Collaborative Research: Investigating Controls on Temporal-spatial Heterogeneous Deformation Along a Transpressive Strike-slip Fault System: The Eastern Denali Fault Corner

2000公里长的德纳里断层是阿拉斯加一个主要的活动断层系统，它连接着地壳块体，这些地壳块体以水平方式相互滑动。该断层在过去6500万年中有着漫长而复杂的历史。由于其复杂弯曲的几何形状，部分断块的运动方向与断裂走向相倾斜，形成盆地、褶皱带和冲断带。在这个项目中，来自普渡大学、雪城大学和阿拉斯加大学的一个研究小组正在研究这个断层的一部分，以更好地了解控制这些地壳块体如何变形的因素。他们特别感兴趣的是确定断层两侧块体的强度或断层的几何形状是否控制了变形。世界上有许多像德纳里断层这样的大型活动断层系统，了解它们的行为是很重要的，因为许多断层都能够产生像2002年德纳里断层7.9级地震这样的大地震。该研究的其他预期社会成果包括：通过支持美国原住民学生和研究人员、向阿拉斯加原住民社区推广、以及通过本科生和研究生培训培养具有全球竞争力的STEM劳动力，充分参与STEM中代表性不足的少数民族。主要走滑运动与斜向辐合带之间的过渡带是走滑断层的共同特征。沿这些逆压断层的变形在一定程度上受施加应力的倾斜度和断层的几何形状（走向和倾角的变化）以及岩石圈和地壳尺度上断层的流变对比所控制。这些逆压断裂带有助于我们了解应变是如何调节的，以及由逆冲带和前陆盆地定义的广阔带是如何沿着走滑断裂系统演化的，因为地壳块体沿着不同倾角的区域被平移。迪纳里断裂带东中部的走向和倾角大致为120公里，几何形状简单，位于两个强度对比强烈的大型复合地体之间，有文献记载的新生代垂直构造史。因此，它可以作为一个天然的实验室来研究这两种不同的边界条件对沿这一活动走滑断裂系统的变形历史的影响。该项目将研究断层几何相对于沿迪纳利断层东角变形非均质性的跨断层岩石圈强度对比的重要性。该区的德纳里断裂由以走滑为主转变为以压迫为主。关于这种逆压断层系统如何调节应变和变形的竞争性假设（强度vs几何）将通过综合热年代学、地质年代学、构造和盆地分析研究来检验。迪纳里断裂带南北两侧的碎屑（现代河流沉积物和地层沉积物）和基岩热年代学（k -长石40Ar/39Ar、磷灰石裂变径迹和磷灰石(U-Th)/He）将作为变形过程的代用物和记录物，与断裂带盆地发育相结合，追踪挖掘的时空格局。40Ar/39Ar和裂变径迹的地层年代学、孢粉学和镜质组反射率将描述盆地沉降、反演、热史和缩短速率的时间。砾岩和砂样碎屑的40Ar/39Ar和U-Pb年代学将有助于了解断裂沿岸盆地的古排水模式和沉积物源的位移。总之，这些综合数据将对两种常见的边界条件在沿大陆走滑断层系统的非均匀变形模式中所起的相对贡献提供重要的新约束。

The 2,000 km long Denali Fault is a major active fault system in Alaska that bounds crustal blocks, which slide past each other in a horizontal fashion. The fault has a long and complicated history over the past 65 million years. Due to its complex and curved geometry, there are portions of the fault where the motion of the blocks is oblique to the fault trend resulting in the formation of basins and fold and thrust belts. In this project, a research team from Purdue University, Syracuse University, and the University of Alaska are studying a portion of this fault to better understand the factors that control how these crustal blocks deform. They are particularly interested in determining whether the strength of the blocks on opposite sides of the fault or the geometry of the fault controls deformation. There are many large active fault systems like the Denali around the world and it is important to understand how these behave since many are capable of generating significant earthquakes such as the 2002 magnitude 7.9 earthquake on the Denali Fault. Additional desired societal outcomes of the study include full participation underrepresented minorities in STEM through support of Native American students and researchers and outreach to Alaskan Native American communities plus development of a globally competitive STEM workforce through undergraduate and graduate student training.Transitional zones between primarily strike-slip motion and oblique convergence are a common feature along strike-slip faults. Deformation along these transpressive faults is controlled in part by both the obliquity of the applied stress and fault geometry (variation in strike and dip), and rheologic contrasts across the faults on the lithospheric- and crustal-scale. These transpressive fault regions offer insight into how strain is accommodated and also how the broad zones defined by thrust belts and foreland basins evolve along strike-slip fault systems as crustal blocks are translated along regions of varying obliquity. The east-central Denali fault segment has a generally simple geometry of unvarying strike and dip for about 120 km, lies between two large composite terranes of contrasting strength, and has a documented history of vertical tectonics during the Cenozoic. Thus, it serves as a natural laboratory to study the affect of these two distinct boundary conditions on the history of deformation along this active strike-slip fault system. This project will examine the importance of fault geometry relative to contrasts in lithospheric strength across faults on the heterogeneity of deformation along the eastern corner of the Denali fault. The Denali fault in this region changes from dominantly strike-slip to a transpressive regime. The competing hypotheses (strength vs. geometry) on how strain is accommodated and deformation occurs along this transpressive fault system will be tested by integrating thermochronology, geochronology, structural, and basin analysis studies. Detrital (modern river sediment and from strata) and bedrock thermochronology (K-feldspar 40Ar/39Ar, apatite fission-track and apatite (U-Th)/He) north and south of the Denali fault will track spatial and temporal patterns of exhumation in conjunction with basin development along the fault as proxies and recorders for deformational processes. 40Ar/39Ar and fission track tephrachronology, palynology, and vitrinite reflectance will delineate timing of basin subsidence, inversion, thermal history, and shortening rates. 40Ar/39Ar and U-Pb geochronology on clasts from conglomerate and sand samples will provide insight into paleo-drainage patterns and displacement of sediment sources from basins along the fault. Together, these integrated data will yield important new constraints on the relative contributions two common boundary conditions play in heterogeneous deformation patterns along a continental strike-slip fault system.