Does Modern Flat-Subduction Cause Subsidence or Uplift?

AbstractThe PI建议确定长波长高程变化的方向和大致幅度，这是智利中部和阿根廷西部现代平坦俯冲系统的结果。具体的研究区域是Sierras Pampeanas省，这是一个类似于北美Laramide Rocky Mountain省的广阔地区。在这两个地区，基底块体都是沿着造山带前陆（南美洲的安第斯山脉和北美洲的科迪勒拉造山带）的逆断层沿着隆起的。但在北美古代的例子中，前陆地区由于平坦俯冲而遭受了长波长的沉降，而今天的Sierras Pampeanas地区位于海平面以上，并高于邻近的前陆地区，具有更多的正常俯冲角。本研究的目的是检验Sierras Pampeanas地区在平坦俯冲过程中上升（长波长）的假设。本项目是对大陆内部的研究，其目的是限制俯冲过程。它的效用是构造的，即使它的方法是地层的。平俯冲值得重点研究，因为它提供了一个极好的机会，从不同的角度来看俯冲板块的性质及其与覆盖板块的相互作用，这将揭示“正常”俯冲系统以及平板系统。俯冲板块和上覆板块之间的接触性质对人类具有巨大的重要性，对世界上绝大多数的地震预算负责。但是，为了使地震学研究和板块相互作用的力学模型产生富有成效的洞察力和准确的预测，我们必须对上覆板块对俯冲带过程的长期反应进行地质约束。PI建议使用三种表征中中新世古地形的方法，将Sierras Pampeanas的现代长波地形与平坦俯冲开始时的地形进行比较。首先，一名研究生和PI将与阿根廷同事合作，确定整个Sierras Pampeanas的中中新世海洋地平线的范围。这些单元在该区域的北方和东部极端附近受到适度的限制，并假设到达Sierras Pampeanas的中部，但这一假设需要严格的检验。其次，他们将使用地震反射数据（由Repsol-YPF提供）来构建中中新世地层上覆的基底表面上的起伏断面，然后构建上中新世地层上覆的表面上的起伏断面。一条样带将从北到南跨越该省的大部分地区，第二条样带将从西到东跨越Sierras Pampeanas。第三，他们将利用这样一个事实，即一个类似平原的低起伏表面早于中新世沉积，并将其作为山脉和盆地的结构标志。他们将构建一个前中新世地表当前高程的数字高程模型，并从中移除中新世晚期至最近断层的短波长变形。将这一“部分校正表面”的长波长高程变化与现代长波长地形、中中新世地层和上中新世地层下方的地形剖面以及海洋海岸线进行比较，将揭示在平坦俯冲过程中隆起或下沉的部分。

AbstractThe PI proposes to determine the direction and approximate magnitude of change in long-wavelength elevation that is the consequence of the modern flat subduction system beneath central Chile and western Argentina. The specific study area is the Sierras Pampeanas province, a broad region that is analogous to the Laramide Rocky Mountain province of North America. In both regions basement blocks are uplifted along reverse faults in the foreland of the orogenic belt (Andes Mountains in South America and Cordilleran orogen in North America). But in the North American ancient example the foreland region suffered long-wavelength subsidence due to flat subduction, whereas the Sierras Pampeanas area today stands above sea level and above neighboring foreland regions with more normal subduction angles. The purpose of this study is to test the hypothesis that the Sierras Pampeanas region has risen (at long wavelength) during flat subduction.This project is a study of a continental interior whose objective is to constrain the subductionprocess. Its utility is tectonic, even if its methods are stratigraphic. Flat subduction merits focused study because it presents an excellent opportunity to view the properties of subducting plates and their interactions with overriding plates from a different perspective, which will shed light on "normal" subduction systems as well as flat-slab systems. The nature of contact between a subducting slab and an overriding plate is of enormous human importance, responsible for the vast majority of the world's seismic budget. But for seismological studies and mechanical models of plate interactions to lead to fruitful insight and accurate predictions, we must have geological constraints on the long-term responses of the overriding plates to the subduction zone processes. The PI proposes to compare modern long-wavelength topography of the Sierras Pampeanas to thetopography when flat subduction began using three means of characterizing the middle Miocenepaleo-topography. First, a graduate student and the PI will collaborate with Argentine colleagues to determine the extent of middle Miocene marine horizons across the Sierras Pampeanas. Such units are moderately well constrained near the northern and eastern extremes of the region and hypothesized to reach central sectors of the Sierras Pampeanas, but that hypothesis needs critical testing. Second, They will use seismic reflection data (provided by Repsol-YPF) to construct transects of the relief on the basal surface across which the middle Miocene strata onlapped, and then the relief on the surface across which the upper Miocene strata were draped. One transect will span most of the province from north to south, and a second will span the Sierras Pampeanas from west to east. Third, they will take advantage of the fact that a peneplain-like low-relief surface pre-dated the Miocene deposits and use this as a structural marker in both the ranges and basins. They will construct a Digital Elevation Model of current elevations of that pre-Miocene surface and remove from it the short-wavelength deformation across late Miocene to Recentfaults. Comparison of the long wavelength elevation variations of this "partially corrected surface" to the modern long-wavelength topography, to the transects of relief underlying the middle and upper Miocene strata, and to the marine shoreline will reveal sectors that uplifted or that subsided during flat subduction.