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

2,000公里长的德纳利断层是阿拉斯加的一个主要活动断裂系统，它以水平方式相互滑动的地壳块体为边界。这条断层在过去的6500万年里有着漫长而复杂的历史。由于其复杂而弯曲的几何形状，在断层的某些部分，块体的运动与断层走向是倾斜的，从而形成了盆地和褶皱冲断带。在这个项目中，来自普渡大学、锡拉丘兹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。世界各地有许多像德纳利这样的大型活动断裂系统，了解它们的行为是很重要的，因为许多系统能够产生重大地震，如2002年德纳利断裂发生的7.9级地震。这项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全面参与STEM，以及接触阿拉斯加原住民美国社区，以及通过本科生和研究生培训发展一支具有全球竞争力的STEM劳动力队伍。主要是走滑运动和倾斜收敛之间的过渡区是走滑断层的共同特征。沿这些海侵断层的变形部分受控于外加应力的倾角和断层几何形状(走向和倾角的变化)，以及岩石圈和地壳尺度上跨断层的流变性对比。这些海侵断裂区提供了对如何适应应变的洞察，以及由逆冲带和前陆盆地界定的宽阔地带如何随着地壳块体沿着不同倾角的区域平移而沿着走滑断层系统演化。德纳利断裂带中东部一般具有简单的几何形状，走向和倾角不变，长约120公里，位于两个强度相反的大型复合地体之间，并具有记录在案的新生代垂直构造历史。因此，研究这两种不同边界条件对该活动走滑断裂系统形变历史的影响是一个天然的实验室。该项目将研究相对于跨断层的岩石圈强度对比的断层几何对沿德纳利断层东角变形的非均质性的重要性。该区德纳利断裂由以走滑为主转变为海侵体制。关于应变如何适应和变形如何沿这个走滑的断层系统发生的相互竞争的假说(强度与几何)将通过整合热年代学、地质年代学、构造和盆地分析研究来检验。德纳利断裂北部和南部的碎屑岩(现代河流沉积物和地层)和基岩热年代学(钾长石40Ar/39Ar、磷灰石裂变径迹和磷灰石(U-Th)/He)将跟踪折返的空间和时间模式，并与沿断层的盆地发展相结合，作为变形过程的代用品和记录器。40Ar/39Ar和裂变径迹年代学、孢粉学和镜质组反射率将圈定盆地下沉、反转、热史和缩短速率的时间。砾岩和砂岩碎屑的40Ar/39Ar年代学和U-Pb年代学有助于了解古水系格局和断裂沿线盆地的沉积物源位移。总而言之，这些综合数据将对大陆走滑断裂系统中两个共同边界条件在非均匀变形模式中所起的相对作用产生重要的新约束。

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.