value. Separated around Mianning, the locked segment is prone to generate two ∼M7.3 earthquakes, posing significant seismic hazard to approximately one million residents nearby. Overall, our updated analysis on the creeping northern DLSF and locked southern ANHF could deepen the understanding of seismic behavior along in-land fault system and guide future seismic hazard assessment in densely populated Southwest China.

The Réunion mantle plume is known to have produced the Deccan Traps in west-central India, but its early evolution before the Deccan eruption remains poorly constrained. In this paper, we report a mafic intrusion in the eastern Tethyan Himalaya, the Manla dolerite sill, with a U–Pb zircon age of 68.7 ± 1.0 Ma and Réunion plume-like geochemical features. Similar to other ∼73–68 Ma pre-Deccan rocks scattered across the northern Indian plate, the Manla dolerite likely represents initial melts from the Réunion plume. Considering the widespread Campanian stratigraphic hiatus throughout the Tethyan Himalaya, we propose that these pre-Deccan geological records in the Himalaya area resulted from the Réunion plume evolution process involving upwelling, ponding and rapid spreading along the base of the northern Indian plate during 80–70 Ma. Major and trace element modeling results show that the Manla rocks, like the largest Western Ghats sequence in the Deccan area, have low melting pressure, suggesting that they formed in preexisting thin areas. Combined with lithosphere thickness variations in the Indian plate, the thick northern Indian plate may have been the key factor inhibiting massive melt production when the Réunion plume head first impinged on it, and the large Deccan eruption was triggered when the thin central-western Indian plate moved over the Réunion plume. The early arrival of the Réunion plume head coincides with the unusual acceleration of the Indian plate starting at ∼75–70 Ma and suggests a prolonged plume - Indian plate interaction period. Our reconstructions suggest that plume heads can impact several million years ahead of large igneous provinces formation and can affect the movements of the overlying plate in an incubation way.

How tectonic plate motions are coupled with mantle flows remains an open question. Quasi-periodic 2000 km wavelength undulations aligned with absolute plate motion in the Pacific and Indian Ocean basins, observed in gravity and seafloor topography and coinciding with seismically imaged low shear velocity fingers in the upper mantle, suggest the presence of meso‑scale convection below the lithosphere. However, the correspondence of sub-lithospheric mantle mass excess, seafloor lows and slow upper mantle seismic velocities cannot be explained by temperature variations alone. Here we introduce a simplified system of bi-dimensional convective cells of width ∼1000 km, extending from the base of the lithosphere through the extended mantle transition zone (down to 1000 km depth), at least partly driven from below. From mass balance considerations in a viscous Earth, we show that the density excess required in the hot upwelling limbs may reflect the formation of stable dense lenses of dehydration-induced partial melt atop the 410 km discontinuity, and upward entrainment of a small fraction of quasi-buoyant partially molten and recrystallized material across the upper mantle. Our model provides an explanation for the thin low shear velocity layer detected intermittently above the 410 km discontinuity in some parts of ocean basins away from subducted slabs, and supports the presence of water in the transition zone.