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Elastic Anomalies Across the α-β Phase Transition in Orthopyroxene: Implication for the Metastable Wedge in the Cold Subduction Slab
Geophysical Research Letters ( IF 5.2 ) Pub Date : 2022-08-11 , DOI: 10.1029/2022gl099366
Luo Li 1 , Ningyu Sun 1, 2, 3 , Weigang Shi 1 , Zhu Mao 1, 2, 3 , Yingxin Yu 1 , Yanyao Zhang 4 , Jung‐Fu Lin 4
Affiliation  

Single-crystal elasticity of both α- and β-orthopyroxene was determined up to 20 GPa and 300 K by Brillouin scattering. Using the derived full elastic moduli (Cij), we investigated the contribution of the metastable pyroxene to the seismically observed 3%–5% low-velocity anomalies along the subducting slab in the top transition zone. Our modeled results show that a harzburgite wedge with a 1000-K colder geotherm and metastable α-orthopyroxene and olivine displays compressional (VP) and shear-wave (VS) velocities 3.0%–3.6(6)% and 2.0%–2.8(6)% lower than the surrounding mantle at 410–460 km depth, respectively. At deeper depth up to 520 km, VP and VS of this metastable wedge with β-orthopyroxene and olivine are 3.6%–4.4(6)% and 2.8%–4.3(6)% lower than the pyrolitic mantle, respectively. The presence of both metastable orthopyroxene and olivine instead of metastable olivine alone helps better explain the origin of the low-velocity anomalies within the subduction slab in the top transition zone.

中文翻译:

斜方辉石中α-β相变的弹性异常:对冷俯冲板中亚稳楔的影响

通过布里渊散射测定了高达 20 GPa 和 300 K 的 α- 和 β- 邻辉石的单晶弹性。使用导出的全弹性模量 ( C ij ),我们研究了亚稳态辉石对沿顶部过渡带俯冲板片的地震观测到的 3-5% 低速异常的贡献。我们的模拟结果表明,具有 1000-K 冷地温和亚稳态 α-斜方辉石和橄榄石的方辉石楔形显示出纵波 ( V P ) 和横波 ( V S ) 速度 3.0-3.6(6)% 和 2.0-2.8(6 )% 分别低于 410-460 km 深度的周围地幔。在高达 520 公里的更深处,V PV S这种含有 β-斜方辉石和橄榄石的亚稳楔的体积分别比热解地幔低 3.6-4.4(6)% 和 2.8-4.3(6)%。亚稳斜方辉石和橄榄石的存在而不是单独的亚稳橄榄石有助于更好地解释顶部过渡带俯冲板片内低速异常的起源。
更新日期:2022-08-11
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