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

点击翻译按钮获取中文摘要

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.