126 / 2023-04-14 14:00:27

High-Pressure Elasticity Measurements of Aragonite: Implication for Low-Velocity Structure of Subducted Oceanic Crust in the Upper Mantle

single-crystal elasticity,aragonite,carbonated MORBs,water and carbon

高压物理与材料科学 > 高压地球科学-海报

Subducted slabs generally exhibit higher velocities than the normal mantle due to their lower temperatures revealed by seismological observations^[1]. However, in the circum-Pacific region at 150-250 km depth, the subducted oceanic crust displays compressional (V_P) and shear-wave velocities (V_S) 3-4% and 3-7% lower than surrounding mantle, respectively^[2]. Previous studies have attributed the observed low-velocity anomaly to the presence of water (lawsonite) alone, which cannot fully explain the observed 3-4% V_P anomaly^[3]. In addition of water, aragonite can also cause a substantial decrease in velocity of subducted oceanic crust. We conducted to determine the single-crystal elasticity of aragonite (CaCO₃) up to 20 GPa and 300 K by Brillouin measurements. Combined with the effects of water and aragonite, we have modelled the velocity profiles of mid-ocean ridge basalt (MORBs) which is the major component of the subducted oceanic crust. Although neither water nor carbonate alone could completely explain the low-velocity anomalies of MORBs at 150-250 km depth, the presence of 4.2-4.4 vol.% aragonite together with 10 vol.% lawsonite can make the V_P and V_S of MORBs 3-4% and 5.9-8.1% lower than surrounding mantle, respectively. At depths greater than 300 km, MORBs will be seismically detected as a high-velocity structure due to complete dehydration of lawsonite and gradual decarbonization with aragonite content less than 8 vol.%. These findings provide important insights into the complex relationship between carbon, water, and depth-dependent velocity anomalies in the subduction process.



[1] Irifune, T., & Ringwood, A. E. (1993). Phase transformations in subducted oceanic crust and buoyancy relationships at depths of 600–800 km in the mantle, Earth and Planetary Science Letters, 117(1), 101-110, https://doi.org/10.1016/0012-821X(93)90120-X.

[2] Abers, G. A. (2005). Seismic low-velocity layer at the top of subducting slabs: observations, predictions, and systematics, Physics of the Earth and Planetary Interiors, 149(1-2), 7-29.

[3] Connolly, J. A. D., & Kerrick, D. M. (2002). Metamorphic controls on seismic velocity of subducted oceanic crust at 100–250 km depth, Earth and Planetary Science Letters, 204(1), 61-74, https://doi.org/10.1016/S0012-821X(02)00957-3.