雅浦俯冲带北段地球物理场及构造活动性分析

Analysis of Geophysical Field and Tectonic Ctivity in the Northern Yap Subduction Zone

雅浦俯冲带北段和马里亚纳俯冲带西南端均受加罗林岛脊俯冲影响,但是二者的地球物理特征存在显著差异。通过分析雅浦俯冲带北段和马里亚纳俯冲带的地球物理特征,对比了二者之间的海底地形、重力异常、地震活动和应力场等特征。结果表明:①雅浦海沟北段外缘发育垒堑构造带,马里亚纳海沟西南端加罗林岛脊俯冲区域水深明显变浅,加罗林岛脊俯冲最前端形成凹角。②雅浦岛弧北段和马里亚纳岛弧西南端加罗林岛脊俯冲区域高布格异常值反映了强烈的构造侵蚀可能导致火山弧地壳缺失,岛弧之下高密度物质上涌。③雅浦俯冲带北段和马里亚纳俯冲带西南端地震活动性弱并且缺乏高震级地震,说明加罗林海脊岛脊的俯冲阻塞降低了俯冲带的构造活动性。马里亚纳俯冲带西南端存在少量的中源地震,表明该区域板片俯冲深度比雅浦俯冲带北段更深。④马里亚纳俯冲带西南端的地震存在更多的走滑分量,与加罗林板块的倾斜俯冲、加罗林岛脊的倾斜碰撞有关。⑤加罗林岛脊相对于海沟走向的俯冲角度是造成雅浦俯冲带北段和马里亚纳俯冲带西南端的地球物理特征存在差异的主要原因。

Both of northern part of the Yap Trench and the southwestern end of the Mariana Trench are affected by the subduction of Caroline Island Ridge,but the geophysical characteristics for these two regions show significant differences.Based on a comprehensive analysis including the submarine topography,gravity anomaly,seismic activity and stress field,this study compared the geophysical characteristics of these two regions.Results shows that,①There is a structural belt of horsts and grabens at the outer edge of the northern part of the Yap Trench.The depth of the southwestern end of the Mariana Trench where the Caroline Island Ridge being subducted is shallower than that of the surrounding area.And a concave angle is formed at the subduction front of the Ridge.②The high Bouguer anomaly in the northern part of the Yap Arc and the southwestern end of the Mariana Arc corresponding to the Caroline Island Ridge suggest that the strong tectonic erosion may lead to the loss of volcanic arc crust,which indicates that high-density materials upwell underlie the arc.③The seismic activities of the northern part of the Yap subduction zone and the southwestern end of the Mariana subduction zone are weak,and there is a lack of high magnitude earthquakes,suggesting that the Caroline Island Ridge subduction inhibits the tectonic activity of the subduction zone.There are a few moderate earthquakes in the southwestern end of the Mariana subduction zone,indicating that the slab subduction depth in the region is deeper than that in the northern part of the Yap subduction zone.④The earthquakes at the southwestern end of the Mariana subduction zone have more strike-slip components,which are related to the oblique subduction of the Caroline plate and the oblique collision of the Caroline Island Ridge.⑤The subduction angle of the Caroline Island Ridge relative to the trench strike is the key factor for leading to the differences in geophysical characteristics between the northern part of the Yap subduction zone and the southwestern end of the Mariana subduction zone.