Collaborative Research: Crustal Thickening, Shortening, and Uplift in the Forearc of an Erosive, Convergent Margin, Pacific Coast, Costa Rica

合作研究：哥斯达黎加太平洋海岸侵蚀汇聚边缘弧前的地壳增厚、缩短和隆起

• 批准号: 0337456
• 负责人: Donald Fisher
• 金额: $ 23.94万
• 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: 2004
• 资助国家: 美国
• 起止时间: 2004-01-01 至 2007-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0337456&HistoricalAwards=false
• 关键词: Collaborative; Research; Crustal; Thickening; Shortening

This project involves analysis of the onland geology of the upper plate along an active convergent plate boundary, where the Cocos plate and associated seamounts and ridges are underthrust beneath the Central American volcanic chain. In general, convergent plate boundaries can be characterized by two end-members: accretionary margins and erosive margins. The processes that occur along accretionary margins (e.g., the Aleutian, Nankai, Barbados, and Oregon-Washington margins) are well known from studies of onland and marine geology, but there is no comparable knowledge for erosive margins (e.g.,. the Japan, Peru, Middle America margins). Consequently, the principal investigators are creating new maps and cross sections of bedrock geology and dating marine and fluvial terraces along the Pacific Coast of Costa Rica to place constraints on shortening, uplift rates, and surface erosion in such a tectonic setting. Mapping of faults and determination of fault offsets from bedrock geology provide an estimate of the amount of shortening over the last 2 million years. Surveys of marine terraces along the coast are being combined with radiocarbon and optical stimulated luminescence dating to determine rates of vertical motion and slip rates on active faults. Analysis of river terraces and fission track dating of apatite grains in both volcanics and sedimentary rocks are being used to establish the rate and total amount of erosional unroofing. Moreover, on the Osa and Nicoya Peninsulas, newly discovered deposits of Neogene and Quaternary marine terraces and shallow marine deposits provide an unprecedented record of vertical tectonism. Paleomagnetic analysis of these deposits should extend this record back into the late Neogene. Recently, new volcanic rocks have been discovered along the coast that can be dated by Ar40/Ar39 methods to better constrain the age of initiation of active thrust faulting in the coastal deformed belt. The methods that are used in this study are designed to quantify the effects of incoming seamounts and ridges on active faulting and landscape evolution of the upper plate. There is an apparent dichotomy between the offshore response to these bathymetric features (tectonic erosion, subsidence) and the onland response (crustal thickening and uplift). By collecting a dataset that constrains timing, kinematics and rates of deformation, this study is defining the fundamental attributes of erosive convergent plate boundaries and the relationship between onland and offshore regimes.

该项目涉及对上层板块沿着主动收敛板边界的onland地质的分析，在该边界上，可可板和相关的海底和山脊在中美洲火山链下面含糊不清。 通常，收敛板边界可以由两个末端成员来表征：增生边缘和侵蚀边缘。 从Onland和Marine Geology的研究中众所周知，沿增生边缘（例如Aleutian，Nankai，Barbados和Oregon-Washington边缘）发生的过程是众所周知的秘鲁，中美洲边缘）。 因此，主要研究人员正在哥斯达黎加太平洋海岸沿着基岩地质和河滨露台约会的新地图和横截面，以在这种构造环境中对缩短，上升速度和表面侵蚀施加限制。 故障的映射和确定基岩地质的故障偏移量，可估算过去200万年的缩短量。 沿海海洋露台的调查与放射性碳和光学刺激的发光日期结合在一起，以确定活动故障上的垂直运动速率和滑动速率。 对火山和沉积岩中磷灰石晶粒的河水露台的分析和裂变轨道日期都用于建立侵蚀不盖的速率和总量。 此外，在OSA和NOCOYA Peninsulas上，新近发现的新近纪和第四纪海洋露台和浅海矿床的沉积物提供了前所未有的垂直构造记录。 这些沉积物的古磁分析应将此记录延伸到新纪晚期。 最近，在沿海地区发现了新的火山岩石，可以通过AR40/AR39方法进行日期，以更好地限制沿海变形皮带中主动推力断层的开始。 本研究中使用的方法旨在量化进入船尾和脊对上板的活动断层和景观演化的影响。 对这些测深特征（构造侵蚀，沉降）的近海反应与越野反应（地壳增厚和抬高）之间存在明显的二分法。 通过收集一个限制定时，运动学和变形速率的数据集，本研究正在定义侵蚀性收敛板边界的基本属性以及Onland和Onland和离岸政权之间的关系。