Research

Recent Highlights

Anisotropic thermal conductivity of antigorite along slab subduction impacts seismicity of intermediate-depth earthquakes 

Nature Communications 15, 5198 (2024)

Double seismic zones (DSZs) are a feature of some subducting slabs, where intermediate-depth earthquakes (~70–300 km) align along two separate planes. The upper seismic plane is generally attributed to dehydration embrittlement, while mechanisms forming the lower plane are still debated. Here, we experimentally demonstrate that the thermal conductivity of antigorite, a hydrous serpentine mineral, has a strong anisotropy along subduction. Our numerical models further reveal that when the low-thermal-conductivity c-axis is aligned normal to the slab dip, antigorite’s strongly anisotropic thermal conductivity enables heating at the top of a slab, facilitating dehydration embrittlement for the seismicity in the upper plane of DSZs. Potentially, such thermal insulating effect also hinders dissipation of frictional heat inside shear zones, promoting thermal runaway along serpentinized faults that could trigger intermediate-depth earthquakes.

A thermally conductive Martian core and implications for its dynamo cessation

Science Advances 10, eadk1087 (2024)

Mars experienced a dynamo process that generated a global magnetic field ~4.3 (or earlier) to 3.6 billion years ago (Ga). The cessation of this dynamo strongly impacted Mars’ history and is expected to be linked to thermochemical evolution of Mars’ iron-rich liquid core, which is strongly influenced by its thermal conductivity. Here we directly measured thermal conductivities of solid iron-sulfur alloys to pressures relevant to the Martian core and temperatures to 1023 Kelvin. We show that a Martian core with 16 weight% sulfur has a thermal conductivity of ~19 to 32 Watt meter-1 Kelvin-1 from its top to the center, much higher than previously inferred from electrical resistivity measurements. Our modelled thermal conductivity profile throughout the Martian deep-mantle and core indicates a ~4 to 6-fold discontinuity across the core-mantle boundary. The core’s efficient cooling resulting from the depth-dependent, high conductivity diminishes thermal convection and forms thermal stratification, significantly contributing to cessation of Martian dynamo.

High thermal conductivity of stishovite promotes rapid warming of a sinking slab in Earth’s mantle

EPSL 584, 117477 (2022)

Thermal transport in subducted slabs and mantle critically influences their thermo-chemical evolution and dynamics, where the thermal conductivity controls the magnitude of conductive heat transfer. We study high-pressure thermal conductivities of stishovite and new-hexagonal-aluminous (NAL) phase, two major slab minerals in the shallow lower mantle, and their impacts on slab dynamics. Pure and Al-bearing stishovite exhibit higher conductivities than the Fe-bearing NAL and assemblage of a pyrolitic mantle or subducted basaltic crust. Numerical simulations indicate that subducted crustal materials particularly with local silica-enrichment would have efficient thermal conduction which promotes faster warming of a sinking slab, altering dynamic stability of slab materials and leading to slab stagnation and crust detachment in the shallow lower mantle. 

Low thermal conductivity of iron-silicon alloy at Earth’s core conditions with implications for the geodynamo 

Nature Communications 11, 3332 (2020)

Earth’s core is predominantly composed of iron alloyed with some light elements. Core’s thermal conductivity determines its thermal evolution (including the age of inner core) and dynamics of Earth’s magnetic fields. We measured the thermal conductivity of iron-silicon alloys at core’s high pressure-temperature conditions and demonstrated that it is much lower than previously thought. Combined with numerical modeling, we further found that the low thermal conductivity of core substantially delays its cooling, suggesting that the inner core could be older than two billion-years. Moreover, the thermal energy alone released by the core could sustain the operation of geodynamo. 

Effects of iron on the lattice thermal conductivity of Earth’s deep mantle and implications for mantle dynamics 

Proc. Natl. Acad. Sci. USA, 115, 4099 (2018)

Iron critically influences the physical properties and thermo-chemical structures of Earth’s lower mantle. Its effects on thermal conductivity, with possible consequences on heat transfer and mantle dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-mantle ferropericlase (Fp) to 120 GPa. The thermal conductivity of Fp with 56% iron significantly drops across the spin transition. Combined with bridgmanite data, we create a self-consistent radial profile of lower-mantle thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a two-fold increase from top to bottom of the lower mantle. Such increase in thermal conductivity delays the cooling of the core, while its decrease with iron content enhances the dynamics of LLSVPs. If the seismic ULVZs are hot and strongly enriched in iron, they have ultra-low conductivity, thus delaying their cooling.

Hydration-reduced lattice thermal conductivity of olivine in Earth’s upper mantle

Proc. Natl. Acad. Sci. USA, 114, 4078 (2017)

Earth’s water cycle can influence the physical properties of the mantle. Lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs. However, the effect of hydration on the thermal conductivity remains poorly understood. We measured the thermal conductivity of San Carlos olivine (Mg0.9Fe0.1)2SiO4 (Fo90) up to 15 GPa. The thermal conductivity of hydrous Fo90 is significantly suppressed at P>5 GPa, and is about half of the anhydrous Fo90 at mantle transition zone, demonstrating the critical influence of hydration. Modeling the thermal structure of a subducting slab shows that the hydration-reduced thermal conductivity in hydrated crust decreases the temperature within the subducting slab. Thus, the olivine-wadsleyite transformation rate in the slab with hydrated crust is much slower than that with dry crust, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity enables hydrous minerals to survive in deeper mantle and enhances water transportation to the transition zone.