Collaborative Research: Distribution and Evolution of Geomorphic Process Zones in Large Mountain Ranges

合作研究：大山脉地貌过程带的分布与演化

• 批准号: 9628737
• 负责人: Thomas Dunne
• 金额: --
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-09-01 至 1999-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9628737&HistoricalAwards=false
• 关键词: Collaborative; Research; Distribution; Evolution; Geomorphic

Dunne 9628737 Large mountain ranges exhibit striking regional scale morphologic heterogeneity which is reflected in the dominance of different geomorphic processes in different parts of the range. The spatial and temporal distribution of these processes and affects the rate and manner in which sediment is evacuated from the range, which feeds back on tectonic processes and affects the behavior of rivers beyond the range front, where human populations are often concentrated. The objectives of the proposed study are to document and mechanistically explain major downstream, inter basinal, and temporal trends in morphology and geomorphic process within a large, important mountain range: the Eastern Cordillera of the Bolivian Andes. Fluvial incision creates relief, which strongly modulates the type and rate of geomorphic processes acting on hillslopes, and the relative ability of a river to transport its sediment load governs loci of incision and deposition, behavior of the river, and therefore morphology of the valley. Understanding spatial and temporal patterns of morphology and geomorphic process in large mountain ranges therefore requires the ability to quantitatively describe fluvial incision into mountain ranges, as well as to link hillslope and fluvial characteristics resulting from incision to specific geomorphic processes. These requirements dictate the methodology to be employed in this study, which involves four major steps. First, the modern pattern of geomorphic regions must be documented within two large drainage basins, the Beni and Pilcomayo, in the Eastern Cordillera. These basins share similar rocktypes and general tectonic histories, but north-south variation in precipitation and total shortening (and therefore fluvial incision history) has produced strikingly different morphologies. Regions dominated by particular hillslope and fluvial geomorphic processes will be identified from field observations and image interpretation. Each region will be characterized morphometrical ly to determine: 1) which indices best reflect the occurrence of particular processed; and 2) what general trends characterize large mountain drainage basins. The second major task of the study is to develop and apply a channel network incision model calibrated with field data to illustrate how channel slopes vary and relief is generated through time. In this model, downcutting rate is proportional to stream power, and the spatial and temporal pattern of uplift is constrained by regional structural geology studies, paleoelevation studies, and a geodynamic model. Third, information derived from the fluvial incision model will be used in "off-line" calculations to determine 1) how hillslopes change shape and local relief grows and diminishes through time; and 2) where incisional and depositional regimes occur and how fluvial regime affect valley morphology. For example, the geometry and rate of hillslope lowering by deep-seated, bedrock landsliding will be calculated using successive Culmann wedge stability analyses on steep hillslopes produced by a known rate of fluvial incision. Calculations will be made at selected times during a fluvial incision model run and at selected places down the network. Finally, the fluvial incision model and the predictions made in off-line calculations will be checked with several sources of independent data. The general geomorphic patterns and morphometric characteristics of simulated landscapes will be compared to those of the modern Beni and Pilcomayo basins. Predicted long-term surface lowering rates will be compared with exhumation rates determined from fission track analysis of igneous and metamorphic rocks from both basins, while predictions of the rates determined from fission track analysis of igneous and metamorphic rocks from both basins, while predictions of the net rate of sediment export from drainage basins of various sizes will be compared with rates obtained from analysis of cosmogenic isotopic abundance in alluvium. The proposed study has many applications ranging from defining the nature of local geologic hazards to anticipating shifts in gobal erosion and sedimentation patterns due to climatic change.

大山脉表现出惊人的区域尺度的形态异质性，这反映在不同的地貌过程在不同的范围内的优势。这些过程的空间和时间分布影响着沉积物从山脉中排出的速度和方式，这对构造过程产生反馈作用，并影响着山脉前沿以外的河流的行为，而人类人口往往集中在那里。拟议研究的目标是记录和机械地解释主要下游，流域间，和时间趋势的形态和地貌过程中的一个大的，重要的山脉：东科迪勒拉的玻利维亚安第斯山脉。河流下切产生的地形起伏，强烈地调节了作用于山坡的地貌过程的类型和速率，河流输送泥沙的相对能力决定了下切和沉积的位置、河流的行为，从而决定了山谷的形态。因此，要了解大型山脉的形态和地貌过程的空间和时间模式，就需要有能力定量描述河流对山脉的切割，并将切割产生的山坡和河流特征与具体的地貌过程联系起来。这些要求决定了这项研究所采用的方法，其中包括四个主要步骤。首先，必须在东科迪勒拉山脉的贝尼和皮科马约两个大流域内记录地貌区域的现代格局。这些盆地具有相似的岩石类型和一般的构造历史，但降水量和总缩短（因此河流切割历史）的南北变化产生了惊人的不同形态。将通过实地观察和图像判读确定以特定山坡和河流地貌过程为主的区域。每个区域将被描述为形态计量学，以确定：1）哪些指数最能反映特定过程的发生; 2）大山区流域的一般趋势是什么。研究的第二个主要任务是开发和应用一个经现场数据校准的河道网络切割模型，以说明河道坡度如何随时间变化，以及如何产生地貌。在该模型中，下切速率与水流功率成正比，隆升的时空格局受区域构造地质研究、古高程研究和地球动力学模型的约束。第三，从河流下切模型中获得的信息将用于“离线”计算，以确定1）山坡如何改变形状，局部地形如何随着时间的推移而增长和减少;以及2）在何处出现下切和沉积状态，以及河流状态如何影响山谷形态。例如，通过对已知河流下切速率产生的陡峭山坡进行连续的Culmann楔形体稳定性分析，计算深层基岩滑坡导致的山坡降低的几何形状和速率。将在河流下切模型运行期间的选定时间和网络下游的选定地点进行计算。最后，河流下切模型和离线计算的预测将与几个独立的数据来源进行检查。模拟景观的一般地貌模式和形态特征将与现代贝尼和皮科马约盆地的地貌模式和形态特征进行比较。预测的长期地表下降速率将与根据两个盆地的火成岩和变质岩的裂变径迹分析确定的折返速率进行比较，而根据两个盆地的火成岩和变质岩的裂变径迹分析确定的速率预测，而对不同大小流域的沉积物净输出速率的预测将与从宇宙成因同位素丰度分析中获得的速率进行比较在冲积层中。这项拟议中的研究有许多应用，从确定当地地质灾害的性质到预测气候变化引起的全球侵蚀和沉积模式的变化。