Inner Forearc Deformation Along an Erosive Convergent Margin, Northeastern Japan

日本东北部沿侵蚀汇聚边缘的内前弧变形

• 批准号: 0809939
• 负责人: Donald Fisher
• 金额: $ 35.5万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0809939&HistoricalAwards=false
• 关键词: Inner; Forearc; Deformation; Along; Erosive

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.

俯冲带在地球地壳材料的长期质量平衡中起着重要作用 - 它们可以用作大陆边缘增长（增生边缘）或大陆边缘剥离（侵蚀边缘）的地点。 这项研究将量化日本东北部经典侵蚀性收敛边缘前臂的缩短率，侵蚀率和表面上升率。将评估整个前臂的质量平衡，并将永久性应变积累的模式与地震和大地测量数据推断出的弹性应变进行比较。侵蚀边缘通常在前臂的内部和外部部分表现出系统性相对的行为，其中1）一个主要是潜艇的外前臂，显示出延伸的证据，并具有广泛的斜率围裙，记录了边缘的沉降； 2）具有沿海山脉，隆升和岩石的内臂，显示出缩短和永久性应变的证据。沿全球侵蚀边缘的这种对联的相对普遍存在表明潜在的遗传关系。该项目正在检验以下假设：基础侵蚀或估价不足引起的外前臂沉降与内部前臂的抬高相匹配，这是由底漆或推翻的。如果该假设是正确的，则基于外前臂沉降的大陆剥离的全球长期估计值严重高估了俯冲的大陆边缘材料的量。研究团队将采用一种多学科方法，包括结构映射和与故障相关的折叠分析，tephrachroantology，低温热化学计（包括磷灰石裂变轨道分析以及（u-th）/HE DAD），海洋露台分析以及海洋露台的分析地球动力（热和变形）建模。在过去的二十年中，它变得越来越明显，以至于许多地球的俯冲区（即使不是大多数）经历了基础侵蚀，从而通过板边界的向上移动去除外侧前臂进入现有的边距楔子。尚不清楚的是，基础侵蚀率持续了多长时间，而侵蚀的材料将在哪里？这项研究通过检查活动系统的内臂来解决这些问题。 Charles Darwin在1846年的Beagle探险期间首先注意到内前臂的隆起，当时他在海平面以上的海洋露台上观察到海洋露台上的海壳，并主张南美西部海岸的区域升高。对海上测深的现代调查表明，由达尔文描述的隆起的当地地区躺在外侧前臂侵蚀的区域内。内臂的隆起可能由于基底侵蚀而平衡前臂沉降。