Collaborative Research: Three-Dimensional Kinematic History of the Wyoming Salient: Implications for Development of Curved Orogens

大多数山带在不同尺度上显示出不同程度的弯曲，记录了复杂的三维变形历史。 然而，尽管它们无处不在的发生，很少有例子存在的变形历史和过程负责造山曲率已充分量化的地质证据。 这些历史是嵌入在区域构造趋势，古地磁方向，中观结构，变形岩石的粒度组构。 塞维尔造山带的犹他-爱达荷-怀俄明州凸起是研究在一定范围内产生曲率的过程的理想地点。 主要逆冲断层和褶皱的区域趋势从凸起的北端到南端弯曲90度，在交叉走向转换带附近有额外的局部曲率。 突出部的岩石还携带多种古地磁成分，并显示出系统的中观和微观结构（包括解理、小褶皱、小断层网络和变形化石），提供了单个逆冲岩席内旋转和内部应变的记录。 在怀俄明州突出的初步研究揭示了初级前逆冲和次级同褶皱古地磁组件，记录复杂的旋转历史有关的逆冲曲率。 初步研究还揭示了大致一致的区域应变模式，广泛的层平行缩短在高角度的推力趋势，轻微的切向延伸平行于推力趋势，和轻微的扳手剪切。 方解石孪生应变，积累在早期层平行缩短之前，大规模的逆冲，提供了另一个参考框架，记录当地显着的旋转。正在进行的工作集中在位于南部，中部和北方前部的突出，并在两个地层水平（侏罗纪双溪石灰岩和红层的三叠纪Ankareh形成），以及暴露，携带多个磁化，并包含多个应变标志物的三个“条带”的组合古地磁和结构研究。 主要逆冲断层的滑移线理数据分析和二维剖面构造表明，逆冲断层的输运方向总体上由凸起北方的ENE向转变为凸起南部的ESE向，断层滑移量向凸起南北两端逐渐减小。 三维横截面，由丰富的地震数据的约束，并纳入新的应变和旋转数据，从这项研究中，正在构建开发一个强大的运动学模型的突出。 该模型将被用来确定控制机制负责山区带曲率，包括地层厚度的变化，强度变化沿着断层，运动的压头，和前陆支墩效应。 这一研究涉及到有关山带演化的几个基本问题。(1)旋转、应变、逆冲断层滑动的变化和凸曲率之间的关系是什么？(2)将应变和旋转数据纳入造山带三维模型的结果是什么？(3)在发展弯曲山区带时，哪些因素最重要，如何最好地确定这些因素？ 最后，将把怀俄明州突出部的发现与其他正在进行的弯曲山脉带的类似研究进行比较，为弯曲造山带的发展提供一系列可行的模型。 最后，将应变和旋转数据纳入三维可压缩变形模型，将提高我们对褶皱-冲断带油气聚集的总体认识。

Most mountain belts display varying degrees of curvature over a range of scales, recording complex, three-dimensional deformation histories. However, despite their ubiquitous occurrence, few examples exist where deformation histories and processes responsible for orogenic curvature have been adequately quantified from geologic evidence. These histories are embedded in regional structural trends, paleomagnetic directions, mesoscopic structures, and grain-scale fabrics of deformed rocks. The Utah-Idaho-Wyoming salient of the Sevier orogenic belt is an ideal location to study processes that produce curvature over a range of scales. Regional trends of major thrust faults and folds curve through 90 degrees from the north to south end of the salient, with additional local curvature near cross-strike transfer zones. Rocks in the salient also carry multiple paleomagnetic components and display systematic suites of mesoscopic and microscopic structures (including cleavage, minor folds, minor fault networks, and deformed fossils), providing a record of rotations and internal strain within individual thrust sheets. Initial studies in the Wyoming salient reveal both primary pre-thrusting and secondary syn-folding paleomagnetic components that record complex rotation histories related to thrust curvature. Initial studies also reveal broadly consistent regional strain patterns, with widespread layer-parallel shortening at high angles to thrust trends, minor tangential extension parallel to thrust trends, and minor wrench shear. Calcite-twin strains, which accumulated during early layer-parallel shortening prior to large-scale thrusting, provide another reference frame that records locally significant rotations. Ongoing work is focused on combined paleomagnetic and structural studies of three 'swaths' located in the southern, central, and northern frontal parts of the salient, and on two stratigraphic levels (Jurassic Twin Creek Limestone and redbeds of the Triassic Ankareh Formation) that are well exposed, carry multiple magnetizations, and contain multiple strain markers. Analysis of slip lineation data from major thrust faults and construction of two-dimensional cross sections indicate that thrust transport directions change overall from ENE in the northern part to ESE in the southern part of the salient, and fault slip magnitude decreases toward the north and south ends of the salient. Three-dimensional cross sections, constrained by abundant seismic data, and incorporating new strain and rotation data from this study, are being constructed to develop a robust kinematic model of the salient. The model will be used to identify controlling mechanisms responsible for mountain belt curvature, including variations in stratigraphic thicknesses, strength changes along faults, motion of indentors, and foreland buttress effects. This investigation addresses several fundamental questions concerning the evolution of mountain belts. (1) What are the relations between rotations, strain, changes in thrust fault slip, and salient curvature? (2) What are the consequences of incorporating strain and rotation data into three-dimensional models of orogenic belts? (3) What factors are most important in developing curved mountain belts and how can these factors be best identified? Ultimately, findings from the Wyoming salient will be compared with similar ongoing studies of other curved mountain belts, providing an array of viable models for the development of curved orogens. Lastly, inclusion of strain and rotation data into three-dimensional restorable deformation models should improve our general understanding of hydrocarbon accumulations in fold-thrust belts.