Does Modern Flat-Subduction Cause Subsidence or Uplift?

国际地球物理研究所建议确定长波高程变化的方向和大致幅度，这是智利中部和阿根廷西部之下现代平坦俯冲系统的结果。具体的研究区域是Sierras Pampeas省，这是一个类似于北美拉莱姆落基山脉省的广阔地区。在这两个地区，基底地块沿着造山带前陆(南美洲的安第斯山脉和北美的科迪勒造山带)的逆断层隆起。但在北美古代的例子中，由于平面俯冲，前陆地区遭受了长波下沉，而今天的Sierras Pam花生地区高于海平面，高于邻近的前陆地区，具有更正常的俯冲角度。这项研究的目的是检验Sierras Pampeasas地区在平面俯冲过程中(以长波)上升的假设。这项研究是对大陆内陆的研究，其目的是限制俯冲过程。它的效用是构造性的，即使它的方法是地层学的。平面俯冲值得重点研究，因为它为从不同的角度观察俯冲板块的性质及其与俯冲板块的相互作用提供了一个极好的机会，这将有助于阐明“正常”的俯冲系统以及平板系统。俯冲板和俯冲板块之间的接触性质对人类具有巨大的重要性，占世界地震预算的绝大多数。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和准确的预测，我们必须对俯冲带过程中俯冲板块的长期响应施加地质约束。PI建议将Sierras Pampeas的现代长波地貌与平坦俯冲开始时的地貌进行比较，使用三种方法来表征中中新生代地貌。首先，一名研究生和PI将与阿根廷同事合作，确定Sierras Pampeas群岛中中新世海相层的范围。这些单元在该地区的北部和东部两端附近受到了适度的限制，并假设到达Sierras Pampeas的中心部分，但这一假设需要关键的检验。其次，他们将使用地震反射数据(由Repsol-YPF提供)在中中新统覆盖的基准面上建立起伏断面，然后在上中新统覆盖的表面上建立起伏断面。一条横断面将从北到南横跨该省大部分地区，另一条横断面将从西到东横跨西拉斯帕姆花生山脉。第三，他们将利用这样一个事实，即在中新世沉积之前有一个类似于准平原的低起伏表面，并将其用作山脉和盆地的构造标志。他们将构建前中新世地表当前海拔的数字高程模型，并从中去除从晚中新世到新断裂的短波形变。将这一“部分校正的表面”的长波高程变化与现代长波地形、中新世中上部地层下的地貌断面以及海洋海岸线进行比较，将揭示在平面俯冲过程中隆起或下沉的地段。

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.