Collaborative Research: Strike-Slip History of the East Gobi Fault Zone, Mongolia: Modes of Intraplate Deformation, Sedimentary Basin Evolution, and Regional Fault Linkages

这项研究有助于理解大陆如何在大陆-大陆碰撞等重大构造事件的响应下变形。亚洲大陆是一个天然的实验室，可以解决以下问题：亚洲内陆是如何因印度和亚洲的碰撞而变形的？随着时间的推移，变形模式可能如何以及为什么会发生变化？沉积记录是如何反映这些事件的？该项目利用构造地质学、地质年代学和沉积盆地分析工具，重建蒙古东戈壁断裂带的位移历史和沉积盆地演化。初步数据表明，自晚古生代以来，这一主要的陆内剪切带至少重新激活了四次；这项工作记录了两次最不受约束的左旋滑移(中生代早期和新生代早期)。由于缺乏来自蒙古东南部的数据，东戈壁断裂带基本上被用作对抗亚洲构造“拼贴”演化模型的通配符。例如，已发表的模型估计左偏移距从中生代早期约200公里到纯新生代约400公里不等，引用了未经现场测试的区域地图关系。后一种解释意味着阿尔金·塔格断层与假设的走滑断层之间存在前中新世的联系--但基本上还没有文献记载--走滑断层穿过蒙古东南部延伸到鄂霍次克海。这项研究通过在东戈壁断裂带建立了新生代走滑断裂的控制点西南的中国-蒙古边界附近的填图来检验这种运动学联系是否允许，并提供了关于滑动时间和强度的第一个现场和分析约束。这些结果进一步验证了东戈壁断裂带重新激活古生代缝合的假设，从而进一步证实了有利于剪切带启动和重新激活的机制。收集了地质年代学数据，以评估蒙古东南部板内变形的时间作为远场力和不断演变的边界条件的函数。因此，这项研究与亚洲中生代以来的碰撞历史中的陆块挤压和连续体缩短模式有关。东戈壁断裂带暴露出的各种构造层次和变形所涉及的岩性为研究上地壳和深部剪切带/断裂带发育的流变控制提供了极好的机会。此外，东戈壁断裂带的变形阶段与东戈壁地区沉积岩之间的关系的研究，制约了扭动构造背景下“多历史”沉积盆地的形成、地层发育和随后的解体机制。合作的多学科性质突出了整合不同的地质数据集以解决一系列复杂问题的力量。这项研究的结果有助于更好地了解我们这个星球上一个研究不足、矿产资源丰富的地区。这项工作的国际性促进了蒙古和美国地质学家之间的合作，其中包括两名职业生涯早期的女性调查人员。此外，来自犹他州和锡拉丘兹的两名博士生和本科生参与了这项研究的所有方面，并接受了使用技术解决科学问题的培训。该项目的支持由构造学项目和国际科学与工程办公室东亚和太平洋小组提供。

This research contributes to the understanding of how continents deform in response to major tectonic events such as continent--continent collisions. The continent of Asia is a natural laboratory to address questions such as: How has the interior of Asia deformed in response to the collision of India and Asia? How and why might the modes of deformation have changed over time? How does the sedimentary record reflect such events? This project employs tools of structural geology, geochronology, and sedimentary basin analysis to reconstruct displacement history and sedimentary basin evolution along the East Gobi Fault Zone, Mongolia. Preliminary data suggest that this major intracontinental shear zone was reactivated at least four times since the late Paleozoic; this work documents two of the least-constrained episodes of left-lateral slip (early Mesozoic and early Cenozoic). Due to paucity of data from southeastern Mongolia, the East Gobi Fault Zone is essentially played as a wildcard against models of evolution of the Asian tectonic "collage." For example, published models estimate left-lateral offset ranging from approximately 200 km of early Mesozoic slip to approximately 400 km of purely Cenozoic slip, citing regional map relations that have not been field-tested. The latter interpretation implies a pre-Miocene linkage between the Altyn Tagh fault and hypothesized--but as yet largely undocumented--strike-slip faults extending through southeastern Mongolia to the Sea of Okhotsk. This study tests whether this kinematic linkage is permissible via mapping near the China-Mongolia border zone, southwest from control sites where Cenozoic strike-slip faulting has been established in the East Gobi Fault Zone, and provides the first field and analytical constraints on the timing and magnitude of slip. These results bear further on mechanisms favoring initiation and reactivation of shear zones by testing the hypothesis that the East Gobi Fault Zone reactivates a Paleozoic suture. Geochronologic data are collected to evaluate the timing of intraplate deformation in southeastern Mongolia as a function of far field forces and evolving boundary conditions. Thus, this research is relevant to models of continental block extrusion and continuum shortening during Asia's history of collisions from Mesozoic-Recent. The great variety of structural levels exposed and lithologies involved in deformation in the East Gobi Fault Zone provide an excellent opportunity to investigate rheologic controls on shear zone/fault zone development in the upper crust and at depth. Furthermore, investigation of the relationship between deformational phases of the East Gobi Fault Zone and sedimentary rocks in the East Gobi region constrain mechanisms of initiation, stratigraphic development, and subsequent dismembering of "poly-history" sedimentary basins in wrench-tectonic settings. The multidisciplinary nature of the collaboration highlights the power of integration of diverse geologic datasets to address a complex set of questions. Results of this study contribute to the greater understanding of an understudied and mineral resource-rich region of our planet. The international nature of this work fosters collaboration between Mongolian and American geologists, including two early-career female investigators. Additionally, two Ph.D. students and undergraduate students from Utah and Syracuse participate in all aspects of the study and are trained in the use of technology to solve scientific problems.Support for the project is provided by the Tectonics Program and by the East Asia and Pacific Group of the Office of International Science and Engineering.