Seismic Velocity Model of Crust and Upper Mantle beneath South Central Andes including Pampean and Payenia

A new seismic model for crust and upper mantle of the south Central Andes is derived from full waveform inversion, covering the Pampean flat subduction and adjacent Payenia steep subduction segments. Focused crustal low‐velocity anomalies indicate partial melts in the Payenia segment along the volcanic arc, whereas weaker low‐velocity anomalies covering a wide zone in the Pampean segment are interpreted as remnant partial melts. Thinning and tearing of the flat Nazca slab is inferred from gaps in the slab along the inland projection of the Juan Fernandez Ridge. A high‐velocity anomaly in the mantle below the flat slab is interpreted as relic Nazca slab segment, which indicates an earlier slab break‐off triggered by the buoyancy of the Juan Fernandez Ridge during the flattening process. In Payenia, large‐scale low‐velocity anomalies atop and below the re‐steepened Nazca slab are associated with the re‐opening of the mantle wedge and sub‐slab asthenospheric flow, respectively.

本研究基于全波形反演（full waveform inversion）构建了安第斯中南部地壳与上地幔新地震模型，研究覆盖范围涵盖蓬帕平坦俯冲带及相邻的帕耶尼亚陡俯冲带两段区域。聚焦地壳的低速异常特征显示，帕耶尼亚段沿火山弧分布的区域存在部分熔融体；而蓬帕段宽阔区域内的弱低速异常，则被解释为残留部分熔融。通过胡安·费尔南德斯海岭（Juan Fernandez Ridge）内陆投影沿线的板片空隙特征，可推断纳斯卡平板俯冲带发生了减薄与撕裂。平板俯冲带下方地幔中的高速异常被解释为残留纳斯卡板片段，该特征表明在平板俯冲过程中，胡安·费尔南德斯海岭的浮力作用曾触发早期板片断离。在帕耶尼亚段，重新陡化的纳斯卡板片顶部及下方的大规模低速异常，分别对应地幔楔的重新开启与板下软流圈流动。