大陆俯冲界面之上大规模硅富集流体的地球物理学证据

俯冲带中的流体可能对俯冲过程产生重要影响.然而,关于大陆俯冲期间流体规模及其作用的地球物理约束仍然有限.西阿尔卑斯造山带是全球保存最完好的大陆俯冲带之一,为认识大陆俯冲过程中流体作用的影响提供了重要的参考.本文综合多种地球物理方法分析了西阿尔卑斯造山带地区的V_(P)/V_(S)比值,发现在俯冲区的上盘侧存在高V_(P)/V_(S)(>1.9)带,与部分蛇纹岩化的上覆地幔楔位置一致;而在下盘侧存在异常低的V_(P)/V_(S)(<1.7)带,异常深度浅于30km.本文认为,观测到的低V_(P)/V_(S)比值异常是由地壳内广泛分布的富硅岩脉导致,指示了在俯冲时期大陆俯冲界面之上可能存在的富硅流体流动.本文的结果暗示俯冲时期的流体流动可能降低了俯冲界面的有效应力,从而促进了大陆俯冲.

Geophysical evidence of large-scale silica-rich fluid flow above the continental subduction interface

Fluids in subduction zones can have major effects on subduction dynamics.However,geophysical constraints on the scale and impact of fluid flow during continental subduction are still limited.Here we analyze the VP/VS ratios in the Western Alpine region,hosting one of the best-preserved fossil continental subduction zones worldwide,to investigate the impact of fluid flow during continental subduction.We found a belt of high VP/VS ratios>1.9 on the upper-plate side of the subduction zone,consistent with a partially serpentinized upper-plate mantle,and a belt of unusually low VP/VS ratios<1.7 on the lower-plate side,at depths shallower than 30 km.We propose that these low VP/VS ratios result from a widespread network of silica-rich veins,indicating past fluid flow along the continental subduction interface.Our results suggest that past fluid flow may have reduced the effective stress along the subduction interface thus favoring continental subduction.