Inner Forearc Deformation Along an Erosive Convergent Margin, Northeastern Japan

俯冲带在地球长期质量平衡中起着重要作用？它们可以作为大陆边生长（增生边）或大陆边剥蚀（侵蚀边）的场所。 本研究将量化缩短率，侵蚀率，和表面隆起率在弧前的一个经典的侵蚀收敛边缘在日本东北部。将评估整个前弧的质量平衡，并将永久应变积累模式与从地震和大地测量数据推断的弹性应变进行比较。在前弧的内部和外部，隆起边缘通常表现出系统性的相反行为，1）外部前弧大部分是海底的，显示出伸展的证据，并有一个广泛的斜坡裙，记录了边缘的沉降;和2）内部前弧与海岸山脉，隆起，和岩石，显示出缩短和永久应变的证据。这种对联沿着世界各地的侵蚀边缘相对普遍存在，表明了一种潜在的遗传关系。这个项目是为了验证这样一个假设，即由于基底侵蚀或俯冲作用而导致的弧前外沉降，与由底侵作用或逆冲作用驱动的弧前内隆起相匹配。如果这一假设是正确的，那么，根据弧前外沉降对大陆剥蚀的全球长期估计就大大高估了大陆边物质俯冲的数量。该研究小组将采用多学科方法，包括构造测绘和断层相关褶皱分析、大地年代学、低温热年代学（包括磷灰石裂变径迹分析和（U-Th）/He测年）、海洋阶地分析和地球动力学（热和变形）建模。的俯冲带经历基底侵蚀，从而通过板块边界向上迁移到现有的边缘楔外部前弧被删除。目前尚不清楚的是，基底侵蚀速率会持续多久，被侵蚀的物质会去哪里？本研究通过研究活动系统的内部前弧来解决这些问题。在1846年的小猎犬号探险中，查尔斯·达尔文首次注意到了弧前隆起，当时他在海平面以上一公里的海洋阶地上观察到了贝壳，并认为南美洲西海岸存在区域性隆起。现代近海水深测量表明，达尔文所描述的局部隆起区域位于弧前侵蚀明显的区域内侧。弧前内部的隆起可以平衡由于基底侵蚀而引起的弧前沉降。

Subduction zones play an important role in the long-term mass balance of earth?s crustal materials - they can serve as either sites of continental margin growth (accretionary margins) or continental margin denudation (erosional margins). This study will quantify shortening rates, erosion rates, and surface uplift rates in the forearc of a classical erosive convergent margin in northeastern Japan. The mass balance across the forearc will be assessed and patterns of permanent strain accumulation will be compared with elastic strain inferred from seismic and geodetic data. Erosive margins often exhibit systematically opposed behavior in the inner and outer portions of the forearc, with 1) an outer forearc that is mostly submarine, showing evidence for extension, and having an extensive slope apron that records subsidence of the margin; and 2) an inner forearc with coastal mountains, uplift, and rocks that show evidence for shortening and permanent strain. The relative ubiquity of this couplet along erosive margins worldwide suggests a potential genetic relationship. This project is testing the hypothesis that outer forearc subsidence due to basal erosion, or underthrusting, is matched by inner forearc uplift driven by underplating, or overthrusting. If this hypothesis is correct, global long-term estimates of continental denudation that are based on outer forearc subsidence grossly overestimate the amount of continental margin material subducted. The research team will employ a multi-disciplinary approach that includes structural mapping and fault-related fold analysis, tephrachronology, low-temperature thermochronometry (including apatite fission track analysis and (U-Th)/He dating), analysis of marine terraces, and geodynamic (thermal and deformational) modeling.It has become increasingly apparent over the last two decades that many, if not the majority, of the earth?s subduction zones experience basal erosion, whereby the outer forearc is removed through upward migration of the plate boundary into the existing margin wedge. What is not known is how long are basal erosion rates sustained and where does eroded material go? This study addresses these problems by examining the inner forearc of an active system. Inner forearc uplift was first noted by Charles Darwin during the Beagle expedition of 1846 when he observed sea shells atop marine terraces located a kilometer above sea level and argued for regional uplift of the western coast of South America. Modern surveys of offshore bathymetry show that the local regions of uplift described by Darwin lie inboard of areas with pronounced outer forearc erosion. Inner forearc uplift may balance forearc subsidence due to basal erosion.