Elasticity of high-pressure clinoenstatite under mantle conditions: Implications for the origin of the X-discontinuity

Elasticity of Anhydrous Phase B Under Mantle Conditions: Implications for the Deep X‐Discontinuity in the Subduction Zones

“…As shown in Figures 4d–4f, we summarized the anisotropy of major minerals in the upper mantle along the normal geotherm (Brown & Shankland, 1981), including olivine & wadsleyite (Núñez‐Valdez et al., 2013), ringwoodite (Nunez Valdez et al., 2012), pyrope (Hu et al., 2016), diopside (Zou et al., 2018), orthoenstatite (Qian et al., 2018), high‐pressure clinoenstatite (J. Song et al., 2023), and anh‐B. Among them, high‐pressure clinoenstatite and diopside, belonging to the monoclinic system, have the largest anisotropy, which are successively followed by olivine, wadsleyite, orthoenstatite, anh‐B, and ringwoodite.…”

“…Both the coesite‐stishovite transition and the OPX‐HPCPX transition have been shown to have the ability to generate X‐discontinuity (Chen et al., 2015; J. Song et al., 2023). Moreover, the combined effect of these two transitions can effectively explain the indistinguishable Clapeyron slopes of the X‐discontinuity (J.…”

“…The choice of pseudopotentials for oxygen, silicon, and magnesium was the same as in previous studies (J. Song et al., 2023; Wang et al., 2019). Local density approximation (LDA) and generalized gradient approximation (GGA) were chosen to handle the exchange correlation energy for the calculations of elasticity and phase boundary, respectively, since GGA produces a more accurate phase transition pressure than LDA (Hamann, 1996; Wentzcovitch et al., 2010; Yu et al., 2011), while LDA is better to predict structure and elasticity than GGA (Wu & Wang, 2016).…”

“…Song et al. (2023) investigated the elasticity of HPCPX under mantle conditions and demonstrated that the OPX‐HPCPX transition is capable of generating the X‐discontinuity. The comprehensive model proposed by J.…”

“…Song et al. (2023) shows that the combined effect of the coesite‐stishovite transition and OPX‐HPCPX transition, controlled by eclogite melting, can well explain various seismological observations, including double X‐discontinuities (Pugh et al., 2021; Rein et al., 2020), unusual shallow X‐discontinuities beneath hotspots (Pugh et al., 2021), and the indistinguishable seismological Clapeyron slopes of the X‐discontinuity (Deuss & Woodhouse, 2004). Although this model provides a novel interpretation of the main features of the X‐discontinuity, it fails to explain the deep X‐discontinuities within subduction slabs, such as ∼300 km X‐discontinuity in the Tonga subduction zone (Gilbert et al., 2001) and ∼330 km X‐discontinuity in northwest Pacific subduction zones (Zhang & Lay, 1993).…”