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首页> 外文期刊>Journal of geodynamics >Contrasts in tectonic style of the Central and Southern Appalachians, United States: Insights from seismic reflection data
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Contrasts in tectonic style of the Central and Southern Appalachians, United States: Insights from seismic reflection data

机译：美国中部和南部阿巴拉契亚人的构造风格对比：地震反射数据的见解

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摘要

Two reflection seismic transects, one across the central Appalachians in Virginia and the other across the southern Appalachians in Georgia, reveal a significant contrast in mid- and lower crustal reflectivity from east to west. Data from east of the Blue Ridge geologic province in Virginia and to the east of the Inner Piedmont in Georgia show a highly reflective crust extending from the near-surface to the Moho, including zones of east-dipping reflections, a sub-horizontal reflection signature at ～7 seconds, and a west-dipping Moho. Reflection seismic data from west of the Blue Ridge in Virginia and Inner Piedmont farther south are characterized by reflector geometries related to deformation above a master decollement, leading to classic 'thin-skinned' tectonic structures in the overlying allochthon, and few if any apparent structures in the underlying basement. The location of the lapetan rifted margin, the preexistence of favorably oriented structures to the east of this point, and sub-horizontal weak zones within the lower Paleozoic shelf strata have played critical roles in the distribution of seismic reflector geometry. Seismic reflection signatures seen in the southeastern United States are a result of multiple episodes of deformation from the early Paleozoic through the middle Mesozoic. Oblique stresses during late Paleozoic time produced transpression that manifested itself as predominantly strike-slip faulting to the east of the Blue Ridge/Inner Piedmont. Onlapping lower Paleozoic shelf strata responded to tectonic stresses through thin-skinned deformation above a master decollement during the late Paleozoic Alleghanian orogeny, aided in part by sub-horizontal zones of weakness in the strata. This partitioning of strain was supported via tectonic buttressing provided by Precambrian continental crust that was little deformed in the Taconic orogeny. During the Alleghanian orogeny, the variations in Valley and Ridge deformational style between the central and southern Appalachians were controlled by the original shape of the continental edge. Further deformation during Mesozoic extension occurred to the east of the Precambrian rift margin in the region where favorably oriented faults were reactivated, leading to the rotation of the fault zones from more steeply dipping initial orientations, the merging of the mid-crustal reflection zone with the Moho, and the formation of Mesozoic basins and antiformal reflections in the seismic sections.
机译：两个反射地震剖面，一个横跨弗吉尼亚州中部阿巴拉契亚山脉，另一个横跨佐治亚州南部中部阿巴拉契亚山脉，揭示了中东部地壳反射率从低到低的显着差异。来自弗吉尼亚州蓝脊地质省东部和佐治亚州内山麓东部的数据显示，从近地表一直延伸到莫霍面的反射性强的地壳，包括东向反射带，次水平反射带大约7秒，还有西倾莫霍河。来自弗吉尼亚州蓝岭山脉以西和内山麓更南端的反射地震数据的特征是反射器的几何形状与主弯折上方的变形有关，从而导致上覆异位层形成经典的“薄皮”构造构造，几乎没有明显的构造在地下室。拉佩坦裂谷边缘的位置，该点以东的优先定向结构的存在以及下古生代陆架地层内的亚水平弱带在地震反射体几何分布中起着关键作用。在美国东南部看到的地震反射特征是从早古生代到中中生代多次变形的结果。古生代末期的斜应力产生了压转作用，其表现为蓝岭/内皮埃蒙特东部的主要走滑断裂。下古生代陆架地层在古生代Alleghanian造山作用后期，通过主弯折之上的薄皮形变对构造应力作出了响应，这在一定程度上得益于地层水平下的弱化带。应变的这种划分是通过前寒武纪大陆壳提供的构造支撑来实现的，该大陆壳在塔康尼克造山带中几乎没有变形。在Alleghanian造山运动期间，中部和南部阿巴拉契亚山脉之间的山谷和山脊变形样式的变化受大陆边缘的原始形状控制。在中生代伸展期间进一步的变形发生在前寒武纪裂谷边缘的东部，在该地区重新定向了有利的断层，导致断层带从更陡峭的初始方位旋转，中地壳反射带与地壳反射带合并。莫霍面，中生代盆地的形成和地震剖面中的反形式反射。

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