Seismic Anisotropy in Subduction Zones: Evaluating the Role of Chloritoid
Seismic Anisotropy in Subduction Zones: Evaluating the Role of Chloritoid
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DOI：
10.3389/feart.2021.644958
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发表时间：
2021-03
期刊：
影响因子：
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通讯作者：
Jungjin Lee;M. Mookherjee;Taehwan Kim;H. Jung;R. Klemd
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作者：
Jungjin Lee;M. Mookherjee;Taehwan Kim;H. Jung;R. Klemd
俯冲带通常具有强烈的沟槽平行地震各向异性和较大的延迟时间。含水矿物由于其大的弹性各向异性和强烈的晶格择优取向(LPO)，经常被用来解释这些观察结果。然而，类绿泥石的弹性和LPO却鲜为人知，它是俯冲带环境中的一种含水相。在这项研究中，我们测量了天然岩石样品中多晶绿泥石的LPO，得到了LPO诱发的地震各向异性，并评价了俯冲带中绿泥石的热力学稳定场。绿泥石集合体的LPO表现出强烈的[001]轴次垂直于岩石面理的排列，[100]轴次平行于岩石面理的环带分布，(010)极次平行于面理。新的单晶绿泥石弹性数据显示出强烈的绿泥石弹性各向异性，S波的弹性各向异性(VS)为47%，P波的弹性各向异性(Vp)为22%。LPO和类绿泥石聚集体的弹性各向异性相结合，产生了强的S波各向异性和P波各向异性，最大AvS为18%，P波各向异性AVP为10%。在天然岩石样品和假想的蓝片岩中，评估了类绿泥石LPO在地震各向异性中的作用。我们的结果表明，沿俯冲界面和俯冲板块的绿泥石强烈的LPO可以影响具有“冷”地温的俯冲带中的沟平行地震各向异性。
Subduction zones are often characterized by the presence of strong trench-parallel seismic anisotropy and large delay times. Hydrous minerals, owing to their large elastic anisotropy and strong lattice preferred orientations (LPOs), are often invoked to explain these observations. However, the elasticity and the LPO of chloritoid, which is one of such hydrous phases relevant in subduction zone settings, are poorly understood. In this study, we measured the LPO of polycrystalline chloritoid in natural rock samples, obtained the LPO-induced seismic anisotropy, and evaluated the thermodynamic stability field of chloritoid in subduction zones. The LPO of chloritoid aggregates displayed a strong alignment of the [001] axes subnormal to the rock foliation, with a girdle distribution of the [100] axes and the (010) poles subparallel to the foliation. New elasticity data of single-crystal chloritoid showed a strong elastic anisotropy of chloritoid with 47% for S-waves (VS) and 22% for P-waves (VP), respectively. The combination of the LPO and the elastic anisotropy of the chloritoid aggregates produced a strong S-wave anisotropy with a maximum AVS of 18% and a P-wave anisotropy with an AVP of 10%. The role of chloritoid LPO in seismic anisotropy was evaluated in natural rock samples and a hypothetical blueschist. Our results indicate that the strong LPO of chloritoid along the subduction interface and in subducting slabs can influence the trench-parallel seismic anisotropy in subduction zones with “cold” geotherms.