Mantle flow in subduction systems and its effects on surface tectonics and magmatism
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Genesis and timing of KREEP-free lunar Mg-suite magmatism indicated by the first norite meteorite Arguin 002
There is ongoing debate about whether lunar magnesian suite (Mg-suite) magmatism was a global, nearly synchronous event with a genetic link to potassium, rare-earth element and phosphorus components (KREEP). Arguin 002, the first whole-rock meteorite classified as a lunar norite, offers a unique opportunity to explore the genesis and timing of Mg-suite rocks. Here we investigated the petrology, mineralogy, geochemistry, and chronology of Arguin 002, revealing it to be an evolved, KREEP-free Mg-suite rock with chemical similarities to atypical Apollo-15 Fe-norites. It likely formed through plutonic magmatism originating from low-degree partial melting of a deep, KREEP-free mantle source and has a 207Pb/206Pb age of 4341.5 ± 9.3 Ma. The potential source of Arguin 002 is within the South Pole-Aitken basin, near the Chang’e-6 landing site. These findings indicate that Mg-suite magmatism was a global and nearly synchronous event, potentially driven by rapid global mantle overturn.
Low-velocity anomaly in the Coral Sea associated with subducting slabs and the Woodlark rift
Classical plume models offer insights into intraplate volcanism and seamount chain formation by assuming a cylindrical upwelling of hot materials from the core-mantle boundary. The interaction of mantle plumes with ridges or subducting slabs disrupts typical plate tectonics, leading to distinctive tectonic phenomena such as ridge jumps or slab stagnation. However, thermal plume models sometimes fall short in explaining perplexing tectonic features, necessitating consideration of compositional heterogeneities within mantle plumes. Here, using multimode waveform tomography, we identify a large, vertically divergent low-velocity anomaly in the upper mantle beneath the Coral Sea in the southwestern Pacific, which circumvents the remnants of subducting slabs toward northeastern Australia with intraplate volcanism, and the Woodlark rift, the most rapidly extending continental rift. Our findings furnish seismic evidence for the widespread propagation of a thermochemical mantle plume spanning over 10° at depths of 270–410 km, facilitating its simultaneous contacts with slabs and rifts.
Persistence of davemaoite at lower-mantle conditions
The lower mantle occupies over half of Earth’s volume, and accordingly, its mineralogy is crucial in determining the structure and dynamics of Earth. Davemaoite, the calcium silicate perovskite, was believed to coexist with bridgmanite in the lower mantle and is considered essential for understanding the chemical evolution and dynamics of Earth’s lower mantle. However, the presence of davemaoite is challenged due to the potential for high calcium silicate solubility in bridgmanite. Here we use an ultrahigh-pressure multi-anvil technique to show experimentally that the calcium solubility in bridgmanite is insufficient to eliminate davemaoite under mantle conditions, including typical mantle pressure, temperature and chemical compositions. We conclude that davemaoite has been stable in Earth’s lower mantle since its formation. Due to the limited calcium solubility in bridgmanite, davemaoite-enriched domains are expected at the core–mantle boundary. These domains could serve as the principal reservoir for incompatible elements in the lower mantle and may be the source for some ocean island basalts. Furthermore, our study offers an explanation for the observed large low-shear-wave-velocity provinces at the bottom of the lower mantle. These provinces may consist of davemaoite-enriched materials crystallized from basal magma ocean in early Earth history.
Gravitational stability of iron-rich peridotite melt at Mars’ core-mantle boundary
Possible existence of dense iron-rich silicate melt layer above Mars’ core is important in understanding the nature and evolution of Mars. However, gravitational stability of iron-rich silicate melt in the Mars’ interior has not been well constrained, due to experimental difficulties in measuring density of iron-rich peridotitic melt. Here we report density measurements of iron-rich peridotitic melts up to 2465 K by using electrostatic levitation furnace at the International Space Station. Our experimentally obtained densities of iron-rich peridotitic melts are markedly higher than those calculated by first principles simulation, and are distinct from those estimated by extrapolating a density model for SiO2-rich basaltic melts. Our determined density model suggests that peridotitic melt with the Fe/(Mg+Fe) ratio more than 0.4-0.5 has higher density than that at the base of the Mars’ mantle, which indicates gravitational stability of the iron-rich peridotitic melt at the core-mantle boundary in Mars.
Fault–fracture mesh development produces tectonic tremor in fluid-overpressured serpentinized mantle wedge
Deep tectonic tremor occurs repeatedly at the base of a forearc mantle wedge corner, where a highly fluid-pressurized serpentinite shear zone is thought to develop. However, the deformation mechanisms that accommodate these tremors within the shear zone remain unclear. Here, we present observations of deformation experiments on water-saturated serpentinite conducted at pressure–temperature conditions relevant to the tremor zone. We find that increasing pore fluid pressure gradually decreases sample strength and leads to a transition in the deformation mechanism from frictional sliding on several fault surfaces to distributed extensional and extensional–shear fracturing. Combined with field observations of a shallow mantle-wedge-derived serpentinite shear zone, our experimental results suggest that numerous brittle failures developing simultaneously throughout the shear zone generate bursts of tectonic tremor. Furthermore, the recurrence interval of the tremors is likely controlled by the time required for the fractures to be hydrothermally sealed through serpentine precipitation.
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